E1,11!)7.rRoracjULY1S988 - World Radio History...B0242 2 6in x 4in speakers, 4 ohm made from Radiomobile so very good quality. B0246 2 Tacho generators, generate one volt per 100 revs

E1,11!"")7.rRoracjULY1S988INCORPORATING ELECTRONICS MONTHLY

VIDEO WIPER".

£1.30

The Magazine for Electronic Et Computer Projects

vPOPULAR BAKERS DOZEN PACKS(still available)All packs are ft each, if you order 12 then you areentitled to another free. Please state which one youwant. Note the figure on the extreme left of the packref number and the next figure is the quantity of itemsin the pack, finally a short description.

BD 1 5 13A junction boxes for adding extra points to yourring main circuit.

BD2 5 13A spurs provide a fused outlet to a ring mainwhere devices such as a clock must not beswitched off.

BD7 4 In flex switches with neon on/off lights, savesleaving things switched on.

BD9 2 6V to mains transformers upright mounting withfixed clamps.

BD11 1 61/2in speaker cabinet ideal for extensions, takesour speaker. Ref BD137.

BD13 12 30 watt reed switches, it's surprising what you canmake with these -burglar alarms, secret switches,relay, etc., etc.

BD22 2 25 watt loudspeaker two unit crossovers.BD29 1 B.O.A.C. stereo unit is wonderful value.BOW 2 Nicad constant current chargers adapt to charge

almost any nicad battery.B032 2 Humidity switches, as the air becomes damper the

membrane stretches and operates a microswitch.6034 48 2 meter length of connecting wire all colour coded.BD42 5 13A rocker switch three tags so on/off, or change

over with centre off.BD45 1 24hr time switch, ex -Electricity Board, automati-

cally adjust for lengthening and shortening day.original cost £40 each.

BD49 10 Neon valves, with series resistor, these make goodnight lights.

BD56 1 Mini uniselector, one use is for an electric jigsawpuzzle, we give circuit diagram for this. One pulseinto motor, moves switch through one pole.

BD59 2 Flat solenoids -you could make your multi -testerread AC amps with this.

BD67 1 Suck or blow operated pressure switch, or it canbe operated by any low pressure variation such aswater level in water tanks.

8D91 2 Mains operated motors with gearbox. Final speed16 rpm, 2 watt rated.

BD103A 1 6V 750mA power supply, nicely cased with mainsinput and 6V output leads.

80120 2 Stripper boards, each contains a 400V 2A bridgerectifier and 14 other diodes and rectifiers as wellas dozens of condensers, etc.

BD122 10m Twin screened flex with white pvc cover.BD128 10 Very fine drills for pcb boards etc. Normal cost

about 80p each.BD132 2 Plastic boxes approx 3M cube with square hole

through top so ideal for interrupted beam switch.8D134 10 Motors for model aeroplanes, spin to start so needs

no switch.BD139 6 Microphone inserts -magnetic 400 ohm also act

as speakers.BD148 4 Reed relay kits, you get 16 reed switches and 4 coil

sets with notes on making c/o relays and othergadgets.

80149 6 Safety cover for 13A sockets -prevent those inqui-sitive little fingers getting nasty shocks.

00180 6 Neon indicators in panel mounting holders withlens.

BD193 6 5 amp 3 pin flush mounting sockets make a lowcost disco panel.

B0196 1 in flex simmerstat- keeps your soldering iron etc.always at the ready.

B0199 1 Mains solenoid, very powerful, has tin pull or couldpush if modified.

80200 8 Keyboard switches -made for computers but havemany other applications.

80210 4 Transistors type 2N3055, probably the most usefulpower transistor.

80211 1 Electric clock, mains operated, put this in a box andyou need never be late.

80221 5 12V alarms, make a noise about as loud as a carhorn. Slightly soiled but OK.

B0242 2 6in x 4in speakers, 4 ohm made from Radiomobileso very good quality.

B0246 2 Tacho generators, generate one volt per 100 revs.BD252 1 Panostat, controls output of boiling ring from sim-

mer up boil.80259 50 Leads with push -on 1/4in tags -a must for hook-

ups -mains connections etc.80263 2 Oblong push switches for bell or chimes, these can

mains up to 5 amps so could be foot switch if fittedinto pattress.

B0268 1 Mini 1 watt amp for record player. Will also changespeed of record player motor.

BD275 1 Guitar mic -clip-on type suits most amps.BD283 3 Mild steel boxes approx 3M x 3in x lin deep -

standard electrical.EI0293 50 Mixed silicon diodes.BD296 3 Car plugs with lead, fit into lighter socket.BD305 1 Tubular dynamic mic with optional table rest.Most other packs still available and you can choose any as yourfree one.

5A BATTERY CHARGER KITAll parts, including case, Only £5 plus ft postage

F.D.D. BARGAIN31/64 F111 WV Disc Drive, made by the Chinon Company of JapanBeasnifelly made and probably the most compact device of its kind asit weighs only 6011g and measures only 104mm wide. 162mni deep andhas a height of only 32nua Other Matures are MD track, high precisionhead positioning single push loading and elect direct drive brushless motor Shogart compatible interlace standard connectionsinterckaageable with most other 31/2 and 5E4 droves Brand new withcopy of maker's manual. Offered this month at 00.50 post and VATincluded.

CASE- adaptable for 31/2" FDD, has room for power supply compo-nents. Price only £4 includes circuit of PSU. Our Ref 4P7.

POWER SUPPLY FOR FDD -5V and 12V voltage regulated out-puts, complete kit of parts will fit into case 4P7 price E8 or with caseE11. Our ref. 11P2

9" MONITORIdeal to work with computer or video camera uses Philips blackand white tube ref M24/306W. Which tube is implosion and X-rayradiation protected. VDU is brand new and has a time base andEHT circuitry. Requires only a 16V dc supply to set it going. It'smade up in a lacquered metal framework but has open sides soshould be cased. Offered a a lot less than some firms are askingfor the tube alone, only 116 plus LS post.

CASE FOR 9" MONITORWe have arranged with a metal worker to make cases for the 9"Monitor. Delivery promised for the end of May and the price £12 plus£2 post. The case will be made from coated sheet steel, overall sizeapprox 10in x 10in x tin high which will give ample space for the PowerSupply and external controls if you fit them.

PROBLEM SOLVED!We have obtained from the manufacturers of the 9" Monitor, the TTLconverter which makes it composite input suitable to work with anycomputer. We have had the printed circuit board made and have allthe components and can supply this converter in kit form price ES. Ourref. 6P4.

AN ALLADINS CAVEWe have opened another shop in Hove, the address is number 12Boundary Road which is between Hove and Ponsiade faidy close tothe seafront, When you want to see before you buy and when youwant to browse around the special bargains available, this is whereyou should make for as the Portland Road shop in future will be justmail order. You can of course collect from Portland Road but youshould bring in an order complete with reference numbers so that thestores can attend to it easily.

MINI MONO AMP on p.c.b. size 4" x r (app.)Fitted volume control and a hole for a tone controlshould you require it. The amplifier hasthree transistors and we estimatethe output to be 3W rms.More technical data will beincluded with the amp. Brand new,perfect condition, offered at the verylow orice of ELM each, or E13 for 12.

THIS MONTH'S SNIPACORN COMPUTER DATA RECORDER ICASSETTET This is a mono datarecorder with switchable motor control intended for use with theAcorn Electron or BBC computers but also functions with almost anyMier computer and can be used for normal record and play -back ofmask and speech.

Six key controls give -PAUSE- "STOP" and -EJECT- -CUE/FASTFORWARD'. "REVUE/REWIND- and "RECORD", fast forward and re-wimad IMO seconds for CM). Also tape minter with reset button. Inputsignal range 5mV to 500mV. Input impedance 40k ohm. Can be batteryoperated bat is supplied with a mains adaptor. Brand new still inniseetaetwors wrapping M. Order Ref. BM a add E2 postage.

VENNER TIME SWITCHMains operated with 20 amp switch, one on andone off per 24 hrs, repeats daily automatically cor-recting for the lengthening or shortening day. Anexpensive time switch but you can have it for only12.95 without case, metal Lase --ass, adaptor kitto convert this into a normal 24hr time switch butwith the added advantage of up to 12 on/offs per24hrs. This makes an ideal controller for the immer-sion heater. Price of the adaptor kit is 82.30. Ex-Elorfriciry Boort

Goarainewi 12 month.

AKAI RV-UM300 MIDI -RACKIs a really excellent piece of furniture, ideal to hold your computer oraudio equipment. Has three shelves in the upper section and a hingedglass fronted lower section. Height approximately 3h, width I31/tin,depth 14in, on castors. dark walnut veneer finish. E15 plus £8 forSecuricor delivery. Order Ref. 15P11.

MULLARD UNILEX AMPLIFIERSWe are probably the only firm in the country with these now in stock.Although only four watts per channel, these give superb reproduction.We now offer the 4 Mullard modules-i.e. Mains power unit (EP9002)Pm -amp module IEP90011 and two amplifier modules IEP90001 all for£800 plus E2 postage. For prices of modules bought separately seeTWO POUNDERS.

25A ELECTRICAL PROGRAMMERLearn in your sleep. Have radio playing and kettleboiling as you wake - switch on lights to warn offintruders -- have a warm house to come home to.You can do all these and more. By a famous makerwith 25 amp on/off switch. A beautiful unit at 12.50.

POWERFUL IONISERGenerates approx. 10 times more IONS than the ETI and similarcircuits. Will refresh your home, office, workroom etc. Makes youfeel better and work harder- a complete mains operated kit,case included. 111.50+13 P&P

OVER 900 GIFTSYOU CAN CHOOSE FROM

There is a total of over 400 packs in our Baker'sDozen range and you become entitled to a free giftwith each dozen packs.A classified list of these packs and our latest "'NewsLetter- will be enclosed with your goods, and youwill automatically receive our next news letter.

J & N BULL ELECTRICALDept. E.E., 250 PORTLAND ROAD, HOVE,

BRIGHTON, SUSSEX BN3 5QTMAIL ORDER TERMS: Cash, PO or cheque with order. Orders underE20 add EL W service charge. Monthly account orders accepted fromschools and public companies. Access and B/ca rd orders accepted.Bright°. 102131 7346411pr 203500

NEW ITEMSSome of the many items described in our current list

which you will receive with your parcel

SOLAR POWERED NI -CAD CHARGER 4 Ni-Cad batteries AA (HP71charged in eight hours or two in only 4 hours.111 is a complete, boxedready to use unit. Price £6. Our ref. 6P3.

501/ 20A TRANSFORMER 'C' Core construction so quite easy to adaptfor other outputs -tapped mains input. Only £25 but very heavy soplease add £5 if not collecting. Order Ref. 25P4.FREE POWER! Can be yours if you use our solar cells -sturdily mademodules with new system bubble magnifiers to concentrate the lightand so eliminate the need for actual sunshine -they work just as wellin bright light. Voltage input is .45 - you loin in series to get desiredvoltage -and in parallel for more amps. Module A gives 100mA, Price£1, Our ref. 80631. Module C gives 400mA, Price £2, Our ref. 2PI99.Module D gives 700mA, Price £3, Our ref. 3P42.15A PANEL METER These have been stripped from Government sur-plus battery charger units made originally for army use. Unused, testedbut of course rather old, diameter tin can be surface or flush mounted.£3 each. Our Ref. 3P40.

SWITCH AC LOADS WITH YOUR COMPUTER This is easy and reliableif you use our solid state relay. This has no moving parts, has highinput resistance and acts as a noise barrier and provides 4kW isolationbetween logic terminals. The turn -on voltage is not critical, anythingbetween 3 and 30V, internal resistance is about 1K ohm. AC loads up to10A can be switched. Price is £2 each. Ref. 2P183.METAL PROJECT BOX Ideal size for battery charger, power supplyetc.; sprayed grey, size 8in x 41/4in x 4in high, ends are louvred forventilation other sides are flat and undrilled. Order Ref. 2P191. Price £2.BIG SMOOTHING CAPACITOR. Sprague powerlytic 39,000uF at WV. E3.Our ref. 3P41.HEAVY DUTY CURLY MAINS LEAD. Can be loaded up to 13A, stretcesto almost 3 metres fitted with 13A plug. £3. Order ref. 3P42.4 -CORE FLEX CABLE. Cores separately insulated and grey PVC coveredoverall. Each copper core size 7/0.2mm. Ideal for long telephone runsor similar applications even at mains voltage. 20 metres U. Our

ref.2PI96 or 100 metres coil Et Order ref. 8P19.BULK -HEAD MOUNTING LOUDSPEAKER. Metal case with chrome grillfront and with mounting lugs for screwing to ceiling, 8in. speaker. El0each. Order ref. 10P43 add £2 post.TWIN GANG TUNING CAPACITOR. Each section is .0005uF with trim-mers and good length Nin spindle. Old but unuse3d and in very goodcondition. El each. Our ref 80630.13A PLUGS Good British make complete with fUse, parcel of 5 for £2.Order ref. 2P185.13A ADAPTERS Takes 2 13A plugs, packet of 3 for £2. Order ref. 2P187.26V -0-20V Mains transformers 21/2 amp 1100 watt) loading, tappedprimary. 200-245 upright mountings DI. Order ref. 4P24.BENCH ISOLATION TRANSFORMERS 250 watt 230V in and out withplenty of tappings to give exact volts. £5 plus f2. Order ref. 5P5.BURGLAR ALARM BELL -6" gong OK for outside use if protected fromrain. I 2V battery operated. Price £8. Ref. 8P2.24 HOUR TIME SWITCH - 16A changeover contacts. up to 6 on/offs perday. Nicely cased, intebnded for wall mounting. Price £8. Ref. 8P6.CAPACITOR BARGAIN -axial ended, 4700AF at 25V. Jae made, nor-mally 50p each, you get 4 for El. Our ref. 613.CLEANING FLUID -Extra good quality -intended for video and tapeheads. Regular price £1.50 per spray can. Our price 2 cans for El. Ref.BD604.PIEZO ELECTRIC FAN -An unusual fan, more like the one used byMadame Butterfly than the conventional type, it does not rotate. Theair movement is caused by two vibrating arms. It is American made.mains operated, very economical and causes no interference, so is

ideal for computer and instrument cooling. Price is only If each. Ref.BD605.

SPRING LOADED TEST PRODS -Heavy duty, made by the famousBulgin company. very good quality. Price 4 for El. Ref. 130599.CURLY LEAD -Four core, standard replacement for telephone hand-set, extends to nearly 2 metres. Price El each. Ref. BD599.TELEPHONE BELLS -These will work off our standard mains through atransformer, but to sound exactly like a telephone, they then must beled with 25Hz WV. So with these bells we give a circuit for a suitablepower supply. Price 2 bells for II. Ref. BONO.ASTEC P.S.U.- Switch mode type. Input set for +230V. Output 3.5amps at +5V, 1.5 amps at + 12V, and 3 amps at + 5V. Should be OK forfloppy disc drives. Regular price £30. Our price only £10. Ref. 10T34Brand new and unused.APPLIANCE THERMOSTATS -Spindle adjust type suitable for convecfor heaters or similar. Price 2 for fl. Ref. B0582.3 -CORE FLEX BARGAIN No. 1 -Core size Stem so ideal for long exten-sion leads carrying up to 5 amps or shop leads up to 10 amps. 15mmfor E2. ref. 2P189.3 -CORE FLEX BARGAIN No. 2 -Core size 1.25mm so suitable for longextension leads carrying up to 13 amps, or short leads up to 25A. 10mfor £2. Ref. 2P190.CASE WITH 13A PRONGS -To go into 13A socket, nice size andsuitable for plenty of projects such as battery trickle charger, speedcontroller, time switch, night light, noise suppressor, dimmers etcPrice - 2 for El. Ref. B0565.ALPHA -NUMERIC KEYBOARD This keyboard has 73 keys giving trou-ble free hie and no contact bounce. The keys are arranged in twogroups, the main area is a OWERTY array and on the right is a 15 keynumber pad. hoard size is approx. IT' x brand new but offered atonly a fraction of its cost, namely £3, plus El post. Ref. 3P27.TELEPHONE EXTENSIONS -It is now legal for you to undertake thewiring of telephone extensions. For this we can supply 4 -core tele-phone cable, 100m coil £8.50. Extension BT sockets £2.95. Packet of 50plastic headed staples £2. Dual adaptor for taking two appliances fromone socket £3.95. Leads with BT plug for changing old phones, 3 for £2.WIRE BARGAIN 500 metres 0.7mm solid copper tinned and p.o.e.covered. Only £3 plus £1 post. Ref. 3P31- that's well under 1p permetre, and this wire is ideal for push on connections.INTERRUPTED BEAM KIT -This kit enables you to make a switch thatwill trigger when a steady beam of infra -red or ordinary light is broken.Main components -relay, photo transistor, resistors and caps, etc.Circuit diagram but no case. Price E2. Ref. 2P15.3-30V VARIABLE VOLTAGE POWER SUPPLY UNIT -with 1 amp DCoutput. Intended for use on the bench for experimenters, students,inventors, service engineers etc. This is probably the most importantpiece of equipment you can own (after a multi range test meter). It

gives a variable output from 3-30 volts and has an automatic shortcircuit and overload protection, which operates at 1.1 amp approxima-tely.) Other features are very low ripple output, a typical ripple is 3mVpk-pk, lmV rms. Mounted in a metal fronted plastic case, this has a

voltmeter on the front panel in addition to the output control knob andthe output terminals. Price for complete kit with full instructions is £15.Ref. 15P7.TRANSMITTER SURVEILLANCE (BUGI-Tiny, easily hidden, but whichwill enable conversation to be picked up with FM radio. Can be housedin a matchbox, all electronic parts and circuit. Price f2. Ref. 2P52.

VOL17No7 JULY '88

EiiRomcsINCORPORATING ELECTRONICS MONTHLY 1ABC

The Magazine for Electronic & Computer Projects

ISSN 0262-3617PROJECTS ... THEORY ... NEWS ...COMMENT . . . POPULAR FEATURES .

Mb*

'Cc) Wimborne Publishing Ltd 1988. Copyright in alldrawings, photographs and articles published inEVERYDAY ELECTRONICS is fully protected, andreproduction or imitations in whole or in part areexpressly forbidden.

ProjectsVIDEO WIPER by Robert Penfold 384Produce professional results from top to bottom, incorporatesan audio fader controlHOME SECURITY -2 by Owen N. Bishop 390An adaptable system that will enable you to secure your homeagainst intruders and fireSPIKE EATER by P. E. Roberts 394Take the "snap, crackle and pop" out of the mains supplySPECTRUM DUAL DAC 404Generate analogue voltages on two independent channelsAUDIO MINI -BRICKS by John Becker 406Part Two: Voltage Controlled Filter; Mock Stereo; Phasingand Ring ModulatorISOLINK by Andy Flind 416Connections without contactUNIVERSAL CHARGER/POWER SUPPLYby Costas Calamvokis 422Keep the power in your NiCads, don't let them drain away.This versatile unit also doubles as a mains adapterDIODE PUMP 434An Exploring Electronics project

seriesINTRODUCING MICROPROCCESSORSby Mike Tooley BA 398Part Nine: Written assessment, fourth practicalassignment and readers'forumON SPEC by Mike Tooley BA 404Readers' Sinclair Spectrum pageBBC MICRO by R.A. & J.W. Penfold 412Regular spot for Beeb fanaticsROBOT ROUNDUP by Nigel Clark 420Investigating the world of roboticsACTUALLY DOING IT by Robert Penfold 432Value of componentsEXPLORING ELECTRONICS by Owen N. Bishop 434Part Twenty -Five: Using diodes

featzfresCROSSWORD No. 6 381Some light-hearted brain teasersEDITORIAL 383FOR YOUR ENTERTAINMENT by Barry Fox 397Smart Money; Death Ray: Home Video NewsSHOPTALK by David Barrington 415Product news and component buyingAMATEUR RADIO by Tony Smith G4FA1 425Student Licence; Polar Radio; Armada 400DOWN TO EARTH by George Hylton 426Power Supply Labelling; Split Supplies; Multiple SuppliesDIRECT BOOK SERVICE 428Special service to EE readersPRINTED CIRCUIT BOARD SERVICE 437ADVERTISER'S INDEX 440

Our August '88 issue will be published on Friday, Readers' Services Editorial and Advertisement Departments 3831 July 1988. See page 411 for details.

Everyday Electronics, July 1988 377

1®1 LIPel]

AMPLIFIERS FROM

The UK Distributor for thecomplete ILP Audio Range

BIPOLAR AND MOSFET MODULESThe unique range of encapsulated amplifier moduleswith integral heatsink.HY30 15W Bipolar amp £11.30HY60 30W Bipolar amp E11.30HY6060 30W Stereo Bipolar amp £23.65HY124 60W Bipolar amp 14ohml £18.50HY128 60W Bipolar amp (Bohm) £18.50HY244 120W Bipolar amp (4ohm) E24.15

HY248 120W Bipolar amp (8ohm) £24.15HY364 180W Bipolar amp 14ohml £36.00HY368 180W Bipolar amp (Bohm) £37.55M0S128 60W Mosfet amp £40.70MOS248 120W Mosfet amp E46.35MOS364 180W Mosfet amp £75.75

POWER SUPPLIESComprising toroidal transformer and DC board topower the ILP amplifier modules.

ApplicationPSU30 Pee -amplifier £ 9.75PSU212 1 or 2 HY30 E17.70PSU412 HY6060, HY124,1or 2 HY60 £19.95PSU422 HY128 E22.00PSU432 MOS128 £23.00PSU512 HY244, HY128 121 E24.40PSU522 HY124 12) £24.40

PSU532 MOS128 (2)PSU542 HY248PSU552 MOS248PSU712 HY244 121PSU722 HY248 (21PSU732 HY364PSU742 HY368PSU752 M0S364,MOS248 121

PRE -AMP and MIXER MODULESThese encapsulated modules are supplied within -line connectors but require potentiometers,switches etc. Individual data sheets on request.HY6HY7HY8HY9HY11HY12HY13HY66HY67HY68HY69HY71HY73HY74HY75HY76HY77HY78HY8386866

Mono pre -amp with bass &trebleMono mixer 8 channelStereo moxer 5 channelStereo preompMono mixer 5 channel with bass & trebleMono pre amp 4 channel with bass, mid & trebleMono VU meter driverStereo pre -amp with bass & trebleStereo headphone driverStereo mixer 10 channelMono prearnp 2 channel with bass & trebleDual pre -ampGuitar pre. amp with bass & trebleStereo mixer 5 channel with bass & trebleStereo pre -crop with bass, mid & trebleStereo switch matrixStereo VU meter driverStereo pre -ampGuitar pre -amp with special effectsMounting hoardMounting hoard

LOUDSPEAKERS3128 350W 12" Bass loudspeaker312WB 200W 12" WIdeband bass loudspeaker

POWER SLAVESThese cased amplifiers are supplied assembled andtested in 60 and 120 watt Bipolar or Mosfet versions.

£25.40£25.40£27.45£29.20E30.20£30.20E32.20E32.20

E 9.25E 8.75E 8.75E 9.30E 9.75E 9.30£ 8.75£15.00£16.60E11.30£15.40£14.95£15.00E15.95£15.40£19.50£14.35£14.70£18.95£ 1.15E 1.75

US12 60 watt Bipolar 14ohm1 £75.00 US32 60 watt MosfetUS22 120 watt Bipolar (4ohml £83.75 US42 120 watt Mosfet

Prices include VAT and carriage 1E1

£78.65£78.65

£99.95£108 35

VISA

Quantity prices available on request

Write or phone for free Data Pack

Jaytee Electronic Services143 Reculver Road, Beltinge, Herne Bay, Kent CT6 6PL

Telephone: (0227)375254 Fax: 0227 365104

NEW THIS MONTH

Z4069 STEREO HEADPHONES - Hi-Fi,compact, fold -up. Amazing value. £1.95

Z4071 MAP LIGHT -In car use with mag-net and magnifier, curly lead and plug.

E1.95Z345 OPTICAL SHAFT ENCODER. Similarto RS631-632, but 80% cheaper! £8.50

UMW s for 5p!Z347 4 x LM358 op amps surface mountedon ceramic substrate, easily removed.

5 panels for ElCOMMODORE INTERFACE1030 Plugs into user port on C64 and givesserial output to 5 pin plug. Uses 27256,6502 plus LS & CMOS E5.95

SET TOP CONVERTER28028 Made by Thorn EMI, this was usedto receive cable television. 2 part alumi-nium case 211 x 158 x 92mm (no frontpanel) contains 2 pcb's: (a) control boardwith multiway switch, dual 7 seg plug-indisplay and a couple of chips; (b) mainboard with mains transformer, tuner, RFsection etc. Rear panel has input and out-put sockets, 2m mains lead with moulded -on 13A plug. £9

2810 KEYBOARD. Really smart alphanumeric standard qwerty keyboard withseparate numeric keypad, from ICUs 'OnePer Desk'. Nicely laid out keys with goodtactile feel. Not encoded matrix outputfrom PCB taken to 20 -way ribbon cable.Made by Alps. Size 333x 106mm. 73 keys.

£8.95'JIMMY'Exciting electronic football game originallysold for £19.95, but this price includedplastic grandstand, stickers, etc. We cansupply the 420 x 93mm neatly cased elec-tronics comprising keypad either end,14 x 5mm red LED'sl'players'). TMS1000chip programmed to make odd noiseswhilst playing and a tune when a goal isscored, also 2 x 7seg LED's to keep score.Cardboard 'pitch' plus instructions sup-plied. £5.00

TOOLSScoop purchase of high quality surgicalinstruments ideal for electronics use.Z308 5in lightweight long nose pliers 99pZ309 51/2in as above but with ratchet. Thisenables pliers to be locked together forholding small components, or as heatshunts, etc. £1.20

JOYSTICKZ004 Skeleton Joystick, switch type. Goodquality, made by AB. Brass spindle has44mm long black plastic handle attached.Body has 4 mounting holes. These reallyare a fantastic bargain!! Only £1

SPEECH SYNTH KIT2315 All parts inc PCB to make a speechsynth for the BBC micro £4.99Z316 De -luxe version -also includes V216case, 1m 20W cable plus connector £7.99VIEWDATA LTUZ697 Interface Panel 166x 150 with3 x LM324, LM339, LM393, 4066, 11 transis-tors, 3 reed relays, etc. 3m lead with BTplug attached. Supplied with comprehen-sive data and ccts. £2.90

ENTERPRISE PANELSZ658 PCB 325x158 with 64K of RAM(8 x 4864). Z80A microprocessor, 21 otherchips, UHF modulator, speaker, etc. ROMand Nick and/or Dave chips missing, sup-plied with cct and data 0.00INTERFACEZ8027 Diecast box 150 x 80 x 50mm.Mounted centrally on top is a 25- way Dtype socket. This is wired to a pcb withinwhich has 12 x 20mm wire ended fusesand 24 12V 1W zener diodes. A 13 corelead 2m long from this board terminates ina 25W D plug. There is also a separateearth lead. £4

1988 CATALOGUE88 -page main catalogue with everythingfrom resistors to 'scopes. PLUS 16 -pageSale List PLUS 24 -page SpringSupplement PLUS Latest Bargain Lists!All this for just £1 inc post!MICRO PANELSZ620 68000 Panel. PCB 190 x 45 believed tobe from ICL's 'One per Desk' computercontaining MC68008P8 (8MHz 16/8 bitmicroprocessor, +4 ROMs, all in skis;TMP5220CNL, 74HCT245, 138, LS08, 38etc. E5.00Z625 32k Memory Board, PCB 170x170with 16 2k x 8 6116 static RAMs. Also 3.6V100mA memopack nicad, 13 other HC/LSdevices, 96w edge plug, 8 way DIL switch,Rs, Cs etc. £4.80SPEAKERS2578 Sub -min speaker 30 x 30 x 3mm thickby Fuji. 16R 0.4W, 60p each; 10 £3.70; 25£7; 100 f22; 1000 £180. 2575 70 x 45mm45R 0.5W 55p each, 10 £3.30;25 £6; 100£20.SOLDER500g reels resin cored, 18g £5.95500g reels resin cored 22g £7.95

LOGIC PROBEFor TTL, CMOS etc LED and sound indica-tion. Pulse enlargement capability allowspulse direction down to 25nsec. Max 4=20MHz 4-16V. UP Z:1M £9.99SWITCHED MODE PSU'sAstec type AA7271. PCB 50x 50mm has 5transistor cct providing current overloadprotection, thermal cut-out and excellentfiltering. Input 8-24V DC. Output 5V 2A.Regulation 0.2%. £5.00Z026 Astec model AC9355 65W unit.115/230V ac input. Outputs: +5V 6A;+12V 1.5A; - 12V 0.25A. Normally over£70. Our price £24.95OF482 130W unit, 5V at 15A; 12V at 4A; -

12V at 2A; -5V at 1A (List £110) f35P350 250W unit, 5V at 50A(List £190) £60Hiflex 750W unit, 5V at 130A; 12V at 20A

(List £800) £250Hiflex 1000W unit, 5V at 200A

(List £800) £250

* STAR BUY *GREEN SCREEN HI-RES 12" MONITORCHASSISBrand new and complete except for case,the super high definition (1000 lines atcentre) makes this monitor ideal for com-puter applications. Operates from 12V DCat 1.1A. Supplied complete with circuit dia-gram and 2 pots for brilliance/contrast,plus connecting instructions. Standardinput from IBM machines, slight mod (de-tails included) for other computers.

Only £24.95+f3 carr.SOLAR CELLSMega size -300 x 300mm. These incorpo-rate a glass screen and backing panel withwires attached. 12V 200mA output. Idealfor charging nicads. £24.00FANZ4056 'PATRIOT FAN'. High quality cool-ing fan for mounting into equipment.170mm dia x 51mm. Only problem is theyoperate on 48V ac (but still work down to24V) £4.00SWITCHBOARDZ8829 Telephone switchboard. Console380 x 250 x 120/40mm contains diallingpad, 50 double pole pushbuttons in stripsof 10, all with indicators, 8 digit display, 50core 2m cable to connector. Made byNorthern Electric. In good used condition.

£15+£3 can.MAINS LEADZ4057 Mains Lead, 2m long grey 3 core 6Alead with 13A plug fitted with 5A fuse.

70p; 10+ 55p; 100+ 40p

SOLDER SPECIAL!!* 15W 240V ac soldering iron* High power desolder pump* Large tube solder

ALL FOR

£7.95COMPASSESPrecision spring bow 88mm long. Max dia70mm. Replaceable pencil lead and steeltip. £1.00

GREENWELDELECTRONICCOMPONENTS

All prices include VAT; just add £1.00 P&P. MM. Access f5.No CWO min. Official orders from schools welcome -min.invoice charge flO. Our shop has enormous stocks ofcomponents and is open 9-5 Mon. -Sat. Come and see us!HOW TO CONTACT US:By post using the address below; by phone (07031 772501 or783740 (ansaphone out of business hours); by FAX 107031 787555,by EMail Telecom Gold 72'MAG36026; by Telex 265871 MONREFG quoting 72MAG36026.

443D MILLBROOK ROAD, SOUTHAMPTON SO1 OHX

378 Everyday Electronics, July 1988

ERLINMERLIN WAY, BOWERHILL,

MELKSHAM, WILTSHIRESN12 6TJ

YSTEMSMISCELLANEOUS1 x I.E.C. 1 amp mains filter socket1 x I.E.C. 3 amp mains filter socket1 x I.E.C. 6 amp mains filter socket5x push latching pcb switches5 x slide pcb switches10x phono plugs5 x 240V panel neonsSo24Vpanel lamps5x MES lamp holders5 x 2 -way 3 -pole switches with knobs4 x 4 -way dill switches

x 13 amp 200V bridge rectifiers3 x I amp 50V bridge rectifiers10 x 5mm x 2mm red leds10 x 5mm x 2mm green leds

1.25

1.50

1.75

70p

70p50p

70p

70p

50p1.20

30p1.20

50p1 00

1.00

NEW!Made by well-known Japanese manufac-turer. Twin cassette mechanism, completewith stereo heads, counter, doors and leads,only f6.00, P&P f1.00Complete working pcb from LW, MW, FM,stereo music centre. Only £5.00, P&P £1.00.

NEW SYSTEMMerlin Systems PC Turbo 256K RAM, 8088CPU, 1 Disk Drive, Hires Mono Monitor, 84Keyboard, Par printer port, Radio and MSDossoftware and Merlin Systems backup.f450.00 plus f15.00 P&P.

2nd USER SYSTEMSApple II+ with diskm drive and software

150.00

Franklin with disk drive and software 150.00Apple parts, 5100 cards, IBM cards, diskdrives, CPN systems, MSDos systems, IBMPC, and mono/colour monitors.

PAYMENT: Credit card, cheque, PO, cash.Post and packaging, £0.00 to DODO add0.50; £10.00 to £20.00 add Et 00. Please addVAT to total.

Tel:0225706886

Look out for Merlin Systemsat the following Rallies andExhibitions: 10th July-Brighton Rally, BrightonRacecourse. 15/16/17thJuly- RSGB Convention,NEC, Birmingham. 31st July-Scarborough Rally.

POWERRADIAL ELECTROLYTICSELECTROLYTICS 5x50ufx5Ouf 200V 60plaza 7uf 25V 30p 2x220uf 3I5V 17510x22uf 10V 307 2x220uf 400V 20010x22uf 25V 35p 2047002000 1.50

10x47u125V 35p 2x15000uf 25V 1 75

10x47uf 35V 40p 2x22000uf 25V 2005x47uf 2500 60p 5x3300uf 25V 1 30

10x100u1 100 35p 2x3400uf a0V 75p10x220uf 10V 35p10x220uf 16V 35P DIGITAL RESEARCH10x2213uf 25V 40P MANUALS10x220ut 40V 45p InGSX Graphics10x220uf 50V 45P PC CPM86 15010x470uf 25V 35p lath Draw PC CPM86 1 5010x470u150V 501) I ',Or Net PC CPM86 1.5010x1000uf 25V 35p I ',Concurrent CPM 1 50

laCPM86 user 1.50

COMPUTER DESKUp -Market Desk, L 102cm x W 14cm x H74cm with keyboard recess and cableingtrunking. New only £50.00 plus f16.00 P&P.

POWER SUPPUESAND TRANSFORMERSBench power supply in blue case, withswitched 240V mains input and HT output.Outputs, 6.3V ac at lamp and 250V dc stabil-ised at 50mA. H 115mm, W 185mm, D 125mm.Just the lob for valves! AS NEW ONLY £9.50.

2nd USER TEST EQUIPMENTSE Labs SN111 18MHz bandwidth, twinbeam, mains or battery input. Only f160.00plus £15.00 p&p. Ring for list.

8052 -BASICMICROCONTROLLER

NEWUnbuffered8K Versionfor ONLY

£99(KIT)

TP

FEATURES INCLUDE* Powerful Enhanced Basic

Interpreter.* On Board EPROM

Programmer.* Program Development from a

VDU.* 32K Bytes of CMOS Static

RAM.* 32K bytes of CMOS EPROM

(expandable to 56K Bytes).* Two RS232 Ports.* Single Unregulated Supply

Requirements.* Small Physical Size (80 by

100mm).* Expansion with range of

Compatible Circuit Boards.

PRICES* KIT including all

components, fullinstructions andoperating manual £129

* MANUFACTURED andfully tested circuit board£229

* All prices exclude VAT.

* Packaging and PostageFREE (UK only)EUROPE £3.00ELSEWHERE £7.00(Customs & Exciseextra)

MONIFIETH BUSINESS CENTREn electronics ltd DUNDEE DD5 aF',I Telephone 0382 534944

CONQUERING NEW HEIGHTS

Yes its 2544fiz for .E319

* Component Comparator* Variable Hold Off

* Triple DC Source\\*- DC -25 MHz

* 4Ons/div* 2mV/div* Low Cost *

Full 2 Year Warranty 4319To scale the heights, just callus for your FREE copy of ourcatalogue ==

VISA *(Ex VAT & Delivery)

Crotech Instruments Limited2 Stephenson Road, St. Ives, Huntingdon, Cambs. PE17 4WJ

Telephone: (0480) 301818


'EE PROJECT KITS MAGENTAFull Kits inc. PCBs, or veroboard, hard-ware, electronics, cases (unlessstated). Less batteries.If you do not have the issue of EEwhich includes the project -you willneed to order the instruction reprintas an extra -80p each. Reprints avail-able separately 80p each plus p&p £1.

THIS MONTH'S KITS(sae or 'phone for prices)SUPER SOUND EFFECTS

GENERATOR May 88DOOR SENTINEL May 88STEREO NOISE GATE April 88CABLE & PIPE LOCATOR April 88INDUCTIVE PROXIMITY DET. Apnl 88LOW FUEL ALERT April 88SEMICONDUCTOR TESTER Mar 88UE DETECTOR Mar 88ENVELOPE SHAPER Mar 88SOS ALERT Mar 88AUTO -WAGGLE JOYSTICK

ADAPTOR Mar 88VARIABLE 25V -2A BENCH

POWER SUPPLY Feb 88CAR LAMP CHECKING SYST. Feb 88GAME TIMER Feb 88QUIZMASTER Jan 88

112.99

212.81

E26.98

£15.354.63£6.43

E23.51

£11.80£14.99

£936

£3.99

49.73£7.10

£14.32118.96

CAPACITANCE METER Jan 88TRANSISTOR CURVE TRACER (BBC) £14.911

CORMNIKTY TESTER Jan 88 £967AUDIO SIGNAL GENERATOR Dec 87 £12.99DUAL MAINS UGHTS FLASHER Dec 87 £19.98

ACCENTED BEAT METRONOME Nov 87 119.95ACOUSTIC PROBE Nov 87 (less bolt & probe) £15.49BBC SIDEWAYS RAM/ROM Nov 87 £2622VIDEO CONTROLLER Oct 87 £27.75TRANSTEST Oct 87 524AUTOMATIC PORCH LIMIT Oct 87 £16.35

CARAVAN FRIDGE ALERT Oct 87 ESTISTATIC MONITOR Oct 87 1825ELECTRONIC MULTIMETER Sept 87 £44.72

NOISE GATE Sept 87 122.14

PERSONAL STEREO AMP Sept 87 E13.63

CAR OVERHEATING ALARM Sept 87 5121BURST -FIRE MAINS CONTROLLER Sept 87 f12.91SUPER SOUND ADAPTOR Aug 87 136.56IMMERSION HEATER TIMER Aug 87 £11.993 BAND 1.6-30MHz RADIO Aug 87 £2527B UCCANEER I.B. METAL DETECTOR inc. coils and

case. less handle and hardware July 87 £25.19

DIGITAL COUNTER/FREO METER (I OMI4z) inc.case July 87 E67.01

MONOMIX July 87 220.91

FERMOSTAT July87 £11.56

VISUAL GUITAR TUNER Jun 87 0199MINI DISCO UGHT Jun 87 111.99WINDSCREEN WASHER WARNING May 87 £4.811

FRIOGE ALARM May 87 E9.41

EOUAUZER (IONISER) May 87 114.79B ULB UFE EXTENDER April 87 (less case) £4.99

EXP. SPEECH RECOGNITION April 87 E19.98

COMPUTER BUFFER INTERFACE Mar 87 £11.96ACTIVE DR BURGLAR ALARM Mar 87 033.95VIDEO GUARD Feb 87 £7.99

MINI -AMP Feb 87 114.99

CAR VOLTAGE MONITOR Feb 87 £11.98

SPECTRUM SPEECH SYNTH. (no easelFeb 87 E19.92

SPECTRUM I/0 PORT less case. Feb 87 11.99

STEPPING MOTOR BOOSTER Dor above)Feb 87 5.19

STEPPING MOTOR MD200 Feb 87 E16.60HANDS-OFF INTERCOM line station) inc. case

Jan 87 E999CAR ALARM Dec 86 E10.97

DUAL READING THERMOMETER (less case)Dec 86 E39.911

RANDOM NUMBER GENERATOR Dec 86 E14.97

II CHANNEL A-0 I SPECTRUMI CONVERTERDec 86 E34.29

BBC 16K SIDEWAYS RAM Dec 86 E12.35MODEM TONE DECODER Nov 86 £10.99

OPTICALLY ISOLATED SWITCH Nov 86 E11.99CAR RASHER WARNING Nov 86 £7.922111/114: DIG. FREQUENCY METER Nov 86 59.9810 WATT AUDIO AMPLIFIER Oct 86 £34.95LIGHT RIDER LAPEL BADGE Oct 86 £9.71

LIGHT RIDER DISCO VERSION £18.69LIGHT RIDER 16 LED VERSION £12.99SCRATCH BLANKER Sept 86 53.17INFRA -RED BEAM ALARM Sept 86 E26.99

FREEZER FAILURE ALARM Sept 86CAR TIMER Sept 86 530BATTERY TESTER Aug 86 C6.85

TILT ALARM July 86 E7.45

HEADPHONE MIXER July 86 E27.69

CARAVAN BATTERY MONITOR July 86 £16.35SOUEEKIE CONTINUITY TESTER July 86 E3.35

ELECTRONIC SCARECROW July 86 5.45VOX BOX AMP July 86 E12.73PERCUSSION SYNTH June 86LIGHT PEN (less easel June 86 5.80PERSONAL RADIO June 86 £10911

WATCHDOG June 86 £715MINI STROBE May 86 £13.11PA AMPLIFIER May 86 E24.95LOGIC SWITCH May 86 £14.93STEREO REVERS Apr 86 225.10VERSATILE PSU Apr 86 E13.51

FREELOADER Apr 86 EROS

STEPPER MOTOR DRIVER Apr 86BBC MIDI INTERFACE Mar 86INTERVAL TIMER Mar 86STEREO HI-FI PRE -AMPMAINS TESTER & FUSE FINDER Mar 86FUNCTION GENERATOR Feb 86POWER SUPPLY FOR ABOVETOUCH CONTROLLER Feb 86SPECTRUM OUTPUT PORT Feb 86TACHOMETER Jan 86ONE CHIP ALARM Jan 86MUSICAL DOOR BELL Jan 86TEL LOGIC PROBE Dec 85DIGITAL CAPACITANCE METER Dec 85SOLDERING IRON CONTROLLER Oct 85VOLTAGE REGULATOR Sept 85P ERSONAL STEREO P.S.U. Sept 85R.I.A.A. PRE -AMP Sept 85FRIDGE ALARM Sept 85LOW COST POWER SUPPLY UNIT Aug 85TRI-STATE THERMOMETER (Batt) Aug 85TREMOLONIBRATO Aug 85STEPPER MOTOR INTERFACE FOR THE BBCCOMPUTER less case Aug 851035 STEPPER MOTOR EXTRAOPTIONAL POWER SUPPLY PARTSCONTINUITY TESTER July 85TRAIN SIGNAL CONTROLLER July 85AMSTRAD USER PORT July 85ACROSS THE RIVER June 85ELECTRONIC DOORBELL June 85GRAPHIC EINAUSER June 85AUTO PHASE May 85INSULATION TESTER Apr 85LOAD SIMPLIFIER Feb 85GAMES TIMER Jan 85SPECTRUM AMPLIFIER Jan 85TV AERIAL PM -AMP Dec 84

ECM56.61117.91

E46.85

£11.40

53.66E1.62

E1225E10.72

E24.57429

£17.12

4.4559.51521E7.46

5.89E15.94

E1.58

216.39

E6.66

£37.92

£13.99E14.50

E5.14

5.90£9.66

£16.83E19.77

020£25.66E11.98

118.65

E19611

5.3916.58

E14.83

Optional PSU 12V E2.44 2400 £11.83DOOR CHIME Dec 84 57.89BBC MICRO AUDIO STORAGE SCOPE INTERFACE

Noy 84 234.52

PROXIMITY ALARM Nov 84 f21.58MAINS CABLE DETECTOR Oct 84 E527MICRO MEMORY SYNTHESISER Oct 84 E57.57

DRILL SPEED CONTROLLER Oct 84 E6/7GUITAR HEAD NONE AMPLIFIER Sept 84 £7.66SOUND OPERATED RASH Less lead Sept 84 5.98TEMPERATURE INTERFACE FOR BBC

Aug 84 £23.64CAR RADIO BOOSTER Aug 84 06.64CAR LIGHTS WARNING July 84 E9.58

VARICAP AM RADIO May 84 112.52EXPERIMENTAL POWER SUPPLY May 84 122.46SIMPLE LOOP BURGLAR ALARM May 84 £16.34MASTERMIND TIMER May 84 E6.52

FUSE/DIODE CHECKER Apr 84QUASI STEREO ADAPTOR Apr 84NI -CAD BATTERY CHARGER May 84REVERSING BLEEPER Mar 84PIPE FINDER May 84SIGNAL TRACER Feb 84

14.14

113.08

51M4.144.32

E17.68CAR LIGHT WARNING Feb 84 4.51BIOLOGICAL AMPLIFIER Jan 84 E22.99

CONTINUITY TESTER Dec 83 111.99

CHILDREN'S DISCO UGHTS Dec 83 111.42

NOVEL EGG TIMER Dec 83 inc. case 11229SPEECH SYNTHESIZER FOR THE BBC MICRO

Nov 83 less cable +sockets E26.38

HOME INTERCOM less link wire Oct 83 E17.26

STORAGE 'SCOPE INTERFACE FOR BBC MICROAug 83 less software 218.42

HIGH POWER INTERFACE BOARDAug 83 no case 52.45

USER PORT VO BOARD less cable +plug E12.59

USER PORT CONTROL BOARD July 83 lesscable (plug ) case £30.16

MW PERSONAL RADIO less case, May 83 £9.14MOISTURE DETECTOR May 83 E6.55

NOVELTY EGG TIMER April 83 less case E6.58BUZZ OFF March 83 5.41PUSH BIKE ALARM Feb 83 54.07ZX TAPE CONTROL Nov 82 £11.55

2- WAY INTERCOM July 82 no case 5.42REFLEX TESTER July 82 E9.32

SEAT BELT REMINDER Jun 82 £4.92EGG TIMER June 82 16.53CAR LED VOLTMETER less case. May 82 DM

SOUND EFFECTS UNIT April 82 0525CAMERA OR RASH GUN TRIGGER

Mar 82 less tripod bushes 56.38MINI EGG TIMER Jan 82 £5.21SIMPLE INFRA RED REMOTE CONTROL

Nov 81 122.44

SUSTAIN UNIT Oct 81 56.79TAPE NOISE UMITER Oct 81 15.97HEADS AND TAILS GAME Oct 81 530PHOTO FLASH SLAVE Oct 81 14.56

FUZZ BOX Oct 81 4.57SOIL MOISTURE UNIT Oct 81 £7.660-11V POWER SUPPLY Sept 81 123.38SOIL MOISTURE INDICATOR E.E. May 81 E539PHONE BELL REPEATER/BABY ALARM

May 81 E7.38MODULATED TONE DOORBELL Mar 81 4.122 NOTE DOOR CHIME Dec 80 £13.62ENE WIRE GAME Dec 80 £15.44GUITAR PRACTICE AMPURER Nov 8014.10

less case. Standard case extra 4.98SOUND TO LIGHT Nov 80 3 channel ULMSPRING UNE REVERS UNIT Jan 80 £32.64UNIBOARD BURGLAR ALARM Dec 79 17.98DARKROOM TIMER July 79 C3.14

MICROCHIME DOORBELL Feb 79 00.91SOUND TO LIGHT Sept 78 110.98

IN SITU TRANSISTOR TESTOR Jun 78 MOOWEIRD SOUND EFFECTS GEN Mar 78 £7.44ELECTRONIC DICE Mar 77 4.97

TOOLSANTEX MODEL C IRON 5.98 LOW COST PLIERS 21.96ANTES 05 SOLDERING LOW COST CUTTERS £1.99

IRON 25W 57.25 BENT NOSE PLIERSST4 STAND FOR IRONS £285 MINI DRILL 12V IMD11 4.38HEAT SINK TWEEZERS 45p MULTIMETER TYPE1 1001)opv 5.93SOLDER HANDY SIZE 5 £1.39 MULTIMETER TYPE 2 20,000opv f17.98SOLDER CARTON £2.50 MULTIMETER TYPES 30,C00opv f27.98SOLDER REEL SIZE 10 E4.67 MULTIMETER TYPE 410M

DIGITAL £39.98

DESOLDER PUMP 6.48SIGNAL INJECTOR E2.98

CIRCUIT TESTER 7812

HELPING HANDS JIG &MAGNIFIER 0.98

MINIATURE VICE I PLASTIC} E1.95

DIGITALTROUBLESHOOTINGTop quality kits & parts for this newseries. Our excellent technical back-upservice helps to ensure that your pro-jects succeed every time.PART 1 BENCH POWER SUPPLY -Fullkit £24.98.LOGIC PROBE -£7.58 including case.LOGIC PULSER-£7.48 including case.VERSATILE PULSE GENERA-TOR -£29.98 including case.DIGITAL I.C. TESTER -£29.21 (casedifferent).CURRENT TRACER -£20.56.AUDIO LOGIC TRACER -£8.99.

EXPLORINGELECTRONICS

A full set of parts including the Veroblocbreadboard to follow the series right up toAug 87 issue 129.43.Follow this excellent beginners series. Full setof reprints ES or 80p per issue.SEPT PARTS 72p; OCT PARTS £2.56; NOVPARTS 0.32; DEC PARTS E4.77; JAN PARTS5.58; FEB PARTS £1.14; MAR PARTS £1.96;APR PARTS £6.49; MAY PARTS £4.44.Extra Verobloc (used in part 171 E7.99.

INTRODUCTIONTO ELECTRONICS

An introduction to the basic principles ofelectronics. With lots of simple experi-ments. Uses soldering. Lots of full colourillustrations and simple explanations. Alovely book. Ideal for all ages.INTRODUCTION TO ELECTRONICSCOMPONENT PACKBOOK EXTRABook also available separately.

f 10.9982.45

NEWBOOKS

Modern Opto DeviceProjects [2.95Electronic Circuits for the Con-trol of Model Railways f 2.95A T 0.-DXers HandbookBP1 76 £5.95Midi Projects. Penfold £2.95Getting The Most FromYour Printer. Penfold [2.95More Advanced

Electronic Music Projects.Penfold £2.95

BOOKSHow to Get Your Electronic ProjectsWorking. Penfold £2.15A practical Introduction to Microprocessors.Penfold £2.10Basic Electronics. Hodder & Stoughton £8.98Beginners Guide to Building Electronic Projects.Penfold £2.25DIY Robotics & Sensors Billingsley. BBC £7.95Commodore 64 E7.99Elementary Electronics. Sled& E5.98Science Experiments with Your Computer £2.43How to Design & Make Your Own PCBs. BP121f 2.15How to Make Computer Controlled Robots. Potter f 3.20How to Make Computer Model Controllers. Ponerf 3.19Interfacing to Microprocessors & Microcomputersf 6.50Machine Code for Beginners. Usborne 12.45Micro Interfacing Circuits Book 1 £2.45Microprocessors for Hobbyists. Coles £4.98Practical Computer Experiments. Parr f 1.95Practical Things to do With a Microcomputer.Usborne 12.19Questions & Answers - Electronics. Hickman £3.45Understanding the Micro. Osborne £1.95

JUST A SMALL SELECTION. LOTS MORE INOUR PRICE LIST

ELECTRONICS TEACH -INMULTIMETER TYPE M10282 as specified. Guaranteed. Top quality. 20k / V, with batterycheck, continuity tester buzzer and fuse and diode protection. 10A dc range.Complete with leads, battery and manual. £14.98VEROBLOC BREADBOARD, DESIGN PAD, MOUNTING PANEL AND 10 CROCODILECLIP CONNECTING LEADS £9.98REGULATOR UNIT AND SAFE POWER SUPPLY. All components including the specifiedcase. Specially re -designed by Magenta. No external transformer or adaptor required. PCBdesign for complete safety and ease of assembly. £26.84COMPONENTS FOR PRACTICAL ASSIGNMENTS. Full set. £16.84

TEACH IN 86 PROJECTSUNIVERSAL LCR BRIDGE Nov 85 (25.830100E/TRANSISTOR TESTER Dec 85 £18.89USEFUL AUDIO SIGNAL TRACERJan 86 216.75AUDIO SIGNAL GENERATOR Feb 86 £26.21R.F. SIGNAL GENERATOR March 86 £24.48FET VOLTMETER Apr 86 £21.48DIGITAL PULSE GENERATOR May 86 £16.68

NEWMINI MODEL MOTORS11-3V, 2 TYPES. MM1-59p MM2----61p

LEGO' Technic SetsTEACHERS WE ARE STOCKISTS OF THEWHOLE RANGE. CONTACT US FOR

BROCHURES. VERY COMPETITIVE PRICESAND QUICK DELIVERIES.

STEPPING MOTORS 12 VOLT48 STEPS 200 STEPS

1035 MD200£14.50 £16.80

MOTOR - GEARBOX ASSEMBLIESMiniature precision made. Complete with quality electric motor. Variable reduction ratiosachieved by fitting from 1-6 gearwheels (supplied) as required. Operates from 1.5V to 4.5V.Small unit type MGS speed range 3rmp-2200rpm depending on voltage & gear ratio. Largeunit type MGL (higher torque motor) 2rpm-1150rpm. Long 3mm dia output shafts. Ideal forrobots and buggies.Small Unit (MGSI £3.49. Large Unit 1MGLI £3.98.PULLEY WHEELS. New Range -PLASTICWITH BRASS BUSH 6" dia. hole -easilydrilled to 3 or 4mm. e" dia. 35p, i" dia.36p, i" dia. 44p. 1" dia. 44p.Metal collar with fixing screw, 3mm bore24p. Flexible spring coupling 5mm. Length31mm 68p.Flexible metal coupling (universal) 3mm£2.98; 2mm £3.34.

CATALOGUEBrief details of each kit, our books, &illustrations of our range of tools & com-ponents. Also stepper motor, interface kit& simple robotics. Plus circuit ideas for youto build. If you read Everyday Electronicsthen you need a copy of the MAGENTAcatalogue.CATALOGUE 8 PRICE LIST - Send II in stampsetc. or add f 1 to your order. Price list - 984 sae.

Catalogue FREE TO SCHOOLS/COLLEGES RE-QUESTED ON OFFICIAL LETTERHEAD.

ADVENTURESWITH

ELECTRONICSAn easy to follow book suitable for all ages. Ideal forbeginners. No soldering, uses an S -Dec Breadboard.

Gives clear instructions with lots of pictures 16 projects- including three radios, siren, metronome, organ,intercom, timer, etc. Helps you learn about electroniccomponents and how circurts work. Component packincludes an S -Dec breadboard and all the components forthe projects.Adventures with Electronics 0.9e.Component peck r2098 less batter,/

MAGENTA ELECTRONICS LTDEE66, 135 HUNTER STREET,BURTON -ON -TRENT,STAFFS. DE14 2ST0283 65435, Mon -Fri 9-5.Access/Barclaycard (Visa) byphone or post.24 hr Answerphone for credit card ordeOur prices include VAT.

rs.

SHOP NOW OPEN -CALLERS WELCOMEADD 11 P&P TO ALL ORDERS.PRICES INCLUDE VAT.SAE AIL ENQUIRIES.OFFICIAL ORDERS WELCOME.OVERSEAS Payment must be sterling.IRISH REPUBLIC and BFPO UK PRICES.

EUROPE UK PRICES plus 10%.

ELSEWHERE krone for quote,SHOP HOURS 9-5 MON-FRI.

VISA

PRICE LIST -FREE WITH ORDERS OR SEND SAE


TOP KITSA SELECTION OF OUR BEST PROJECT KITSAs usual these kits come complete with printed circuit boards, cases,all components, nuts, screws, wire etc. All have been tested by ourengineers (many of them are our own designs) toensure that you get excellent results.

INSULATION TESTERAn electronic High Voltage tester for mainsappliances and wiring. An inverter circuitproduces 500 volts from a PP3 battery andapplies it to the circuit under test. Readsinsulation up to 100 Megohms. Completelysafe in use.

OUR KIT REF E444£18.65

DIGITAL CAPACITANCE METERSimple and accurate (1%) measurementsof capacitors from a few pF up to 1,uF. Clear 5 digit LED display indicatesexact value. Three ranges - pF, nF,and uF. Just connect thecapacitor, press thebutton and read thevalue.

£39.57OUR KITREF E493

3 BAND SHORTWAVE RADIOCovers 1.6-30 MHz in 3 bands usingmodern miniature coils. Audiooutput is via a built-in loudspeaker.Advanced design gives excellentstability, sensitivity and selectivity.Simple to build.

OUR KIT REF E718 £25.27

DIGITAL FREQUENCY METER200 MHZAn 8 digit meter reading from A.F.up to 200 MHz in two ranges. Large0.5" Red LED display. Ideal for AFand RF measurements, Amateurand C.B. frequencies.

KIT REF E 563 £59.98

DigitalFrequency Meter

'EQUALISER' IONISER

oreputga

A mains powered Ioniser thatproduces a breeze of negativeions in the air. A compact,safe, simple unit that uses anegligible amount of electricity.

KIT REF E707 £14.79

VISUAL GUITARTUNER

A crystal controlled tuner with aNew type of 'rotating' LED display.Clockwise or Anticlockwise rotationindicates high or low frequency.Perfect tuning is obtained when thepattern is stationary. Suitable forelectric guitar pick-ups or may beused with a microphone foracoustic instruments. Also has anaudio 'pitch pipe' output.

KIT REF E711 £21.99

NEW 1988/9 CATALOGUE

FROM MAGENTA}

EE CROSSWORD 6

CLUES ACROSS5 You are left with this after removing the harmonics.

(11)6 Form of gain control used in t.v. (5, 1, 1, 1)9 Bulk transfer of data. (4)

11 To be honest, a table. (5)12 Power when the current and voltage are in quadra-

ture. (8)13 Only a small charge is made. (7)16 When a signal undergoes any change. (7)19 Circuit that takes the uncertainty out of a switch. (8)21 See 26.23 Vertical line of data. (6)24 One volt through one ohm produces this unit of

measurement. (6)25 Unwanted addition to a signal. (5)26 and 21 This determines the secondary voltage. (5, 5)

DOWN1 State that solder goes through. (8)2 The perfect transformer. (5)3 A reactance coil. (8)4 Logically, don't be up the creek without this. (6)7 Can be used as a dielectric. (3)8 Add blue and green. (4)

10 These cause a shadow in c.r.t's. (5)14 Formerly the wireless. (5)15 Compensated volume control. (8)17 A circuit that maintains a signal at a fixed reference.

(8)16 A million times the basic unit of resistance. (6)18 Plenty of room for this instrument. (5)20 Step backwards to daub this code. (6)22 A balancing transformer. (5)

For fun only-answers on page 420.

II 11 IIII

fi 111111=Mill ilM" III BMUS IIIMIN1111111111

91111119111111111111111111111

Mt 111111M11111 EMI=MI A DI 01111E11111 EMI=II

El 0 MING 1111111111111111

kI II T


ORDERS: RING (01) 567 8910 - 24 HRS.GIANT SOLAR CELLS VERSATILE REMOTE

NOW IN STOCK these giant size solar panels12 x 12in will deliver 12 volts 200mA inbright sunlight and 11.5 volts 60mA on atypical British summer day (dull and over-cast). HUNDREDS OF USES in the car orcaravan, e.g. Charging NiCads, poweringlow voltage circuits where mains or batterysupplies are inconvenient or coupled to alead acid battery and a simple inverter youcould build yourself a self contained mainssupply for low power appliances. Stock No.303 145. £14.50 (plus £1.75 for p&p on totalorder).

SOLID STATE RELAY BARGAIN*Zero Voltage Switching: No radio interfer-ence problems 2.5KV Input to Output Iso-lation: No risk of damage to your computeror driver circuits. *4KV Terminals to Heat -sink Isolation: Simply bolt onto a heatsink. 3V to 32V Input Voltage: easily interfacedto TTI or CMOS Logic. 24V to 240V rmsLoad Voltage: Allowing mains loads to beswitched. *Built in Snubber Network: Ena-bling switching of inductive loads. *10AMaximum Current: 4A with no heatsink fit-ted at 40 deg C.C D240/10

ELECTRONIC GUARD DOG KIT

woos

One ofthe best deterrents

to a burglar is a guarddog and this new kit provides the barking withoutthe bite! The kit when assembled can be connect-ed to a doorbell, pressure mat or any otherintruder detector and will produce a random seriesof threatening barks making the would be intruderthink again and try his luck elsewhere. The kit issupplied complete with high quality PCB, trans-former. all components and instructions. All youneed is a mains supply, intruder detector and alittle time. The kit even includes a horn speakerwhich is essential to produce the loud soundrequired. The "dog" can be adjusted to producebarks ranging from a Terrier to an Alsatian andcontains circuitry to produce a random series ofbarks giving a more realistic effect.XK125 Complete kit of parts £24.00

DISCO LIGHTING KITSO L1000K - This value -for -money 4 -way chaserfeatures bi-directional sequence and dimming.1kW per channel £19.250LZ1000K -A lower cost uni-directional versionof the above. Zero switching to reduceinterference £10.80D IA/1 (for DL & DLZ 1000K) Optional opto inputallowing audio 'beat'/light response .... 77pDL3000K -3 -channel sound to light kit featureszero voltage switching, automatic level controland built-in microphone. lkW per channel E15.60

The DL8000K is an 8 -way sequencer kit with builtin opto-isolated sound to light input which comescomplete with a pre-programmed EPROM con-taining EIGHTY - YES 801 different sequencesincluding standard flashing and chase routines.The KIT includes full instructions and all compon-ents (even the PCB xannectors) and requires onlya box and a control knob to complete. Otherfeatures include manual sequence speed adjust-ment, zero voltage switching. LED mimic lampsand sound to light LED and a 300 W output perchannel. And the best thing about it is the price.

ONLY£31.50

TEN EXCITING PROJECTSFOR BEGINNERS

This Kit has been specially designed for the beginnerand contains a SOLDERLESS BREADBOARD, COM-PONENTS, and a BOOKLET with instructions toenable the absolute novice to build TEN fascinatingprojects including a light operated switch, intercom,burglar alarm, and electronic lock. Each projectincludes a circuit diagram, description of operationand an easy to follow layout diagram. A section oncomponent identification and function is included,enabling the beginner to build the circuits withconfidence. ORDER NO. XK118 E15.00

CONTROL KIT

This kit includesall components(+ transformer)to make a sensi-tive IR receiverwith 16 logicoutputs (0-15V) which with suitable interfacecircuitry (relays, triacs, etc - details supplied)can be used to switch up to 16 items ofequipment on or off remotely. The outputsmay be latched (to the last received code) ormomentary (on during transmission) by spe-cifying the decoder IC and a 15V stabilisedsupply is available to power external circuits.Supply, 240V AC or 15-24V DC at 10mA.Size (excluding transformer) 9 x 4 x 2 curs.The companion transmitter is the MK18which operates from a 9V PP3 battery andgives a range of up to 60ft. Two keyboardsare available-MK9 (4 -way) and MK 10 (16 -way), depending on the number of outputs tobe used.MK1 2 IR Receiver (incl. transformer)

£16.30MK18 Transmitter £7.50MK9 4 -Way Keyboard £2.20MK 10 16 -Way Keyboard £6.55601 133 Box for Transmitter £2.60

HOME LIGHTING KITSThese kits contain all necessary compon-ents and full instructions and are de-signed to replace a standard wall switchand control up to 300W of lighting.TDR300K Remote Control Dimmer £18.00MK6 Transmitter for above £5.10TD300K Touchdimmer £9.30TS300K TouchswitchTDE/K Extension kit for 2 -way

switching for TD300K £2.95LD 300K Light Dimmer E4.75

£9.30

POWER STROBE KITDesigned to produce a

N high intensity light pulseL:Iat a variable frequency of

1

1 to 15Hz this kit alsoincludes circuitry to trig-ger the light from an ex-

-5--

ternal voltage source leg. a loudspeaker) viaan opto isolator. Instructions are also sup-plied on modifying the unit for manualtriggering, as a slave flash in photographicapplications or as a warning beacon insecurity applications. The kit includes a highquality pcb, components, connectors, 5Wsstrobe tube and full assembly instructions.Supply: 240V ac. Size, 80 x 50 x 45.XK124 STROBOSCOPE KIT £13.75

0:14 HIGH SECURITY LOCK KITDesigned for use with our lockmechanism (701 1501 this kit will

operate from a 9V to 155 supplydrawing a standby current of only

501LA There are over 5000 possi-

ble 4 -digit combinations and the sequence can be easily changed

To make things even more difficult for an unauthorised user an

alarm can be sounded aher 3 to 9 incorrect entoes-selectable by

mans of a link. The alarm can sound for a few seconds to over 3

minutes during which time the keyboard is disabled preventing

further entries A latched or momentary output is available making

the unit ideal for dour locks, bulgier alarms, car immobilisers, etc.

A membrane keyboard oi pushbutton switches may be used and a

beep sounds when a key is depressed. Kit includes high quality

PC8, all components, connectors, high power pun buuer and full

assembly and user instructions

XK121 LOCK KIT £15.95350 118 Set of Keyboard Switches £4.00701 150 Electric Lock Mechanism

12 volt f16.50

PROPORTIONAL TEMPERATURE

CONTROLLER KIT

Uses "burst fire" tech-nique to maintain tem-perature to within0.5*C. Ideal for photog-raphy, incubators,wine -making, etc. Max.

load 3kw (240V ac) Temp. range up to 90*C. Size7x4x2.5cms.MK4 f7.80

BARGAINCOMPONENT

PACKSRefill those empty component drawers at a fraction ofthe normal price and don't be caught without that odd

resistor or capacitor to complete your project. Allcomponents supplied are full specification and not

seconds or surplus stock.PACK A: 650x0.25W resistors 47R to 10M £425

PACK B: 60xElectrolytics 1uF-1000uF E3.25PACK C: 30xPolyester Capacitors 0.01-1uF E4.50

PACK D: 36xHorizontal presets 1k -1M £3.00PACK E: 30xIC sockets 8, 14 & 16 Pin E2.00

PACK F: 25xRed LEDs 5mm E1.75PACK G: 25xGreen LEDs 5mm E2.00

PACK H: 30x5mm LEDs- red, green, yellow £2.50PACK J: 50x1N4148 Si. diodes CIAO

PACK K: 40xNPN/PNP transistors BC1821212 GeneralPurpose E2.25

10% OFF when you buy ALL 10 PACKS

$:4 riftFIP

Good quality tools selected to offer outstandingvalue for money.

650 004 bin mini. Snipe Nose Pliers. Serratedjaws and return spring. £2.10650 005 bin lap jointed side cutters: Insulatedhandles and return spring. £2.10650 006 Light duty cutters. Cutting capacity0.22-1.2mm copper wire. £1.60TOOL KIT - Contains, side cutters, snipe nosepliers, wire strippers, flat blade screwdriver, phil-lips screwdriver in black textured, reinforced andpadded case which when opened out measures240x205mm £6.80

650 007 Self -adjustable automatic wire stripperwith built-in cable cutter. £3.95650 012 Watchmakers Screwdriver Set1.0/1.4/2.0/2.4/3.0/3.8mm £1.75650 019 Set of 4 Stainless Steel Tweezers.Straight nosed, straight noosed -reverse action,bent nosed, flat nosed. 110mm long. £3.65650 502 Reliant 9-12V dc Drill. £6.90650 500 Titan 12V dc Drill. £10.25650 570 Saturn Mains Drill. £16.50WE ALSO STOCK ANTEX IRONS AND

ACCESSORIES

LOGIC PROBE

A MUST for working with TTL & CMOS devices.Displays logic levels and pulses down to 25nSwith LEDs and sound. Comprehensive instructionbooklet supplied.Working voltage 4-16V dcInput Impedance 1MMax. i/p frequency 20MHz

ONLY£9.50

0-\14 SUPER -SENSITIVE FMMICROBUG

RECHARGEABLE SOLDERING IRONPowerful cordless iron complete with table -top/wall -mounting charging bracket. Reaches solder-ing temperature in 10 seconds. Includes lampwhich lights when soldering. Comes with mainscharging unit and 12V car batteryadaptor.S ecial offer £15.95

HELPING HANDS

Magnifier and croco-dile clips on ball andsocket joints mount-ed on a heavy base.Ideal for holding andinspecting PCBs dur-ing soldering, faultfinding, etc.(650 035) (3.95

Highly sensitive FM transmitter measuringonly 45x25x15mm, including the built-inmicrophone. Frequency 88-100MHz ena-bling reception on a standard domestic FMradio. Range approximately 300mdepending on terrain. Powered by 9V PP3(7mA). Its small size and highly sensitiveelectret microphone makes it ideal for sur-veillance, baby alarm, etc.INTRODUCTORY PRICE £5.50

LOW COST M ULTIMETERA versatile meter with 19 ranges including 10A DCPt BATTERY TEST. Case is tilted for easy reading.Supplied complete with batteries, test leads and amanual. Ideal meter for the beginner. Inputimpedance 20K ohm per volt. AC Volts:0-10-25-1000V 5%. DC Volts: 0-2 5 20 25 250 +

1000V + 5%. DCCurrent: 0-2.5-25m250mA-10A + 4%.Resistance: 0-10K -100K -10N1Battery test: 9V -1.5VAA -1.5V C Er DProtection: FuseDimensions: 154 x 77 x43mm

405 103 £8.62

SOLAR POWERED NICAD CHARGERTakes up to 4 x AA size.Charges 2 batteries in 4-6hrs. depending on strengthof sunlight. Ideal forboating, caravanning,modellers, etc. £6.50

ELECTRONICWEIGHING SCALES

This kit contains aSingle Chip Micro-processor, PCB,displays and all elec-tronics to produce adigital readout ofweight in Kgs. or Sts.and Lbs. in normal usea toothed wheel(pattern provided) is

m de to rotate when a weight is placed onto thescales, interrupting two infra -red beams. Theprocessor counts the number of teeth passing thesensor lup or down, depending on which beam isbroken first), and shows the reading on the LEDdisplay in Sts. and Lbs., Lbs or Kgms. A PCB linkselects the scale for bathroom or two types ofKitchen Scales. A linear version of the toothedwheel could also be used. Other uses includeup/down counters. A low cost digital ruler could bemade by using a wheel with the correct tooth todiameter ratio. ES! £6.50

I.

ritELECTRONICS SEND 9"x 6" S.A.E.&50p FOR CATALOGUE13 BOSTON RD OR CALL AT SHOP

LONDON W7 3SJ MON-FRI 9-5pmTel: 01-567 8910 SATURDAY 10-4pm

ORDERING INFORMATION:ALL PRICES EXCLUDE VAT=

FREE P&P on orders over £20 (UK only), otherwise addEl 75p + VAT. Overseas P&P: Europe £2.75. Elsewhere

£6.50. Send cheque/PO/Barclaycard/Access No.with order. Giro No. 529314002.

LOCAL AUTHORITY AND EXPORT ORDERS WELCOMEGOODS BY RETURN SUBJECT TO AVAILABILITY


EVERYDAY

INCORPORATING ELECTRONICS MONTHLY

The Magazine for Electronic & Computer Projects

VOL. 17 No. 7 July '88

Editorial OfficesEVERYDAY ELECTRONICS EDITORIAL,6 CHURCH STREET, WIMBORNE,DORSET BH21 1JHPhone: Wimborne (0202) 881749

Fax: (02021 841692See notes on Readers' Enquiries below-weregret that lengthy technical enquiries cannot beanswered over the telephone

Advertisement OfficesEVERYDAY ELECTRONICS ADVERTISEMENTS4 NEASDEN AVE., CLACTON -ON -SEA, ESSEXC016 7HG. Clacton (0255) 436471

VIDEO IMPROVEMENTSWITH the ever increasing use of video cameras to make home videorecordings we find many readers are now keen to improve the

quality of the finished video with better methods of editing. In this issuewe describe a unit that is relatively simple to build but which willprovide a professional style "top to bottom" wipe effect betweenscenes.

Camcorders become more sophisticated almost every month andprices seem set to fall with the introduction of an Amstrad camera at lessthen £500 in the near future. Little wonder that almost every amateursporting event is now avidly videoed either for later dissection to aidtraining or simply for future enjoyment. We hope the projects we havepublished will add to the enjoyment of making your own videos.

KEEPING YOUR PROPERTYOne problem with owning a large range of consumer equipment-

most households now have a colour TV (or two) a video and hi-fisystem-is that such items attract the attention of a seemingly growingband of burglars.

There cannot now be many home owners who have not had theexperience of being burgled or of knowing of neighbours, friends orrelatives who have been. While it seems that little can be done toapprehend the casual thief, it is quite easy to protect our homes from hisunwanted attentions.

With this in mind the Home Security Systems series shows somesimple but efficient circuits for the protection of house and contents.The series also describes a fire alarm add-on so the protection affordedis quite wide. Why not build and install an alarm system instead ofwaiting until "after the horse has bolted" as I did?

SUBSCRIPTIONSAnnual subscriptions for delivery direct to

any address in the UK: £14.50. Overseas:f17.50 (£34 airmail). Cheques or bank drafts (in

£ sterling only) payable to EverydayElectronics and sent to EE Subscriptions Dept.,6 Church Street, Wimborne, Dorset BH211J H . Subscriptions can only start with thenext available issue. For back numbers seebelow.

BACK ISSUES & BINDERSCertain back issues of EVERYDAY ELEC-

TRONICS are available price £1.50 (f2.00overseas surface mail) inclusive of postageand packing per copy. Enquiries with remit-tance, made payable to Everyday Electron-ics, should be sent to Post SalesDepartment, Everyday Electronics, 6 ChurchStreet, Wimborne, Dorset BH21 1JH. In theevent of non -availability remittance will bereturned. Please allow 28 days for delivery.(We have sold out of Sept. Oct. & Nov. 86,April, May & Dec. 86, Jan, Feb, April & May87 & April 88.)

Binders to hold one volume 112 issues) areavailable from the above address for £4.95(£9.00 overseas surface mail) inclusive ofp&p. Please allow 28 days for delivery.

Payment in sterling only please.

Editor MIKE KENWARDSecretary PAMELA BROWNDeputy EditorDAVID BARRINGTONEditorial AssistantCOLETTE McKENZIEEditorial: WIMBORNE (0202) 881749Advertisement ManagerPETER J. MEW Clacton (0255) 436471Classified AdvertisementsWimborne 10202) 881749READERS' ENQUIRIES

We are unable to offer any advice on theuse, purchase, repair or modification ofcommercial equipment or the incorpora-tion or modification of designs published inthe magazine. We regret that we cannotprovide data or answer queries on articlesor projects that are more than five yearsold. Letters requiring a personal replymust be accompanied by a stampedself-addressed envelope or a self-addressed envelope and inter-national reply coupons.

All reasonable precautions are taken toensure that the advice and data given toreaders is reliable. We cannot, however,guarantee it and we cannot accept legalresponsibility for it.COMPONENT SUPPLIES

We do not supply electronic com-ponents or kits for building the projectsfeatured, these can be supplied byadvertisers.OLD PROJECTS

We advise readers to check that all partsare still available before commencing anyproject in a back -dated issue.

We regret that we cannot providedata or answer queries on projectsthat are more than five years old.ADVERTISEMENTS

Although the proprietors and staff ofEVERYDAY ELECTRONICS take reason-able precautions to protect the interests ofreaders by ensuring as far as practicablethat advertisements are bona fide, themagazine and its Publishers cannot giveany undertakings in respect of statementsor claims made by advertisers, whetherthese advertisements are printed as part ofthe magazine, or are in the form of inserts.

The Publishers regret that under nocircumstances will the magazine acceptliability for non -receipt of goods ordered,or for late delivery, or for faults in manufac-ture. Legal remedies are available in re-spect of some of these circumstances,and readers who have complaints shouldaddress them to the advertiser or shouldconsult a local trading standards office, ora Citizen's Advice Bureau, or a solicitor.

TRANSMITTERSWe would like to advise readers that certain

items of radio transmitting equipment whichmay be advertised in our pages cannot belegally used in the U.K. Readers should checkthe law before using any transmittingequipment as a fine, confiscation of equipmentand/or imprisonment can result from illegaluse.

The law relating to this subject varies fromcountry to country; overseas readers shouldcheck local laws.


Constructional Project

ROBERTPENFOLD

Add the professional touch to your videos.This wiper will blank the screen from top tobottom then restore the new scene frombottom to top or vice -versa.

THE most basic method of editing ahome video is simply to cut straightfrom one scene to the next, but much

more professional results can be obtainedusing some form of fader or wiper. With avideo fader the picture is faded down at theend of one scene, and faded back up again atthe beginning of the next one. This gives amuch smoother transition from one scene tothe next, and is generally much better fromthe viewer's point of view.

Wipers take various forms, and some unitscan provide a whole range of wipe effects.What is probably the best general purposewipe effect, and the one provided by thisunit, is the top to bottom type. In otherwords, at the end of a scene the screen isprogressively blanked from the top down-wards until it is fully blanked. At thebeginning of the next scene the screen is

progressively restored from the bottom up-wards.

An added feature of this wiper is that itwill do an inverse of the standard wipe effect,where the screen is blanked from the bottomupwards, and restored from the top down-wards. It also incorporates an audio fadercontrol so that, if required, the audio andvideo signals can be faded up and down inunison.

The audio fader is purely passive inciden-tally, and is just a volume control style vari-able attenuator. Although only a mono typeon the prototype, there should be no diffi-culty in using a twin gang control to accom-modate a stereo audio signal. The unitoperates with a standard PAL compositevideo signal at 75 ohms impedance (not au.h.f. television signal).

VIDEO BASICSA video signal, if viewed in slightly over-

simplified fashion, consists of two basicparts. There is a positive going picture mo-dulation signal, and negative going synchron-isation pulses. A television picture is, ofcourse, produced by scanning an electronbeam in a series of lines across the screen,starting at the top and working downwards.The modulation signal varies the strength ofthe electron beam, which has the effect ofvarying the intensity of light produced at thepoint where it hits the screen (we will ignorethe complications of a colour system).

There are two types of synchronisationsignal; the line synchronisation pulses andthe longer frame synchronisation variety. Aframe pulse is produced prior to each com-plete scan of the screen, and the line pulses

0 V

f EE11.3361

PICTURE MODULATION SIGNAL

NNNNNN:\,./LINE SYNC. PULSES

FRAME SYNC. PULSES

Fig. 1. Simplified representation of a composite video signal.

are produced prior to each line beingscanned. This permits very accuratesynchronisation of the transmitting and re-ceiving equipment, with minimal picture dis-tortion. There is a slight complication in thata system of interlacing is used. All this meansis that on the first frame scan only everyother line is produced, with the missing lines(and only these lines) being scanned on thenext frame.

The British PAL system has fifty framesper second, but only twenty-five completepictures each second. The purpose of theinterlacing is to reduce picture flicker. Thescanning process is certainly too fast for thedot of light being scanned over the screen tobe seen as such, but close scrutiny of a tele-vision screen will clearly show the individuallines of the picture. Also, some screen flickermay be apparent on parts of the screenwhere there is high contrast.

The general nature of a television signal,albeit in greatly simplified form, is shown inFig. I. In reality the modulation signal isvery complex, and has a bandwidth of a fewmegahertz. Also, there are over three hun-dred lines per frame.

SYSTEM OPERATIONA video wiper must blank out the modula-

tion signal at the beginning of each frame,progressively increasing the blanking perioduntil each frame is entirely removed. How-ever, the synchronisation signal must be leftfully intact, and it is not just a matter ofswitching out the entire signal during theblanking periods.

The block diagram of Fig. 2 shows thearrangement used in this video wiper unit.The video input signal is split three ways.One route is via a diode clipper circuit whichclips off the modulation signal but leaves thesynchronisation signal intact. The output ofthe clipper circuit is fed to one input of anelectronic changeover switch. The otherinput of the switch is fed with the video inputsignal. The output of the switch is fedthrough to the output by way of a videoamplifier, which really just acts as a bufferstage and provides the unit with the rightoutput characteristics.

The wipe effect can be obtained by apply-ing a suitable signal to the control input ofthe electronic switch. The direct video signalmust be switched through to the output dur-ing the periods when the picture is required,and the clipped signal must be fed through tothe output during the periods when ablanked screen is required.

A large part of the unit is devoted to pro-ducing the control signal, and this is the func-tion of the top row of blocks. The basic


VIDEOINPUT

DIODECLIPPER

WIPECONTROL

-aVv`--

ELECTRONICSWITCH

VIDEOAMPLIFIER

vuTEL(?n.

Fig. 2. The video wiper block diagram.

function of these is to filter out the framesynchronisation pulses and to use these totrigger a pulse generator which provides thecontrol signal.

First the input signal is taken to a bufferamplifier, and from here it is fed to a lowpassfilter. The frame synchronisation signals arerelatively long, and contain a large low fre-quency component. The line synchronisationpulses, being much shorter and at a substan-tially higher frequency, have comparativelylittle content at low frequencies. The effectof the filtering is therefore to leave the framesynchronisation pulses largely unaltered, butto severely attenuate the line pulses.

The next stage of the unit is an amplifier,but this has its bias level set much higherthan the normal mid -supply level. As a resultof this it tends to clip off the modulationsignal, and provides an output that is vir-tually just the negative going framesynchronisation pulses.

TRIGGER CIRCUITThe next stage is a trigger circuit, and this

provides trigger pulses to the monostablemultivibrator when the input signal goesbelow a certain threshold voltage. In practicethe trigger level is adjusted so that the framepulses reliably operate the unit, but there areno problems with spurious triggering byother signals.

A monostable multivibrator provides anoutput pulse of a duration that is controlledby a C -R timing circuit, and which is inde-pendent of the input pulse duration. Nor-mally this circuit provides a very brief outputpulse, and it blanks only a small section atthe top of each frame. This does not actuallyremove any of the picture at all, as there are

The semi -wiped screen.

ONOSTABLE

WIPETYPE

so-called "spare" lines at the beginning ofeach frame, and it is only some of these thatare removed.

There is a variable resistor in the monosta-ble's C -R timing circuit, and by adjusting thisfor increased resistance the length of theoutput pulses can be increased. This resultsin more and more of the top section of thescreen being blanked off. If the variable re-sistance is set at maximum value, the lengthof each output pulse becomes equal to theduration of one complete frame, and thescreen is fully blanked. Adjusting the vari-able resistance back to its original (min-imum) setting gradually reduces the output

pulse length, and "wipes" the picture backon to the screen.

The opposite wipe effect is obtained sim-ply by using the complementary output ofthe monostable. Whereas the main ("0")output is normally low and provides positiveoutput pulses, this second output (the "notQ" output) is normally high and providesnegative output pulses. With the wipe con-trol at minimum resistance, the screen isblanked. As the wipe control is set for higherresistance, the negative output pulses be-come longer, and the screen is gradually "un-wiped" from top to bottom. A switch is usedto select the appropriate output for the re-quired wipe effect.

CIRCUIT OPERATIONThe main circuit diagram for the Video

Wiper is shown in Fig. 3. The circuit diagramfor the mains power supply is shown sep-arately in Fig. 4.

Taking Fig. 3 first, the input signal isapplied to two simple video fader circuits.One of these is based on Dl and D2 whilethe other is based on D3 and D4. Both thefaders have preset controls (VR4 and VR6),and one of these is set to fade the signal rightdown so that only the synchronisation signalis allowed to pass. The other one is set atmaximum output, but it can be backed offslightly if the non -blanked output of the unitproves to be slightly excessive.

Potentiometer VR5 is adjusted so that thed.c. output levels of the two fader circuits are

The semi -wiped output waveform.


SE 1

10k

4=z. Clmo 1000

C247yII* C3

47y

R2 R3 R510k 1k 100k

-1-129

V13447k

R4104

SR47k

R1510k

D21N414/3

R164k7

cia2200

011N41411

4414

100k

D3£1N4148

R17

(44143541

C433n

C547n

C6

T"'

4176 R1947k 15k

C11220

4420i,

IC5c4016 BE

IC5b4016 BE

IC5PIN 7

f

IC2TLC/ 1

CPR10

100k

894 k 7

7

822k2

IC3CA3140

VR14 k7

R113 k3

R2222k

C121000

TR2BC 549

R25 R264k7 22k

CI eeTR3

C131

Fvvs_ER 51(24430

OUT

R26 4700 68

BC549 6k0

I165

P19512814

R23 R24IC5c 240 6BE

2 k 1k

TR4BC 549

R123k9

SK4AF IN

22k 470 AFOUT

C

R27 R29 SK3 ) '7

COMPONENTS

ResistorsR1, R2, R4,R15, R18 10k (5 off)R3, R17,R20, R24R5, R10, R14R6, R7, R8R9, R16, R25R11R12R13R19R21R22, R23,R26, R27 22k (4 off)R28 6k8R29 470R30 68

All 1/4 watt 5% carbon

1k (4 off)100k(3 off)1k8 (3 off)4k7 (3 off)3k33k9560k18k2k2

PotentiometersVR1 4k7 sub -min hor.

presetVR2 470k lin. sliderVR3 1M sub -min hor.

presetVR4, VR5, VR6 47k sub -min hor.

presetVR7 10k log. slider

CapacitorsC1, C12 100p radial elect.

16V (2 off)C2, C3 47µ radial elect.

25V (2 off)C4 33n polyesterC5 47n polyesterC6 3n3 polyesterC7 22µ radial elect. 25VC8 1n ceramic or mylar

Fig. 3. Circuit diagram of the Video Wiper.

240V ACMAINS

ION/OFFI

S 20

S2b

240V

IEEIC366j

12

V

OUTPUT

Fig. 4. Power supply circuit.

C9 22n polyesterC10, C11 220µ radial elect.

16V (2 off)C13 470µ radial elect. 16VC14 1000µ radial elect. 25VC15, C16 100n ceramic (2 off)

SemiconductorsIC1 p.A741C op. amp.IC2 TL081CP bifet op. amp.IC3 CA3140E PMOS

op. amp.IC4 4047BE CMOS astable

monostableIC5 4016BE or 4066BE

CMOS quad switchIC6 7812 12V 1A regulatorTR1 to BC549 npn siliconTR4 (4 off)D1 to 1 N4148 silicon signalD4 diode (4 off)D5, D6 1N4002 100V 1A

rectifier

VEZMiscellaneous

SK1 toSK4 phono socket (4 off)S1 s.p.d.t. miniature

toggle switchS2 rotary mains switchT1 12-0-12V 250mA

mains transformerFS1 250mA anti -surge

fuse, 20 mm.Case 230x 133 x 63mm; printed

circuit board, available from the EEPCB Service, order code EE612;20mm fuse -clips; slider poten-tiometer bezel (2 off); slider controlknob (2 off); rotary control knob; 8pin i.c. holder (3 off); 14 pind.i.l. i.c. holder (2 off); mains leadand plug; screened lead; wire; fix-ings; etc.

See page 415

Approx. cost £25Guidance only


identical. This is essential, as the output sig-nal will otherwise jump from one d.c. biaslevel to another as it is switched backwardsand forwards between the two signalsources. This would effectively modulate theoutput signal with a 50Hz pulse signal thatcould upset both the synchronisation andpicture processing circuits of the unit fedwith the output signal.

The 4016BE (IC5) is a CMOS quads.p.s.t. analogue switch. The pin compatible4066BE also seems to function properly inthe IC5 position incidentally. In order toobtain the required s.p.d.t. action froms.p.s.t. switches, two switches must havetheir outputs wired together, and their con-trol inputs must be driven with anti -phasesignals. In this case the two switches are IC5aand IC5b. IC5c is merely used as an inverterahead of the control input of IC5b. Thus,when the control input is high, IC5a is

switched on and IC5b is switched off. Takingthe control inputs low reverses the states ofthe switches.

Note that the fourth switch in IC5 is leftunused, but its control input is connected tothe positive supply rail to prevent spuriousoperation and to avoid the risk of damagedue to static charges.

The output of the switching circuit is fed toa standard three transistor video amplifier.This has TR2 as an emitter follower inputstage, TR3 as a common base amplifier, andTR4 as an emitter follower output stage. R30attenuates the output signal to the correctlevel, and provides the unit with the correctoutput impedance.

Transistor TR1 is the buffer stage at theinput of the frame pulse stripper circuit, andthis is an emitter follower stage. The lowpassfilter is a standard three stage (18dB peroctave) type based on ICI. The filter's cutofffrequency is at about 5 to 6kHz. Although itmight seem that a much lower frequencycould be used as the frame synchronisationpulses are at a frequency of just 50Hz, it has

to be borne in mind that the mark -space ratiois far from one-to-one. As a result of this, thepulses consist mainly of harmonics at fre-quencies many times higher than the 50Hzfundamental frequency. A cutoff frequencyof 5 to 6kHz is quite adequate to discriminatewell between the frame and line synchronisa-tion pulses.

AMPLIFIERIC2 operates as the amplifier, and this is

an operational amplifier non -inverting typewhich is direct coupled to ICI. Its voltagegain is set at about 26dB (20 times) by thenegative feedback resistors (R9 and RIO).C8 introduces some further lowpass filtering.

As explained previously, the bias level ofthe amplifier is purposely set very high sothat the positive going content of the signal isseverely clipped. Accordingly, R4 has beenmade much lower in value than R5. Thisnetwork also controls the biasing of the low-pass filter stage, but this factor is not of anyreal practical significance.

The trigger circuit has operational ampli-fier IC3 connected as a straightforward volt-age comparator. VRI is used to set theoptimum trigger threshold level. Under mostsignal conditions the setting of VR1 is farfrom critical, and the unit will trigger reliablyregardless of its setting. Unusually bright ordark pictures effectively produce shifts in thecircuit's bias levels, although the clippingaction counteracts these to some degree. Forreliable operation with a wide variety of pic-ture brightnesses it is still necessary to set upVR1 quite carefully.

Integrated circuit IC4 is a CMOS 4047BEmonostable/astable which is used here in thenegative edge triggered monostable mode.C9 is the timing capacitor and VR2 is thewipe control. It is important that the pulselength from IC4 should never exceed thetime taken per frame. If this should occur,IC4 will fail to trigger on alternate trigger

pulses as it will not respond to trigger pulseswhile an output pulse is still in progress. VR3is adjusted so that, with VR2 set at maximumvalue, the output pulse duration is just belowthe critical point. It is then impossible to setVR2 for an excessive output pulse duration.

Potentiometer VR7 is the audio fader, andthis is a passive circuit that is really totallyseparate from the video wiper circuit. Forstereo operation a twin gang potentiometeris required, plus an extra set of input andoutput sockets. The second gang and pair ofsockets are wired in exactly the same way asVR7, SK3, and SK4.

POWER SUPPLYTurning to the circuit diagram of the

power supply (Fig. 4.), this is a simple designhaving full -wave push-pull rectification and amonolithic regulator to provide a wellsmoothed and stabilised output. On the pro-totype TI is a 12-0-12 volt type with a sec-ondary rating of 250 milliamps. A typehaving twin secondaries wired to give 12-0-12volt operation should be equally suitable. A15-0-15 volt transformer (or twin secondarytype) with a secondary rating of 150 milli -amps or more should also be suitable.

The current consumption of the videowiper circuit is around 80 milliamps, al-though it could be somewhat higher than thisunder worse case conditions. A low power(100 milliamp) regulator could be used forIC6, but there would be a slight risk that itwould not be able to supply enough current.There would be a greater risk of it havingexcessive heat dissipation, and a standard (1amp) 12 volt regulator is a better choice. Itshould not require a heatsink.

Fuse FSI should be an anti -surge type.Using an ordinary quick -blow fuse therewould be a strong likelihood of this blowingat switch -on due to the initial surge of cur-rent as smoothing capacitor C14 charges up.


IC6 O

R22 R25

TR2 TR3+

24 fill

IT2

TR 4

c

1

TSK2

ns00-D6

FS1

NEIL3761

EE612 I

0

0 0

t-to

&I0 00

6 6

? a 1 : -; tres- 24)

- A9FDi lreic9c a ?

CONSTRUCTIONThe main and power supply circuits are

accommodated by a single printed circuitboard (Fig. 5). IC3, IC4 and IC5 are MOStypes, and require the standard anti -statichandling precautions to be observed. Fitthem in holders, but do not plug them inplace until the unit is in other respects com-plete. Handle these devices as little as poss-ible.

Component 106 is mounted horizontally,and its leadouts should be preformed prior tofitting it on the board and soldering it inplace. Do not connect it and then bend theleadouts to shape as this is quite likely todamage the board. The fuse is mounted in apair of fuse- clips soldered to the board.

Five link -wires are required, and they canbe made from 22 s.w.g. tinned copper wire,or pieces of wire trimmed from the resistorswill do just as well.

The preset potentiometers must be sub-miniature horizontal types if they are to fit

Fig. 5. P.c.b. layout for the Video Wiper.

on to the board properly. Similarly, the elec-trolytic capacitors must be miniature radial(single -ended) types, and the polyestercapacitors must have a pitch of 7.5 milli-metres. At this stage only pins are fitted tothe board at the points where connections tooff -board components will be made.

CONTROLSThe prototype was constructed in a metal

instrument case, with slider controls for thewipe and audio fader controls. Slider con-trols operate in -phase, but with S1 in theto operate the two controls in unison. Notethat with S1 in one position these two con-trols operate in- phase, but with S1 in theother position they must be moved inopposite directions.

Provided both hands are available thisanti -phase operation is not too difficult withslider controls. Alternatively, using ad.p.d.t. component for Sl, the extra sectioncould be used to switch the track connec-

H

tiuons of VR2 so that it always operates withthe same sense as VR7. In any event, I

would not recommend the use of rotarypotentiometers in this particular application.

Two slits are required in the left handsection of the front panel for the slider con-trols, and for most slider potentiometersthese will need to be 65 millimetres long andonly about 3 or 4 millimetres wide. In theabsence of special tools for this kind of job,probably the easiest way of making these slitsis to first drill a series of closely spaced 3millimetre diameter holes along the length ofeach slit. A miniature round file is then usedto join up the holes and produce the finishedslits.

Self-adhesive slide control bezels are nowreadily available, and these can give a reallyneat finish, even if the slits in the panel areslightly less than expertly made. The bezelswill probably be a little too wide to fit intothe available space, but they can easily betrimmed down to a suitable size. The slider


C D E

fEE,3161

MAINS LEAD

Fig. 6. Transformer andcontrol wiring for theVideo Wiper.

potentiometers each require two short M3panhead mounting screws. Note that theseare not normally supplied with thepotentiometers.

Switch S1 is mounted to the right of theslider potentiometers, with S2 to the right ofthis. The sockets are mounted on the rearpanel. I used phono sockets for both theaudio and video signals, but these can bechanged for any other types which are moresuitable for your particular setup.

The printed circuit board is mounted on

the base panel of the case as far to the left aspossible. The fixings should include spacersabout 12 millimetres long so that the board isheld well clear of the base panel. It must alsobe held clear of the fixing screws for theouter casing (one of these will damage theboard if 6 millimetre spacers are used, as Ilearnt the hard way).

Transformer T1 is mounted on the basepanel in the vacant area to the right of theprinted circuit board. A soldertag fitted onone of its mounting bolts acts as a chassisconnection point for the mains earth lead.An entrance hole for the mains cable is madein the rear panel, close to T1, and this shouldbe fitted with a grommet and cable clamp toprotect the cable.

Details of the point-to-point style wiringare shown in Fig. 6 (in conjunction with Fig.5). This wiring is mostly quite easy, but it isadvisable to use screened leads for the con-nections between VR7 and the audio in-put/output sockets. Take due care with themains wiring where a mistake could be verydangerous.

The case must be a metal type with a screw -on lid (not a clip -on type) and the case mustbe connected to the mains earth lead. It is a

good idea to insulate the tags of S2 and theconnections to them.

ADJUSTMENT AND USEStart with VR1, VR3, and VR5 at a mid

setting, VR4 set well in a clockwisedirection, and VR6 set fully anticlockwise.For initial testing the best setup is to have thevideo input of the wiper fed from the outputof a video recorder, and the output of thewiper feeding a monitor (or a television setvia a second video recorder).

The unit might work reasonably well withthese settings, but some trimming of VR5will probably be needed before a stable pic-ture is obtained. If a stable picture cannot beobtained try backing off VR4 slightly, orreverse the settings of VR4 and VR6, andthen try readjusting VR5.

For optimum results the fader used to pro-vide the blanked part of the screen should bebacked off no further than is really necess-ary. The fader used to provide the directvideo signal will normally need to be set atmaximum, but it can be backed -off slightly ifthe output of the unit seems to be excessive.It should only be backed -off slightly though,as there is otherwise a risk of upsetting thecolour balance of the signal.

Adjustments to VR4 and VR6 will necessi-tate slight readjustment of VR5 incidentally.

If you have access to an oscilloscope thatcan display video signals, using this to moni-tor the output can make precise adjustmentof these presets much easier. This is espe-cially the case with VR5 where any mis-matching of the d.c. signal levels will beimmediately evident, and easily trimmedout. Without the aid of an oscilloscope acertain amount of patience may be needed inorder to optimise results.

When the unit is adjusted correctly and thescreen semi -blanked, changing the setting ofSI should swop the blanked and normal partsof the screen without any "jumping" of thepicture. Operating the wipe control shouldnot produce any picture scroll or roll.

In order to give VR3 the correct settingfirst set VR2 at maximum resistance. VR3 isthen set for very nearly the highest resistance(most clockwise setting) that does not causethe picture to flicker. It is possible that thisflicker will not occur even with VR3 at maxi-mum resistance, and R13 must then be raisedin value (1M2 should suffice). If the flickeroccurs when VR3 is at minimum resistance(which is unlikely), then simply replace R13with a link -wire.

A certain amount of trial and error isneeded in order to give VR1 the optimumsetting. Try feeding the unit with unusuallylight and dark material, and find a setting forVR1 that gives reliable triggering with bothtypes of scene. A setting that just about pro-vides reliable triggering on very dark sceneswill probably be the optimum one.



HOMESECURITYSYSTEMS PaOWEN BISHOPPart 2 Construction -Extending the systemIn this series our main concern will besecuring the home against intruders, butwe shall also describe devices for securingit against fire. The system is modular, sothat you can adapt it to your needs.

CONSTRUCMON details of the controlsystem are given below, followed bytwo circuits which are "optional ex-

tras" to Part 1, (which outlined the HomeSecurity System).

CONSTRUCTIONIt you are building the p.s.u., the case

should he large enough to hold this, the con-trol circuit hoard and possibly the hack -upbattery as well. If the system uses a mainsadapter or is battery -powered a muchsmaller case will suffice.

The stripboard diagram (Fig. 2.1) showscomponents for stabilizing an unstahilizedsupply, battery hack -up circuit and the con-trol circuit (sections may he omitted if notrequired). Construction presents no prob-lems apart from taking the usual precautionsin handling the CMOS 4011 i.e. Sockets arerecommended for i.c.s to make replacementeasier in case of failure. If your system hasISDs, the power transistor(s) may need smallheat sinks.

The remainder of the wiring depends onthe exact facilities provided. Mount the tog-gle switches in a row on the side of the case.These switches, which include the mainpower switch, should not he labelled (just tomake things difficult for any intruder whofinds the unit). You may prefer to have akey -operated switch as the main powerswitch.

There should he a row of sockets at theback of the case for connecting to the exter-nal wiring. Again, these sockets should nothe labelled, but it is convenient to have themof different colours, to match with plugs of

corresponding colours on the external wir-ing. Opportunities abound for confusing theintruder who manages to discover the controlunit. For instance you could mount a distinc-tive toggle switch on the front of the case andlabel it "Power". The switch could actuallyhe part of the peripheral loop. Turning it offimmediately sounds the alarm!

Fig. 2.1. Construction of the ControlUnit.

UNREGULATED12V DC

(FROM C1+I

A

TR1:

05

Ov(FROM C1- I

A

IEF1 312 GI

1R2

T

TO D6

REGULATOR

0 0 0 0 00 0 0 0 0 0 0 00 0 0 0 0 0 0 00 0 0 00 000

TO 52I LOOP OR -41-ThEXIT LOOP(

15

TO 51

BACK- UP SW ITCH

10 15

0 0 0 0 0 0 0 00 0 0 0 0 0 0 0 0 0

TO 51/52I MA SI

TO SIRENS +

TO LOOP

CONTROL UNIT

20 25 30

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 00

TO

INTL.SIREN8. 55

TO MATS

TO 54

35 37

0 U 0 GI0010

1000 o oc, o 000000000000 0 00 0 0 0 0 00 00000 00 00 00 0 00 0

O 00000000 alo 0 o cO 0 0 o o 0 CI oooc 0 0 ooooo0 0 o 0-'

oc(00000000oo (!) 000000000 00000oooooo0000000000 000000 o0000 0000000000000000 000000 0000000000000000000.0000g01 000

...000000000000000000000000 00000O 0000000000000000000000 5500000'

100 0 0 0 0 00 00 00 0 0 0 0 00 0 0. 0 0 0 0.ooo

BD131,BD132

ro 0 (.2)c 6 e

ZT X 300,ZTX500

390

11110

Everyday Electronics, July 1988

+12V

4FROM

BISTABLE V Ai,*140111 181,

SYSTEM CONTROLCONTROLUNIT

Cl100n

12VLOOP/SIREN +

lEE, 4 66 I

INTERNALSIREN -

EXTERNALc.47)SIREN

Fig. 2.2. Time -Limited alarm circuit.

TIME -LIMITED ALARMThe purpose of the time -limited alarm

circuit is to limit the sounding of the siren orsirens to a period of fixed length. In mostsituations there is little point in allowing thealarm to sound indefinitely. Action needs tobe taken within a few minutes of the alarmbeing triggered. If not, the thieves will haveescaped, or the building been burnt down,depending on what caused the alarm tosound.

If it was a false alarm, perhaps the result ofa faulty or over -sensitive sensor, then allow-ing the alarm to continue is an unwarrantedpublic nuisance. Moreover, neighbours tendto ignore a system that is forever "cryingwolf' for hours on end. An alarm thatsounds frequently for no good reason losesmost of its effectiveness. Although we haveclaimed that our basic system never givesfalse alarms, there still remains the possi-bility of something triggering it off!

If you live in a quiet neighbourhood, youprobably do not relish the idea of shatteringthe calm, should your system be set off acci-dentally while you are away on a fortnight'sholiday. Moreover, there are moves afoot tomake it illegal for an external alarm to soundfor more than 20 minutes, so this extensionto the system will help you comply with thelaw.

TIME CIRCUITThe circuit in Fig 2.2 is an addition to the

control unit (see Fig. 1.9 last month). Ittakes its power supply from the unit. Itsinput comes from the collector terminals ofTRI and TR2 of the unit.

Instead of wiring the siren (or sirens) asthe collector load of these transistors, wereplace them by a resistor (RI). When thealarm is triggered, the potential at the col-lectors falls sharply. This causes a negative -going pulse to pass across capacitor CI. Thetrigger input of the 555 timer i.c. (ICI) isnormally held high by R2, but the low pulsetriggers it. Its output at pin 3 rises from lowto high. This turns on TRI, which has thesiren or sirens in its collector circuit. WhenTR1 is turned on, the siren(s) sounds.

The values of R4 and C2 are chosen so thatthe output of ICI remains high for about 20minutes. If you wish to calculate values forperiods of other lengths, the time in secondsis given by:

t=1.1RC,where R is the resistance of R4, in ohms, andC is the capacitance of C2, in farads. Notethat the period obtained depends upon theactual value of C2, which may be 20 per centgreater or less than its nominal value.

At the end of the period the output goeslow again and the siren is silenced. Note thatICI is triggered by the pulse that is generatedwhen the input potential falls. The fact thatthe main system may still be activated at theend of the 20 minutes (i.e. the peripheralloop is still broken, or a pressure pad is stillunder pressure) does not cause the alarm tobe re -triggered.

RESETThe reset button is provided to allow the

siren to be silenced should it inadvertently heturned on when the system is being set.

The timer circuit is assembled on a smallpiece of stripboard (Fig. 2.3) which is housedin the same enclosure as the control unitboard. The only additional off -hoard compo-nent is SI, which is mounted alongside theother switches. It makes testing quicker if acapacitor of lower value (say, 22/z) is usedfor C2 to begin with. The period for whichthe output of ICI is high is then only about11 seconds.

Do not connect the siren(s) at this stage. Avoltmeter connected as the load to TRI willread OV normally, and about 12V when thecircuit is triggered. When all has been as-sembled and tested, wire the 2200/2 capaci-tor in place. Now the voltmeter should

COMPONENTS

TIME -LIMITED ALARM

ResistorsR1 1kR2 1MR3 10kR4 470kR5 1k5

All VaIN carbon

VairSee page 415

CapacitorsC1 100n polyesterC2 2200µ elec.

16 or 25V

SemiconductorsTR1 ZTX300 npn transistor

Integrated circuitsIC1 555 timer

MiscellaneousS1 SPST switch2.5mm matrix stripboard (10

stripsx 24 holes); 1mm terminalpins (7 off), 8 -pin i.c. socket;connecting wire; fixings; etc.

EXIT DOOR PROTECTIONS3 3 -pole 4 -way rotary switchKnob for S3; mains -switch case

(or similar); Formica for panel (seetext); connecting wire.

Approx. costGuidance only £5

register I2V for about 20 minutes after thecircuit is triggered. If the period is too long,try another capacitor of the same or smallernominal value, or decrease the value of R4.Finally, disconnect the voltmeter and con-nect the siren(s) and the external sirenswitch, if installed previously in the controlunit.

B

10

TrRESET

SI

15 20 24C) 000000000000C 002' , 00C 0000 0,' oil 000 00000n," t 0000 0()OuO 4 g oono0000000000 000000000000 000c 00000000000c 000000000 00 C 00000000000000 00 00 000 000 00 000000000000

Fig. 2.3. Construction of the Time -Limited Alarm.


DOOR JAMBINSIDE I

SWITCHCASE

s

FORMICAPANEL

(EE11.606

BELL- PUSH(OUTSIDE!

Fig. 2.4. Positioning of the exit doorswitch.

EXIT DOOR PROTECTIONThe exit door is always a problem in any

security system. This is the door that youleave by when you go out. Other doors canbe heavily bolted and barred from the inside,but the exit door depends only on its lockwhich is accessible from the outside. Inhe-rently, the exit door is the least secure out-side door of the house. It is obvious that astrongly constructed exit door with a lockconforming to BS standards will minimisethe risks of a break-in. Indeed, havinginstalled such a door, you may decide that itis so secure physically that it need not befurther protected. However, with the aid ofdrills, sledge -hammers and the like, thedetermined intruder can usually breach thestoutest of doors. Electronic security is animportant additional protection.

A simple and reliable system for the exitdoor was described last month, but this hadsome disadvantages. The rather more elab-orate circuit given here overcomes most ofthese. The circuit is based on a rotary switchplaced just inside the exit door (Fig. 2.4).This has three positions:

(1) Inactive-used while you are at home.(2) Leaving-while you are leaving or re-

turning to the house.(3) Unoccupied-when you have left the

house.You need to have an electric door -bell

installed, with a bell -push just outside thedoor. This can be any ordinary low -voltageelectric bell system and may be powered bybattery or mains transformer. Use Fig. 2.5 inconjunction with Fig. 1.9 (from part 1) tofollow the explanation below.

In position 1, the bell -push is connected toits bell circuit by way of S3a and S3b. Thereis no electrical connection between the bellcircuit and the security system. When thebell -push is pressed the door -bell rings. S3cis open, so the exit door switch (S2, usually amagnetic one, in the peripheral security loopor the special exit -door loop) operates nor-mally when the system is activated (forexample, at night when the house is occu-pied).

EXIT PROCEDUREWhen you are about to leave the house

unoccupied, turn the switch to position 2. Inthis position, the bell -push is disconnectedfrom the bell circuit. Switch S3c closes, by-passing S2. The exit door may now beopened or closed without affecting the secur-ity system. Set the security system, prepara-

BELL-PUSHI

S

53c

rEr146511

04

04

03

04

S2 BY -PASS

2 EXITDOORSWITCH

TO BELLCIRCUIT

PERIPHERALSECURITY

LOOP

Fig. 2.5. Circuit for Exit Door Protect-ion.

tory to leaving the house. Leave the housewhen the system is set. In contrast to theoriginal system there is no need to vacate itwithin 20 seconds.

After leaving the house, but before closingthe door, press and hold the bell -push.Reach in through the door and turn theswitch to position 3. In this position, S2 is nolonger by-passed by S3c. Instead it is by-passed by the hell -push, through switchesS3a and S3b. Keeping your finger on the bell -push, close the door. Release the bell -pushbutton. Since the exit door is now closed, S2is closed. The alarm does not sound. Lockthe door before leaving.

While you are away the bell -push button isnot connected to the door -bell. If a potentialintruder tries ringing the bell to test if anyoneis at home, it will seem that the bell is out oforder.

When you return home, the operations arerepeated in the reverse order. Unlock thedoor, press the hell -push, open the door,reach inside and turn the switch to position2. Release the bell -push, enter the house (noneed to hurry!) and turn off the securitysystem. Remember to turn the switch back

Fig. 2.6. Wiring of the exit doorswitch.

to position 1 soon afterward, to reinstate thedoor -bell.

The wiring of the switch is shown in Fig.2.6. The rotary switch is a 3 -pole 4 -wayswitch, with the "stop" set so that it cannotrotate to position 4. Any small plastic casecan be used to house it. For the prototype, aneat housing was made from a white wall -mounting mains -switch case. The switch wasmounted on a square panel of white For-mica, bolted into the case where the mainsswitch unit would normally go. The existingwiring of the door -bell was easily interceptedand run into the housing.

The sequence for operating the switch issimple to learn yet must be carried outexactly. Any incorrect step triggers thealarm. It is unlikely that an intruder wouldknow precisely what to do. However, in abusy area it would be as well if the exit doorwas not readily visible from the street, sothat the sequence cannot be observed byunauthorised persons.

Next month: Smoke Alarm and Temper-ature Monitor.

II 392 Everyday Electronics, July 1988

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393

Constructional Projec

this low-cost suppressor and banishmains spikes and noise to the land of theTrolls. -It will devour them for breakfastand dinner!

EVER had the experience of hearing aloud CRAAAK! from your stereosystem when the 'fridge switches on?

Or spent all afternoon entering a long listinginto your computer only to have the wholelot corrupt?.

Perhaps you've come home looking for-ward to watching EastEnders which you setthe video to record while you were out, onlyto find a blank tape as the machine somehow"forgot" its settings. These are all actual mis-haps the author has come across which havebeen caused by spikes and noise on themains, see Fig. I .

These come from both natural and man-made sources, with r.f. noise generally dueto switch arcing, discharge lamps (neon signsand fluorescent lamps) and r.f. pickup byoverhead lines. Spikes are high voltage tran-sients caused by nearby lightning strikes andswitching large inductive loads such asmotors and transformers. Spikes of nearly2kV on the mains near an installation usinglarge d.c. motors controlled by thyristordrives have been seen on an oscilloscopedisplay.

PLUGFUSEL 0---

N

Cl =DELTA CAPACITOR240V A.C.CLASS UT

fEE11.596)

Fig. 2. Circuit diagram for the Spi-keater.

Whilst suppressing your own appliancesmay help, there's not much you can do aboutyour neighbours', particularly should youlive in a block of flats. Any nearby industrialestates will add their sixpen'orth. and thosewho live in the back of beyond needn't gloateither as farm equipment can be just asnoisy. Overhead power cables and pole

Fig. 1. Effects of noiseand spikes on the mainswaveform.

(=citbool

transformers are particularly vulnerable tonearby ightning strikes.

Commercial computer systems use sophis-ticated filter systems in the mains supplies toremove noise. These devices use LC filtersand transient suppressors and in really criti-cal applications constant voltage trans-formers are often employed. Unfortunately,these devices (especially CVT's) also havesophisticated price tags.

The device to be described is very simple,using only two components, and should costless than three quid to make. It can be usedanywhere and needs no modification to theequipment to be protected and like a certainbleach, should kill 99 percent of householdnoise!incorporated in any mains powered projectwhich may be sensitive to mains noise.

CIRCUITThe circuit diagram, which uses a varistor

and a capacitor network, for the Spikeater isshown in Fig. 2. The varistor clips incomingtransients and is wired across live (L) andneutral (N). It is a semiconductor device of asimilar physical construction to a ceramiccapacitor, with a cocktail of metal oxidestaking the place of the ceramic dielectric.

The varistor presents a very high re-sistance as long as the applied voltage doesnot exceed the rated working voltage. As

TO CAPACITOR

Fig. 3. Wiring to therubber moulded 13Afused mains plug.


soon as a transient happens along, the deviceswitches to a low resistance state, dissipatesthe transient's energy as heat, and then re-verts to its virtually non-conductive state.

Incidentally, metal oxide varistors switchfar more rapidly than the voltage dependantresistors previously used in this application.Varistors are available in a wide range ofoperating voltages, and the one used in thisproject is rated at 275V a.c.

Whilst the varistor takes care of transientsmuch over 275V we've still got smaller spikesand noise to deal with. This is the job of thethree capacitors Cla, Clb and Clc. These alltake the form of a multiple capacitor in asingle package, known as a "Delta" capaci-tor because of its appearance in the circuitdiagram.

Delta capacitors are usually fitted toappliances to suppress interference atsource, but they will help to remove incom-ing noise. For example, when i.c. poweramplifiers first came out in the early 70's(remember the Sinclair IC10 and PlesseySL103D?), a stereo amplifier was built for afriend using two of these devices. The firsttime his elderly 'fridge switched on one ofthese expensive new devices went to that bigp.c.b. in the sky! After fitting a new device, adelta capacitor was wired across the incom-ing mains supply which prevented anyfurther occurrence.

SAFETYBefore leaving the subject of the capaci-

tor, a word or two of warning. The mainssupply carries the risks of both high voltageand high fault currents. This means thatcomponents connected to the mains supplymust be suitable.

NEVER connect any old capacitor, whateverthe working voltage, across the mains supply.Mains capacitors are specially made and con-form to one or both of two standards.

The lower standard is class "X" whichdefines a capacitor intended to be connectedacross the mains supply, between live andneutral. Such a capacitor must be designedfor continuous operation at 250V r.m.s., beself -healing, and under catastrophic failuremust not explode and have limited flamma-bility.

Class "X" capacitors must not be usedwhere failure could expose someone to ashock hazard. Where such a hazard wouldexist a class "Y" capacitor must be used.These capacitors conform to all class "X"

COMPONENTSCapacitors

Cl 0.1µ4-5n+ 5n deltasuppression 250V a.c.

OrCl 0.1p, 250V a.c. Class "X"

(Non -earthedsuppression)

MiscellaneousVaristor, 275V a.c.; standard

industrial rubber 13A fused plug;insulating sleeving and Superglue.

See page 415

Approx. cost c3Guidance only

Wiring to the rubber moulded13A mains plug. The varistorleads should be coveredwith insulatingsleeving.

requirements but, putting it simply, aremade to an even higher standard. They areintended for connection between live or neu-tral and earth.

Whilst separate capacitors could be used inthis project, they would be considerablymore expensive than the delta unit. Also, thenest of capacitors would be bulky and needenclosing to cover the interconnections, de-feating the simplicity of this project. Thedelta capacitor has approval to both class "X"and "Y" standards.

The final item for consideration is the plugitself. I used a rubber industrial type whichhad sufficient room inside to mount the va-ristor. Some of the all plastic domestic typeswill not have sufficient room.

CONSTRUCTIONAssembling the device is very simple.

Firstly bend the varistor leads as shown inFig. 3, push short pieces of rubber or plasticinsulating sleeving over the varistor's leadsand connect the device between live andneutral. The varistor is not polarity con-scious and may be connected either wayround.

Next the delta capacitor has to be con-nected. This has three leads; usually two arethe same colour but one is always different.Where different colours are used these arebrown, blue and green/yellow and are con-nected exactly as a mains lead.

Where there is only one different colouredlead, which may be green/yellow or justplain, this is the "earth" lead. The other twoleads connect to live and neutral, either wayround. When wiring the delta capacitor takeparticular care when routing the leads inparticular the earth lead where it has to findits way past the varistor.

Don't forget to thread the capacitor's leadsthrough the cable entry in the plug top be-fore wiring up. It would probably be a goodidea to change the plug fuse to a 5A or even a3A.

After checking tightness of all connec-tions, and that the delta capacitor's leads aresecured by the cable clamp, fit the plug top.If the top won't fit check your lead routing.Finally, Superglue the delta capacitor inplace on the plug top as shown in the pho-tograph, and the unit is ready for use.

The completed Spikeater with the delta capacitor glued to plug top.


II 1 II 1

E 0

FUSE TO SUITCD <la

DELTA CAPACITOR

0 y1 VARISTOR

MAINST1 04

PRIMARY

OO

OO

IRE145751

Fig. 4. Mains input suppression of earthed equipment.

IN USEActually using the device couldn't be

easier. Many houses have double mainssockets in which case the equipment to beprotected is plugged into one socket and thedevice into the other. Don't forget that bothswitches, where fitted, must be turned on.

Where single sockets are fitted a two-wayadapter may be used. Best of all is whereequipment is fed via a multi -way socket setwhich is the usual method of powering hi-fisystems or computers. Here the device isplugged into the socket nearest the cableentry.

Next, a word or two about safety. Littlefingers would no doubt find trying to dis-lodge the capacitor irresistable, so it's best tokeep the device out of harm's way. It must

only be used where a proper earth connec-tion exists.

Incidentally, the small amount of earthleakage current passed by the capacitor isinsufficient to trip a domestic earth leakagetrip. The prototype is in daily use in my ownhome where an ELCB is fitted.

Finally, there's no reason why the ideas setout in this article cannot be incorporated intopotentially sensitive mains powered projects.Where the equipment is earthed, the deltacapacitor and varistor are wired as shown inFig. 4.

Where the equipment is double -insulatedand an earth connection not used the deltacapacitor cannot be used. Instead connectthe varistor as before but a single class "X"capacitor wired across live and neutral isused instead as in Fig. 5. D.

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FORE

I

YOURENTERTAINMENT

BY BARRY FOX

Death RayRadar was born in 1935 out of an idea

for a death ray. The government askedRobert Watson -Watt of the Radio Re-search Stations at Slough to see whetherit would be possible to generate an elec-tromagnetic beam strong enough to cookhuman flesh or heat an aircraft in flightand explode its bombs. Watson -Wattcalculated that there was no way of gen-erating the power needed, but went on toprove that it was possible to detect air-craft by beaming radio waves at themand receiving the reflections.

It is only now, with nuclear powersources and lasers, that there is a chanceof making a working death ray. PresidentReagan's Strategic Defence Initiative or"Star Wars" project will rely on highpower lasers to destroy missiles in flight.

The German government was still try-ing to make death rays work in World WarII. The army built a high frequency radiotransmitter near Frankfurt. The plan wasto beam signals at aircraft and their elec-tronic ignition. The system did not work,because the signals were of insufficientpower.

After the war, the US army SignalsCorp sent specialists to examine thefailed equipment. Their journey was notwasted; they found and confiscated, Tele-funken tape recorders which had beenused to broadcast Hitler's speeches fromone city while he was safely in another.

During the Falklands War, TV newsteams found that their video cameras andrecorders would not work on the taskforce ships. The pictures and sound wereblemished with cyclic blips and bleeps asthe radar aerials turned. The Marantzsound recorders routinely used by manyradio news reporters quite literallyburned out, as currents induced in thecircuit wiring by the ship's radar signalsfried transistors.

The recorders have plastic cases, whichare fine for domestic use and most re-

porting. But only a metal chassis canscreen against the field from a megawattradar. It exceeds 100 volts/metre. Themilitary used to test equipment immunityonly to fields of five volts/metre; somemodern equipment is now tested at 200volts/metre.

One news crew in the Falklands evenasked the ship's captain to switch off hisradar for a while....

News on Home VideoFirst, some interesting "how it works"

from Mitsubishi in Japan. "Digital Track-ing" is found on new Mitsubishi VHSmachines.

VHS relies on a linear control trackalong the edge of the tape which carriespulses at the picture frame rate (25Hz forEurope). These control the tape transportand keep the rotating video heads in linewith the magnetic tracks which are re-corded obliquely across the tape width.For accurate tracking the stationary headreading the pulse track must remain79mm apart from the video head which isreading the helical track. Any error willcause misalignment of the heads over thetracks and poor pictures on screen.

Difficulties arise for hi-fi recordings,where the f.m. audio and video signalsare superimposed on the tape by twoseparate heads on the rotating drum.Adjusting tracking for a perfect picturemay upset tracking for sound and vice -versa.

Mitsubishi's digital tracking systemdetects the audio and video waveformenvelopes, converts them into digitalcode and sums the two codes. A micro-processor then varies the tracking controlbackwards and forwards until it finds thetracking point at which the summedenvelope is at its largest. This is the opti-mum tracking setting for sound andvision. The whole process takes onlythree seconds.

Smart MoneyShortly before the last Budget the DTI,

Britain's Department for Enterprise, putout a statement by Francis Maude,Minister for Corporate Affairs. Maudewas warning people to think twice beforebuying on credit. In a speech to theNational Consumer Council, Maude cameacross as a smart man with money.

As an example he took a three piecesuite, costing £1,000 and paid for it oncredit over two years.

"With a bank loan at 19.7% AnnualPercentage Rate the total cost would be£1,200-and £1233 using a credit card"he explained.

By coincidence I had just been asked bya magazine to review the Formulatorsoftware pack recently released for theOrganiser. This is a ROM pack containingjust about every scientific, mathematical,

electronic and engineering formula youwill ever need. As a convenient practicaltest I tried to enter Maude's figures andfound I needed extra information, e.g. onhow often the repayments were made.

"The figures came from one of ourspecialists", said Maude's spokesperson.So I spoke to the Specialists' department.They couldn't help either.

So I spoke to the Office of Fair Trading,who said they had got them from sometables and weren't too sure how thetables were concocted.

Eventually I got an answer that talliedwith the Formulator software.

'It's a difficult concept to explain",confided the OFT. "We had to give theDTI the figures because no-one therecould work it out".

It is nice to know that the country is insafe hands.

"Theoretically we can do away with allmanual tracking controls", says inventorYasuo Mitsuhashi, "But so far the publicis not ready for that, so we leave manualcontrol for people to use if they want to-and for shop demonstrations".

The next step is to give the video headssmall freedom for movement, underservo control so that they physically fol-low the line of the tracks on tape even infast search replay. This is Dynamic TrackFollowing. Sounds familiar? Yes, DTFwas used by Philips, in the ill-fated V2000system, by Panasonic in a one-off proto-type VHS deck and by Sony and Ampex inprofessional 1 inch C format machines.But whereas previous DTF machineshave used heads mounted on piezo crys-tals, Mitsubishi is mounting the heads ona moving coil, like a gramophonecartridge.

A piezo crystal needs several hundredvolts to move it, but a magnetic coil re-quires only about 10 volts. Also a headmounted on a piezo crystal twists fromside to side, thus touching only part of thetape surface as it tilts; but a magneticallymounted head can move parallel to thetape surface, maintaining full contact.This improves signal pick-up and thussignal-to-noise ratio.

So far the magnetic heads move only ata fixed rate, for tracking at a fixed speedin fast search mode, known as "noiseerase search". For automatic tracking innormal play, the head will need to adjustcontinually under control of the servosystem. This is much more difficult.

Mitsuhashi makes an interesting point.Sony's Video 8 system (like PhilipsV2000) has no linear control pulse trackand relies for tracking on pilot tones bu-ried in the video signal. With digital track-ing circuitry it would in theory be possibleto do away with both the pulse track andpilot tones.

"If this system had been developed twoyears ago", says Mitsuhashi, "the 8mmformat would probably have been quitedifferent".

VIS and VASAn increasing number of new VHS re-

corders, from all makers, now use theVideo Index and Video Access Searchfacilities recently standardized for theVHS format. Here's how VIS and VASwork.

The linear control track contains 25square wave pulses per second. Nor-mally these are symmetrically shaped.But because the servo control system isgoverned by the leading edge of eachpulse, it is possible to modify the trailingedge without upsetting the servo control.For VIS and VAS the pulse is shortened,to represent a digital one, and left at itsnormal length to represent a digital zero.

The pulse track can thus carry 25 bits ofdata per second. This is arranged in 64 bitwords to label the start and end indexpoints of selected sections of the tape. Toadd extra information on sections of arecording, for instance a numberedaddress point on the tape, an extra 92 bitsare added to the standard 64 bit word.

With the 25 bps data rate, it takes themachine around 2.5 seconds to read anindex start or stop point code and around6.25 seconds to read a numbered addresspoint. Inevitably the recorder overshoots,but it then automatically back tracks tothe exact index or acess point.


City and Guilds

C+3

INTRODUCINGMICROPROCESSORSMIKE TOOLEY B.A.

REVISIONPart 9

In the last part we dealt with programming of microprocessorsystems, introduced flow charts and languages, and also gavedetails of the third Introductory Microprocessors Practical As-signment. In this part we shall bring our series to a conclusionby preparing readers for the second Written Assessment andfourth Practical Assignment. Our final Readers' Forum providesanswers to just a few of the many questions raised by readers.

LEARNING OBJECTIVESThe general learning objectives for

Part Nine of Introducing Micropro-cessors are encompassed in thosealready stated for Parts Five to Eightof the series.

FOURTH PRACTICALASSIGNMENT

Readers who have successfullycarried out the third Practical Assign-ment and who have also followedthe text in part eight will now beready to undertake the fourth (andfinal) Practical Assignment. This as-signment is entitled "Assembly Lan-guage Programming" and the

PAO

Si(GN DO

(WOW

Fig. 9.1. Representative switch inputarrangement.

objective reference is 6.2.6 (see parteight).

As usual, the practical assignmentmust be undertaken at an approvedlocal centre where candidates will beprovided with supervision andappropriate working conditions.Candidates should, however, pro-vide their own A4 note paper, pensand pencils. For its part, the Centrewill provide candidates with anyhardware, data sheets, books orhandbooks required (including fulldocumentation for the microproces-sor -based system, a full instructionset for the microprocessor and de-tails of port connections andaddresses).

Candidates will be supplied withan 8 -bit microprocessor -based sys-tem with (at least) four I.e.d.s fittedto an input port and (at least) fourswitches fitted to an output port.These switches and I.e.d.s are inva-riably fitted to I/O modules andapplications boards designed for usewith educational microprocessor -based systems. The circuits shownin Figs. 9.1 and 9.2 respectively showtypical arrangements employed forswitch input and I.e.d. output andcentres may wish to constructboards specifically for use in this as-signment.

Note that the four least -significantlines of Port A (which must be con -

Fig. 9.2. Representative I.e.d. driver arrangement.


figured for input) are connected tothe switches whilst the four least -significant lines of Port B (whichmust be configured for output) areconnected to the I.e.d.s. The re-maining four lines on each port maybe treated in a similar manner orsimply left floating (i.e. unused).

Candidates are required to writean assembly language programwhich will continually read the stateof the four switches and write theresult to the I.e.d. bank.

The following sub -tasks areinvolved:

(a) Producing an algorithm forsolving the problem.

(b) Draw a flowchart to illustratethe sequence of processes.

(c) Provide details of the necess-ary software routine for con-figuring the port (your tutorwill help with this). The routineshould appear as a processwithin the flowchart andshould be included in your as-sembly language program (to-g et h er with appropriatecomments.

(d) Write (using the instruction setprovided), hand -assemble,enter, test, and debug the pro-gram.

(e) Demonstrate the program toyour tutor (who will check thateach switch correctly controlsits respective I.e.d.).

(f) Hand -in the complete docu-mentation package to yourtutor for marking. Note thatthis assignment should becompleted in 2 hours 30 min-utes and a requirement foradditional time may prejudiceyour chances of success.

MarkingCandidates will have satisfactorily

completed the Practical Assignmentif they can demonstrate success in allitems marked with a square and atleast ONE of the TWO items markedwith a circle in the list below:

Completed within 2 hours 30 min-utes 0

Appropriate algorithm or flow-chart developed

Assembler mnemonics producedusing instruction subset

Program correctly hand as-sembled from assembler codes

Program reads all switches oninput port

Program correctly illuminates allcorresponding I.e.d.s on output port

Program repeats function contin-ually 0

As usual, a period of at least sevendays should elapse before candi-dates are permitted to retake the as-signment. Candidates should alsonote that centres may require that a

retake is carried out using a differentmicroprocessor -based system (andinstruction set!).

SECOND WRITTENASSESSMENT

By now, reade should be ade-quately prepared or the second writ-ten assessment which again takesthe form of a straightforward mul-tiple choice test. The test contains 34questions and the candidate is againasked to select the answer whichthey think is correct from the fouranswers provided. Answers shouldbe transferred to the standard Cityand Guilds Answer Sheet. Candi-dates are reminded that there is onlyONE correct answer to each ques-tion.

The following Pre -Test has beenprovided in order to assist readerswith preparation for the assessment:the questions are similar (though notidentical!) to those with which candi-dates will be confronted.

SECOND WRITTENASSESSMENT PRE-TEST

The following questions are pro-vided in order to nrepare readers forthe style and format of the secondwritten assessment. Prospectivecandidates should carefully readthrough and then answer each ques-tion in turn. When completed, answ-ers should be compared with thosegiven on page 403

The time allowed for the test isextremely generous and has beenset so that candidates should not beconstrained by having to answerquestions in a hurry. Adequately pre-pared candidates should be capableof answering the questions withinapproximately 45 minutes.

Candidates InstructionsThis test contains 34 multiple-

choice questions. In order to passyou must answer a minimum of 24 ofthem correctly. The first number foreach qiistion is the question num-ber whilst the number in bracketsrelates to the module reference.

1. (3.1.2) Which one of the followingis an application for read-onlymemory (ROM) within a micro-processor -based system?

(a) Storage of transient data(b) Storage of binary screen

images(c) Storage of control/monitor

programs(d) Storage of user -programs and

program variables.

2. (3.1.2) Which one of the followingtypes of memory provides rapidaccess non-volatile storage forcontrol programs?(a) Semiconductor dynamic RAM(b) Semiconductor static RAM(c) Semiconductor ROM(d) Magnetic tape.

x

ADDRESSBUS

rEE1460 6 I

Fig. 9.3. See question 3.

3. (3.1.3) Fig. 9.3 shows the simpli-fied arrangement of a memorycell matrix. The feature marked"X" is a

(a) shift -register(b) decoder/latch(c) a parallel to serial converter(d) a serial to parallel converter.

4. (3.1.4) A ROM is to be fitted into amass-produced TV games con-sole. What type of ROM is mostsuited to this application?

(a) Mask -programmed ROM(b) Fusible -link PROM(c) UV -erasable PROM (EPROM)(d) Electrically programmable

ROM (PROM).

5. (3.1.5) A mask -programmed ROMis programmed

(a) during production of the semiconductor wafer

(b) by exposing the device to UVlight after manufacture

(c) using a special programmingdevice which delivers pulses ofcurrent

(d) by a bank of dual -in -lineswitches fitted to the ROM'sdata bus input.

6. (3.2.1) Transient data present in amicroprocessor system is storedin

(a) one, or more, I/O devices(b) a read-only memory (ROM)(c) a read/write memory(d) a write -only memory.

7. (3.2.2) In a microprocessor -basedsystem, read/write memory isusually provided by

(a) semiconductor ROM(b) semiconductor RAM(c) an EPROM(d) a PROM.

8. (3.2.3) In a microprocessor -basedsystem, user -programs and vari-ables are generally stored in

(a) fusible -link ROM(b) mask -programmed ROM(c) either dynamic or static RAM(d) dynamic RAM only.


AO A9

(EE11.89G I

Fig. 9.4. See questions 10 and 15.

9. (3.2.4) Which one of the followingtypes of memory needs constantrefreshing?

(a) Static RAM(b) Dynamic RAM(c) Magnetic tape(d) Magnetic disk.

10. (3.2.5) The block marked "X" inFig. 9.4 represents

(a) a dynamic RAM(b) a static RAM(c) an I/O device(d) an address decoder.

11. (3.3.1) Fig. 9.5 represents a(a) Truth Table(b) Flowchart(c) Memory Map(d) Trace Table.

12. (2.1.3) In the diagram shown inFig. 9.5, the highest address (ex-pressed in decimal) within the

FFFFN

C00011

7EFF.

0000H

ODFFIA

0000.

(EE1/900)

SYSTEMROM

BASICROM

USERRAM

RESERVEDRAM

Fig. 9.5. See questions 11, 12 and 13.

System ROM is(a) 49151(b) 49152(c) 65535(d) 65536.

13. (3.3.2) In the diagram shown inFig. 9.5, the memory space occu-pied by the BASIC ROM (ex-pressed in bytes) is

(a) 3.5K(b) 16K(c) 28.5K(d) 32K.

14. (4.1.2) One feature which dis-tinguishes a system which usesport I/O from one which em-ploys memory -mapped I/O isthe need for

(a) IN and OUT instructions(b) fast dynamic RAM(c) external disk storage(d) specialised I/O devices

15. (4.1.2) In the memory -mappedsystem shown in Fig. 9.4, theoutput signals from the blockmarked "X" are

(a) chip -select signals(b) memory read/write signals(c) memory request signals(d) I/O request signals.

16. (4.1.3) In the system shown inFig. 9.6,

(a) block X is ROM and block Y isI/O

(b) block X is RAM and block Y isI/O

(c) block X is I/O and block Y isROM

(d) block X is I/O and block Y isRAM.

17. (4.2.1) A two -wire connection isemployed for the transfer of databetween a microcomputer and adistant peripheral device. Thissystem employs

(a) a serial data transfer methodand is likely to operate at arelatively slow speed

(b) a serial data transfer methodand is likely to operaterelatively high speed

CPU

Ao

A15

1,PED'

Do

D7

I ORO

ADDRESSBUS

Al()

Als

CS

s../7 AC -AS

CS1

DATA BUS

EEE159ic.1

A0

A7

Cs

CS 1

Y



(c) a parallel data transfer methodand is likely to operate at arelatively slow speed

(d) a parallel data transfer methodand is likely to operate at arelatively high speed.

18. (4.2.2) In order to program a PIOdevice a

(a) sequence of software com-mands must be issued by theCPU

(b) special external programmingdevice is required

(c) hexadecimal keyboard is re-quired

(d) serial I/O port must be pro-vided.

19. (4.2.3) Which one of the follow-ing gives the function of thelines marked CA1 and CA2 inFig. 9.7?

(a) Read/Write control lines(b) Peripheral control lines(c) Register select lines(d) Serial data I/O lines.

20. (4.2.4) Which one of the follow-ing describes the function of thecontrol register in Fig. 9.7?

(a) To determine the mode ofoperation for the port in ques-tion

(b) To determine whether indi-vidual I/O lines within a portare configured as inputs oroutputs

(c) To provide a means of continu-ing I/O operation in the eventof a CPU failure

(d) To decode commands re-ceived from peripheral devicesand pass these on to the CPUfor subsequent execution.

21. (5.1.1) Which one of the follow-ing gives the typical maximumsource current for a PIO outputline?

(a) 1mA(b) 10mA(c) 100mA(d) 1A

OUTPUTPORT

B

RELAYDRIVER

(FE14930

A

B


22. (5.1.2) Which one of the follow-ing output loads will NOT nor-mally require the services of anoutput driver when connected toa PIO?

(a) A CMOS logic gate(b) A conventional relay(c) An I.e.d.(d) A filament lamp.

23. (5.1.3) Fig. 9.8 shows the blocksrequired to interface a relay to amicroprocessor -based system.Which one of the following givesthe connections required?

(a) A to C and B to D(b) A to B and C to D(c) A to D and B to C(d) A to D and B to D.

24. (5.1.2) Which one of the follow-ing is a characteristic of pro-grams written in a low-levellanguage when compared withtheir equivalent written in a

high-level language?(a) Easy to read and understand(b) Written in plain English(c) Operate at a relatively slow

speed(d) Generally require less memory

for storage.

DATA

ADDRESS

CONTROL

NE, 92G(

A CONTROL

A DATA DIRECTION

A DATA REGISTER

B CONTROL

B DATA DIRECTION

B DATA REGISTER 41

CAICA2

PAO -PA7

CBIC B2

PBO -PB7

Fig. 9.7. See questions 19 and 20.

25. (6.1.2) In which of thefollowing applicationsis the speed at which aprogram executesusually considered tobe of paramountimportance?

(a) Data processing soft-ware

(b) Word processingsoftware

(c) Spreadsheet pro-grams

(d) Real-time controlsystems.

26. (6.2.1) The operationsinvolved in developinga program may bestated as:

EE1494$


A Write and enter codeB Formulate an algorithmC Test and debugD Construct a flowchart.

Which one of the following gives thecorrect sequence of events?

(a) ABCD(b) ABDC(c) B DAC(d) B D C A.

27. (6.2.3) Which one of the follow-ing gives the final value of"total" produced by the flow-chart shown in Fig. 9.9?

(a) 0 (c) 3(b) 1 (d) 7

28. (6.2.3) Which one of the flow-chart symbols shown in Fig. 9.10represents a subroutine?

(a) A (c) C(b) B (d) D.

A

OC

(EE14954I

B



29. (6.2.4) Mnemonics are used inassembly language programs to

(a) make programs difficult toread

(b) make hexadecimal arithmeticeasier

(c) represent operations in a formof shorthand

(d) represent addresses with easyto remember symbols.

30. (6.2.5) Which one of the follow-ing assembly language instruc-tions transfers data from theCPU to a port?

(a) INC A(b) DEC A(c) IN A. (FEH)(d) OUT (FEH) ,A

31. (7.1.1) Which one of the follow-ing gives the name of the num-bering system which uses base16?

(a) binary(b) decimal(c) hexadecimal(d) octal.

32. (7.1.2) Which one of the follow-ing gives the hexadecimal rep-resentation of the decimalnumber 114?

(a) 68(b) 6E(c) 72(d) 7E.

33. (7.1.3) Which of the followingdescribes a method of rep-resenting negative numbers in amicroprocessor -based system?

(a) Placing a negative sign in frontof the number

(b) Placing a negative sign behindthe number

(c) Using the most significant bitas a sign bit

(d) Using the least significant bitas a sign bit.

34. (7.1.4) Which one of the follow-ing gives the result of addingtogether the hexadecimal num-bers 47 and 3C?

(a) 77(b) 7C(c) 83(d) 8E

Now CHECK YOUR ANSWERS be-fore looking to see how you scored!

READERS' FORUMSeveral readers have taken me to

task over not giving a sufficiently ri-gorous explanation of the internalworkings of a microprocessor. Inparticular, it would appear that sev-eral of you would have liked furtherdetails of how internal control isapplied. This is, unfortunately, a

rather "meaty" topic and one whichcould require quite a lengthy expla-nation.

Furthermore, there are quite a

number of differences betweenpopular 8 -bit CPUs and any text onthis topic would have to explore thedetailed architecture of several typesin order to be reasonably compre-hensive. However, for the benefit ofthose who would like further infor-mation on this (and other) topics I

have suggested some further read-ing at the end of this instalment.

R. W. Davis writes from Dorchesterto point out that the gate circuitsshown in Fig. 3 of Part One shouldhave been referred to as NAND andnot AND. Roger Seymour -Lee haswritten from Oyster Bay, New York,to mention several errors whichcropped up in Part Four. In particu-lar, the answers to questions 1 and 7of the First Pre -Test should havebeen shown as (c) and (a) and not (d)in both cases.

Roger also says that he found Figs.4.1, 4.2 and 4.3 'totally incomprehen-sible. In fairness, these were in-cluded simply as typical examples ofthe displays produced by a monitorprogram to which I added a fewhand-written notes. readers are notmeant to extract any particular infor-mation from them and they wereprovided simply to indicate the typi-cal format employed.

When using a monitor it is, ofcourse, essential to follow theinstructions provided for the pro-gram concerned. Indeed, it willusually take some time to becomefamiliar with the displays produced.

Lastly, Roger has expressed someconcern over the fact that some ofthe incorrect answers (known ratheraptly as distractors by those respon-sible for writing City and Guildsmulti -choice questions) were termsthat he was not familiar with. In gen-eral, incorrect answers are chosen soas to be plausible but it is not alwayspossible to produce three (incorrect)answers based on correct termino-logy. Sometimes the examiner hasto use phrases and expressionswhich may sound plausible to a

weak candidate but which canquickly be discounted by those hav-ing a little more knowledge!

A number of centres have writtento offer support for IntroductoryMicroprocessors These includeITECs (Information TechnologyCentres) as well as several Collegeshaving Open -Learning Units. In par-ticular Gloucestershire, Rochdaleand Basildon ITEC are hoping tooffer assessment andtutorial/workshop groups as are col-leges at Brighton, Hall Green andDarlington.

Unfortunately, despite this in-creasing interest from educationaland training providers, it stillappears that some readers are hav-ing difficulties with finding anassessment centre. Introductory

Microprocessors is a brand new Cityand Guilds scheme and, despite ajoint letter from EE and C & G sentlast October, many colleges are onlyjust finding out about it. So, if thishas been your problem, please don'tgive up; an enquiry later this yearmay bring success where it has pre-viously failed to produce any reac-tion.

Finally, I would like to offer sincerethanks to all those who have writtenwith comments, suggestions, andqueries. Indeed, my "in-tray" hasbeen kept full to overflowing duringthe last nine months and this hasmade it impossible for me to answereach and every letter.

WHAT NEXT?By the time that you read this, a

follow-up module (ElementaryMicroprocessors) should be avail-able from City and Guilds. This mo-dule should be available from mostcolleges and centres currently offer-ing Introductory Microprocessorsand is designed to provide furtherstudy in the field of microprocessorsand microprocessor -based systems.

Readers may also like to know thata further E.E. series linked to a Cityand Guilds scheme is planned for theautumn. This series will be devotedto the rather more general field ofDigital Electronics (another modulein the City and Guilds 726 Infor-mation technology series. So, as thesaying goes, watch this space....

FURTHER READINGThe following reading is rec-

ommended for those who wish toprogress beyond Introductory Micro-processors:

Microprocessors and Digital Sys-tems by Douglas Hall (published byMcGraw Hill, ISBN 0-07-025552-0).

This book provides an excellentand very comprehensive introduc-tion to microprocessor -based sys-tems and includes chapters on theuse of test equipment, digital logic,interfacing, microprocessor architec-ture, programming, as well as proto-typing and troubleshooting. Severalpopular 8 -bit microprocessors aredescribed in some detail. This bookcan be very highly recommended.

Microelectronics and Microproces-sor -based Systems by Noel Morris(published by Macmillan, ISBN 0-333-36190).

This book covers both hardwareand software and includes chaptersdevoted to memory systems, inter-facing, timing, and program cre-ation. The book makes extensivereference to the Intel 8085 and thusshould suit readers who wish to gainfurther experience of this particularmicroprocessor.


Microprocessor Engineering by B.Holdsworth (published by Butter -worths, ISBN 0-408-013261-3).

This book provides a useful intro-duction to microprocessor systemsand, like the previous title, makesextensive reference to the Intel 8085though some other popular 8 -bitmicroprocessors also get a mention.The book contains chapters whichdeal with logic, memory, small com-puter architecture, instruction sets,assembly language, and data con-version.

16 -Bit Microprocessors by Ian R.Whitworth (published by Collins,ISBN 0-00-383113-2).

This book will be useful for thosewho wish to get to grips with 16 -bitmicroprocessors and it provides acomprehensive introduction to a va-riety of popular 16 -bit processor fam-ilies. Chapters are also devoted tointerfacing, instruction sets, as-sembly code software and develop-ment, system software andoperating systems.

Digital and Microprocessor Electron-ics by Byron Putman (published byPrentice -Hall, ISBN 0-13-214354-2).

This book provides a comprehen-sive guide to the design and trouble-shooting of modern digital andmicroprocessor based systems. Thisbook also uses the 8085 as a rep-

resentative microprocessor and sev-eral chapters deal with this device(the Z80 and 6800 are covered onlyrather briefly). The last two chaptersdeal with an analysis of a microcom-puter system (the IBM-PC) and troub-leshooting methods are discussed.

Microprocessor Systems Engineer-ing by J. Ferguson (published by Ad-dison-Wesley, ISBN 0-201-14657-6).

This book describes the basicskills, tools and techniques requiredto devise, develop and implement amicroprocessor -based project. The6502, Z80, 8086 and 68000 micropro-cessors are considered and usefulchapters are included on softwareproduction, testing and debugging,system development, and interfacesand peripherals.

PRE-TEST ANSWERS1. c 12 c 23.c2. c 13 .b 24.d3. b 14 .a 25.d4. a 15. a 26. c5. a 16. b 27. a6. c 17. a 28. d7. b 18. a 29. c8. c 19. b 30. d9. b 20. a 31. c

10. d 21. a 32. c11. c 22. a 33. c

34. c

How well did you do?Score less than 17: Don't underes-

timate the amount of work that youstill need to do! We suggest that youcarefully work through Parts Five toEight before making a second at-tempt at the Pre -Test.

Score 18 to 27: You have still gotplenty of work to do before you areready to sit the Written Test! Checkthe answers to those which youanswered incorrectly, referring to therelevant part of Introducing Micro-processors in order to see where youwent wrong.

Score 28 to 34: Well done! Youshould be well able to cope with theWritten Test. It is, however, stillworth checking the answers to anyquestions which you answeredincorrectly.

PLEASE NOTEThe Introducing Micropro-

cessors series has proved to bevery popular with both readersand lecturers/teaching estab-lishments etc.

To meet this on -going de-mand for the series we will berepublishing it in book form.The book will be availablefrom Newsagents and fromthe Direct Book Service duringOctober -watch out for full de-tails.

The Archer Z80 61)CThe SDS ARCHER - The Z80 based single boardcomputer chosen by professionals and OEM users.* Top quality board with 4 parallel and 2 serial ports.

counter -timers, power -fail interrupt, watchdog timer.EPROM & battery backed RAM.

* OPTIONS: on board power supply. smart case.ROMable BASIC, Debug Monitor. wide range of I 0 &memory extension cards.

The bowman 68000 61)CThe SDS BOWMAN - The 68000 based single boardcomputer for advanced high speed applications.* Extended double Eurocard with 2 parallel & 2 serial

ports, battery backed CMOS RAM. EPROM. 2 counter -timers, watchdog timer, powerfail interrupt. & anoptional zero wait state half megabyte D -RAM.

* Extended width versions with on board power supplyand case.

6herwood Data6)germ LtdSherwood House, The Avenue, Farnham Common, Slough SL2 3JX. Tel. 02814-5067


by Mike Tooley BA

THIS month, as promised, we embark onanother constructional project in the

form of a Dual Digital -to -Analogue Con-verter (DAC). This device can be used togenerate analogue voltages on two indepen-dent output channels yet only requires mini-mal additional circuitry in order to interfacewith the Spectrum.

Before we begin, however, there's justtime to deal with a query raised by two read-ers who, it seems, may be considering takingtheir Spectrums "out and about" this sum-mer!

Portable Spectrum?A. Holland and J. Thorpe both wish to

operate a Spectrum directly from a 12V carbattery. Happily, this does not present anyreal problem since the Spectrum powersupply delivers a nominal +12V (actuallynearer 10V!); the mains unit can be dis-pensed with and d.c. fed directly from thecar battery to the Spectrum's d.c. power con-nector.

There are, however, two pitfalls to avoid.firstly, since the Spectrum's mains unit deliv-ers nearer 10V than the nominal 12V, dissi-pation within the Spectrum's +5V regulatormay increase somewhat.

Overheating was a perennial problem witholder versions of the Spectrum (Issue 3, andearlier) and thus it would be useful to incor-porate some circuitry to reduce the d.c.supply by a volt, or so. Secondly, since inad-vertent reversal of the Spectrum's d.c.supply will undoubtedly result in permanentdamage, some form of reverse polarity pro-tection is highly desirable.

1.

TOSPECTRUM

POWERCONNECTOR

(EE1461G1

Fig. 1. Suggested 12V d.c. poweradaptor.

Fig. 2. Connections for theSKB2/02L5A bridge rectifier.

Both of these minor problems can besolved using nothing more than an encapsu-lated bridge rectifier, as shown in Fig. 1. Therectifier ensures that the Spectrum receivesthe correct supply polarity regardless of theactual connection of the battery (the 2A fuseis added merely to provide over -current pro-tection in the event of misconnection of, orfailure within the bridge rectifier itself).Furthermore, the total forward voltage dropwithin the rectifier is approximately 1.4Vand it is thus instrumental in reducing thesupply voltage to the d.c. power connector ofthe Spectrum to a more manageable 10.6V.

Provided it is rated at 1.5A, or more, al-most any encapsulated bridge rectifier willoperate satisfactorily in Fig. 1. The pin con-nections for the suggested rectifier (anSKB2/02L5A) are shown in Fig. 2.

DUAL DACAlmost three years ago (in September

1985) we described a Simple Digital -to -Analogue Converter based on the ZN428E.Since then, a number of other DAC chipshave become available including the 7528which offers two identical converters housedin a compact 20 -pin DIL package.

Separate internal data latches are providedfor each DAC which greatly simplifies thetask of interfacing the device to a microcom-puter bus. The 7528 operates from a singlesupply rail (of between +5V and +15V) withextremely low power consumption. The indi-vidual converters employed within the 7528operate using the technique of four quadrantmultiplication and separate reference voltageinputs are provided for each.

The internal arrangement of the 7528 isshown in Fig. 3. Data from the system databus is fed, via an input buffer and internal 8 -

bit data bus, to the two internal 8 -bit datalatches. Data is clocked into a latch whenselected by internal control logic (note thatonly one latch can be enabled at any giventime and that data is held within the latchand the analogue output voltage maintainedat the corresponding level, until new data iswritten to the latch).

The summed output of each converter's"R -2R" ladder network appears at the out-put (pin -2 for Channel A and pin -20 forChannel B). Outputs must be taken to theinverting input of an external operationalamplifier for which an internal feedback re-sistor is provided. This component is fittedbetween pins 2 and 3 in the case of ChannelA and between pins 20 and 19 in the case ofChannel B and it is accurately matched tothose within the "R -2R" ladder network.

Circuit DescriptionThe complete circuit of the Spectrum Dual

DAC is shown in Fig. 4. IC2d and IC2aconstitute summing amplifiers for theinternal "R -2R" resistor networks whilstIC2b and IC2c act simply as unity gain in-verting amplifiers. The outputs of ChannelsA and B are respectively available at SKIand SK2.

IC3 provides address decoding such thatthe 7528 is selected whenever an I/O writeoperation is performed with A7 low.Address line A6 is used to determine whichChannel data latch is selected and this resultsin the address decoding shown in Table 1.

Table 1:Address decoding for the Dual DAC

AddressLines*

DACSelected Address

A7 A6 HEX. DEC.

0 0 A 3F 630 1 B 7F 127

`N.B.: Address lines AO-A5 MUST all beat logic 1.

ConstructionThe Dual DAC may be assembled on a pieceof stripboard measuring approximately80mm x 100mm. The precise dimensions of

Fig. 3. Internal arrangement of the7528 Dual DAC.

VDD

V REF A

080DATAINPUTS

0

DAC ADAC B

CS

WR

0 ONO

DB7

INPUTBUFFER

CONTROLLOGIC

N LATCH

7528

LATCH

EACA

DAC B

(EE14635 I

TVREF B

ORFB A

0OUT A

AGND

ORFB B

20 OOUT B


+5V OW MINI COMPONENTSR1

270C1 oppu min

100 gm OMC2

100n

Ovi681imis

0 0 16A) MIN

D I I 7A !VIM02 IBA I OEM

03111A I liMffi1

04 112A1 Mr

05 110AINIM06 I9A Ina07 13A I NMI

WR 119A1A6 12281 1M1

DI

LED

PIN 14

IC3

PIN 7

00

4

12

TP

R2390

A7 12181 3

10R0117A1IMIlf - 2

IC374 LS32

OV 178111111IN

-5I/120AI NM

IC17528

OR 1

10k

C3 ZV8810p C3V0

02

2 13

IC2LM 324

12

2

IC2aL0324

R310k

R610k

R410k

9

R54k7

OV

IC2bM324

VOUTIB)

RB46 7

R710k

SIC?

(EE146501

Fig. 4. Complete circuit of the Spectrum Dual DAC.

the board are unimportant provided that ithas a minimum of 28 tracks aligned in thevertical plane sufficient to allow the mount-ing of a 28 -way double sided edge connector.This connector should be fitted to the loweredge of the board and will require five holesacross the full width of the stripboard so thatthe board stands vertically when the connec-tor is mated with the Spectrum.

Before soldering any of the components(including the three i.c. sockets) it is import-ant to allow some clearance for the rear over-hang of the case. For the Spectrum this gapshould correspond to 8 rows of holes (20mmapprox.) whilst for the Spectrum Plus and128, the gap should be increased to 12 rowsof holes (30mm approx.).

Component layout is generally uncriticalthough, as with most of our On Spec pro-jects, considerable economies can be madeby carefully planning the layout in advanceof mounting the components and i.c. sock-ets. Readers are advised to carry out thisexercise on paper first (using, if desired, thelayout sheet provided with our On Spec Up-date).

After mounting the i.c. sockets, great caremust be taken to ensure that all unwantedtracks are cut (including, in particular, thosewhich link the upper and lower sides of the28 -way connector). A purpose designedspot- face cutter is ideal for this purpose or, ifsuch a tool is not obtainable, a small sharpdrill bit may be used.

The remaining components (diodes, fixedresistors, capacitors, connectors and pre-setresistor) should then be fitted to the board.As usual, the decoupling capacitors (Cl andC2) should be distributed around the boardwith C2 being placed in close proximity tothe supply input of ICI.

Links on the underside of the board shouldmake use of appropriate lengths of miniatureinsulated wire (of the wirewrapping type).

When the stripboard wiring has been com-pleted, the three integrated circuits shouldbe inserted into their sockets (taking care toensure correct orientation of each device).Finally, the entire board and wiring shouldbe very carefully checked before attemptingto connect it to the Spectrum. (Note that theSpectrum should ALWAYS be disconnectedfrom its supply before either connecting ordisconnecting any interface module). If all iswell, when power is re -applied, the normalcopyright message should appear. If not, dis-connect the power, remove the interface andcarefully check again!

Initial AdjustmentThe procedure for adjusting and testing

the Dual DAC is extremely straightforwardand simply requires the services of an accu-rate (preferably digital) voltmeter or digitalmultimeter switched to the d.c. voltageranges. The interface should be connected tothe Spectrum (as before) and power applied.The voltmeter should be connected with itspositive lead to the test point (marked "TP"in Fig. 4) and its negative lead to OV. VR Ishould then be adjusted for a reading ofexactly 2.56V.

Now transfer the voltmeter leads to SKI(the output of Channel A) and enter thefollowing BASIC commands and, at eachstage, note down the voltage produced:

OUT 63,0OUT 63,255

The voltmeter should read 0.00V and2.55V, respectively.

Finally, transfer the voltmeter leads toSK2 (the output of Channel B), enter thefollowing BASIC commands and again notedown the voltages produced:

OUT 127,0OUT 127,255

The voltmeter should again read 0.00Vand 2.55V, respectively.

ResistorsR1 270R2 390R3 10kR4 10kR5 4k7R6 10kR7 10kR8 4k7

All 0.25W 5% carbon

See page 415

PotentiometerVR1 10k min. pre-set

(preferably multi -turn)

CapacitorsCi 1Oµ p.c. elec. 16VC2 100n polyesterC3 10p, p.c. elec. 16V

SemiconductorsD1 Red I.e.d.D2IC1IC2IC3

BZY88 C3VOAD7528LM32474LS32

Miscellaneous14 -pin low -profile d.i.l. socket (2

required); 20 -way low -profile d.i.l.socket; 2 -way 0.1in pitch p.c.b.mounting connectors (2 required);stripboard, 0.1in pitch, measuringapprox. 80mm x 100mm; 28 -wayopen end double -sided 2.54mm(0.1in) pitch edge connector (e.g.Vero part number 838-24826A);connecting wire; solder etc.

Approx. costGuidance only £18This completes the adjustment and testing

of the Dual DAC and the interface is nowready for use!

Next month: We shall provide some dem-onstration software for the Dual DAC andwe shall also be describing an I/O AddressSelector.

ANALOGUEGROUND

OUTPUT A

RF8 A

VREF A

DIGITAL GROUND

OAC A/DAC B

IMSI31087

DB6

DB5

DB6

1E0 146 4 61TOP VIE

OUTPUT B

RFB B

VREF 8

VDD

WR

Cs

DBO ILSBI

DB1

82

DB3

Fig. 5. Pin connections for the 7528Dual DAC.



AUDIOMINI -BRICKSJOHN BECKER Part 2A planned series of audio building "bricks" that can be connected together in numerousdifferent ways to produce all kinds of sound effects. These basic building modules areexamined in detail and, with one exception, all the circuits use identical i. c. s and a masterprinted circuit board.

The circuits are all self-contained and you can select whichever circuits you want tobuild. All projects are suited to assembly by novice and experienced constructor alike.

Tills month we turn our attention tocreating sound effects using the Volt-age Controlled Filter and also investi-

gate the Ring Modulator.

VOLTAGECONTROLLED FILTER

The principle of operation of the VoltageControlled Filter (VCF) is shown in the cir-cuit diagram Fig. 2.1, and is similar to thatfor the Low Pass Filter. Frequencies are ex-tracted from an a.c. signal by varying capaci-tor charge rates. In this case there are twocapacitors and three stages.

The signal comes into op. amp IC2a whichacts as a mixer stage. Its output is taken in bythe first filter stage around ICla and ICIb.Capacitor Cl absorbs some of the upper fre-quencies. Part of the output is fed back toIC2a, another part is fed forward to the sec-ond filter stage at ICIc and ICId. More ofthe upper frequencies are taken out bycapacitor C15, and further feedback is madeto IC2a.

Due to the nature of the current transferthree frequency pass parameters are devel-oped. Upper frequencies appear at IC2a,and this is the High Pass (HP) output.

VOLTAGECONTROLLED

FILTER (VCR-PLAN B

Fig. 2.1. Circuit diagram for the Voltage Controlled Filter (VCF) giving high pass (HP), low pass (LP) and band pass (BP)outputs.

ICi = LM13600

IC2= TL082

C7 R221R 100k

111-1 IC2a

IRE,3520)

016100k

131k

OCk

RIlock

C3 Ri1p 1

P4.

IC1b

C2

v ERHP OUT BP CUT

020ICC

R1 VR110k 100k

R21CONTROL

100k

'Cid

R39 R34 IBCp,10k 1

LP ,,LJT


201

474

1001

200k

5102

2M2

00112

OUT

CI CIS US00

9v

CIS A100

GU

C /F. 0 B/G E

MAX

,/,LEVEL A

MIN

HIGH PASS

F1 IF16.2.11F2 1,10.1,

LOW

BAND PASS LOW PASS

Graph 3. Filter response in respect ofvarying values of node current andcapacitance values.

10kHv 1002 Mk 3001011

At first sight this may seem odd as it mightbe expected that the signal here should con-tain low frequencies as well. The fact that itdoes not is due to the current transfer charac-teristics of the entire network.

The far end of the circuit at ICId is theLow Pass (LP) output. In the middle atICI b, frequencies between high and low passappear. This is the Band Pass (BP) output.

The spectral range of the three sections isgoverned by the amount of current goinginto the control nodes at pins I and 16. Sincethese are coupled, they both see the samecurrent as delivered from the chosen sourcespreviously discussed.

Filter response in respect of varying valuesof node current and capacitance value is

shown in Graph 3. The maximum and halflevel regions shown relate to the signalstrength seen at the outputs compared to theoriginal level.

VCF LPOUT

+v

(SEIM 301

Fig. 2.3. Block diagram showing thearrangement for a tone control/equaliser.

MIX OUTMIXER

134

(EE1l9UGj

R29

VR6

1534 CIE

535

RII

I I.R3 R4

T

R21 H.

R20 t

T

514

I) 11 .1)545 546 547 R48 R49

Tj

516

R2

HP

IN 3

NJ

-C7-1-INSIN

...It C20 Fo

c 10

C7

I I

RANGE

1510DUI

LOW PASS

VR 9

I I

BAND PASS

5R8

HIGH PASS

N

NV

Fig. 2.2. Printed circuit board component layout for the VCF and Mixer. A fullsize copper foil master pattern was given in Part One, last month.

CONSTRUCTION-PLAN B

The positioning of the VCF componentson the printed circuit board is shown in Fig.2.2 (Plan B). It is optional whether theoutputs are taken via the potentiometers.They could equally well be switched tofurther circuits or equipment.

TONE EQUALISINGWith the wiring shown the outputs are

taken to a mixer stage. This is identical tothat used for the Hex VCO and the configu-ration becomes the Tone Control/Equalisershown in Fig. 2.3.

By varying the signal level passed to themixer inputs, so the output will consist onlyof those frequency bands selected in con-junction with VR6. Between them the fourcontrols allow the VCF to he used as apowerful frequency correction tool.

One useful side effect of this set-up is thatnotch filtering can be introduced. This re-sults in the ability to extract frequencies in anarrow middle range by only using the lowpass and high pass regions. The positioningof the notch is variable by adjusting VR6.Several VCFs may he coupled for increasedfiltering.

Another use of a VCF comes from itsability to change the characteristics of a sig-nal by emphasising its upper harmonics. As

COMPONENTS

VCF and

MIXER

ResistorsR1 R39, R46 10k(3 off)R3, R4, R34,R35 1k (4 off)R8 20kR11 R14,R16R20 R22, R41 100k (12 off)R45 R49R28,R29 4k7 (2 off)

All 0.25 W 5°A ,:arbon

4PACSee page 415

PotentiometersVR' 100k skeletonVRb 100k mono rotaryVR8-VR10 100k log mono

rotary (3 off)

CapacitorsC1. C15C2, C3, C7,C10, C16.C19 -C22C11C23

180p polysty (2 off)

} 1 µ 63 elec. (9 off)

22µ 16V elec.100n polyester

SemiconductorsICI LM 13600 Trans-

ductance op.amp

IC2 TL082 Dual BIFETop. amp.

MiscellaneousPrinted circuit board, 255A, p.c.b.

clips (4 off); 8 -pin i.c. socket; 16 -pini.c. socket; knobs (4 off); connec-ting wire; solder etc.

Approx costGuidance only 6


previously mentioned, waveforms other thansine waves contain upper harmonics. Using aVCF, the basic or fundamental frequencycan be tuned out leaving only a selectedharmonic.

As any synthesiser owner will know, thiscan dramatically change the nature of thesound. This can also be shown by feeding thenon -sinusoidal outputs of the VCO into theVCF and experimenting with different set-tings of the controls.

The effect can be further enhanced bycoupling the control nodes of both a VCOand VCF so that they track in unison. Anobvious control source is to use the voltageoutput of a synthesiser to produce total andharmonic manipulation.

MOCK STEREOAn interesting effect can be produced by

feeding the VCF to two mixers, as in Fig.2.4. This results in a mono signal being splitinto a simple stereo simulation.

Only two of the inputs on each of themixers are used. The low pass output goes toone input of Mixer 1 and the high pass to oneinput of Mixer 2. The hand pass though is fedto the second inputs of each mixer. The out-puts can be fed to separate channels of astereo amplifier.

Thus bass frequencies will be heard on oneside and high frequencies on the other.Middle frequencies form the central image,and their two level controls can be used forpanning or balance. A dual -ganged pot couldbe used instead of two separate controls. Thestereo image can also he shifted by using thehand pass control VR6.

SIMPLE PHASERThe VCF can be coupled to the VCO in

another way, so producing a phasing effect,as in Fig. 2.5. The familiar phasing or "sky-ing" sound as it is sometimes called, comesabout when two signals of identical basiccontent, but varying in relative phase, aremixed across each other.

The change of phase can he achieved byusing a delay module, as will he seen later. Itis also readily obtained by changing thecharacteristics of a filter. It is inherent in asimple filter design that a signal phase shiftoccurs during filtering.

Since the VCF can he controlled by achanging voltage source the phase shift canhe varied in response to the control level. AVCO produces a changing voltage at its out-put and this can he used to automaticallyvary the phase change.

On its own a phase changed signal will notsound any different. But as soon as it ismixed in similar proportions with the originalthe phasing effect will occur.

PHASINGThe triangle wave output of the VCO in

Fig. 1.4 is coupled to the control node of theVCF. Music is fed simultaneously to both theVCF and one channel of the mixer from Fig.1.6. The VCF output goes to the secondmixer channel.

Phase shift rate is controlled by VR6, andis best when at a cycle period of severalseconds. Basic phase shift regions are vari-able by VR7.

Mixer input controls should he set so thatthe two levels arc identical. This will result inalmost complete cancellation of the releventfrequencies as the phases become directlyopposed.

When they shift into total phase agree-ment. a doubting of the output level will

+V

MOCKSTEREO

OUT

OUTCHANNEL

2

(FE 135

Fig. 2.4. Arrangement for producingmock stereo. The bass frequencieswill be heard one side and high fre-quencies the other.

ICi = LM13600

R37100k

P *:_,EF TEXT

Fig. 2.6. Circuit diagram for a simplevoltage controlled oscillator (VCO).The output waveform is shown inphotograph 6.

+V

VR71M

IEEMSO

OUT

Fig. 2.5. Block diagram showing how the VCF can be coupled to the VCO toproduce phasing.

Graph 4. Control resistance/capacitor against frequency for the simple VCO

RI

RIO

101.

20

QI

100k

2000

100

102

IN?10002

R32

CONTROL

C24.6

VOX) F102.6

--0 IOUi

100l0


result. The mixer controls must therefore heset down a bit to avoid overload distortion.

The phasing effect will be most apparentwith complex waveforms, particularly in theupper frequency ranges. With smootherwaveforms of a more sinusoidal nature theeffect will be less noticeable to the ear,though it will be seen on a scope, and per-haps on the VU meter of an amplifier sys-tem.

SIMPLE VCOEarlier, details of a multiwaveform VCO

were given. There are though, many ins-tances when waveform shape is not too criti-cal and a simpler VCO can equally well dothe job. Fig. 2.6 shows how a single stage ofa TCA can be connected to produce a some-what mis-shaped triangle wave. The outputwaveform for the simple VCO is shown inphotograph 6. This is perfectly suitable as afrequency source in all sorts of applicationsranging from signal tracing, to sound effectsproduction. It is also usable as a modulationcontrol source.

As before, the frequency is determined bythe rate at which a capacitor varies its chargein response to a control current. Herecapacitor C24 is connected for positive feed-back to (Cie with the threshold trip point setby the back-to-back diodes D13 and D14.

ICId buffers the capacitor charge, and theresulting waveform is available at C16.Graph 4 shows the plots of frequencies pro-duced by different values of C24 and controlresistance.

RING MODULATORRing modulation effects are second only to

delay effects in popularity. Much has beenwritten on the subject, including a lengthyarticle by the author some months ago. Evenin its simplest form a ring mod can imposemost profound changes on a music or voicesignal.

R45100k Fig. 2.7. Circuit diagram for the Ring

C21 R47 AModulator.1J9

MOD IN

SIGNALIN

R46100k

100k

V REF

(IE199161

IC1. LM13600

1C2=TL082

IC1b C21

IHO OUTI

R3910k

RING MODULATORBRICK-PLAN C

6-Simple VCO output waveform.

7-Ring Modulator: Upper trace, I.f. mo-dulation. Lower trace, combined h.f. and1.f. modulation.

COMPONENTS

RING MODAND SIMPLE VCO

ResistorsR1, R8, R10R32, R39, 10k (6 off)R40R7 20kR12, R28, R29 4k7 (3 off)R13 -R15R37,R45-R47R35 33k

100k (7 off)

All 0.25W 5% carbon

PotentiometersVR1 50k skeletonVR2VR3VR6VR8

CapacitorsC2, C8, C10C16, C21C11C14C23

1k skeleton100k skeleton100k mono rotary100k log. monorotary

See page 415

1µ elec. 63V (5 off)

22µ. elec. 16V15n polyester100n polyester

SemiconductorsD13, D14 1N4148 (2 off)IC1 LM13600 transcon-

ductance op. ampIC2 TL082 dual BIFET

op. amp

MiscellaneousPrinted circuit baord, 2551; p.c.b.

clips (4 off); 8 -pin i c. socket; 16 -pini.c. socket; knobs (2 off); connec-ting wire and solder, etc.

Approx costGuidance only E 15

409

O

CD

I R10 k

4.1 RB 1.4

V01

4E\1\3;61VR6

I I

LJvC0 RATE

T

ri R37 j.3C3333C13

nrnrcrn

irt R12 ).

002

R14 R15 1116

T T

VR8

RING MODOUT

I I

LJVCO OUTPUT/

MODULATION INPUT LEVEL(EE14.77G I

+V

00

SIGNAL

Fig. 2.8. Printed circuit board component layout for the Ring Modulator and the Simple VCO.

In essence two signals arc brought to-gether. They are not combined as happens ina mixer, but instead they intermodulate.Normally the speech or music signal goes toone input and an oscillator signal to theother.

The method of combination results inextra harmonics being produced. A typicalRing Modulator waveform is shown in pho-tograph 7. These are related to the sum andthe difference of the two. In this way it ispossible to build up rich chord structuresfrom otherwise unremarkable sounds. Sim-pler effects can also he easily produced, suchas robot or Dalek type voices.

The circuit diagram for a Ring Modulatoris shown in Fig. 2.7. This circuit shows abasic way of producing ring modulation byusing the transconductance amplifier (TCA)i.e. as a four quadrant multiplier.

The two signals to be combined arebrought in via the op. amps IC2a and IC2b.They are simply buffers, and play no activepart in the modulation. The voice or musicsignal goes to the inverting input of ICI. Themodulating signal goes to ICI control nodeand varies the gain factor in response tochanges in the waveform amplitude.

The gain of the TCA (ICI) is alsogoverned by the current going into resistorR7. Since this is connected to the output ofIC2a, the gain is additionally controlled byvariations in the signal level.

Preset VR2 sets a bias level to both theinverting and non -inverting inputs of ICla.With careful adjustment a balance point canbe set so that in the absence of a modulatingsignal the TCA will not pass the primarysignal.

Likewise, preset VR1 needs to be set so

Fig. 2.9. Showing how the Ring Mod and Simple VCO can be connected toproduce robot voices and music modulation.

EXTERNALSPEECH

ORMUSIC

fEE139201

OR

VCO

FIG1 8OR VCO

FIG 26

VCO

FIG1 8 ORVCO

FIG 26

VRB100kLOG

R9100k

LOG

sG

RING MODFIG 2 6

OUT

that the modulator signal does not passthrough in the absence of the primary. Thebalance precision is not as accurate as will befound in more complex ring modulators, butthe unit is a worthwhile addition to a soundeffects armoury.

CONSTRUCTION-PLAN C

The printed circuit board componentlayout for the Ring Modulator and theSimple VCO is shown in Fig. 2.8.

Some of the ways in which the module canbe connected to various speech, music andVCO sources is shown in Fig. 2.9 and thep.c.b. layout combines this arrangement toform one unit (Plan -C). Robot voices andmusic modulation effects can be directly pro-duced from the unit connections shown.More complex results can be created by feed-ing synthesiser VCOs into the two inputs.

Next Month: Frequency Doubler, Fuzz,Tremolo, Wobble Wah and an EnvelopeShaper.


SUN -TANTIMER

Sunburn, ,unstroke and peeling could all beavoided if there was a device to let you know whenyou have just the right amount of sunlight todevelop a tan but not enough to cause damage.Such a device now exists in the form of theSun -tan Timer. This compact lightweightpocket -sized project sounds a penetratingalarm, piercing enough to wake anyone fromthe deepest slumber when it has received aset amount of sunlight. This set amount is

fully adjustable to allow for any sort of skintype and so that built up tolerances to

sunlight acquired after several days in thesun can be compensated for.

STREET -WISE CARSMotorists should find it moredifficult to get lost in the 1990sthanks to electronic navigationsystems. Several carmanufacturers and electronicscompanies have alreadydemonstrated prototypes. Systemsemploying satellite receivers and CDdata storage plus RadioData System traffic and roadreports will soon be possible.

TEA -TUNEThe Tea -Tune is designed to hangon the side of a cup where itmonitors the drink until thetemperature falls below a presetlevel, upon which it loudly plays amedley of popular tunes. Ofcourse, the device has otherapplications; being pocket -sizedit can be used to monitor andsignal a fall in temperature inalmost any liquid (fish tanks,photographic processing etc.) oreven ambient air temperature,e.g. it could be used as a personaltemperature monitor for theelderly-warning of a fall in roomtemperature below a "safe"level, or as an ice warning etc.

All this plus our regular features and parts 3 of Home SecuritySystems and Audio Mini -Bricks. Make sure of your copy-placean order with your newsagent or take out a subscription now!

pAY

BrinErRomicsAUGUST ISSUE ON SALE FRIDAY JULY 1


b...11eeb...13eeb...BeebBe. . . EPROM Programming . . EPROM Programming . .

"rHE accompanying listing is the pro -I gramme for the EPROM programmer

described in the previous two BEEB Microarticles. It is menu driven and is largely selfexplanatory when run, but a few notes toclarify things are in order. Option 1 allowsyou to enter data into the buffer used to storethe programme.

The actual BBC memory addresses andthe relative addresses (i.e. the offsets fromthe base address, which are effectively theEPROM addresses) are both displayed, to-gether with the value in each location. Thelatter are given in both hexadecimal and de-cimal, but can only be entered in hexadeci-mal. You can scroll up and down to get toany desired address, or the jump facility canbe used to move straight to any (relative)address.

Option 2 is essentially the same, but itallows data to be entered in decimal form.With option 3 you have access to operatingsystem commands. This is primarily so thatthe contents of a disc can be displayed, andthe buffer can be saved to disc and reloaded.

Option 4 is used to blow an EPROM,having first selected 8 or 16K operation usingoption 5 (and having remembered to set theright programming voltage on the pro-grammer). The programme gives a scrollingdisplay which shows how far it has pro-gressed, and it will indicate a programmingerror if one should occur.

Option 6 simply stops the programme andtakes the computer back to the BASIC CLI.

ImprovementsThe programmer does not use a fast pro-

gramming algorithm, and it will take a fewminutes to programme even an 8K EPROM.Line 2130 controls the time for which theprogramme waits while each byte is pro-grammed. You can try values lower than 8 inan attempt to speed things up slightly.

There are two obvious additions to maketo the programme, or to have as separateprogrammes. The first is to have an erasurechecking facility. This only requires a verysimple programme. It is basically just a mat-ter of setting the user port lines as inputs,enabling the output enable terminal of theEPROM, and then reading in the value fromeach address of the EPROM. Each byteshould be &FF (255 decimal), and the pro-gramme must indicate that erasure is imper-fect if any other value is detected at anyaddress. The setup procedure followed by areading procedure based on a FOR . . .

NEXT loop should suffice.Reading in the contents of an EPROM for

copying purposes is much the same, but thevalues obtained must be written into a blockof free RAM. This is again just a matter ofusing the setup procedure plus a routinebased on a FOR . . . NEXT loop (with theupper and lower RAM addresses being usedas the maximum and minimum values in the

loop). It is then a matter of using anotherFOR . . . NEXT loop to output the contentsof the RAM block to the new EPROM,using a blowing/checking routine of the typeused in the listing shown here.

Morley EPROM ProgrammerThe BBC Micro has one of the largest

range of readily available commercial add-ons-possibly the biggest range of all. Itseems especially rich in the number and va-riety of add-on EPROM programmers. Itseems as though every manufacturer of BBCadd-ons produces at least one of thesedevices. It is probably a popular add-on forthe BBC micro due to its sideways ROMfacility, rather than because a lot of BBCmicro owners are into developing their ownmicro based systems.

Prices and facilities vary enormously fromone unit to another. Some seem able to pro-gramme any EPROM under the sun (includ-ing some that I have never heard of before),while others are strictly for the 27*** series,as used for the sideways ROMs. The unit Ihave been using for the last few months is theMorley EPROM programmer V2, which is inthe low cost category. It can programme2764, 27128, and 27256 EPROMs, with both12.5 and 21 volt programming potentialsavailable. In this respect it is similar to theEPROM programmer described in the pre-vious two articles in this series, but my designcannot handle the 27256 (32k) devices.

This unit seems to have been designedwith simplicity of operation very much inmind. The nearest thing it has to a control isthe lever on the 28 way ZIF socket! It is fully

software controlled. In common with mostcommercial EPROM programmers for theBBC micro, it connects to the user port, andthis is the only port that is used. Clearly a fairamount of multiplexing and demultiplexingis required in order to control everythingfrom the nine output lines of the user port,but it seems to work flawlessly.

SoftwareThe manual for this device does not exist

as such. There is a photocopied A4 sheetgiving some basic details, including how toobtain help screens when running the soft-ware supplied with the unit. This softwarecan be on disc or EPROM. I obtained thedisc software and tried out the unit by trans-ferring this onto a 27128 EPROM (the ROMimage is included on the disc). The helpscreens are brief but concise.

While documentation is not a strong pointof this product, the unit and software arevery easy to use, and I had no real difficultiesin using the unit. It is not one of the pro-grammes where you tend to keep gettingstuck, and have to reset the computer to getback in control! It should also be borne inmind that an EPROM programmer is notreally a beginner's add-on, and mostEPROM programmer documentation seemsto (quite reasonably) assume a fair amountof technical knowledge on the part of theuser.

The programme is menu driven, and youare presented with the main menu as soon asit is up and running. You can select thedesired EPROM type, and alter the pro-gramming voltage if the default voltage is

The main menu screen.

411.- Fursc t i on

SELECT EPROM TYPE, 2764d,128.0'256

B LOAD/SAVE BUFFER

C VERIFY ERASURE

D READ EPROM INTO BUFFER

E PROGRAM EPROM

F EXAMINE BUFFER

G VERIFY PROGRAMMING

H SELECT PROGRAMMING VOLTAGE

SELECT HELP

(C) Morley Electronics 1987 v2.01


A_

10 REM EPROM BLOWER PROGRAM

560

20 REM J.W.P. 4/88

570 DEF PROCscreen

30 MODE 7

580 CLS

40 DIM BUFFER 16384

590 PRINT "Enter values and press RETU

50 dec$="1234567890"

RN"

60 hex$="1234567890ABCDEF"

600 PRINT "'J' to jump to (relative) a

70 BASE=BUFFER:LIMIT=BUFFER+8191:S=BU

ddress"

FFER:C=BUFFER:F=BUFFER+16

610 PRINT "ESCAPE to end"

80 ON ERROR GOTO 370

620 PRINTTAB(6,6)"ADDRESS"

90 *FX4,1

630 PRINTTAB(3,7)"ABS";TAB(7)"REL";TAB

100

(18)"HEX";TAB(31)"DEC"

110 VDU26,I2:REM menu start

640 VDU28,3,23,37,8

120 PRINTTAB(13,4)CHR$(141);"EPROM BLO

650 PROCfillscreen

WER"

660 ENDPROC

130 PRINTTAB(13,5)CHR$(141);"EPROM BLO

670

WER"

680

140 PRINTTAB(5,9)"1.

ENTER HEX DATA T

690 DEF PROCprintline(line,addr)

0 BUFFER"

700 PRINTTAB(0,1ine)SPC(35);

150 PRINTTAB(5,10)"2.

ENTER DECIMAL 0

710 PRINTTAB(0,1ineWaddr;TAB(8,1ine)

ATA TO BUFFER"

;"addr-BASE;TAB(19,1ine)'?addr;TAB(32,1i

160 PRINTTAB(5,111"3.

O.S. COMMANDS

(ne)?addr;

LOAD/SAVE, ETC.)"

720 ENDPROC

170 PRINTTAB(5,12)"4.

BLOW EPROM"

730

180 PRINTTAB(5,13)"5.

CONFIGURE 8/16K

740

BUFFER"

750 DEF PROCfillscreen

190 PRINTTAB(5,14)"6.

QUIT PROGRAM"

760 FOR lines=0 TO 15

200 PRINTTAB(5,18)"Select by number ke

770

PROCprintline(lines,S+lines)

YE":

780

NEXT lines

210 REPEAT

790 ENDPROC

220

KII=GET$

800

230

K=VAL(KS)

810

240

UNTIL (K>0) AND (K<7)

820 DEF PROCenter

250 IF K=1 HEX=TRUE:PROCenter

830 PROCscreen

260 IF K=2 HEX=FALSE:PROCenter

840 IF HEX col=19:length=2:valid$=hex$

270 IF K=3 PROCoscli

ELSE col=32:length=3:valid$=dec$

280 IF K=4 PROCblow

850 VDU31,col,C-S

290 IF K=5PROCconfigure

860 inp$=FNvir(length,valid$)

300 IF K=6 GOTO 350

870 IF inp$="" GOTO 920

310 GOTO 110

880 IF HEX inp$="&"+inp$

320 END

890 inval=EVAL(inp$)

330

900 ?C=inval

340

910 PROCprintline(C-S,C):IF inval>255

350 *FX4,0

VDU7:GOTO 850

360 STOP

920 C=C+1:PROConscreen

370 *FX4,1

930 GOTO 860

380 IF ERR=17 GOTO 110

940 ENDPROC

390

REPORT:PRINT "

at line ";ERL

950

400

PROCkey

960

410

GOTO 110

970 DEF PROConscreen

420

END

980 IF (C<S) AND (S>BASE) PROCscrolldo

430 DEF FNvir(length,valid$)

wn

440 LOCAL out$

990 IF (C=F) AND (F<=LIMIT) PROCscroll

450 *FX21,0

up

460

in=GET:in$=CHWin)

1000 IF C<BASE C=BASE

470 IF in>127 PROCline(in):GOTO 450

1010 IF C>LIMIT C=LIMIT

480 IF in=74 PROCjump:GOTO 450

1020 VDU31,col,C-S

490 IF in=13 THEN=out$

1030 ENDPROC

500 IF in=127 AND LEN(out$)<>0 THEN ou

1040

t$=LEFTS(out$,LEN(out$)-1):VDU 127:GOTO

1050

450

1060 DEF PROCscrolldown

510 IF INSTR(valid$,in$)=0 OR LEN(out$

1070 VDU30,11

)=length THEN VDU7:GOT0450

1080 F=F-1:S=S-1

520 out$=out$+in$

1090 PROCprintline(0,C)

530 VDU in

1100 VDU31,co1,0

540 GOTO 450

1110 ENDPROC

550

1120

1130

1140 DEF PROCscrollup

1150 VDU31,0,15,10

1160 F=F+1:S=S+1

1170 PROCprintline(15,C)

1180 VDU31,co1,15

1190 ENDPROC

1200

1210

1220 DEF PROCline(code)

1230 PROCprintline(C-S,C)

1240 IF code=138 C=C+1

1250 IF code=139 C=C -1

1260 PROConscreen

1270 ENDPROC

1280

1290

1300 DEF PROCconfigure

1310 CLS

1320 PRINT:PRINT

1330 PRINT "Buffer can be configured as

:-" 1340 PRINT "1 x 16K block"

1350 PRINT "OR 2

x 8K blocks."

1360 PRINT:PRINT

1370 PRINT "Please select:-"

1380 PRINTTAB(5,12)"1.

BOTTOM 8K BLOCK

1390 PRINTTAB(5,13)"2.

TOP 8K BLOCK"

1400 PRINTTAB(5,14)'3.

16K BLOCK"

1410 REPEAT

1420

K$=GET$

1430

K=VAL(K$)

1440

UNTIL (K>0) AND (K<4)

1450 IF K=1 BASE=BUFFER:LIMIT=BASE+8191

1460 IF K=2 BASE=BUFFER+8192:LIMIT=BASE

+8191

1470 IF K=3 BASE.BUFFER:LIMIT=BUFFER+16

383 1480 S=BASE:C=BASE:F=BASE+16

1490 ENDPROC

1500

1510

1520 DEF PROCjump

1530 line=VPOS

1540 PRINTTAB(0,1ine)SPC(35);

1550 VDU31,8,1ine

1560 addr$=FNvir(4,hex$)

1570 IF addr$="" PROCprintline(C-S,C):V

DU 31,col,C-S:ENDPROC

1580 addr=EVAL("&"+addr$)+0ASE

1590 IF addr<C PROCjumpup

1600 IF addr>C PROCjumpdown

1610 CLS

1620 PROCfillscreen

1630 VDU31,col,C-S

1640 ENDPROC

1650

1660

1670 DEF PROCjumpup

1680 IF addr<BASE addr.BASE

1690 IF addr-line<=BASE S=BASE ELSE S=a

ddr-line

1700 C=addr

1710 F=S+16

1720 ENDPROC

17734g

1750 DEF PROCjumpdown

1760 IF addr>LIMIT addr=LIMIT

1770 IF addr-line+16>=LIMIT F=LIMIT+1 E

LSE F=addr-line+16

1780 IF addr-line+16<LIMIT F.addr-line+

16 1790 C=addr

1800 S=F -16

1810 ENDPROC

1820

1830

1840 DEF PROCoscli

1850 CLS

1860 *FX4,0

1870 PRINT "Enter MOS (*) commands at *

prompt.'

1880 PRINT "(*LOAD,*SAVE,*CAT etc.)"

1890 PRINT "All addresses in HEX"

1900 PRINT "Current block starts at ";

BASE;" length ";'"LIMIT -BASE

1910 PRINT "Null entry or ESCAPE to exi

t." 1920 VDU 28,0,24,39,5

1930 INPUT "*"cmd$

1940 IF cmd$."" THEN *FX4,I

1950 IF cmd$=""ENDPROC

oo

1960 OSCLI cmd$

1970 GOTO 1930

1980

2000 DEF PROCblow

2010 CLS

2020 PRINT "Blowing EPROM..."

2030 ?&FE62 = 255

2040 ?&FE63 =

255

PM

2050 ?&FE6C =

224

2060 ?&FE61 =

6

2070 ?&FE61 =

4

2080 FOR byte=BASE TO LIMIT

2090

PRINT "Memory addr. ";-byte;" EP

ROM addr. ";"byte -BASE

2100

?&FE60=?byte

2110

?&FE6C =

192

2120

?&FE6C = 224

2130

T.TIME:REPEAT UNTIL TIME -T>8

2140

?&FE62 =

0

2150

?&FE61

=0

2160

IF ?&FE60<>?byte PRINT "Failed a

t ";"byte:PROCkey:ENDPROC

2170

?&FE61

=4

2180

?&FE62 =

255

2190

?&FE61

=5

2200

?&FE61 =

4

2210

NEXT byte

2220 PRINT "Operation successful."

2230 PROCkey

2240 ENDPROC

2250

2260

2270 DEF PROCkey

2280 PRINT "PRESS ANY KEY TO CONTINUE"

2290 REPEAT UNTIL GET

2300 ENDPROC

EPROM -EDIT Escape to3760 00 00 00 00 00 003768 00 00 00 00 00 003770 00 00 00 00 00 003778 00 00 00 00 00 003780 3C 66 66 7E 66 663788 00 00 3C 66 60 663790 00 00 3C 66 66 663798 00 00 6C 76 60 6037A0 00 00 7C 66 66 6637A8 00 00 00 00 00 0037E30 <18).38 18 18 18 183788 7E 06 OC 18 30 3037C0 7E 06 OC 18 30 3037C8 3C 66 6E 7E 76 663700 00.00 00 00 00 003708 70 6C 66 66 66 6C37E0 7E 60 60 7C 60 6037E8 3C 66 60 3C 06 6637F0 00 00 00 00 00 0037F8 00 00 00 00 00 003900 00 00 00 00 00 003808 00 DO 00 00 00 00

end00000000663C3C6066007E30303C0078603C00000000

00000000000000000000000000000000000000000000

<ff.4-fff...<4£f<...<fff...1v£££...111ffff.

000.000.

<fn÷vf.xifffix.+ECM 1E£E .< f C< . f < .

The EPROM edit screen. You must scroll to the desired address.

wrong for the device you wish to pro-gramme. You can also load or save data todisc, verify erasure, load data from anEPROM into memory, examine the block ofmemory used for data storage (and edit itscontents), verify correct programming, or gointo the help pages.

EditingEditing the buffer is very straightforward.

You are presented with a display that showslines of eight bytes of data in hexadecimal.Addresses are shown to the left of these,

with ASCII characters for the bytes dis-played on the right hand portion of thescreen. This ASCII display is useful forchecking purposes when entering data that istext for a screen display, or something of thisnature. Maybe I am misinterpreting the dis-play, but the ASCII data seems to be headed"HEX"! Changing byte values is very easy.It is just a matter of moving the cursor usingthe cursor keys, and typing in new values.Tile screen scrolls vertically and seems to beable to display any part of memory if youscroll it far enough. It seems to be contin-

ually reading values from memory, and willshow changing values if you display (say) theinput/output area of the memory map!

I had no difficulties in using the Morleyprogrammer and software to copy EPROMs,or to load EPROMs with my own pro-grammes entered into the buffer. The unituses a fast programming algorithm, andclaims to programme a 16K EPROM in anaverage time of under 30 seconds. I did nottake any programming times to check this,but programming was being completed in amatter of seconds rather than minutes.

ConclusionThe Morley EPROM programmer is a

very neat and efficient product, as is thesoftware supplied with it. Building your ownEPROM programmer can certainly becheaper, but the Morley unit represents verygood value for money. The do-it-yourselfapproach is likely to provide worthwhile butnot really massive savings when compared tothis unit. It you only wish to programme2764, 27128, and 27256 EPROMs this pack-age is certainly worthwhile considering, and Ihave no hesitation in recommending it.

If you require a unit that can handle awider range of devices you will need to lookelsewhere, but you will probably have to payabout twice as much (or more) to satisfy yourrequirements. When comparing EPROMprogrammer prices bear in mind that thesoftware is sold separately in some cases, andsometimes at quite a high price. Make sureyou know exactly what you are buying beforeparting with hard earned cash.

Further details from: Morley Electronics,Unit 3, Maurice Road Industrial Estate,Tyne and Wear, NE28 6BY (Tel. 0912627507).

(0983) 292847 Xen-Electronics (0983) 292847 1E3VISA

Just a sample of stock. Ask for items not listed. Super Project Kit BargainsIC's4001118 12

401108 12

4011 12

4017 31

4028 29

4040 .38

4053 32

4066 19

4081 12

45148 .95

2130ACPU 1.85

280APIO I.687217IPI 4.006402IPL 730555 41

558 3.30

741 25LM380N 1.87

TDA3810 556TL074CP .51

SG3526N 3.69

563526J 4.92

SL4860P 220SL49000 /13M19260P 3.04

55766

LE.D.'s5rnm dmRed 13

Green 12

Orange 21

Yellow .15

3rnm diaRed .13

Green .13.Orange ."-'Yellow 13.

MTPBNIO 144

TIP121 34

TIP126 34TIP31C .30

TIP32C 302N2646 1.18

253055 .47

I5W Cover 10725W Ski 60

25W Plug 53

25W Cover 1.16

PCB Mount15W Skt 10215W Plug .39

25W Plug 215

MetalisedPolyester5/7.5mm Pitch3.3nF 400V .08

0.010µF 100V .08

0.0220 63V .08

0.0470 100V 080.1µF 63V 080.1W 63V .11

0.33µF 63V 33

0 47iif 63V .17

Z80 BASED CONTROLLER BOARDThis super little micro board using the very powerful Z80A CPU runningat 4Mhz has all the necessary hardware to control menial to the mostcomplex tasks. The PTH PCB measuring only 107 x 118 comprises 2KEPROM (empty), 2K static RAM, 16 input lines using two 74LS244 and 16output lines using two 74LS373. The port connections are via four 10Wpin strips, each having eight data lines, one ground and either NMI, INT,WAIT or RESET. A must for the small application.

Order as: 280A-CTRUK Kit Form £20.45Z80A-CTRUB Built and Tested £24.95Z84C-CTRUK Cmos Kit Form £26.95Z84C-CTRL/B Cmos Built and Tested. £31.45

RS232 TO CENTRONICS CONVERTERThis handy little interface is ideal for running parallel printers from aserial port, the low cost way out of buying expensive parallel ports foryour computer. Originally designed for the Sinclair QL and NorthstarDimension in mind. The PCB measuring 60 x 62 comprises of the 6402UART, Baud rate generator and all necessary logic, comes complete withwire and ribbon cable and 36W Centronics plug. (For 'D' Type connectorand hoods see selection on left. Sinclair QL SE -131 Plug available extra at£1.68, order as 900-71052F).

Order as: RS232 -8/K Kit Form £18.40RS232 -8/B Built and Tested £23.90

DISTANCE MEASURING INSTRUMENTAn invaluable handy instrument ideal for quickly measuring rooms nobigger than 50 feet sq. The ultrasonic processing PTH PCB measuringonly 77 x 85 has all the necessary components to output the distance infour digit BCD (multiplexed) reflecting either feet, meters or yardsselectable by a three position switch. The kit comes complete with Para -bolic reflector and transducer. Available extra is a liquid crystal displayboard measuring 51 x 101 which can be wired to the BCD output to theabove board directly to display the distance in 0.5 inch high digits.

Order as: UDMI26/K Kit form £24.95UO114126/13 Built and Tested £34.95LCDM4/K LCD Kit form £14.30LCDM4/B LCD Built and Tested £16.95

TrMcs2560705 100045 1.29135137 600V 162 Capacitors

Radial Lead2.2µF 50V 06

F 63V 112.2o .

4.7µ1 63V 0633µF 16V 0447,2F 10V 06

41µF250 0647oF 35V

08

47oF 63V 08

47oF 1000 .15

10oF35V M10µF 630 .06

22µF1000 .21

100oF 10V 86100µF 16V .06

IOW 25V .07

1000 350 -08

100oF 50V 19

100µF 63V 21

220µF700 06

3300 160 19

470of 160 25470µF 500 40

470o163V S31000µ .F 10V 23

1000µF 16V .27

2200µF160 .45

Fixed VoItageRegulators7805 36

7803 .68

7812 .36

7815 36

7824 68

79°5 .39

7912 2.10

7915 39

7924 39.

78105 2818108 28

78112 .28

78115 36

79105 .30

79112 30

79115 30

Infra -Red Emitter115105A 69

Disc Ceramic10pF 63V 05100p1500 p6160pF 50V .05

220pF 50V .05

0.0)µF257500 .05

001oF 1 kV .27

0.022µF 630 10.

00.047µF 50V12

.1 F 25V ..0.1µgF 50V .07

Infra -Red Sensor

TP57035 1.89

I.C. SocketsLow Cost6 Way 05

8 Way .07

14 Way .11

16 Way .13

18 Way 15

20 Way22 Way .18

24 Way 20

28 Way .23

40 Way 33

Turned Put6 Way 12.

8 Way 16

14 Way 28.

16Way .32

18 way .36

20 W40

ay.44

24

22 WayWay 48

28 Way 56

40 Way 80

ResistorsCarbon Film0.25 Wan 5%1 to 1011

.02 each0 5 Wan 5%1011 to 10845/

.04 each

Diodes154061 05104.002 .05

104003 05

1N4004 .05

154005 .05

1N4007 .06

155401 12

155406 14.

TransistorsBC107 16

BC10/1 21

BC109C 19BC182 ,05BC212 -05BC546B 04BC556A 04BD233 42

806755 32

806765 32

BFY51 54

BF259 58

BSR50 49

1R1520 161

IRF840 4.10

JI12 57

Thennister Bead

INICI0 M 4 7 2 W14.7 1(111 1.95

Potentiometers

1'03 M....Carmel Top Adj1001, 30

I Ki! 30

5(11 30

1001? .50

20811 50

100811 50200(81 50

-

Axial 1.064/.4.7p163V 06

10oF 35V .11

47µF 25V 10

1000 25V 18

100.F1000 18470µF100 .22

1000pF 10V 31.

Zeoer Diodes2V7 4W .05

5VI 9W 057V5 4W 06

9V1 4W .06

10V 4W 06

1 IV 4W 05

ConnectorsD -Type solder9W Ski 43

9W Plug 38

MCom m15W Ski 60

15W Plug .53

Mail or Telephone Orders only please to:Dept 14, Samuel Whites Estate, Bridge Road, Cowes, Isle of

Wight P031 7LP. Please add £1 for 1st class post andpackaging, and 15% VAT to total. Stock listing available

soon, please send SAE to be put on the mail list.


SHOPTALKOptical Encoder

A product that should appeal to theexperimenter, and being offered at a spe-cial price, is announced by Greenweld.

The Optical Shaft Encoder, made bySharp, produces two phase -shifted out-puts plus a sync pulse once every revol-ution. It is claimed that the opticalencoder is ideal for use in robotics appli-cations or anywhere the position andspeed of a rotating shaft needs to beknowr

The complete unit, with comprehensivedata, costs just £8.50 inclusive and isavailable from: Greenweld ElectronicsLtd., Dept EE, 443D Millbrook Road,Southampton, SO1 OHX. n0703 772501.

Extension LeadWhy is it that whenever there's an elec-

trical breakdown around the home, or inthe car, it nearly always happens wellaway from the nearest electric powerpoint and you end up cursing that thesoldering iron lead or electric drill leadfalls short by inches! This is certainly acase where the purchase of an extensioncable reel more than makes up for theinitial outlay.

The latest cable reel range of productsfrom Briticent include models whichincorporate a safety cutout to protectagainst overloads and a neon light to in-dicate mains on. The cable reels are sup-plied with cable and fused plug.

The 1500W version comes with 10m ofcable and the 3250W version with 8m ofcable. Both versions are fitted with twinsocket outlets.

For further information and addressesof nearest stockists write to: BriticentInternational Ltd., Dept EE, Crow ArchLane, Ringwood, Hants, BH24 1NZ(T10425 474617).

CONSTRUCTIONAL PROJECTS

Video WiperThe slider potentiometers required for

the Video Wiper project are about twicethe price of rotary types but do add that"professional" touch to the finished unitand are certainly worth the extra outlay.You can, of course, use rotary types if youwish.

Looking at the author's prototypemodel, we see that a 4066BE quad bilate-ral switch has been used for IC5 insteadof the 4 -pole 1 -way analogue switch type4016BE specified. The 4066 is pin -for -pincompatible with the 4016, but has a lower"on" resistance. The 4016 is rec-ommended for sample and hold circuits.Both devices should work in this circuit.

The rest of the components seem to bestandard items and should not cause anypurchasing difficulties. The printed circuitboard for the Video Wiper is availablefrom the EE PCB Service, code EE612

Audio Mini -BricksThe master printed circuit board 1E7.90)

for the Audio Mini -Bricks series of pro-jects is available from Phonosonics, 8 Fi-nucane Drive, Orpington, Kent, BR5 4ED.

Universal Charger/Power SupplyMost component suppliers should

carry stocks of the 3 -pin DIN "In -Line"socket called up in the comp list for theUniversal Charger/Power Supply. Provided a larger case is used, you can, ofcourse, use a chassis mounting DINsocket.

The type and physical size of mainstransformer purchased will also governthe size of case used. The one used in theprototype model was a miniature p c.b.mounting type and just about fitted intothe "PSU box", fitted with an integral 3 -pin 13A plug. These type of cases arenow quite common and stocked by mostcomponent advertisers.

It should be noted that the "tab" of thevoltage regulator i.c., type LM317M, isalso connected to the Vout pin and careshould be taken to avoid shorting it toother components. Because of the pres-

ence of mains voltages it is important totake extreme care when carrying out anywork on the unit.

SpikeaterThe three -in -one 250V a.c. suppression

capacitor used in the Spikeater was pur-chased from Maplin. This three lead deltacapacitor is listed as a "Motor Suppres-sor", code HWO7H (Delta Cap).

If readers experience any difficulties inlocating a local source for the Varistor, itis currently listed by Maplin as a "mainstransient suppressor", type HW13P(Mains Trans Supp). They are also stock-ists of the Class X capacitor (order codeFF56L) required for "non -earthed" sup-pression.

Although it is suggested that thecapacitor can be "Superglued" to the out-side cover of the rubber mains plug, itmight, for safety reasons, be a better ideato build the unit inside a PSU box, fittedwith an integral plug. A typical exampleof this type of case is shown in the pho-tographs of the Universal Charger/PowerSupply in this issue.

lsolinkThe high voltage, high sensitivity opto

transistor isolator, RA57M, called for inthe lsolink is a Maplin type number. It isquite possible that other advertisers, suchas Xen, Greenweld and Marco, might beable to offer an equivalent. However, theyhave not been tried in -circuit and it isimportant that they have identical specifi-cations. This means a minimum 100 percent transfer ratio and be capable of iso-lation voltages of 5300V r.m.s. (7500Vpeak).

The p.c.b. foil pattern for this projectshows an 8 -pin configuration for the optoisolators, even though they are 6 -pindevices. The reason for this is that 6 -pini.c. holders seem to be non-existent andthe 8 -pin holder is universally stocked.The i.c.s should be plugged into the topsection, i.e. at pin one, usually designatedby a notch or cutout in the holder.Another alternative would be to employsoldercon pins and make up a 6 -pin "sta-tion".

The printed circuit board for this projectis available from the EE PCB Service,code EE613 (see page 000).

Spectrum Dual DACReaders may experience difficulties in

locating a source for the dual 8 -bit digital -to -analogue converter i.c. specified in thismonth's On Spec feature.

The only listing for the AD7528 dual 8 -bit DAC chip we have been able to locateis from Electromail ISS0536 204555),order code 633-600 or 301 921.

Home SecurityMost of the components required for

this month's circuits in our new series onHome Security are standard products andshould be stock items. However, the bat-tery back-up i.c. is only listed by Maplin,code UH36P (ICL7673).

A large range of specialist intruder sen-sors are stocked by Riscomp and theyshould be able to supply all of the various"detectors" called for in this series ofarticles. Riscomp Ltd., Dept. EE, 51 PoppyRoad, Princes Risborough, Bucks, HP179DB (n084 44 6326).

We cannot foresee any componentbuying problems for the Diode Pump, thismonth's Exploring Electronics project.


1


ISOUNKANDY FUNDConnections without contact!

HE "Isolink" conducts voltage signalsfrom d.c. to around 30kHz between itsinput and output terminals. "Amaz-

ing", you might say, "hut surely two hits ofwire can do that?"

Well yes, but the Isolink does offer somesignificant advantages over wire. For a start,it will withstand high voltages between theinput and output connections without pass-ing current, allowing measurements to bemade on normally inaccessible circuits suchas those connected directly to live a.c. mains.

The capacitance between input and out-put, due mainly to stray coupling, is less than10pF. As this presents an impedance greaterthan 300 megohms at 50Hz it enables investi-gation of sensitive battery -powered circuitryby mains powered test gear with virtually nocoupling of mains "hum".

This has obvious applicationsareas of electronics, but should be of especialinterest to bio-feedback enthusiasts. Theprototype was in fact designed to assist withthe development of a brain -wave monitorcircuit.

OPTO-ISOLATORAn "opto-isolator" device was chosen as

the basis for this project as it offers efficientsignal transfer with low supply current. Mostother methods require tens of milliamps (atleast) of transmitter drive current, and it wasintended from the outset that this circuitwould be battery powered.

(6E143961

Fig. 1. Simplified representation ofthe opto-link circuit stage.

Another factor in this choice was avoid-ance of the need to "encode" signals fortransmission. Fibre -optic and infra -red sys-tems usually employ frequency or pulsewidth modulation, but these involve an extra

OUT

O'r

oscillator which might interfere with sensi-tive bio-feedback circuitry. Although opto-isolators are not totally linear, the problem isquite easily overcome, as will be seen.

A simplified version of the circuit appearsin Fig. 1. The input is applied to one side ofamplifier Al. The output from this amplifieris routed through the input I.e.d.s of twosimilar opto-isolators in series, so that bothreceive exactly the same current, and feed-back taken from the output of one of them isfed back to Al. This enables the amplifier tocompensate for most errors in the isolatorresponse, so both of the isolator outputsshould be accurate copies of the input. Thesignal from the second isolator is buffered byA2.

CIRCUIT DESCRIPTIONOf course, it's not quite that simple, as a

glance at the full circuit diagram (Fig. 2) ofthe Isolink will show. To begin with, theinput may be an alternating voltage. Theremust therefore be a quiescent current in theisolators which can both rise and fall, and theinput and output "grounds" must be placedsomewhere between the supply rails. IC1bwith resistors R3 and R4 set the input groundto about 1V.

Stability caused a few design headaches.There seems to be a brief delay between theapplication of a signal to an isolator inputand its appearance at the output, possiblydue to charge storage in the transistor. Atany rate, if the transistor is the sole source offeedback the circuit bursts into uncontrolla-ble oscillation, so some h.f. feedback is pro-vided from the input side through capacitorC I .

As it is taken after the I.e.d.s, at least theirerrors will be compensated for. Low fre-quency and d.c. feedback is derived entirelyfrom an isolator output, so the performancehere is excellent and even temperature -in-duced drift is mostly cancelled out.

The isolator type specified for this projecthas a stated "transfer ratio" of 100 per cent,meaning that for each milliamp of input amilliamp should be conducted by the outputtransistor. In practice there is a fair degree ofvariation between individual devices, so pre-set adjustment is necessary to compensatefor this.

Starting with the high frequency compen-sation, if the ratio between the two feedbackpaths is adjustable, it is possible to trim thecircuit for optimum high frequency response.This is carried out by preset VR1 which va-

_ .t ' between the return resistances


from the isolator inputs and the transistor in1C2.

Next, the transfer ratios of the two iso-lators probably won't be exactly the same, sogain adjustment with preset VR3 sets thecorrect output level. The "ground" connec-tion on the output side is also offset to permitnegative signal swings and, as the d.c. out-puts of the two isolators are unlikely to heexactly the same, preset VR2 gives a smallrange of compensatory adjustment.

COMPONENTSResistors

R1, R3, R5R2R4R6, R7, R14R8, R15R9, R11,R16, R18R10, R17R12R13

10k (3 off)1M2k7220 (3 off)33k (2 off)

22k (4 off)68k (2 off)3k3470

All 0.6W 1% metal film

PotentiometersVR1,

VR3 470 sub -min horiz.preset (2 off)

VR2 1k sub -min. horiz.preset

CapacitorsCi 1n polyestyreneC2, C3,C6, C7

C4, C8

C5, C9

See page 415

100n polyester layer(4 off)100µ axial elec. 10V(2 off)470,a axial elec. 25V(2 off)

SemiconductorsD1, D2 3mm Hi -bright I.e.d.

red (2 off)IC1, IC5 CA3240E Dual op -amp.

(2 off)IC2,1C6 High -sensitivity,

high voltage Opto Iso-lator. (Maplin RA57M)(2 off)

IC3,1C7 CA3130 Op -amp.(2 off)

IC4, IC8 78L05 5V 100mApositive voltageregulator (2 off)

MiscellaneousS1 Miniature d.p.s.t.

toggle switchSK1,

SK2 Chassis phonosockets (2 off)

Case, ABS box, 150x 80x 50mm;printed circuit board, availablefrom EE PCB Service, code EE613;8 -pin DIL socket (6 off); 12V batteryholder (2 off) (for 8 x "AA" cellseach); interconnecting wire;solder; etc.

Approx. costGuidance only £20

POWER SUPPLYRegulated supplies are essential for both

sections of the circuit, these being providedby two 5V 1(X1nA "78" series regulators. Asthe circuit is battery operated, a warning ofimpending supply failure on either side is aworthwhile addition.

Two 3130 op -amps, 1C3 and 1C7, comparevoltages derived from the battery and the

SKIINPUT

SIGNAL

R1

10k

INPUTGROUND,

stablised 5V rails. With the resistor valuesgiven, the I.e.d.s will light when the supplyvoltage has dropped to about 8V.

Note that the 3130's have no compensationcapacitors, this being unnecessary in a

switching comparator application. Alsothere arc no series limiting resistors in theiroutputs, as these effectively limit the currentto about 8mA anyway.

Fig. 2. Complete circuit diagram for the lsolink.

(2 /OUT

R310k

8218

IC1b

SK2OUTPUL

SIGN A

R510k

IC2RA57M

R6220

vRI470

R

220

RE335

H

TRI

R922k

R1058k

3

IC3CA3130

C2100n

e"A

,== C_102u

01H, B

IC45y

CC)

I 3 1

IN 1(

IC5oCA3:

12 /OUT

OUTPUTGROUND 7 IC5b

CA324OE

(Eft,. 40 GI

IC6RA57M

SETZERO

VR21k

R13470

SETGAIN

814220

VR3470

615 R1733k 6Ek

R1622

IC7CA3130

R113

22k

IC85v

IN (11

C6100n

=C8

Hi Or

100p

COM31

C7100n

C94708

12VBATTERY

A

Stbi\

12 V

BATTERY


fEEI<LIG

flEE613

a

LEDDI

57

D-1

11111117.111

of:

co °

Fig. 3. Component layout and full size printed circuit board copper foil master pattern.Note that 8 -pin i.c. holders have been used for the isolator chips IC2 and IC6. The i.c.sshould be plugged into the top section of the holders as indicated.

CONSTRUCTIONDespite the apparent complexity this circ-

uit is quite simple to construct on a smallprinted circuit hoard. The component layoutand full size copper foil master pattern isshown in Fig. 3. This board is available fromthe EE PCB Service, code EE613.

Sockets are recommended for all i.c.sexcept regulators IC4 and 1C8, as this assiststhe test procedure. The p.c.b. has beendesigned to accept 8 -pin sockets for theisolators although these are 6 -pin devices,the reason being that 6 -pin sockets are fairlyhard to find. The isolators are fitted at thetops of these, leaving the bottom two holesunused. Do not fit any i.c.s at this stage asthey will he added later whilst setting up.

The I.e.d.s can be connected to leads justlong enough for the final installation in thecase. Lengths of screened lead can be con-nected to the input and output points at thisstage. long enough to allow easy access fortesting. They can be cut short for termin-ation to the sockets when the project is com-pleted.

The "low supply voltage" indication isoptional, by the way, if it is not required thenthe two 3130's (IC3/1C7) and their eight asso-ciated resistors may be omitted.

Resistor R2 provides a d.c. path to"ground" for the input so that when this isopen circuit the output is zero. About onemegohm is a reasonable choice of input re-sistance but it can he higher, lower or evenomitted altogether if required.

SETTING UPSetting up requires the use of an oscillo-

scope as this is the only viable way to set upthe h.f. trimmer preset VR1. As this is es-sentially a project intended for use with a'scope this should not pose problems to mostconstructors.

Before starting, set all three preset trim-mers to mid -position. Power the "in" side ofthe circuit with a voltage between 9V andI 2V and check that the 5V regulated supplyappears across the capacitor C4.

The current drain at this stage should beabout 4mA. If this is correct, fit 1C3, a 3130.If the supply voltage is now gradually re-duced, the I.e.d. (D1) should light at around8V. This process should be repeated for the"out" side of the circuit.

When the power supplies have beenchecked for both sections, testing of the sig-nal processing areas can proceed. Fit ICI,the "input" 3240, and both opto-isolators,IC2 and IC6 (at the tops of the sockets, asdescribed above).

Power the "in" side and check the currenttaken, which should now be about 16mA.The input "ground" should be about 1Vpositive of the negative supply rail, and pin 4of IC2 should also be at about 1V.

If this seems correct, fit the other 3240,105 to the "out" side, power up and checkcurrent drain, again about 16mA, and meas-ure the output "ground", which should beadjustable from about 0.5V to I .75V (withrespect to negative supply) with preset VR2.

If all seems well at this stage, it's probablya good idea to test the complete board andtry setting it up before installation. Theprocedure is to power both sides, apply a IVpeak -to -peak squarewave to the input, andobserve the output on a 'scope. To avoidproblems it is best to have both sections ofthe circuit operating from independent bat-tery supplies at this stage to avoid problemsif the "grounds" become connected throughthe scope and signal generator.

Preset VR1 is adjusted for best square -wave output; on one side there will bemarked overshoot on the leading edges, onthe other excessive rounding in bothdirections. This can be done at I kHz. thoughthe effect is easier to see at 10kHz.

Next, with frequency set to 1 kHz, presetVR3 is adjusted for an output amplitudeexactly equal to the input. Finally, with thesignal removed, preset VR2 should beadjusted to remove any d.c. potential acrossthe output.

As there is a fair degree of to!, -trancespread between individual opto-isolators itmay he worth swapping them over and set-ting up again to see which arrangement givesthe best performance. This applies especiallyif VR1 or VR3 is near the end of its rangewhen the settings appear correct. Exper-iments with four different isolators in theprototype produced overall frequency re-sponses ranging from 10k Hz to nearly30kHz, so the benefit of some patient exper-iment is obviously worthwhile.


INTERWIRINGThe general layout of the project in the

case can be seen from the photographs, withconnections as shown in Fig. 4. Most of thespace is taken up by the battery packs. Batte-ries are a matter for the individual con-structor; the circuit will operate from 9V,indeed two PP3's could be used. However,as it is intended as a design tool it may beused for fairly long periods so the additionallife given by packs of "AA" cells seems advi-sable.

The maximum signal amplitude that canbe handled depends on the supply voltageand the characteristics of the opto-couplers,and in the worst case a 1V r.m.s. signal willstart clipping when the supply falls to 8V. Inview of this 12V supplies were fitted to theprototype with indication of impending fail-ure at 8V.

Packing this lot into the specified case issomething of a shoehorn job. The p.c.b. isattached inside the top with doubled -sidedsticky foam, and the sockets, l.e.d.'s andswitch SI fit alongside it.

This leaves just sufficient space for the twobattery packs. A piece of foam plastictopped with stiff cardboard is placedbetween the board and batteries.

A larger case could be used, the only rulebeing that it MUST be a plastic type, both forSAFETY and to minimise stray capacitancebetween the two sections of the circuit. Alarger case would allow the inclusion of ex-tras such as switched input attenuation,which might be preferred by some users.

A final check of the adjustments should becarried out after completion. If the unit is tobe used for safety isolation, a check with a"Megger" between input and output"grounds" is advisable to ensure the insu-lation is sound.

The Isolink is designed to handle signalsup to about 1V peak -to -peak. The lowerlimit is governed by the inherent circuitnoise, which is less than 5mV. The inputimpedance is about one Megohm, whilst theoutput impedance is low, a couple of hun-dred ohms.

The frequency range extends from d.c. toat least 10kHz, on the prototype it is around30kHz. This means that most audio fre-quency signals will pass through it virtuallyundistorted, and squarewaves will still lookreasonably square at 1kHz.

SKIINPUT SOCKET ct.

LED DI SIG LED D2

Sta IttiL APO

I2VBATTERYP KA

EV44261

SWITCH

SK2OUTPUT SOCKET

+12VBATTERYPACK 8

Fig. 4. Interwiring from the circuit board tomounted on one side of the plastic case.

If it is required to handle larger signals asimple resistive attenuator can be used. Theinput is protected to some extent by the 10kresistor R1 and the internal protectiondiodes of IC1, but external diode protectionis not provided as it was found that thiscaused some signal degradation. Suitableprecautions should be taken to avoid poss-ible overload where this might occur.

IN USEThe way in which Isolink should be used

depends upon the actual application. Themost obvious use is investigating signals incircuitry at potentials other than earth.

The opto-isolators specified are quoted as"High Voltage", this being specified as7500V peak, 5300V r.m.s. Whilst it might beinadvisable to operate at this sort of voltageit is quite in order to, for example, insert alow value resistor in the live lead of a mainsappliance and, through Isolink, inspect thevoltage developed across it with an earthedoscilloscope.

the switch, l.e.d.s and sockets

This will give an indication of the currentflow. Similarly, low voltage signals in sec-tions of h.t. circuitry could he measured.Always be very sure you know what you aredoing and check connections carefully beforeswitching on with this kind of work, though.

At a lower level, it can be used to takemeasurements across points that wouldotherwise be hard to access as neither end isgrounded, and connecting them to groundthrough, say, the earthy side of a 'scopewould cause faulty operation or damage.

In the case of sensitive battery operatedequipment, earthing of any point of the circ-uit will often introduce a high level of mains"hum", making test measurements withmains -powered equipment difficult or evenimpossible. Bio-feedback circuits are aclassic example of this.

The stray capacitance between the twosections of the prototype was measured witha bridge and found to he in the region of10pF, which will offer an impedance of morethan 300M to 50Hz signals. This shouldgreatly attenuate the "hum" problem, butthe actual manner in which the Isolink is

used should be considered carefully in suchan application. If you are measuring a signalfrom your own body, for example, it wouldhe better to place the isolator on your lapthan on the workbench close to mainspowered equipment, where it might pick upa lot of hum in the input circuit throughcapacitive coupling.


tobot HoNIGEL CLARK P

rHE high profile enjoyed by roboticsI can be a doubled -edged sword. On

the one hand it has a visible end productwhich can encourage the learning of avariety of skills, as mentioned in this col-umn many times before. On the otherhand it creates expectations which, withthe present level of technology, cannot befulfilled and results in people losing theirinterest as quickly as it was aroused.

Now there is a new benefit from thesubject's ability to attract interest. Aschool in St Albans, Hertfordshire hasdiscovered it is a good way in which tobuild-up close links with industry. Theheadmaster of Beaumont School, Mr.Colin Isted said that in their dealings withschools, companies seemed to look forprojects which would have an impact onthe general public and robotics was asubject which satisfied this, having edu-cational as well as presentational value.

Although appreciating the benefits ofrobotics his main concern is with buildinglinks with industry at all age levels withinthe school. He believes that seeing whathappens in the outside world helps chil-dren put their formal education into per-spective.

So when Hertfordshire schools wereasked to take part in competitions sup-ported by industry, Beaumont was onlytoo willing to join in. The projectsinvolved making a special gripper forRolls-Royce aero-engine manufacturer,working with children from France andGermany to set up a production line formaking a remote -controlled buggy kitand designing a robotic device for BritishAerospace at Hatfield which would drawthe school's coat of arms.

GRIPPERThe gripper was part of Hertfordshire

County Council's Engineering EducationScheme, which is sponsored bySainsbury Trusts. Rolls-Royce required amechanism which would transfer a widerange of ring -type components from aconveyor belt into a lathe for machiningand off again.

The children, all studying maths andphysics in the lower sixth, had five days'training in teamwork and problem solv-ing and three months in which to com-plete the project.

Out of 17 schools in the county Beau-mont came first with an ingenious designemploying three discs revolving aroundthe same axis and three pegs for grippingwhich move in and out across the planeof the discs by the relative movement ofthe discs. Pressure sensors on the pegsindicate when the component is firmlyheld.

Two grippers, each operated by a

single d.c. motor at the axis, are mountedat right angles to each other and can berotated together by another d.c. motor sothat the one facing the chuck can take offthe finished component before changing

places with the other gripper to allow thenext component to be placed in the lathe.

The gripper, which RR is consideringfor industrial use, will now go forward tothe national finals in October.

PRODUCTION LINEThe production line was part of the

county council's Tripartite TechnologyProject with schools in the Burgundy re-gion of France and Rheinland-Pfalz inGermany. Technology weeks have beenheld in the last three years and this year itwas the turn of Hertfordshire to preparethe project.

In the early days it was decided thateach year's work should contain ele-ments of computer applications, electron-ics and pneumatic control. A roboticsproject was an obvious area.

The end result was to be a boxed kit formaking a simple buggy with a number ofseparate but linked stages. These in-cluded moulding and punching a basicchassis and putting the components intoa box, onto which a lid was then put.

In addition the students had to preparean instruction manual in three languagesand make an interface, with the necessarysoftware for the main computers in eachcountry. The British one was for the RMLNimbus.

The two -wheeled buggy, driven by d.c.motors with optosensor feedback, wasmade in sufficient quantities for everyoneinvolved to have one. It is planned tomake it available to primary schools inHertfordshire, at a price sufficient tocover costs, but it is not intended that itwill go on general sale.

BAe PROJECTThe BAe project was the result of the

school's long association with the com-pany at nearby Hatfield. When the com-pany set up Schooltech '88, Beaumont

was asked to take part. The school hopesthat it will become an annual event.

Most of the benefits to the studentswere seen in the context of improvingtheir view of the outside world. JaneMeasures, head of Physics and theschool's industrial liaison co-ordinator,said that it gives them a chance to workwith industrialists and see what was re-quired in industry. They were able to putthe theoretical and practical knowledgethey gained in school to good use.

BENEFITSIn addition there were the usual bene-

fits of robotics; artificial barriers betweensubjects were broken down. This is par-ticularly noticeable in the use of com-munication skills (to explain what hadbeen done in technological subjects) inthe writing of the reports and workingtogether as a team.

For the school there were the benefitsof teachers also getting to know the re-quirement of industry so that coursescould be given added interest by puttingtheoretical work into a practical context.

The involvement also gave the stu-dents an enthusiasm for learning bythemselves. An example is the BAe pro-ject in which the students were given thedetails before their summer holidays.They organised meetings during the hol-idays to set the groundwork before tack-ling the work in earnest during the nextschool term.

At the moment the number of pupilsable to take part in the projects is limitedby the present resources of the school.Funds were insufficient to do all the workrequired on the projects described andoutside help had to be sought.

Whether greater numbers of studentswill be able to take part in roboticscourses in the future as part of the gen-eral curriculum, rather than outside nor-mal school hours depends on moreresources being made available.

EE CROSSWORD 6 ANSWERS

ACROSS5 FUNDAMENTAL6 GATED AGC9 DUMP

11 TRUTH12 WATTLE SS13 TRICKLE16 PROCESS19 DEBOUNCE23 COLUMN24 AMPERE25 NOISE26 TURNS RATIO

DOWN1 EUTECTIC2 IDEAL3 INDUCTOR4 PADDLE7 AIR8 CYAN

10 MASKS14 RADIO15 LOUDNESS17 CLAMPING18 SCOPE20 BAUDOT22 BALUN


POWER CONDITIONER

FEATURED IN ETIJANUARY 1988

The ultimate mainspurifier Intended mainlyfor lowering the noisefloor and improving the

analytical qualities oftop-flight audio equipment

The massive filter section contains thirteen capacitors andtwo current balanced inductors, together with a bank of sixVDRs, to remove every last trace of impulsive and RF

interference. A ten LED logarithmic display gives a second bysecond indication of the amount of interference removed.

Our approved parts set consists of case. PCB, allcomponents (including high permeability toroidal cores, ICstransistors, class X and Y suppression capacitors. VDRs,etc.) and full instructions.

PARTS SET £28.50 a VAT

0000000000

Some pans are available separately. Please send SAE for liRs, or

SAE+ cr for lists, circuit. construction details and lather information(free with pans set).

THE DREAM

MACHINEFEATURED IN ETIDECEMBER 1987

Adjust the controls to suit your mood and let the gentle.relaxing sound drift over you. At first you might hear soft rain,sea surf. or the wind through distant trees Almost hypnotic.the sound draws you irresistably into a peaceful, refreshingsleep.

For many, the thought of waking refreshed and alert fromperhaps the first truly restful sleep in years is exciting enoughin itself. For more adventurous souls there are strange andmysterious dream experiences waiting. Take lucid dreams,for instance. Imagine being in control of your dreams and ableto change them at will to act out your wishes and fantasies.With the Dream Machine its easy!

The approved pans set consists of PC8, all components.controls, loudspeaker, knobs, lamp, fuseholders, fuse, mainspower supply, prestige case and full instructions.

PARTS SET £16.50 a VAT

AVAILABLE WITHOUT CASE FOR ONLY £11.90 +or

MAINS

CONDITIONERFEATURED IN ETISEPTEMBER 1986

Cleans up mains pollutioneasily and effectively.You'll hardly believe thedifference in your Hi-Fi, TV, Video, and all other sensitiveequipment.

PARTS SET £4.90 + VAT

RUGGED PLASTIC CASE £1.65 + VAT

esdkAnak

O

POWERFUL AIR

IONISERFEATURED IN ETIJULY 1986

Ions have been described asvitamins of the at( by thehealth magazines. and havebeen credited with everything

from curing hay lever and asthma to improving concentration andputting an end to insomnia. Although some of the claims may be

exaggerated. there is no doubt that ionised air is much cleanerand purer, and seems much more invigorating than dead air

The DIRECT ION ioniser caused a great deal of excitement wheno appeared as a constructional project in ETI. At last, an ioniser

that was comparable with (better than') commercial products.was reliable. good to build and funs. Apart from the serious

applications. some of the suggested experiments were outrageous.

We can supply a matched set of parts. fully approved by thedesigner to build this unique project The set includes a rollertinned printed circuit board 66 components case mains leadand even the pads for the tester. According to one customer, the

set casts about a third of the price of the individual componentsWhat more can we say? diSfr0OhOdS

-1

are 1'

PARTS SET WITH BLACK CASE £11.50 + VAT included

PARTS SET WITH WHITE CASE £11.80 + VAT

KNIGHT RAIDERFEATURED IN ETI JULY 1987

The ultimate in lighting effects for your Lamborighini. Maserati. BMW(or any other car, for that matter). Picture this, eight powerful lights inline along the front and eight along the rear. You leek a switch on thedashboard control box and a point of light moves lazily from left toright leaving a comets tail behind it. Flip the switch again and thepoint of fight becomes a bar, bouncing backwards and forwardsalong the row. Press again and try one of the other six patternsAn LED display on the control box lel s you see what the main lightsare doing

The Knight Raider can be fitted to any car (it makes an excellent foglightli or with low powered bulbs a can turn any child s pedal car orbicycle into a spectacular TV age toy.

The parts set consists of box. PCB and components tor control. PCBand components for sequence board, and full instructions.

Lamps not included.


The S101 professionalrespir-

ation and heart -rate monitor is the idealinstrument to keep track of your progress inany kind offitness or sports training. The average adult resting heart rate is around

80 beats per minute. Foran athlete at the

peak of physicalfitness it can be

50 or less.

trainin sirenHow fit are you?

How quickly is your jogging or sportsgstrengtheningyour heart and

respiratiun? Howquickly do

you recover fromoxygen debt after

exercise? For your ownsake, you need to know

The approvedparts set consists of:

case, 3 printedcircuit boards, allcomponents (including

17 ICs, quartzcrystal over

75 transistors,resistors, diodes and

capacitors), liquid crystaland full instructions.

display, switches,plugs, sockets,

LEDs, leads, electrodesand sensors.

CREDIT CARD

CASINOFEATURED IN ETI,MARCH 1987

This wicked Mile pocketgambling machine measuresonly 3'x2"x Mb It will

play all kinds of casino

games. Including'

Roulette

.Craps

Pontoon

Our approved parts set comes complete with case,self-adhesive fascia; tinned and drilled printed circuit board:

all components: hardware, full instructions and three

different games to play!

PARTS SET ONLY £5.90! + VAT

Five extra games FREE with

every order!

LM2917

EXPERIMENTER SET

Consists of LM2917 IC, special printed circuit board anddetailed instructions with data and circuits for eight differentprojects to build. Can be used to experiment with the circuitsin the 'Next Great Little IC' feature (ETI, December 1986).

LM217 EXPERIMENTER SET £5.80 + VAT

LEDs

Green rectangular LEDsfor bar -graph displays

50 for 23.50 500 for E25

100 for £6 1000 for £45

DIGITAL AND AUDIO EQUIPMENT LEDs

Assorted 3mm LEDs, red, green, yellow and orange.

25 of each (100 LEDs) for £6.80

Prices shown are exclusive of VAT so please add 15% to theorder total. UK postage is 70p on any order. Carriage and

insurance for overseas orders f4.50 Please allow up to 14 daystot delivery

D)U1g7C1LIMITED

SALES DEPT ROOM 111 , FOUNDERS HOUSE, REDBROOK, MONMOUTH, GWENT.

MAINS

CONTROLLERFEATURED IN ETIJANUARY 1987

Have you ever wondered whatpeople do with all thosecomputer inted aces? Put yourcomputer in control,' say theads The Spectrabeeb has eight TTL outputs. What on earth canyou control with a TTL output? A torch bulb?

The ETI Mains Controller is a logic to mains interface which allowsyou to control loads of up to 500W from your computer or logic°nuns An opto-coupler gives isolation of al least 2.500V. so thecontroller can be connected to experimental circuits, computersand control props* in complete safety. Follow your computerinterface with a mains controller and you re may in business withautomatic control.

The mains controller connects directly to most TTL families withexternal components, and can be driven by CMOS with theaddition of a transistor and two resistors (supplied)

Your mains controller parts set contains high quality roller tinnedPCB, MOC3021 opto-coupier, power can with heatsink. mounting thardware and heatsink compound: all components. includingsnubber components for switching inductive toads. transistor andresistors for CMOS interface, full instructions.

PARTS SET £6.20 a VAT!

ARMSTRONG 75W

AMPLIFIERFEATURED IN PEJULY 1988

A.J. Armstrong's excitingnew audio amplifiermodule is here at last!Delivering a cool 75W (conservatively rated - you'll getnearer 100W), this MOSFET design embodies the finest

minimalist design techniques, resulting in a clean.

uncluttered circuit in which every component makes a

precisely defined contribution to the overall sound.You can read all about it in the July issue of PE, but why

bother with words when your ears will tell you so muchmore?

Pans set includes top grade PCB and all components.

SPECIAL INTRODUCTORY PRICE FOR FULLYUPGRADED MODULES.

SINGLE PARTS SET £14.90 VAT

STEREO PAIR £25.90,- VATReam send SAE. El for data and ca -puns Pree eft pans sell, Includngdiagrams for maiming pre.mp and power supply This amplifier will notbe avallade from your usual ado summer wopromme the only designerapproved pans set.

B10 -

FEEDBACKFEATURED IN ETIDECEMBER 1986

Biofeedback comes of agewith this highly responsive,self -balancing skinresponse monitor! Thepowerful circuit has found application in clinical situationsas well as on the biofeedback scene. It will open youreyes to what GSR techniques are really all about.

The complete parts set includes case, PCB, allcomponents. leads, electrodes, conductive gel. and fullinstructions.


BIOFEEDBACK BOOK £3.95 no VAT)

Please note the book. by Stern and Ray is an authorised guide tothe potential of bio-feedback techniques. It is not a hobby book,and will only be of interest to intelligent adults.

BRA

FEATURED IN ETIAUGUST 1987

The most antontshing project ever to have appeared in anelectronics magazine. Similar in principle toe medical EEGmachine. this protect allows you to hear the characteristicrhythms of your own mind! The alpha. beta and theta forms canbe selected for study and the three articles give masses ofinformation on their interpretation and powers.

In condinction with Dr. Lewis s Alpha Plan. the monitor can beused to overcome shyness to help you feel confident instressful situations. and to train yourself to excel at things you'no good at

Our approved parts set contains case. two PCBs, screening canfor Po -amplifier. all con ilonents (including three PMI precisionamplifiers), leads, brass electrodes and full instructions.


ALPHA PLAN BOOK £2.50 + VAT

Pans set available separately We also have a range of accessoriesprofessional electrodes. books. etc. Please send SAE for lists. or

SAE. E2 for lists construction details and further information Mee witspans sell

421


UNIVERSALCHARGER/POWER SUPPLYCOST/JS CALAMVOKISAble to charge almost any size NiCad cell. itwill also double as a low-cost mains adapterso you will not have to drain batteries whilstusing equipment at home.

NICKEL CADMIUM batteries (NiCads)are so cheap in the long run, that it isa wonder that ordinary non-rechar-

gable batteries are still used. The UniversalCharger/Power Supply described here willgive you the opportunity to discover thesesavings. It is able to charge almost any size ofcell, it will also double as a mains adapter soyou will not have to drain your batterieswhilst using the equipment at home.

The problem with NiCads is that a con-stant current source is needed to charge themand although there are many cheap chargerson the market this unit offers certain advan-tages over similarly priced commercial ones.The first is, of course, its ability to act as amains adapter, but there are more subtleadvantages.

Most cheap commercial chargers do notactively regulate the current delivered to thebatteries, so this current depends to someextent on the resistance of the cell or cellsunder charge.

CHARGING RATEAnother problem is that al-

though different batteries havedifferent recommended chargingcurrents, these chargers usuallyonly have one charging current(although different sized batteriescan he inserted) and so often smallcells are charged too fast,shortening their life. To makematters worse large cells arecharged too slowly, unnecessarilyincreasing the charging time.

This unit avoids these pitfalls byhaving an "intelligent" plug socketinto which a battery holder is

plugged. This socket "detects" thesize of the batteries to he chargedfrom a resistor mounted in theholders plug and the current is setaccordingly.

240AC

6V

OV

fiV

Gy

1+

LCCC

The current is actively regulated so it doesnot change during use. The constant voltageis also regulated when used (unlike manycheap mains adapters whose voltage dependson the loading and which show marked volt-age rises at low current).

VIN

10000

1)3

(a)(EE145461

Fig. 1. Full circuit diagram for the Universal Charger/Power Supply. Thetwo small diagrams are for (a) power supply mode and (b) charger mode.

VOUT

L+,1 ,17M

C2001

AD) 131

470

SK1

Table 1

Current Time

AAA/HP16 20mA 14 -16 Hours

AA/HP7 50mA 12 -14 Hours

C/HP11 120mA 14-16 Hours

D/HP2 120mA 14 -16 Hours

PP3 11mA 12-15 Hours

Notes: These values are fairly typical, if your batterieshave a different recommended charging current andtime printed on them by all means use it. Calculate thevalue of R1 from the formula given in the text. If thecharging current is higher than 200mA use a 1/2W re-sistor. R1 should NOT be decreased below three ohms.

' (b)

The resistor which controls theconstant voltage is also mountedin the plug so if a different lead ismade for each item to be poweredthe correct voltage will always bedelivered.

The unit will charge one PP3battery or up to six AAA, AA, Cor D cells at once (depending onthe size of the battery holderused). But only one type of bat-tery can be charged at one time(see Table 1 for typical chargingrates and times). Alternatively theunit could act as a mains adapterdelivering from 1.5V to 12V at upto 400mA.


CIRCUIT OPERATIONThe full circuit diagram for the Universal

Charger/Power Supply is shown in Fig. 1.

The mains is brought down to about 12V a.c.by the transformer Tl. This is then rectifiedby the bridge arrangement of diodes D1 -D4and smoothed by capacitor Cl. CapacitorsC2 and C3 remove spikes.

The only active component is an adjust-able voltage regulator, ICI, which works byadjusting the voltage at the Vu, pin so that itis 1.25V higher than the voltage on theadjust pin (ADJ).

In the Power Supply mode of operationthe circuit is as shown in Fig. 2 (simplified).Between the Vo, and ADJ pins is a 470 ohmresistor (RI). As the voltage across it is al-ways 1.25V the current is always:

I= V/R=1.25/470= 0.0027A =2 .7mAAs the current flowing out of the ADJ pin

is only 50µA it can be ignored so the currentthrough resistor R, is always 2.7mA. Theoutput voltage is the sum of the voltagesacross resistors 121 and R, and can be calcu-lated from

V001=1.25+(lxR)

=1.25+(0.0027 x Rv)

so Rv= ( V, -1.25)/0.002 7

From this formula values for R can hecalculated for whatever supply voltage is re-quired, from I .5V to I2V. See Table 2.

CONSTANT CURRENTWhen the unit is acting as a Charger the

circuit is as shown in Fig. 3. Resistor R1 isplaced in parallel with resistor RI and thecurrent which flows through them also flowsthrough the batteries being charged. As thevoltage across resistors RI and R1 is keptconstant by regulator ICI, so is the currentthat flows through them. In this way a con-

rEE145261

VIN BOUT...17

V

LM 317M

AOJ1V25

504JA

470 RI

I OUT

1+IBATTERY I

(U145761

Fig. 3. Simplified arrangement forcharger operation. The value of thecharging resistor R1 can be found byreferring to Table 3.

Table 3

Batterytype RI

AAA 82 ohms'/8W 5%

AA 27 ohms YEAN 5%

C 12 ohms 1/4W 5%

D 12 ohms 1/4W 5%

PP3 180 ohms 1/8W 5%

Notes: These values are based onthe currents given in Table 1. Theyare independent of the number ofbatteries to be charged.

Fig. 2. Simplified regulated powersupply arrangement. The value of Rvcan be found by referring to Table 2.

Table 2

Voltage Rv 1/8W, 5%

1.5V 100ohms

3V 680 ohms

4.5V 1200 ohms (1k2)

6V 1800 ohms (1k8)

9V 2700 ohms (2k7)

12V 3900 ohms (3k9)

scant current is maintained through the bat-teries.

This is calculated from:/,= RI's current + R1's current

=(1.25/470)+(1.25/R1)

=0.0027+1.25/RI

So R1=1.25/(/,,,,, -0.0027)

Values for resistor R1 are shown in Table 3for typical NiCads.

COMPONENTSResistors

R1 470R1 See Table 3Rv See Table. 2

All 5% carbon

Capacitors See page 415

C1 100011 radial elec.35V

C2 0.1p,f ceramic discC3 11.Lf tantalum bead 35V

SemiconductorsD1 -D4 1N4001 1A 50V diode

(4 off)IC1 LM317M +1.2V to 37V

500mA Adj. Voltage Reg.

MiscellaneousT1 Mains transformer 240V

a.c. prim, 0-12V 500mAsec. or 0-6V, 0-6V 500mAsec.

SK1 3 -pin In -line DIN socketStripboard, 0.1in matrix size 10

stripsx 10 holes; 3 -pin DIN plugs(plastic covered); battery holders;PSU box with integral 13A plug;small heatsink; connecting wire;solder pins and solder etc.

£10.50Approx. costGuidance only

(excludingbatteries)


1 2 3 5 6 7 8 9 10

RI

031 ' t,

kiE4C1 " D2

,fid DI 04

4-

C3

2

RAN SFORMERT1

1 2 3 4. 5 6 7 8 9 10 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0

0 0 0 0 0 0 0 0 0 00 0 0 0 0 0 0 0 0 00 0 0 0 0 0 00 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0 0 00 0 0 0 0 0 0 0

rtEE14565'

Fig. 4. Component layout and detailsof wiring to the mains transformersecondary winding and to the DINsocket.

CONSTRUCTIONThe circuit is built up on a small piece of

0.1in. matrix stripboard, size 10 strips by 10holes. There are no track breaks on thehoard and the component layout is shown inFig. 4.

Commence construction by mounting thediodes and link wire on the board followedby the capacitors. The regulator ICI shouldhe soldered on last and a small heatsinkbolted on to it. When mounting the diodesand electrolytic capacitor CI be sure toobserve the correct polarity of these devices.

The completed circuit board is housed in apower supply unit box with an integral 3 -pin,mains type, plug. The miniature mains trans-former was fitted first by bending its mount-ing tags round the box's internal mouldingand the circuit board was connected to itusing stiff wires. If a 0-6V, 0-6V secondarywinding is used, the wires to the circuitshould be connected to the OV of onewinding and the 6V of the other, with theremaining two tags connected together.

In the prototype unit the DIN connectingsocket was a non -chassis type and a shortlead was attached to the "wander" socket,fed through a small hole in the case side and

03

(5814555

202

TO LOAD

TO BATTERYHOLDER

Fig. 5. Wiring to the DIN plugs for power supply and charger mode. It issuggested that the resistor leads are covered with insulating sleeving to avoidshorting to the other pins.

soldered to pins on the circuit board. If achassis type socket is used a suitable holeshould be drilled in the case and short wiressoldered from the circuit board pins to thesocket tags. As the components are such atight fit inside the case it might be best ifconstructors kept to the "wander" type DINsocket method.

CONNECTING LEADSThe construction of the battery charging andpower supply leads are shown in Fig. 5.

Some care is needed when mounting theresistors in the plugs to ensure that the leadsdo not touch any terminals. For this reasonplastic barrelled plugs should be used, wrap-ping the resistors in insulating tape is not abad idea either.

For charging large batteries higher powerresistors are used (half or quarter watt

types-see Table 3) and these may not fit inthe plug barrel. If this happens the resistorshould be mounted on the battery holder, athree -wire plug lead will then he needed.

NiCADSThe life of your nicads can be drastically

shortened if they are mistreated so some careis needed. They should not be used in verylow current applications such as clocks andLCD calculators where a dry cell would onlybe replaced once a year.

NiCads should never be short circuited asthey have very low internal resistance andcan, if shorted, deliver very high currentswhich may destroy the cell itself. The rec-ommended charging times should be kept tohut no real harm results in charging for toolong. You should never try to recharge drycells.

ELECTRONICS TEACH -IN ONLY £1.95

By Michael Tooley BA andDavid Whitfield MA MSc CEng MIEE

ACOMPREHENSIVE background to modernelectronics including test gear projects. This 104

page, A4 size book forms a complete course in basicelectronics; designed for the complete newcomer it willhowever also be of value to those with some previousexperience of electronics. Wherever possible the course isrelated to "real life" working circuits and each partincludes a set of detailed practical assignments.

To complement the course computer programs have been producedfor the BBC Micro and Spectrum or Spectrum Plus. The software isdesigned to reinforce and consolidate important concepts and principlesintroduced in the course, it also allows readers to monitor their progressby means of a series of multi -choice tests.

The book includes details of eight items of related test gear giving fullconstructional information and diagrams for each one. The items of testgear described are: Safe Power Supply; Universal LCR Bridge;Diode/Transistor Tester; Audio Signal Tracer; Audio Signal Generator;RF Signal Generator; FET Voltmeter; Pulse Generator.

This book is an excellent companion for anyone interested inelectronics and will be invaluable for those taking G.C.S.E. orB.T.E.C. electronics courses.

See Direct Book Service -page 428 -for full ordering details.


STUDENT LICENCETo attract younger newcomers to ama-

teur radio, the Radio Society of Great Bri-tain has decided to work for the creationof a new kind of transmitting licence forbeginners. Provisionally titled a "StudentLicence", the idea is that students shouldbe allowed access to limited sections of afew amateur bands (with low power andmodest antennas thus providing practi-cal experience in a learning situation.

The Society says it has identified twomain reasons why young people todayrarely become interested in amateurradio. It says that 11 to 16 year olds seethe usual one-year study period for theRadio Amateurs' Examination (RAE) astoo long, and that the price of most equip-ment required to get on the air is toohigh.

While the typical RAE course involvessome 150 class -hours, the Student Li-cence would only require about 30 hoursof study, plus whatever was necessary tolearn Morse code at six words per min-ute. The emphasis throughout would beon practical requirements-how to oper-ate an amateur station properly, includ-ing correct procedures and banddiscipline-but naturally the student li-censees would still have to go on toobtain their full licence in due course.

The RSGB is currently developing a syl-labus and formulating proposals for theLicence to put to the Department of Tradeand Industry (DTI). It plans to create astudent section within the society and toproduce special publications and kits forbeginners.

MIXED FEELINGSThese proposals have been received

with mixed feelings by the amateur radiofraternity. While most recognise the needto ensure a continuing input of new-comers to the hobby, some feel that arelaxation of the present rules and regu-lations to allow relatively untrained oper-ators on the already overcrowdedamateur bands will be a retrograde step.

The RSGB says that students would belimited to operating on the less -popularbands with restrictions placed on them toensure the least possible interferencewith existing licensees. The concept ofstudent -entry sounds fine but one can'thelp wondering how successful it will beif the "target" population already dislikesthe idea of having to pass an examinationto take up a hobby.

Although the RSGB doesn't seem towant to admit it, CB radio has created anenormous boost for amateur radio in re-cent years. Large numbers of people whodiscovered a liking and an aptitude forradio communication became frustratedby the various limitations of CB and weremotivated to go on to take up amateurradio with its greater scope.

The CB boom created a mini -amateurradio boom, yet CB is still apparently ig-

TONY SMITH G4FAI

nored by the RSGB. The boom has longgone but CB still provides a steady sourceof new entrants to amateur radio whichthe RSGB could well cultivate.

There is, however, no mention of it everappearing in the columns of Radio Com-munication. It's a great pity, and anopportunity lost. . . . However, I will re-port further on the Student Licence ideaas matters progress.

POLAR RADIOThe first attempt at radio communica-

tion from polar regions was made by theAustralasian Antarctic Expedition of1912. Groups of explorers spent monthstrying to get massive 90ft high aerial sys-tems to stay up in the face of howlinggales, while they obtained only limitedsuccess with their 1.5kW spark transmit-ters. Further experiments were carriedout in the 1920's and 1930's by the Ameri-cans in the South and the Russians in theNorth and gradually radio became an es-sential, life-saving, aspect of polar explo-ration.

Compare those 1912 experiences withwhat has been planned for the USSR/Ca-nada Skitrex Expedition this year. Agroup of Soviet and Canadian scientistsset out in March from Severnaya Zemlyafor a 1750km journey via the North Poleto Cape Columbia on Ellesmere Island.

A member of the expedition is Sovietradio amateur Leonid Labutin, UA3CR,who is maintaining daily radio contactbetween the expedition and teams of So-viet and Canadian amateur radio oper-ators at base stations in SevernayaZemlya, Resolute Bay on Cornwallis Is-land as well as in Moscow, Dikson, Ot-tawa and Toronto.

The amateur radio equipment beingused is provided by lcom, and includesh.f. and v.h.f. base stations as well as"handie-talkies" for two metres includingcommunication with supply -drop aircraft.Using the facilities of SARSAT/COSPAS,the search and rescue satellites, as wellas amateur radio satellite UOSAT 11, witha "talking computer" on board, the expe-dition can hear their location read to themvia a 2 -metre hand-held radio as UOSATpasses over about every 100 minutes.

Both licensed amateurs and short-wavelisteners can obtain a fine bilingual certifi-cate to commemorate this expedition.The Canadian Radio Relay League isawarding the "1988 Polar Bridge Dip-loma"for contacts (or SWL loggings) dur-ing the period of the expedition with anumber of northerly Canadian and Rus-sian stations, one of the base camps, andwith stations in the national capitals.

A great deal of planning and effort hasgone into the arrangements for the expe-dition. The amateur radio involvementhas resulted in an unusual reciprocal andthird party traffic licensing agreementbetween Canada and the Soviet Union,which is a recognition of the competence,

ability and flexibility of which amateurradio is capable when required.

WORKED ALL BRITAINWith amateur radio's potential for

world-wide communication it may comeas a surprise to non -amateurs to learnabout the "Worked All Britain" (WAB)award scheme which is related to con-tacts made within the British Isles.

It is, in fact, a series of awards based onthe number of contacts made with sta-tions located in the large 100km NationalGrid Squares, the small 10km squares,counties, and rateable districts. There isgreat enthusiasm among participants inthis scheme which stimulates on -the -airactivity by British amateurs.

They gain a very good knowledge ofthe geography of the UK and some travelto the more remote parts of the mainland,or to islands, to "activate" rare squareswhere there is normally no amateur radiotransmitting. There is a growing interestfrom overseas amateurs which in turnmakes UK stations more popular with dx(long distance) stations who want to"work the squares".

Every participant has a special recordbook which lists each WAB area, countyby county, together with a list of thetowns and villages lying in the area.There are over 4,000 WAB areas in all sothere's plenty to do in trying to makecontact with each area. Awards are givenfor each level of achievement, eg, forworking 300 areas, 500, 750, and so on.

Getting a "rare" square can be as excit-ing as getting a rare country and WABmounts a number of contests and specialactivity weekends to keep the pot boiling.Listeners can enjoy the fun just as muchas licensed amateurs and full details canbe obtained by sending a large stampedaddressed envelope to Brian MorrisG4KSQ, 22 Burdell Avenue, Sandhills Es-tate, Headington, Oxford OX3 8ED.

ARMADA 400July sees the 400th anniversary of the

routing of the Spanish Armada by SirFrancis Drake. The event is being cele-brated not only in Plymouth, Devon, butin many other Plymouths around theworld.

During July, Plymouth Radio Club willbe on the air from Plymouth Hoe with aspecial call -sign, GB400A, to enable radioamateurs in other countries to make con-tact with Plymouth during the celebra-tions. A special commemorative QSLcard will be used during the period 21 to28 July, and on the 28 July the club hopesto put the Lord Mayor in contact withsome of the 38 other Plymouths ident-ified, so far, worldwide.

Further information can be obtainedfrom Philip J. Daymond G1WVH, P.R.O.Plymouth Radio Club, Radford House,Plymstock, Plymouth, PL5 3AH.


DowNTLJ0

BY GEORGE HYLTON

POWER SUPPLY LABELLINGONE OF OUR readers says he is some-times puzzled about the way d.c.

power supply leads are labelled on circuitdiagrams. In particular, the "common"side of a supply is sometimes marked"0", sometimes "-", and sometimeswith a voltage, such as "-9V". Which isright?

CLARITYSince the purpose of a diagram is to

give information, the method which doesso as clearly as possible must be the best.In this magazine you'll generally find thatwhere a circuit is driven by a d.c. supplysuch as the 9V battery of Fig. la and thenegative side is common or earthed thenthe common side is marked "0" or "OV"and the other side with the battery volt-age and polarity (+9V).

If, in the accompanying text, a portionof the circuit such as Fig. 1b is discussedin isolation, the power -line markings areas shown. Sometimes, to make it clearthat "0" is connected to battery negative,the diagram draught person puts "0 1-)"or something similar.

In diagrams found somewhere else,and especially in old texts, the commonline for Fig. 1 may be labelled "-9V".This can be misleading, and the reason isthat nowadays there are often "split"supplies with positive, negative and com-mon. A modern reader, seeing "+9V"and "-9V", will think there's also a "OV"line.

SPLIT SUPPLIESThe operational amplifier circuit of Fig.

2 illustrates the point. In order to makepossible the direct interconnection ofcircuits, without the need for d.c. blockingcapacitors, op. amps are designed so thatthey can be used with a split, dual, orcentre -tapped supply whose mid -point isthe common or "earth" line.

In the absence of an input signal, out-put terminal B is at "earth" potential WV)and can if necessary be connectedstraight to the input of a following ampli-fier, or back to the input of its own ampli-fier (A) without upsetting the circuit.

In describing an op. amp, the powersupply requirements may be specified as"±15V", or "15V -0-15V" or "30V ct"(centre -tapped). Of these, the '±15V"

style is commonest. It is strictly incorrect,since the symbol "±" means, in its nor-mal mathematical context "plus orminus", whilst the meaning in op. ampspecifications is "plus AND minus". How-ever, I've not heard of any catastrophesas a result of this ambiguity.

WITHIN LIMITSSome recent kinds of op. amp are able

to work (within limits) from a single, un-tapped supply voltage as well as themore usual dual voltage. I have a datasheet for the OP -90 quad op. amp. Thiscan work from a wide range of supplyvoltages, single or centre -tapped. Thedata sheet indicates the following:

Single Supply Operations+1.6V to +36V.

Dual Supply Operations+0.8V to ±18V

I also notice that on an accompanyingdiagram the positive and negative railsare labelled "V+" and "V-", meaningthat, whatever voltage is actually used,this is the appropriate polarity.

MULTIPLE SUPPLIESIt's quite common for a piece of equip-

ment to require a number of supply railsall of different voltages. A colour TV, forinstance, may need a 12V line for its low-level stages, a 50V one for its frame out-put stage, 100V for line output, 250V forvideo output and 25kV for the picturetube.

Even a relatively straightforward pieceof equipment like an audio amplifier mayhave several supplies. In Fig. 3, the poweramplifier (P.A.) section works from a splitsupply of 30V -0-30V. The upper (+30V)part of this is used also to power the pre -amp., via a stabilizer which reduces thevoltage to +20V.

In such an amplifier it is quite usual torun separate connections to the common(OV) supply from the high-level and low-level sections. This reduces the risk ofinstability caused by accidental feedbackof small voltages dropped across the con-nections themselves by the high currentsin the output stage. When the low-levelpart is drawn separately its common linemay be labelled to indicate this sep-aration.

Fig. 1 (a.) Circuit with single 9V supply; (b) detail of the circuit showing one way oflabelling the supply lines or rails.

A

iN

OV

I EEC 2/4

R2

+15V

15V

R3

CIRCUIT SUPPLY

aOUT

OV

Fig. 2. Operational amplifiers usually have dual supply lines. This circuit has a +15Vrail, a - 15V rail and a common rail which is the junction between the two (labelled OV).

IN ®

EEO., I

OV

4. 20 VSTAB

+30V

LOW - LEVEL ' EARTH '

-30V

Fig. 3. Audio amplifier with split (dual, centre -tapped) supply for the power amplifier(P.A.) part and a reduced -voltage single ended supply for the low-level stages. Notethe common ("earth") connections, where separate lines are provided for PA and pre -amp, joined only at the tags of the reservoir capacitors in the power supply.


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DIIIRECTIS 0 0114

PROJECT CONSTRUCTIONHOW TO GET YOURELECTRONIC PROJECTS WORKINGR. A. PenfoldWe have all built projects only to find that they did notwork correctly, or at all, when first switched on. The aimof this book is to help the reader overcome just theseproblems by indicating how and where to start lookingfor many of the common faults that can occur whenbuilding up projects96 pages Order code BP110 £2.50

HOW TO DESIGN AND MAKEYOUR OWN P.C.B.sR. A. PenfoldDeals with the simple methods of copying printed circuit

The books listed have beenselected as being of specialinterest to everyoneinvolved in electronics andcomputing. They are sup-plied by mail order direct toyour door. Full ordering de-tails are given on the lastbook page.

board designs from magazines and books and covers allaspects of simple p.c.b. construction including photo-graphic methods and designing your own p.c.b.s.80 pages Order coda BP121 £1.95

BEGINNER'S GUIDE TO BUILDINGELECTRONIC PROJECTSR. A. PenfoldShow; the complete beginner how to tackle the practicalside of electronics, so that he or she can confidently buildthe electronic projects that are regularly featured inmagazines and books. Also includes examples in theform of simple projects.112 pages Order code No. 227 £1.95

ELECTRONICS SIMPLIFIED-CRYSTAL SET CONSTRUCTIONF. A. Wilson, C.G.I.A., C.Eng., F.I.E.E., F.I.E.R.E.,F.B.I.M.Especially written for those who wish to participate in theintricacies of electronics more through practical con-struction than by theoretical study. It is designed for allages upwards from the day one can read intelligently andhandle simple tools80 pages Order Code BP92 £1.75

ElectronicsSimplified -Crystal SetConstruction

50 CIRCUITS USING GERMANIUMSILICON AND ZENER DIODESR. N. SoarContains 50 interesting and useful circuits and applica-tions, covering many different branches of electronics,using one of the most simple and inexpensive ofcomponents-the diode. Includes the use of germaniumand silicon signal diodes, silicon rectifier diodes andZener diodes, etc64 pages Order Code BP36 £1.50

50 SIMPLE LED CIRCUIT'SR. N. SoarContains 50 interesting and useful circuits and applica-tions, covering many different branches of electronics,using one of the most inexpensive and freely availablecomponents-the light -emitting diode (LED). Also in-cludes circuits for the 707 common anode display64 pages Order Code 8P42 £1.95

A PracticalIntroduction toMicroprocessors

Cod Design andConstructionManual

COIL DESIGN AND CONSTRUCTION MANUALB. B. BabaniA complete book for the hJrne constructor on -how tomake" RF, IF, audio and power coils, chokes andtransformers. Practically every possible type is dis-cussed and calculations necessary are given and ex-plained in detail. Although this book is now rather old,with the exception of torroids and pulse transformerslittle has changed in coil design since it was written96 pages Order Code 160 £2.50

CIRCUITS AND DESIGNMICRO INTERFACING CIRCUITS -BOOK 1MICRO INTERFACING CIRCUITS -BOOK 2R. A. PenfoldBoth books include practical circuits together with detailsof the circuit operation and useful background informa-tion. Any special constructional points are covered butp.c.b. layouts and other detailed constructional informa-tion are not included.

Book 1 is mainly concerned with getting signals in andout of the computer;. Book 2 deals primarily with circuitsfor practical applications.Book 1 112 pages Order code BP130 £2.25Book 2 112 pages Order code BP131 £2.75

A MICROPROCESSOR PRIMERE. A. Parr, B.SC., C.Eng., M.I.E.E.Starts by designing a small computer which, because ofits simplicity and logical structure, enables the languageto be easily learnt and understood. The shortcomings arethen discussed and the reader is shown how these canbe overcome by changes and additions to the instructionset. In this way, such ideas as relative addressing, indexregisters, etc are developed96 pages Order code BP72 £1.75

A PRACTICAL INTRODUCTION TOMICROPROCESSORSR. A. PenfoldProvides an introduction which includes a very simplemicroprocessor circuit which can be constructed so thatthe reader can experiment and gain practical experience96 pages Order code BP123 £1.95

How To UseOP Amps

HOW TO USE OP -AMPSE. A. ParrThis book has been written as a designer's guidecovering many operational amplifiers, serving both as asource book of circuits and a reference book for designcalculations. The approach has been made as non -mathematical as possible160 pages Order code BP88 £2.95

PRACTICAL ELECTRONICBUILDING BLOCKS -BOOK 1

PRACTICAL ELECTRONICBUILDING BLOCKS -BOOK 2

R. A. PenfoldThese books are designed to aid electronic enthusiastswho like to experiment with circuits and produce theirown projects, rather than simply following publishedproject designs.

BOOK 1 contains: Oscillators-sinewave, triangular,squarewave, sawtooth, and pulse waveform generatorsoperating at audio frequencies. Timers-simple mono -stable circuits using i.c.s, the 555 and 7555 devices, etc.Miscellaneous-noise generators, rectifiers, compara-tors and triggers, etc.

BOOK 2 contains: Amplifiers-low level discrete andop -amp circuits, voltage and buffer amplifiers includingd.c. types. Also low -noise audio and voltage controlledamplifiers. Filters-high-pass, low-pass, 6, 12, and 24dBper octave types. Miscellaneous -1.c. power amplifiers,mixers, voltage and current regulators, etc.

BOOK 1 128 pages Order code BP117 £1.95BOOK 2 112 pages Order code BP118 £1.95

ELECTRONIC CIRCUITS HANDBOOKMichael Tooley BAThis book aims to explode two popular misconceptions con-cerning the design of electronic circuits: that only those withmany years of experience should undertake circuit designand that the process relies on an understanding of advancedmathematics. Provided one is not too ambitious, neither ofthese popularly held beliefs is true.

Specifically, this book aims to provide the reader with aunique collection of practical working circuits together withsupporting information so that circuits can be produced inthe shortest possible time and without recourse to theor-etical texts.

Furthermore, information has been included so that thecircuits can readily be modified and extended by readers tomeet their own individual needs. Related circuits have beengrouped together and cross-referenced within the text (andalso in the index) so that readers are aware of which circuitscan be readily connected together to form more complexsystems. As far as possible, a common range of supplyvoltages, signal levels and impedances has been adopted.

As a bonus, ten test gear projects have been included.These not only serve to illustrate the techniques describedbut also provide a range of test equipment which is useful inits own right.277 pages Order code NE05 £14.95

to Design

Electronicprojects

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HOW TO DESIGN ELECTRONICPROJECTSR. A. PenfoldThe aim of this book is to help the reader to put togetherprojects from standard circuit blocks with a minimum oftrial and error, but without resorting to any advancedmathematics. Hints on designing circuit blocks to meetyour special requirements are also provided128 pages Order code BP127 £2.25

POPULAR ELECTRONIC CIRCUITS-BOOK 1POPULAR ELECTRONIC CIRCUITS-BOOK 2R. A. PenfoldEach book provides a wide range of designs for elec-tronic enthusiasts who are capable of producing workingprojects from just a circuit diagram without the aid ofdetailed construction information. Any special setting -upprocedures are described.BOOK 1 160 pages Order code BP80 £1.95BOOK 2 160 pages Order code BP98 £2.25


ELECTRONIC CIRCUITS FOR THE COMPUTER CONTROL OFMODEL RAILWAYSR.A. PenfoldHome computers may easily be applied to the control ofmodel railways and really quite sophisticated control, whichneeds only simple programming, is not too difficult toachieve. The main problem lies in interfacing the computerto the layout, but fortunately it is not too difficult or expens-ive to build suitable interfaces, and this book shows youhow.The projects consist of various types of controller, includinga high quality pulse type, as well as circuits for train positionsensing, signal and electric points control etc. The use ofcomputers does not have to be restricted to massive layouts.Something as simple as an oval of track with a single sidingcan be given a new dimension by adding computer controland much fun can be had from these relatively simple set-ups.88 pages Order code BP180 E295

MODERN OPTO DEVICE PROJECTSR.A. PenfoldIn recent years, the range of opto devices available to thehome constructor has expanded and changed radically.These devices now represent one of the more interestingareas of modern electronics for the hobbyist to experimentin, and many of these devices have useful practical applica-tions as well. This book provides a number of practical

designs which utilize a range of modern opto-electricdevices, including such things as fibre optics, ultra brightI.e.d.s and passive IR detectors etc.While many of these designs are not in the "dead simple"category, they should be within the capabilities of anyonewith a reasonable amount of experience in electronics con-struction and some of the more simple designs are suitablefor beginners.104 pages Order code BP194 £2.95

ELECTRONIC CIRCUITS FOR THE COMPUTER CONTROL OFROBOTSRobert PenfoldRobots and robotics offer one of the most interesting areasfor the electronics hobbyist to experiment in. Today themechanical side of robots is not too difficult, as there arerobotics kits and a wide range of mechanical componentsavailable. The micro controller is not too much of a problemeither, since the software need not be terribly complex andmany inexpensive home computers are well suited to thetask.The main stumbling block for most would-be robot buildersis the electronics to interface the computer to the motors,and the sensors which provide feedback from the robot tothe computer. The purpose of this book is to explain andprovide some relatively simple electronic circuits whichbridge this gap.92 pages Order code BP179 E2.95

ELECTRONICS TEACH -INMichael Tooley BA and David Whitfield MA MScCEng MIEE (published by Everyday Electronics)This value for money EE book provides a comprehensivebackground to modern electronics including test gearprojects. A complete course in basic electronics; designedfor the complete newcomer it will however also be of valueto those with some previous experience of electronics.Wherever possible the course is related to "real life"working circuits and each part includes a set of detailedpractical assignments. Includes details of eight items ofrelated test gear giving full constructional information anddiagrams for each one. They are: Safe Power Supply;Universal LCR Bridge; Diode/Transistor Tester; AudioSignal Tracer; Audio Signal Generator; RF SignalGenerator; FET Voltmeter; Pulse Generator. An excellentcompanion for anyone interested in electronics andinvaluable for those taking G.C.S.E. and BTEC electronicscourses.104 pages (A4 size) Order code EE/T-1 £1.95

PRACTICAL ELECTRONICSCALCULATIONS AND FORMULAEF. A. Wilson, C.G.I.A., C.Eng., F.I.E.E., F.I.E.R.E.,F.B.I.M.Bridges the gap between complicated technical theory,and "cut -and -tried" methods which may bring successin design but leave the experimenter unfulfilled. A strongpractical bias-tedious and higher mathematics havebeen avoided where possible and many tables have beenincluded.

The book is divided into six basic sections: Unitsand Constants, Direct -current Circuits, Passive Compo-nents, Alternating -current Circuits, Networks and Theo-rems, Measurements256 pages Order Code BP53 £2.95

ESSENTIAL THEORY FOR THEELECTRONICS HOBBYISTG. T. Rubaroe, T.Eng (C.E.I.), Assoc.I.E.R.E.The object of this book is to supply the hobbyist with abackground knowledge tailored to meet his or herspecific requirements and the author has brought to-gether the relevant material and presented it in a readablemanner with minimum recourse to mathematics.728 pages Order Code 228 £2.50

MICROPROCESSING SYSTEMS AND CIRCUITSF. A. Wilson, C.G.I.A., C.Eng., F.I.E.E., F.I.E.R.E.,F.B.I.M.A truly comprehensive guide to the elements of micro -processing systems which really starts at the beginningTeaches the reader the essential fundamentals that areso important for a sound understanding of the subject256 pages Order Code BP77 £2.95

DATA AND REFERENCE

Electronic

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erControl °`,Robots

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ElectronicCircuits for theComputerControl ofModel Railways

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ELECTRONIC HOBBYISTS HANDBOOKR.A. PenfoldProvides an inexpensive single source of easily locatedinformation that the amateur electronics enthusiast is likelyto need for the day-to-day pursuance of this fascinatinghobby. Covers common component colour codes. Detailsthe characteristics and pinouts of many popularsemiconductor devices, including various types of logicICs, operational amplifiers, transistors, FETs, unijunctions,diodes, rectifiers, SCRs, diacs, triacs, regulators andSMDs, etc. Illustrates many useful types of circuits, suchas timers and oscillators, audio amplifiers and filters, aswell as including a separate section on power supplies.Also contains a multitude of other useful data.88 pages Order code BP233 f4.95

AUDIOF. A. Wilson, C.G.I.A., C.Eng., F.I.E.E., F.I.E.R.E.,F.B.I.M.Analysis of the sound wave and an explanation ofacoustical quantities prepare the way. These are fol-lowed by a study of the mechanism of hearing andexamination of the various sounds we hear. A look atroom acoustics with a subsequent chapter on micro-phones and loudspeakers then sets the scene for themain chapter on audio systems-amplifiers, oscillators,disc and magnetic recording and electronic music.320 pages Order Code BP111 £3.50

HOW TO IDENTIFY UNMARKED ICsK. H. RecorrShows the reader how, with just a test -meter, to goabout recording the particular signature of an unmarkedi. c. which should enable the i. c. to then be identified withreference to manufacturers' or other data. An i csignature is a specially plotted chart produced by mea-suring the resistances between all terminal pairs of an i.c.Chart Order code BP101 £0.95

RADIO AND ELECTRONIC COLOUR CODES ANDDATA CHARTB. B. BabaniAlthough this chart was first published in 1971 itprovides basic information on many colour codes in usethroughout the world, for most radio and electroniccomponents. Includes resistors, capacitors, transfor-mers, field coils, fuses, battery leads, speakers, etc. It isparticularly useful for finding the values of oldcomponents.Chart Order code BP7 £0.95

CHART OF RADIO, ELECTRONIC,SEMICONDUCTOR AND LOGIC SYMBOLSM. H. Banani, B.Sc.(Eng.)Illustrates the common, and many of the not -so -com-mon, radio, electronic, semiconductor and logic symbolsthat are used in books, magazines and instructionmanuals, etc., in most countries throughout the worldChart Order Code BP27 £0.95

RECOMMENDED READING

FOR...INTRODUCING

MICROPROCESSORS(THE EVERYDAY ELECTRONICS

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PRACTICAL DIGITAL ELECTRONICS HANDBOOKMike Tooley (Published in association with Everyday Elec-tronics)The vast majority of modern electronic systems rely heavilyon the application of digital electronics, and the PracticalDigital Electronics Handbook aims to provide readers witha practically based introduction to this subject. The bookwill prove invaluable to anyone involved with the design,manufacture or servicing of digital circuitry, as well as tothose wishing to update their knowledge of modern digitaldevices and techniques. Contents: Introduction tointegrated circuits; basic logic gates; monostable andbistable devices; timers; microprocessors; memories; inputand output devices; interfaces; microprocessor buses.Appendix 1: Data. Appendix 2: Digital test gear projects;tools and test equipment; regulated bench power supply;logic probe; logic pulser; versatile pulse generator; digitalIC tester; current tracer; audio logic tracer; RS -232Cbreakout box; versatile digital counter/frequency meter.Appendix 3: The oscilloscope. Appendix 4: Suggestedreading. Appendix 5: Further study.208 pages Order code PC100 £6.95

BEGINNERS GUIDE TO MICROPROCESSORSE.A. ParrAn excellent grounding in microprocessors, this book isbroadly relevent to the whole of our IntroducingMicroprocessors course. It is easy to read and wellillustrated.224 pages Order code NE03 f4.95

MICROELECTRONIC SYSTEMS 2 CHECKBOOKR. VeersThe aim of this book is to provide a foundation inmicrocomputer hardware, software and interfacingtechniques. Each topic is presented in a way that assumesonly an elementary knowledge of microelectronic systemsand logic functions. The book concentrates on 6502, Z80and 6800 microprocessors and contains 60 testedprograms, 160 worked problems and 250 further problems.194 pages Order code NE04 £4.95

RECOMMENDED READING


DATA AND REFERENCE

OSCILLOSCOPES: HOW TO USE THEM -HOW THEY WORKIan HickmanOscilloscopes are essential tools for checking circuit oper-ation and diagnosing faults, and an enormous range of mod-els is available. But which is the right 'scope for a particularapplication? Which features are essential, which not soimportant? What techniques will get the best out of theinstrument?Ian Hickman, experienced in both professional and hobbyistelectronics, has revised this well -established book to help alloscilloscope users and potential users.133 pages Order code NE09 £5.95

1.000E°35a'legwil.OSCILLOSCOPES

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PRACTICAL ELECTRONICS HANDBOOKIan SinclairIan Sinclair has now revised this useful and carefully selec-ted collection of standard circuits, rules -of -thumb, anddesign data for professional engineers, students andenthusiasts involved in radio and electronics. Covering pass-ive and active components, discrete component circuits(such as amplifiers, filters and oscillators) and linear anddigital i.c.s, the book includes many items which are notelsewhere available in a single handy volume. The operationand functions of typical circuits are described, while math-ematics is limited to that necessary for deciding componentvalues for any application.This revised edition contains more details on computers andmicroprocessors and has been brought up to date through-out.199 pages Order Code NE06 £7.95

BEGINNER'S GUIDE TO HI-FIIan SinclairThe Beginner's Guide to will appeal to the audioenthusiast, whether newly won over by advances in tech-nology or well established and wondering whether to up-date equipment. The book deals with the sound from itssources in the studio to its ultimate end in your ears, andshows what sound is, how it is recorded and how it is repro-duced.Every aspect of Hi-Fi, from pickup cartridges to loudspeak-ers, has been covered, and the emphasis has been on ex-plaining design aims. Cassette systems have been givenconsiderable prominence, including the more modern DolbyC and dbx noise reduction systems. The CD record has beencovered in detail so that you can find out just why thissystem of sound reproduction is so superior.194 pages Order Code NE07 £4.95

COMMUNICATIONF. A. Wilson, C.G.I.A., C.Eng., F.I.E.E., F.I.E.R.E.,F.B.I.M.A look at the electronic fundamentals over the whole ofthe communication scene. This book aims to teach theimportant elements of each branch of the subject in astyle as interesting and practical as possible. While notgetting involved in the more complicated theory andmathematics most of the modern transmission systemtechniques are examined including line, microwave,submarine, satellite and digital multiplex systems, radioand telegraphy. To assist in understanding these morethoroughly, chapters on signal processing, the electro-magnetic wave, networks and transmissions assess-ment are included, finally a short chapter on opticaltransmission256 pages Order Code BP89 £2.95

trYlA1310& ELECTRONIC

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CHART

GETTING THE MOST FROM YOUR MULTIMETERR.A. PenfoldThis book is primarily aimed at beginners and those oflimited experience of electronics. Chapter 1 covers the bas-ics of analogue and digital multimeters, discussing the rela-tive merits and the limitations of the two types. In Chapter 2various methods of component checking are described, in-cluding tests for transistors, thyristors, resistors, capacitorsand diodes. Circuit testing is covered in Chapter 3, withsubjects such as voltage, current and continuity checksbeing discussed.In the main little or no previous knowledge or experience isassumed. Using these simple component and circuit testingtechniques the reader should be able to confidently tackleservicing of most electronic projects.96 pages Order code BP239 £2.95

PRACTICAL MIDI HANDBOOKR.A. PenfoldThe Musical Instrument Digital Interface (MIDI) is sur-rounded by a great deal of misunderstanding, and many ofthe user manuals that accompany MIDI equipment are quiteincomprehensible to the reader.The Practical MIDI Handbook is aimed primarily atmusicians, enthusiasts and technicians who want to exploitthe vast capabilities of MIDI, but who have no previousknowledge of electronics or computing. The majority of thebook is devoted to an explanation of what MIDI can do andhow to exploit it to the full, with practical advice on connec-ting up a MIDI system and getting it to work, as well asdeciphering the technical information in those equipmentmanuals.128 pages Order code PC101 £5.95

INTRODUCTION TO DIGITAL AUDIOIan SinclairDigital recording methods have existed for many years andhave become familiar to the professional recording engin-eer, but the compact disc (CD) was the first device to bringdigital audio methods into the home. The next step is theappearance of digital audio tape (DAT) equipment.All this development has involved methods and circuits thatare totally alien to the technician or keen amateur who haspreviously worked with audio circuits. The principles andpractices of digital audio owe little or nothing to the tradi-tional linear circuits of the past, and are much more compre-hensible to today's computer engineer than the oldergeneration of audio engineers.This book is intended to bridge the gap of understanding forthe technician and enthusiast. The principles and methodsare explained, but the mathematical background and theoryis avoided, other than to state the end product128 pages Order code PC102 E5.95

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INTERNATIONAL TRANSISTOREQUIVALENTS GUIDEA. MichaelsHelps the reader to find possible substitutes for a popularselection of European. American and Japanese transis-tors. Also shows material type, polarity, manufacturerand use320 pages

t

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TRANSISTOR RADIO FAULT-FINDING CHARTC. E. MillerUsed properly, should enable the reader to trace mostcommon faults reasonably quickly. Across the top of thechart will be found four rectangles containing briefdescription of these faults, vis-sound weak but undis-torted, set dead, sound low or distorted and backgroundnoises. One then selects the most appropriate of theseand following the arrows, carries out the suggestedchecks in sequence until the fault is cleared.Chart Order code BP70 £0.95

DIGITAL IC EQUIVALENTSAND PIN CONNECTIONSA. MichaelsShows equivalents and pin connections of a popularselection of European, American and Japanese digitali.c.s. Also includes details of packaging, families, func-tions, manufacturer and country of origin.256 pages Order code BP140 £4.95

LINEAR IC EQUIVALENTSAND PIN CONNECTIONSA. MichaelsShows equivalents and pin connections of a popularselection of European, American and Japanese lineari.c.s. Also includes details of functions, manufacturerand country of origin.320 pages Order code BP141 £4.95

INTERNATIONAL DIODEEQUIVALENTS GUIDEA. MichaelsDesigned to help the user in finding possible substitutesfor a large selection of the many different types of diodesthat are available. Besides simple rectifier diodes, alsoincluded are Zener diodes, I.e.d.s, diacs, triacs, thyris-tors, OCIs, photo and display diodes.144 pages Order code BP108 £2.25

NEWNES ELECTRONICSPOCKET BOOKE. A. ParrNewnes Electronics Pocket Book has been in print forover twenty years and has covered the development ofelectronics from valve to semiconductor technology andfrom transistors to LSI integrated circuits and micro-processors. To keep up to date with the rapidly changingworld of electronics, continuous revision has beennecessary. This new Fifth Edition takes account of recentchanges and includes material suggested by readers ofprevious editions. New descriptions of op. amp. applica-tions and the design of digital circuits have been added,along with a totally new chapter on computing, plusother revisions throughout315 pages (hard cover) Order Code NE02 £8.95

TRANSISTOR SELECTOR GUIDEThis unique guide offers a range of selection tablescompiled so as to be of maximum use to all electronicsengineers, designers and hobbyists.Section 1: Covers component markings, codings andstandards, as well as explaining the symbols used.Section 2: Tabulates in alpha -numeric sequence thecomprehensive specifications of over 1400 devices.Section 3: Tabulates the devices by case type.Section 4: Considers particular limits to the electricalparameters when compiling the tables.Section 5: Illustrates package outlines and leadouts.Section 6: Consists of a surface mounting device markingsconversion list.192 pages Order code BP234 £4.96

Everyday Electronics, July 1988

RADIO/TELEVISION

An Introductionto Programmingthe BBCModel B Micro

AN INTRODUCTION TO RADIO °XINGR. A. PenfoldAnyone can switch on a short wave receiver and playwith the controls until they pick up something, but to finda particular station, country or type of broadcast and toreceive it as clearly as possible requires a little more skilland knowledge The object of this book is to help thereader to do just that, which in essence is the fascinatinghobby of radio DXing112 pages Order code BP91 £1.95

INTERNATIONAL RADIO STATIONS GUIDEP. ShoreProvides the casual listener, amateur radio DXer and theprofessional radio monitor with an essential reference workdesigned to guide him or her around the ever more complexradio bands. This new edition has been completely revisedand rewritten and incorporates much more informationwhich is divided into the following sections:Listening to Short Wave Radio; ITU Country Codes; World-wide Short Wave Radio Stations; European, Middle East andNorth African Long Wave Radio Stations; European. NearEast and North African Medium Wave Radio Stations; Cana-dian Medium Wave Radio Stations; USA Medium WaveRadio Stations; Broadcasts in English; Programmes forDXers and Short Wave Listeners; UK FM Radio Stations;Time differences from GMT; Abbreviations; Wavelength/Frequency Conversion.320 pages Order code BP255 E4.95

BEGINNER'S GUIDE TO AMATEUR RADIOF.G. Raver Second edition revised by Gordon King G4VFV.Whether you are new to radio, or have become interested byway of CB, it is hoped that this book, will further whet yourappetite and put you in good stead for passing the RadioAmateur's Examination and becoming a licensed radio ama-teur.188 pages Temporarily out of print

AN INTRODUCTION TO SATELLITE TELEVISIONF.A. WilsonAs a definitive introduction to the subject this book is pre-sented on two levels. For the absolute beginner or anyonethinking about purchasing or hiring a satellite TV system, thestory is told as simply as such a complex one can be in themain text.For the professional engineer, electronics enthusiast, stu-dent or others with technical backgrounds, there are numer-ous appendices backing up the main text with additionaltechnical and scientific detail formulae, calculations, tablesetc.There is also plenty for the DIY enthusiast with practicaladvice on choosing and installing the most problematic partof the system the dish antenna.104 pages Order code BP 195 E5.95

COMPUTINGGETTING THE MOST FROM YOUR PRINTERJ. W. PenfoldDetails how to use all the features provided on most dot-matrix printers from programs and popular word proces-sor packages like Wordwise, Visawrite and Quill, etc.Shows exactly what must be typed in to achieve a giveneffect.96 pages Order Code BP181 £2.95

A Z80 WORKSHOP MANUALE. A. Parr, B.Sc., C.Eng., M.I.E.E.This book is intended for people who wish to progressbeyond the stage of BASIC programming to topics suchas machine code and assembly language programming,or need hardware details of a Z80 based computer.192 pages Order Code BP112 £3.50

AN INTRODUCTION TO 68000 ASSEMBLYLANGUAGER. A. & J. W. PenfoldObtain a vast increase in running speed by writingprograms for 68000 based micros such as the Commo-dore Amiga, Atari ST range or Apple Macintosh rangeetc., in assembly language. It is not as difficult as onemight think and this book covers the fundamentals.112 pages Order Code BP184 £2.95

THE ART OF PROGRAMMING THE ZXSPECTRUMM. James, B.Sc., M.B.C.S.It is one thing to have learnt how to use all theSpectrum's commands and functions, but a very differ-ent one to be able to combine them into programs thatdo exactly what you want them to. This is just what thisbook is all about-teaching you the art of effectiveprogramming with your Spectrum144 pages Order code BP119 £2.50

AN INTRODUCTION TO PROGRAMMING THECOMMODORE 16 & PLUS 4R. A. PenfoldHelps you to learn to use and program these twoCommodore machines with the minimum of difficulty byexpanding and complementing the information suppliedin the manufacturer's own manuals128 pages Order code BP158 £2.50

AN INTRODUCTION TO PROGRAMMING THEBBC MODEL B MICROR. A. & J. W. PenfoldWritten for readers wanting to learn more about pro-gramming and how to make best use of the incrediblypowerful model B's versatile features. Most aspects ofthe BBC micro are covered, the omissions being wherelittle could usefully be added to the information providedby the manufacturer's own manual.744 pages Order code BP139 £1.95

THE PRE -BASIC BOOKF. A. Wilson, C.G.I.A., C.ENG., F.I.E.E., F.I.E.R.E.,F.B.I.M.Another book on BASIC but with a difference. This onedoes not skip through the whole of the subject andthereby leave many would-be programmers flounderingbut instead concentrates on introducing the technique bylooking in depth at the most frequently used and moreeasily understood computer instructions. For all new andpotential micro users192 pages Order code BP146 £2.95

AN INTRODUCTION TOCOMPUTER PERIPHERALSJ. W. PenfoldCovers such items as monitors, printers, disc drives,cassette recorders, modems, etc., explaining what theyare, how to use them and the various types andstandards. Helps you to make sure that the peripheralsyou buy will work with your computer80 pages Order code BP170 £2.50

COMPUTER TERMINOLOGY EXPLAINEDI. D. PooleExplains a wide range of terms that form the computerjargon used by enthusiasts Includes a reference guide tothe more commonly used BASIC commands.96 pages Order code BP148 £1.95

AN INTRODUCTION TO PROGRAMMING THEACORN ELECTRONR. A. & J. W. PenfoldDesigned to help the reader learn more about program-ming and to make best use of the Electron's manyfeatures. Adds considerably to the information alreadysupplied in the manufacturer's own instruction manual144 pages Order code BP142 £1.95

AN INTRODUCTION TO PROGRAMMING THEATARI 600/800 XLR. A. & J. W. PenfoldEspecially written to supplement the manufacturer's ownhandbook. The information supplied will help the readerto master BASIC programming and to make best use ofthe Atari's many powerful features128 pages Order code BP143 £1.95

AN INTRODUCTION TO PROGRAMMING THEAMSTRAD CPC 464 AND 664R. A. & J. W. PenfoldThe Amstrad CPC 464 or 664 running with LocomotiveBASIC makes an extremely potent and versatile machineand this book is designed to help the reader get the mostfrom this powerful combination. Written to complementrather than duplicate the information already given in themanufacturer's own manual. Also applicable to the CPC6128144 pages Order Code BP153 £2.50

AN INTRODUCTION TO PROGRAMMING THESINCLAIR QLR. A. & J. W. PenfoldHelps the reader to make best use of the fantastic SinclairQL's almost unlimited range of features. Designed tocomplement the manufacturer's handbook.112 pages Order code BP150 £1.95

AN INTRODUCTION TO Z80 MACHINE CODER. A. & J. W. PenfoldTakes the reader through the basics of microprocessorsand machine code programming with no previous know-ledge of these being assumed. The Z80 is used in manypopular home computers and simple programming ex-amples are given for Z80 -based machines including theSinclair ZX-81 and Spectrum, Memotech and the Am-strad CPC 464 Also applicable to the Amstrad CPC 664and 6128144 pages Order code BP152 £2.75

AN INTRODUCTION TO 6502 MACHINE CODER. A. & J. W. PenfoldNo previous knowledge of microprocessors or machinecode is assumed. Topics covered are assembly lan-guage and assemblers, the register set and memory,binary and hexadecimal numbering systems, addressingmodes and the instruction set, and also mixing machinecode with BASIC Some simple programming examplesare given for 6502 -based home computers like the VIC-20, ORIC-1/Atmos, Electron, BCC and also the Commo-dore 64112 pages Order code BP147 £2.50

HOW TO GET YOUR COMPUTER PROGRAMSRUNNINGJ. W. PenfoldHave you ever written your own programs only to findthat they did not work' Help is now at hand with this bookwhich shows you how to go about looking for yourerrors, and helps you to avoid the common bugs andpitfalls of program writing Applicable to all dialects ofthe BASIC language144 pages Order code BP169 £2.50

AN INTRODUCTION TO COMPUTERCOMMUNICATIONSR. A. PenfoldProvides details of the various types of modem and theirsuitability for specific applications, plus details of con-necting various computers to modems, and modems tothe telephone system. Also information on commonnetworking systems and RTTY96 pages Order code BP177 £2.95

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NEWNES COMPUTER ENGINEER'SPOCKETBOOKMichael TooleyAn invaluable compendium of facts, figures, circuits anddata, indispensable to the designer, student. serviceengineer and all those interested in computer andmicrocomputer systems It will appeal equally to thehardware or soft ware specialist and to the new band of'software engineers- This first edition covers a vast

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ZA\IQ UZA\L

ge) (Q rFQ __Pco_ao, Co-LIKE MOST hobbies, electronics is litteredwith difficulties for the beginner that

are actually quite easy once you knowhow. A lot of things seem very complexat first, but are really pretty straightfor-ward once they have been rationalisedand explained properly.

A good example of this is componentvalues. They are expressed in variousunits, and a given value can usually beexpressed in more than one way. Thissecond point can make it difficult to selectthe right components from componentscatalogues, and is responsible for a smallbut steady flow of enquiries from read -e rs.

PICO TO TERRAUnderstanding component values is

very much easier once you are familiarwith the prefixes used ahead of the letterthat indicates the type of units. For ins-tance, in the inductance value 33mH the"m" stands for "milli", or one thousandthin other words, and the H indicates thatthe units in use are Henries. The value istherefore 33 millihenries, which is thirty-three thousandths of a Henry, or 0.033Henries.

These prefixes are used, where necess-ary, with any units of metric measure-ment, and are not restricted to use inelectronics. Our "milli" example is to befound in millimetres, milligrams, andprobably many other non -electronicforms of measurement.

Electronics involves very small quanti-ties, very large quantities, and the fullrange of intermediate amounts. Conse-quently you may encounter prefixes inelectronics that you will not have cause touse elsewhere.

Note that these prefix letters are notonly used to indicate fractional units, butare also much used to indicate multipleunits. The letter "k" (which stands for"kilo") is probably the most used of

these, and it means so many thousandsof the basic units. Thus 10 kilohms is10000 ohms, and 22 kilometres is 22000metres.

Table 1 below gives a list of prefixesand their "values".

These prefixes enable an enormousrange of values to be covered withouthaving to resort to very large numbers, ornumbers having a decimal point followedby a large number of zeros. The rangecovered is so wide that the full range ofpico to terra would not normally be utili-zed with one type of units. In fact onlytwo or three prefixes are used with mosttypes of units. With resistors for example,only kilo (k) and mega (M) are normallyrequired. Table 2 shows the units usedfor various types of components, to-gether with the normal range of values.Details of basic electrical units ofmeasurement are also provided, includ-ing the range of values you are likely toencounter.

Note that the "R" for ohms is oftenreplaced by the greek letter omega (S1).The value ranges can only be a generalguide, and there may be the odd compo-nent, voltage, or whatever, that has whatcould only be regarded as an exception-ally high or low value.

As one example of this, a few catalo-gues now list capacitors with a value of 1farad (1000000µF)! This is a special ultra-high value type intended for what wouldnormally be considered battery back-upapplications. This is exceptional though,and few catalogues list capacitors above4700µF.

If you see something like an electrolyticcapacitor value given as 100pF, it isreasonable to assume that it is a misprintand that it should be 100µ. However, if indoubt you can always check with the pub-lisher concerned, and a routine enquiry ofthis type will normally receive a fairlyswift reply.

VALUE JUDGEMENTA lot of confusion seems to result from

the ways values are marked on compo-nents, and on the ways they are markedon capacitors in particular. It is standardpractice these days for values to be ex-pressed without the type of units (farads,ohms, etc.) being included.

Also, the prefix which indicates themultiplier/divisor is often used to indicatethe position of the decimal point as well.This is a general means of expressingvalues, and it is not one that is confined tocomponent value markings.

The idea is to express the value usingas few digits as possible, mainly with theaim of making it easier to find space forthe labels on ever more complex circuitdiagrams. It is obviously more compactto specify a value as 2n2 than as 2.2nF or2200pF.

The current "standard" for marking va-lues on ceramic plate capacitors havingvalues from 100p to 820p seems to beessentially as described above, but withthe value given in nanofarads with what Isuppose could be termed "leading zerosuppression". In other words, a value of470pF would be marked on a ceramicplate capacitor as "n47".

For some reason trailing zeros are notsuppressed, and 100pF is marked as"n10". This system reduces the numberof digits required from four to three, butgetting used to this method of valuemarking can take a while if you are usedto the old style markings in picofarads.

Disc ceramic capacitors seem to causeeven more confusion. These use anotherform of three digit value marking, and thefirst two digits are simply the first twodigits of the value. The third is a multi-plier, rather like the ones used in resistorcolour codes.

In this case the number simply indi-cates the number of zeros to be added tothe first two digits in order to give the fullvalue. For example, with a third digit of"2" it is just a matter of adding two zeros,or multiplying by one hundred if you pre-fer to look at it that way.

A capacitor market "473" would there-fore have a value of 47 plus three zeros,or 47000 in other words. This value is inpicofarads though, and not nanofarads. Itmust be divided by one thousand to con-vert from the former to the latter. Thevalue is therefore 47000pF, or 47nF.

Table 3 provides a few examples thatmight help to clarify the system for you.

This method of value marking nowseems to be turning up on one or twoother types of capacitor, such as Mylarand some Polyester types. It is probablywell worthwhile familiarising yourself

Prefix

Table 1

Lettet"Value" Component/Measurement Type

Table 2

Units Letter Value Range

PicoNanoMicroMilliKiloMegaGigaTerra

n

M

T

0.0000000000010.0000000010.0000010.0011000

100000010000000001000000000000

Capacitor (non -electrolytic)Capacitor (electrolytic)Capacitor (variable)ResistorInductorResistance (general)ImpedanceVoltageCurrentPower

FaradsFaradsFaradsOhmsHenriesOhmsOhmsVoltsAmperesWatts

F

F

F

H

R

R

V

AW

1pF to 2µ2470nF-47000µF5pF- 500pF0.1R -10M0.1µH -4H1mR-1TR1mR-1TR1/2V-20kV1nA-10A1µW-1kW

431 Everyday Electronics, June 1988

with this system, as it seems likely tobecome a standard for medium valuecapacitors.

Table 3

ValueMarking in pF

Valuein nF

Valuein iLF

102 1000 1 0.001

332 3300 3.3 0.0033472 4700 4.7 0.0047103 10000 10 0.01

223 22000 22 0.022473 47000 47 0.047104 100000 100 0.1

334 330000 330 0.33

WORKING VOLTAGE AND TOLERANCEYou may find other markings on

capacitors. These are not necessarily any-thing of interest, and could simply besomething like a manufacturer's batchnumber.

However, in some cases these givefurther information about the compo-nent. The most simple example is wheresomething like "50V" is marked on acomponent, and this is merely the maxi-mum d.c. "working" voltage to which itshould be subjected.

This type of marking is quite commonon electrolytic and tantalum capacitors(which often have quite low maximumvoltage ratings), but are not always foundon other types of capacitor. Where theyare to be found, the marking is often a bitambiguous as the "V" for volts is oftenomitted.

Capacitors sometimes have their toler-ance rating simply written on as "5%" orwhatever, but these days it seems to bemore common for the tolerance simply tobe omitted, or in some cases a singlecode letter is used to indicate the toler-ance. Details of this system of coding areprovided below.

Code Letter ToleranceF

G1%

2%

H 2.5%J 5%

K 10%

M 20%

While on the subject of tolerancecodes, some years ago there were a lot ofresistors in circulation which had the va-lues marked using four letter codes. Thefirst three letters gave the value in con-ventional form (e.g. 4R7, 2k2, 10M, etc,)and the fourth letter gave the toleranceusing the coding system detailed above.

This method did not seem to catch on,but I have recently encountered a fewcomponents that have this system ofmarking, and there are still some re-sistors of this type around. In particular,you may well be supplied with compo-nents having this method of coding if youorder some close tolerance resistors.

Capacitors sometimes have othermarkings to indicate their temperaturecoefficient and (or) power factor. Theseare not normally of any great interest orsignificance to the home constructor, butthey can tend to shroud the main valuemarkings.

What is the value of a capacitor marked104K1D or 05BX472M? Reasonableguesses of 100n 10 per cent and 4n7 20per cent respectively could be made byextracting the figures that look like valuecodes and ignoring the rest. In this casethis would give the right values.

CAPACITOR TESTINGA capacitance meter or bridge is a very

useful piece of test gear for anyoneinvolved in a lot of project construction as

settle any doubts about the value ofan ambiguously marked component.With many types of capacitor the mark-ings are far from indelible, and again,some form of capacitance measuringdevice can reliably sort out any doubts.

Unfortunately, apart from a few multi-purpose digital instruments there are fewmultimeters that have any capacitancemeasuring ranges. However, one usefuldodge that can sometimes be of use withan analogue multimeter is to switch theinstrument to the highest resistancerange and then connect it across a testcapacitor. This should result in a small

"kick" of the pointer with most compo-nents, due to the capacitor charging up.

With very low values of a few nanofa-rads or less, the initial charge may be toosmall to produce any significant deflec-tion of the meter. With high value capaci-tors it might take a significant time for thepointer to fall back to zero.

The point here is that the "kick" fromthe meter is proportional to the value ofthe test component, and can be used topermit the value of most capacitors to beroughly gauged. It does not permit accu-rate measurement, but comparisons withcapacitors of known value can givegreater precision than you might expect.

Doubts about the values of capacitorsoften involve uncertainty about the po-sition of the decimal point. This methodshould certainly permit you to determinewhether a capacitor has a value of (say)33nF or 330nF.

Note that with polarised capacitors thetest leads are connected with what isapparently the wrong polarity (i.e. thepositive probe connects to the negativeterminal of the capacitor). This does infact give a voltage of the correct polarityacross the test component.

INDUCTORSMost small inductors, or r.f. chokes as

they are sometimes called, have the valuemarked in the standard fashion (e.g.4/LH7), often with a letter to indicate thetolerance. I have encountered a few thatuse different methods though.

The use of colour codes seems to beincreasingly common. The system usedis a four band type that is actually nodifferent to the standard resistor colourcoding. However, the value is in nano -henries, and for larger values it must bedivided by one thousand to obtain a valuein microhenries.

The other method is essentially thesame as the three digit capacitor type.The first two digits are the first two digitsof the value, and the third one indicatesthe number of zeros that must be addedto give the full value.

The value is again in nanohenries. Thisvalue marking is usually accompanied bya letter to indicate the tolerance. Thus acomponent marked "103J" has a value of10000 nanohenries (10 millihenries), anda tolerance of 5%.

19" RACK MOUNTING EQUIPMENT CASESThis new range of 19' rack equipment cases have been designed with economy andversatility as their objective. These cases are supplied as a flat pack kit with assemblyinstructions.The equipment cases feature a black coated finish 1/2" (3mm) aluminium frontpanel withthe rest of the case constructed from 7mm or 9mm 'Stelvetite' PVC coated steel. All kitsinclude front panel handles and rubber feet.They are available in the following popular sizes with all the units having a standard frontpanel width of 19", and an enclosure width of 111/e (438mm) by a depth of 10" (254mm).

ORDER CODE HEIGHT PRICEU1 13/4 (44mm) 16.80U2 3W (88mm) 18.90U3 5I/'(133mm) 21.00U4 7" (178mm) 23.00WU Sloped mixer console £23.62All prices exclude VATPlease include E2.50+VATfor post and packing.Flat pack size ---500 x 260 x 3212.75 plus VAT plus E150for each additional item

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This series is de-signed to explain theworkings of electroniccomponents and circuitsby involving the readerin experimenting withthem. There will not bemasses of theory or for-mulae but straightfor-ward explanations andcircuits to build and ex-periment with.

THE "semiconductor diode", Fig.25.1a and Fig. 25.16, was the firstelectronic component device that

we studied in this series. We showedthat its characteristic property is that itconducts current in one direction only.

If it is connected as in Fig. 25.1c,current flows freely through it, providedthat the voltage exceeds 0.7V for a sili-con diode. But, if it is reverse -biassed asin Fig. 25.1d, then only a minute leak-age current flows, even though the volt-age across the diode may be severalhundred volts. A high reverse voltagemay cause the diode to break down.Current then flows readily but it is nolonger a diode!

ASTABLE CIRCUIT

This month's circuit requires an alter-nating waveform. For this purpose weuse the 555 timer i.c. connected as anastable multivibrator (April 1987).With the values of resistors R3, R4 andcapacitor CI shown in Fig 25.2, the fre-quency is about 10kHz.

When the timer is driven by a 6Vbattery we normally consider the output

Fig. 25.2. Pulse generator and potentialdivider circuit diagram.

fEE1444G1

ANODEla

A

B

BAND

C._11

CATHODEk

+VC

ovD

F

OV

I 0

I LEAK+V

A = THE DEVICE

B = THE SYMBOLC = FORWARD -BIASSED0 = REVERSE - BIASSED

IEE144301

Fig. 25.1. The semiconductor diode.

of the astable to be a square wave alter-nating between +6V and OV. For thepurpose of describing the action of thecircuit we are going to change the refer-ence level from which we measure volt-ages. Instead of thinking of the batteryterminals as OV and +6V, we will thinkof them as -3V and +3V

Obviously, we need a reference lineat the OV level. This is obtained byusing two equal resistors (RI, R2) as apotential divider (Fig. 25.2). Measuredfrom this level, the output of the astablealternates between +3V and -3V.

on the board. After one final checkoverthe circuit can he powered -up.

To check that the generator is work-ing, connect a crystal earphone to ICIpin 3 (at socket B6), its other terminalbeing connected to the OV line (atF25). You will hear a high-pitched note,this being the 10kHz waveform pro-duced by the circuit.

If you were to connect a voltmeter tothe same points in the circuit, and if thevoltmeter was one which has its needlein the centre of the scale when readingOV, then the needle might be seen tovibrate rapidly as the voltage alternatedbetween -3V and +3V/. This is not

Fig. 25.3. Demonstration breadboardcomponent layout for the pulse gener-ator, potential divider and diode pump.

+3V...\

PULSEGENERATOR

DI ODEPUMP

DI

1-

I --- -( f--/-

{elude resistors RI and R2 and the OVP8ITVEItC'lEt ...t R2

-1'Cl

V OUT

YVOLTMETER

O

CONSTRUCTIONAssemble the pulse generator and

potential divider as in Fig. 25.3. Do notassemble the diode pump section yet.

Commence construction by insertingthe 8 -pin i.c. holder and link wires fol-lowed by the resistors. This should in -

and -3V link wires in the bottom halfof the breadboard. At this stage,capacitor C2 can also be inserted on theboard.

Finally, ICI should be plugged intoits holder and the supply leads inserted

R1

(EE14450


likely to happen in practice as the iner-tia of the needle prevents it from vibrat-ing 10000 times a second.

If an ordinary voltmeter is connectedat these points, its needle is apparentlystationary, close to zero. It may read alittle bit higher than this because the"low" period of the output is shorterthan the "high" period.

DIODE PUMP

Now add the Diode Pump (Fig. 25.4)to the demonstration breadboard, seeFig. 25.3. Make sure that the diodes arethe right way round-current leaves thediode by the cathode (k) terminal,which is the end marked with the band.

To see the "pump" in operation, thevoltmeter is connected across capacitorC3, as in Fig. 25.3, and measures theoutput from the circuit. Switch on andmeasure the output voltage, VouT.Check the voltage reading at socketB19-it is still very close to zero. Wheredoes this extra voltage come from?

C20 a

02y 1148

V1N DI1N4148

OUTPUT

1000p VOUT

0

0v

(EE144601

Fig. 25.4. Circuit diagram for the DiodePump.

Imagine that in Fig 25.4, VIN is -3V.Thus plate A of capacitor C2 is at -3V.Plate B is also at -3V to begin with, butcurrent flows through diode D1 untilplate B is at OV. Then the input startsto rise. When the potential of a plate ofa capacitor is suddenly changed, thepotential of the other plate changes byan equal amount. As the potential at Arises from - 3V to +3V (a rise of 6V),

the potential of B rises by an equalamount. Since it is at OV to start with,it rises from OV to +6V.

Current cannot flow back throughdiode D1 since DI is now reverse -biassed. Instead, the current flowsthrough diode D2, charging plate C ofcapacitor C3. Next the input falls againfrom +3V to -3V, but the charge thathas passed to plate C cannot returnthrough diode D2, for this is now re-verse -biassed. Capacitor C3 holds itscharge. Charge may pass from C3 toany circuit that may be connected to theoutput terminal. C3 receives morecharge every time VIN rises from -3Vto +3V. In summary, electric chargepasses from the OV line through D1 toplate B as VIN falls, and it is pumpedfrom plate B through D2 to plate C asVIN rises.

The action is very similar to that of apump with two valves-an inlet valveand an outlet valve. The old-fashionedvillage pump and the modern bicyclepump are both examples of this. In thebicycle pump the rim of the piston isone valve and the valve on the innertube is the other. Air is sucked in pastthe rim of the piston as we pull thepump -handle out, and is pushed outthrough the inner tube valve as we pushthe handle in.

LEAKAGEA voltmeter such as we are using, or

any other external circuit connected tocapacitor C3 allows charge to leak awayfrom C3. In the bicycle analogy we canthink of this as air leaking away througha small puncture in the tube. If thepuncture is large, air leaks away as fastas or faster than it is being pumped. Thesame applies to the diode pump, andexplains why it is able to supply only alimited amount of current.

Experience tells us that the faster wepump, the greater the pressure in thetyre. Conversely, if we reduce the rateof pumping, the pressure gradually falls

COMPONENTS

ResistorsR1, R2 68 0.5W (2 off)R3 330 0.25WR4 560 0.25W

All 5% carbon

CapacitorsC1, C2 100n polyester (2 off)C3 1000µ elec. 10V

See page 415

SemiconductorsDI, D2 1N4148 silicon diode

(2 off)IC1 555 timer i.c.

MiscellaneousBreadboard (Verobloc); 8 -pin i.c.

holder; B1 6V battery and connec-tors; connecting wire and Voltme-ter, set to 10V d.c. scale.

Approx. cost .1 a= (excludingGuidance only Li" meter)

to a lower level. Does this happen withthe diode pump? Try this out by substi-tuting 3k3 and 5k6 resistors for R3 andR4. The "pumping" frequency is nowonly 1 kHz. What effect does this haveon the voltage across capacitor C3?

You will notice the effect best with acheap voltmeter that takes a relativelylarge current. If you are using anexpensive moving coil voltmeter or adigital voltmeter, it may take such asmall current that changing the fre-quency makes no appreciable differ-ence. In this case connect a 22k resistoracross C3 to increase the rate at whichC3 loses charge. Insert the resistor insockets J19 and J25.

The explanation above is an over-simplified one (for example, it does not


MIL

MIC

AMP

AMP

(EE,447 0)

BACKGROUNDNOISE LOW ALARM

VOLTAGE SILENT

OWLOW VOLTAGE

PUMPING

BABYCRYING

TRANSISTOROFF

HIGHVOLTAGE ALARM

TRIGGERED

TRANSISTORON

ACTIVEPUMPING

Fig. 25.5. One suggested application for the diode pump is as a Baby Alarm. With smallbackground noise, amplifier output is low (alarm silent). When baby cries, output levelsshoot up, switching transistor on and triggering alarm circuit.take into account the voltage dropacross the diodes), but it is sufficientlyaccurate to explain the general principleof the diode pump. If you scan though

the circuit diagrams in this magazineeach month, you will sometimes comeacross one that has two diodes con-nected to make a pump.

BABY ALARMAn example of a circuit in which a

pump might be used is a Baby Alarm(Fig. 25.5). A microphone beside thebaby's cot is connected to an amplifier,the output of the amplifier is connectedto a diode pump.

With small background noises, theoutput of the amplifier rises and falls bysmall amounts, charging the capacitorof the pump slightly. The voltagechanges are small and any chargepumped to the capacitor leaks away asfast as it is pumped.

But when baby cries, the output fromthe amplifier rises and falls rapidly andby large amounts. The increased rateand amplitude of pumping causes asteady increase in potential across thecapacitor. After a few moments thepotential has risen to a level at which atransistor connected to the capacitor isswitched on, triggering the baby alarmto sound.

This is just one of many examples ofthe usefulness of this simple diodepump circuit.

Next Month: We look at the Diode/Capacitor Ladder.

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565566

£2.40£4.10

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567568

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1E3

6 MILL CLOSE, BORROWASH, DERBY DE7 3GU. Tel: 0332 674929

THE UNDISPUTED PACK KING FOR OVER 20 YEARS, we offer you the very best in Electronic Components and Semiconductors that your money can buy. Look at our listsand prices, they are unbeatable in value and quantity and you always have our -Satisfaction or money back guarantee-. For 1988 we offer more and more Super ValuePacks. All goods advertised in stock at time of going to press. This is just a small part of our stocks. Send a stamped SAE for our full lists FREE. please note our new mailorder address: BI-PAK, PO BOX 33, ROYSTON, HERTS SG8 5DF. Telephone 0763 48851.

RESISTORSPakNo Oty Des/nation Price

VP1 300 Assorted Resistors. mixed values Er types CI 00VP2VP4

300200

Carbon Resistors. 5 5 watt. pre formed mixed5 I watt Resistors, mixed values and types

0 1 0001.00

VP16 50 Wirewound Resistors. mixed watt values 01.00VP140VP181

50100

Precision Resistors, 1% toleranceI and 2 watt Resistors, assorted values

01.0001.00

VP2137 103 Close tolerance Resistors. 05-216 10910 ohms. mixed 01.50VP2803 101 Close tolerance Resistors. 062%. 11-82011. mixed 0150vvms 100 Metal oxide high stab Resistors ,w 2%. muted values 0110

CAPACITORSVF5 200 Assorted Capactiors all types 01 00

VP6VP9

200100

Ceramic Capacitors. Mon mixed valuesAssorted Polyester Polystyrene Capacitors

01.00C.00

VPtO 60 C293 Capacitors. metal fool. mused values CIAOVP11VP12

5040

Electrolytics all sortsElectrolytocs 047, 15Orn1. 'nosed volts

01 .00

01.01)

VP13 30 Electrolytom 150mf 1000rnf. mixed volts C1.00

VPI4 50 Solver Mica Cap, mixed values_...... n.00VP15VP180

2525

01,250v Min Layer Metal CapsTantalum Seed Caps. assorted values

01.00C 00

VP182VP19.2

4

30

1000u1 50v Electrolyt deMin Electrolytic, mixed values. 0.17rod.1000, 616e

01.0001.00

VP193 6 Sub Min Electrolytes. 2t 1000/2200/ 3300nd 10,16v 01.00

VP25VP26VP27vvzxUPS)V P130VP131V P133VPI34VP138VP147VP199VP203V P204VP2C6VP206V P207VP200VP741VP242VP243VP266VP267V P260V P299V P284VP286

OPTOS10 125 clear showing Red LEDsto Mixed shape a, colour LEDs15 Small 125 Red LEDs15 Large 2 Red LEDs10 Rectangular 2- Rood LEDs25 Opto spacial peck. Assorted Super Value

RED 7 Sag CC lernm 7 5mm IMP Fa10363 LED DisplayGREEN 7 Seg. CA 6 LOP 0AN8520 LED DisplayRED Overflow 8 ' 3 . CA 3 x CC WO/ 50 LED CMOs,GREEN Overflow CA XAN6530 LED Display

20 Assorted LED Displays Our mix with dataPair Opto Coupled ModulesL57075 LED Displays CA

1 Triangular shape LEDs Mixed colours1 Large Green LEDs. 5rnm1 Small Green LEDs, 3rnm1 Large Yellow LEDs. Smm1 Small yellow LEDs. 3mrn1 Large LEDs clear showing Red. 2

ORP12 Light Dependent ResistorTn colour LEDs Smon Dia SmA 2v R G YToo colouo LEDs Rectangular Sinm R G Y

1 Change LED's. Sonon largeStackable LED s Rectangular. rooked 8 G

I LED Panel Mounting Clops. metal and plastic 3 5mmRed Flashing LED's. 5mmOpto Isolator 1174 4827. singleDual Opton Isolator 11074

fl 00C 00fl 00fl 00CI 00fl 000.000.000.000.0005.0000.1001.00CI 00C1 00

C1.0001 0001 .00

01.50CI 50Cl OD01.000 1 CO

01.00C.0001.011

01.0001.00

PakTRANSISTORS

PakMISC.

No City Descnalson Price No Qty Descroption Price

VP1T2 10 SM1502 PNP TO 39 Sol Trans 100v 100mA 10e100 C1.00 VPt77 1 Pack assorted Hardware nuts. bolts. etc 01.03VP100 30 0071 type germ AF Transistors. uncoded 01.00 VP178 5 Assorted Battery holders and clips PP3,9 AAA D etc MOOVP201 25 OM gown RF Transistors 01.00 VP223A 6 Tag Boards. 18 way pax/ohne 01.00

VP261 4 Programmable Unijunction Transistors. MEU22 CI 00 VP225 20 DIN Plugs, plastic 28 pin. 181:0240.360. mixed 050V P270 10 FET's UHF/VHF Amplifiers. switching b choppers data 01.00 VP226 20 DIN Chassis Skis. metal 28 pin 1130,240°, 360° ended 02.50

V P271 10

V P272 10

FET's general purpose like 2133819 285457 dataMOS FEr s Sognetics. SD304

01.000.00

VP227 18

VP228 10

DIN In line Skts. plastic 2.8 pin 180,210,360. mixedCIS Computer Cassette Tapes. leadless

02.50.03.00

VP280 12 ITX300 NPN Salmon Transistors 01.00 VP232 t Cassette Head C leaner/ Demagnetizer. in case MOO

V P290 15

V P428 10

MPSA06 Sol Transistors 14PP4 90, 500mA HFE50 TO92

AC12811 PNP Germanoum Translator. lA 32v0t.00C1.00

VP233VP244

1 Revolving Cassette Rack. holds 32. unokey Perspex1 Noah Power Piece Electric Siren Finns earpoercong

050

V P429 10 AC1761( NPN Germano m Transistors to 32v 01 00 warbling sound Ideal alarm. White plastic body withVP433VP431 25

4 2N3166 Sol Power Transistors full specPNP Sol Transistors TO -3910e 2N2905A

0.0001 00

mounting bracket Power 12vDC 150mA Output 100db IA Iat lm tyo trap 25K0. Size 57 12 37mm MAO

V P293 1 9 6 Elliptical 8 ohms 117W RMS Speaker Freq Res60 10000 114 Gauss 10003 Centre HE cone 04.50

I.G.S. VP260A 1 2, Transducer Waterproof Speaker Polyester folmdiaphragm Moisture rest 8 ohms 300m. Freq Res

VP40 40 TTL I C s all new gates Flip Flop MSI Data 0400 20-20000 Hz 01.00VP54 20 Assorted) C DIL Sockets. 8-40 pin 0.50 VP273 10 106 Lin Rotary Potentiometers. slim spindle MOOVPS9 20 Assorted I C s knee, etc all coded 2.00 VP281 4 Plug in Relays Mixed volts etc fleeVP209 12

VP210 12

VP211 10

741500741574C040001

0.00C 2 000.00 TOOLS

VP212 10

V P214 10

CD4011130010698

0.000.00

vP96VP97

Plastic Vice. small. with suction baseLogic Probe.,Tester. supply 4.5v 18v DIL.TTL CMOS

01.750150

VP215 10 741P 8 con aro VP99 Universal Tester. with ceramic buzzer MOOV P216 10

V P123 50565 Tomer, 8 pmAsst 74111 I C s ALL GATES' new and coded

0.00 V P103V P139

6 pc Stanley screwdriver set. flet and crosspoontPick up Tool. spring loaded.

(3.50C1.75

our is 74E0 7453 0800 V P217 Help., Hand £4.00V P224 100 Ass, 74 Ill I C s ALL GATES" new and cod,

our moo 7400 7453 010.00V P218VP219

Watchmakers Screwdriver Set 6 piecesMiniature Side Cutters

C. MC1.55

VP282V P291

Prog Sound Gen Chop AY 3.8912.2813ACPU Mocroprocessor 40 pin 011.

000000

V P220Vpn1

Miniature Bent nose PliersMiniature long nose Pliers

C1.550155

V P292V P293

2130AP10 Parallel Interface Controller. 40 pin OILMAGIC Counter Timer Circuit. 2$0. DIL

0.00000

V P237V P238

Universal Ni Cad Battery Charger AA HP11 HP2 PP3AA Ni Cad Batteries 1 25v 500mAh C R mA

01.011

C4.00

VP294VP2%

173213 220 Eprom6821P Peripheral Interface Adaptor IPIAI

(3 00(1 .50

V P239V P240

C:11P11 No Cad Batteries RechargeableD HP2 Ni Cad Batteries. Rechargeable

£3 .5004.00

V P296VP297

15432414 pm DIL Ouad Op AmpCA3130E MOS-FET I,P. CMOS OoP. Op Amp

0000.00

V P246VP247

25yr Quality Low Cost Soldering Iron 240vAC raw15w "Lightweight" Quality Low Cost Soldering Iron 240vACC350

VP298 MC1310P Stereo Decoder. 11 pin OIL 000 V P248 High Suction Desoldering Pump Teflon nozzle Auto electVP299VP100

CA3065 Pos Volt. Regulator. 1.7,16v. 8 pin TO5271281280 Eprom

011

0.50 V P250Heavy duty return UM,Long Forlorn Grip Soldering Aid. Heavy metal use. Serrated

04.00

VP401 LM317T Adler Voltage Regulator 1 5A 01.00 laws with rev Tweezer action. Ideal for holding smallVP402 2114111 Static Ram 0.00 components Fully adjustable 0.00V P403V P404

TA7201 Audio Amp I C 42w. 13v 2 4 ohms089461 Audio Power Amp 4 5.

01.0001 50

V P254V P255

250 grams Etchant Granules )Ferric Chlondel makes , pontEtching Pen Etch resistant Spare, Blue

£1.0001.00

VP4N C1310168 0.00 V P258 Multocore Solder 5m total 10 and 22 SWG 0100V P433 CD40178 0.00 VPM9 PCB Holder Fully adjustable from 0 320mrn wide and toV P434 013402413 000 any angle Complete with iron stand and spongeVP435VP7413

C04028B7413 Dual Nand Schmitt Trigger. 4-onput

0.0001 .00

Strong metal construction with rubber feetVery high Quality C15.00

VP7440 7440 Dual 4 input Positive.Nond Buller fl 00 VP2B6 Etch Reps, PCB Transfer Sheets. Asst symbols Imes Et INV P7470 7470 A, gated Positive -edge -triggered Flip Flop

with preset 018VP405V P406

Steel Rules 1 4 1 . 10 measuring ins and mmJunior Hacksaw b 3 blades hobby Moo, Er 2 blades

01.0001.00

VP7480 7480 Get, full Adder . ........ CI 00 VP407 10 Piece Needle File Set 03.00V P7481 7481 16 bit Random Access memories CI 00 V P408 4 Piece Stainless Steel Tweezer Set 04.00VP7490VP7491

74911 Decade Counter74918 Bo Shih Register

n0001.00

V P409 Set of 4 mon low cost Side b End Cutters. snipe b combinationPliers 5 onsul handles 04.50

Send your orders to:BI-PAK DEPT EE PO BOX 33, ROYSTON, HERTSTernis Cash with order. Personal cheques, Access andBarclaycard. Giro 388 7006. Saline day despatchTel' 0763454851. Add 11 50 P&P per order and 15% VAT

lam REMEMBER YOU MUST ADD E1.50 P&PAND 15% VAT TO TOTAL ORDER


OSCILLOSCOPESTELEOUIPMENT De3. Dual trace SOMIli Delay Swoop largeTube with manual DSO

S E LABS SMIll Dual Trace 18MHr Solid Stare PortableAC or External DC operation 8 lOorn display with Manual

E160

SCOPES 4D10A Dual trace 10MHz with manual E150

TELEOUIPMENT 554A. Single Trace 10MH, Solid Stay-..With Manua! E90

GOULD ADVANCE 00255 Doe Trace 15MHz. WithManual - ... E225HAMEG 207 Single Trace 8M11, With Manual rap

SPECIAL OFFERSCOSSOR OSCILLOSCOPE CDU150. Dual Trace 35MHEDelay Sweep. Solid State. Portable 8 i 10cm DisplayWith Manual NOW ONLY £180 eachOptional Front Protection Cover containing 2 Prob. &Viewing Hood EIO

SOLARTRON OSCILLOSCOPE CD1400. Dual Beam15MHz. With Manual ONLY E85 eachAVO VALVE TESTER CT160. Suitcase style. 22 Bases

. ONLY £25 each(P&P fll

AVO TRANSISTOR ANALYSER MK 2 ICT4461 Suitcase style.Complete with banenes Si operating instructions

Wm E35 reek (P&P £71

MULTIMETERSAVO 8 Complete with Batteries Et Leads From f 45AVOB MkV Complete with Batteries & Leads

190Ayr, TEST SET tun 1 (Military version of AVO 81 Cornplate with batteries & leads 165TEST LEADS suitable for AVOMETERS. Red & Black with 2trot. Clips Si 1 Prods (P&P E3) ES

AVO Model 7x Complete with Batteries, leads and CarryingCase E40

AV072 Pocket Mutemeter no AC current range. With bane-ries & leads -E10

ANALOGUE POCKET MULTIMETERS Philips & Taylor etc.With Batteries and leads hem 010

DISK DRIVE PSU 240V in 5V lOA & 12V 1.5A out.Size W125rnm, H75mrn, DI8Omm cased unused

Only EIO (p&p E31.OWERTY KEYBOARD las in LYNX MICRO) push tomake. Cased E5 each (p&p E31SWITCH MODE PSI.)5V 40A, V 12V 5A... ..... E30 each (p&pE41

MARCONI AF POWER METER TF893A 201-1,35kHz20aW10W. With Manual (P&P E71 ONLY E35MARCONI RF POWER METER TF1152A. IDC 500MHz. 0.5 to 25 Watts 50 Ohm. With ManualIP&P E7/ ONLY E45MARCONI AM/FM Sig Gen TF106613 10-470MHz

E250MARCONI AM/FM Sig Gen TF995 range from E150FARNELL SINE/SQUARE type LFM2 11-1, 1MHzCompact E130

ADVANCE SG628 AM 150K Hz-220MHz EIS

1ABGEAR CROSSHATCH GENERATOR CM6038 OB .Crosshatch/Grey scale/blank raster. mains or BatteryIP&P E31 Unused EMI Used E12

LABGEAR Colour Bar Generator KG1 8 Test Patterns (P&P(Cl ONLY E40 each

NEW EQUIPMENTHAMEG OSCILLOSCOPE 601. Dual trace 60Mill DelaySweep. Component Tester & 2 Probes BISHAMEG OSCILLOSCOPE 203.6 Dual Trace 20MHz.Component Tester Et 2 Probes £314

All Other Models Available.

AVO TRANSISTOR TESTER 7169Hand held GO NO GO for In situ Testing. Complete withbatteries. leads E, ,,,,,,,,ons 1 p&p 131

unused NOW ONLY Os

ISOLATING TRANSFORMERS240V INPUT

040V out 500VA CIS 'p&p fli, 100VA ES (p&p E31: 240 out500VA ES I pike (Si, 000VA (*p&p Eat

BLACK STAR FREQUENCY COUNTERS P&P 14Meteor 100 100MHz E99

Meteor 600 600MHz E126Meteor 1000 IGHz E175

BLACK STAR, JUPITOR 500 FUNCTION GENERATOR.Sine Square Trianglh 0.1Hz-500kH. P&P 14 E110BLACK STAR ORION. PAL TV/zVIDEO COLOURPATTERN GENERATOR E199

STEPPING MOTORSType 1.200 Steps per rev 4 Phase 15 wirel 12 24V. Torque25oz inch. will run on 5V with reduced torque .. £15 ea.Type 2. 6 12 Steps per rev. 3 phase. 12 24V twill work on5Vi £2 ea 5off aspType 3. NORTH AMERICAN PHILIPS 24 Steps per rev.4 wire 5V 3.3 Amps 0 250rprn 0.200 PPs ...... E6 ea.Type 4. 200 Steps per rev, 120V 13 wirel Torque 25 ozinch E4 ee.Type].WARNER 24 Steps per rev, 3 Phase (A wrimi, 28V,Holding Torque 45oz inch is.

HUNG CHANG DMM 7030. 315 digit. Hand held 28ranges including 10 Amp AC/DC 0.1%. Complete withbatteries & leads. P&P E4 E39.50AS ABOVE. DMM 6010 0.25% 133.50

CARRYING CASE FOR ABOVE 131 each

OSCILLOSCOPES PROBES. Switched . 1: x10.P&P E2 CI 1

Used equipment - with 30 days gua antee. Manuals supplied if epistle.This is a VERY SMALL SAMPLE OF STOCK. SAE or Telepnone or Lists. Please check availability before

ordering. CARRIAGE all units £16 VAT to be added to Total of Goods & Carriage.

= STEWART OF110 WYKEHAM ROAD, READING,

READINGBER KS RG6 1 PL I

Telephone: 0734 68041 Callers welcome 9am - 5.30 pm Mon. -Fri. (until 8 pm Thurs.)

INDEX TO ADVERTISERS

A& G ELECTRONICS 427AUDIOKITS 439BARRIE ELECTRONICS 427BENCHMARK BOOK CO 433BICC-VERO ELECTRONICS 393BI-PAK 439B.K. ELECTRONICS Cover iiiBULL, J. & N Cover iiCIRKIT DISTRIBUTION 427CROTECH INSTRUMENTS 379C -SCOPE INTERNATIONAL 436ELTRAK ELECTRONICS 379GREENWELD ELECTRONICS 378ICS 439JAYTEE ELEC. SERVICES 378LIGHT SOLDERING DEVELOPMENTS 396LONDON ELECTRONICS COLLEGE 396MAGENTA ELECTRONICS 380MAPLIN ELECTRONICS Cover ivMARCO TRADING 436MERLIN SYSTEMS 379NATIONAL COMPONENT CLUB 439OMNI ELECTRONICS 427PHONOSONICS 440RACKZ PRODUCTS 433RADIO COMPONENT SPECIALISTS 438SHERWOOD DATA SYSTEMS 403SPECIALIST SEMICONDUCTORS 421STEWARTS OF READING 440TK ELECTRONICS 382WALTONS OF WOLVERHAMPTON 438XEN ELECTRONICS 414

MUSIC, ECOMPUTSECURI

* POPULAR PROJECTS FROM A

BURGLAR ALARMCONTROLLERS

DETECTORS DETER DELINQUENTS

MULTIZONE CONTROL(PE) SET280 £22.77Two entry -zones, anti -tamper loop, personal attack,entry -exit timing, timed duration, automatic resetting,latching LED monitors.

SINGLE ZONE CONTROL(PE) SET279 £9.32With timed duration control and latching LED monitor.

Both units can be used with any standard detectiondevices, such as contact or magnetic switches,pressure pads, tremblers, ultrasonics, infrared etc, andwill activate standard bells, strobes or sirens.

CHIP TESTER (PE) SET258F £39.30Computer controlled logic and chip analyser

CHORUS-FLANGER (PE) SET235 £59.99Mono -stereo. Superb dual -mode effects.

CYBERVOX (EE) SET228 £44.76Amazing robot type voice unit, with ring -modulator andreverb.

DISCO -LIGHTS (PE) SET245F £62.503 chan sound to light, chasers, auto level.

ECHO-REVERB (PE) SET218 £57.66Mono -stereo. 200ms echo, lengthy reverb, switchablemultitracking.

FFECTSER AND

TY KITSLEADING AUTHOR

edOEttIO

011001 0 011-111

EPROM PROGRAMMER(PE) SET277 £25.25Computer controlled unit for 41( Eproms.

EVENT COUNTER (PE) SET278 £31.504 -digit display counting for any logic source.

MICRO -CHAT (PE) SET276 £64.50Computer controlled speech synthesiser.

MICRO -SCOPE (PE) SET247 £44.50Turns a computer into an oscilloscope.

MICRO -TUNER (PE) SET257 £55.32Computer controlled, tuning aid and freg counter.

MORSE DECODER (EE) SET269 £22.16Computer controlled morse code -decoder.

POLYWHATSIT! (PE) SET252 £122.69Amazing effects unit, echo, reverb, double tracking, phasing,flanging, looping, pitch change, REVERSE tracking! 8Kmemory.

REVERB (EE) SET232 £27.35Mono, with reverb to 4 secs, echo to 60ms.

RING MODULATOR (PE) SET231 £45.58Fabulous effects generation, with ALC and VCO.

STORMS! (PE) £29.50 each unitRaw nature under panel control! Wind & Rain SET250W.Thunder & Lightning SET25OT.

*COMPUTER KITSThe software listing published with the computer kit projectsare for use with C64, PET and BBC computers.

MANY MORE KITS IN CATALOGUEKITS include PCBs and instructions, Further details incatalogue. PCBs also available separately.

LOW COSTGEIGER

COUNTERS DETECTORS

NUCLEAR FREE ZONES?CHECK THEM OUT -

GET A GEIGERDetectors for environmental and geological monitoring.

THE PE GEIGER was shown on BBC TV "TakeNobody's Word For It" program.

METERED GEIGER (PE MK2)Built-in probe, speaker, meter, digital output. Detectortube options - ZP1310 for normal sensitivity. ZP1320for extrasensitivity.Kit -form - SET 264 - (ZP1310) £59.50, (ZP1320)£79.50

GEIGER -MITE SET271 £39.50Miniature geiger with ZP1310 tube, LED displaysradiation impacts. Socket for headphones or digitalmonitoring. Kit -form only.

WEATHER CENTRE AND 32CHANNEL VOICE

SCRAMBLERDETAILS IN CATALOGUE

Send SAE for detailed catalogue, and with all enquiries (overseassend £1.00 or 5 I.R.C.'s), Add 15% VAT. Add P&P - Sets over£50 add £2.50. Others add £1.50. Overseas P&P in catalogue.Text photocopies - Geigers 264 & 272 £1.50 each, others 50p,plus 50p post or large SAE. Insurance 50p per £50. MAIL ORDER,CWO, CHO, P0, ACCESS VISA. Telephone orders: Mon -Fri, 9am- 6pm. 0689 37821. (Usually answering machine).

PHONOSONICS, DEPT EE87, 8 FINUCANE DRIVE, ORPINGTON, KENT BR5 4ED. MAIL ORDERPublished on approximate!, the first Friday of each month by Wimborne Publishing Ltd., 6 Church Street, Wimborne, Dorset 13H21 I JH. Printed in England by Benham & Co. Limited, Colchester,Essex. Distributed by Seymour, 334 Brixton Road, London SW9 7AG. Sole Agents for Australia and New Zealand - Gordon & Gotch lAsia) Ltd., South Africa - Central News Agency Ltd.Subscriptions INLAND E14.50 and OVERSEAS E17.50 payable to "Everyday Electronics" Subscription Department, 6 Church Street, Wimborne, Dorset BH2I 11H. EVERYDAY ELECTRONICSis sold subject to the following conditions, namely that it shall not, without the written consent of the Publishers first having been given, be lent. resold, hired out or otherwise disposed of by way of Tradeat more than the recommended selling price shown on the cover, and that it shall not be lent, resold, hired out or otherwise disposed of in a mutilated condition or in any unauthorised cover by way ofTrade or affixed to or as part of any publication or advertising, literary or pictorial matter whatsoever.

CP POWER AMPLIFIER MODULES PRICES INCLUDE V.A.T. PROMPT DELIVERIES FRIENDLY SERVICE LARGE S.A.E.28p STAMP FOR CURRENT LIST

OMP POWER AMPLIFIER MODULES Now enjoy a world-wide repu.Cation for quality, reliability and performance at a realistic price. Four models available to suit the needs ofthe professional and hobby market, i.e. Industry, Leisure, Instrumental and Hi-Fi etc. When comparingprices, NOTE all models include Toroidal power supply, Integral heat sink, Glass fibre P.C.B. and Drivecircuits to power compatible Vu meter. Open and short circuit proof.Supplied ready built and tested.

OMP100 Mk II Bi-Polar Output power 110 wattsR.M.S. into 4 ohms. Frequency response 15Hz-30KHz -3dB, T.H.D. 0.01%, S.N.R. -118dB, Sensfor Max. output 500mV at 10K. Size355x 115x 65mm.PRICE E33.99+0.00 P&P.

OMP/MF100 Mos-Fet Output power 110 wattsR.M.S. into 4 ohms, Frequency Response 1Hz-100KHz -3dB, Damping Factor 80. Slew Rate45V/uS, T.H.D. Typical 0.002%, Input Sensitivity500mV, S.N.R. -- 125dB. Size 300x 123 x 60m m.PRICE E39.99 -1-E3.00 P&P.

OMP/MF200 Mos-Fet Output power 200 wattsR.M.S. into 4 ohms, Frequency Response 1Hz-100KHz -3dB, Damping Factor 250. Slew Rate50V/uS, T.H.D. Typical 0.001%, Input Sensitivity500mV, S.N.R. - 130dB. Size 300x 150x 100mm.PRICE £62.99-143.50 P&P.

OMP/MF300 Mos-Fet Output power 300 wattsR.M.S. into 4 ohms, frequency Response 1Hz-100KHz -3dB, Damping Factor 350. Slew Rate60V/uS, T.H.D. Typical 0.0008%, Input Sensitivity500mV. S.N.R. - 130dB. Size 330x 147x 102mm.PRICE £79.99+E4.50 P&P.

NOTE: Mos-Fets are supplied as standard 1100KHz bandwidth & Input Sensitivity 500mV). II

required, PA version (50KHz bandwidth & Input Sensitivity 775mV) Order - Standard or P.A.

Vu METER Compatible witj our four amplifiers detailed above. A veryaccurate visual display employing 11 L.F.D. diodes (7 green, 4 red) plusan additional on/off indicator. Sophisticated logic control circuits forvery fast rise and decay times. Tough moulded plastic case, with tintedacrylic front. Size 84 x27 x 45mm.PRICE f8.50+50p P&P.

BURGLAR ALARMBetter to be 'Alarmed' than terrified.Thandar's famous 'Minder' Burglar Alarm System.Superior microwave principle. Supplied as three unitscomplete with interconnection cable. FULLY GUARAN-TEED.Control Unit -Houses microwave radar unit, range upto 15 metres adjustable by sensitivity control. Threeposition, key operated facia switch -off -test -armed.30 second exit and entry delay.Indoor alarm -Electronic swept freq. siren. 104d8 out-put.Outdoor alarm Electronic swept freq. siren, 98dB out-put. Housed in a tamper -proof heavy duty metal case.Both the control unit and outdoor alarm contain rechar-geable batteries which provide full protection duringmains failure. Power requirement 200/260 Volt AC50/60Hz. Expandable with door sensors, panic buttonsetc. Complete with instructions.SAVE £138.00 Usual Price 1228.85BKE's PRICE E89.99 -1-E4.00 P&P

>Why boy a collection of self -assembly boards!

COMP LINNET LOUDSPEAKERSThe very best in quality and value. Made specially to suit today's needfor compactness with high sound output levels. Finished in hardwearing black vynide with protective corners, grille and carry handle.All models 8 ohms. Full range 45Hz-20KHz. Size 20"x15"+ 12". WattsR.M.S. per cabinet. Sensitivity 1W. 1 mtr. dB.OMP 12-100 Watts 100dB. Price £149.99 perpair.OMP 12-200 Watts 102dB. Price £199.99 perpair.Delivery' Securicor £8.00 per pair

IDEAL for Work-shops, Fac-tories, Offices,Home, etc. Sup-plied readybuilt.

rala 19" STEREO RACK AMPS

LOUDSPEAKERS 5" to 15" up to 400 WATTS R.M.S.Cabinet Fixing in stock. Huge selection of McKenzieLoudspeakers available including Cabinet Plans.Large S.A.E. (28p) for free details.

POWER RANGEr 50 WATT R.M.S. Hi-Fi/Disco.20oz magnet, 11/2" ally voice coil. Ground ally fixing escutcheon. Res. Freq. 40Hz Freq. Resp. to 6KHz. Sens92dB. PRICE E10.99. Available with black grille 111.99. P&P E1.50 ea.12" 100 WATT R.M.S. Hi-Fi/DiscoWoz magnet, 2" ally voice coil. Ground ally fixing escutcheon. Die-cast chassis. Whoite cone. Res. Freq.25Hz Freq. resp. to 4KHz. Sens 95dB. PRICE 08.604-0.00 P&P ea.

McKENZIEtr 85 WATT R.M.S. C1285GP Lead Guitar/Keyboard/Disco.2" ally voice coil, Ally centre dome. Res. Freq. 45Hz. Freq. Resp. to 6.5KHz. Sens. 98dB. PRICE 134.57+(3.00P&P ea.12" 85 WATT R.M.S. C1285TC P.A./Disco 2" ally voice coil. Twin cone.Res. Freq. 45Hz Freq. Resp. to 14KHz. PRICE 135.35+13.00 P&P ea.15" 150 WATT R.M.S. C15 Bass Guitar/Disco.3" ally voice coil. Die-cast chassis. Res. Freq. 40Hz Freq. Resp. to 4KHz. PRICE [66.394-14.00 P&P ea.10" 60 WATT R.M.S. 1060GP Gen. Purpose/Lead Guitar/Keyboard/Mid. P.A.2" voice coil. Res. Freq. 75Hz Freq. Resp. to 7.5KHz Sens 99dB. PRICE £23.72,12.00 P&P.10' 200 WATT R.M.S. C10200GP Guitar/Keyboard/Disco.2" voice coil. Res. Freq. 45Hz. Freq. resp. to 7KHz. Sens. 101dB. PRICE 147.49+13.00 P&P.15" 200 WATT R.M.S. C15200 High Power Bass.Res. Freq. 40Hz. Freq. Resp. to 5KHz. Sens 101413. PRICE 173.26+14.00 P&P.15" 400 WATT R.M.S. C15400 High Power Bass.Res. Freq. 40Hz. Sens. 102dB. PRICE 194.12 +14.00 P&P.

WEM5" 70 WATT R.M.S. Multiple Array Disco etc.1" voice coil. Res. Freq. 52Hz. Freq. resp. to 5KHz. Sens. 89dB. PRICE (22.00+11.50 P&P ea.r 150 WATT R.M.S. Multiple Array Disco etc.1" voice coil. Res. Freq. 48Hz. Freq. resp. to 5KHz. Sen. 92dB. PRICE (32.004-11.50 P&P ea.10" 300 WATT H.M.S. Disco/Sound re -enforcement etc.112" voice coil. Res. Freq. 35Hz. Freq. Resp. to 4KHz. Sens. 92dB. PRICE (36.00+12.00 P&P ea.12" 300 WATT R.M.S. Disco/Sound re -enforcement etc.11/2" voice coil. Res. freq. 35Hz Freq. resp. to 4KHz. Sens. 94dB. PRICE E47.00 E3.00 P&P ea.

SOUNDLAB (Full Range Twin Cone)5'60 WATT R.M.S. Hi-Fi/Muhiple Array Disco etc.1" voice coil. res. Freq. 63Hz Freq. resp. to 20KHz. sens. 86d8. PRICE 0.99 0E1.00 P&P ea.Or 60 WATT R.M.S. Hi-Fi/Muhiple Array Disco etc.1" voice coil. Res. Freq. 56Hz. Freq. Resp. to 20KHz. Sens. 8940. PRICE (10.99+11.50 P&P ea.r 60 WATT R.M.S. Hi-Fi/Muhiple Array Disco etc.11/4" voice coil. Res. Freq. 38Hz. Freq. resp. to 20 KHz. Sens 89dB. PRICE (12.99+0.50 P&P ea.10' 60 WATT R.M.S. Hi-Fi/ Disco etc.11/4" voice coil. Res. Freq 35Hz. Freq. Resp. to 15KHz Sens 89dB PRICE (16 490E2 00 P&P ea.

PA

1

HOBBY KITS. Proven designs including glass fibreprinted circuit board and high quality componentscomplete with instructions.

FM MICROTRANSMITTER (BUG) 90/105MHz with very sensitive micro-phone. Range 100/300 metres. 57 x 46 x 14mm (9 volt). Price £8.62+75pP&P.3 WATT FM TRANSMITTER 3 WATT 85/115MHz varicap controlledprofessional performance. Range up to 3 miles 35x 84 x 12mm (12 volt).Price £14.49+75p P&P.SIMGLE CHANNEL RADIO CONTROLLED TRANSMITTER/RECEIVER27MHz. Range up to 500 metres. Double coded modulation. Receiveroutput operates relay with 2 amp/240 volt contacts. Ideal for many applica-tions. Receiver 90 x 70 x 22mm (9/12 volt). Price £17.82. Transmitter80x 50+ 15mm (9/12 volt). Price 111.29+75p P&P each. SAE for complete 3 watt FMlist Transmitter

TEC.

Professional 19" cased Mos-Fet stereoamps. Used the World over in clubs, pubs,discos etc. With twin Vu meters, twin toroi-dal power supplies, XLR connections.MF600 Fan cooOled. Three models (RatingsR.M.S. into 4 ohms). Input sensitivity 775mV.MF200 (100+100)W. £171.35 SecuricorMF400 (200+2001W. £228.85 DeliveryMF600 (300+3001W. £322.00 £10.00

POSTAL CHARGES PER ORDER £1 .00 minimum. OFFICIAL ORDERS1-__

iasA WELCOME, SCHOOLS, COLLEGES, GOVERNMENT BODIES, ETC.'--- PRICES INCLUSIVE OF VAT. SALES COUNTER VISA/ACCESS/C.O.D.

_ ACCEPTED.

BSR P295 ELECTRONIC TURNTABLE* Electronic speed controls 45 & 331/3 rpm * PlusMinus variable pitch control * Belt driven * Alumi-niun platter with strobed rim * Cue lever * Antiskate(bias device) * Adjustable counter balance * Manualarm * Standard 1/7' cartridge fixings * Supplied com-plete with cut-out template * D.C. Operation 9- 14VD.C. 65mA

Price 136.99+0.00 P&P

ADC 04 mag. cartridge for above. Price E4.99ea.+50p P&P

1 K -WATTSLIDE DIMMER

Control loads up to1 kW

Compact size47tzx 1"x21/2"* Easy snap in fixingthrough panel/cabi-net cut out* Insulated plasticcase* Full wave controlusing 8 amp triac* Conforms toBS800

* Suitable for both resistanceand inductive loads. Innume-rable applications in industry,the home, discos, theatres,etc.PRICE £13.99+75p P&P

.IINNEMENIMMI=10

PIEZO ELECTRIC TWEETERS -MOTOROLAJoin the piezo revolution. the low dynamic mass (no voice coil) of a Nem tweeter produces an improvedtransient response with a lower distortion level than ordinary dynamic tweeters. As a crossover is notrequired these units can be added to existing speaker systems of up to 100 watts (more if 2 put in series).FREE EXPLANATORY LEAFLETS SUPPLIED WITH EACH TWEETER.

TYPE 'A' (KSN2036A) 3" round with protective wire mesh,ideal for bookshelf and medium sized Hi-Fi speakers. PriceE4.90 each+ 40p P&P.TYPE 'B' IKSN1005A) 31/2" super horn. For general pur-pose speakers, dico and PA systems etc. Price E5.99each+40p P&PTYPE 'C' IKSN6016A)2"x5" wide dispersion horn. Forquality Hi-Fi systems and quality discos etc. Price E6.99each+40p P&PTYPE 'D' IKSN1025A) 2"06" wide dispersion horn. Upperfrequency response retained extending down to midrange (2KHz). Suitable for high quality Hi-Fi systems andquality discos. Price E9.99 each +40p P&PTYPE 'E' IKSN1038A) 33/4" horn tweeter with attractivesilver finish trim. Suitable for Hi-Fi monitor systems etc.Price E5.99 each+40p P&PLEVEL CONTROL. Combines on a recessed mountingplate, level control and cabinet input jack socket.85 x 85mm. Price £3.99+40p P&P

TYPE

TYPE C

TYPE

PE

TYPE E

STEREO DISCO MIXERSI EREO DISCO MIXER with 2 x 5 band L & R graphicequalisers and twin 10 segment LED Vu meters. Manyoutstanding features. 5 inputs with individual fadersproviding a useful combination of the following: 3Turntables (Magi, 3 Mics, 4 Line plus Mic with talkover switch. Headphone monitor, Pan Pot L & R Mac I I ister Output controls. Output 775mV. Si,

,iof -lr- jot360 x280 x 90mm ix

Price E134.99+(3.00 P&P

A;)!Atil

I 1 I

B. K. ELECTRONICSUNIT 5, COMET WAY, SOUTHEND-ON-SEA,

ESSEX. SS2 6TR TEL: 0702-527572

SALES0702 - 554161

A self-contained alarm system disguised as a video cassette.

Gives audible alarm if machine moved or cassette ejected.

Full details in Project Book 24 (XA24B) Price 85p.

C HECK THOSE UNMARKEDcapacitors with this versatile, low-cost,

piece of test equipment.

Full details in Project Book 23 (XA23A) Price 85p.

K T ICE-

/-4

OWER

BREAKTHROUGH!

ORDER

CODE

LM28F

A superb 1 kW Mosfet amplifier, a major new source in sound!

Full details in Project Book 26 (XA26D) Price 85p.

This project is made up from 4 kits.

KIT PRICEDRIVER OUTPUT MONITOR PSU

KIT KIT KIT

£11.95 £99.95 £19.95 £89.95

P0

ROTECT YOUR VHS VIDEO PLAYER

WITH THIS VHS VIDEO ALARM PROJECT!

M OSFET AMPLIFIER

giving 150W of incredible

power! High reliability

and performance.

Full details

in Best of E B MM

XH61R) Price £1 .00.

KIT PRICE

N UCLEAR RADIATION

MONITOR -1

ORDER

CODE

LW51F

capable of measuring

the level of Alpha and

Beta particles, and Gamma

and X -Rays. Full details

in Project Book 24

(XA24B)

Price 85p.

KIT PRICE

All items subject to availability

DER

DE

24B

M USICAL DOORBELL

with 28 tunes

and chimes

with selectable

piano to organ

like sounds.

Note: case and

front panel not

in kit. For full

details see

Project Book 13

(XA13P) Price 85p.

All prices

include VAT.

Please add

50p towards

postage.

4m.iwJJJJJA.....,,JJJJ

KIT PRICEORDER

CODE

LK57M

aph Electronics

P.O. Box 3, Rayleigh, Essex, SS6 8LR.

MANY

MORE

PROJECTS

INSIDE!

Pick up a

copy ot our

giant 512 page

catalogue from

WH SMITHfor just £1.60.

Shops at: 0 Sutton New Road, Erdington, Birmingham. 302

Gloucester Road, Bristol. 0159-161 King Street. Hammersmith,

London 0 8 Oxford Road, Manchester. 046-48 Bevois Valley

Road, Southampton. 0 282-284 London Road, Southend-on-Sea.

1\1

Documents

E1,11!)7.rRoracjULY1S988 - World Radio History...B0242 2 6in x 4in speakers, 4 ohm made from Radiomobile so very good quality. B0246 2 Tacho generators, generate one volt per 100 revs