Project Electronics For Everyone MODEL PROJECTS · 2021. 1. 24. · +r-ntc-F,1-"AlT1' =1;.' AMBIT INTERNATIONAL'S Prices shown EXCLUDE VAT. Access/Barclaycard may be used with written

SEPTEMBER 1982ISSN 0142-6192

70p

Project Electronics For Everyone

MODEL PROJECTSThree -Aspect Lights Controller

PLUS...RADIO RULES MONITORBREADBOARDS MICROTRAINING

NICADS: UK's LOWEST PRICESAMBIT'S NEW CONCISE COMPONENT CATALOGUE IS OUT NOW -

tlae at yonewsagent orAmbit's new style catalogue continues to lead the market withlow prices, new items, info, 3 £1 discount vouchers. In a recentsupplier survey, we were one of only two suppliers listed in allcategories!There's a few examples of some super low prices78XX 1A 37p

BC237/8/9 8p3SK51 54p

10MHz XTALS£2

8 Pole 10.7MHz XTALfilters £14.50

2GHz coax relay150W £10.95

All the "usual" stuff at rockbottom prices + Toko coils,crystal and ceramic filters,micrometals toroids, Fairiteferrites, Alps switches, OKILSI, Piezo sounders, RF, IFModules + Kits etc.

CMOS4000 0.11

4031 0.11

4002 0.12

4007 0.134008 0.504008AE 0.8040)9 0.254010 0.3040114E 0.244011 0.114013 0.25

4015 0.504016 0.224017 0.004019 0.384020 0.554021 0.554022 0.554023 0.154024 0.334025 0 154026 1054027 0.26

0.500.550 350.670.50

4042 0.504043 0.5000434E 0.934044 0.604046 0.604047 0.684049 0.244050 0.244051 0.554052 0.554053 0.554054 1304055 1304056 1304059 5 754060 0.754063 1 15

4066 0 304067 4304068 0.16

40694E 0.104070 0 164071 0.16

4028402940304035

4072407340754076407740784081408240934099417545024503450645074508451045114512

0.160 160 160.550 180 180.120.180.300.800.800.600.500.700.371.500550.450.55

451445154516451845204521452245274528452945314532453445364538453945434549455345544555455645574558455945604561456245664568456945724580458145824583458445854702470347044705470647204723472447254031440085403984010640160401614016240163401744017540192401934019440195

1.251.250.600.350.601.300.890000.850.700.650804.002.500.850.800.803.502.701.200.350.402300.803.502.501.002.501.201 451.700.223.251.400.700B00.270.454 504484 244 244.504.000950952.240.540 990540.691.051.051.05

1.051.051.051.081.081.081.08

TTL N74013N C 107401N 0.107402N 0207403N 0 117404N 0 127405N 0 12

740614 0227407N 0.227408N 0 157409N 0 157410N 0 127411N 0 18741214 0.197413N 0 277414N 0 517416N 0 277417N 0 277420N 0 137421N 0287423N 0.227425N 0 227426N 0227427N 0 227430N 0 137432N 0 237437N 0227438N 0227440N 0 147441N 0547442N 0 427443N 0 627444N 0627445N 0627446N 0627447N 0.627448N 0567450 0 147451N 0 14745314 0 147454N 0 147460N 0 147470N 0.287472N 0 277473N 0 287474N 0 287475N 0.357476N 0 30748014 0 267481N 0.207482N 0.757485N 0 757486N 0 247489N 1057490N 0307491N 0557492N 0 357493N 0 357494N 0 707495N 0607496N 0 457497N 1 4074100 1 1074104 0 6274105 06274107 0 2674109N 0 3574110N 05474111N 06874112N 1 7074116N 1 9874118N 0 8574119N 1 2074120N 0 9574121N 03474122N 03474123N 040

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Prices shown EXCLUDE VAT.Access/Barclaycard may be usedwith written or telephone orders,official MA details on application.E & EO.POSTAGE and PACKING

50p per order74125N 040 74153N 0 55 74170N 1 2574126N 040 74154N 0.55 74173N

1 1074128N 0 65 74155N 0.55 74174N 0.7574132N 050 74156N 055 7017514 0 7574136N 0 65 74157N 0.55 74176N 0 7574141N 0 45 74159N 190 74177N 0 7574142N 1 85 74160N 0.55 74178N 09074143N 250 74161N 0.55 74179N 1 3574144N 250 74162N 0.55 74180N 0 7574145N 0 75 74163N 0.55 74181N 1 2274147N 150 74164N 0.55 74182N 0 7074148N 109 74165N 0.55 '74184N 1 2074150N 0 79 74166N 0 70 74185N 1 2074151N 0_55 74167N

1 25 74188N 300

74190N74191N74192N741931474194N74195N74196N74197N74198N74199N74221N74246N74247N74248N74249N74251N74265N742731474278N74279N74283N74284N74285N74290N74293N74297N74298N74365N74366N74367N74368N74390N74393N74490N

I direct, for 70p inc.

0 550 550 550550550 550 550550 85

1 601 631 501 51

1 890 111 050662 672 490 89I 303 503 501 001 052 361 85

74LSN74LSOON74LSOIN74LS02N74LS03N74LSO4N74LS05N74LS08N74LS09N74LS ION74LS11N74LS12N74LS13N74LS14N74LS15N74LS20N74L 521N74LS22N74LS26N74LS27N74LS28N74LS30N74LS32N74LS33N74LS37N74LS38N741_540N74LS42N74LS47N74LS48N74L 549N74LS51N74LS54N74LS55N74LS73N

0.85

0.850851 851.85I 85

0.100.100.110.110.140.130.120.120.120.120.120.200 300120.120.120.120.140.120.150.120.120.150.150140 130.300.350.450.55,0.130.140.100.21

CAPACITY TYPE 1-9 10-49500 mAh AA 80 742200 mAh C 2.35 1.991200 mAh D 2.14 2.064000 mAh D 3.05 2.85110 mAh PP3 3.70 3.50,)

74LS74N74LS75N74LS76N74LS78N74L SEt3N74LS85N74LS86N74LS90N74LS91N74LS92N

0.160.220.200.190.400 600.140320.280.31

74LS93N 0.3174LS95N 04074LS96N 1 2074LS107N 0 2574LS109N 0.2074LS112N 0.2074SL113N 0.2074L11122 14NN 0.19

74LS123N 0.3574LS124N 1.8074L S 125N 0.2474LS126N 0.2474LS132N 0.4274LS133N 0.2474LS136N 0.2074LS138N 0.3074LS 139N 03074LS145N 1 2074L S151 N 0.3077:LLsS115453NN 00..0207

74LS155N 0.3574LS156N 0.3774LS157N 0.3074LS158N 0.30777444LLLsSs17606:3NNN

00.

0.700000

74LS169N 0.857744LLsSi1770N 0.90

0.8074LS174N 0.4074LS175.0N 0.4010

74LS181N74LS183N 1 7574LS189N 1 2874LS190N 045

74LS197N 0.6074LS200N 3.4074LS202N 3 4574L S221N 0.5074LS240N 0.8074LS241N 0.8074LS242N 0.7074LS243N 0.7074LS244N 0.6074LS245N 0.8074LS247N 1 35

740874C1074C1474C2074C3074C3274C4274C4874C7374C74

74LS248N74LS249N74LS251N74LS253N74LS257N74LS258N74LS259N74LS260N74LS266N74LS273N74LS275N74LS279N74LS280N74LS283N74LS290N74LS293N74LS295N74LS298N74LS365N74L 5366N74LS367N74LS368N74LS373N74LS374N74LS375N74LS377N74LS378N740 S379N74LS384N74LS385N74LS386N74LS390N74LS393N74LS395N74LS396N7405398N74LS399N74LS445N74LS447N7405493N74L 5669N74LS669N74LS670N

RAM210221122114 240274116 24116 34864P6116P 36116P 48264

74CXX

1 351.350.350.350.400.370.600.500.220.703.200.352.500.420.500.401 500.760.320.340.320.350.700.700.400.850.650.602.502.050 290680 612 101 992 75230

409510

050570

1 703 401 495 78

1 591 49

12 509.00

11 2512 50

74C00 0.2074CO2 0.2074C04 0.20

0200 200 550.200200 200.801 030500.50

74C7674C8374C8574C8674C8974C9074C9374C9574C10774C15174C15474C15774C16074C16174C16274C16374C16474C16574C17374C17474C17574C19274C19374C19574C20074C22174090174C90274C90374090474090574C90674C90774C90874C90974C91074C91474C91874C92574C92674C927

0480980980 262680800800 94048

1 522261 521 051 051 051 050800840 721 051.051.081.081 08

4521 060380380380385640380380 841 523620860 984 324 324 32

Processors8080 series9330AFC/2 67.308212 2.308214 3.508216 1.958224 3.508251 8.218255 5.40

Z80 seriesZ804 63.75

180AORT 7502804P10 3.50280ASIO, 1 11.00Z804510,2 11.00ZE0AS10/9 5.55Z80CTC 400ZHOACTC 45078001 65 00

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0SEPTEMBER 1982Vol 4 No 9

PROJECTS* HE 'JUNIOR' 9A low-cost method to improve a slot -car's performance.POPULAR COMPUTINGZX INTERFACE BOARD 14Eight bits of input and output for ZX computersMICROTRAINING 25First steps to using the HE Micro Trainer.* BREADBOARDS 34Designing and building tone controls.* MODEL RAIL SIGNAL LIGHTS 39Three -aspect signal project.

PROJECT:MUSICAUDIO ANALYSER 57Concluding our audio spectrum analyser project.

FEATURESINTO RADIORADIO RULES 20The classes of radio power.* FAMOUS NAMES 37Sir Edward Appleton.GADGETS, GAMES AND KITSTESTON AUTO -RANGE DVM 47Hands-off meter reviewed.* PLANNING ON SUCCESS 49Get your projects working - first time!

REGULARSMonitor 6Whats On Next 18Points of View 31Buylines 33Subscriptions 33Clever Dick 54Breadboard Exhibition 53HE Bookshelf 45Backnumbers 60PCB Printout 62PCB Service 64Classified Advertisements 65

Editor: Ron KeeleyEditorial Assistant: Paul Coster BScAdvertisement Manager: Gary PriceManaging Editor: Ron Harris BScManaging Director: T.J. Connell

Hobby Electronics is normally published on the second Friday of the month prior to the cover date.Hobby Electronics, 145 Charing Cross Road, London WC2H OEE, 01-437 1002. Telex No 8811896. Published by Argus Specialist Publications Ltd.

Design and Organisation by MM Design and Print Ltd, 145 Charing Cross Road, London WC2H OEE, 01-437 1002.Distributed by S. M. Distribution Ltd, 16/18 Trinity Gardens, London SW9 BDX.

Printed by QB Ltd, Colchester. Covers printed by Alabaster Passmore.Notice: The contents of this publication including all articles, designs, plans, drawings and programs and all copyright and other intellectual property rights therein

belong to Argus Specialist Publications Limited. All rights conferred by the Law of Copyright and other intellectual property rights and by virtue of internationalcopyright conventions are specifically reserved to Argus Specialist Publications Limited and any reproduction requires the prior written consent of the Company. Allresonable care is taken in the preparation of the magazine to ensure accuracy, but Argus Specialist Pulications Ltd cannot be held responsible legally. ©Copyright

1982 Argus Specialist Publications Ltd. Member of Audit Bureau of Circulation.

Hobby Electronics, September 1982 3

HEATH

ShortwaveListener's

Receiver

With Heathkit, you're all set for agreat deal. And not just big savings.

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Locator

Windspeed and DirectionIndicator

To Heath Electronics(UK) Limited, Dept (HE9)Bristol Road, Gloucester GL2 6EE.

HE9To start me off, please send me

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Name

Address m.0

rE,0-11 Youbuildonour e

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5T31 NUT DRIVER SET5 precision nut drivers in hinged plastic case.With turning rod. £1.75Sizes: - 3. 3.5, 4, 4.5 and 5mm

5T41 TOOL SET5 precision instruments in hinged plastic case.Crosspoint (Phillips) screwdrivers: -H 0 and H 1 Hex key wrenches: -1.5, 2 and 2 5mm 51.75

5151 WRENCH SET5 precision wrenches in hinged plastic case.Sizes: - 4. 4.5. 5, 5.5 and 6mm. £1.76

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5 watt IRMS) Audio AmpHigh Quality audio amplifier Module. Ideal for use inrecord players, tape recorders, stereo amps andcassette players, etc full data and hack up diagramswith each module

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MW398 NI -CAD CHARGERUniversal NI -Cad battery charger. All plasticcase with lift up lid. Charge/Test switch-. LEDindicators at each of the five charging points.Charges: - Power: -PP3 (9V) 220-2400 ACU12 (1.5V penlite) Dims, -U11 (1.5V"C") 210 x 100 x 50mmU2 (1.5V "D") £6.05

POWER SUPPLY OUR PRICE £3.25Power supply fits directly into 13 amp socket.Fused for safety. Polarity reversing socket.Voltage switch. Lead with multi plug.Input: - 240V AC. 50HZ Output: -3. 4.5.6.7.5, 9 & 12V DC Rating: - 300 ma MW88

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4 Hobby Electronics, September 1982

HE PROJECT KITS I.C.s TOOLS CASES

TRANSISTORS RESISTORS KITSCAPACITORS HARDWARE MAGENTA

Make us your No. 1 SUPPLIER OF KITS and COMPONENTS for H.E. Projects. Wesupply carefully selected sets of parts to enable you to contruct H.E. projects. Kitsinclude ALL the electronics and hardware needed. Printed circuit boards (fully etched,drilled and roller tinned) or Veroboard are, of course, included as specified in the originalarticle, we even include nuts, screws and I.C. sockets. PRICES INCLUDE CASES unlessotherwise stated. BATTERIES ARE NOT INCLUDED. COMPONENT SHEETINCLUDED. If you do not have the issue of H.E. which includes the project - you willneed to order the instruction reprint at an extra 45p each.

Reprints available separately 45p each + p

TVA FILTER Jly 82 f4.98SUNBURN TIMER - TANOVER Jly82 £8.99

AUTO WAH June 82 £17.89 inc case or£11.48 less case.AUTO GREENHOUSE SPRINKLERJune 82 £14.38 less pump and powersupply 112V 2A1.TELEPHONE TIMER June 82 £31.24less power supply (suitable typebelow).POWER SUPPLY DESIGN 12V 500mAJune 82 £9.79.ECHO REVERB UNIT May 82. Less caseE31.82. Economy case WB3 E3.76 extraDIGITAL THERMOMETER May 82 ex-cluding case + bezel £15.80LIGHT SEEKER May 82 £4.99AUDIO SIGNAL GENERATOR May 82£19.69CABLE TRACKER May 82 £9.37DIGITAL CAPACITANCE METER Apr 82£19.98SIGNAL TRACER Apr 82 £3.61BIKE ALARM Apr 82 £10.98DIGITAL DICE Mar 82 E6.82BICYCLE SIREN Mar 82 £10.18NOISELESS FUZZBOX Feb 82 £9.77SOUND SWITCH Feb 62 £8.31MASTHEAD AAMPLIFIER Feb 82 £13.74DRUM SYNTHESIZER Dec 81. Full kit£19.98GUITAR HEADPHONE AMPLIFIERDec 81 £3.48IN CAR CASSETTE POWER SUPPLYDec 81 £4.46SCRATCH FILTER Nov 81 Mono £5.44Stereo E8.40LED VU METER Nov 81 less case £4.56SIMPLE STYLUS ORGAN Nov 81 lesscase £4.74METRONOME Nov 81 £11.88TELEPHONE BELL REPEATER Oct 81£12.78Med Linking wire extra 14p metreCOMBINATION LOCK Oct 81 lesssolenoid £17.43BABY ALARM Oct 81 £8.14, Fig 8 linkingwire 7p metre'DIANA' METAL LOCATOR Sept 81£32.25POWERPACK Sept 81 £9.58

. B p. 40p.REACTION TESTER GAME Sept 81£11.98VARIABLE BENCH POWER SUPPLYAug 81 E25.35ULTRASOUND BURGLAR ALARMJuly 81 £18.67ELECTRONIC DOOR BUZZER July 81£5.65ELECTRONIC METRONOME July 81£4.67CONTINUITY CHECKER June 81 £5.34ENVELOPE GENERATOR June£16.85AUDIO MIXER June 81 E4.99PUBLIC ADRESS AMPLIFIER March81 £1821, Extras - horn speakers £6.83each, PA MIC £4.40FUZZBOX March 81 £10.35WINDSCREEN WIPER CONTROLLERMarch 81 £7.67STEAM LOCO WHISTLE March 81

£12.26PHOTOGRAPHIC TIMER March 81

£3.28HEARTBEAT MONITOR Feb 81 £23.40TWO-TONE TRAIN HORN Feb 81 £5.24less caseMEDIUM WAVE RADIO Feb 81 £7.67BENCH AMP Jan 81 £10.10NICARD CHARGER Jan 81 £7.67CHUFFER Jan 81, less case 17.04BATTERY CHARGE MONITOR Dec 80£5.40MEMORY BANK - MINI SYNTH-ESISER Nov & Dec 80 £28.40TRANSISTOR TESTER Nov 81 £6.12 inctest leadsGUITAR PRE -AMP Nos 80 £5.65 caseIdiecastl extra E2.29INTRUDER ALARM Oct 80 £19.61TOUCH SWITCH Sept 80 £2.57 less case& contactsGUITAR PHASER Sept 80 £15.22SOUND OPERATED FLASH TRIGGERJuly 80 no skt £4.99FOG HORN June 80 £6.21SPEED CONTROLLER FOR RIC April 80£16.41 (less case)DIGITAL FREQUENCY METER april 80£39.35DIGI-DICE Jan 80 £10.97GUITAR TUNER Nov 79 £11.99CAR ALARM Feb 79 £12.07

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PLEASE QUOTE REF. NO. WHEN ORDERING61 PEST CONTROL 'Ultrasonic catscam.' E6.98B2 COMPONENT TESTER £8.38B3 ENLARGER TIMER - relay output£26.99B4 GUITAR NOTE EXPANDER £16.87B5 CAMERA OR FLASH GUNTRIGGER Infra red system £11.98B6 SIMPLE INFRA RED REMOTECONTROL £16.39B7 0-12V POWER SUPPLY £16.99B8 SOIL MOISTURE MONITOR £4.23B9 SOUND TO LIGHT - singlechannel £7.97610 THREE CHANNEL SOUND TOLIGHT £19.98

811 IN SITU TRANSISTOR TESTER£6.73612 WEIRD SOUND EFFECTSGENERATOR £5.68B13 AUDIBLE VISUAL METRO-NOME £5.98B14 ELECTRONIC DICE £5.7181521( RAM PACK Less case for ZX81£13.34B16 MINI EGG TIMER £4.14817 AUDIO EFFECTS UNIT FORWEIRD SOUNDS £12.71818 LED JEWELLERY - Cross brooch£2.77 Star brooch £9.71 Spiral brooch£7.50

MORE KITS ANDCOMPONENTSIN OUR LISTS

FREE PRICE LISTPrice list included with

orders or send sae 19 x 41CONTAINS LOTS MORE

KITS, PCBs EtCOMPONENTS

1982 ELECTRONICSCATALOGUE

Illustrations, product descriptions, circuits all in-cluded. Up-to-date price list enclosed. All productsare stock lines for fast delivery.Sends 80p in stamps or add 80p to order.

MORE H.E. PLUS E.E. and E.T.I. PROJECT.KITS IN THE PRICE LIST

MAGENTA gives you FAST DELIVERY OF QUALITY COMPONENTS & KITS.All products are stock I ines.and are new & ful I specification. We give personal servicequality products to all our customers -HAVE YOU TRIED US?

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DE14 2ST. 0283 65435. MON-FRI 9-5. MAIL ORDER ONLYADD 45p P&P TO ALL ORDERS PRICES INC VAT

ACCESS and BARCLAYCARD (VISA) Prices inc. VATORDERS ACCEPTED BY PHONE OR OFFICIAL ORDERS WELCOMEPOST. OVERSEAS. Payment must be in sterling.SAE ALL ENQUIRIES. IRISH REPUBLIC and BFPO: UK PRICES.

EUROPE: UK PRICES plus 10%.ELSEWHERE: write for quote.

SOLDERINGANTEX X5 SOLDERING IRON

SOLDERING IRON STANDSPARE BITS. Small standard,65p each. For X5 + )C25SOLDER. Handy sizeSOLDER CARTONDESOLDER BRAIDHEAT SINK TWEEZERSDESOLDER PUMPHOW TO SOLDER LEAFLETLOW COST CUTTERSLOW COST LONG NOSE PLIERS

WIRE STRIPPERS Et CUTTERS..

HELPING HANDSHeavy base. Six ball and socketjoints allow infinite variation ofthrough 360°. Has VA" diameter125x I magnifier attached, usedrecommended by our staff.VERO SPOT FACE CUTTER ..PIN INSERTION TOOLVEROPINS (pk of 10010.1"MULTIMETER TYPE 111,000 opyl

MULTIMETER TYPE 2120,000with transistor tester. Very good

£14.75.CROCODILE CLIP TEST LEAD10 leads with 20 clips

25W£5.48£2.40

large,

£1.84

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and

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SET.99p

I TOOLS

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RESISTOR COLOURCALCULATORCONNECTING WIREED. 11 coloursILLUMINATED MAGNIFIERS

Small 2" dia. (5 xLarge 3" dia. 14 x

CAST IRON VICESCREWDRIVER SETPOCKET TOOL SETDENTISTS INSPECTION

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mag.l .... E1.14magi £2.40

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MIRROR£2.85£1.5069p

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SPEAKERS. Miniature, 8 ohm 87p MIN. BUZZERS. 6V. 50p. 9V. £1 10.64-75 ohm 89p 12V. 65',.CRYSTAL EARPIECE 65p MAGENTIC EARPIECE 15PMONO HEADPHONES £2 96 STEREO HEADPHONES £4 35TELEPHONE PICK-UP COIL 72p F.M. AERIAL 49p

VEROBOARD 0.1" COPPER STRIPS10 strips 24 holes £1.20 per 524 strips 37 holes 78p24 strips 50 holes 89P36 strips 37 holes 89P36 strips 50 holes 990Terminal pins 0.1- . 52p'100

PP3 CLIPS 10pPP9 CLIPS tip PANEL METERS

EUROBREADBOARD ..... , E6 20S DEC BREADBOARD £3.98BIMBOARD 1 BREADBOARD £11.98

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50t1A; 100uA; IrnA,1A, 25V. 100uA-0-100uA; 5A. AUE4.98 each. Statevalue.

IVIULTIMETER TYPE 2 -£14.75

BOOKSSEMICONDUCTOR DATA BOOK Newnes

E5. 90ELECTRONIC PROJECTS FOR HOMESECURITY r3'35ELECT. PROJECTS IN PHOTOGRAPHY

E3.35110 ELECT. ALARM PROJECTS £5.35MODEL RAILWAY PROJECTS £1.95BASIC ELECTRONICS. Theory & practice

E7.98BEGINNERS GUIDE TO BUILDING ELECT.PROJECTS EI.50

ADVENTURES WITH ELECTRONICS

5

e yteer .2A06 0 0+0 gpcv .

volts.Includes transistor ,1s

useful resistance ranges.We've used it and we like it.

ADVENTURES WITHMICROELECTRONICS

Similar to 'Electronics' below.Uses I.C.s. Includes dice, elec-tronic organ, doorbell, reactiontimer, radio, etc. Based on Bim-board 1 bread board.Adventures withMicroelectronics £2.55

Component pack £29.64 lessbattery.

by TornDuncan

An easy to follow book suitable for all ages. Ideal for beginners.No soldering, uses an S -Dec breadboard. Gives clear instructionswith lots of pictures. 16 projects -including three radios, siren,metronome, organ, intercom, timer, etc. Helps you learn aboutelectronic components and how circuits work. Component packincludes an S -Dec breadboard and all the components for theprojects.Adventures with Electronics £2 40. Component pack £1798 lessbattery.

ADVENTURES WITH DIGITAL ELECTRONICS

New book by Tom Duncan in the popular 'Adventures' series. This book ofentertaining and instructive projects is designed for hobbyists, and students. It

provides a stepping stone to the microprocessor.The first part deals with the properties of some basic ICs used in digital

electronics.The second part gives details of how to build eight devices - shooting gallery, 2way traffic lights, electronic adder, computer space invaders game etc.For each project there is an explanation of 'how it works' and also suggestions for'things to try'.No soldering - all circuits built on 2 Bimboard 1 breadboards.Adventures with Digital Electronics book £3.25. Component pack £42.50 refETDC. All the components needed including 2 breadboards and hexadecimalkeyboard. Available less breadboards £29.98 ref ETDF. Both less battery.

4,


MONITORHave A Good TimeThe cost of Casio's latest quartz digitalwatch works out at less than 1/2 p perday, based on a retail price of £5.95 anda five year life from the lithium battery!The timing facilities of the F10 includecontinuous hour, minute, second anddate display, together with indicators foram/pm and day of the week. The calen-dar is automatic, but needs adjustmentfor leap years. The standard F 1 0 has ablack resin case and strap though if youfancy something with a little more class,the B81 5, priced at £9.95, is identicalexcept for the traditional stainless steelcase and bracelet.

For something a little different,Casio have come up with the MM400watch. It has a normal daily alarm,another which can be set up to a weekahead, and a third with a monthly cycle;each alarm has a different melody! TheLCD readout shows hour, minute, se-cond, date and day, plus indicatorsshowing which alarms are set. It alsofeatures a stopwatch function accurateto 1/1000th of a second. The MM400has a stainless steel bracelet and case,and a recommended retail price of£34.95 at any High Street Casiostockist.

Would'n You Like One?A new range of stabilised power supplies(right), specially designed for the UKmarket, are being released byTelecomms, the exclusive distributors ofSHF Electronic products.

The range will be of particular in-terest to both CB and electronics en-thusiast. There are five models, from a2A unit for standard 40 -channel CB rigsup to a 12A heavy duty supply. Theprices are very attractive, ranging from£11.90 to £49.95, retail. The cases aremade from a toughened nonconductivematerial and have been designed to besafer and more pleasing to the eye thanconventional metal -cased units. Nicepicture, too!

SHF Electronic supplies aredistributed by Telecomms, 189 LondonRoad, North End, Portsmouth; Tel.0705 660036.

PCB JigNo, it's not a new dance, simply two ad-ditions to the Carlton Nichol range ofPCB holders/assembly-jigs.

The CNC 16 (above) will hold anyboard of up to 420 x 205 mm. The PCBis clamped between two easily ad-justable rails and this also gives it theuseful facility for holding a number ofsmaller boards, rather than one largeone. A clip -on foam pad is also available,enabling components to be inserted inthe board before soldering.

The CNC 10 holder is designed totake boards up to 203 x 203 mm, heldbetween two rails and locked in positionby means of a single, central clamp.When in position, the PCB may berotated through 360° and locked at anyangle. The holder can be folded flat, forstorage, simply by loosening one bolt.

These products are available direct-ly from the manufacturer, Carlton Nicholand Co. Ltd., Goldkey Industrial Estate,Kelveden, Essex. The CNC 16 is pricedat £21.75 and the foam pad is £6.90;the CNC 10 costs £16.10 and an op-tional pad is £5.63. These prices includ-ed VAT, but £1.50 should be added tocover postage.

Displays On ShowA new range of high quality, reliable, lowcost displays (below) from Liton have justbeen launched by Stotron Ltd. Theyfeature high brightness, low power drainand wide angle visibility, and are com-patible with ASCII and EBCDIC codes.

The ten -step bar graph is available ineither red or green with a bar point size of1.5 x 5 mm. The clock display has a redcolour filter for better contrast.

Further details are available from


MONITORStotron Ltd, 72 Blackheath Road,Greenwich, London SE10 8DA, or'phone 01 691 2031.

Call For The DoctorThis one is for serious computer buffs.Normally, faults in memory chips arevery difficult to locate as the usualmethods, using a 'scope or logic probe,are not well suited to the job. TheMicrodoctor, an intelligent device fromDataman Designs, is designedspecifically for the purpose.

It is an intelligent device for faultfinding on computers or microprocessorbased equipment generally, with thecapability of performing a series of pro-grammed tests on the memory chips ofany computer to which it is attached andprinting out the results. In addition,unknown systems can be memory -mapped, with the contents printed out inHEX or in ASCII; any device in thememory or I/O space can be read from orwitten to.

The Microdoctor is Z80 based and issupplied with a free Z80 disassembler,allowing it to produce a listing in HEX orASCII of the contents of any ROM in aZ80 system. As it stands, the Microdoc-tor is applicable to microprocessorsystems, and disassemblers for otherpopular MPUs will soon be available atlow cost.

The Microdoctor costs £339.25,including VAT and carriage, fromDataman Designs, Lombard House, Cor-nwall Road, Dorchester, Dorset DT11 RX. Tel. 0305 68066.

Logic Logged HereFault-finding on digital circuitry is notone of the easier tasks in electronics, andany assistance is generally verywelcome. Enter Global Specialiaties,with a new 1 6 -pin logic monitor.

The IM -2A (above) is specificallydesigned to monitor dual -in -line packag-ed integrated logic circuits. It has a built-in LED display which gives rapid,simultaneous readout of the static anddynamic states of eight, 14 and 16 -pinICs. Connection to the circuit under testis via a 610 mm long cable and a 16 -pin'Proto Clip' test probe. Using the LMA-9optional cable, up to 16 independentpoints can also be monitored.

The front panel mode switch selectseither TTL, CMOS or variable thresholdlogic levels; the thumb -wheel controlselects threshold from + 1V to + 9V,allowing the LM -2A to monitor practical-ly all non-standard logic levels, and the

external voltage sense line used in theCMOS mode ensures that the 70%threshold for CMOS is accurately met.All inputs are IMO impedance and pro-tected to ± 26V.

The LM -2A measures 30 x 81 x150 mm and weighs in at 0.3 kg. Thecase is high -impact plastic, and the unitis supplied complete with the 16 -waycable terminated in the IC test clip.

The suppliers are Global SpecialitiesCorporation. Shire Hill Industrial Estate,Saffron Walden, Essex CB11 3AQ; tel0799 21682 for further information.

Catalogue NewsFinding sources of electronic com-ponents and hardware is one of the elec-tronics hobbyist's greatest problems. Ofcourse, our super Electronic SuppliesDirectory which will appear in the Oc-tober issue, will help, but beyond that, agood catalogue collection is essential.

A new 28 page release, fromspecialist suppliers Roadrunner Elec-tronic Products, features a wide range ofcircuit board and enclosure accessories.The Roadrunner 'solder -wrap' wiringsystem is highlighted, together withtheir extensive range of prototypingboards, connectors and electronic pro-duction accessories.

For further information, contactRoadrunner Electronic Products Ltd.,116 Blackdown Rural Industries, HasteHill, Haselmere, Surrey GU27 3AY. Tel.0428 53850.

Another recent arrival was the latestcatalogue from Rapid Electronics, whohave considerably extended their pro-duct range. New additions include awider range of linear devices, with datasheets, more capacitors, PCBtransformers and tools. The total stockline now covers over 2000 items atprices that are "the most competitive inthe industry", backed by a return postservice.

Copies of the catalogue areavailable free with orders over £10 or bysending 45p to Rapid Electronics, HillFarm Industrial Estate, Boxted, Col-chester, Essex C04 5RD. Tel. 020636412.

Calculator With A DifferenceThe Hioki 3208, from Dorman SmithInstrumentation, combines the func-tions of a powerful scientific calculatorand a digital multimeter in one compactunit.

The me V ranges cover AC and DCvoltage, ohms, low -power ohms for in -circuit testing, and it has current measur-ing capability up to 200 mA in tworanges. A single key converts the meterreading into scientific notation, for ins-tant calculations.

The unit is supplied complete withtester probes, and a battery, giving 100hours of continuous operation. It isavailable by mail order for £72.50,direct from Dorman Smith Instrumenta-tion, Blackpool Road, Preston PR2 2DQ.Tel. 0772 728271.

Hobby Electronics, September 1982

SPECIALIST

MarshallOF

ELECTRONIC

Bradley

EDGWARE

Tel:COMPONENT

723-4242

ROADLtd

DISTRIBUTORS

PROBABLY THE SPECIAL BAHCO TOOLSLARGEST STOCK OFFER SIDE CUTTERSOF ICs a, 2132 £7 10TRANSISTORS STEINAL 2112 £11' 40IN THE SOUTHTRY US FIRST

MULTICHECKL7.50 END CUTTERS

2211 £10 43LARGE RANGE OF + VAT

ACCESSORIESPlugsSockets

Normal price £1026 PLIERS2411 E6 -752415 £6 78BUY WITH

Audio Connectors ACCESSVeroboards BARCLAYCARD

ICE MULTIMETERSMicrotest 80 £16. 60IC Sockets

Soldering equipmentScrew drivers

A/EXPRESSDINERS

Supertest 680 R £32. 00Su pertest 680E £2450

(BAHCO) Just phone we do theSifam Knobs rest EXPERIMENTERetc. BREADBOARD'S

MAIL EXP 325 EXP 600LARGE RANGE OF EXPICs

ORDER EXP 350 650

Transistors FASTER EXP 300 EXP 4B

Capacitors SERVICE LOGIC PROBESDiodes PHONE LP1 £31 00Triacs 723-4242 LP2 £1800ThyristorsOptoResistorsPotentiometers

16, 24, 40 WAYRIBBON CABLE

EXPERIMENTERKITS

FusesBridges

£1.10; £1.40; £2.20metre

PB6 £9 20PB100 £11 80

Please send S.A.E. for Header plugs 14 way, PLEASE REMEMBERlist. 16 way, 24 way, 40 way ! To ADD 15% VAT

BRADLEY MARSHALL LTD FOR

CrimsonElektrikPROFESSIONAL AMPLIFIER MODULES

PRICE LIST --ELECTRONIC MODULES Et ASSEMBLIES - APRIL 1981

CODE DESCRIPTION Less VAT INC WTVAT VAT (Kg)

£ £ £CE 608 Power Amplifier Module 18.26 2.74 21.00 0.16CE 1004 Power Amplifier Module 21.30 3.20 24.50 0.20CE 1008 Power Amplifier Module 23.90 3.60 27.50 0.21CE 1704 Power Amplifier Module 30.43 4.57 35.00 0.22CE 1708 Power Amplifier Module 30.43 4.57 35.00 0.22CE 3004 Power Amplifier Module 42.60 6.40 49.00 0.40BD 1 Bridge Driver Module 7.13 1.07 8.20 0.06TR 80 Toroidal Transformer 80VA 18.00 2.70 20.70 2.00TR 150 Toroidal Transformer 150VA 20.07 3.01 23.08 2.35TR 250 Toroidal TRansforiner 250VA 25.43 3.81 29.24 3.35TR 2500 Toroidal Tansformer (low noise) 33.20 4.98 38.18 2.80B 6 Bridge Rectifier (6 amp) 0.99 0.15 1.14 0.02B12 Bridge Rectifier 112 amp) 1.80 0.27 2.07 0.03C4700/40 Reservoir Capacitor and Clip 1.91 0.29 2.20 0.09C4700/63 REservoir Capacitor and Clip 2.40 0.36 2.76 0.11C4300/63 Reservoir Capacitor and Clip 2.60 0.39 2.99 0.11CPS 80 Power Supply 22.82 3.42 26.24 2.10CPS 80D Dual Power Supply 27.63 4.14 31.77 2.25CPS 150 Power Supply 25.86 3.88 29.74 2.50CPS 150D Dual Power Supply 31.65 4.75 36.40 2.60CPS 250 ' Power Supply 32.03 4.80 36.83 3.50CPS 250D Dual Power Supply 39.43 5.91 45.34 3.65TS 70 Thermal Switch 70°C 1.92 0.29 2.21 0.02HS 50 50mm Heatsink 1.60 0.24 1.84 0.15HS 100 100mm Heatsink 2.60 0.39 2.99 0.30HS 150 150mm Heatsink 3.65 0.55 4.20 0.45FM 1 Fan Mounted on 2 x HS 100 32.13 4.82 36.95 1.20FM 2 Fan Mounted on 2 x HS 150 36.10 5.42 41.52 1.50CPR lx Pre -Amplifier Module 31.30 4.70 36.00 0.15MC 2 Moving Coil Pre -Pre -Amplifier Module 20.00 3.00 23.00 0.07REG 1 Regulated Power Supply 8.09 1.21 9.30 0.07TR 6 6VA Mains Transformer 2.87 0.43 3.30 0.21X0 2 2 Way Crossover Module 17.39 2.61 20.00 0.07X0 3 3 Way Crossover Module 26.09 3.91 30.00 0.07MU 1 Muting Circuit for X0 2 or X0 3 8.35 1.25 9.60 0.04CK 1010 Complete Pre -Amplifier Kit 78.26 11.74 90.00 2.50CK 1040 Complete 40 Watt Power Amplifier Kit 103.48 15.52 119.00 0.30CK 1100 Complete 100 Watt Power Amplifier Kit 129.56 19.44 149.00 7.30MC 2K Add On Moving Coil Kit 21.74 3.26 25.00 0.12PSK 1 Pre -Amplifier Power Supply Kit 17.39 2.61 20.00 0.75

' SOLE DISTRIBUTION BRADLEY MARSHALL LTD OF EDGWARE RD325 EDGWARE RD. LONDON W21 BN

TEL: 01-723 4242

TECHNICAL TRAININGIN ELECTRONICS,TELEVISION AND AUDIOIN YOUR OWN HOME- AT YOUR PACEICS can provide the technical knowledge that is so essentialto your success,knowledge that will enable you to take advant-age of the many opportunities open to the trained man. Youstudy in your own home, in your own time and at your ownpace and if you are studying for an examination ICS guaranteecoaching until you are successful.

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111Constructor Series Speakers

IT'SSO

EASYHave fun, savemoney, buildinga Kef designwith aWilmslow AudioCS Total kit.No electronic orwoodworkingknowledgenecessary andthe end result isa proven top-quality designthat you'll be proud of.Each kit contains all cabinet components, accurately machined for easyassembly, speaker drive units, crossovers, wadding, grille fabric,terminals, nuts, bolts, etc.The cabinets can be painted or stained or finished with iron -on veneer orself adhesive woodgrain vynil.Easy foolproof assembly instructions supplied. Set of constructor leafletssent free on receipt of large S.A.E.

Prices:CS1 (As 101) £110 pr. inc. VAT, plus carr./ins. £ 5.50CS1A(simplified LS3/5A) £103 pr. inc. VAT, plus carr./ins. £ 5.50CS3 (as 103.2) £129 pr. inc. VAT, plus carr./ins. £10.00CS5 (as Carlton II) £192 pr. inc. VAT, plus carr./ins. £15.00CS7 (as Cantata) £250 pr. inc. VAT, plus carr./ins. £18.00

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SK9

Mom


Project

HE Junior" Slot -Carontroller

Jonathan Scott

Put more zap in your slot -car's zip with our economy modelcontroller

IN their May issue, this year, ourcousins at Electronics TodayInternational presented a super,souped -up Slot Car Controller project,providing (amongst other things) fueltank simulation and controlledovershoot. In the course of developingthat project, fierce argument ragedaround the authors' household, somearguing for the 'no -holds -barred'approach - the method ultimatelyadopted by ETI - while others arguedfor 'cost effectiveness'.

If you are a dedicated slot carfanatic, with hundreds of poundsinvested in your layout, then you'veprobably already built the ETI SuperController. On the other hand, ifyou're not sure that you are a fanatic,or you have just bought a layout, say,then this cost-effective approach, theHE 'Junior', is the one for you. It isrelatively simple to construct, cheap,and easy to get going. It is basically areplacement for whatever you areusing to power your set now. It offersoperation from AC or DC, car battery,model train transformer, door -belltransformer or a range of typicalproject transformers or powersupplies. It gives independentprotected supplies for each lane,

adjustable for most car set typesavailable.

In addition, we're giving tips foroptimising your set and ideas forlayouts. These should be sufficient toturn a simple rig into a first-class slotcar racing set-up.

Theory And PracticeIn practice, the basic rheostat in serieswith the track (car) system is not at alla bad compromise. For a given controlsetting, the car accelerates fairlyrapidly towards a final speed. This isbecause torque is proportional tocurrent (in the permanent magnetmotors used) and current is atmaximum when the car is standingstill; as the engine RPM increase sodoes the back EMF, or rather theinternal EMF of the engine, whichrepresents the mechanical poweroutput in the mathematical model ofthe engine. As this rises, the voltagedrop across the control resistancedecreases, and so does the current,the torque and the acceleration(Figure 1). This gives a very car -likeperformance for a minimum of parts.The final speed is fixed by theminimum DC path resistance, theavailable supply voltage and the

amount of friction and other losses inthe car. Overall performance includescornering ability, which is affected bythe car weighting and wheel type andcondition. Attention to these factorswill effectively 'tune' the car.

If you think you have a two -car setwith one car better than the other, thechances are that checking the abovepoints will reveal a silly fault in one ofthem. You can end up, after sometinkering, with two improved cars. Letus go through a typical tuning -up of asmall car, such as those in thecheaper sets. We will start at the carand end up at the controller.

Firstly, the wheels. It is importantto check that these do not have somewobble or severe out -of -roundness.The tyres should be slightly rough, sothat they grip, and fairly flat at thepoint of contact with the track, sothat they do not bounce when thewheel rotates quickly. See that thetyre is fitted straight, if you haveremovable tyres, and that the wheelsare squarely mounted on the axles.

Next, it is worth opening the carup. Check that the axles and cogs arefree of dust and carpet fluff. A verysmall touch of light machine oil onbearings and cogs is a good idea,


Projectthough not absolutely necessary. Donot oil the tyres or any exposed bit ofthe car. See that the cogs mesh neatlyand fairly silently. On an expensivecar, these things should be in orderalready.

Now let's look at the brushes.These are, in our experience, the mostvulnerable point in the car. Brushfriction usually accounts for 90% ofcar performance problems. Thebrushes should be clean and dust free.There will be some unravelling of thebraid, this is good. The ends of thebrushes seem to benefit from a bit of'combing', done with a smalljeweller's screwdriver, a scriber orscalpel. About three to five millimetresof combed braid is nice. Finally, theshape of the brushes is important.There are several ways to bend thebrush, and you should experiment tosee which is better. We used thedown -and -then -straight pattern (SeeFigure 2).

Next, the minimum rheostatresistance is important. Somecontrollers have such high resistiveleads that the series resistance nevergets below an ohm or two. If youhave a protected voltage source this isa disadvantage.

Finally, the supply potential is vital.If it is too high, the control becomestoo critical and it is too hard to getjust the right amount of power. Itcannot be too low, of course, as youwould not get anywhere near enoughpower to realise maximum speedwithout crashing - which takes outall the skill. As well, if the supply isnot regulated, one car can interactwith the other; an extreme case iswhen one car suddenly 'shuttingdown' causes such a surge that theother spins off the track (it canhappen!).

One further factor is worthdiscussing, with respect to the car:weighting, and this is an area whereyou are going to have to experimentfor yourselves. Most cars have spacesinside the plastic shells where nuts orother pieces of metal can be securedwith a little Blutac, or similar adhesive,to add weight. Weight will reduce theacceleration for a given power, but itwill increase wheel adhesion on theroad. It will also change the handling,possibly making spinouts more likely,and reduce the period of time requiredbetween brush realignments. In ourexperience, a couple of 2BA or similarnuts in a small car, near the middleand low down, are quite beneficial ifyou have adequate power, as with ourcontroller.

The SupplyAs we have said, all that is necessaryto achieve quite adequate performanceis a voltage supply for each car. Itneeds to be the right voltage, and thecars should not interact with eachother via the supply. The HE 'Junior'is a simple supply that meets thesestandards. It is versatile in that it willoperate from whatever source ofvoltage you have available; it simplyneeds to deliver at least three volts

more than the cars need (average) andto be able to supply the maximumcurrent, typically 0A5 to 1 A per car.

If you think you have a two -car setwith one car better than the other, thechances are that checking the abovepoints will reveal a silly fault in one ofthem. You can end up, after sometinkering, with two improved cars. Letus go through a typical tuning -up of asmall car, such as those in thecheaper sets. We will start at the carand end up at the controller.

Firstly, the wheels. It is importantto check that these do not have somewobble or severe out -of -roundness.The tyres should be slightly rough, sothat they grip, and fairly flat at thepoint of contact with the track, sothat they do not bounce when thewheel rotates quickly. See that thetyre is fitted straight, if you haveremovable tyres, and that the wheelsare squarely mounted on the axles.

Next, it is worth opening the carup. Check that the axles and cogs arefree of dust and carpet fluff. A verysmall touch of light machine oil onbearings and cogs is a good idea,though not entirely necessary. Do notoil the tyres or any exposed bit of thecar. See that the cogs mesh neatlyand fairly silently. On an expensivecar, these things should be in orderalready.

Now let's look at the brushes.These are, in our experience, the mostvulnerable point in the car. Brush

accounts for 90% of

car performance problems. Thebrushes should be clean and dust free.There will be some unravelling of thebraid, but this is good. The ends ofthe brushes seem to benefit from a bitof 'combing', done with a smalljeweller's screwdriver, a scriber orscalpel. About three to five millimetresof combed braid is nice. Finally, theshape of the brushes is important.There are several ways to bend thebrush, and you should experiment tosee which is better. We used thedown -and -then -straight pattern (seeFigure 2).

Next, the minimum rheostatresistance is important. Somecontrollers have such high resistiveleads that the series resistance nevergets below an ohm or two. If youhave a protected voltage source this isa disadvantage.

The CircuitThe complete circuit is shown inFigure 3. It is basically a crude seriesvoltage regulator, based on the 723variable regulator IC, that suppliespower to the rheostat in the handcontroller. The rheostat is in serieswith the motor in the car, via the trackconnections. The voltage supplied tothe controller and car can be presetanywhere between about 3 V and 12V.

The circuit is designed to bepowered from a variety of sources -bell transformer, car battery,plugpack, model train transformer or

240 VAC to 15 V/1-2 A

I- SUPPLY -1 HAND CONTROL E----- 7(e.g. BATTERIES) I VARIABLE I ENGINE

RESISTOR) I

EMF

EMF IN THE ENGINE REPRESENTSTHE MECHANICAL OUTPUT.

Figure 1. A circuit model of a slot carset-up.

ACINPUT

SUPPLY SECTION

CAR CAR

DOWN AND COMBED DOWN AND STRAIGHT(PREFERRED METHOD)

CAR CAR

SPREAD OUT NOT COMBED(SMALL CONTACT AREA)

Figure 2. Various brush arrangements.

CONTROLLER SECTION

NEXTCONTROLLER

SECTION

01 D2

4 DJ

ZD

LE DI

oV

RI470R

3

RV11k

R2390R

R3820R

ICI10

EXISTING CONTROLS

(CONTROLLER -II -AAA"-,

R4OR47

RE2k7

CIIn R6

2k2

L

R7470R

LED2

OUTPUT(TRACK)+ --0 0

NOTES:01 IS MJ2955D1 -D4 ARE 1N4002ZD1 IS BZY61C7V5IC1 IS 723LED( IS TIL211LED2 IS TI L209

Figure 3. Circuit diagram of one controller; note that the components in theSupply Section are required for one board, only.


Project

TRACKPOSITIVE

TRACKNEGATIVE

Figure 4. Component overlaydiagram for a single controller,including the SupplySection components.

EXISTINGCONTROLLER

T

_J

0 0

0 0

it

T

AC FROMTRANSFORMER

LED1

transformer - whatever is available. Ifthe source is AC, such as that directfrom a transformer secondary, thediode bridge rectifier formed by Dl -D4rectifies this, supplying unfiltered DCto the circuit. These four diodes maybe deleted if the unit is run from a DCsupply, or they may be left in,provided the DC exceeds the voltagerequired by the car by about fourvolts. Leaving Dl -D4 in place has theadvantage that the device can be runoff AC at any time, and when runningit off a DC supply it can be connectedeither way round as polarity doesn'tmatter and no possible damage can becaused by accidental reverse polarityconnection.

To indicate that a supply ofsufficient voltage is connected to thecircuit, ZD1, RI and LED1 make asimple indicator. When the supplyvoltage between the +V and 0 V railsis high enough to overcome the zenervoltage plus the voltage drop acrossLED 1 and RI at a current of a fewmilliamps, LEDI will light. You need toproduce a minimum of approximately10 V between the + V and 0 V rails.Note that, while this is sufficient forthe IC regulator circuit to operate, itmay not be enough for some slot carsets. For those that require 12 VDC,at least 14 V between the + V and 0V rails will be required. An AC input ofup to 24 VAC (RMS) may be used.

Following the rectifier and indicatorsections of the circuit is the regulator,which consists of IC1, Q1 andassociated components. Each lane in

the slot car set should be suppliedwith a separate regulator circuit toensure that one lane does not interferewith the operation of the other,especially in the event of a shortcircuit due to a crash or a fault, etc.Two regulator sections may be runfrom a single rectifier section.

The 723, IC1, controls the basecurrent of Q1 to deliver the requiredvoltage to the hand controller, exceptwhen the external circuit (controllerand car motor, via the track) attemptsto draw current above about 1A2. Inthis case, the 723 reduces the voltagesupplied to the external circuit toprevent possible damage.

The output voltage is set by RV1.By adjusting this preset control, thevoltage delivered to the controller andexternal circuit may be variedanywhere between about 3 V and 12V maximum. This should be adjustedto suit the particular slot car set youare using by setting its position so asto deliver a suitable amount ofacceleration to the car when the handcontroller is set full on.

LED2 indicates that a voltage isreaching the track. This is useful tocheck correct operation and fordetecting shorts on the track.

ConstructionConstruction of the HE 'Junior' isrelatively straightforward. You willrequire one PCB for each lane, thoughsome components will not be requiredon any but the first board. Furtherlanes will simply demand a larger box

Parts ListRESISTORS

(All 1/2 watt 5% carbon, unlessnoted)

R1,7 470RR2 390RR3 820RR4 OR47

1 wattR5 2k7R6 2k2

POTENTIOMETERS

RV1 1kminiature vertical preset

CAPACITORS

C1 1ndisc ceramic

SEMICONDUCTORSD 1 -D4 1N4002

rectifier diodesZD1 BZX61C7V5

zener diodeLED1 TIL211

0.2" green LEDLED2 TIL209

0.2" red LEDIC1 LM12310 pin TO -100 regulator (see

Buylines)Q1 MJ2955silicon PNP power transistor

MISCELLANEOUSCase (see Buylines); PCB; terminalblock; nuts, bolts, wire, solder etc.

BUYLINES page 33

and a repeat of the wiring of the firstboard, less ZD1, R1 and LEDI. Thecomponent layout for a single -laneboard is shown in Figure 4.

The first step is to drill the box. Weused a cheap metal box, but if youwant it to look particularly good, or ifit will have to withstand nasty knocks,a diecast aluminium or extruded boxof sufficient size can be used,although it will add to the cost. Theadvantage of a metal box is that thefront panel doubles as a heat sink.

Drill the MJ2955 mounting holesand the LED mounting holes first. Theonly other hardware preparation is forthe PCB mounting screw holes andthose for the wires and the terminalblock.

After drilling, assemble the boards.The first should have all componentsfitted. It is best to include D1 to D4even if you have a DC supply, as theunit cannot, then, be connected thewrong way round, and can still beused with AC if required. The diodesshould only be omitted if the DCsupply is too low to tolerate thevoltage drop across them, ie below 12V, on average (omitting the diodes willallow it to run on around 10 V). It


Project

Figure 5. Rational constructs.

Figure 7. Zig-zags cancel out.

Figure 8. HE's Grand Prix track!

Figure 6. Rational right-angle constructs.

should also be noted that the supplywill have to be a bit higher if the carset is a 12 V type - around 15 V atleast.

Fit all the components as shown inthe overlay, starting with the resistorsand finishing with the IC. Take carewith the IC orientation. Once theboard is assembled, connect the off -board wiring as shown. The currentlimiting resistors, R1 and R7, aremounted behind the LEDs themselves.For the output leads to the tracks andthe controllers, we used an ordinaryplastic terminal block, as these arecheap. Once the assembly iscomplete, label the supply and trackLEDs, on the panel.

TestingThe HE 'Junior' is so simple that itdoes not require much setting up.After completing the assembly andwiring it up to your controllers and tothe tracks, you should be 'on theroad' immediately. The onlyadjustment that needs to be made isthe setting of RV1, which controls theoutput voltage as mentioned in thecircuit description. For safety, make atrial run with RV1 set for minimumvoltage, first!

The TrackWhen it comes to track, there arethree factors worth mentioning whichmay influence your choice if you haveyet to purchase it. These factors are:range of pieces available, flexibilityand width. If you are going to buy acheap set, and let's face it, that is the

most economical approach, you willhave to accept that the track comes infixed quantities; probably multiples ofwhat it takes to make up one loop or asmall figure -8. However, you can geta good selection of 45° curves andstraights, not to mention two cars andcontrollers, and fences, etc, for under£25 in some places. For this, plus oneof our controllers, you can get a reallygood set-up, and for a bit more youget a really fantastic set.

Laying OutIn designing a layout, the mainproblem is not to find a shape which isparticularly interesting, but one whichis fair, or equal, for both lanes, as wellas 'rational'.A layout is said to be rational if it fitstogether exactly. For this to happen,there must be no uncancelled irrationalconstructs. Even if you are luckyenough to have a range of bits, it isquite a challenge to sort out a fair andrational track.

First, let us define some terms. A'construct' is any group of tracksection. It does not necessarily meetup to form a closed loop, but isusually a familiar shape which canoften be found in layouts. A rationalconstruct is one which replaces asection of an oval track - either aright angle, a single straight section,or a combination of these.

To explain this, consider Figure 5.The right angle turn introduces a one -unit displacement along and one unitdown. The U -bend introduces a two -unit shift along and no shift down.

The S -bend introduces three along,and two down. These are all rationalconstructs in the system of track usedhere - that is, one where straightsare exactly one radius of curvaturelong, as is common. The constructs inFigure 6 are all equivalent to a rightangle, and are thus rational.

The zig-zag in Figure 7is irrational,but the construct next to it is rational,as the zig-zags clearly cancel out.

Some constructs favour one lane.For instance, in a plain 180° bend,the outside lane is longer, and thusyou might expect it to take longer tonegotiate. If there are fences it maybe faster, as the car can bounce offthem and thus allow greater speedwithout accident.

Experiment will determine howeach construct favours lanes. Onceyou have an idea of each constructand how it favours lanes, you canassemble them into a fair layout. Eventhough a completely flat layout willinevitably have one lane longer on theoutside, it can be made fair by theaddition of constructs to favour theworse lane - such as zig-zags at theends of long straights.

If you are really getting involved,you can devise a catalogue ofconstructs. We developed a computerprogram for checking rationality and alayout plotting routine, and here is anoptimal layout (Figure 8Iwhich uses allthe track from two cheap figure -eightsets.Our thanks to Hornby Hobbies, whosupplied the pictures featured in this HEarticle.


'.'..the quality of the colour display is excellent.'Popular Computing Weekly.

"The graphics facilities are great fun'." Personal Computer World.

"...the Spectrum is way ahead of its competitors'.' Your Computer.

"The world's bestpersonal computer

for under f5007Sinclair ZX Spectrum16K RAM f125, 48K RAM f175.This is the astonishing new ZX Spectrum-a powerful professional's computer ineverything but price!

There are two versions - 16K or areally powerful 48K. Both have a full8 colours, sound generation, a full-sizemoving -key keyboard and high -resolutiongraphics. Plus established Sinclairfeatures such as 'one -touch' keywordentry, syntax check and report codes!

Key features of the SinclairZX Spectrum

Full colour -8 colours plus flashingand brightness -intensity control.

Sound - BEEP command withvariable pitch and duration.

Massive RAM - 16K or 48K.Full-size moving -key keyboard - all

keys at normal typewriter pitch, withrepeat facility on each key.

High resolution - 256dots horizontallyx 192 vertically, each individuallyaddressable for true high -resolutiongraphics.

ASCII character set - with upper- andlower-case characters.

High speed LOAD & SAVE -16K in 100seconds via cassette, with VERIFY andMERGE for programs and separatedata files.

The ZX Printer - available nowThe printer offers ZX Spectrum

owners the full ASCII character set -including lower-case characters andhigh -resolution graphics.

Printing speed is 50 characters persecond, with 32 characters per line and9 lines per vertical inch.ZX Microdrive - coming soon

Each Microdrive will hold up to 100Kbytes on a single interchangeablemicrofloppy - with a transfer rate of16K bytes per second. And you'll beable to connect up to 8 ZX Microdrivesto your ZX Spectrum - they're availablelater this year, for around £50.

01/%;("

How to order your ZX SpectrumBY PHONE - Access, Barclaycard or

Trustcard holders can call 01-200 0200for personal attention 24 hours a day,every day.

BY FREEPOST - use the couponbelow. You can pay by cheque, postalorder, Access, Barclaycard or Trustcard.

EITHER WAY - please allow up to 28days for delivery. And there's a 14 -daymoney -back option, of course. We wantyou to be satisfied beyond doubt - andwe have no doubt that you will be.

ZX SpectrumSinclair Research Ltd,Stanhope Road, Camberley, Surrey,GU15 3PS. Tel: Camberley (0276) 685311.

170: Sinclair Research, FREEPOST, Camberley, Surrey, GM 3BR. Ord71Oty Item Code Item price Total Please tick if you require a VAT receipt

Sinclair ZX Spectrum -16K RAM version

Sinclair ZX Spectrum -

I

48K RAM version

Sinclair ZX Printer

Printer paper(pack of 5 rolls)

I Postage and packing:1 orders under £100I orders over £100

I

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'I enclose a cheque/postal order payable to SinclairResearch Ltd for £

100 125.00 'Please charge to my Access/Barclaycard/Trustcardaccount no. Please print.

101 175.00I 1 I I I I I I I I I 1 I I I I 1

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IN Popular Computing

ZX InterfaceBoard

AS discussed last month, I/Ointerfaces for the ZX81 are bestdesigned to look like normal memory('Memory Mapped I/O'). For theSpectrum, on the other hand, it makesmore sense to use the Z80's I/O addressspace ('I/O Mapped'). We havetherefore designed the PCB so that thecircuit can be constructed as either aMemory Mapped or an I/O mappedinterface.

Whichever version is built, it willgive you eight separate TTL leveloutputs, which can be controlled bythe ZX, to drive LEDs, relays orwhatever you will. There are alsoeight TTL inputs to the board, and theZX can examine the states of signalsapplied to these inputs.

The ZX81 version of the board isdesigned to work with the basic (1KRAM) ZX81, and also with the ZXprinter and the Sinclair 1 6K RAMpack. It should also be compatiblewith most ZX81 add-ons offered byother firms except for those which usememory addresses in the range 8192to 16383.The Spectrum version will also workwith the ZX printer and - as far aswe can tell from the limitedinformation available at this time -will be compatible with future Sinclairadd-ons such as the Microdrive andRS232 interface.

Circuit DescriptionThe circuit for both versions of the

Last month's article gave ageneralised description oftechniques for interfacingexternal circuits to the SinclairZX81 and Spectrum.This month we present apractical circuit, an Input /Output interface board whichcan be built to work with eitherthe ZX81 or the Spectrum.

board are shown inFigure 1. In theZX81 (MemoryMapped) version, IC4and IC3c, IC3d monitor the states ofthe ZX address lines A13, A14, A15,and also the ZX ryFiffline. When Al 3is high (logic '1'1, and A14, Al 5 andMREQ are all low, then the output, pin11, of IC3d will go low. This willhappen whenever the ZX81 accessesany memory address in the range8192 to 16383. At the same time,the ZX81 ROMCS line is pulled highthrough D1, to disable the unwanted'echo' of the ZX81 8K ROM whichwould otherwise appear at theseaddreses.

For the Spectrum (I/0 Mapped)version, IC4, D1 and R1 are not fitted,and IC3d is connected so that itsoutput, pin 11, goes low whenaddress line A5 and the Spectrum loanlines

are both low.In either case, pin 11 of IC3d going

low enables IC3a and IC3b so thatduring a ZX 'write' operation, whenWR goes low, the output, pin 6, ofIC3b goes low. Similarly, during a ZX'read', the output of IC3a pin 3, willgo low.

Both versions of the board dorespond to a wide range of ZXaddresses rather than to a singleaddress. This has been done forsimplicity, since to reduce the numberof addresses that the board would

respond to would mean adding moregates to monitor the states of more ofthe ZX's address lines. In both cases,the address decoding provided isadequate to allow the I/O board towork properly both with the computerand with Sinclair add-ons.

The eight board outputs are via PL1and PL2 from the outputs of the 8 -bitlatch, IC1. The eight inputs to IC1 areconnected to the ZX data bus linesDO -D7, so that when IC3b pin 6pulses low the data present on DO -D7is clocked into the latches. It will beheld there until another ZX 'write'operation, to a suitable memory or I/Oaddress, updates it.

IC2 contains 8 'tri-state' buffers.The inputs to these buffers areconnected to the I/O board inputpoints on PL3 and PL4. The output ofeach buffer is connected to one of theZX data bus lines, but normally has noeffect because the IC2 outputs areheld open -circuit by a 'high' input topins 1 and 19. When, however, theZX does a 'read' operation from asuitable memory or I/O address, sothat pin 3 of IC3a goes low, theoutput circuits of the buffers areenabled, transferring the information


Popular Computing

present at IC2 inputs to the ZX databus lines.

ConstructionRefer to the component overlay,Figure 2. Begin by adding wire links inthe positions shown. You should endup with 15 links (including the strapa -b) for the memory mapped version,or 16 (including straps a -c and d -e) forthe I/O mapped board. Insulatingsleeves should be fitted over the wirefor the longer links, which mightotherwise be liable to bend and toucheach other.

Newcomers to the art of electroniccircuit building may be interested tolearn an old trick for making neatsleeved -wire links. It involves taking apiece of solid cored (not stranded)plastic insulated tinned copper wireabout 18" (457.2 mm) long andcarefully - without nicking theconductor - stripping a short lengthof insulation from each end. You thengrip one bare end firmly in a vice or apair of pliers. Then, holding the otherbare end with the pliers, pull firmlyuntil the wire suddenly stretches.Stretching the wire this waystraightens it, and removes most ofits 'spring'. It also breaks the wire freefrom the inside of the insulation andreduces its diameter slightly, so thatwhat was insulation now becomes thecorrect sized sleeving.

Next, solder in D1 and R1 - butonly if you are making the ZX81(Memory Mapped) version of theboard. Note that D1 must be fitted theright way round, with the broadcoloured band away from the edge ofthe board. Now fit and solder the ICsockets and then Cl. The pins of theIC sockets are fairly close together, somake sure that you don't leave anyunwanted solder 'bridges' betweenadjacent pins.

Parts ListRESISTORSR1 470R

1/4 watt, 5%

CAPACITORS100n

polycarbonateSEMICONDUCTORSIC 1 74LS273

TTL octal D type flip-flopIC2 74LS244

TTL octal tri-state bufferIC3 74LS32

TTL quad 2 -input ORIC4 74LS00

TTL quad 2 -input NAND

MISCELLANEOUS20 -pin DIL socket (2); 14 -pin DILsocket (2); 23+23 way ZX edgeconnector socket, polarising key inposition 3; 23 + 23 way ZXconnector, matching socket;10 -pin 0.1" PCB plug (4); 10 -way0.1" socket housing (4); crimpterminal for socket housing (24);PCB, wire, solder, etc.

SKI TO ZX

DO

DI 5A

D2

D3 0 9AD4

BA

OA

D5D6 0D7 0

+5V 0

OV o

Cl

B

OV

WR 0

RD 0

A5

MREO

Al5

A14

A13

IORO

ROMCS

0

0O

B

0 +5V

/7777 OV

+5V0

18

+5V

18

A

B

A 10

B 9

128 1

O

t2 IC4a

136 5

2

12 13

O OAC

O

O

15A

B

E

0

jIB

IC4b

20

2

ICI

IC2

1

19

16

15

12

+5V 0 O

5

100

/771770V

+51/0 00000

7

ov

10

12

IC4c

13 1 IC4d

19110

8

17

15

13

11

2

4

6

8

+5V0

/7)77 OV

1.-5V0 00 I/P 4

O I/P 5

O I/P 6

o VP 7

O

0/P 00/P 10/P20/P 3

0/P 40/P 50/P 60/P 7

0 I/P 0

0 UP 1

I/P 2

0 I/P 3

4

OV

+Sy

NOTES.IC1 IS 74LS273IC2 IS 74LS244IC3 IS 74LS32IC4 IS 74L500D1 IS 1N4148

0

0

FOR I/O MAPPED VERSION(FOR USE WITH THE SPECTRUM)STRAP 'A' TO 'C' AND '0' TO 'E',AND DO NOT FIT IC4, Al OR 01.

FOR MEMORY MAPPED VERSION(FOR USE WITH ZX81) STRAP

Al 'A' TO 'B'470R

01

PL 2

PL 1

PL4

PL 3

SKI PIN NUMBERS ARE FOR A23+23 WAY SOCKET WITH APOLARISING KEY IN POSITION3, WHICH WILL THEN WORK WITHBOTH THE ZX81 AND THE SPECTRUM.

Figure 1. The circuit diagram shows both versions; note the links required to fit theboard for one or the other.

00

0

0

0

0

00

O

0

0

0

9A

B

do

A1

B

SK1 23

Figure 2. The component overlay diagram.

u1

T


Popular Computing

The four Input / Output connectors,PL1-4, can now be soldered in, butbefore doing so pull out the metal pinsfrom the positions for which there isno corresponding hole in the PCB. Theplastic moulding and the long ends ofthe plug pins should be on thecomponent side of the board, theshort ends of the pins should gothrough the board to be soldered onthe track side.

The 23 + 23 way ZX socket cannow be fitted so that the body of theconnector is on the component side ofthe board, as close to the board as it willgo. Tack -solder a couple of the cornerpins first, then make sure that thesocket is exactly perpendicular to theboard before proceeding. Formechanical soundness, each pin of thesocket should be soldered to its PCBpad, even though there may be no trackgoing to that pad. Make sure that nosolder bridges are formed betweenadjacent pads or tracks.

If you want to use other add-onssuch as the ZX81 16K RAM pack, thena 23 + 23 way double -sided PCB plugmust be fitted, projecting at right -angles from the track side of the I/Oboard. Each connection pad on this plugmust be soldered to the corresponding'tail' of the 23 + 23 way socket.Again, take care to avoid solder bridges,and make sure that the plug ispositioned so that it is exactlyperpendicular to the PCB and in linewith the 23 + 23 socket.

Note that although the Spectrumactually has a 28 + 28 way plug, thewanted connections lie within thescope of a 23 + 23 way ZX81connector and - if the polarising key isfitted - in the correct positions to suitboth machines.

Finally ICs 1, 2 and 3 (and IC4 forthe ZX81 version) may be fitted intotheir sockets, making sure that they areoriented with the semi -circulardepressions in the IC mouldingspointing towards the top edge of theboard as shown in Figure 2, and that allpins are properly engaged in theirsockets.

Testing ItThe first, and most important, test is toplug the board onto your computer andcheck that the computer itself stilloperates properly! If all is OK, we cantest the input side of the board by firstkeying one of the instructions:

PRINT PEEK 8192(for the ZX81 version);

PRINT IN 65503(for the Spectrum board).

The correct answer is 255 (not 42!),as all eight inputs to IC2 are, for themoment, open circuit and thereforelook to the I/O board as logic '1's.

Repeating the instruction with atemporary connection between OV(PL3 pin 10 is a suitable point to makeconnection to the OV rail) and one ofthe inputs (PL3 or PL4 pin 3,4,6 or 8)should give the results shown in Table1 . Only one input should be connectedto OV at any one time for this test.

Now for the output. Connect a DCvoltmeter, switched to its 5 or 10 voltrange, between OV and o/p 0 (PL2 pin3). Now key in one of theseinstructions;

POKE 8192,0(for the ZX81 version);

OUT 65503,0(for the Spectrum version.

This should result in a voltage readingof between OV and OV4. Then input:

POKE 8192, 1 or

OUT 65503,1

which should make the voltagechange to between 2V5 and 5V.

The other seven outputs can thenbe tested, in turn. For each one, POKE8192,0 or OUT 65503,0 should giveless than OV4, while POKE 8192,n orOUT 65503,n should give between2V5 and 5V, where n is a numbercorresponding to a particular output,as shown in Table 2.

ProgrammingConsidering the output half first, wehave eight separate TTL level outputswhich can each be set to give a logic'1' or '0' level by a program commandwhich loads a suitable value into the8 -bit latch, IC1. The value will affectall eight lines simultaneously so, if wewant to change just one output, we

TABLE 1 TABLE 2 TABLE 3

254 IF I/P 0 (PL4 PIN3) IS CONNECTED TO OV n = 1 FOR 0/P 0 (PL2 PIN3) 0/P SET TO '1' DECIMAL VALUE253 2 0 1

251 41 2

247 8 2 4239 4 (PL3 PIN3) 16 4 (PL1 PIN3) 3 8223 32 4 16191 64 5 32127 128 6 64

Testing the outputs; each will go high7 128

(between 2V5 and 5V) when theTesting the inputs to the board; the result corresponding value of 'n' is POKEd or Each output is set by loading a decimalis '255' if all inputs are logic 1. OUTput to the latch. value, as shown above.


Popular Computing MI

PL1 PL2

5V

0/P 4

0/P 5

0/P 6

0/P 7OV

PL3

4-5V

0/P 0

0/P 1

0/P 2

0/P 3

OV

MISSING PINS SHOWN AS 0

+5V

I/P 4

I/P 5

I/P 6

I/P 7

OV

PL4

+5V

I/P 0I/P 1

I/P 2

I/P 3

OV

Figure 3. The I/O connectors. PL1 and 2 carry the output lines; PL3 and 4 carry theinputs.

+5V

4k7

/7777 OV

47OR

f:CONTACT OPEN CONTACT CLOSED

FOR A'1' FOR A'1'

+5V

4k7

OPTO-ISOLATOR

JOV

NO CURRENT INLED FOR A '1'

POINTS 'I' CONNECT '1' TO THE I/O BOARD INPUTS

Figure 4. Inputs to the I/O board; points 'I' connect to the board inputs.

330R 100R

x 0v

LED OFF FOR A'1' LED ON FOR A'1'

+12V

RELAY OPERATED FOR A'1'

Figure 5. Outputs from the I/O board; points 'X' connect to the output pins.

RELAY COIL(>240 OHMS)

PIN Now for Input. The combined states ofthe 8 inputs applied to the I/O boardare read by the ZX as a single decimalnumber in the range 0 to 255. Forexample, if a '1' were applied toinputs 0 and 7, and '0' to the othersix inputs, then the variable X wouldbe given the value 129 by a ZXBASIC instruction of the form:

LET X = PEEK 8192(for the ZX81) or

1

2

3

4

5

6

7

98

10

must remember to load a value which- as well as affecting the output wewant to change - will also preservethe previous states of the other sevenoutputs.

This value can be calculated byconsidering the eight output lines asindividual bits on an 8 -bit byte, o/p 0being the least significant bit and o/p7 the most significant, and convertingthe result to decimal. To do this, addtogether the values from Table 3corresponding to the wanted '1' leveloutputs. For example, if we wanted toset outputs 2 and 5 to '1', and theother 6 lines to '0', the value to beloaded into the latch would be00100100 binary, or 4 + 32 = 36decimal, and the correct BASICinstruction would be;

POKE 8192,36(for the ZX81) or

OUT 65503,36(for the Spectrum).

If we wanted to then change output 2to a '0' without affecting the otherlines, then the appropriate instruction

would be: POKE 8192,32 or OUT65503,32.

Alternatively, we could let thecomputer do the hard work byinserting the following lines near thebeginning of our program:

LET OPO = 1

LET OP1 = 2LET OP2 = 4LET OP3 = 8LET OP4 = 16LET OP5 = 32LET OP6 = 64LET OP7 = 128

Then, to set, say, o/ps 1, 5 and 7 to'1', use the program line:

POKE 8192, (OP1 + OP5 + OP7)

or

OUT 65503, (OP1 + OP5 + OP7)Spectrum programs could use the BINfunction, which takes an 8 -bit binarynumber expressed as a string of '1'sand '0's and converts it to the decimalequivalent. For example:

OUT 65503,BIN 10100010

LET X = IN 65503(for the Spectrum).

The following routine can then be usedto sort out the states of the eigntindividual inputs;

DIM 1(8)

FOR J = 1 TO 8LET 1(J) = X - 2 * INT (X/2)LET X = INT (X/2)NEXT J

This routine will give each of the eightarray elements 1(1) to 1(8) the value '1'or '0', depending on the logic levelapplied to the individual I/O boardinputs.

Using ItThe whole point of an I/O board is thatit will be connected to otherequipment, and to this end the boarddescribed here has four 10 -way plugs(PL1-4) fitted to it. As shown in Figure3, PL1 and PL2 each carry four of theoutput lines, as well as OV and + 5Vrails. PL3 and PL4 each have four ofthe input lines, and also the OV and+ 5V connections. Leads can besoldered to the pins of the plugs or -more professionally - the matingsockets shown in the components listcan be used; note that these consist ofa shell moulding with separatelysupplied contacts.

The I/O board inputs can, of course,be connected directly to TTL or 5VCMOS outputs, and switch or relaycontacts can be easily interfaced asshown in Figure 4, which also showshow a LED-phototransistor opto-isolatorcould be used to sense signals that itmay not be possible to connect to thecomputer's OV rail.

LEDs or low power relays can bedriven from the board's output lines, asshown in Figure 5. In all cases, thetotal amount of current drawn from the+ 5V rail on pin 1 of PL1-4 should benot more than about 50 mA, as it isbeing provided by the regulator in theZX, which runs hot enough anyway!

Note also that any large or inductiveloads such as motors or relay coilsshould have interference suppressorsfitted to cut down the risk of noisepulses upsetting the computer. For thisreason it is advisable to isolate anylarge loads with a relay or opto-isolator, so that high voltage or heavycurrent circuits are completelyseparate from the computer. This willalso reduce the chance of high voltagesgetting accidentally connected to yourvaluable ZX! HE


COMING SOON TO . .if 1Th

_FL 0 0 0

0 at,DIRECTORY OF ELECTRONIC SUPPLIES

Hobby Electronic's October issue features the largest, most comprehensive survey of electroniccomponents and hardware ever published.

The Directory consists of three large pull - out wall charts showing 40 categories ofcomponents, hardware and information for the electronics constructor. More than 60 company

names and addresses are listed separately, with comments on product lines, specialities andservices, and mentioning any items not covered in the charts.

With all this information presented so efficiently, the October issue of Hobby Electronics is amust for all electronic enthusiasts.

CB SQUELCH UNITStamp out noise!

This device is the companion to our Stereo Noise Gate, also under preparation for October, butdesigned to eliminate CB receiver noise when the channel is open. If you find noise annoying, this

easy -to -build and economical unit will sooth your nerves!

CIRCUIT MAKERA complete kit for making PCBs at home, using the photographic process, has recently been releasedby Electrolube Limited. In October, Owen Bishop reports on his experiences with the photo -resists, the

light frames and the bags of ferric chloride. His conclusions? See for yourself in the October issue ofHobby Electronics!

Remember the HEBOT?Way back in November 1979 we published one of the first ever mobile robot projects, which wechristened HEBOT. It proved to be enormously popular and, judging by the mail we still receive,

reader's enthusiasm for simple robotics has not decreased over the years!

HEBOT has long since 'passed on' but now, in conjunction with Powertran Ltd., we are proud topresent its successor.

HEBOT II is a very similar animal - er, robot - but using today's more sophisticated circuitry andoperating under the control of a microcomputer. Like the original, it is a 'turtle' robot, propelled by two

large, independently controlled rubber wheels which enable it to perform a wide variety ofmovements. Obstacle -sensors allow it to explore its environment, discovering the limits of movement

or the shape of a room, or it can draw patterns or graphs using a pen, which presses down on com-mand. Its blinking eyes and on -board beeper can be programmed to communicate with the operator,

eg to indicate that it has finished a task.

The projected cost of this educational and inspirational robot is under 100, and it is initially intendedto be controlled via a Sinclair ZX81 microcomputer - though future developments will open still

greater possibilities. Look out for HEBOT II in the November issue of Hobby Electronics.

Please reserve

111

copies of the October issue of

forName

Address

October issue on sale atyour newsagent

from 10th September.

Place your order now!Although these articles are being prepared for the next issue, circumstances may alter the final content.


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£31.00*ONIriirr.1 l' :1 dtwo,...,1

LP -2 Logic ProbeThe LP -2 performs the samebasic functions as the LP -1,but, for slower -speed circuitsand without pulse memorycapability. Handling aminimum pulse width of 300nanoseconds, this 300 K ohmprobe is the economical wayto test circuits up to 1.5 MHz.It detects pulse trains orsingle -shot events in TTL, DTL,HTL and CMOS circuits,

replacing separate pulse detectors,pulse stretchers and mode stateanalysers.(Available in kit form LPK-1 £12.50)

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II


Into Radio

RADIO RULIan Sinclair

Radio Frequency Power Amplifiers.

THE SAMPLE examination papers forthe Radio Amateur's exam don't mentionvalves - though they do mention anumber of topics that aren't covered toany great extent in the manual! Yet thefact is that the output power permitted tobe used on the most popular amateurbands cannot easily be achieved usingtransistors. The good ol' fashioned valveis still the only way of ensuring that youhave a beefy signal, without spendingyour whole income on the output stage!Unless you have some understanding ofvalve operation, then, the higher powerstages of transmitters are going to be abit of a mystery to you, and that doesn'tsound like a good idea to me. So, for thebenefit of those whose hair has not yetturned gray, let's look at the low-downon high -vacuum devices.

A valve relies for its action onelectrons moving across a vacuum.Only electrons are involved, becauseholes can't exist outside a solid crystal,so the action of the valve resembles thatof the N -channel MOSFET rather thanthat of a bipolar transistor,: and there isno valve -type device which.00rrespondsto the P -channel MOSFET. Theelectrons are emitted from a hotmaterial, the cathode, which iscylindrical in shape and is heated by awire filament, the heater (Figure 11. Thecathodes of the smaller valves use anon -conducting (at room temperature)white material (the oxide cathode)which becomes an electron -emittingconductor when it is heated to atemperature of around 700°C, when itglows a dull red. Larger transmittingvalves work with large currents andvoltages, enough to damage a coating ofthis type, so that a filament of tungsten,either pure or coated with thorium, isused and carries out the tasks of bothheater and cathode.

Electrons released into the vacuumof the valve from a hot cathode will,obeying the law that unlike -charges -attract, move to anything that is at amore positive voltage than the cathode.Surrounding the cathode, then, is ametal cylinder, called the anode, whichis maintained at a positive voltage ofanything from 100 V to 25kV,depending on valve size and power, soas to pull electrons away from thecathode at high speed. This electrodecorresponds to the drain of theMOSFET.

A valve with only a cathode and ananode is a diode and can be used forrectification, though nowadays we usevalves as rectifiers only for very highvoltages, like the 100 kV'supplies usedin X-ray work. But if we add a thirdelectrode, called a grid, between thecathode and the anode, it can control

the flow of electrons and make the valvea useful amplifier or oscillator. The gridis usually a coil of wire held on metalposts between the cathode and theanode, but very much closer to thecathode (Figure 3). When the voltageon the grid is the same as the cathodevoltage, electrons will pass throughbetween the wires, practicallyunaffected by the grid, and will reachthe anode. If the grid voltage is madenegative, however, the electrons will berepelled from the grid wires and thespace immediately around the wires,reducing the number of electrons thatcan reach the anode. At some particularnegative voltage on the grid, thisrepulsion effect will be so strong that nomore electrons will reach the anode andin this state, the valve is said to be 'cutoff'. Therefore, a varying voltage on thegrid, which must be biased so that itsstarting voltage (with no signal) is

ESsuitable (usually negative), will cause avarying anode current, just as a varyinggate voltage on a FET causes a varyingdrain current.

The important difference is that thevalve can operate at much higher powerlevels. If we try to operatesemiconductors at high power, we havea problem conducting away the heatwhich is generated inside the material,as electrons and holes flow through it.Heat is also generated in a valve, ofcourse, but most of it is released at theanode and the anode is made of a metalwhich can withstand much highertemperatures than a semiconductorjunction made of silicon. In addition,the valve can dissipate heat by radiationthrough its glass envelope (as used inthe smaller valves) or even by makingthe anode part of the outside of the valveand 'finning' it, so that it can be air-cooled, or by forming a water -jacket

CATHODE CYLINDER(NICKEL COATED WITHEMITTING MATERIAL)

ALUMINIUM OXIDEINSULATION

-- HEATER WIRE

Figure 1. The cathode and heater of avalve. The heater is insulated from thistype of cathode.

aP

TUNGSTEN WIRE

Figure 2. A tungsten filament, acting ascombined heater and cathode, for thelarger types of transmitting valve.

ANODE

GRIDWINDING

CATHODE

HEATER

Figu e 3. Arrangement of cathode, gridand anode in a small transmitting valve.

-50 UP TO OV

+100 TO 1000V

DV

Figure 4. Valve symbol (triode) withtypical voltage ranges (heater notshown).

LOAD CONVERTSCURRENT SIGNAL -a,

TO VOLTAGE SIGNAL

INPUT(VOLTAGE

SIGNAL)

V

OUTPUT(CURRENTSIGNAL)

DEVICE (VALVE,TRANSISTOR ETC)

DV

Figure 5. The principle of using a load toconvert current signals to voltagesignals.


Into Radio around the anode so that it can becooled like the cylinder -block of a car.

For powers of more than 100W, thenvalves are simpler and more reliablethan transistors and in countries wherehigh powers (several kilowatts) arepermitted and used, valves areunchallenged.

ClassesNo, it's not like the Post - first-class orpigeon. Class of operation means theway that we use a device, valve ortransistor, to amplify signals; and it'simportant. There are three main classesof operation, termed (imaginatively)A,B and C, and you need to understandthem thoroughly because all three areused in radio circuits.

Before we start, let's clear the way bymaking sure that we know what'sinvolved in an amplifier. What it does isstraightforward enough - create ahigh -power signal under the control of alow -power signal. An amplifier is an'enlarger' of signals, using electronsinstead of light.

The electronic devices, valves orsemiconductors, that we used forconstructing amplifiers do not, bythemselves, amplify signal voltage.Rather, they create a current signal atthe output, from a voltage signal (lowcurrent) at the input. What we usuallyneed, however, is a voltage signal at the

output, and to convert current signalsinto voltage signals we need a load -something that obeys Ohm's law so thatthe voltage across the load isproportional to the current through it.Audio amplifiers use a resistor or loudspeaker as load, but radio frequencyamplifiers use a tuned circuit which, atthe frequency of resonance, behaveslike a resistor for AC signals, but as aresistor of a very different and lowervalue for DC bias currents. We'velooked at this point previously, when wedealt with tuned circuits and theirdynamic resistance. Now: whatdistinguishes one class of operationfrom another is the way in which theload and the amplifying device worktogether.

Class AClass A is the most familiar operatingclass because it's used so extensively foraudio amplifier circuits - the ones thatmost of us cut our teeth on. In a Class Acircuit, the transistor or valve never cutsoff and is never saturated. In otherwords, the biasing and the signalamplitude will be arranged so that achange in the voltage of the input willalways cause a change in the current atthe output. For a silicon transistor, thismeans that the bias voltage betweenbase and emitter must never fall muchbelow OV6 and the collector voltage

*0V6

(BIAS DETAILSNOT SHOWN)

TV

OV

V/2

SIGNAL

COLLECTORVOLTAGE ---

WITH NO SIGNAL

OV

POSITIVE PEAK

NEGATIVE PEAK ti

Figure 6. Class A bias - the collectorvoltage, when there is no signal input isat around half of supply voltage.

OUTPUT SIGNALAMPLITUDE

INPUT SIGNAL AMPLITUDE

Figure 8. Linear amplification - thegraph of output plotted against input is astraight line.

0V6BIAS

AVERAGE

OV

2x(TV)

POSITIVE PEAK

+V

NEGATIVE PEAKOV

Figure 7. Adapting Class A to radiofrequencies. The load is tuned circuit,and the no -signal collector voltage isequal to supply voltage.

AC OUT

Figure 9. An old-fashioned audio push-pull stage, which can use Class B biasbecause the two output transistors eachuse half of the signal wave.

must not fall much below the basevoltage; a typical audio Class Aamplifier is shown in Figure 6. With nosignal input, the collector voltage isaround half the supply voltage and thesignal amplitude, when a signal isapplied, must never cause the outputvoltage to reach either the supplyvoltage or earth level.

Radio frequency amplifiers workingin Class A are similar - but different.To start with (Figure 7) the load will be atuned circuit or a choke (inductor)rather than a resistor. Since the DCresistance of such a load is small, thenormal no -signal voltage on thecollector will be equal to the supplyvoltage and when a signal is applied,the voltage at the collector will be belowsupply voltage on one half of the cycleand above it on the other half. Therestrictions are the same though - thecurrent must never cut off and thecollector voltage must never go as lowas the base voltage, give or take afraction. Using Class A for a radio -frequency amplifier produces what iscalled 'linear amplification', meaningthat a graph of the amplifier signalcurrent output plotted against the signalvoltage at the input is a straight line.This is the type of amplifier that isneeded for FM or single-sideband (SSB)signals, as we shall see later. One veryimportant feature of a linear amplifierstage like this is that the DC current isconstant - the amplifier takes the sameamount of current from the supply whena signal is being amplified as it doeswhen there is no signal and this makesdecoupling and supply filtering a loteasier.

The trouble with the Class Aamplifier is its low efficiency. Like thehorse which is eating its head off evenwhen it is not working, the Class Aamplifier is taking current from thesupply even when there is no signal, sothat the ratio of power output from theamplifier to the DC power taken fromthe supply (confusingly called thepower input) is low - always less than50%. This ratio implies that a Class Astage will always run hot if it is handlingmore than a few milliwatts.

Class BThe Class B amplifier operates ratherdifferently. To start with, the amplifyingdevice is biased back, almost to cut off.This means that current flows mainly forthe positive half -cycles of the signal(assuming a NPN transistor or valve)only. This type of stage can be usefullyemployed in audio amplifiers only in theform of balanced pairs (the push-pullcircuit so that one transistor handlesthe positive half -cycles and the othertransistor handles the negative half -cycles. This is the basis of push-pullClass B circuits which, at one time, usedtransformers for splitting the signal intotwo opposite phases and recombinedthe phases later, but which now alwaysdeal with the two half -cycles directly byusing a PNP and NPN transistor in seriescombination (Figure 10).

Radio frequency amplifiers canmake more effective use of Class Bamplifiers because they can use a load


NI Into Radio

which is a tuned circuit. A tuned circuitreacts to short duration electrical pulsesas a bell reacts when it's struck - itrings! A suddenly applied voltageacross a parallel tuned circuit (Figure11) will charge the capacitor, which willthen discharge through the inductor,which re -charges the capacitors . . . andso on, with the cycle continuing untilthe energy of the original pulse hasbeen dissipated in the resistance of thecircuit. A tuned circuit will, in fact,produce a continuous signal at itsresonant frequency with only a littlehelp - it needs just enough signal atthe right frequency to compensate forwhat is being lost in the resistance. It'slike a swing - once you get it going, itneeds only a very small amount of effortto keep it going.

A Class B tuned amplifier dependson this; the transistor or valve needs toconduct only for part of a cycle to keepa complete cycle going. Providing thatthe Q -factor of the tuned circuit is nottoo low, this works well and the Class Bamplifier can be used for near -linearamplification. In many cases, however,the tuned circuit is loaded by otheramplifier stages and has a low Q, so thatthe bias current has to be increased toobtain more linear operation. This neednot necessarily be to the extent that isused in a Class A stage, and sucharrangements are called Class A -Bamplifiers.

The Class B amplifier has muchhigher efficiency than the Class Aamplifier, meaning that a greaterproportion of the power taken from thesupply is converted into signal power(up to 80%), but it also means that thecurrent is taken from the power supplyin pulses, making smoothing difficultand requiring very good decoupling ifthese pulses are not to affect otherstages in the circuit.

Class CClass C amplification carries the"ringing" principle to its logicalconclusion by biasing the transistor orvalve so far into cut-off that the deviceconducts only on signal peaks (Figure13). Unless the load has a high -Q, thiswill distort the signal considerably andso Class C amplification is used mainlyfor power stages of conventional AMtransmitters. The fraction of the signalwave for which the transistor or valveconducts is called the 'conductionangle', and is given in degrees. If weimagine a complete cycle as being360°, then the fraction of the wavefor which the Class C stage conducts isgiven by the conduction angle dividedby 360° so that a 30° conductionangle would mean that the transistor orvalve was passing current for only onetwelfth of the cycle, a lot less than thehalf cycle (180° conduction angle) ofthe Class B amplifier. The mainadvantage of Class C is its very highefficiency - the DC power that is takenfrom the supply is only slightly morethan the AC signal power at the output,so that Class C is particularly useful forhigh -power stages which do not needlinear amplification. Such poweramplifiers need to be carefully designed,

Figure 10. The more modern type ofseries Class B audio circuit - eachtransistor conducts alternately.

PULSE RINGINGWAVEFORM

Figure 11. A ringing circuit. The pulsecauses the transistor to conduct briefly- but the tuned circuit continues tooscillate even after the transistor has cutoff. By feeding a small portion of theoutput back to the base of the transistor,this circuit can be made to oscillate, asdescribed in an earlier part of this series,or it can be used as the basis of a Class Cradio frequency amplifier.

BASE VOLTAGE CUT-OFF

CONDUCTING

NON CONDUCTING

a I INPUT

BASE VOLTAGE

I'TUNED

CIRCUIT -1

TRANSISTOR

(I, / OUTPUT

Figure 12. Using Class B for radiofrequency - the tuned circuitcontributes half of the output; this ispossible only if the Q is fairly high.

CONDUCTINGEt CUT-OFF

I I

ACIN

NON -CONDUCTING

BIAS OV

SUPPLYVOLTAGE

TRANSISTORPASSING

CURRENT

Figure 13. Class C radio frequencyamplification. The transistor conducts foronly a small portion of the input cycleand the tuned circuit contributes theremainder. Class C amplifiers are themost efficient, but the distortion theyintroduce means they can only be usedfor radio frequency amplification.

however, because the large pulsecurrents which flow for very shorttimes will cause feedback to otherparts of the circuit, and radiate fromthe supply leads! It is good practice tofeed a Class C stage from a separatesupply and to have a large decouplingcapacitor across the Class C stage,between the 'cold' end of the load andearth. Large capacitance, in thisrespect, means about 100nF or less,depending on the frequency at whichthe stage is being operated.Electrolytics, which usually have ratherlarge RF resistance, are quite definitelyunsuitable.

Frequency Multipliers.Up till now, we've been considering thebest ways of obtaining, from anamplifier, a reasonable copy of theinput signal but with higher power.Another problem that is tackled by

surprisingly similar methods is that ofobtaining a signal which is not a goodcopy but is, in fact, a differentfrequency! A frequency multiplier's anamplifier which is deliberately made todistort the shape of the sinewave so thatharmonics appear. These harmonics areat multiples of the input frequency(twice, three times, and so on) and anyone of them can be selected by using atuned circuit so that it is amplified to amuch greater extent than the others. Byusing an amplifier with low bias, such asa Class C stage, and with a load whichis tuned to a multiple of the inputfrequency, we can produce an outputwhich is a signal at the frequency towhich the load is tuned. (Figure 15).

This circuit is useful because we canuse crystal oscillators operating atcomparatively low frequencies togenerate outputs at VHF. We can, forexample, multiply the frequency of an


Into Radio

DECOUPLINGCAPACITOR

DECOUPLINGCAPACITOR

ov

AC SIGNAL IN

BIAS OV

C

OV

RFC = RADIO FREQUENCY CHOKE.AN INDUCTOR WITH A 'LOSSY' CORESO THAT IT HAS A VERY LOW CI

Figure 14. Decoupling a Class C circuit.

PARALLEL RESONANTCIRCUIT f0 = 21MHz

SERIES RESONANTCIRCUITfo = 7MHz

(A)INPUT 7MHz

BIAS

I-0 21MHzOUTPUT

EFFECT OFUNBIASED

TRANSISTOR,OV RESISTIVE LOAD

EFFECT OFTUNED LOAD

Figure 15. Frequency multiplication -the transistor output would be a squarewave but for the tuned circuit, whichrings at a harmonic of the inputfrequency so that, each time thetransistor conducts, the result is in thecorrect phase to maintain oscillation.

"T'c

I c C )(tLEI- - - -I. I

OV

Figure 16. Stray capacitance andinductance around an amplifying stage.Each length of wire has someinductance, and there will be straycapacitance between any two points atdifferent voltage.

GATE

SOURCE DRAIN

\ /

Figure 17. A FET, illustrating whytransit time of electrons is important.

8 MHz crystal to 144 MHz, using severalstages of multipliers. The amounts ofmultiplication that are used are mainlyx2 and x3, though x4 is possible for low -power stages.

Frequency LimitationsAn ideal amplifier stage design wouldbe one that could be used at allfrequencies - but there's no suchanimal. What we do in practice is to usedifferent designs for different parts ofthe frequency range. Just to complicatematters, there are several effects whichcombine to restrict the highestfrequency that an amplifier can operateat and we have to be aware of all ofthem, if we are to make wise choices forcomponents and circuits.

One of the most important limitingeffects is stray capacitance. Any twopoints in a circuit which are not directlyconnected will have some stray

capacitance betwen them and thisinvisible capacitance is as real in itseffect as a capacitor soldered in place.Stray capacitance can even existbetween two bits of metal that areconnected together because, when aradio frequency wave moves along astrip of metal, some points will be athigh voltage and some at low voltage, sothere can be capacitance between them.

The second effect is strayinductance. Any length of wire has aninductance and, though the inductanceof a few centimetres of wire is verysmall, even this will be significant if weare using UHF signals. Finally, thetransistors and valves that we use asamplifying devices can't operate atfrequencies above the limit set by thespeed of their current carriers legelectrons).

That last one needs someexplanation; suppose you imagine a FET

in which electrons move from the sourceto the drain and are controlled by a gate(Figure 17). Suppose, also, that thevoltage on the gate is a sinewave at ahigh frequency, perhaps 10 MHz. Nowa 10 MHz signal means that onecomplete cycle takes 100 nS and onequarter of a cycle takes 25 nS. What'sthe significance of this? Think of themovement of the electrons; if anelectron starts moving from the sourcewhen the wave on the gate is at itspositive peak, then it has to get past thegate before 25 nS has elapsed. If itdoesn't, it will be slowed down or evenrepelled because the gate voltage will,by that time, have reversed. As ithappens, we can make the gate and thesource very close to each other, so thateven with the slow speed of electrons insemiconductors, it's possible to operateFETs at fairly high frequencies,certainly more than 10 MHz - but onlyif the FET has been designed with itsgate very close to the source. A similareffect occurs in valves and is called'transit time'. The limitation here is thatit's impossible to get the grid reallyclose to the cathode without riskingthem touching, particularly when theelectrodes expand due to heat.Transistors suffer from another effect,'charge storage', meaning that the baseof a NPN transistor, which conductsbecause of hole movement, will fill upwith electrons while the transistor isswitched on and it takes some time toclear these electrons when the transistoris switched off.

Whatever the cause, we have tochoose amplifying devices that will copewith the frequencies that we want to use.This may, for example, mean usingtransistors in common -base circuitsrather than in common -emitter circuits.

For audio amplifiers, there are noserious frequency limitations. Evenpower amplifier transistors now havegood frequency responses, provided weuse modern transistor designs. Thelimitations caused by the effects of straycapacitance, along with the use ofresistor loads have very little effect ataudio frequencies.

In tuned -load amplifiers, the straycapacitance can actually be made partof the tuned circuit and becomes aproblem only when we use such highfrequencies that the stray capacitance islarger than the total capacitance that weneed! At such frequenices, we are alsoup against the frequency limitations ofthe device itself and the effects of strayinductance, so that specialisedconstructional techniques are neededwhen we work at 400 MHz or above.Ultimately, if we want to use frequenciesabove 1 GHz (1000 MHz), we have touse pulsed devices such as klystronsand magnetrons to generate signals,and linear amplification eventuallybecomes out of the question.

We've now dealt with a lot of piecesof circuitry - oscillators, amplifiers andbasic component theory - so we'reready to start putting the bits together tosee how they are used in radio receiversand transmitters. We'll kick off nextmonth, then, with the AM superhetreceiver. Out. HE


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Antes CS 17W Soldering iron2.3 and 4.7mm bits to suitCS 17W elementAntes XS 25W Soldering iron3.3mrn and 4.7mm bits to suitSolder pump desoldering toolSpare nozzle for above10 metres 22swg solder

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OPTO

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404060es9060

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100 100111313 0.3' 105 TIL312 0.3' 1%TIL322 0.5' 116 TIL321 0.5' 115LCD: 33 digit 51109 4 digit 820p

INICLAYCAPID

FA.LINEAR

IC L7622*555CM0S 80 ICL8038*556CMOS 150 IC L8211A709 25 ICM7224*741 14 ICM7555748 36 LF3519400CJ 350 LF353AY -3-1270 840 LF356AY -3-8910 600 LM1OAY -3-8912 625 LM3014CA3046 60 LM311CA3080 65 LM318CA3089 215 LM324CA3090AQ 375 LM334ZCA3130E 90 LM335Z*CA3140E 45 LM339CA3161E 100 LM348CA3169 290 LM358*CA3240E 110 LM377ICL7106 790 *LM380ICL7611 96 LM381

180 1_1'1 :

180 LM384320 LM386200 LM387785 LM39390 LM70945 LM71185' LM72590' LM733

360 LM74125 LM74770 LM1458

120 LM291740 LM3900

100 *LM3909

152011-12814LM3915

501 LMI3600150 MC131085 MC1496

120, MC3340

120 1 ML922 400 ' SL76018 150 fULN2003130 ML924 1% SN76477 250 I ULN2004

85 ML925 210 SP8629 250 *X112206120 ML926 140 TBA120S 70 ZN414100 ML927 140 T0A800 80 ZN42325 ML928 140 TBA810 96 ZN42460 ML929 140 TBA820 80 ZN425E

350 MM5387A 465 1134950 290 ZN426E75 NE529 225 TDA1008 320 ZN427E14 NE531 150 *TDA1022 525 ZN428E75 NE544 205 11341024 125 ZN45940 *NE555 16 1710131 40 ZN1034E

200 *NE556 45 TL062 6050 NE565 120 TL064 9670 NE566 150 TL071 30

NE567 100 TL072 50NE570 400 TL074 95NE571 400 *TL081 25*RC4136 68 *TL082 45*RC4558 60 *TL084 95SL480 170 TL170 50SL490 250 *UA2240 120

22012015068

135

TRANSISTORSAC125 35 BC157AC126 25 BC158AC127 25 0C150*Aci 28 20 BC160

AC187 22

BC168CBC169C

AC176 25

AC188 22 9C17040142 120 BC171

AD149 80 BC, 72AD161 40

AF124 60

BC178BC177

40162 40BCI79

AF126 50AF139 40AF186 70AF239 75BC107 10*B C81c0170B, 192

BC108B 128C108C 12*BC109 9BC109C 12BC114 22BC115 22BC117 22BC119 358C137 40BC139 40BC140 30BC14I 30BC142 25BC143 258C147 8BC148 8BC149 9

BC548 10 13E880 25 TIP29C 60 ZTX300 14 *2143702BC549 10 BFX29 25 TIP30A 45 ZTX301 16 2143703

1011 8C558 10 BFX84 25 TIP3OB 50 ZTX302 15 *25370410 BCY70 18 BFX85 26 TIP30C 60 ZTX304 17 21437058 BCY71 18 8FX86 28 TIP31A 45 ZTX341 30 2143706

45 BCY72 18 BFX87 26 TIP31C 55 ZTX500 15 2143707 1

10 BD115 80 BFX88 25 TIP32A 45 ZTX501 15 253708 1

10 813131 35 BEY50 23 TIP32C 60 ZTX502 16 2143709 1

8' 813132 35 BEY51 23 TIP33A 50 ZTX503 18 253772 19010 130133 50 BFY52 23 TIP33C 75 ZTX504 25 2N3773 2108 80135 50 5EY53 32 TIP34A 60 2N697 20 *2N3819 18

18 BD135 30 BFY55 32 TIP34C 85 25698 40 2N3820 4018 BD137 33 BFY56 32 TIP35A 160 2N706A 20 2143823 6518 BD138 30 BRY39 40 TIP35C 180 2N708 20 2143866 90

BC182 10 80139 35 BSX20 20 TIP36A 170 25918 35 253903 10*BC182L 8 B0140 35 BSX29 35 TIP36C 195 2N1132 22 253904 10BC183 10 80204 110 BSY95A 25 TIP41A 60 2N1613 30 253905 6BC183L 10' 80206 110 1311205 160 TIP42A 60 2N2218A 45 253906 10BC184 10 80222 85 BU206 200 TIP120 90 2N22194 25 254037 45*BC184L 7 8E180 35 BU208 170 TIP121 90 2N22214 25 2144058 10

C212 10 8E182 35 MJ2955 99 TIP122 90 2N2222A 20 2N4060 10C212L 10 8E184 25 MJE340 50 TIP141 120 252368 25 2N4061 10

213 10 6E185 25 MJE520 65 TIP142 120 252369 16 2N4062 10C213L 10 BF194 12 MJE521 95 TIP147 120 2N2484 25 255457 36

214 10 8E195 12 MJE3055 70 TIP2955 60 *2N2646 46 2145458 36BC214L 8 13E196 12 MPF102 40 TIP3055 56 2N2904 20 2145459 300237 8E197 12 MPF104 40 TIS43 40 2529044 20 255485 36C238 14 8E198 10 MPSA05 22 TIS44 45 2N2905 22 2145777 45,0308 15 8E199 18 MPSA06 25 TIS45 45 2N29054 22 2146027 300327 14 8E200 30 MPSA12 30 TIS90 30 2N2906 25 40360 40

328 14 *BF244B 22 MPSA55 30 TIS91 30 2N2906A 25 40361 50C337 14 13E245 30 MPSA56 30 *VN1OKM45 2142907 25 40362 50C338 14 BF2568 45 MPSU05 55 VN46AF 75 2N2907A 25 40408 70C477 30 8E257 32 MPSUO6 55 VN66AF 86 2142926 9

478 30 13E258 25 MPSU55 60 VN88AF 95 2N3053 23479 30 8E259 35 MPSU56 60 *ZTX107 8 2N3054 56

C517 40 8E337 40 TIP29A 40 *ZTX108 8 2N3055 50C547 7 BE540 23 TIP298 56 ZTX109 12 253442 120

CMOS4000 10*4001 104002 124006 504007 154008 484009 244010 24*4011 11

4012 15*4013 254014 504015 50411

*401740184019402040214022402340244025*402640274028402940304031

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100360275

3535

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140

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7

37 LS22137 LS24037 LS24143 LS24276 LS24375 *LS24485 *LS245561 LS24746 LS25146, LS25746, LS258451 LS25945 LS26645 LS27336 LS27950 LS283

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LS390 55LS393 ssLS399 175L5541 120LS670 150

TTL*7400740174027403740474057406740774087409741074117412

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741777417974180741817418274190741917419274193741947419574196741977419874199

VERO

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290370300370300270220240120150150125

5.0M6.0M6.144M7.0M8 OM10.0M12.0M16.0M18.0M18.43238.66748.0M116M

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Popular Computing

41

MicroTrainingConcluding the main partof our MicroTrainerproject.

In the first article of this series wedescribed the general principles ofmicroprocessor operation, using the1802 as a particular example. In thisissue, we continue with a detaileddescription of the 1802 instructionset, and a discussion of simpleprogramming techniques using theseinstructions. Then we should have laidthe foundations for aspiring designersof control systems, so that in futurearticles we may concentrate on theapplications aspects ofmicroprocessing. We also said, at theoutset of the Microtrainer series, thatwe were not aiming to produceexperts in machine code programming,but rather to encourage the use ofmicroprocessors in a wide range ofhobbyist applications, and we believethe average hobbyist will be well ableto produce his own useful designswith only a basic understanding ofmachine code software.

Instructions ExecutedA microprocessor operates bysequentially fetching data bytes froman external random access memory(this includes ROM) and interpretingeach one as an instruction to performspecific operations on data stored ineither internal registers or in externalmemory. The task that a micro-rocessor system performs isdetermined almost entirely by theparticular sequence of instructionsheld in the memory, know as softwareor, more simply, a program. Aparticular microprocessor, such as the1802, is distinguished by the set ofinstructions available, and by thefunctions of a closely related set ofinternal registers, as well as itspeculiar hardware features.

We have already given a table of1802 instructions and arepresentation of the register set (June'82 issue and to supplement this, theinternal architechture of the 1802 has

been drawn in Figure 1 and theinstruction set is reproduced here asTable 1. This information is alsoavailable in the RCA programmingmanual. The architechture of the1802 reveals some of the 'hidden'registers leg the instruction holdingregisters I and N) as well as the useraccessible registers, but a descriptionof the MPU's operation at this level isbeyond the scope of this article.

The instruction set can besubdivided into broad categories,which we will look at in turn. Thecategories are: register operations,memory references, logical operations,arithmetic operations, branch and skipinstructions, control instructions andinput/output instructions.

Register Instructions

The 1802 register set includes a bankof 16, 16 -bit registers, each of whichcan hold 2 bytes of data or one 16 -bitaddress. The instructions that operateon these registers show that they areprimarily intended for use as memoryaddress pointers for subsequentinstructions. Here are the registerinstructions:

INC RN)DEC RINIIRXGLO RINI

PLO R(N)

GHI RN)

PHI R(N)

Increment register N.Decrement register N.Increment register X.get low byte of registerN and place inaccumulator.put accumulator in lowbyte of register N.get high byte ofregister N, place inaccumulator .put accumulator in highbyte of register N.

These are the only instructions whichspecifically alter the contents of the16 -bit registers (some instructionshave a 'register auto -increment/decrement' addressing mode,

however). In order to set-up a sixteenbit address in any of the registers,data must be fetched from memoryvia the accumulator, one byte at atime. An example will best illustratethis (the prefix '$' and suffix 'H' bothdenote hexadecimal):

LDI $40 ;load accumulator with40H

PHI R5 ;R5.1 = 40HLDI $E0 ;load accumulator with

EOHPLO R5 ;R5.0 = EOH

At the end of this sequence ofinstructions, register 5 will hold theaddress 40E0H. The LDI instructionhas been described earlier in theseries. Two other instructions, INC EtDEC, provide a quick means ofchanging this address to adjacent ornearby memory locations, eg two INCinstructions will advance R5 toaddress 40E2H.

Each of the register instructions is asingle -byte op -code which can befound in the instruction table. Clearly,since these instructions can be appliedto any of sixteen registers, there mustbe sixteen possible codes in eachcase. Happily, these codes can easilybe worked out by, firstly, looking upthe first digit of the hex op -code andthen using the register number as thesecond hex digit. For example, theinstruction 'DEC' has a quoted op -code of '2N' where 'N' is the registernumber, so that 'DEC R9' has the op -code '29H'. In fact, any of the 1802instructions which make use of the16 -bit registers can be worked out inthis way.

Memory Reference

These instructions allow transfers ofdata bytes between the accumulatorand memory locations. You havealready met the two -byte instructionLDI (Load Immediate), wherein thebyte stored after the op -code is copiedinto the accumulator. There are fourother instructions that will also loaddata from memory into accumulator,and which illustrate the differentaddressing modes of the MPU:

Memory Immediate mode (LDI): hasbeen described already.

Register Indirect (LDN): the memorybyte pointed to by register N isloaded into the accumulator.

Indexed Addressing mode (LDX):the memory byte pointed to by theindex register RIX) is loaded intothe accumulator.

Register Indirect with auto -increment (LDA): as RegisterIndirect but the register isautomatically incremented by oneafter loading the data byte.

Indexed Addressing with auto -increment (LDXA) - as withIndexed Addressing but the indexregister is automaticallyincremented after the loadoperation.

All but the LDI instruction are asingle byte.


III Popular Computing

MEMORY ADDRESS LINES

AO Al A2 A3 A4 A5 A6 A7

I/O REQUESTS

CONTROL STATEI/O FLAGS Is CODES

,:cE 0

rE §

'MITT? TT"TTTYTTMMUX

1161

rINCR/DECR

(16)

DO

D1

D2

D3

D4

05

D6

D7

A 116)

R0.1 R0.0

R1.1 R1.0

R2.1 R2.0

(8)

R9.1

RA .1

RE.1

RF 1

RA.0

RE.0

RF.0

CONTROL LOGIC

REGISTERARRAY R

4M14 gC1111-E E

CF 111

AC IS)

BIDIRECTIONAL DATA BUS

ALU

N 141

0 FF -00

1 141

P141

T IS)

X (4)

Figure 1. The 'internal architecture' of the 1802 microprocessor.

TIMING

0N2 0

2N1 2

0NO

00

16 V cc

'4-C) VDDC1 vss

The immediate mode of addressingallows data to be placed in theprogram during writing, as analternative to setting up an addresspointer and then loading the data bytefrom elsewhere in memory. RegisterIndirect and the very similar IndexedAddressing modes are the mostpowerful and often used; they permitseveral data blocks within memory tobe speedily accessed, using the largenumber of address registers available.The auto -increment addressing modesare useful when a program isoperating on a large array of datastored successively in memory, wherethe improved execution time is avirtue.

There are two instructions whichallow storage of the accumulator inmemory; STR uses Register Indirectaddressing and STXD is IndexAddressed with auto -decrement.

The instructions described so farprovide a flexible system fortransferring data between memorylocations and the main 1802registers. A few of these instructionsleg STXD) may, for the moment,seem obscure, however they comeinto play in more advancedprogramming techniques.

Logic Operations

Most readers will be familiar with thelogic functions 'OR', 'AND' and'Exclusive OR' (EX -OR) which operateon two single -bit operands to producea single bit result. The 1802 has logicinstructions, of this form, whichopeate on a memory byte and the

IDL 00 Wait for interrupt or SHLC 7E Shift left with carry RET 70DMA request (accumulator)

LDN

INC

ON

1N

Load accumulator, viaregister NIncrement register N

SMBI 7F Subtract with borrow,immediate data fromaccumulator

DIS 71

DECBRBQ

2N3031

Decrement register NBranch alwaysBranch if Q= 1

GLO 8N Load accumulatorwith low order byte ofregister N

LDXA 72

BZ 32 Branch if accumulator GHI 9N Load accumulator

BPZ

B1B2

33

3435

is zeroBranch if positive orzeroBranch if EF1 =0Branch if EF2 = 0

PLO AN

with high order byte ofregister NStore accumulator inlow order byte ofregister N

STXD 73

B3B4BRN

363738

Branch if EF3 = 0Branch if EF4 = 0Branch never

PHI BN Store accumulator inhigh order byte ofregister N

ADC 74

BNQ 39 Branch if 0= 0 LBR CO Long branch always SDB 75BNZ

BM

3A

3B

Branch if accumulatornot zeroBranch if minus

LBQLBZ

C1C2

Long branch if Q = 1Long branch ifaccumulator is zero

BN 1BN2

3C3D

Branch if EF1 = 1Branch if EF2 = 1

LBPZ C3 Long branch if positiveor zero

SHRC 76

BN3BN4

3E3F

Branch if EF3 = 1Branch if EF4 = 1

NOP C4 No operation (longskip never)

SMB 77

LDA 4N Load accumulator, viaregister N, then

LSNLSNZ

C5C6

Long skip if Q = 0Long skip if

increment register N accumulator not zero SAV 78STR 5N Store accumulator in

memory, via register NLSMILSKP

C7C8

Long skip if minusLong skip always

IRX

OUT

60

6N

Increment indexregisterIN = 1,71 Transfer via

LBNQLBNZ

C9CA

Long branch if O.= 0Long branch ifaccumulator not zero

MARK 79

index register to LBMI CB Long branch if minus REQ 7Aoutput device N, then LSIE CC Long skip if IE = 1 SEQ 76

68

increment indexregisterIllegal instruction

LSQLSZ

CDCE

Long skip if Q = 1Long skip ifaccumulator zero

ADCI 7C

INP 6N IN = 9,F) Transfer toaccumulator frominput device IN -81,then store via indexregister

LSPZ

SEP

SEX

CF

DN

EN

Long skip if positive orzeroSet program counterto register NSet index register to

SDBI 7D

Table 1. The instruction set of the 1802.

Return from interruptor subroutineReturn from interruptwith interruptsdisabledLoad accumulator, viaindex register, andincrement indexregisterStore accumulator inmemory, via indexregister, anddecrement indexregisterAdd with carry, viaindex register, toaccumulatorSubtract with borrow,accumulator frommemory, via indexregisterShift right with carry(accumulator)Subtract with borrow,memory fromaccumulator, via indexregisterSave T register inmemory, via indexregisterPush X, P registers onstack, via indexregisterReset Q flag to zeroSet Q flag to oneAdd with carry,immediate data toaccumulatorSubtract with borrow,accumulator fromimmediate data

LDX FO

OR F1

AND F2

XOR F3

ADD F4

SD F5

SHR F6

SM F7

LDI F8

ORI F9

ANI FA

XRI FB

ADI FC

SDI FD

SHL FESMI FF

register NLoad accumulator viaindex registerLogic OR, memorywith accumulator, viaindeic registerLogic AND, memorywith accumulator, viaindex registerLogic XOR, memorywith accumulator, viaindex registerAdd memory toaccumulator, via indexregisterSubtract accumulatorfrom memory, viaindex registerShift rightaccumulatorSubtract memory fromaccumulator, via indexregisterLoad accumulatorwith immediate dataLogic OR, accumulatorwith immediate dataLogic AND,accumulator withimmediate dataLogic XOR,accumulator withimmediate dataAdd to accumulator,immediate dataSubtract accumulatorfrom immediate dataShift left accumulatorSubtract fromaccumulator,immediate data


Popular Computing

A B A.B A B A+B A B AC)B

0 0 0 0 0 0 0 0 0

0 0 0 0

0 0 0 0

0

TRUTH TABLEA AND B

0 0 1 0 1 1 1 1

0 0 0 0 0 1 0 0

0 0 0 0 0 1 0 0

(2FH) AND (04H) = 04H

2FH

04H

TRUTH TABLEA OR B

0 0 0 0 0 0 0 0

0 0 0 0 0 1 0 0

0 0 0 0 0 1 0 0

(2FH) OR (04H) = 2FH

OOH

04H

TRUTH TABLEA EX -OR B

0 0 1 0 1 1 1 1

1 1 1 1 1 1 1 1

1 1 0 1 0 0 0 0

(2FH) EX OR (FFH) = EOH

2FH

FFH

Table 2. Above, the truth tables for AND, OR and Exclusive -OR functions. Below;AND, OR and Exclusive -OR operations performed on a data byte.

CARRYFLAG

CARRYFLAG

0 0

5CH = 93 DECIMAL

0

SHIFTLEFT

SHIFTRIGHT

CARRYFLAG

BAH = 186 DECIMAL

0

2DH = 46 DECIMAL

Table 3. A shift left is equivalent to 'multiply by two' and shift right performs'divide by two'.

accumulator byte to produce a resultin the accumulator, doing so on a bit -by -bit basis. For each of thesefunctions, there is an instruction (tofetch the memory byte) in ImmediateAddressing mode and an instruction inIndexed Addressing mode. The needfor these instructions in a controlsystem is obvious, however they havean important but not so apparentsecond use, that of 'bit manipulation'.For example, suppose the accumulatorhad the initial value of B7H and thenwe executed the instruction ANI $OF(AND Immediate) the result would be07H, in the accumulator. The effecthas been to mask the first four bits ofthe data byte. Looking at the 'AND'function analytically, we can say thatthe effect of a logic zero in a particularbit of one operand has the effect ofresetting, to logic zero, the state ofthe corresponding bit in the otheroperand. This can be used for testingthe state of an individual bit within abyte (you shall see what is meant bythis later). For example, ANI $04 willmask out all but bit 2 of theaccumulator data (04H = 00000100binary). Table 2 shows that the 'OR'function has a bit -setting capability,whilst the 'Exclusive Or' function maylogically invert bits.

The remaining logical operations fallin to the category of Shifts andRotates, and are single operandfunctions operating on theaccumulator. 'SHL' (Shift Left), forexample, causes all the bits ofaccumulator data to move one placeleft (bit 0 becomes bit 1 etc; forexample, after SHL, 0101 1 101becomes 101 1 1010. A fewcalculations should convince you that

this operation is equivalent to a'multiply by two' (but see Table 3, ifin doubt), and the primary use of suchan instruction is to permit arbitrarymultiplications and divisions, inconjunction with the arithmeticfunctions (Subtract and Add).Similarly, the Shift Right instruction,'SHR', is, in effect, a 'divide by two'.Note that the MSB, in the case ofSHL, and LSB in the case of SHR, areshifted out of the accumulator into theone -bit carry -flag, CF. The setting ofthe carry -flag indicates that thedivision or multiplication by two is notquite right; it may be looked upon as aarithmetic carry (multiplication) or as aremainder (division). At the other endof the accumulator, a zero is copied induring shift operations.

There are two other instructions(RSHL, RSHR), 'ring shifts' or'rotates', in which the previous stateof CF, rather than a zero, is shiftedinto the 'trailing' end of theaccumulator. In conjunction withordinary shifts, these instructionsallow the shift operation to beextended to multiple byte words.

Arithmetic Operations

The 1802 has only two basicarithmetic operations, Add andSubtract, and they are as simple asyou might guess. The only difficulty iswhen the result goes above FFH orbelow OOH. A useful model, here, isto consider the accumulator a 'binary'bicycle mileometer. For example,when adding 07 to FD theaccumulator counts up to FF thencycles back through 00, finallyarriving at the value of 04 after seven

counts. Similarly during subtraction,the accumulator counts down to 00then switches back to FF andcontinues to decrement. In bothcases, the carry flag indicates that theresult has 'overflowed' or'underflowed'. If you look at the otherAdd and Subtract instructions in Table1 you will find that there areinstructions for 'accumulatorsubstracted from memory' as well as'memory subtracted fromaccumulator' (the result always falls inaccumulator) together with Add andSubtract with Carry/Borrowinstructions (again, to cope withmultiple -length arithmetic) all of theseinstructions use the two basicaddressing modes of memory,Immediate and Indexed.

Branch instructions

Theoretically, any program could bewritten with a sequential string ofarithmetic, logic and transferinstructions. However, if you considerprograms that require operations to beperformed many thousands of timesover, this prospect becomes plainlyridiculous. Branch instructions allowprogram control to be transferred to anew address by directly altering theprogram counter, rather than the usualincrement after each instruction. Thesimplest branch instruction is 'BR $XX'where 'XX' is the byte following theop -code. In executing this instruction,the byte 'XX' is copied into the low -order byte of the program counter, sothat execution continues with theinstruction found at that address. Theexampled below shows how arepetitive loop can be set-up using thisbranch instruction.

0000H 1F INC RF;increment register 'F'

0001 H 30 00 B R $00;branch back to 0000H

Normally, loops are constructed toterminate when certain conditions areset, and so a number of ConditionalBranch instructions are provided.Conditions, such as the state of thecarry flag or whether the accumulatoris zero, are tested by the Branchinstruction and a branch takes placeonly if the condition is met, otherwiseexecution continues with the nextinstruction. Suppose, for example, wewished to increment the 'F' register100 times:

0000 F8 64 LDI $64;100 = 64H

0002 Al;initialise

PLO R1counter with one hundred

0003 1 F INC RF;increment RF

0004 21 DEC R1;decrement counter

0005 81 GLO R1;bring count into accumulator fortesting


Popular Computing

0000 F8 20 LDI $20 ;load 20H in accumulator 002E 52 STR R2 et last digit to zero0002 B2 PHI R2 ;put in high byte of R2 002F 22 DEC R2 ;R2 = 207AH0003 F8 77 LDI $77 ;load 77H 0030 02 LDN R2 ;load third digit (tens of minutes)0005 A2 PLO R2 ;put in low byte of R2 0031 FC 01 ADI $01 ;add 1

;2077H is centre screen address 0033 52 STR R2 ;put back in display0006 F8 00 LDI $00 0034 FF 06 SMI $06 ;subtract 6 to test if greater than 50008 52 STR R2 ;store in memory pointed to by R2 0036 3A 19 BNZ PO ;go to delay loop if less than 60 minutes0009 12 INC R2 ;R2 = 2078H 0038 52 STR R2 ;set to zero if 6000A F8 00 LDI $00 0039 22 DEC R2 ;R2 = 2079H; ":"000C 52 STR R2 003A 22 DEC R2 ;R2 = 2078H000D 12 INC R2 ;R2 = 2079H 003B 02 LDN R2 ;fetch second digit (hours)000E F8 3A LDI $3A 003C FC 01 ADI $01 ;add 10010 52 STR R2 003E 52 STR R2 :put in display0011 12 INC R2 ;R2 = 207AH 003F FF OA SMI $0A ;subtract 10 to test for 9 hours0012 F8 00 LDI $00 ;"0" 0041 32 52 BZ P1 ;goto to P1 if hours greater than 90014 52 STR R2 0043 02 LDN R2 ;if not, load hours digit again0015 12 INC R2 ;R2 = 207BH 0044 FF 03 SMI $03 ;subtract to test if 3 hours0016 F8 00 LDI $00 0046 3A 19 BNZ PO ;if not, go back to delay loop0018 52 STR R2 display now shows "00:00" 0048 22 DEC R2 ;R2 = 2077H0019 F8 7B PO LDI $7B ;start of delay loop 0049 02 LDN R2 ;load first digit (tens of hours)00113 A2 PLO R2 ;sets R2 to point to last digit of display 004A FF 02 SMI $02 subtract to test if 20 hours001C F8 00 LDI $00 ; 004C 3A 19 BNZ PO ;if not go to delay loop001E A5 PLO R5 004E 52 STR R2 ;if 23 hours, set tens to zero001F F8 OF LDI $OF 004F 12 INC R2 ;R2 = 2078H0021 B5 PHI R5 ;OFOOH sets the delay period 0050 02 STR R2 ;set hours to zero0022 25 LO DEC R5 ;start of loop LO 0051 30 BR PO goto to delay loop0023 95 GI -11 R5 ;load accumulator with high byte of R5 0052 52 P1 STR R2 ;set hours to zero0024 3A 25 BNZ LO go back if not zero 0053 22 DEC R2 ;R2 = 2077H0026 02 LDN R2 ;fetch last digit 0054 02 LDN R2 fetch first digit (tens of hours)0027 FC 01 ADI $01 ;add 1 0055 FC 01 ADI $01 ;add 10029 52 STR R2 ;put in display 0057 52 STR R2 ;put in display002A FF OA SMI $OA ;subtract 10 to test if greater then 9 0058 30 BR PO go to delay loop002C 3A 19 BNZ PO go back if not zero

Table 4. A simple program to simulate a 24 -hour clock. The timing is set by the data byte loaded in lines 001 CH to 0021 H;OFOOH gives a delay of approximately one minute, and may be adjusted for more accurate timing.

0006 3A 03 BNZ $03;branch to 0003 if count not yetzero

0008next instruction

Notice that loop counters are usuallydecremented to zero rather thanincremented from zero, because it iseasier to test a zero condition than acontent of 64H. Besides loops,conditional branches are used totransfer control to different sections ofa program, according to certainconditions. If, for example, a controlsystem required the illumination of anLED in the event of an 'underflow'following the subtraction of twovariables, then a conditional branch'BM' (Branch if Minus) immediatelyfollowing the Subtract instructioncould transfer control to a section ofcode designed to light the LED.

There are other Branch andConditional Branch instructions thatpermit a program counter jump toanywhere within the memory system.These are 'long branches' and have atwo -byte address, following the op -code, which is copied into theaccumulator, eg LBR $A007.Obviously these take longer toexecute, and take up more memoryspace.

The Skip instructions of the 1802may be considered a luxury, in thatthey can always be replaced by one ormore Branch instructions simply bywriting the program in a slightlydifferent way. An example of the skipinstructions is:0005 CE LSZ

;long skip if zero (skip 2 bytes)

0006 . . . . . .

0007 FC 01 ADI 01;add 1

0009 C4 NOP;continue

000A . . .

The instruction to add one to theaccumulator is executed only if theaccumulator was non -zero.

Control InstructionsThere are two instructions, in thisgroup, that we are particularlyconcerned with, namely SEP and SEX(no comments, please!). As describedin earlier issues, these twoinstructions define a particular 16 -bitregister as program counter and indexregister, respectively.

Often, large programs will containsections of code which occurrs manytimes, and it is useful to be able tocondense this code into one routine or'subroutine' to which control can betransfered from various points in theprogram. The greatest difficulty withthis scheme is finding a method ofstoring the address of the programcounter before control is transfered tothe subroutine so that, when thesubroutine has completed, control canbe returned to the correct point in themain program. How this is achievedwith the 1802 is outlined below:0000 F8 10 LDI $10

;load immediate, 10H.

0001 B1 PHI R1;store in high byte of register 1.

0002 F8 00 LDI $00;load immediate, OOH

0003 Al PLO R1;store in iow;byte of R1; R1 nowpoints to subroutine.

0030 D 1 SEP R1;go to subroutine; program counteris now Rl.

0050 D 1;go to subroutine.

SEP R1

OFFF D 0 SEP RO;return to main program; programcounter is now RO; R1 incrementsto 1000H.

1000;start of subroutine

100F C 0 LBR OFFF;long branch to OFFF;

Note that it is necessary to reset thesubroutine pointer (register R1) to thesubroutine address (1000H) beforereturning to the main programbecause, since it is the programcounter, R1 is automaticallyincremented after each instruction. Areturn at, say, 100FH would leave R1pointing to 1010H. Instead, a jump ismade to the address just before thestart of the subroutine; control isreturned to RO and R1 automaticallyincrements to 1000H. The other catchis that the subroutine must not useRO, else the return address will belost!

It is possible to have manysubroutines, each with a differentpointer register, for as many registersas you can spare; it is also possible tonest subroutines (call a subroutinefrom a subroutine) provided thatcareful track is kept of the registersused. Often, each subroutine will haveits own data space in memory, andthis can be quickly accessed by asubroutine by reserving a register topoint to this data area and defining itas the index register (SEX), on call.

Much of this may seem veryacademic, but it is a necessaryrequirement before useful programscan be written. We'll finish, however,by listing a quite complex practicalprogram (Table 41. The commentsshould prove a sufficient explanation.

Next time we will look at thelargely hardware -orientatedinstruction, so far ommitted, when wediscuss I/O interfaces. HE


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8 pin 25p 18 pin 50p 24 pin 70P14 pin 35p 20 pin 60p 28 pin 801716 pin 40p 22 pin 65p 40 pin 100P

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FND500 90p 9368 2506E111440 1 25p8E1179 2, TIP 29C 40p 2522194 25P

252222/5 25p

1000LC1 306 1504

24 4000 4543A 200V 60p

DC ,240V AC 12501

74365 50p74366 50p

40094010 249

11p!

F5D507 90pMAN3640 175p

937040N6118

30093z2P

RF R80/ I 25p81096 1804

TIP304 35pTIP30C 40p 2523596 25p

262484 300

2SC 1307 150p2SC 1957 911p

30 6000 72pAA 1000 95p LOUD.74367 54

74368 50040114012 1660

MAN4640 200p 11006184 320P BFX29 40pBF030 274

TIP31A 40pTIP31C 45p

2,,2SCrtSp

262904' 5 30P

1969 195p2SC2028 1202SC2029 250P

dA 4000 104

664 8°P

SPEAKERS

S'eBFX84/ 5 40pi

TIP324 OP 2629013A 30p 350, Z ,/,'t 41a° "111P

2

645 80pBFX86/7 27p

I

TIP32C 45P774334

2629074 30p262926

2SC2335 2509 I0A 4000 200 21/2- 85 80P

IIIBFX88 27p 70p 90

263053 30P25C2612 250P35128 120p 2SA 4000 0004

'

2' BR 9011/2 ' 811 1 P

AIL ORDERS TO: 17 BURNLEY ROAD, LONDON NW10 lED PLEASE ADD 40p P&P Er 15% VAT (Export no VAT)HOPS AT: 17 BURNLEY ROAD, LONDON NW10 Government, Colleges, etc. ORDERS WELCOME

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Lit

Feel like sounding off?Then write to the Editor stating your Point Of View!

The most interesting Point of View,this month is from Mr. A.G. Meakins,who comments on writing style of cer-tain points mentioned in "Scaling theHiFi Heights" (HE January issue.

Unimpressed

Dear Sir,Your cover puts H.E. as having "a downto earth approach to electronics", but it'sa pity you don't impress this on yourwriters, who use long words like"parameters" when "limits" would do.

In Scaling the HiFi Heights, yourwriter should come down to earth. Whenhe states that £400 is the loweststarting point, he is way off target. Iwould suggest that, for most HE readers,that would be the extreme top limit.

Another piece of pie in the sky thatcomes from his pen is the wattage of theamplifier. I have a room of 1200 cubicfeet, my amplifier is 14 W per channeland with the volume control at 30%, Ican comfortably fill my room with amplepower left to take the peaks. Perhapsyour writer destroyed his hearing in adisco, when young.A.G. MeakinsRichmond,Surrey.

First, this letter was attached to a latereturn of our Reader Survey, also fromthe January issue. We have sincechanged our masthead slogan but not,we hope, our approach.

Every article which appears in HE iscarefully edited to ensure that it caneasily be understood. However, this mustnot be overdone; an article consistingentirely of words of one syllable wouldnot only be an insult to our readers, itwould also be boring and, most likely,inaccurate because it is not alwayspossible to find a 'short word' tosubstitute for a long one. Remember thatelectronics is a technical subject, thatcertain words have very precisemeanings and, therefore, cannot bechanged.

In fact, the word 'parameter' is onefor which there is no suitable substitute.It means " . . . a constant in the caseconsidered but varying in differentcases." (C.O.D.). In general usage, aparameter is a factor by which a deviceor property is defined or measured, forexample the small -signal parameterswhich define transistor operation undercertain conditions. A limit is a border orboundary line or point, and not the samething at all.

The suggestion that £400 is the toplimit of spending for HE readers is anexample of a limit that is somewhat

arbitrary. True, it is a lot of money, but asystem costing this much or more is notout of the question. It is possible to buildup a very expensive hifi over a period ofyears buying units one at a time. Also,the figure was mentioned as the lowesttotal " . . . for serious sound pursuit."and considering that it is possible tospend over £1000 on audio gear, a£400 system only just qualifies as hifi!

For example, a 14 W per channelamplifier, while adequate for normallistening, would not satisfy a dedicatedhifi fanatic. It has to be said that opinionson listening levels are extremelysubjective (one man's pleasure isanother's pain), nevertheless, all otherfactors (type of programme material, thesize of the room and acoustic treatment,the efficiency of the speakers etc) beingequal, a large amplifier will come closerto reproducing the original dynamic rangeof music, at comfortable levels, than asmall amp. This, after all, is the goal ofhifi - accurate reproduction of theoriginal music.

Finally, it's worth pointing out thatconcert musicians, sitting in the middle ofan orchestra which can produce soundpeaks of up to 100 dB SPL, do notusually destroy their hearing. There is noreason why these levels, accuratelyreproduced, should destroy the hearingof a listener in the middle of his loungeroom. What the neighbours think isanother question!

No KittingDear Sir,I have been trying to get you by phone toask about the LED VU Meter project fromthe November '81 issue. I waswondering if the kit you did for it includedthe integrated circuit U267B BargraphDriver.

If so, could you please send a full kitfor the VU Meter and when I receive it Iwill send on the money.S. Harvey,Cleethorpes,South Humberside.

Sorry, but we do not sell kits orcomponent parts for HE projects except,of course, the printed circuit boardswhich are advertised in each issue.However, there are companies whosupply kits for our projects and theyusually advertise in the magazine. One ofthem should be able to help you.

This reply should also answer S.N.Heider of Dedridge, Livingstone, WestLothian, who wrote with a similarenquiry.

Trying to 'phone us is not a goodidea - we cannot, unfortunately, accept

telephone enquiries because of the timeinvolved. There simply aren't enoughhours in a day! One other thing; mostcompanies would want to see the colourof your money before sending the goods.

'Diana' Hunted

Dear Sir,Please will you let me have a copy ofyour article, from the September 1981issue of Hobby Electronics, on the DianaMetal Detector. I work at Plessey Radioat Cowes, here on the Isle of Wight, as atest engineer. Our librarian hascontacted on my behalf our local libraries,Portsmouth and Southampton librariesand, finally, the British Museum, for acopy of the issue but all without success.

I hope you will be able to assist me.G.M. Store,Ryde,Isle of Wight.

The quickest and easiest method forobtaining most back issues of HE is towrite to our Backnumbers Department -see the advertisement in this or anyrecent issue. It certainly beats chasingaround libraries and museums.

Meanwhile, interested readers mightlike to know that the add-on VCO for'Diana' has been finalised and will appearin the near future.

Into Electronics Lost

Dear Sir,Recently a friend loaned me one of yourbooks, 'Into Electronics Plus',published in 1979. I found it of greatinterest and wondered if you couldadvise whether it is still possible toobtain a copy, and the price.

Three years since publication is along time, I realise, but if a copy couldbe located I would very muchappreciate it.D. C. Holmes,Bury St. Edmunds,Suffolk.

Regretably, this book is no longeravailable. It has been 'out of print' forsome time. However, you might find'Electronics - It's Easy' a suitablealternative; it provides a slightly lessdetailed, broader introduction toelectronics. It is available from ourSpecials Department, 513, LondonRoad, Thornton Heath, Surrey CR46AR, for £4.95 including p&p; don'tforget to ask for it by name! HE


Kit includes tape transport mechanism, ready punchedand back printed quality circuit board and all electronicparts. i.e. semiconductors, resistors, capacitors, hard-ware, top cover, printed scale and mains transformer.You only supply solder andhook-up wire.Featured in April issue P.E.Reprint 50p. Free with kit.

Self assembly simulatedwood cabinet -Only £4.50 + £1.50 p&p.

£32.+ £2.75 p&p.

'ELECTRONICS ONLY! 1Ideal for updating your existing cass-ette. Includes pcb diagram, all semi-conductors, IC's, Capacitors, resistors. +£1.40p&p

HIFl STEREOCASSETTE

RECORDER KIT NOISE REDUCTION SYSTEM

AUTO STOP TAPE COUNTER SWITCHABLE E.Q.

INDEPENDENT LEVEL CONTROLS.IN V.U. METER

C.u\A' & FLUTTER 0 1 RECORD PLAYBACK I.C. WITH

ELECTRONIC SWITCHING FULLY VAR)ABLE RECORDING BIAS FORACCURATE MATCHING OF ALL TAPES

STEREO AMPLIFIER KIT 125W HIGH POWER AMP MODULE

o

1 1' Featuring latest SGS/ATES TDA 2006 10 watt outputIC's with in-built thermal and short circuit protection. Mullard Stereo Preamplifier Module. Attractive black vinyl finish cabinet, 9"x 8'/."x 3%"

(approx). 10+10 Stereo converts to a 20 watt Disco amplifier.To complete you just supply connecting wire and solder.Features include din input sockets for ceramic cartridge,microphone, tape or tuner. Outputs - tape, speakers andheadphones. By the press of a button it transforms intoa 20 watt mono disco amplifier with twin deck mixing.The kit incorporates a Mullard LP1183 pre -amp module,plus power amp assembly kit and mains power supply.Also features 4 slider level controls, rotary bass andtreble controls and 6 push button switches. Silver finishfascia with matchingknobs and contrastingcabinet. Instructionsavailable, price 500.Supplied FREE with kit. + £2.90 p&p.SPECIFICATIONS: Suitable for 4 to 8 ohm speakersFrequency response 40Hz - 20KHzInput sensitivity P.U. 150mV. Aux. 200mV.

Mic. 1.5mV.Tone controls Bass L12db @ 60Hz

Treble t..12db @ 10KHzDistortion 0.1% typically @ 8 wattsMains supply 220 - 250 volts 50Hz.8" SPEAKER KIT Two 8" twin cone domesticspeakers. £4.75 per stereo pair plus £1.70 p&p. whenpurchased with amplifier. Available separately £6.75 &£1.70 p+p.

E16.50

PRACTICAL ELECTRONICSCARRADIOKITsERIEs II

2 WAVE BAND, MW - LW --""ollir Easy to build. 5 push button tuning. Moderndesign. 6 watt output. Ready etched and punchedPCB. Incorporates suppression circuits.All the electronic components to build the radio, yousupply only the wire and the solder, featured in PracticalElectronics. Features: pre-set tuning with 5 pushbutton options, black illuminated tuning scale. TheP.E. Traveller has a 6 watt output neg. ground and in-corporates an integrated circuit output stage, a MullardIF Module LP1181 ceramic filter type pre -aligned andassembled, and a Bird pre -aligned push button tuning unit.Suitable stainless steel fully retract-able aerial (locking) and speaker(6"x4"app.) available as a corn -

ate kit. £2.50/pack + £1.50 p&p. + £2.00 p&p. A

BIRD AUDIOSTEREO CARRADIO BOOSTER

To boost your car radio or radiocassette to 15W r.m.s. per channel.

£9.951+ f1.50 p&p.

KIT: e10.50 BUILT:e14.25+f1.15 p&p + £1.15 p&p.

The power amp kit is a module for high power applicat-ions - disco units, guitar amplifiers, public addresssystems and even high power domestic systems. The unitis protected against short circuiting of the load and issafe in an open circuit condition. A large safety marginexists by use of generously rated components, result, ahigh powered rugged unit. The PC board is back printed,etched and ready to drill for ease of construction andthe aluminium chassis is preformed and ready to use.Supplied with all parts, circuit diagrams and instructions.ACCESSORIES: Suitable mains power supply kit withtransformer: £7.50 plus E3.15 p&p.Suitable LS coupling electrolytic: £1.00 plus 25p p&p.

HI-FI SPEAKERSAT BARGAINPRICESGOODMANS TWEETERSBohm soft dome radiator tweet-er (3'4"sq.) for use in up to 40Wsystems; with 2 element crossover.

£3.50 each (p&p £11 or £5.95 pair (p&p £2).

P.E. STEREO TUNER KITThis easy to build 3 band stereo AM/FM tuner kit is de-signed in conjunction with Practical Electronics (July 81issue). For ease of construction and alignment it incorp-orates three Mullard modules and an I.C. IF. System.FEATURES: VHF, MW, LW Bands, interstation mutingand AFC on VHF. Tuning meter. Two hack printedPCB's. Ready made chassis and scale. Aerial: AM - ferriterod, FM - 75 or 300 ohms. Stabalised power supplywith 'C' core mains transformer. All components supp-lied are to P.E. strict specification. Front scale size: 10/"x 2'4" approx. Complete with diagram and instructions.

£17.95Plus £2.50 p&p.

TV SOUNDTUNER KIT

E11.45

Self assembly simulated woodcabinet sleeve to suit tuner only.Finish size: 11%"x 8`4"x3'4".£3.50 Plus £1.50 p&p.

+£1.50 p&p.

As featured in E.T.I. December '81 issue. Kit of partsincluding PCB, UHF tuner and selector switch with allcomponents excluding case.

Transformer £1.50 + £1.50 p&p (p&p free on trans-former if ordered with kit). Ready built LP1183 Mod-ule for simulated stereo operation. £1.95 + 75p p&p.

SPECIFICATIONS:Max. output power (HMS): 125W.Operating voltage (DC): 50 - 80 max.Loads: 4 - 16 ohms.Frequency response measured @ 100 watts: 25Hz -20KHz.Sensitivity for 100 watts: 400mV @ 47K.Typical T.H.D. @ 50 watts, 4 ohms: 0.1%.Dimensions: 205 x 90 and 190 x 36 mm.

35 WATT MICRO 2 -WAY SPEAKER SYSTEMUnit comprises one 50w (4"epp.) Audaxsoft dome tweeter HD100. And one5" Audax bass/midrange 35wdriver HIFI IJSM.Complete with 2element crossover.Total impedanceof system 4 ohms.

£7.95PER SET + £2.70 p&p.

SPECIAL OFFER! TUNER KIT PLUS: Matching I.C. 10 watt per channel Power amp kit. Mullard LP1183 built pre -amp, suitable for ceramic pick-up and aux. inputs . Matching power supply kit withtransformer. Matching set of 4 slider £21.95controls for bass, treble and volumes. + £3.80 P&P.

MONOMIXERAMP

50 WATT Six individually mixed inputs for two pick ups(Cer. or mag.), two moving coil microphones and twoauxiliary for tape, tuner, organs, etc. Eight slider controls- six for level and two for master bass and treble, fourextra treble controls for mic. and aux inputs. Size: 13'4"x6%"x334"app. Power output 50 wattsR.M.S. for use with 4 to 8 phm spkrs.Attractive black vinyl case withmatching fascia & knobs. Ready built. + £3.70 p&p.

9.95All mail to:21E HIGH STREET, ACTON, W3 6NG.Note: Goods despatched to U.K. postaladdresses only. All items subject to avail-ability. Prices correct at 30/8/82 andsubject to change without notice.Please allow 7 working days from receiptof order for despatch. RTVC Limitedreserve the right to update their productswithout notice. Send S.A.E. for full list.

ALL CALLERS TO: 323 Edgeware Road,London W2. Tel: 01-723 8432. 9.30 - 5.30,closed all day Thurs. Prices include VAT.Telephone or mail orders by ACCESS arewelcomed.

R C32 Hobby Electronics, September 1982

VIN THE constant search for new ways toensure Hobby readers get the best dealwhen buying components, we are in theprocess of re -thinking Buylines. Nextmonth, we will be presenting acomprehensive survey of componentsuppliers and hope to provide a specialordering service to supplement this page.For this month, though, we areintroducing an improved system forfinding sources of hard -to -get items, aswell as attempting to produce moreaccurate estimates of building costs. Wewould be interested to know what youthink of the changes.

Signal LightsNot much here to trouble theconstructor. The TTL ICs can all beobtained from Watford or Technomatic.Remember, it's a good idea to usesockets just in case you have to replaceany faulty chips; most companies sell thecomplete DIL socket range at areasonable price, so why not buy a fewas spares?

The three differently coloured LEDs -red, amber (yellow) and green - can be

11111111111

1111111

bought from Rapid and TK, or for a widerange of shapes try Ace Mailtronix.

The only source we can find for one-off Y8 watt resistors is Maplin, thoughmost suppliers sell 1/4 watt types that willdo just as well.

Cost is £2.60 for the junction moduleand £3.50 for the main module (inclusiveof PCBs).

'Junior' Slot CarIt was quite difficult finding a source forthe low value (OR47) 1 watt resistor.This was due to the fact that mostcompanies sell these values in 21/2 wattpackages only. However, Greenweldcame to the rescue and they can alsosupply the unusual 10 pin metal can 723regulator IC (LM123). An alternativesource for this IC is ElectroValue.

The MJ2955 is stocked by mostpeople, but the cheapest source wefound was Ambit, whose quoted price is25% lower than their nearestcompetitor!

The best case for your controller willdepend on your particular slot -car set-up.

However, Newrad do a range of highquality low - cost cases, should you findno room on your present layout. Costexcluding the case, should be about £5for each board with rectifiers andindicators.

ZX PCBQuite a useful little board, this, thoughyou may be unfamiliar with a couple ofthe components. The low -powerSchottky ('LS') TTL integrated circuitsare stocked by both Technomatic andWatford, though most other retailers sellthem at widely differing prices. Theappropriate DIL sockets can be boughtfrom either Bi - Pak or Greenweld.

The only supplier of the exact SILplug -pin strip was Ambit, though Maplindo a 6 -way and 4 -way version makingup the required 10 -way strip.

Finally, the edge plug and matchingconnector (double sided) are to be foundin the RS range (codes 468-709 and467-021 respectively) and must beordered from your supplier. These are43 -way connectors with the polarisingpin at position 7, and must be carefullysawn to convert them to 23 -way, withthe polarising pin at position 3. You maybe able to find other sources for the edgeconnector, probably not with thematching plug, but it's worth lookingaround. Cost of the board, using thespecified components, will be £8 - plusthe edge connector/plug combination ofyour choice.

Do yourself a favour. Make 1982 the year you start to take HobbyElectronics, regularly. Delivered fresh every month.

SUBSCRIPTION ORDERFORM

Cut out and SEND TO :Hobby Electronics Subscriptions513, LONDON ROAD,THORNTON HEATH,

SURREY,ENGLAND.

Please commence my personal subscription to HobbyElectronics with the issue.

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JHobby Electronics, September 1982 33

Project

BreadboardsDesign and build your own tone controls.

JUST one project for this month'sBreadboard, but it's a winner - highperformance tone controls in a simplearrangement that you can modify forany application. The controls are bas-ed on a standard op -amp circuit, usingthe TL081. This has high impedanceFET inputs and a high slew rate, enabl-ing it to operate over a wide band of fre-quiencies. The circuit also allows you toexperiment with different componentvalues.

Talking of experimenting, we areoffering £5 to any reader whose designis original and/or ingenious enough forpublication. All you need to supply is acircuit diagram, a breadboard layout anda brief description of how the circuitworks plus any ideas for modificationsor experiment. Put them all in anenvelope marked 'Breadboards' and ad-dressed to us - remember to enclosean SAE if you'd like the contents return-ed.

Gain ControlledIt is just about thirty years since thepublication of the first practical circuitfor varying bass and treble independent-ly within a single network, without usingswitches. It is known as a Baxandall cir-cuit, after its inventor, and is stillused, more or less modified, in mostaudio equipment.

The simplest way to understandhow the circuit (Figure 1) operates is tolook at what's happening to the gain ofthe op -amp at different frequencies.The gain is controlled by the feedbackresistance from pin 6 to pin 2 of ICI , viathe tone control network consisting ofRV1, R2, R3, C3 and RV2, R5, C4, andR3 again.

At very low frequencies, capacitorsC2, 3 and 4 may be compared to verylarge resistances. To all intents and pur-poses, they are open circuit and the gainis dependent on the values of theresistors only, and mainly on RV1. Atlow frequencies, the gain will be max-imum (boost) when RV1 is maximum,and minimum (cut) when RV1 isminimum, as indicated in Figure 1. Athigher frequencies, however, the im-pedence of C3 decreases, so that theeffective value of RV1 is reduced and atmid -frequencies, the gain is about one(unity gain).

At stil higher frequencies, the im-pedance of the capacitors decreases fur-ther until, at some frequency, RV1 is ef-fectively shorted out by C3. The gain,then, will depend on the setting of RV2,as indicated in the circuit diagram.

NOTE:IC1 IS TL081

INPUT

9V

RV2

{ENDS 4

WIPER

OV 4

RV1WIPER

RV1

2u2

BOOST .0- BASS CUT

RV1RI 100k R212k LIN 12k

R4 RV2 R54k7 470k 4k7

LINBOOST -4-- TREBLE -8. CUT

119

a

i2

A BCDEF GHJKL31 r.7Hfr...17-r-c 31

9V

--9V

-0 251

C5lu

OUTPUT

+9V

OUTPUT

RV2ENDS

INPUT


Project IN

+20

+17 -

+10-

+3 -

GAIN (dB) 0

3 -

-10 -

-17 -

-20

fb ft

fl

BASSBOOST

fh

TREBLEBOOST

T

LBASSCUT

I <

T

TREBLECUT

FREQUENCY/1.

Table 1

1. Choose the upper and lower cornerfrequencies, fh and fi, and themaximum boost/cut (gain, Av) required.

2. Select values for RV1 and R3.

RV13. R1 = R2 = Av

1

4. C2 = C3 -(27r)(fI)(R2)R2 + 2R3

5. R4 = R5 -Av

6. C4=1

(20110)(fh)(R5)

7. RV2 >- 10(R2 + R5 + 2R3)

Alternatively, to set the maximumboost/cut at frequencies fb and ft,use:

4. C2 = C3 -(27r)(10)(fb)(R2)

1

6. C4 -(27r)(ft)(R5)

1

Example:

1. Design a bass and treble tone controlwith a gain of 10 20 dB) and cornerpoints at 500 Hz and 2 kHz.

2. Let RV1 = 50k, let R3 = 10k.

RV1 50k3. R1 = R2 = -

Av=

10= 5k

4. C2 = C3 -1

(27r)(fi)(R2)

163n

(27)(500)(5k)R2 + 2R35. R4 = R5 - Av

5k + 20k- 2k5

- 10

Preferred value = 2k7

1

6. C4(277)(10)(fh)(R5)

1- 2n9

- (27)(10)(2k)(2k7)

Preferred value = 2n7

7. RV2 > 10(R2 + R5 + 2R3)

->- 10(5k + 2k7 + 20k) 277k

Therefore, choose RV2 = 500k.

Alternatively, to set the maximumboost/cut at fb = 60 Hz and ft = 12kHz:

4. C2 - C3

1

1

(27r)(10)(fb )(R2)

(27r)(10)(60)(5k)

Preferred value = 56n.

- 53n

1

6. C4 -(27)(ft)(R5)

1

- (27r)(12k)(2k7)- 4n9

Preferred value = 4n7

Shaping UpThe three factors which determine theresponse curve of a tone control (Figure3) are the slope of the curve, the max-imum boost/cut, and the frequencies atwhich the curve breaks away from theflat - the 3 dB or 'corner' points.These parameters are all set by selectingthe appropriate values for the tone con-trol network. The full design procedureis quite complicated but, as is usuallythe case, a simplified 'rule -of -thumb'method gives the right results! One ofthe most important simplications is that,in the circuit, Al = R2, R4 = R5 andC2 =C3.

At low frequencies, with allcapacitors effectively open circuit, thegain is more or less equal to RV1 /R2; avalue for RV1 is simply selected and R2calculated to give the requiredboost/cut. The values used here give amaximum gain of approximately 8 (18dB) at low frequencies.

At high frequencies, the capacitorsare all effectively short circuits and thegain is set by RV2, provided it is higherthan 10 times (R2 + R5 + 2R31, but themaximum gain is approximately equal to(R2 + 2R3)/R5. Here, the value of R2has already been found, R3 is merelyselected and R5 calculated for the re-quired amount of gain. Again, thevalues have been chosen to give a max-imum gain, at treble frequencies, of18dB.

All that remains is to set the lowand high frequency corner points, whichwe will refer to as fi and fh; these aredetermined by the values ofC3 and C4, respectively.

The value of C3, for any desiredis equal to 1/12 7r )1f1)(R2). Anotheruseful characteristic of this circuit is thatthe bass corner frequency is alwaysabout ten times the frequency, fb, atwhich the boost/cut is maximum; thevalue of C3 in our circuit puts the basscorner at 400 Hz, so the maximum ef-fect is at 40 Hz. To select a value of C3to give maximum boost/cut at a desiredfrequency, simply multiply the selectedfb by ten to find the corner frequencywhich is used in the equation.

Similarly, the point at which the tre-ble boost/cut is maximum, ft, is tentimes the treble corner frequency, andthe value of C4 which will give a par-ticular corner frequency is 1 /(2 Tr )( 10fh)(R5). To find the value of C4which gives a desired ft, simplysubstitute for 10fh in the formula. Thevalues in our circuit place the treble cor-ner at 1 kHz and give maximum effectat around 10 kHz.

Finally, remember that RV2 mustbe chosen to be greater than100;12 + R5+ 2R31. The values of RV1and R3 are then chosen; any close tothose used in our circuit will do.Remember also that Al = R2, C2 = C3and R4 = R5.

These rule -of -thumb formulas aresummarised in Table 1; using them, thetone controls can be re -designed to givea selected amount of boost and cut atany desired frequency. HE


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L5139 28LS145 70LS147 150LS148 85LS151 40LS153 40LS155LS157

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CL8038CC 300CM7204 550CM7205 1150CM72164 1950CM7217A 790CM7224 7%CM7555 80CM7556 150LA3350 250LA4031 340LA4032 295LA4400 440LC7120 300LC7130 340LC7137 395LF347 150LF351 48LF353 50LF355 85LF356 90LF357 110LF398 475LM3014 24LM308 95LM311 70LM318 150LM319 215LM324 30LM339 47LM348 64LM349 115LM358 60LM377 175LM379 480LM380 75LM381 145LM382 115LM384 140LM386 90LM387 120LM389 95LM393 100LM394 290LM733 100LM1458 40LM2917 1%LM3900 50LM3302 90LM3900 50LM3909 85LM3911 125LM3914 210LM3915 220LM3916 220LS7220 280M252 625M253A 1150MC1303 88MC1304 P 260MC1310 150MC1455 150MC1458 55MC1488 55MC1458 40MC1469 300MC1488 40MC1489 55MC1495 350MC1496 70MC1596 225

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5V 7805 146p 7905 2200 411. .../120 7812 1450 7912 2200 .4si `''15V 7815 145p -18V 7818 145p

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TRANSISTORSAA4422111142728651//27

30

AC176/8730

ACY17/18 70ACY20 /1 75ACY22 60AD140 120A0149 79AD161/2 42AF115 66AF139 40AF178 75AF180/6 70AF239 55BC107 /8 10BC108B 128C108C 126C109 106C1098 12B132110179% m12

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BC140/3 30BC147/8 9BC149 9BC153 /4 27

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Famous Names II

Sir Edward AppletonA pioneer of radio and radar who won a Nobel prize for his

work on the ionosphere.

You don't have to be a student of radiohistory to have heard of the Appletonlayer - but the fact remains that a lotof people who ought to know the name,just don't. Edward Appleton wasborn in Bradford in 1892, and startedhis academic career, after conventionalschooling, at St. John's College,Cambridge. In 1920 he becameassistant demonstrator in ExperimentalPhysics in that most famous of alllaboratories, the Cavendish, where hisown particular interest was in thepropagation of radio waves, followingthe work of Heaviside and Kennelly in1901. The situation at that time wasthat everyone knew that radio wavescould be used to send messages oververy large distances, but no-one couldshow, with any real proof, why thisshould be so.

By the end of the 18th Century,Oliver Heaviside had put forward thetheory that the intense radiation fromthe Sun, which is a nuclear fur-nace that no-one protests about, wassplitting atoms in the low-pressure air atthe outer fringes of our atmosphere.These split atoms are electricallycharged and can move fairly freely (theyget the name 'ions' from an ancientGreek word meaning "wanderer" buteven at the low pressures a hundredmiles or so above the Earth, these ionsare still sufficiently close to each otherto affect a radio wave.

Ionic EffectsThe effect depends on the radiowavelength. A radio wave will passfairly easily between metal objectswhich are spaced by a distance equal toseveral wavelengths, but when theobjects are closer than a wavelengthapart, they act to reflect the wave.Heaviside's theory was that the spacingbetween the charged particles would beclose enough to act as reflectors ofradio waves, certainly for wavelengthsdown to 10 metres.

The idea had been stronglysupported by the American physicist,Kennelly, but few other people tookvery much notice until Marconisucceeded in doing what so many hadsaid was impossible - transmitting aradio signal across the Atlantic. Thismade many engineers and phyicists,who had scoffed at Heaviside, payrather more attention to his ideas, and itstarted a rush to find and measure thesereflecting layers.

Appleton had the idea ofusing a method which was direct,elegant, and which used whatnowadays would be called "state-of-the-art" technology. In doing so, he

devised the essential principle of radarand the principle was simple! A burst ofradio waves could be beamed directlyupwards, and the time for it to bereflected back could be measured.Since radio waves travel in space at thesame speed as light (around 300 millionmetres per second) the distance thatthe waves had travelled to thereflecting layer and back could beprecisely measured.

Trouble With TimeThe trouble with direct, simple andelegant methods is that they are usuallyextremely difficult to carry out! Thesnag, in this particular example, washow to measure the time which, fromrough calculations, looked as if it wouldbe about 300 microseconds. Measuringa time period as short as that wasn't

IONOSPHERE

OUTWARDWAVE 11 REFLECTEDWAVE

Figure 1. The Appleton experiment.This was an early use of the principle ofradar to measure the distance of theAppleton and other layers from thesurface of the earth.

PULSE OUT PULSE BACK

TIME

Figure 2. An oscilloscope display usedto measure the distance. With a

constant speed timebase, distancealong the screen represents time, whichin turn represents distance travelled bythe wave.

exactly a routine matter in 1923, andAppleton solved it by turning to newtechnology - the cathode-ray tube.

He saw that the electron beam couldbe moved rapidly across the screen byusing changing voltages on thedeflection plates, and if the deflectingvoltage is a sawtooth shape, then thespeed of the spot across the screen ispractically constant. Even better, itsvalue can be calculated from the size ofthe deflection plates and their distancefrom the screen, thus the position of aspot can be used to represent time fromsome starting position.

Appleton's LayersAppleton's classic 1 923measurements showed that there wereseveral layers of reflecting particles,labelled D,E, and F, above theatmosphere, at heights ranging from 50to 400 km. The shorter wavelengthsthat penetrated the lower layers of this"ionosphere", as it was called, werereflected higher up in the F -layer, whichfrom then onwards was called theAppleton layer. The F -layer is about100 miles above the surface of theEarth and, during the day, actuallyconsists of two layers; a thin Fl layer,and a higher, more strongly ionised F2layer. At night, the Fl layer rises to theF2 level and reflects wavelengths downto 10 m (around 30 MHz), so providingthe excellent short-wave conditionsthat we experience at night. Thesedays, the heights of the layers aremonitored continually - using methodsvery similar to Appletons - by weatherresearch stations all over the world, andionospheric predictions are available foranyone who is occupied with short-wave transmission. The main UKionospheric station is at Slough.

Appleton's brilliant research workeventually led him to London, where hebecame Wheatstone Professor ofPhysics, and subsequently back toCambridge as Jacksonian Professor ofNatural Philosophy (Physics). At theoutbreak of war in 1939, he wasattached to the Department of Scienceand Industry (they associated the two,in those days!) to work on radarresearch, along with the pioneers oftelevision, from EMI, and of shortwavetransmission, from Marconi. He wasawarded the Nobel prize in 1947, forhis work on the ionosphere, andbecame Vice-chancellor of EdinburghUniversity in 1949, a post which heheld for several years. He died in 1965after a brilliant career which coveredsome of the most exciting develop-ments in electronics, and with his nameimmortalised in the Appleton layer. HE


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Project

Three -AspectSignal LightsJust the right lights for a realistic model rail set-up.RAILWAY signal lights are intended toindicate whether or not the way aheadis clear. In the simplest case a coloursignal, either a red or a green light,shows if it is safe for a train to proceedinto the next section of track. As soonas the train passes a green signal, thelight changes to red.

This was the first type of signalsystem to replace the older semaphoresignals; today, they are used only in afew isolated cases. Withthree -aspect signalling, an additionalamber light indicates that the lineahead is clear but that the next signal isset to red - danger ahead! More com-mon still, these days, is thefour -aspect system, where a secondamber light is used. A display of twoamber lights indicates two clear sec-tions before the next red signal, allow-ing the driver to adjust his speed accor-dingly (regular commuters can observethe system from almost any British Railplatform - if the trains are running!).

Signalling a simple junction, where a

branch line leaves the main line, re-quires an extra arm to the signal; this ispositioned on the signal stand, on thesame side as the branch and shows arow of four or five white lights,together with a green or an amber light,when the points are set for the branchline. A green or amber signal alone in-dicates that the points are set for astraight -through run.

In the real world, these signals arecontrolled by track circuits whichdetect the position of a train on theline. The axles span electricallyisolated sections of rail, thereby com-pleting a circuit to indicate its location.Of course, the settings of points andlevel crossings also control the signals.

Prototypes and ModelsIn the prototype, failsafe requirementslead to considerable circuit redundancy- backup units in case one should fail- but for model railways, the basicfunctions of a three -aspect signallingsystem can be provided quite simply.

The electronics of the system con-sist of two circuit modules. The basicTrack Module controls one set of signallights for one section of track; itresponds to the location of the trainand the settings of any points, levelcrossings etc in that section of track.The second module is a JunctionModule, required to drive the whitelights of a branch line indicator and tocontrol the Track Modules either side ofthe junction.

For the signal lights, it is easy to useLight Emitting Diodes (LEDs) which,conveniently, are available in red,yellow (amber) and green. There areseveral methods that can be used todetect the position of a train; one of thesimplest and most reliable is to usesmall bar magnets attached under thelocomotives at axle height, andmagnetically operated reed switchespositioned on the track between therails. Model points do not usually pro-vide a signal suitable for driving the cir-cuits but, with a little ingenuity,


Project

INPUTS OUTPUT

A B A -B

0 0

0

0

INPUTS OUTPUT

A B A+B

0

0 0

0

NAND NOR

OUTPUT = NOT IA AND B) OUTPUT - NOT (A OR BI

Table 1. Truth tables for NAND and NORgates.

microswitches can be attached to thepoints to give suitable inputs to themodules.

The Track ModuleThe circuit diagram of Figure 1 is for asingle Track Module; a model layoutwill need one of these for each set oflights. The circuit itself is quite simple(though as we shall see, the interactionof two or more modules becomesslightly more complicated!). The'brain' of the circuit is the bistable flip-flop consisting of NAND gates IC 1 cand IC 1 d (truth tables for both NANDand NOR gates are shown in Table 11.Switches SW2 and SW3 are themagnetic reed switches which closemomentarily when the locomotivepasses over them.

When SW2 closes, pin 5 of IC 1 c istaken to OV (logic 0 or 'low') for just amoment, so that the output at pin 6goes high (logic 1, + 5V). This high iscoupled to pin 2 of IC1d and, since itspin 1 input is already held high throughR6 and R7, pin 3 goes low. This iscoupled back to the other input of IC1cat pin 4, ensuring that output stayshigh. Thus the momentary low on pin5 is 'latched' by the flip-flop and it willmaintain this state, which indicatesthat there is a train in the section con-trolled by the module.

When the train leaves the section oftrack, SW3 closes and pin 1 of 'Cidgoes low for a moment; this is coupledto pin 4 of IC1 c and, since pin 5 in be-ing held high through R4, R5, the out-put at pin 6 goes low. This is fed backto the pin 2 input, maintaining the highoutput on pin 3. So, the new state islatched in and this indicates to thefollowing circuitry that the train hascleared the section.

Resistors R4 and R6 provide the+ 5V to ensure that the inputs are nor-mally high. The other components, R5,C1 and R7, C2, provide interferencesuppression which works satisfactorilyeven in the presence of high frequencytrack cleaning systems. The value ofR6 has been chosen to provide a'power -on -reset'.

When the power is first switchedon, both Cl and C2 conduct heavily sothat both plates of the capacitors aremomentarily at OV. They soon begin tocharge up but, because R6 is more thantwice the resistance of R4, C2 will takemore than twice as long to reach fullcharge. In fact, the voltage on C2 willstill be at logic 0 level when Cl is fullycharged. Thus at power -on, a lowpulse is effectively applied to pin 1 ofIC1 d and a high pulse to pin 5 of IC1c.As previously described, these are theconditions for the flip-flop to be reset to'track clear', thus making sure that all

+5V0

13

NEXTSECTION

100n

L-

/7777 ov

Figure 1. Circuit diagram of the Track Module.

TS1

TS2

TS3

PS1

a

IC2

TERMINAL 1

IC1a

IC1b

12

1l8

9RI14

11 270R 15ICI a

R2

10 IC113

NOTES:ICI IS 7400IC2 IS 7425LED1 IS TIL232LED2 IS TIL212LED3 IS TIL209

R339OR \\

9

LED1GREEN

LED2AMBER

LED3RED

PREVIOUSSECTION

(110TRAIN INSECTION

RED

L1 { AMBER

GREEN ON

ON

ON

RED

L2 AMBER

GREEN ON

ON

ON

ON

ON

RED

L3 AMBER

GREEN ON

ON'

ON

ON

I I I I I I I

I II

I

II

TRAIN 1

! RESET ENTERS ' ENTERS I ENTERS I LEAVES I POINTS !

ICONDITIONSI SECTION 1 I SECTION 2 I SECTION 3 I SECTION 3 I SWITCHED I

Figure 3. Timing diagram for "Keeping Track".


Project

41 -BRANCH LINE

MAIN LINE

TS3

9

0

0 PS1

L3

TS2

R1

0

/7777

L2

T5

0

L1

TS1

MODULE 213

!Cie12

10 R2 167

6 9 8IC1b

R3 173

MODULE 3 MODULE 129

10 IC211

116 SET12

11 I 12 121 RESET 124

OV OV OV OV OVOVOV

+5V 5V +5V

(!)0V

5V +5V1

5V+5V+5V 4

10 10

Figure 2. Combines Module circuit and track layout diagram; note that the flip-flop has been drawn here in standard 'block' form.

signal lights are green when the systemis first turned on. It will probably benecessary to adjust the value of R6 tosuit a particular layout and power supp-ly; a little experimenting should soondetermine the correct value.

If the flip-flop is the brain of the cir-cuit, the quad -input NOR gate IC2 is its'heart'. Its output at pin 8 directlydrives the red signal light, LED3, andindirectly controls the other two lights.As shown in Figure 1, two of the inputsare wired directly to OV, one to OV viathe normally closed points switchSW1, and the fourth is connected tothe pin 6 output of the flip-flop. Whenall four inputs are low, the output willbe high and the LED is biased off, with+ 5V on both the anode and cathode.However, when the flip-flop is trig-gered by a train entering the section,pin 9 of IC2 goes high, pin 8 goes lowand LED3 turns on. The result is thesame if SW1 is opened (indicating thatthe points are set against an oncomingtrain), since the internal circuit of theTTL gate puts a high on any open cir-cuit input.

If the section of track monitored bya module does not contain a set ofpoints, then terminal 2 should also bewired to OV. The other two inputs, atmodule terminals 3 and 4, are availablefor other switch functions within a sec-tion of track, eg for level crossing in-dication, etc.

Keeping TrackTo understand how the remainder ofthe circuit works, it is easier to look atthe interaction between severalmodules, controlling two or more sec-tions of line, and to trace the logic se-quence as a train passes through. Thecomposite circuit diagram of Figure 2shows the internal circuit of the modulecontrolling Section 2 of a length of line,together with the outlines and ter-

minals of the adjacent modules. Theinternal circuit has been simplified bydrawing the flip-flop as a block withSET and RESET inputs, and Q and -aoutputs, in standard notation;however, its operation is exactly asdescribed earlier. The timing diagram,Figure 3, will be helpful in tracing theaction of the sequential logic.

First, though, we should establishthe starting conditions. After a power -on reset, all inputs to IC2 are low andthe red LED is turned off. The outputfrom Module 2 terminal 9 is a high, in-dicating that the section is clear.Similarly, the terminal 9 output fromModule 3 is high. Therefore, the inputsto NAND gate ICI a are both high; itsoutput will be a low and the green light,LED1 , turned on. The gate IC1b has ahigh input from IC2 and a low fromICI a so its output will be high and theamber light, LED2, is turned off. Thelogic conditions are the same forModules 1 and 3.

What happens, then, when a trainleaves Section 1 and enters Section 2?First, Track Switch one (TS1) closes fora moment and the Q output of the flip-flop goes high. This forces the outputof IC2 to a low and the red LED of L1comes on. This low is also applied tothe terminal 1 input of Module 1, in-dicating that there is a train in Section2. At the same time, then output ofthe flip-flop goes low, and this point(terminal 10) can be wired back to acurrent limiting resistor and LED on atrack layout panel near the controller,to indicate train movements.

At this point the inputs to ICla are:a high from IC2 and a low from the ter-minal 1 input (because Section 3 is stillclear). Therefore, the output of IClagoes high, turning off the green LED.The inputs to ICI b are: a high fromIC 1 a and the low from IC2. The outputstays high and the amber stays off.

The lights change again as the trainleaves Section 2; now L3 will show redand the terminal 9 output of Module 3will go low. However, TS3 is also con-nected to the terminal 1 2 input ofModule 2 so when it closes, as thelocomotive passes, it resets the flip-flop with the Q output low and the Iraoutput high. With all inputs low, IC2goes high, turning off the red LED. Theinputs to ICla, now, are a high fromIC2 and the low from terminal 1, so itsoutput will stay high and the greenLED, off. However, the inputs to ICI bare both high, its output is low and theamber LED is turned on -indicating that Section 2 is clear butthat L3 is showing red.

When the train clears Section 3,eventually, the same sequence takesplace within Module 3; its terminal 9output goes low so that ICla now goeslow, turning on the green light.

The low input from IC1a forces IC1boutput to a high, turning off the amberlight; LED3 simply remains, off.

The only other operation is when thepoints are set for the branch to join themain line. Points switch PS2 is normal-ly closed, maintaining the low on thatinput to IC2. When it is opened, the in-ternal TTL circuitry take the input high,forcing the output to a low and turningon the red LED. The low to the inputsof ICs la and 1 b forces their outputshigh, so that both the green and amberlights are held off until the points arereset.

Junction ModuleThe function of the second circuitmodule is to control the signal lights in-dicating a branch leaving the main line,and to connect the Track Modules oneither side of the junction, according tothe setting of the points. The com-posite diagram, Figure 4, shows the in- 0,ternal circuit of a junction module and


Project

BRANCH LINE

TS2

NEXTBRANCH

LINEMODULE

TS3

5

0

0

6 7

5V

OV

12

MODULE 3BRANCH

LINE

NEXT MAINLINE MODULE

tt A

-I5V OV 1 12

+5V

V

2

3

11 10

4

2

3

4

MODULE 2MAINLINE

6

7

8

OV

11

NOTE'ICI IS 7402IC2 IS 7400

POWER CONNECTIONSHAVE BEEN OMITTED

10 9

5V

2

r"-°

1(M)

HBO

121811

MAIN LINE

TS1

10

JUNCTION MODULE

IC2d

9

11

V

12

2 MODULE 1

5

6

7

8

11

OV +5V

12

P. 1

+5V +5V

Figure 4. Combined Junction Module circuit and track layout diagram.

OV

+5V

its connections to the Track Modules. Itis most easily understood with the aidof the timing diagram Figure 5, whichtraces the logic sequence of trainspassing through the junction, and withthe truth tables of the NAND and NORgates.

We can assume, at the start, that allsignals are showing green, ie, all TrackModules are in their reset condition,and that the points are set for astraight -through run. The inputs andoutputs of the Junction Module are asfollows: the inputs to IC2d are a high(since TS1 is open) and a low (fromPS1 , which is closed); therefore its out-put is high and the branch lights areturned off.

Both terminal 9 outputs fromModules 2 and 3 are high (tracks clear)and these force the outputs of ICs laand 1c to low: IC1 b output, therefore,will be high, sending a 'track clear'signal to Module 1. Similarly tracing thelogic levels through ICs 1 d, 2a, b and2c will show that the input to the resetterminal of Module 1 is high, as itshould be.

Now, a train moving along thetrack will momentarily close TS1, trig-gering the Module 1 flip-flop and swit-ching L1 to red. The input to IC2d fromTS1 also goes low, but this has no ef-fect.

Normally, in a straight section oftrack, Module 1 is reset by the trainpassing over TS2; in this case,however, it is reset via the JunctionModule. When TS2 closes, it takes oneinput of IC2a low for a moment, forcing

the output to go high. With both its in-puts high, IC2c will go low, providingthe reset pulse to terminal 12 ofModule 1 and turning off the red LED ofL1.

At the same time, terminal 9 onModule 2 has gone low, taking one in-put of IC1a with it; the other input is alow from PSI, so the output will gohigh, forcing IC1 b output low; thisturns on the amber LED of signal LI.Finally, when the train clears Section 2,terminal 9 goes high, IC1a goes highand IC1b goes high, turning off theamber light in Li and turning on thegreen.

Now let's see what happens whena train takes the branch line. First, thepoints must be set, opening PSI ; bothinputs to IC2d go high, so its outputgoes low, turning on the branch line in-dicator. At the same time, all inputsconnected to PS1 will change state (in-cluding those to ICs lc and 2a, which

are via inverter IC2d). These changesswitch the logic to accept inputs fromModule 3, rather than from Module 2.

As a train passes over TS1, signalL1 will turn to red, as before. A side -effect of TS1 closing is that the branchline indicator lights turn off for an ins-tant.

The train now moves through Sec-tion 1 and takes the branch line, whichwe have called Section 3. As it does,TS3 closes, turning L3 to red and put-ting a low on one input of IC2b, so thatits output is forced high. The other in-put of IC2c is being held high by PS1,via ICs 1 d and 2a, therefore IC2c willgo low, putting a reset pulse on ter-minal 12 of Module 1 and turning offits red LED. Simultaneously, terminal 9of Module 3 has gone low; IC1c nowhas two low inputs (the other is heldlow by PS1 via IC 1 d), so its outputgoes high, forcing ICI b high and thusturning on the amber LED in L1 via


Project

L2

TS1

TS2

TS3

PS1

IC2d

1(M)

IC1a

1(B)

ICid

IC1c

IC1b

IC2a

IC2b

IC2c

BRANCH

Li

n J

1

RED

AMBER

GREEN ON

ON ON

ON

ON

1

ON

RED

AMBER

GREEN ON

ON

ON

LON

ON

ON

1 ON

RED

3 AMBER

GREEN ON

ON

ON

TRAIN INSECTION 1

RESET

I TRAIN INI SECTION 2

I CLEARS I

I SECTION 2 I

(CLEARSNEXT

SECTION) I

POINTS I

SWITCHED I SECTION 1

Figure 5. Timing diagram for tracing the Junction Module operation.

CLEARSSECTION 3 I SECTION 3 I

(CLEARSNEXT I POINTS I

SECTION) I SWITCHED I

ON

Module 1.A similar sequence of logic will set

L1 to green when the train finally clearsSection 3. The timing diagram, Figure5, shows this sequence as well as thatwhich results when the points arereset.

These circuits, although very sim-ple by themselves, can be quite com-plicated in their interactions, as wehave just seen! Everthing depends onthe timing of the various switchclosures, together with the conditionswhich resulted from the last operation.Timing diagrams are essential forunderstanding circuits of this kind.

In fact, if the timing of the switchclosures (which trigger the logicchanges resulting in the appropriatesignal lights) are not correct, thesystem will not produce the rightresults. The track switches must bepositioned very carefully, at the start ofeach section of line, to produce thedesired signals. Another small trap,which should not normally be of anybother, is that a set of points cannot bechanged until the train has cleared thesection controlled by the branch in-dicator. In other words, the points can-not be set for the branch line, in our ex-ample, until the train has cleared Sec-

tion 2. Otherwise the amber light on L1will not clear.

Construction and LayoutThe component overlay diagrams for aTrack Module and for a Junction Moduleare shown in Figures 6 and 7, respec-tively. Full sized PCB patterns arereproduced on the PCB Printout page.

The construction is quitestraightforward and should not give anydifficulty. The ICs are all TTL, so nospecial handling procedures are neededexcept for normal care not to overheatthem or bend the pins. The compositecircuit diagrams, Figures 2 and 4,


MI Project

BRASS

72 (DIAMETER)

70

18

7

COPPER18 SWG

4.1 (DIAMETER)

3.5

5

O

BRASS

2 (DIAMETER)

4.1(OUTER

DIAMETER)

3(INNER

k-°-1DIAMETER)

6

DIMENSIONS IN mm

Figure 8. Mechanical details of a simplesignal stand.

Parts ListTrack ModuleRESISTORS(All Y. watt 5% carbon)R1,2 27ORR3 390RR4 1kR6 2k2R5,7 330R

CAPACITORSC1,2 100n

C280 polyester

SEMICONDUCTORSIC1 7400

TTL quad 2 -input NANDIC2 7425

TTL dual 4 -input NORLED1 T I L232

green 0.2" LEDLED2 TIL212

orange 0.2" LEDLED3 T I L209

red 0.2" LED

MISCE LLANEOUSSW1 SPST switch

track switch - see textSW2 SPST switch

points switch - see text

PCB; signal stands (see text);wire, solder etc.

Junction Module

RESISTORS(All Y4 watt 5% carbon)R1 1k

SEMICONDUCTORSIC1 7402

TTL quad 2 -input NORIC2 7400

TTL quad 2 -input NAND

MISCELLANEOUSSW1 SPST switch

points switch - see text

BUYLINES page33

Figure 6. Component overlay for theTrack Module.

should be used as a guide to positioningthe track switches and signal stands.The modules are most convenientlymounted under the track layout andconnected together, as shown inFigures 2 and 4, by lengths of four-wayribbon or multicore cable. The connec-tions to the signal lights can also bemade with four-way cable.

In a track layout as shown in Figure2, there would normally be anothersignal stand on the branch line, near itsjunction with the main line. To connectanother control module into the systemat this point, simply wire it in parallelwith the four-way module bus.However, point switch PS2 must nowbe a two-way type, with the change-over terminal connected so that terminal2 of the new module is connected to OVwhen the points are set for the branchline to join.

Power SupplyAll the circuit modules are powered from+ 5V, which can easily be derived usinga three -terminal 5V regulator; a suitablecircuit to operate from a smoothed DCsupply of 12-15V appeared in the Juneissue of Hobby Electronics, this year.Each module will draw approximately50 mA, so the source must have thecapability to supply this current, timesas many modules are there are in thelayout.

Signal Stands AloneMany model signals currently availableuse miniature coloured incandescentbulbs, but these are rather expensive

.4-(11/ 11(0,,

UV

*

Figure 7. Component overlay for theJunction Module.

and draw considerable current. Dedictedmodellers might, therefore, be in-terested in Figure 8, which shows thedetails of a signal stand especiallydesigned for 3mm LEDs.

The bracket holding the LEDs is cutfrom 18SWG copper, bent at rightangles and soldered to the post. Thelight shields are formed from brass tub-ing with an inside diameter of 3mm totake the LEDs, and the post is cut from2mm tubing. These parts are allavailable from model shops and youcan, if you wish, add to the constructionwith a ladder and safety rails made fromtinned copper wire.

The connections to the LEDs shouldbe made with appropriately colour cod-ed wire -wrap wire (!), which is thinenough so that four or more leads canbe fed up the post and through a smallhole in the bracket. The connections canbe covered by a cowling made from thincard, lightly glued in place.

The only other question which re-mains to be answered is: what to usefor the branch line indicator lights? Un-fortunately, white LEDs are notavailable! Well, one suggestion is to uselow current miniature light bulb and fibreoptic filaments to simulate the line oflights. However, the solution to this pro-blem, as with many other practical pro-blems in modelling, depend on particularset-ups and individual ingenuity. That,after all, is half the fun!

Photo Credits. Our thanks to: HornbyHobbies for the photo on page 39 andC.J. Freezer (Editor, Model Railways) forthe picture on page 42.

HE44 Hobby Electronics, September 1982

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VMOS PROJECTS£1.95Contains a number ofvaried and interestingprojects using VMOSpower FETs.

DIGITAL ICPROJECTS £1.95Simple and advancedprojects based ondigital ICs.

INTERNATIONALTRANSISTOREQUIVALENTSGUIDE £2.95Find possibleequivalents for apopular user-orientated selectionof moderntransistors.

HOW TO USE OP -AMPS £2.25All you need to knowabout Op -Amps, asource book ofcircuits and designcalculations.

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45

ELECTRONICS IS AFINE HOBBYVELLEMAN-KIT

In less than a year we have become well-known for ourvaried and interesting range of electronic kits and ourefficient service.

Graded by difficulty, the kits are of high quality, wellpackaged and have applications covering a wide field.

The range includes kits using microprocessors, infra -redsystems, power supplies, dimmers, motor control units,amplifiers, sound and light units, digital counters, timers,VU's and many, many more.

New kits are:K2580 - electronic powerswitch dimmer £9.34K2581 - stereo volume and tone control £11.27K2582 - stereo audio input selector £11.27

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The Velleman 'top ten' are:K1682 - Microprocessor timer £48.37K1771 - FM Oscillator £5.45K1798 - Stereo VU using LED's £16.91K1823 - 1 amp Power supply £6.99K2544 - Complex sound generator £8.28K2569 - Three tone chime £6.56K2575 - Microprocessor doorbell £15.53K2577 - Motor speed control £7.57K2578 - Eprom programmer £207.00K2579 - Start stop timer £6.21(prices include VAT)

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This new style course will enableanyone to have a real understandingof electronics by a modern, practicaland visual method. No previousknowledge is required, no maths, andan absolute minimum of theory.

You learn the practical way in easysteps mastering all the essentials ofyour hobby or to start or further acareer in electronics or as a self-employed servicing engineer.

All the training can be carried out inthe comfort of your own home and atyour own pace. A tutor is available towhom you can write personally at anytime, for advice or help during yourwork. A Certificate is given at the endof every course.

You will do the following:Build a modern oscilloscopeRecognise and handle current electronic

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Learn how to test and service every typeof electronic device used in industry andcommerce today. Servicing of radio, T.V.,Hi-Fi and microprocessor/computerequipment.

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HE: 9


Gadgets, Games Et Kits

Hands Off!Paul Coster

Hobby's hardworkingeditorial assistant washappy to come to gripswith this handy auto -

ranging multimeter. Readon for his hard-hittingcomments . . .

ABOUT the most surprising feature ofthe Teston LCD multimeter is its size.For a meter that auto -ranges, measuresAC and DC and has a continuitychecker ( with tone generator), to fit in-to your hand, is pretty impressive. Thecomplete package, available fromStotron, is supplied with test leads, car-rying strap, test clip, current shunt andsoft case. There is also a small foldedsheet - entitled ( optimistically) 'In-struction Manual' - which describeseach range and how to use it. However,despite this lack of a decent manual,the meter was easy to use and verygood value for the facilities offered.

Its full title is the ISI-Teston DM 2350and it is an auto -ranging digitalmultimeter with only three scale -selectbuttons; current, voltage andresistance. A small switch, - push -to -changeover, selects AC/DC or ohms/loohms (more about this later). The meteris powered from two AAA batteries andprotected against overload by a 200mA fuse. It is cased in grey plastic witha clear lOmm display. Input impedancewas a creditable 10 megohms on bothAC and DC voltage ranges; rising to100 M on the 200 mV DC range. Ac-curacy on all ranges was also good, atbetter than 1% (the highest resistancerange is quoted at 2%, but our unit waswell within this). Overload protection isprovided by an external fuse andspecial FET circutry - the meter also'bleeps' to warn of a dangerously highinput.

Wide Ranging

The DM2350 has five DC and fourAC voltage ranges. The DC scale ex-tends down to 200 mV FSD, whichmakes possible measurements as lowas 100uV. Maximum DC input is 1000volts, accurate to better than 1% of thereading. The AC scale is not quite assensitive but is adequate for most pur-poses. The range is 2-600 volts, with aresolution on the lower range down to1 mV. This would have been excellentfor audio measurements, except for thenarrow frequency response - 40 to500 Hz (though, in fairness, this iscommon to just about all comparable

meters) - and the inductive pick-upwhich results from using non -screenedtest leads; its easy enough to makeyour own screened lead's, however.

Both the AC and DC ranges workedwell - it was possible to switch bet-ween AC and DC without plugging thetest leads into different sockets - andthe AC frequency limitations were not amajor drawback (just use 440 Hz in-stead of 1 kHz as a test frequency).

There are two resistance scales, onefor normal measurements and one fortaking readings with components 'in cir-cuit'. This latter facility is extremelyuseful for measurements around siliconjunction components - silicon diodesand transistors etc - since the low out-put (0V4) is not sufficient to activatethem. Both scales read up to 2 M, withthe out -of -circuit range going down to 1ohm resolution. Accuracy was found tobe better than 1% on all ranges. An ad-ditional feature on both these ranges isthat the tone generator can be used toindicate continuity. By connecting theleads between any two points in a cir-cuit (power off!), and switching toresistance, the meter will bleep if a

direct path is 'made' (a DC resistance ofless than 1 ohm).

The two current scales are the onlyones that do not auto -range, simplybecause both have a single limit of

200mA. This meant the sensitivity suf-fered (only 100 uA resolution) and verylow current readings - quiescent supp-ly in CMOS circuits etc - were notpossible. However, this did not seemtoo important in the tests carried outand with the 10 A shunt fitted, the ex-tended range made up for the deficit.The current scales were slightly less ac-curate at just over 1 %, but, since mostcurrent readings will vary from deviceto device, higher accuracies are not soimportant. More significantly, theDM2350 compares favourably with itscompetitors in this particular respect.

Getting To Grips

Using this multimeter was a sheerdelight, with the push-button controlsand auto -ranging capability enablingone -handed operation - you can twid-dle knobs and take readingssimultaneously! In fact, the only aspectI found slightly annoying (as did theeditor!) was the bleep every time arange was automatically switched. It'sa good idea for continuity testing - in-deed, vital - and as an overload warn-ing signal, but does get a bit irritatingafter a while. Perhaps something lesspiercing is called for?

So, bearing in mind the comments onfrequency response and current sen-sitivity, I found this meter had a lot torecommend it. The simple operationand auto -ranging facility made it a realpleasure to use and, for anyone thinkingabout buying professional test gear -hobbyists and engineers alike - it'sworth including on your shortlist.

The price for the complete package ofmeter, test leads and case etc is£56.93 (all inclusive). Further detailscan be obtained from Stotron Limited,Haywood Way, Ivyhouse Lane,Hastings, East Sussex.

HE


MOnpc 6010

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SPECIFICATION 6010 Et 7030BATTERY: Single av dry cellBATTERY LIFE: 200 hoursDIMENSIONS: 170 x 89 x 38mmWEIGHT: 400g inc batteryMODE SELECT: Push buttonAC DC CURRENT: 200µA to 10AAC VOLTAGE: 200mV to 750V - 6 RangesDC VOLTAGE: 200mV to 1000V - 5 RangesRESISTANCE: 2005I to 20MSZ - 5 RangesINPUT IMPEDANCE: 10M12 - 6 RangesDISPLAY: 31 Digit 13mm LCD0/LOAD PROTECTION: All rangesOTHER FEATURES:

Auto polarity. Auto zero. Battery -low indicator.Strong ABS plastic case with tilt stand.Battery and test leads included.Optional carrying case.

15% to your order for VAT. Postage 8- Packing is free ofcharge. Trade enquiries invited.

ARMON ELECTRONICS LTD.Cottrell House. 53-63 Wembley Hill Road, Wembley Middlesex H49 8BH. EnglandTelephone 01-9024321 13 lines ) TELEX No 923985

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SAFOAN OSCILLOSCOPES- 5 mV/div sensitivity. Choice of Band-width 10, MHz. 15 MHz, 20 MHz. 1S/div-100n S/div. Calibratedtimebase. Solid trigger with bright line auto, normal and TV.XY facility. Z modulation. Calibration output. Bright and cleardisplay. Portability. Model DT410-10 MHz £205.85.Model DT415-15 MHz £217.35. *Model DT420 20 MHz£228.85. Send S.A.E. FOR FULL spec.

THANDAR PDM35 DIGIT L.E.D. DIGITAL POCKET MULTI-METER.0C volts (4 ranges) ImV to 1000V. AC volts 1V to 500V DC current (6 ranges) 1nA to 200MA Resistance (5 ranges) IS2to 20 meg.12. £39.95. AC adaptor £5.95. carrying case £3.65 MN1604 Battery £1.57.

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DC volts 1 mV to 100(ly AC volts 1V to 500 V AC rms OC current1,ua to 2A Resistance 112 to 2 MO Diode check Basic accuracy(0.75% of reading + 1 digit) Battery life typically 2000 hrs leadsinc. £45.94 40KV Probe £34.95Universal test lead set £12.95.

THANDAR TM352 3', DIGIT LCD DIGITAL POCKET MULTIMETER DC volts: 100/44 to 10000 AC volts: 11/ to 1000V DC current:100 nA to 10A Resistance 1S2to 2 N t2Diode check hFEmeasurement Audible continuity check Basic accuracy t(0.5% of reading + 1 digit Battery life 150 hrs + £57.44 inc.leads Battery Universal test lead set £12.95 40 KV probe £34.95

THANDAR SC1I0 SINGLE TRACE LOW POWDER 2"OSCILLOSCOPE Bandwidth DC to 10 Mhz Sensitivity: 10mV/div to 513 V /div. Sweep speeds: 0.1/u secs / div to 0.5 secs/div.

Power requirements 4-10 0 DC 4 'C' cells : Size & weight, 255.150.40mm : 800gms £159.85 a truly portable and superb

instrument Carrying case £8.86 AC Adaptor £5.69. Nicad Batt.Dace £8.63..1 probe £9.78..10 probe £11.50 Complete range ofThandar instruments available from stock S.A.E. for CAT. & prises. vi,01

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EXP-600 15mm 152mm fi1mm 550 110 328pin £7.25

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EXP-48 n/a 152mm 25mm 160 32 n/a £2.65

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Please send S.A.E. for catalogue listing complete range of G.S.C.Instruments and Boards.

SABTRONICS LCD MULTIMETER MODEL 2033. DC volts 100 uV-1000V Accuracy + 5% AC volts 100AV-1000 V Accuracy 1%

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TMK 500 MULTIMETER 30 kopv. AC volts 2.5 10 25 100 250500 1000V DC volts 0.25 1 2.5 10 25 10 25 100 250 1000 DCcurrent 50/da 5MA 50MA 12 amp Resistance 0-66 60K, 60 meg. Decibels -20 to 56 d/b Buzzer continuity test Size 160.110,65 Batteries and leads inc. £26.95

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PRICES INCLUDE VAT. PLEASE ADO 75p POSTAGE TOORDERS UNDER £10.00


Feature

Planning on SuccessFirst-time success with a project depends on careful planning andexecution. Here's how to go about it ...

WE'VE ALL done it; spent long hourswith a hot soldering iron and bags ofcomponents, seeing a once bare PCBgradually filling up, mounting switchesand controls, lettering the control panel,wiring up, and finally coming to themoment of truth, the switch -on.

Perhaps for the first time, a

moment's anxiety - will it work? Whatwill happen if it doesn't? With anaccelerating pulse rate, we turn theswitch. Our worst fears are realised,nothing happens, or perhaps there issome sign of activity but nothing likewhat it should be. Worst still, maybe atiny curl of smoke drifts upward fromsome undetermined component on theboard!

From satisfaction at havingcompleted the project, we are plungedinto gloom and despondency. Withgrowing despair we make haphazardchecks on this and that, but can find nocause. Sooner or later we switch off,wishing we had taken up pigeonfancying instead of electronics. Ofcourse, with or without help, we mayget the thing going eventually but, evenif not, it isn't long before some newcircuit fires our imagination and we aremaking out our shopping list ofcomponents. This one will be different- it's bound to work first time. Hopesprings eternal . !

If you have ever built a project andthat, or something like it, has neverhappened to you, you are eitherfortunate or careful - or both.Sometimes, getting a project workingsatisfactorily can take as long if notlonger than building it in the first place.So what can be done about it?

Prevention vs CureAs the old saying has it, "prevention isbetter than cure" and that is certainlytrue with project -building. Thefoundations for a "work -first-time" arelaid from the start. First of all, we musthave a sound design and layout, and ifthe project is one that is published by areputable electronics magazine thereshould be no worries on that score. If itis one of your own designs thenobviously you are well qualified tohandle any problems that may turn up.However, most projects are built frompublished circuits by constructors whodiffer in technical competance. Somemay have only a hazy idea of how thecircuit works, in which case fault-finding, should it be necessary, couldpose problems. Careful building of agood design is the only sure guaranteeof success.

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Sometimes a constructor will modifysome part of the published design inorder to improve its performance or toadd or change some feature or facility;this is where caution must be exercised.In most cases, performance will havebeen optimised by the original designerand further improvements are unlikely,other than by going beyond the originalframework of design. Almost anycircuit can be improved, but only if oneis prepared to make it a lot morecomplex and expensive!

Modifications to change somefacility to one more in keeping withone's own requirements are legitimate,but you need to be sure of what you aredoing. It is often better to construct itas designed, get it working, thenmodify it afterward. At least you knowthen, where you are and where thetrouble lies if problems should arise. Thesection it is planned to modify can bebuilt on a temporary basis, with com-ponents not permanently fixed andsoldered into place.

ConstructionIn the majority of cases, the design isconstructed as published, withoutalteration, and success then dependson the quality of construction, and thecomponents.

There are a number of commonconstruction errors which arefrequently responsible for many faultsand which we will now discuss. Mostpublished designs include a PCB patternthat can be copied and etched, butsome use a Veroboard layout.

With the custom -designed PCB, caremust obviously be taken in copying,masking and etching and, especiallywhere fine circuit tracks and/orspacings are involved, a carefulexamination with a magnifying glassshould be made to see that all thecopper has been etched away betweentracks and that no etching solution hasencroached on to a track due to faultymasking. The larger areas of spacing orconductor are usually fault -free, unlesssomething has gone radically wrongwith the etching.

Veroboard has its drawbacks, butcan be very useful for many smallapplications where high currents are notinvolved. However, although theconstructor is spared the task ofcopying and etching, rather more care isneeded in the actual construction. Forexample, cuts are required in certainplaces along the tracks and all theseshould be inspected through amagnifying glass, however clean theyappear to the naked eye. Another pitfallin making track cuts is their position.Errors can easily occur and the wrongtrack or position cut. To avoid this,count the number of holes along thetrack from the nearest end and placethe cutting tool on the hole while youcount back again to the edge. Then,select the right track by counting infrom the edge, moving the tool to thetrack so counted and, as before, countback to the edge to double check. Thetool should thus finish up on the correcthole. Now make the cut without

11removing the tool or, if for some reasonit must be taken off, at least make a


Featuredefinite mark with it so that the positioncan be identified.

ComponentsA problem that frequently arises is thatcomponents of the specified type orvalue are not available. The choice is,therefore, between waiting an idefiniteperiod in the hope that the required partwill be obtained, or substitutingsomething else. Substitutions can bemade providing they are of a type whichis equal or superior to that specified.

In the case of resistors, carboncomposition types are the cheapest andused for general applications wherenothing else is required. Other typeshave particular characteristics whichmay be important in the particularcircuit. High stability carbon filmresistors generally have improvedcharacteristics, with about double thevalue -stability when not in use andsome four times the stability ofcomposition resistors when operated atfull power rating; generated noise isabout a third, the maximum operatingvoltage is higher and the temperaturecoefficient is less, but amount dependson the value.

Metal oxide resistors have evenbetter characteristics than the carbonhigh -stab types, with particularly lowself -noise generation - about a tenth ofthe high -stab value - and a lower tem-perature coefficient; value -stability issome four times better at full rating, butthe voltage rating is lower than eithercomposition or film resistors.

Metal -film resistors generate aboutthree times as much noise as the oxidetypes, but are still better than thecarbons. They excel in temperaturestability, being some two -and -a -halftimes lower than the oxides, but theyhave the lowest maximum voltagerating. Another type is the thick -filmmetal glaze resistor. This combines thelow noise properties of metal -oxidewith the stability of metal -film and isalso the smallest, for a given wattage; itis also the most expensive!

Thus, the choice depends on theuse, and the designer has taken this intoconsideration when specifying a certaincomponent. However, if a substitutemust be made, then another type withsimilar characteristics can be chosen.

The wattage rating of resistorsshould not be lower than that specifiedbut can, with advantage, be higher.This will improve reliability but will takeup more room,so where close packedcomponents are involved, larger sizescould be difficult to accomodate.

Resistance values are always givenin the preferred E12 range, whichadvances in 20% increments. There isalso an E24 range which increases in10% steps; these are less commonbut may occasionally be specified (seeUnderstanding Component Values, inHE June '82 issue). Usually, if aparticular type of resistor is stocked bya supplier, all the values in the range willbe held. Sometimes particular valuesmay go out of stock, but the value canusually be made up by connecting twoothers in series or parallel, using Ohm'sLaw to calculate the values.

The same is true of capacitors,where the type of dielectric isdetermined by the application.Polyester is a good general purposematerial; polycarbonate has a lowtemperature coefficient and so isdesirable when stability at temperatureextremes is required; polystyrene has avery high insulation resistance, of theorder of a hundred times greater thanmost others, while polypropylene isbest for pulsed voltages and ACoperation. Large values requireelectrolytics, but these have a highleakage factor, so where this isimportant, tantalum capacitors, withabout a third of the leakage, should beused. They are smaller, and also nearlythree times the price of electrolytics.

The voltage rating of all capacitorsshould exceed the voltage across them,under all operating conditions, by acomfortable margin. Reliability isimproved if higher voltage ratings thanspecified are used, but this usuallymeans larger components.

At the low capacitance end of thescale there are polystyrene, silver -micaand ceramic capacitors. Ceramics arecommonly used, but silver -mica typeshave better temperature stability incircuits where the value must beconstant. As they have a positivetemperature coefficient (whereasceramics are negative), the requiredvalue is sometimes made up byparalleling one of each type in criticalcircuits, to improve the temperaturestability.

With diodes and transistors, thereare often equivalents of another makewhich can be satisfactorily used, but

not if the circuit is designed to takeadvantage of some particular propertypossessed by a certain device. Therewill be some cases where a listedequivalent may not work as well! If atransistor is specified with a suffixletter, A, B, or C, this should not beignored. The suffix refers to the gaingrouping - lowest for the A types andhighest for the Cs. Many circuits aredesigned for a specific gain, and will notfunction correctly with any other.

Although seemingly simple, diodescannot be substituted withoutconsideration of the characteristics. If agermanium type is called for, do notthink that a silicon diode will do.Germanium has a lower forward voltagedrop, and this may be needed in a circuitinvolving low voltages. Also, a point -contact diode has a low capacitancewhich makes it suitable for high -frequency circuits, and so could not besuccessfully changed for a junctiondiode.

Integrated circuits are morespecialized and substitutions cannotusually be made without circuitmodification, unless the replacement isa direct equivalent of another make.The only room for manoeuvre, here, isthat some ICs come in differentlypackaged versions, and one may beavailable while another is not. Of coursethis could upset the PCB connections!

Mounting ComponentsAssuming all the components, orsuitable alternatives, are to hand, andthe PCB is prepared, the next stage is tomount them. Some constructors like tomount the parts one at a time and solder

0 0 0 0 0 0 0 0 0 0 00 0 0 0 0 O 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0TRACES OF COPPER

LEFT AT EDGE OFTRACK AFTER CUTTING

Figure 1. When cutting Veroboardtracks, ensure that no fine copperbridges are left at the edge of the cut.

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Figure 2. Check that component wiresare all going to the right holes. It iseasy to make mistakes, as can be seenby comparing (a) and (b).

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Figure 3. When a component straddlesseveral holes on a matrix board countthe number as it is fitted. It is not soeasy to check when the part is in place.

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Figure 4. The easy way to rememberthe connections to a diode; the bandmarks the straight line of the symbol(the cathode) and with power diodes,the taper points in the same directionas the arrow.

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Figure 5. Transistors can be fitted moreeasily, and errors reduced, by cuttingthe wires to unequal lengths. Theemitter wire is left full length, the baseis cut shorter and the collector theshortest. They are inserted in the sameorder.


Feature each one, while others prefer to mountthem all, retain them by bending thewires, then solder all at once. The lattermethod has some advantages in thatany mistake can be rectified withoutunsoldering, and it is usually quicker todo all the soldering operations together.

Whichever method is followed, it is agood practice to leave all thesemiconductors to last, mounting andsoldering the passive components first.Thus, the transistors or ICs will not berepeatedly subjected to conducted heatfrom the iron as associated componentsare soldered in. In the case of ICs, it iswise to use sockets rather than solderthe device directly in to the circuit. Notonly does this remove any possibility ofdamage by heat but it facilitateschanging the device, should it provefaulty. Furthermore, suppliers are moreinclined to change a faulty IC if the pinsare unsoldered.

There is always the likelihood ofcomponent wires being inserted in thewrong holes - even in a PCB, butespecially with Veroboard, where allholes are in rows. Take special carewith this, and where the componentstraddles several holes, count them!After getting the first hole right, it iseasy to put the other wire in, say, thesecond instead of the third hole along.

Watch that you have the correctresistor values, because some coloursare difficult to distinguish on smallcomponents; red and orange, forexample, can easily be mistaken. Inparticular, make sure that you arereading the colour code from the rightend! There are four values, especially,that can be easily mistaken. A 270k,

(red -violet -yellow) can be mistaken fora 4k7, (yellow -violet -red), while a 1 k2,(brown -red -red) could be thought to bea 220 ohm (red -red -brown) and, ofcourse, vice -versa in both cases.

When mounting capacitors, it is agood practice to fit them with theirvalues uppermost, or where they can beread. While not affecting the working ofthe circuit, it will help with componentidentification should the circuit needservicing later. Ensure that allelectrolytics and tantalum capacitorsare wired in with the correct polarity;this is another very easy error to make,so check when fitting and alsoafterward.

The same is true of diodes; someconstructors find difficulty inremembering which way diodes aremarked. An easy method is to regardthe band, at one end, as the straight lineused to depict the cathode in thediagram. In the case of power diodes,the tapered end is also the cathode andcan be remembered as the end to whichthe 'arrow' in the diagram is pointing.

Care is likewise necessary in fittingtransistors, and double-checking isnecessary to make sure they are wiredcorrectly. Difficulty is sometimesexperienced in getting all three of thewires in their holes at the same timewithout any slipping out, so here is a tipwhich aids this operation and alsoreduces the possibility of incorrectfitting. Cut the wires to unequal lengthsby leaving the emitter as it is, cuttingthe base somewhat shorter and thecollector the shorter still. Now fit thelongest wire in its hole first, followed bythe next and finally the shortest; Each

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(a)

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(b)

Figure 6 (a). Untidy fitting with wiresleft too long, leading to possible shorts;(b) the same layout wired neatly, as itshould be.

Figure 7. Testing diodes; with themeter positive to the anode, the ohmsreading should be very high. When thecathode is connected to the meterpositive, the reading should be around1,000 ohms.

Figure 8. Checking a NPN transistorwith a meter; with positive to emitterand negative to collector, there shouldbe very high or infinite reading.Connecting a 10k resistor betweenbase and collector should give areading much less than 10k. Reversethe polarity for PNP device.

b

Figure 9 (a). A good soldered joint issmooth and rises gradually from thetrack; (b) a bad joint is lumpy, curlsunder at the base and dips inwardtoward the wire, but not all bad jointshave all these features.

one being longer than the next, it staysput in its hole, without coming out.When all are in place, bend, solder andcrop off the excess. If the habit isestablished of fitting the emitter firstand collector last, correct insertion isalmost guaranteed!

In the case of ICs we have theproblem of being able to insert them, inthe PCB or in their holders, the wrongway round. Not only are there twoways of plugging in an IC, but theidentification is not at all clear. A dot atone end marks 'pin one', but it is oftenno more than a shallow depression, sowatch out for this; it is all too easy,when turning the board over andworking on both sides, to get it wrong.It is a good idea, when preparing theboard initially, to put a mark either withpaint or a marking pen, at the site of allICs on the 'pin one' end. Then, whenassembling or changing them later, thechance of a mistake is reduced.

As to the actual mounting, fitcomponents fairly close to the board sothat surplus wire is minimised. Shortscan occur between wires of adjacentvertically mounted components, somake sure that these are well spaced.Also ensure that vertical componentsare seated firmly on the board,otherwise they man lean over andtouch. Transistors should have shortleads - but not too short, they man bedamaged by heat, when soldering, andfuture servicing may be hampered.

Checking ComponentsIs it necessary to test componentsbefore they are fitted? With many, thisshould not be necessary; resistors, forexample, are very rarely faulty fromnew, other than obvious physicaldefects such as loose end -caps orwires. Also, it is most unusual for avalue to be outside the rated tolerance.Wire -wound resistors could bechecked, as occasionally one is foundto be open circuit.

Electrolytic capacitors should betested for leakage, as any held in stockby the suppliers for any length of timecan develop high leakage currents.Resistance, when measured with anohmeter, should be well above amegohm, although it will be lower ifmeasured reverse -connected (note thatthe positive lead of the meter is actuallyof negative polarity when switched toohms).

Diodes should be tested beforefitting. Cases of new diodes being opencircuit are certainly not unknown, and inat least one case a power diode wasfound with reversed polarity! This couldhave been disastrous had it not beenchecked before fitting. To test, connectthe ohmeter across the diode with thepositive lead to a cathode (band orrounded end) whereupon a reading offrom a few hundred to a thousand ohmsshould be obtained. Then reverse themeter leads to obtain a very high or in-finite reading.

It is prudent to check transistors, andthis can also be done with an ohmeterand a resistor. For NPN devices,connect the positive -marked meter lead(which is actually negative) to the


Featureemitter and the negative -marked lead tothe collector; there should be noreading. Now connect a resistor ofabout 10k from the base to collector. Areading of around 10k should beobtained; the actual reading depends onthe gain of the transistor and the valueof the resistor, which can be any valuefrom 10k to 33k. If the reading is a littlehigher than the value of the resistor,you are looking at the base/emitterjunction, through the resistor, whichmeans that the collector is open circuit.If you get no reading at all, the emitter isopen circuit; a low reading beforeconnecting the resistor means eitherthe device is short circuit or is reversedpolarity. Try reversing the meter leads;if the reading is still low, it is definitelyshorted, but if it now gives normalresults, the polarity is wrong and youactually have a PNP transistor! Fortesting PNP transistors, connect thepositive meter lead to the emitter. Asnew transistors have been found to beshorted, open, and with wrong polarity,it is by no means a waste of time to dothis!

If constructing is your hobby, andyou regularly build circuits. it isrecommended that you equip yourselfwith a transistor tester such as theEagle TT 145 or similar instrument, aswell as the obligatory multimeter. Youwill then be able to measure gain,leakage, polarity, and be able to matchup transistors for complementary cir-cuits.

SolderingQuite a number of faults are due tosoldering defects so take care; thesymptoms they produce can be quitebaffling. Firstly, always ensure thework is clean; handling the board canleave greasy deposits that resist thesolder but a clean -off with a spot ofmeths will get rid of most of the grease.Apply the iron to the work with a littlesolder on the bit to facilitate the flow ofheat and, after a second or two,introduce the solder, which should melton the joint itself. Wait another coupleof seconds until the solder can be seento be flowing freely, then remove theiron. Do not carry the solder to the workon the iron, and do not try to 'paste' iton like applying putty.

After the board (or the section youare working on, if it is a large one) iscompleted, examine every joint with amagnifying glass, scanning across theboard in strips to ensure none aremissed. With Veroboard this is easy, asyou only have to run along each track inturn. Every joint should be smooth witha gradual rise from the copper and asmooth taper to the component wire.Any sudden rises, hollows around thewire, or blobby looking lumps of solderspell bad joints. Re -heating with the ironfor a few seconds will, in most cases,put things right.

Another possibility is the presence oftiny whiskers of solder between tracks.So, when scanning the board fordoubtful joints, examine the spacesbetween close running tracks; with theVero, examine every space! A furtherpotential cause of trouble is the wire

cropped off from components; piecescan lodge in all sorts of places andescape detection so, when cutting thesurplus wire, hold the board so that itfalls away onto the bench, then gatherthem up and dispose of them beforethey find their way into trouble.Likewise screws, washers or otheritems of hardware that may be droppedinto the works when assembling. If itseems to have disappeard, don't takethe easy way out and fit another;search for the truant, even if it meansupending the project and shaking it.Wandering screws can be responsiblefor all kinds of future problems.

Fault-findingIf all the above suggestions are carriedout during the building, the chances ofnon -operation at first switch -on aregreatly reduced. However, it can stillhappen, so what do we do then? Themost likely causes in order of probabilityare: soldering faults, including damageto components by soldering; PCBfaults; incorrect assembly or use ofwrong components; defectivetransistors or ICs; defective passivecomponents.

As can be seen from this list,construction faults are still the mostlikely in spite of your precautions, so acareful visual check over the wholething is the best first step. It issurprising how obvious errors can besitting there, looking right at you, yetpass unobserved. So do not takeanything for granted; check everythingagain.

If this fails to reveal the cause of thetrouble, use the multimeter to checkvoltages. The absence of a voltage will,in many cases, indicate where the faultlies. Sometimes a voltage will bepresent but incorrect, such as a fullsupply voltage on a transistor collector.This suggests zero current due to noforward bias on the base, an opencircuit emitter junction or transistor.

Actual voltage readings dependentirely on the type of circuit, but a fewbasic rules are: the collector of a NPNdevice must be positive when measuredfrom the emitter, usually by severalvolts; if the emitter does not go directlyto chassis or earth, it will be slightlypositive, usually by less than one volt;the base should be OV6 more positivethan the emitter, in the case of silicontransistors. If the device is used as agate or switch it may be biased off,normally, in which case the voltagewould be high on the collector and lowor zero elsewhere.

Check all the supply points to theICs, measuring on the actual pins, butbe careful! Use fine pointed meter prodsto avoid bridging two adjacent pins, asthis might put supply voltage where itshouldn't be, with disastrous effects.Measure the voltages on the circuit sideof stabilizers and across zener diodes,to ensure that they are workingproperly.

With PNP devices, the collectorvoltage will be negative and the baseOV6 negative with respect to emitter.For germanium transistors, the voltagedifference will be OV1 5.

If voltage readings fail to show upthe cause of the trouble, we will have todelve deeper. Try to establish whatparts of the circuits are working. Howthis can be done depends on thefunction of the circuit and what it issupposed to do. Usually, the circuit isintended to operate on some sort ofsignal, whether audio, RF, DC control ordigital pulses, and respond in some wayby amplifying, triggering, controllinganother circuit or an electro-mechanicaldevice.

It may be possible to determinewhether the input signals are presentor, if this is uncertain, suitable signalsmay be produced by other means.Disturbance testing has long been usedby professional engineers as a quickcheck; this can be as simple asscratching a test prod on the input pin,thereby producing pulses that extendinto the RF spectrum. If this producessome response at the output, even ifnot the required result, it shows that thecircuit is working to some extent.

The main thing is to worksystematically, not hopping from onepoint to another, hoping to alight on thetrouble by chance. Establish the area ofthe fault by eliminating those parts ofthe circuit that appear to be working,and concentrate on the doubtful ones. Itis not unlikely that more than one faultexists and that possibility must alwaysbe considered.

Resistance readings with, of course,the equipment switched off, can oftenbe illuminating. Measurements to earthfrom points that normally carry novoltage sometimes show up short-circuits that would not otherwise berevealed.

The IC will probably come undersuspicion, at some point. Unliketransistors, it cannot be tested out ofthe circuit before fitting, so when theother components in the affected partof the circuit have been absolved,attention naturally turns to the IC. Manycircuits use several of the same type inwhich case, if they have been fitted bymeans of sockets, a swop can easily bemade to see if that makes anydifference. If faulty, it means that, now,some other part of the circuit will notwork.

It is a good idea to keep a few sparesof the cheap, commonly used ICs, as itis with general-purpose transistors anda selection of resistors and capacitors.All told, the cost of a small stock is verylittle but can be well worth while whenchasing faults or experimenting.

Although publishers of the originalcircuit will, in most cases, offer whatsuggestions they can in response to aletter for help(and provided an SAE isenclosed! - Ed.), servicing at a

distance, without being able to maketests and observe results is rarelysatisfactory; they will often suggestthings you will have already tried.

However, if care is taken in the initialconstruction, and systematic testsmade in the event of trouble arising, thefault should eventually be localised.Although it may be irritating at the time,it will add to your experience - andmake the next project that much easier! HE


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Nostalgia is a wonderful thing ... why,it seems like only yesterday when I firsthad the chance to parade my jour-nalistic talents before an unsuspectingpublic. Since that epic day, way backin August 79, I've stood firm againstoverwhelming odds (and editors!) tocontinue to answer your questions. I

hope you appreciate it! But now forthis month's offerings, the first ofwhich had me working overtime!

Dear CD,How good is your memory? Can youremember if any faults appeared in theEnvelope Generator project published inthe June '81 issue of Hobby?

I'm at the point of filing the projectfor future reference (ie finishing it!) soI'd be grateful for any advice.

Also, am I right in assuming that if Iuse a BC183L in place of a BC183,then the leadout wire configuration ischanged?

Your replies will a) cure my insomniaand b) prevent hair loss (due to metearing it out!)Kevin McKeourn,Cirencester,Gloucs.

PS Have you ever thought of publishingan auto - wah project?PPS The sounds I can get with your ef-fects hooked up to my penny whistleand chime bar set-up are amazing!

I hope you realise that my memory isvery good ... in fact, it's excellent! So,I can tell you, categorically, that theEnvelope Generator was without errors- check your unit again. As you say,changing the BC1 83 for a BC183L willmean wiring the leads differently.However, this is not the only compo-nent that must be correctly oriented, somake sure all the others are right.

Can't say I've ever thought ofpublishing anything (not even mymemoirs), but the editor tells me thatHE did an Auto-Wah in June 82,though it was designed with guitaristsin mind. Maybe it's time for you tomove onto something a little moremusically adventurous - dustbin lidsperhaps?

Dear CD,I like playing with TV games and handheld electronic games but I haven't gotone of my own. I'm sure that yourteam could come up with an idea. Imostly like playing with TV games,please please I am only 10 and am nottrying to scrounge a binder.David Ovington,Camberley,Surrey.

PS Is the Digi-Die in the January 80issue a Digital Dice?

Surprising how many young HE -menseem to spend most of their time play-ing games. In my day ... ah, but that'sanother story. Anyway, "our team",as you call them, is working on such aproject at this very moment - aftertheir tea-break of course - so youshould see it within this noble tome inthe near future.

As for the Digi-Die, it displays thenumbers on seven LEDs arranged likethe spots on a standard die and it isdigital since it deals with logic signalsor binary digits.

Dear CD,Re: HE OCTOBER 1981 - BABYALARM

Unfortunately you have neglected toprint the track breaks in the Veroboardlayout for this project. Please can youeither send me a diagram of the breaksor print them in the next issue.Paul Brade,Herne Bay,Kent.

Unfortunately you have neglected toenclose a SAE, which must accompanyletters enquiring about Hobby projects.Of course, if you were a regular readeryou'd know that already. You'd alsoknow that we published the answer toyour question in 'Your Letters' March82. So now you know ... eh? I stillhaven't told you where the breaks aresupposed to be - well, since you didsay 'please': the breaks were merely toprevent the mounting bolts shortingany of the tracks. Omit the bolts (usedouble sided adhesive pads) andyou've solved the problem. Happynow? Good.

Stop me if you've heard this one - let-ters to Hobby Electronics must includea SAE if they require a personal reply.You're right, it's not a joke and you'veprobably heard it before, but if it meansone less letter using up the precioustime of our back -room boys (as someof you like to call them), then it's worthrepeating. So, I will: letters needingwritten replies must include a SAE.However, just to be awkward, lettersto my own honourable personage don'tneed a SAE because questions willusually be answered through themagazine. Indeed, in an effort to allowothers to share the limelight, letters Ireceive WITH a SAE are usually passedto the Technical Queries department,leaving me to concentrate on giving myall for readers of this page. Aren't Igood to you?

Dear CD,I am writing in the hope that you maybe able to answer the following ques-tion:

Is it possible to receive an electric

shock from a 12V car battery?I have asked several people the

same question and they all said yes.This leaves me puzzled however, as Iwouldn't have thought it possible,since 12 V doesn't seem to be a harm-ful voltage level.

I would be most grateful for any in-formation on this matter as I wouldprefer to use a battery for low voltageequipment thus eliminating the need formains connections to power suppliesetc.Wm. Lumsden,Glasgow.

Interesting one, this, because it reallyboils down to 'What is an electricshock?' The truth of the matter is thatreactions to a shock vary greatly bet-ween individuals. Some are almost un-shockable, while others jump at thesmallest things (small rodents in-cluded!). However, I diverge, theanswer to your question is no - unlessthe voltage has been stepped up. Infact as the potential gets higher,assuming the current is not limited, themore dangerous the possible shock.

More to the point, though, if youbuild a proper PSU then the wholeissue becomes irrelevant. They're a loteasier to carry around and a lotcheaper!

Dear CD,Please, Please, Please, Please, Please,Please, Please can I have a binder. Thepages of my March '82 issue havealready fallen out. You'd better, oryou'll have my mum to deal with (my,you should see her). Secondly, howabout a digital, I repeat digitalvoltmeter (DC). I've looked in manymagazines and haven't seen one. Ithink that ones with meters in areuseless! As your loyal and faithful ser-vant would indeed love a binder.Yours sincerely, loyaly (or loyally?),F. Woodroffe.

PPS Where can I get a book aboutbuilding experimental circuits onVerobloc?

PPPS Sorry about thepunktchewayshun but I came 28th outof 31 in lnglish.

Faced with all that, what can a peace -loving man (or woman) do but send abinder - so, that's where this month'sblue and gold delight is going.Regarding the question about a DCdigital voltmeter, you'll be happy to hearthat one was printed last month. Also,you need look no further than our'Breadboards' page, for a source ofcircuits to experiment with. Oh, and,incidently, you're punctuation wasn'tthat bad, just your spelig! HE


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Project

Audio Analyser

CONSTRUCTION of this project is notfor the faint-hearted! To make thisproject handheld has meant using twofairly dense PCBs. so you can put awayyour gas -fired soldering irons andpliers; delicacy, finesse and a steadyhand are required. Use an iron with asmall bit and make sure you don't leavehuge blobs of solder that bridge thePCB tracks. IC sockets are not justrecommended; we insist upon them. Fitthe components to the boards in theusual way, filter board first, takinggreat care to observe componentpolarity where this is important. Don'tmiss out any of the wire links; anddon't try to finish it all in one evening- or two. Time 'saved' duringcontruction will be wasted on fault-finding, later!

The nice men who designed the4017 didn't put its sequential outputs'sequentially' on the IC pins and thisoften leads to tricky PCB layouts whenusing the IC. Fortunately we can cheat,because all we need in this project is tolook at each of the 10 channelsseparately - so long as they appear onthe right display columns it doesn'tmatter what the actual order is. This iswhy the filters don't run in sequencedown the PCB - it's purely forconvenience.

To avoid the use of a double -sidedPCB for the display matrix, a rathercunning technique has been adopted.Solder in one row of LEDs only and cutoff one pin only - the ones whosesolder pads are linked by copper tracks.Now solder a length of tinned copperwire to the pad indicated, bend it overso it touches the other LED pins about3/4" away from the board, then solderall the pins to it and trim them off. Thendo the next row, and so on. Mistakesmade here will be almost impossible tocorrect later, so check that every LEDin every row is the right way roundbefore you solder it. The most certainmethod is to use Figure 2; flats, dotsand 'one leg is shorter than the other'can all lead you astray.

The case used was a Vero type 1(reference number 202-21034),external size 205 x 140 x 40 mm; afair bit of work with a sharp chisel isrequired to make everything fit,though. The vertical slot guides at bothends of both case halves should beremoved, plus all the PCB mountingpillars in the grey (bottom) half and theouter set of four pillars in the white(top) half. Everything mounts on thetop half except the on/off switch,which is fitted in the side aluminiumpanel.

The two PCBs are bolted togetherwith stand-off pillars and have anumber of wire links between them.The easiest way to do this is to solderlengths of tinned copper wire to therelevent pads of the display board andcut them down slightly to differentlengths, gradually increasing as youmove down the board (Figure 3). Thenyou can insert the longest link onto the

Concluding theAudio SpectrumAnalyser projectwith the method ofconstruction andsetting up.

filter board, move the two closertogether, insert the second and so on,until they're all through.

Assembly starts by test -fitting thedisplay board and making a hole for thedisplay. It's a good idea to glue a pieceof red plastic or polarising filter behindit to improve the contrast of the LEDs.Fix the pillars to the display board andscrew into the case - the transistorsand tantalum capacitors will probablyhave to be bent over to give clearance.Now slide the main board over thewires, as described above, solder allthe links and trim them. Now the wiringfor the off -board components can becompleted.

We found the cheapest way ofgetting an electret mic element was tobuy a cheap electret cassette recordermic (about £3) and cut the end off it.Do this very carefully as you musn'tdamage the insulation on the internalwiring; you'll need it to link the mic to

LED CATHODES

LED ANODES 1 TINNED COPPER WIRE

tt. t, t, t,t,t\PC'mt0000.

Figure 1. Wiring the LED matrix; it is bestto check all the LEDs before solderingthem in, because replacing one will bevery difficult once the boards areassembled.

Figure 2. Pinconnections of aLED.

TINNED COPPER WIRE

1101711

PCB 2

PCB 1

Figure 3. Fitting the links between thetwo boards.

SIGNAL

Figure 4. Connections to an electretmicrophone.


Project

81

0 0 0 0 00

c,

82

I I I I

L

PINK NOISEOUTPUT

(cab)-4 R75 1--

SKI

13110 009 13130 0D15 D190 0 017 UZI

00120100 0" 0160 0020

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put

32 H:

PR?

63 Hz

PR?

125 H,

PR5

500 Hz

PR 4 PRES

250 Hz 1 kHz

PR?

2 kHz

PR9

8 kHz

PR9

4 kHz

PR 10

16 kHz

D3

NOTE: D3.022 ARE MOUNTED VERTICALLY e g (32-k ir

Figure 7. The filter board component overlay.

t-1

the PCB. Glue the mic into a suitable -sized hole cut in the end of your caseand connect it to the PCB as shown onthe overlay; the existing batteryterminals of the mic will tell you whichare the positive and negative supplies,while the third wire is the signalconnection (probably screened by theearth wire). If you don't feel yourconstructional abilities are up to this,just plug a mic into the external jacksocket; not as compact but mucheasier.

If choosing an alternative case, bearin mind that you'll want easy access tothe batteries; the current consumptionof the unit is quite high and you'll eitherhave to replace your alkalines regularlyor, if you've been sensible, rechargethe Nicads.

Anyone who attempts to improve onour PCB design is on his own. Anyonewho attempts to build the circuit onVeroboard will be recommended forcommittal to a mental institution.

Figure 5. View of the LED display fromthe foil side.

.XiVrA.

as -

---

444.4-ti

Figure 6. The completed display board.

Setting up and UseThe unit can be set up using either thebuilt-in pink noise generator or, betterstill, with a sine wave oscillator. AdjustPR10 to about 75% of its travel (wipertowards the clockwise direction). Withthe unit switched on and the sine waveoscillator connected to the externalinput, by sweeping the oscillatorfrequency, each column should comeup in sequence. Adjust the sine wavefrequency and the analyser levelcontrol until the 16 kHz column ispeaking at a column height of abouteight LEDs.

Now, using the same amplitude andwithout touching the level control,adjust the signal generator frequencyuntil the 8 kHz column peaks andadjust PR9 to give the same height.Repeat this adjustment for each of thefilters. Due to component tolerancesthe actual peak of a filter may not


Project

NOTE: The parts list publishedlast month contained several errorsand these are corrected here.

RESISTORS (All 1/4 watt 5% carbon)R1,2 220kR3 2k2R4,5,69 15kR6-10,31-35,72 10kR11-15,21-25,36-40,46-50,78 1MR16-20,41-45 220RR26-30,51-556876 . 100kR56 680kR57 6k8R58-67 47kR68 100kR69 15kR70 430RR71 27kR73 4k7R74 180kR75 18kR77 390k

POTENTIOMETERSRV1 47k

log carbonPR1-10 220k

min horiz preset

CAPACITORS (All metallisedPolycarbonate unless noted)

Parts ListC1,13,43,49,50 100nC2,3,41 10u 16V

tantalum beadC4,5,7 1u0C6 56nC8,10 27nC9,11 270nC16-20,35-39 2u2 35V

tantalum beadC12 6n8C14 18nC15 3n9C21,22 39nC23 1n5C24 33nC25,32,33 2n2C26,44 820p

ceramic discC27 12nC28 3n3C29 470p

ceramic discC30 10nC31 180p

ceramic discC34 100p

ceramic discC40 22nC42 1nC45 2n7C46 5n6C47,48 220u 16V

axial electrolytic

SEMICONDUCTORSICI LF353

dual BIFET op -ampIC2-6 TL064

quad lo -power op -ampIC7 4011

CMOS quad 2 -input NANDIC8,9,10 4016

CMOS quad analogue switchIC11 LM3915

bargraph driverIC12 4017

CMOS decade counter/dividerIC13 4070

CMOS quad EX -ORIC14 4006

CMOS 18 -stage shift registerQ1-11 BC184L

silicon NPN transistorD1-22 1N4148

signal diodeLED1-100 . high efficiency red LED

(see Buylines)

MISCELLANEOUSSK1 % " jack socket

with break contactsMIC1 electret microphone

(see Buylines)PP3 battery clips (2 off); IC sockets(13 off); case; wire; solder; PCBs,etc.Buylines page 33

correspond exactly to its nominalcentre frequency. The 16 kHz filterhas the greatest loss which is thereason for starting with it near itsmaximum gain.

If a sine wave oscillator isn'tavailable, connect the pink noiseoutput to the external input and adjustthe presets to give an even responseacross the 10 channels. Each columnshould be approximately the sameheight; due to the nature of noise, thetop of the columns may jump up anddown slightly and this should beaveraged out by eye. If one of thecolumns appears dimmer than the rest,replace the transistor that drives thatcolumn; if only a single LED appearsdim then it must be replaced but aswe've pointed out, the method ofcontruction make this a bit tricky. It's agood idea to either buy good qualityLEDs or test them individually for dudsbefore commencing construction.

To measure a room set-up, feed thepink noise into the hi-fi or PA systemvia a cable from the listening positionand adjust the graphic equalisercontrols until a flat response isindicated.

A final point; the microphone usedmust be fairly flat or its frequencyresponse will affect the measurementsyou're making. If you use one with alimited bandwidth it's possible to usethe presets to compensate; however,to do this properly you'll need to playthe pink noise into the mike via a soundsystem/location you already know tobe flat.

Figure 8. Display board component overlay.

LED1 -100

'd0 G G 0 CI C COO- =aGO00GOOGGC1-000000000C0000000000-0000000000-0000000000-00000000GO-00000000GO-0000000000-0000000000-

® CODODDD'3-33D'c

e"

® ED CD CD ®

IC8

4f., PI re ',AAAIC9

NOTE: CIRCLED PADS INDICATE LINK -WIRES BETWEEN THE PCBs (SEE TEXT) HEHobby Electronics, September 1982 59

r-

BACKNIUMBERSFebruary 1980 September 1980 April 1981Passion Meter, Win Indicator, MicroMixer, Reaction Tester, Pre -Amplifier Part 1, SuperShort Circuit Special, Kit Review Guitar Phaser, Development Siren, Guitar Tremolo, RussianSpecial, Into Electronics Timer, Teletext Explained, Into Roulette Game, Doorbell VAConstruction Part 1. Digital Electronics Part 1. Monitor, Anatomy of a Space **...

Shuttle.

In." M...RATUK. CS warts

-;4.4_P..

If ti

May 1980MiniClocks, 5080 Preamp, ModelRailway Track Cleaner, 5080Loudspeakers, LoudspeakerCrossover Design, RadioControlled Model Survey.

June 1980Microbe Radio Control System,Egg Timer, Two Watt Amplifier,Fog Horn, Short Circuits, LEDsand LED Displays.

July 1980Sound -Operated Flash Trigger,18+ 18 Car Stereo Booster,Hazard Flasher, Electronics inPhotography, ElectronicEspionage, Piezo Electricity.

August 1980EquiTone Car Equaliser, Pass -The -Loop Game, Gaztec GasDetector, OP -Amp Checker, In -Car Entertainment Survey,Introducing Microprocessors.

October 1980Kitchen Timer, Tug 'o' WarGame, Light Dimmer, FreezerAlarm, Intruder Alarm,Temperature -ControlledSoldering Iron.

January 1981Car Rev -Counter, BenchAmplifier, Sound -Into -LightConverter, Chuffer, ElectronicGames reviewed.

February 1981Heartbeat Monitor, High -Impedance Voltmeter, MediumWave Radio, Two -Tone TrainHorn, Audio Signal Generator.

March 1981Public Address Amplifier,Windscreen Wiper Controller,Bicycle Speedometer,Photographic Timer,Microcassettes.

May 1981Electronic Organ, Voice -Operated Switch, Infra -RedController, Pre -Amplifier Part 2,Audio Millivoltmeter.

June 1981Power Amplifier Part 1,Continuity Checker, EnvelopeGenerator, Early Radio, Gadgets,Games and Kits Supplement.

July 1981Burglar Alarm, Doorbuzzer,Treble Booster, Electronic Aidsfor the Disabled, PowerAmplifier Part 2.

August 1981Electronic Ignition,Thermometer, Electronic Organ(final part), RPM Meter, BenchPower Supply, Radio ControlSurvey, Into ElectronicComponents Part 1.

All of the 1980 issues, except January and April, are still available togetherwith the remaining issues from 1981.

II

e-*

All backnumbers cost £1.25 each. For those of you who only want copies of articles, wedo offer a photocopying service. Each copy costs £1.25 and information as to its title andpublication date should be given. Ordering backnumbers and photocopies could hardly be

easier, just fill in the coupon, cut it out and send it to:

Hobby Electronics,145 Charing Cross Road,

London WC2H OEE

Please remember to mark your envelope with the service you require,BACKNUMBERS or PHOTOCOPIES,otherwise our mailroom won't like you.

HOBBY ELECTRONICSBACKNUMBER ORDER FORMPlease send me the following items:

NAME

ADDRESS

Back issues at £1.25 each

I encloseLCheques and Postal Orders should be made payable to ASP Ltd.

HOBBY ELECTRONICSPHOTOCOPY ORDER FORMPlease send me the following items:

NAME

ADDRESS

Photocopies of in the

issue at £1.25 each

I enclose £Cheques and Postal Orders should be made payable to ASP Ltd


Lighning4,

4

ELECTRONIC COMPONENTSNEW SHOWROOM NOW OPEN * * * *

For a vast choice of electronic components & equipment of all kinds:- Here isjust a selection of our stocks.

TRANSISTORS CMOS ICs LINEAR ICs 74LS TTL ICs

BC182L 10 4000 14 LM301AN 26 74L500 12

BD124IM) 1-58 4001 14 LM380N 75 74 LSO4 15

BFR39 24 4011 15 LM381N 1-45 74 LSO8 15

BFR64 3-00 4013 34 LM386N 90 74LS10 15

BFR79 26 4017 42 LM387N 1-18 74L513 29

BLY93A 14-20 4022 55 MC1458 47 74LS20 15

MJ15003 4-05 4046 74 NE555 20 74LS30 18

MJ15004 5-04 4049 30 NE556 60 74 LS74 24

TIP41C 48 4066 35 TBA120 90 74LS107 40

TIP42C 48 4070 25 TBA440 2-52 74LS154 as

2N3055 48 4093 35 TBA800 85 74LS244 80

2N3773 2-25 ' 40106 56 74118 pin) 18 74LS386 28

40673 90 4511 62 555 20

V.Regulators (Fined) V.Regulators (Variable)78L05 - 78L12 - 78L15 0-31 LM317K 1.5 Amp. 3-3679L05 - 79L12 - 79L15 059 LM338K 5 Amp 4-70

7805 - 7812 - 7815 0-60 LM396K 10 Amp 11-00

7905 - 7912 - 7915 0-65 L723 14 DIL 0-45

MANY more types listed in our catalogue - AUDIO POWER TRANSISTOR SPECIALISTS- LIST AVAILABLE FOR BULK BUYERS - S.A.E.

CATALOGUE ONLY 70p Post Paid.ListinG: - Resistors. Capacitors. Semiconductors, Triacs. Switches. Relays. Cases, Connectors,PCB Equipment, Vero Products, Test Equip, Tools, Books, Denco Coils, Transformers, PLUS MUCHMORE for the keen constructor. Don't delay send today. (Slight delays on new catalogues at themoment as we are awaiting second print)

BARGAIN PACKS12 Asstd Panel Mounted Pots (1.10 12 Asstd Presets 0-50

20 Asstd Electrolytic Caps. 85 30 Asstd Silver Mica Caps 90

7 Asstd Blob Boards 1-10 5 Asstd Relays 1-10

1 50pF Trimmer Capacitor 20 30 Asstd C296 Polyesters 80

30 Asstd Min Ceramic Caps 70 250 Asstd Preformed Resistors 75

9 Asstd CD4000 Type CMOS 1-10 8 Asstd Switches, Micros, Slide Lever Key,10 Black & Red Croc Clips 80 push, Toggle. Excellent Value at 90p

THE LIGHTNING PROMISE - Mail order despa ched within 24 Hours, Callers welcome. If any partordered by mail fails to please just return within 7 days for refund.

Postage Et Packing 50p per order (FREE OVER C10). PLEASE add VAT at 15%Telephone orders welcome by Access & BarclaycardShowroom and Mail Order Distribution Centre at: -

18, Victoria Road TAMWORTH Staffs. B79 7H R.Telephone 0827-65767

DESOLDERING TOOL Now everyone can afford one of these superb, blue anodised aluminium highpressure hand desoldering tools at nearly half our normal price. Normal Price E6.50 + VAT. With thisad E3.85 VAT. Spare Teflon screw -in noses 75p + VAT.JAPANESE TRANSISTORS Equivalents available for most types. Please call, phone or write.

LOW COST VERSATILE MULTIMETERTHE MIGHTY MINI MULTI.TESTER 2,000 ohms per volt. DC & ACVoltage ranges: 10v, 50v, 250v, 1000, DC current ranges 100mA.Resistance ohms x 10 x 100db from -10db to + 22db. Mirror arcscale, overload protected, complete with battery, test leads &instructions. Usual price £8.65 -i- VAT; with this Ad: (4.95 + VAT.ORDER FORMNameAddress

Desoldering tools at (3.85Spare Teflon noses at 75p - EMighty Mini Testers at (4.95 = E

Postage, pecking and insurance at 60p per one device, 25p for each additional device E

Sub totalAdd 15% VAT

I enclose cheque no/P.O. noAlternatively please credit my VISA/ACCESS NoSignatureThis offer applies to UK only. Please allow 7-10 days delivery. Overseas customers please do not addVAT but allow to cover postage. TRADE ENQUIRIES WELCOME.

CRICKLEWOOD ELECTRONICS LTD.40 Cricklewood Broadway, London NW2 3ET. Tel: 01-452 0161

Goodmans Fane Richard Allan Celestion AltaiMultimeters &Accessories

UK P/P 65p or £1.00 for twoKRT 100 12 range pocket1K/volt £4.95NH55 10 range pocket2K/volt E5.95NH56R 22 range pocket20K/ volt £10.95YW360TR 19 range plus hfetest 20K/volt £14.9557303TR-21 range plus hfetest 20K/volt £17.95TMK500 23 range plus 12adc plus cont. buzzer

£23.95

High QualitySo...torsEl' to

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350W

CROSSOVERS2 way3 way4 way

NEL° ELECTRICTWEETERS

PI(ZO ROAM TWFFTFatUp lo 00 woos eachover mcpumel Rs. MornsPAO rano. Flared Horn. In

stoat now L.ro range alput, address

Ou.P.,111 ,,uoo,nos.musr. kririff or, uvrirr.

ssePno Chombs.

Anlopu Echo Charnlwrfee Si

100W Bohm100W 8 ohm80W 8 ohm

Power Amplifier Modules loon to nowStockists of leading makes of Disco Units& Lighting Equipment.

CITRONIC, FAL, TK, ICE,OPTIKINETICS, PLUTO.

SEND LARGE SAE FOR LISTALLOW 10 DAYS FOR DELIVERY

"Wpm. meradle VAT al 15% Mad Orders welcome.

sUSICIRAFT303 EDGWARE ROAD

LONDON W 2 f NG L ANDI t L LPHONE 01 402 9729 01 402 269F

CAMBRIDGE LEARNINGSELF -INSTRUCTION COURSES

A PRACTICAL DIGITALELECTRONIC KIT FOR* LESS THAN £20 *

SUPERKIT

i 1151,

-isInSJrHE;i-i4t-i

Digital Electronic Kit

suitable for beginners

SUITABLE FORBEGINNERS

NO SOLDERING!

Learn the wonders of digitalelectronics and see how quicklyyou are designing your owncircuits. The kit contains:seven LS TTL integrated circuits,breadboard, LEDs, and all the

DIL switches, resistors, capacitors, and other components tobuild interesting digital circuits; plus a very clear andthoroughly tested instruction manual ( also available sepa-rately). All this comes in a pocket size plastic wallet foronly £19-90p inc VAT and p&p. This course is for truebeginners:- needs no soldering iron.- asks plenty of questions, but never leaves you stuck and

helpless.- teaches you about fault-finding, improvisation, and

subsystem checking.- the only extra you need is a 44V battery ( Ever Ready

1289, or similar), or a stabilised 5V power supply.Using the same breadboard you may construct literallymillions of different circuits.

DIGITAL COMPUTER DESIGN £8.50 NEW!An up-to-date course on the design of digital computers- from their individual logic elements and fromintegrated circuits. You are first shown the way inwhich simple logic circuits operate and then, through aseries of exercises, arrive at a design for a workingmachine.

This course, as well as our beginners' theory course,Digital Computer Logic and Electronics, supports tnepractical Superkit series.GUARANTEE No risk to you. If you are not completelysatisfied, your money will be refunded upon return ofthe item in good condition within 28 days of receipt.CAMBRIDGE LEARNING LIMITED, UNIT98 RIVERMILL SITE,FREEPOST, ST IVES, CAMBS, PE17 4BR, ENGLAND.TELEPHONE: ST IVES (0480) 67446. VAT No 313026022

All prices include worldwide postage (airmail is extra -please ask for prepayment invoice). Giro A/c No 2789159.Please allow 28 days for delivery in UK.

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J


HE PCBs

Above: The PCB pattern for the 'Junior' Slot Car and (below)the foilside pattern for the ZX PCB.

Computer PSU

We apologise to all thosereaders who attempted tobuild the Computer PSUfeatured in the July issue. Asyou probably realised, the PCBpattern was shown half sizebut we omitted to say this inthe caption - sorry! The fullsize foil pattern is shown onthe left.


a

v

6 ocremamoommer 1.1.11 a.°

11.m01ei...441.19 as

9 6 qP06

6 9 ct ce-to6

a 9 d,°1/711

V CLImma12".°0000 0=0

db9 6 V111.1 o -o

*ADce- agoaalci(T11 -7.°43.1nolle4o

6 9 db op

do

011°1111111111010111000001110000100111100001811110000001101800001808110001000181010

HE 9B2 -I

0

0

The two PCB foil patterns for the AudioAnalyser. The display board (left) is fixed on topof the filter board (above).

0.0....4.110014.114\14104

Above: The two foil patterns for the SignalLights; uppermost is the signal module andbelow that the junction module board.


/Rea--; -HE PCB SERVICE PCBY msadei

PRINTED CIRCUIT BOARDS (PCBs) for HE projects have often represented an For Readers!obstacle for our readers. Some of you, no doubt, make your ownbut our PCB Service saves you the trouble.NOW you can buy your PCBs direct from HE. All (non -copyright) PCBs will be availableautomatically from the HE PCB Service. Each board is produced from the same master asthat used for the published design and so each will be a true copy, finished to a high stan-dard.Apart from the PCBs for this month's projects, we are making available some of thepopular designs from earlier issues. See below for details. Please note that only boards forprojects listed below are available: if it isn't listed we can't supply it.

June 80Fog HornEgg Timer

£1.87£2.11

May 81Voice Operated SwitchOrgan 1

£1.67£4.64

April 82Digital Capacitance MeterDual Engine DriverBike Alarm

£4.73£3.37£2.64

August 80Equitone Car EqualiserPass The Loop Game

£2.39£2.64

June 81Envelope GeneratorOrgan 2

£1.87£2.53

May 82Digital Thermometer(Set of Two) £5.31

September 80 Echo-Reverb £5.81Guitar Phaser £1.97 July 81 Cable Tracker £2.21Development Timer £1.80 Organ 3 £6.00 June 82Bench PSU £2.93 Organ 4 £6.00 Power Supply Design £2.64October 80Nobell DoorbellIntruder Alarm

£2.64£2.51

Ultrasound Burglar Alarm

August 81RPM Meter

£2.53

£1.77

Auto-WahAuto Greenhouse SprinklerTelephone Timer

£3.58£3.88

Tug 0' War £2.65 Thermometer £1.67 (Set of Two) £7.39

November 80Memory Bank Synth:

Mainboard PCB £3.31

September 81Power PackReaction Tester Game

£1.69£1.71

July 82TanoverTVI Filter

£2.31£2.17

Keyboard PCB £3.60 'Diana' Metal Detector £3.31 Computer PSU £8.72Party Grenade (set of three) £3.47 October 81 Solar Radio £2.15Double Dice £2.95 Combination Lock £2.65 August 82December 80Stereo Power MeterJanuary 81Car Rev Counter

£2.83

£2.99

November 81Sound Torch (Set of Two)December 81

£5.31Digital Millivoltmeter(Set of Two)Audio Analyser

£4.82

February 81 Pedalboard Organ £5.97 (Set of Two) £12.30Heartbeat Monitor £2.53 January 82 September 82Audio Signal Generator £2.47 Intelligent NiCad Charger £3.04 Flash Point Alarm £2.31March 81 February 82 Signal lightsSteam Loco Whistle £2.65 Relay Driver £2.20 Main Module £2.34

April 81 Mast -Head Amp £1.31 Junction Module £2.27Super Siren £1.97 March 82 ZX PCB £3.75Russian Roulette Game £1.60 Digital Dice £1.95 Slot Car Controller £1.99

PLACE an order for your PCBs using the form below (or a piece of plain paper if you prefer not tocut the magazine), then simply wait for your PCBs to drop through your letterbox, protected bya Jiffy bag.

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THE SCIENTIFICWIRE COMPANY

PO Box 30, London, E.4. 01-531 1568ENAMELLED COPPER WIRE

SWG 1 lb 8 oz 4 oz 2 oz8 to 34 3.30 1.90 1.00 0.80

35 to 39 3.52 2.10 1.15 0.8540 to 43 4.87 2.65 2.05 1.4644 to 47 8.37 5.32 3.19 2.5048 to 49 15.96 9.58 6.38 3.69

SILVER PLATED COPPER WIRE14 to 30 6.63 3.85 2.28 1.50

TINNED COPPER WIRE14 to 30 3.97 2.41 1.39 0.94

10 x 10 rntr reels 3 amp PVC cable mixed colours 5.00.Prices include P G P vat. Orders under E2 add 20p.

SAE for list of copper and resistance wire. Dealer enquirieswelcome.

H.E. ORGAN KITS £99.50 inc. p&p. 61note keyboards £32.00. 13 note paddleboards £25.00 inc. p&p. A.T. Hawkins, 23,Blenheim Road, St. Albans, Herts. AL14NS.

TECHNICS organ; double manual, basspedals, 12 rhythms, voices upper andlower. Cost £976. 5 months old £650;includes headphones Bench music andcover. Tel. 0978-822141

KIA RETURN ANAD No 1 FREE -Quality - Capacitor Pak!! Post this ad+ S.A.E. (121p) NOW to 8 Cunliffe Rd,Ilkley, LS29. KIA - REPAIR - AMPS -FAST!

ZX81 with 16K RAM pack and number ofcassettes, £80 ono. Almost completeHebot, £40 ono. Video space invaders £40ono. Peter Aziz, 38A Portland Road,Bishops Stortford, Herts. Tel. 0279 55683.

COPPER CLAD PCB 3p per square inch.Single sided 2p. Brand new 7 segmentdisplays bargain 45p. PCB containing eight7 segment display bulb after 2nd display toform DP £3.50. All displays tested. IC's onPCB 7p each. 100 resistors free on ordersabove £10.00 Worth £1.00. pap 30p. Freeabove £2.75. G. Dickinson, 4, StationCottages, Kippax, Leeds.

ADVERTISEMENTRATES Semi -Display (min 2 cms)

1-3 insertions £6.00 per cm4-11 insertions £5.50 per cm12+ insertions £5.00 per cmLineage 21p per word (min 15 words)Box Nos. £2.00Closing date 2nd Friday of the monthpreceding publication date.All advertisements in this section must be prepaid.Advertisements are accepted subject to the terms andconditions printed on the advertisement rate card (availableon request)

HOBBY ELECTRONICS CLASSIFIEDADVERTISING, 145, CHARING CROSS RD,LONDON WC2H OEE.

PCB DESIGN SERVICE - for cost ofartwork mail circuit diagram to 39A NewRoad, Clanfield, P08 ONR.

TELETEXT (Oracle/Ceefax) add-onadaptors for your existing television. Only£149.95 inclusive. Also Prestel. Fantasticcolour graphics for microcomputers. AvonOffice Services (HE), FREEPOST, Bristol,BS10 6BR. (0272) 502008 anytime.

SOLAR CELLS 3" dia. 900mA at 0.45V£7.59. Price lists 75p. Edencombe Ltd., 34Nathans Road, Wembley, Middx. HAO 3RX

SCOOP PURCHASE - TELEPHONESBlack G.P.O. type for extension use. As new only E4.75 each,Carriage £1.75. 2 for E12.00 Carriage paid.

HAVE YOU SEEN THE GREEN CAT?1000s of new components, radio, electronic, audio at

unbelievably low prices. Send 40p and receive list and FREERecord Speed Indicator. Try a JUMBO pack, transistors, caps,resistors, pots, switches, radio and electronic devices. Over£50 worth for E11 plus carriage £2.50.'MYERS ELECTRONICS, Dept HE1, 12/14 Harper Street, LeedsLS2 7EA. Tel: 452045. Callers Welcome.

WORKBENCHES, secondhand.a Ex -ITTTV factory. Open or cubicle style. Needspace. Details: 042 486 3464.

SECURITY SYSTEM KITS . . . All com-ponents and full instructions. Send largeS.A.E. for latest catalogue of advancedprojects for car, caravan and home.COMPU-TECH SYSTEMS, WorsteadLab's, N. Walsham NR28 9SA. Tel. (0692)405600.

BURGLAR ALARM EQUIPMENT. Pleasevisit our 2,000 sq. ft. showrooms or writeor phone for your free catalogue. C.W.A.S.Ltd. 100 Rooley Avenue, Bradford BD61DB. Telephone 0274-308920.

KWIKMAIL ELECTRONICS BargainComponents. Send S.A.E. for list or £1 forsample. Super bag. I.C.'s, Capacitors,Resistors, and more. 135 Tany's Dell,Harlow, Essex.

AMAZING ELECTRONICS PLANS.Lasers, Super -powered Cutting Rifle,Pistol, Light Show, Ultrasonic Force Fields,Pocket Defence Weaponry, Giant Tesla,Satellite TV Pyrotechnics, 150 moreprojects. Catalogue £1 - From Plancentre,46, Bye Street, Ledbury, HR8 2AA.

ELECTRONIC GAMES. Build your ownmicrochip games from our detailedcircuits. S.A.E. for details. GHT Ltd. POBox DR95, Dover, Kent CT16 1UL.

LONDON SCHOOL OF ELECTRONICSFull time/part time courses in analogue anddigital electronics and electronic design-ing. City and Guild courses also available.Fees: Full-time £1300 pa. Part time £350 for6 months. £500 for 9 months. Please applyto London School of Electronics, 67-83Seven Sisters Road, London N7. Tel. 263-5937.

ELECTROLYTIC capacitor tester/reforming units, instructions, mains/testleads, £12, Phone (07431 59492 after6.30pm

PSU's 5V5A £25.99, 1 -2V -27V 1-2A withvoltmeter £24.99. (with toroidaltransformers). Fully fused and protected.Top brand VHS video cassettes. E120£7.65, E180 £8.10. Prices include p&p. Mailorder only. Edwards Electrics, 30 St.James Square, London SW1.

MANUFACTURERS surplus new com-ponents, I.C.s, transistors, diodes,capacitors, resistors, etc. 100 assorted£1.25 post free. U.H.A. Ltd., 62 WellingtonRoad South, Stockport, SK1 3SU.

STEREOPOWER 200 watt poweramps(100 + 100W protected) 4 x T03 outputs- MJ3001 fibreglass, case + controls +D.I.N. sockets. Boxed £11.95. A. Law, 8Cunliffe Rd (Over Incatile) Ilkley LS29 9D2


POCKET COMPUTERS FROM THE SPECIALISTSSHARP PC -1500 PC -1211 CASIO FX-702P

Hardware Software Books ConsumablesIN STOCK NOW CE -155 I8K RAM) E79.95

Trade in your PC1211 for a PC1500Send for a free copy of "THE ELKAN FILE". Full of "Top

Secret" information. See us on Presto! - page 258 2022

ELKAN ELECTRONICSFREEPOST no stamp required) 28 Bury New Road, Prestwich,

Manchester M25 6LZ. Tel: 061 773 8714

SPECIAL OPENING OFFER, 1000 ITEMCOMPONENT PACK! Sockets, Presets,Diodes, Pots, Knobs, Resistors,Capacitors - : Discs, Polyesters, Plates,Electrolytics, HV-Caps, Insulators,Hardware, Etc. JUST £10+ £3.83P&P/VAT. TOTAL £14.03. Also 60 (approx)Electrolytics pack (good values) £1.20 +£1.04 P&P/VAT. TOTAL £2.24. 100 MiniDiscs £1.50 + 80p P&P/VAT. TOTAL £2.30Ideal gifts for experimenters & hobbyists,Callers welcome, Lists 50p, free withorders. Letchworth ElectronicComponents, Spirella Building, BridgeRoad, Letchworth, Herts., SG6 4ET. Tel.(04626) 70354.

CENTURIONALARMS

We manufacture, you save £££'sSend s.a.e. or phone for our Free list ofprofessional D.I.Y. Burglar Alarm Equip-ment and accessories-.Discount up to 20% off list prices,e.g. Control Equipment from £15.98,Decoy Bell Boxes from £5.95 inc.

TRADE ENQUIRIES WELCOME0484-21000

or 0484 35527 124 hr. ans.)CENTURION ALARMS IHE)

1265 Wakefield Road, Huddersfield9BE, W. YorkshireiAccess 8- Visa

Orders Welcomed

PARAPHYSICS JOURNAL (Russian 2rans-lations); Psychotronic Generators, Kirliano-graphy, gravity lasers, telekinesis. Details:S.A.E. 4 x 9" Paralab, Downton, Wilts.

PRINTED CIRCUITS. Make your own sim-ply, cheaply and quickly! Golden Fotolaclight-sensitive lacquer - now greatly im-proved and very much faster. Aerosolcans with full instructions, £2.25. De-veloper 35p. Ferric Chloride 55D. Clearacetate sheet for master 14p. Copper -cladfibreglass board, approx. 1mm thickf1.75 sq. ft. Post/packing 75p. WhiteHouse Electronics, Castle Drive, PraaSands, Penzance, Cornwall.

FIND -A -FRIEND through FIND -A -FRIEND'Snew confidential, inexpensive service. Yourideal friendship/relationship - all ages -countrywide. SAE/Telephone: FIN D -A -FRIEND (HE), Temple House, 43-48 NewStreet, Birmingham B2 4LH. 021-4296346.

BUILT TRANSMITTERS £2.90 88-110MHzFM range 150 yds. Refund guarantee(unlicensable). P. Faherty, 37, College Dr.,Ruislip.

ELECTRONICS component shop in MAID-STONE, KENT! Thyronics Control Systems,8 Sandling Road, Maidstone, Kent.Maidstone 675354.

DIGITAL WATCH REPLACEMENT parts.Batteries, displays, backlights etc. Alsoreports, publications, charts. S.A.E. for fulllist. Profords, Copnersdrive, Holmergreen,Bucks HP15 6SGE.

AERIAL AMPLIFIERS Improve weaktelevision reception. Price £6.70. S.A.E. forleaflets. Electronic Mailorder, Ramsbottom,Lancashire BLO 9AGH.

AD INDEXAitken Bros 48Ambit IFCArmon Electronics 48Bic Vero 56Bi-pak 4

B K Electronics BCBNRS 46Bradley Marshall 8Brian J Reed 38Cambridge Learning .61

Cricklewood 61

E.D.A. Sparkrite OBCElectronize Design 55

Expo 55Global Specialties Corporation 19

Greenweld 56Heath Electronics 4

ICS 8

ILP 29J. Baker 38Lightening 61

Magenta 5

Musicraft 61

Rapid Electronics 24RTVC 32Sandwell Plant 38Sinclair Research 13

Technomatic 30T K Electronics 38Velleman (UK) 46Watford Electronics 36Wilmslow Audio 8

USE HOBBY ELECTRONICS CLASSIFIED(21p per word, minimum 15 words. Box Nos. £2.00 extra or £6.00 per single column

centimetre - all prepaid).Just write the details on the form below and send it with your cheque, made payable to

A.S.P. Ltd, to Hobby Electronics Classified,145 Charing Cross Road, London WC2 OEE

1. 2. 3. 4. 5.6. 7. 8. 9. 10.11. 12. 13. 14. 15.

Please place my ad in the next available issue of Hobby Electronics:Name

Address

Tel. No.

I enclose my cheque/P.O. for the value of £


MULLARD SPEAKER KITA PURPOSELY DESIGNED 40 WATT R.M.S.8 OHM SPEAKER SYSTEM RECENTLYDEVELOPED BY MULLARD'S SPECIALISTTEAM IN BELGIUM. Kit comprises a MullardrWoofer with foam surround and aluminiumvoice coil. Mullard 3" high power dometweeter. B.K.E. built and tested crossover,based on Mullard circuit combining low losscomponents, glass fibre board and recessedloudspeaker terminals. Recommended cabinetsize 240 x 216 x 445 mm.A superb sound at a relatively low cost.Complete with instructions. Price E14.90 +

E1.50 p&p per kit.

New 5' 30 watt mini version of above now available. Recommended cabinet size180 x 155 x 295 mm.Price E13.90 + £1.00 pep per kit.

STEREO CASSETTE TAPE DECK MODULE.Comprising of a top panel and tape mechan-ism coupled to a record/play back printedboard assembly. Supplied as one completeunit for horizontal installation into cabinet orconsole of own choice. These units are brandnew, ready built and tested.Features: Three digit tape counter. Auto -stop. Six piano type keys, record, rewind,fist forward, play, stop and eject. Automaticrecord level control. Main inputs plussecondary inputs for stereo microphones.Input Sensitivity: 100m V to 2V Input Im-pedance: 68K. Output level: 400mV to bothleft and right hand channels. Output Im-pedance: 10K. Signal to noise ratio: 45dB.Wow and flutter: 0.1%. Power Supply re-quirements: 18V DC at 300mA. Connections:The left and right hand stereo inputs andoutputs are via individual screened leads, allterminated with_phono plugs (phono socketsprovided). Dirminsions: Top panel 51/2in x111/4in. Clearance required under top panel21/4in. Supplied complete with circuit dia-gram and connecting diagram. Attractiveblack and silver finish.Price £26.70 + £2.50 postage and packing.Supplementary parts for 18V D.C. power supply(transformer, bridge rectifier and smoothingcapacitor) £3.50.

NEW RANGE QUALITY POWER LOUD-SPEAKERS (15", 12" and 8"). Theseloudspeakers are ideal for both hi-fi anddisco applications. Both the 12'. and 15"units have heavy duty die-cast chassisand aluminium centre domes. All threeunits have white speaker cones and arefitted with attractive cast aluminium(ground finish) fixing escutcheons.Specificaton and Price: -

15" 100 watt R.M.S. Impedance Bohm59 oz. magnet, 2" aluminium voice coil.Resonant Frequency 20Hz. FrequencyResponse to 2.5KHz. Sensitivity 97dB.Price £32 each. £2.50 Packing and Car-riage each.

12" 100 watt R.M.S. Impedance 8 ohm, 50 oz magnet. 2 aluminium voice coil.Resonant Frequency 25Hz. Frequency Response to 4KHz. Sensitivity 95dB. Price£23.70 each. £2.50 Packing and Carriage each.

8" 50 watt R.M.S. Impedance 8 ohms, 20 oz. 1'6" aluminium voice coil, ResonantFrequency 40Hz, Frequency Response to 6KHz, Sensitivity 92dB. Also available withblack cone fitted with black metal protective grill. Price: White cone £8.90 each. Blackcone/grill £9.50 each. P it P £1.25 each.

PIEZO ELECTRIC TWEETERS - MOTOROLAJoin the Piezo revolution. The low dynamic mass (no voice coil) of aPiezo tweeter produces an improved transient response with a lowerdistortion level than ordinary dynamic tweeters. As a crossover is notrequired these units can be added to existing speaker systems of upto 100 watts (more if 2 put in series). FREE EXPLANATORY LEAFLETSSUPPLIED WITH EACH TWEETER.

TYPE 'E'

TYPE 'D'

TYPE 'F'

TYPE 'A' IKSN2036A) 3" round with protectivewire mesh, ideal for bookshelf and mediumsized Hi-fi speakers, Price £3.45 each.

TYPE 'B' (KSN1005AI 3 '4" super horn. Forgeneral purpose speakers, disco and P.A.systems etc. Price £4.35 each.

TYPE 'C' IKSN6016A) 5" wide dispersionhorn. For quality Hi-fi systems and qualitydiscos etc. Price E5.45 each.

TYPE 'D' IKSN1025A) 2" it 6" wide dispersionhorn. Upper frequency response retainedextending down to mid range (2K Hz). Suitablefor high quality Hi-fi systems and qualitydiscos. Price t6.90 each.

TYPE 'E' (KSN1038A13%" horn tweeter withattractive silver finish trim. Suitable for Hi-fimonitor systems etc. Price £4.35 each.

TYPE 'F' (KSN1057A) Cased version of type'E'. Free standing satellite tweeter. Perfectadd on tweeter for conventional loudspeakersystems. Price f10.75 each.U.K. post free (or SAE for Piezo leaflets).

'e -

An.

1000 MONO DISCO MIXERA superb fully built and tested mixer/pre-amp with integral power supply. 4Inputs 2 turntables (ceramic cartridge). Aux. for tape deck etc., plus Mic. withoverride switch, all with individual level controls. Two sets of active tone controls(bass and treble) for Mic. and main inputs. Master volume control. Monitor outputwith select switch and volune control.Outputs Main 750 mV Monitor 500 mW into 8 ohms. Supply 220/240V AC50 /60HzSize 221" x 4r x 21" price E39.99 + £2.50 P&P

1K.WATT SLIDE DIMMER Controls loads up to 1KW Compact size

13 "434" x x21/2"16

Easy snap in fixing throughpanel/cabinet cut out

Insulated plastic case Full wave control using Samp

triac Conforms to BS800 Suitable for both resistance

and inductive loadsInnumerable applications inindustry, the home, and discos/theatres etc.

Price: £11.70 each + 50p PEtPI A ny quantity)

BSR P256 TURNTABLEP256 turntable chassis S shaped tone arm Belt driven Aluminium platter Precision calibrated counter balance Anti -skate (bias device) Damped cueing lever 240 volt AC operation (Hz) t --Cut-outtemplate supplied Completely manual arm,This deck has a completely manual arm and isdesigned primarily for disco and studio usewhere all the advantages of a manual arm are

required:Price: £28.50 + £2.50 P&P

di) POWER AMPLIFIER MODULES

BK ELECTRONICSPrompt Deliveries

VAT inclusive

prices

Audio Equipment

Test Equipment

by

Thandar

and

Leader

GENERAL PURPOSE 41/2" MINISPEAKER

General purpose full range loudspeaker, idealfor mini systems etc.

'Rolled fabric surround 'Twin cone 08ohmimpedance 15 watt RMS I" voice coil

13oz magnet Frequency range 50/15000Hz

Price: £6.90 each + 75p P&P

100 WATT R.M.S. AND 300 WATT R.M.S.MODULESPower Amplifier Modules with integral toroidaltransformer power supply, and heat sink. Suppliedas one complete built and tested unit. Can be fittedin minutes. An LED Vu meter is available as anoptional extra.SPECIFICATION:Max Output Power: 110 watts R.M.S. IOMP 1001

310 watts R.M.S. IOMP 3001Loads: Open and short circuit proof. 4-16 ohms.Frequency Response: 20Hz - 25KHz ±3d12.Sensitivity for Max. Output:500mV at 10K IOMP 1001 1V at 10K IOMP 300)T.H.D.: Less than 0.1%Supply: 240V 50HzSizes: OMP 100 360 x 115 x 72mm

OMP 300 460 x 153 x 66mmPrices: OMP 100 £19.99 each + E2.00 P&P

OMP 300 E69.00 each + E3.00 P&PVu Meter £6.50 each + 50p P&P

Matching 3 -way loudspeakersand crossoverBuild a quality 60watt RMS system 8ohms

Build a quality 60 watt R.M.S. system.

* 10" Woofer 35Hz-4.5KHz* 3" Tweeter 2.5KHz-19KHz* 5" Mid Range 600Hz-8KHz* 3 -way crossover 6dB/oct 1.3 and 6KHz

Recommended -Cab -size 26" x 13" x 13"Fitted with attractive cast aluminium fixing es-cutcheons dint mesh protective quills which areremovable enabling a unique choice of cabinetstyling. Can be mounted directly on to bafflewith or without conventional speaker fabrics.All three units have aluminium centre domesand rolled foam surround. Crossover coin -limes spring -loaded loudspeaker terminals andrecessed mounting panelPrice £22.00 per kit + £2.50 postage and pack-ing. Available separately, prices on retiest.

12" 80 watt R.M.S. loudspeaker.A superb general pOrpose twin cone loud-speaker. 50 oz, magnet. 2'. aluminiumvoice coil. Rolled surround. Resonant fre-quency 25Hz. Frequency response to13KHz. Sensitivity 95dB. Impedance Bohm.

Attractive blue cone with aluminiumcentre dome.Price £17.99 each + E2.50 P&P.

B.K. ELECTRONICS37 Whitehouse Meadows, Eastwood, Leigh -on -Sea, Essex SS9 5TY

* SAE for current lists. * Official orders welcome. * All prices include VAT. * Mail order only. * All items packed (whereapplicable) in special energy absorbing PU foam. Callers welcome by prior appointment, please phone 0702-527572.

110visA

Step-by-stepfully

illustratedassembly

and fitting instructions

are includedtogether

with circuit descriptions.Highest

quality

componentsare

used throughout.

UNINITItaBRANDLEADING ELECTRONICS

NOW AVAILABLE IN KIT FORM4,

7 .*Ily

/

S X 1000Electronic Ignition

Inductive Discharge Extended coil energy

storage circuit Contact breaker driven Three position changeover switch Over 65 components to assemble Patented clip -to -coil fitting Fits all 12v neg. earth vehicles

'

SX2000Electronic Ignition

The brandleading systemon the market today

Unique Reactive Discharge Combined Inductive and

Capacitive Discharge Contact breaker driven Three position changeover switch Over 130 components to assemble Patented clip -to -coil fitting Fits all 12v neg. earth vehicles

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1111AT -80Electronic Car Security System

Arms doors, boot, bonnet and has security loop to protectfog/spot lamps, radio/tape, CB equipment

Programmable personal code entry system Armed and disarmed from outside vehicle using a special

magnetic key fob against a windscreen sensor pad adhered tothe inside of the screen Fits all 12V neg earth vehicles

Over 250 components to assemble

MAGIDICEElectronic Dice

Not an auto item but great funfor the family

Total random selection Triggered by waving of hand

over dice Bleeps and flashes during a 4 second

tumble sequence Throw displayed for 10 seconds Auto display of last throw 1 second in 5

Muting and Off switch on base Hours of continuous use from PP7 battery Over100 components to assemble Supplied in superb presentation gift box

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TX2002Electronic Ignition

The ultimate system Switchablecontactless. Three position switch with

Auxiliary back-up inductive circuit. Reactive Discharge. Combined capacitive

and inductive. Extended coil energy storagecircuit. Magnetic contactless distributor trigger -head. Distributor triggerhead adaptors included

Can also be triggered by existing contact breakers Die cast waterproof case with clip -to -coil fitting Fits

majority of 4 and 6 cylinder 12v neg. earth vehicles Over 150 components to assemble

VOYAGER Car Drive Computer A most sophisticated accessory. Utilises a single chip maskprogrammed microprocessor incorporating a unique programmedesigned by EDA Sparkrite Ltd. Affords 12 functions centredon Fuel, Speed, Distance and Time. Visual and Audible alarmswarning of Excess Speed, Frost/Ice, Lights -left -on. Facility tooperate LOG and TRIP functions independently or synchronously. Large 10mm high 400ft-L fluorescent display with autointensity. Unique speed and fuel transducers giving aprogrammed accuracy of + or -1%. Large LOG & TRIPmemories. 2,000 miles. 180 gallons. 100 hours. Full Imperialand Metric calibrations. Over 300 components to assembleA real challenge for the electronics enthusiast!

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All EDA-SPARKRITE products and designs are fully covered by one or more World Patents

EDA SPARKRITE LIMITED 82 BattSELF

ASSEMBLYKIT

READYBUILTUNITS

SX 1000 £12.95 £25.90SX 2000 £19.95 £39.90TX 2002 £29.95 £59.90AT. 80 £29.95 £59.90

VOYAGER £59.95 £119.90MAGIDICE £9.95 £19.90

PRICES INC. VAT. POSTAGE & PACKING

INI ME IM ME IN NM = NI Ell MN IMStreet, Walsall, West Midlands, WS1 3DE England. Tel: (0922) 61479

NAME HE882

ADDRESS

I ENCLOSE CHEQUE(S)/POSTAL ORDERS FOR

£, KIT REF.

CHEQUE NO24 hr. AnswerphonePHONEYOURORDERWITHACCESS/BARCLAYCARDSEND ONLY SAE IF BROCHURE IS REQUIRED PAllow 28 days for delivery

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Documents

Project Electronics For Everyone MODEL PROJECTS · 2021. 1. 24. · +r-ntc-F,1-"AlT1' =1;.' AMBIT INTERNATIONAL'S Prices shown EXCLUDE VAT. Access/Barclaycard may be used with written