AN ARGUS SPECIALIST PUBLICATION

JULY 1984

roject IeSor veryone

Car Map Light Dimmer

Positive/Negative Reading DC Voltmeter

61-04780

HA1388 61-01388

TDA2002 61-02002

ULN2283 1W max. 3-12V power amp 61-02283 1.00

MC3357 Low power NBFM IF systemand detector 61-03357 2.85

ULN3859 Low current dual conversionNBFM IF and detector 61-03859

LM3900 Quad norton amp 61-39000

LM3909N 8 -pin DIL LED flasher 61-39090

KB4445 Radio control 4 channelencoder and RF 61-04445 1.29

KB4446 Radio control 4 channelreceiver and decoder 61-04446 2.75

uA748CN 741 with external frequencycomp 0.40

18W PA from I4V 2.75

8W into 2 ohms power amp 1.25

2.95

0.60

0.68

1CM7555 Low power CMOS version oftimer 61-75550 0.98

ICL8038CC Versatile AF signal generatorwith sine/square/triangleOPs 61-08038 4.50

TK10170 5 channel version of KB4445 61-10170 1.87

HA12002 Protection monitor systemfor amps, PSUx. TXs etc 61-12002 1.22

HA12017 83dB S/N phono preamp0.001% THD 61-12017 0.80

MCI4412 300 baud MODEM controller(Eduro/US specs) 61-14412 6.85

it y y

Microprocessor & MemoriesZ80A Popular and powerful

8 -bit CPU 26-18400 3.40

Z80APIO 2 port parallel input/output 26-18420 2.95

Z80A CTC 4 channel counter/timer 26-18430 2.90

Z8671 Z8 Micro comp. and Basic 26-08671 17.50

6116-3 I 6K (2kx8) CMOSRAM 200nS 26-36116 6.68

Z6132-6 32K (4kx8) quasiRAM 350nS 26-06132 15.00

4116-2 16K (16kx1)150nS 26-24116 1.59

2764 64K (8kx8) 450nS 26-02764 9.50

2732 32K (4kx8)450nS 26-02732 5.70

Voltage Regulators7805 5V IA positive 27-78052 0.40

7812 12V IA positive 27-78122 0.40

7815 15V IA positive 27-78152 0.40

7905 5V IA negative 27-79052 0.49

7912 12V IA negative 27-79122 0.49

7915 I5V IA negative 27-79152 0.49

TransitorsBC182 General purpose 58-00182 0.10

BC2 12 General purpose 58-00212 0.10

BC237 Plastic BC107 58-00237 0.08

BC238 Plastic BC108 58-00238 0.08

BC239 Plastic BC109 58-00239 0.08

BC307 Complement to BC237 58-00307 0.08

BC308 Complement to BC238 58-00308 0.08

BC309 Complement to BC239 58-00309 0.08

BC327 Driver/power stage 58-00327 0.13

BC337 Driver/power stage 58-00337 0.13

MPSA13 NPN Darlington 58-04013 0.30

MPSA63 PNP Complement toMPSAI3 58-04063 0.30

1310 JFET for HF-VHF 59-02310 0.69

1176 JFET analogue switch 59-02176 0.65

171

LinuPi new name ifor a better service.

This year Ambit will stop being Ambit.And become Cirkit.

Cirkit is more than just a change of name.It means a better service for you. Fasterdelivery.

There's a technically skilled staff to helpyou.

We keep in touch with the manufacturersaround the world and we know what's goingon.

Computer ProductsA complete range from Connectors to

Board Level product

Cl2 Computer Cassette 21-00012 0.55

BBC to Centronics Printer 03-10019 7.25

BBC to 25 way D Male 03-10021 4.50

25 way D Socket 10-25200 1.90

25 way D Plug 10-25100 1.30

Cover for 25 way D 10-25322 0.93

20 up Eprom Eraser 40-82100 31.25

Z80 A Industrial Controller 40-82000 49.95

6802 Industrial Controller 40-68020 49.95

6502 Industrial Controller 40-65020 49.95

Z8 Basic/Debug Controller 41-00904 50.00

Nicad Batteries & Chargers1-9 10-49

AA 12V 500mAH 01-12004 0.80 0.74

I.2V 2.2AH 01-12024 2.35 1.99

1.2V 4.0AH 01-12044 3.05 2.85

PP3 8.4V 110mAH 01-84054 3.70 3.50

CH1/22 PP3 Charger I 1mA for 16 hours01-00159 4.30

CH 8/RX Multi -purpose Charger01-02204 9.40

Will recharge AA, C, D and PP3 size cellswith automatic voltage selection. Willrecharge following combination: 6x D,

xAA, 6xC, 2 xPP3, 2xD+2xC,2 xD+2xAA, 2xD+IxPP3, 2 xC+2 xAA,2xC+1xPP3, 2xAA+1xPP3.

SemiconductorsLinear IC'sLM30 IAN DIL version 61-03011 0.44

LM308CN DIL version 61-03081 0.65

LM311CN Popular comparator 61-00311 0.46

LM324 Low power quad op amp 61-03240 0.67

LM339N Low power quad comparator 61-03390 0.68

LM346 Programmable quad op amp 61-00346 3.72

LF347 Quad Bi-FET op amp 61-00347 1.82

LM348 Quad 741 type op amp 61-03480 1.26

LF351 Bi-FET op amp 61-03510 0.49

LF353 Dual version of LF351 61-03530 0.76

LM38ON IW AF power amp 61-00380 1.00

NE555N Multi -purpose low cost timer 61-05550 0.45

NE556N Dual version of the 555 61-05560 0.50

uA741CN DIL low cost op amp 61-07411 0.22

uA747CN Dual 741 op amp 61-07470 0.70

ft

3SK51 Dual gate MOSFET-VHFamp

3SK88 Dual gate MOSFET-Ultra tonoise

TIP31A Output stage

TIP32A Complement to TIP31A

VN66AF VMOS Power FET

ZTX3866 E -line version 2N3866

IN4001 Rectifier diode

IN4002 Rectifier diode

IN4 I 48 General purpose silicon

60-04051

60-04088

58-15031

58-15032

60-02066

58-03866

12-40016

12-40026

12-41486

0.99

0.35

0.35

0.95

0.45

0.06

0.07

0.05

Silicon Controlled RectifiersBRY55-100 100V .8A 52-55100 0.50C106D1 400V 4.0A 52-00106 0.70C122DI 400V 8.0A 52-00122 1.45

3mm Diameter LEDsV178P Red 15-01780 0.15V179P Green 15-01790 0.16VI8OP Yellow 15-01800 0.18

5mm Diameter LEDsCQY4OL Red 15-10400 0.12CQY72L Green 15-10720 0.15CQY74L Yellow 15-10740 0.15

Infra -Red LEDsCQY99 Emitter 15-10990 0.56BPW41 Detector 15-30410 1.51

Tri Colour LEDV518 Orange -Green -Yellow 15-05180 0.60

R F ComponentsCrystal Filters 2 Pole Types10M15A 10.7 Centre Freq. 20-10152 2.10

10M08AA 10.695 Centre Freq. 20-11152 3.49

InductorsWe offer the complete Toko range of fixedand variable inductors. Over 500 coils fromaudio to V.H.F. See catalogue for details.

Soldering Irons (Antex)CS240 Iron 240VAC 17 Watts 54-22300 5.20

XS -240 Iron 25W 240V High heatcapacity 54-22500 5.40

SK6 Presentation pack of oneXS -240 with ST4 stand 54-22510 720

MUGS Handy 12V 15W solderingiron complete withcrocodile clips and solder 54-20004 5.60

Please add 15% VAT to all advertised pricesand 60p post and packing. Minimum ordervalue S2 please. We reserve the right to varyprices in accordance with marketfluctuation.

For further information send for ourlatest catalogue or visit one of our threeoutlets at:200 North Service Road, Brentwood, Fssex,CM14 4SG; 53 Burrfields Road, Portsmouth,Hampshire, P03 5EB; Park Lane,Broxbourne, Hertfordshire, ENIO 7NQ.

Fro: Cirkit Holdings PLC, Park Lane, Broxbourne,Hertfordshire.I enclose 80p. Please send me your latest catalogueand 3 x £1 discount vouchers!If you have any enquiries please telephone us onHoddesdon (0992) 444111.

Name

Address

TelephoneArea of Special Interest

irkitBigger Stock. Better Service. HE

JULY 1984Vol. 6 No. 7

PROJECTS* MAP LIGHT DIMMER 16A nifty auto -accessory for navigators.* HI Fl CONTROL AMPLIFIER 19Part of HE's own modular control system, or a stand-alone

ultra hi-fi preamp.* ± DC VOLTMETER 54Low cost lab equipment.* SHORT CIRCUITS 52Simple Oscillator: 18 Watt alarm:

Short Circuit Protected PSU.

FEATURES* ALL ABOUT ELECTRONICS PART 12Concluding the series on electronics and systems for

the beginners* ALL ABOUT BATTERIES 57Power cells for portable purposes.

SPECIAL* SOFT OPTIONS 27Our cover story, on the implications of computer

education via television, plus features on hardwarefor learning, experiments with computers at a ruralprimary school, and reviews of some outstanding software.

REGULARSMonitor 6What's On Next 18Buylines 26Forward Bias 43Points Of View 50HE PCB Service 63HE PCB Page 64

Editor: Ron KeeleyDeputy Editor: Helen P. Armstrong BATechnical Editorial Assistant: Terry JohnsonTechnical Illustrator: Jerry FowlerAdvertising Manager: Joanne JamesCopy Control: Lynn CollisManaging Editor: Ron Harris BScChief Executive: T. J. Connell

We are not normally able to deal with technical enquiries by'phone, so please don't ring, Write to us with an SAE.

44 Map Light Dimmer - page 14

Soft Options - page 27

DC Voltmeter -- page 54

Hobby Electronics is normally published on the second Friday of the month prior to the cover date.Hobby Electronics, No. 1, Golden Square, London MR 3AB, 01 437 0626. Telex No 8811869. Published by Argus Specialist Publications Ltd.

Origination by Ebony Typesetting, Trion House, 13 Dean Street, Liskeard, Cornwall PL14 4AB.Distributed by S. M. Distribution Ltd, 16/18 Trinity Gardens, London SW9 8DX

Printed by The Garden City Press, Letchworth, Herts SG6 1JS. Covers printed by Alabaster Passmore.Notice: The contents of this publication including all designs, plans, drawings and programs and all copyright and other intellectual property rights therein belong to ArgusSpecialist Publications Ltd. All rights conferred by the Law of Copyright and other intellectual property rights by virtue of international copyright conventions are specifically

reserved to Argus Specialist Publications Limited and any reproduction requires the prior written consent of the Company. All reasonable care is taken in the preparation of themagazine to ensure accuracy, but Argus Specialist Publications Ltd cannot be held responsible legally. ©Copyright 1984 Argus Specialist Publications Ltd. Member of Audit Bureau

of Circulation.

Hobby Electronics, July 1984 3

OMTU

TOROIDAL TRANSFORMERS7 DAYS DELIVERY FOR SMALL QUANTITIES

V/ASecondary Volts

(Dual)Primary Volts

(Dual)

PRICE

Unit Price P/P VAT Total

15 3v- 30v 0 - 120 5.60 0.75 0.95 7.30

30 3v- 30v 0 - 120 6.00 0.91 1.03 7.95

50 3v- 30v 0 - 120 6.65 2.00 1.30 9.95

80 3v - 30v 0 - 120 7.25 2.00 1.38 10.63

120 3v - 30v 0 - 120 8.00 2.00 1.50 11.50

160 3v - 30v 0 - 120 9.00 2.00 1.65 12.65

225 3v- 30v 0 - 120 11.50 2.50 2.10 16.10

300 3v - 30v 0 - 120 13.50 2.50 2.40 18.40

500 3v- 30v 0 - 120 19.00 2.80 3.27 25.07

625 3v- 30v 0 - 120 24.00 3.00 4.05 31.05

1. Prototype Sample Service Available for Special Requirements With Short Lead Time ForProduction.2. Quantity Prices Available On Application.3. Mail Order: CHEQUES TO: WYE WINDING CO. - ACCESS CARD WELCOME.We also manufacture to customer requirements laminated transformers, R.F. chokes, I.F. Inductorsand current transformers

[1 El 1UWinding

WYE WINDING Co.27 STATION ROAD, BRIMINGTON,CHESTERFIELD, ENGLAND.

Telephone: Chesterfield (0246) 70297/819Telex: 54284

BSR P256 TURNTABLEP256 turntable chassis S shaped tone arm Belt driven Aluminium platter Precisioncalibrated counter balance Anti -skate (bias)device) Damped cueing lever 240 volt ACoperation (Hz) Cut-out template supplied Completely manual arm. This deck has a com-pletely manual arm and is designed primarilyfor disco and studio use where all the advan-

tages of a manual arm are requiredPrice £33.60 each £2.50 P&P.

PIEZO ELECTRIC TWEETERS - MOTOROLAJoin the Piezo revolution. The low dynamic mass (no voice coil) of a Piezotweeter produces an improved transient response with a lower distortionlevel than ordinary dynamic tweeters. As a crossover is not required theseunits can be added to existing speaker systems of up to 100 watts (more if 2put in series). FREE EXPLANATORY LEAFLETS SUPPLIED WITH EACHTWEETER.

lit POWER AMPLIFIER MODULENEW OMP100 Mk.II POWER AMPLIFIERMODULE Power Amplifier Module complete

READY BUILT with integral heat sink, toroidal transformerpower supply and glass fibre p.c b. assembly.Incoporates drive circuit to power a compat-ible LED Vu meter New improved specifi-cation makes this amplifier ideal for P.A..Instrumental and Hi -Ft applications.SPECIFICATIONOutput Power:- 110 watts R.M.S.Loads:- Open and short circuit proof 4/16ohms.Frequency Response:- 15Hz -30KHz - 3dBT.H.D.:- 0.01%.S.N.R. (Unweighted): - - 118dB x 3 5d8Sensitivity for Max Output:- 500mV at10K.Size - 360 115 x 72mm. £31.99

£2.50 P&P. Vu Meter Price:- £8.50 - 50pP&P

OMP100 Mk.II

Vu meterNew model.

Improved specification

MOS-FETHIGH SPEC.MODULES

1

MOS -FET VERSIONS AVAILABLE UP TO 300 W. R.M.S.<100 Watt 300mm n 123mm X 60mm Price: £39.99 + £2.50 P&P.200 Watt 300mm X 150mm X 100mm Price: £62.99 , £3.50 P&P.300 Watt 330mm x 147mm X 102mm Price: £79.99 £4.50 P&P.

LARGE S.A.E.For details ofdisco mixers.speakers, kits,amp - modules,bugler alarms.turntables, etc.

TYPE 'A' (KSN2036A) 3" roundwith protective wiremesh, ideal for bookshelf and medium sized Hi-fispeakers. Price £4.29 each + 30p P&P.TYPE 'B' (KSN1005A) 31/2" super horn. For generalpurpose speakers, disco and P.A. systems etc. Price£4.99 each + 30p P&P.TYPE 'C' (KSN6016A) 2" X 5" wide dispersionhorn. For quality Hi -ft systems and quality discos etc.Price £5.99 each + 30p P&P.TYPE 'D' (KSN1025A) 2" x 6" wide dispersionhorn. Upper frequency response retained extendingdown to mid range (2KHz). Suitable for high qualityHi -ft systems and quality discos. Price £7.99 each+ 30p P&P.TYPE 'E' (KSN1038A) 3,/,," horn tweeter withattractive silver finish trim. Suitable for Hi-fi monitorsystems etc. Price £4.99 each + 30p P&P.

1

HOBBY KITS. Proven designs including glassfibre printed circuit board and high qualitycomponents complete with instructions.

FM MICBOTRANSMITTER (BUG) 90/105MHz with very sensitivemicrophone Range 100 300 metres. 57 X 46 X 14mm (9 volt)Price; £8.62 + 75p P&P.3 WATT FM TRANSMITTER 3 WATT 85, 115MHz varicap controlled,professional performance. Range up to 3 miles 35 84 t 12mm(12 volt) Price: £13.74 + 75p P&P.SINGLE CHANNEL RADIO CONTROLLED TRANSMITTER/RECEIVER 27MHZ Range up to 500 metres. Double coded modulation.Receiver output operates relay with 2amp/240 volt contacts. Ideal formany applications. Receiver 90 X 70 X 22mm (9/12 volt) Price:£17.82. Transmitter 80 X 50 X 15mm (9/12 volt). Price: £11.27P&P + 75p each S A E for complete list

3 wall FMTransmitter

LOUDSPEAKERS POWER RANGETHREE QUALITY POWER LOUD-SPEAKERS (15". 12" and 8" See 'Photo)Ideal for both Hi-Fi and Disco applications.All units have attractive cast aluminium(ground finish) fixing escutcheons Specifi-cations and Prices.15" 100 watt R.M.S. Impedance 8 ohms.50 oz magnet 2" aluminium voice coil. Res.Freq. 20 Hz. Freq. Resp. to 2.5KHz. Sens.97dB. Price: £34.00 each + £3.00 P&P12" 100 watt R.M.S. Impedance 8 ohms.50 oz. magnet. 2" aluminium voice coil. Res.Freq. 25Hz. Freq. Resp. to 4 KHz. Sens. 95d8Price: £24.50 each -I- £3.00 P&P8" 50 watt R.M.S. Impedance 8 ohms. 20oz magnet. 17," aluminium voice coil Res.Freq 40Hz. Freq. Resp. to 6 KHz. Sens 92dBBlack Cone. Price: £9.50 each. Also availablewith black protective grille Price: £10.50each. P&P £1 50

12" 85 watts R.M.S. McKENZIE C1285GP (LEAD GUITAR, KEYBOARD, DISCO) 2"aluminium voice coil, aluminium centre dome, 8 ohm imp Res. Freq 45Hz., Freq. Resp. to6.5kHz., Sens. 98dB. Price £24.99 £3 carriage12" 135 watt R.M.S. McKENZIEC1285TC (P.A., DISCO) 2" aluminium voice coil. Twin cone.8 ohm. imp., Res. Freq 45HZ., Freq. Resp. to 14KHz. Price £24.99 I- £3 carriage.15" 150 watt R.M.S. McKENZIE C15 (BASS GUITAR, P.A.) 3" aluminium voice coil. Die castchassis. 8 ohm imp., Res. Freq. 40Hz., Freq. Resp. to 4KHz. Price £49 t £4 carnage. Cabinetsfixings in stock S.A.E.

* SAE for current lists. * Official orders welcome. * All prices include VAT. * Sales Counter. *

B. K. ELECTRONICSUNIT 5, COMET WAY. SOUTHEND ON -SEA.

ESSEX SS2 6TR TEL 0702-527572 VISA

4 Hobby Electronics, July1984

Send for my CATALOGUEONLY 75p

(plus 25p post/packing)My all-inclusive prices quoted in theCatalogue are the lowest. All below

normal trade price - some at only onetenth of manufacturers quantity trade.

Millions of components: thousands of different lines

Rechargeable Nickel Cadmium batteries (ex unused equipment)AA(HP7) 1.25volt 500ma. Set of four £2I.T.T. Mercury Wetted relay 20-60 VDC Coil. SPCO. 2A 79p or 10 for £7Clear L.E.D. illuminates Red, Green orYellow depending upon polarity/current.Oblong 5 x 21/2mm Face 25p or 100 for £23 or 1000 for £2005mm Red Flashing L.E.D. 25p or 10 for £2.25

Watch/Calculator/Lighter etc, Mercury batteriesRW52(PX675) RW54 Made by Ray -O -VACRW56 (DH323,WH8) 31 p each orRW57, RW58 10 for £2.60, 100 for £21IN4004 or IN4006 Diodes. 300 for £6.48pTO5 or TO18 Heatsinks 71/2p, 100 for £6.50, 1000 for £55Clipover Heatsink for I/C or T0202 device 21 x 18mm

18p or 100 for £16.50 or 1000 for£155Heatsink for TO3 or Plastic Power 19p, 100/£17.50, 1000/£165Modern Telephone Handset and lead in white, red, blue, grey, yellow,green or black £2Plessey SG403. 3 Watt amp. From bankrupt source, hence sold asuntested, at 4 for 60p or 10 for £1.20p.

SEND PAYMENT PLUS 16p SAE OR LABELPrices you would not believe before inflation!

BRIAN J. REEDTRADE COMPONENTS

ESTABLISHED 27 YEARS161 St. Johns Hill, Battersea, London SW11 1TC)

Open 11 arn till 6.30pm Tues. to Sat. Telephone: 01-223 5016

MAKE YOUR OWN P.C.B s.

Top quality FR4 Grade Epoxy Glass FibreLaminate be thick

NB/019 4 x 3 inches single sided (3) £1.26HB/020 6 x 4 inches single sided (2) £1.68HB/021 6 x 9 inches single sided (1) £1.89HB/025 4 x 3 inches double sided (3) £1.44HB/026 6 x 4 inches double sided (2) £1.92HB/027 6 x 9 inches double sided (1) £2.16Assorted single & double sided approx 1 sq. foot £2.25Ferric Chloride etchant granules to make 1 litre £1.25HB/016 Protective Gloves (3 pairs) £1.05HB/084 1 litre storage bottle £0.50HB/014 plastic etching tray £2.54HB/088 Instruction sheet for PCB making £0.60HB/630 "How to Design & Make Your Own PCB" Book £1.95HB/017 Copper cleaning block £1.49HB/001 Etch resist transfers (assorted pads) £2.08HB/004 Transfer spatula £0.70HB/083 Etch resist pen £1.35HB/209 0.020 inch track tape £1.05HB/211 0.031 inch track tape £1.05Full Catalogue (refundable with 1st order over £10) £1.50Prices inclusive of VAT, carriage 60p in U.K. Overseas orders please addextra carriage to published prices.

a division of - --KELAN ENGINEERING Ltd.27-29 Leadhall Lane,Harrogate, N. Yorks.

EUROPA ELECTRONICSMail Order to 160 High Road, Willesden, London NW1 0 2PB

TEL: 01-907 1659

SEND FOR A FREE LIST OF OUR LARGE RANGE OF ITEMSALL DEVICES ARE NEW, FULL SPEC AND GUARANTEED

Post & Packing: Add 30p to all orders under £5.VAT: All UK orders add 15% to total cost including p&p.

741_500745501741_502741_503741_504741_505741_506741_509741_510745511741_512745513745514745515745520741_521745522741_524741_527745528741_530741_532741_533741_537741_538741_540745542745547741_548741_551741_554745555745573745574741_575741_576741.583745585745586741_590741_591741_59274559374559574559674551077455109745511274551137455114745512274551237455124745512574551267455132745513374551367455138745513974551457455147745514874551517455153

20p20p20p20p20p20p20p20p20p20p20p25p3402020p0

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180P34p34p34p34p100p100p60p60p120p

VOLTAGE REGULATORS iPLASTIC. 00220

781276,7818

40, 790544 7912imp 7915mp 7918,p 7924

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Hobby Electronics, July1984 5

MONITORClip That ChipOK Industries' "Chip Clips" allow safetesting of ICs without stressing ordisplacing the chips as do someconventional "Clothespin" type testclips, claim the company. Built-inmoulded separators eliminate shortcircuits, and units to fit 8, 14, 16, 24-28,36-40 and 64 pin ICs are available.

OK's range of stripping tools canhandle insulated wires up to 6mm. TheSP series includes the SP01, which ismade of fibreglass reinforced polyamidefor lightness, which can take 0.5 to2.5mm round and flat cable andemploys a single action. The SPO2 MiniStripper is a pocket tool with a cutter forconductors from 0.08 to 1.0mm.

The SPO3 is dual purpose forstandard electrical cable as well as lightgauge electronic cable up to 4 or even6mm, automatically adjusting to cablearea to avoid damage. All the tools havea typical cutter life of around 100,000cuts.

The 784 is automatic and adjustsitself for wire and cable up to 6mm. The787 removes insulation on cables up to45mm wide and 0.1 to 0.75mm thick,with a stripping length of up to 7mm.

Industrial cleaners now availablefrom OK include Technosolve degreaserand cleaner for metals and mostplastics, Technolube for an antistaticcoating on most materials, includingprecision moving parts, and Oilube is anoil -based lubricant for use wheresilicone lubricants are unsuitable.

All of these come as aerosols.Further information from OK Indust-

ries UK Ltd., Dutton Lane, Eastleigh,Hants S05 4AA. Tel: (0703) 619841.

New ShopMicrorange Electronics is a companyworking from Stratford in East Londonwhose main line is PCB manufacture,making up small runs of electronicequipment and manufacturing 19inrack cases. They also retail components

direct to the public at their shop,including panel meters and componentboxes.A price list should be available bythe time you read this, and the addressto visit/call is Unit 258, StratfordWorkshops, Burford Rd., London E152SP. Tel: 01-536 1415.

Control Board"Control 68" is a new low cost microcontroller from J. P. Designs designedto give small 'stand alone' terminalsintelligence and flexibility. This compact75x100mm PCB needs a +5V supply,and uses the 6802 microprocessorrunning at 4MHZ, 2KB of user RAM, upto 8KB of EPROM decoding, and 16TTLcompatible Input/Output lines. On-board links allow 2716 or 2732 EPROMtype devices to be used. PIO interruptsare serviced for quick I/O responsetime.

Applications extend into educationaland experimental spheres, providing anopportunity to become familiar with the6802 microprocessor,

The card, which can be easilyprogrammed, is supplied with full usernotes and circuit diagram at £49.95 +VAT.

Enquiries to J. P. Designs, 37 OysterRow, Cambridge CB5 8LJ. Tel:(0223) 32234.

New NameRoxburgh Suppressors are coping withincreased demand by moving officesand adopting a new trading name: RSL,Haywood Way, Ivyhouse Lane,Hastings, E. Sussex TN35 4PL. Acatalogue of all RSL standard filters isavailable from the Sales Office at thataddress. This division of RSL is alsoknown as Stotron.

Soft ToolkitIn response to the growing demand for'useful' software, Timedata are pleasedto announce TT -S, a powerful andsophisticated Spectrum programmers'toolkit. TT -S contains five utilityprograms which were written for theirown use by Timedata's developmentprogrammers to make the job ofprogram writing as painless as possible;'gamma', a relocatable BASIC extensiongiving new keywords with syntax'checking, including TRACE, FIND,AUTO, as well as intelligent RE-NUMBER and MOVE commands;'screens', a high -resolution drawingprogram with proper 'fill' and text printfacilities; 'udg', (I) a powerful aid whencreating user defined graphics char-acters; 'tape', which reads and displaysthe contents of tape file headers and

6 Hobby Electronics, July 1984

MONITOR

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'ram' a thorough RAM test program.All five programs can be used with

16K or 48K Spectrum, with or withoutInterface 1 and Microdrives. 'gamma'can also be used with most types ofprinter interface. TT -S is supplied with acomprehensive 28 -page manual andcan be obtained from leading computershops or direct from Timedata at £7.95inc. VAT and carriage.

Orders and enquiries to TimedataLtd., 16 Hemmells, High Rd., Laindon,Basildon, Essex SS15 6ED. Tel:(0268) 418121.

Peripherals On ShowA show of interest to every micro owneris projected for The Barbican in Londonduring the 13 -16th September. This isthe What Peripheral Show, and wegather that this means what it says: theexhibition organisers are invitingdealers and manufacturers in every kindof perhipheral from stationery to discdrives.

Trade enquiries to ComputerMarketplace (Exhibitions) Ltd., 20Orange St., London WC2H 7ED. Anextensive advertising campaign ispromised nearer the date with fulldetails for visitors.

Fast RecorderIkon Computer Products have come upwith a high-speed cassette datarecorder, now available for Dragonmicros, with versions for the BBC, Oric,Electron, Commodore, Nascom andTandy following in subsequent months.

The Ultra -drive has a read/writespeed of 1200 characters a second (tentimes faster as an ordinary domesticcassette recorder), with a capacity ofabout 200K per cassette.

The Ultra -Drive is completely auto-matic, and is based on the Philips mini

digital cassette recorder. It is availablefrom Ikon Computer Products, KilnLake, Laugharne, Dyfed SA33 4QE.Tel: (099421) 515. The price is£79.95, plus £3.45 p&p. Cables,operating system, interface, a micro -cassette, and VAT are all included in theprice.

Have A Byte Of SerialA serial controller with 4K byte buffermemory and communication via anRS232 is available as a peripheraldevice to the Velleman microprocessor -controlled EPROM programmer. In kitform the EPROM programmer and serialcontroller are both available fromElectronic & Computer Workshop ofChelmsford.

The EPROM programmer is a

microprocessor -based stand-alone unitcomplete with power supply, housingand test socket. Requiring no personal-ity model, once built it will test, verify,copy and program the followingEPROMs: 271 6 (Intel or second source);TMS2526 (Texas Instruments); 2732(Intel or second source); 2732A (HMOSversion of Intel). An adaptor socket for IC2532 is also available.

The programmer has a twenty-fourkey pad which includes hexadecimalkeyboard and function keys, twelveaddress LEDs, four function LEDs (error,prog, OK and size) and two hexadecimaldisplays. The serial controller acts as aperipheral device to the EPROMprogrammer allowing serial dataloggingfrom any computer, mini or microcom-puter system.

Three power supplies in kit form arenow available. The Velleman 1 A powersupply has an adjustable voltage from1V2 to 35V, a typical line regulation of0.01%, load regulation of 0.1%, 100%electrical burn -in and 180dB ripplerejection.

The Velleman 5-14VDC/1A series asa power supply for Velleman kits

needing a PSU of that power rating.Input voltage is 6-16V/1A.

The Pantec stabilized power supply kitno. 3 is a professional power supply ableto feed transmitters, receivers, stereosand car radios, and the high degree ofstabilization and regulation make itsuitable for lab. use.

A full auto ranging DMM, the Pan2101, is currently available. This hasinput impedance of 10MR AC/DC, autoranges from 200mV-1000VDC, 21600 -VAC, resistance 200-2000kR, andlower power resistance from 2kR to2000kR. AC/DC current measurementis from 200mA to 10A and all rangesexcept 10A are protected up to250VAC/VDC. The Pan 2101 costs£79.90 plus £1.00 p&p/VAT.

Enquiries to Electronic & ComputerWorkshop Ltd., 171 BroomfieldRd., Chelmsford, Essex CM1 1 RY.Tel: (0245) 262149.

Mind The StepA new two-part hand-held case, with a24° sloping display panel, designed toincorporate a range of LCDs togetherwith bezels, a PP3 battery compartmentwith removable cover, has beenlaunched by Boss Industrial Mould-ings.

Moulded as standard in easily drilledand punched black, grey and brown ABSthis new BIM 2900 case measures, 165x 24.5 mm and tapers from 87mm at thesloping display panel end to 82.5mmwhere hand held.

Having recessed fixing holes underthe base to accept the supplied feet, fourinternal PCB mounting bosses withinthe lid key area, plus two more bosseswithin the sloping display sections, thiscase can be used in a wide range ofhand held meter, controller andthermometer type applications.

Enquiries to Boss Industrial Mould-ing, James Carter Rd., Mildenhall,Suffolk IP28 7DE. Tel: (0638)716101.

Hobby Electronics, July 1984 7

MONITORSoldering OnA new soldering unit from Litesoldcombines the features of their ETC -4Bunit with CALPLUG temperatureselection, and the ETC -4C unit withdigital temperature display. Called(not surprisingly) the ETC -4D, the newunit gives instantly variable, butinterference -proof temperature select-ion by means of seven colour codedCALPLUGS, which are available forselected temperatures from 210° to400°C.

The operating temperature of the ironcan be constantly monitored during useby an LCD on the front of the unit whichis operated by a thermocouple sensorinside the iron bit. Proportional bandtemperature control ensures rapidheating and eliminates swing. Idlingtemperatures are held around ±1°C, andspiking, RFI, static and magneticinterference are totally avoided.

The plug-in iron is interchangeablefor all ETC -4 units, and a choice of bits insixteen shapes and sizes is available.Enquiries to Light Soldering Develop-ments Ltd., Spencer Place, 97/99Gloucester Rd., Croydon, CR0 2DN.Tel. 01 689 0574.

PSU KitA new triple output bench power supplyfrom Grenson Electronics, retailing at£99, is available in kit form at £59, allinclusive.

The BPU-4's three outputs are 3 to 8Vat 2A5, 8 to 1 6V at 0A5 and -8 to -16Vat 0A5. The 8 to 16V supply lines aretracking outputs providing a true +/-supply across that range.

The outputs are highly stabilized withan output change of less than 0.05% of a10% input change, and less than 0.10%output change from zero to a full load.Ripple is better than 0.05% p -p. Alloutputs are protected against long termoverloads, shorts and the injection ofexternal voltages.

Information and data sheet fromGrenson Electronics Ltd., High March,Daventry, Northants N N11 4HQ. Tel.(0327) 705521.

Getting HeavyA heavy-duty cassette recorder for theBBC, Acorn and other home micros hasbeen developed jointly by Bell &Howell, and Leasalink Viewdata, anddesignated the Bell & Howell/LVL317CX.

This machine is based on a recorderdesigned specifically for schools and isbuilt to particularly robust specificat-ions, with facilities not always found oncassette recorders, such as an internalelectret microphone (as well as anexternal socket), headphone socketsand a socket for remote control of thedrive motor by the computer.

As well as fast forward and rewind,there is cue and review so that playback

can begin as soon as the requiredportion of tape has been located (asfound on most video recorders, andpersonal stereos, come to that).Operation is from either mains orbatteries.

Load and Save connections to theBBC computer are via an IEC/DINinput/output socket and a 2.5mm jackfor computer -controlled load and start.For computers such as the ZXSpectrum, the signal is taken from oneof the 1/4in headphone sockets, fromwhich up to 40V is available.

The 3179CX costs £39.95 (RRP inc.VAT). A specification sheet is available.Enquiries to Bell & Howell, AlpertonHouse, Bridgewater Rd., Wembley,Middx HAO 1EG Tel: 01 902 8812.

Carry OnTwo new products are announced bythe Kings Lynn firm of Maxview,suppliers of TV aerials to the "itinerantmarket" of caravan, yacht and HGVusers.

The Cara aerial amplifier, 41/2 x 23/4 in,has integral brackets to allow it to bebolted permanently at an appropriateposition between a caravan televisionreceiver and the incoming aerial lead,and covers the whole of the UKtelevision and VHF radio spectrum from40 to 900MHz. There is provision foreither 1 2V or 24V operation to render itsuitable for the supply voltagesgenerally available on land vehicles andmarine craft. The required voltage isselected by means of a switch on the topof the unit. Supplied with the amplifieris a generous length of coaxial cableterminated at each end with a standard -TV -type plug to interconnect amplifierwith television receiver. A power lead topick up the DC supply is also included inthe kit.

A Weatherproof TV Aerial Socket isdesigned to be secured as a permanent

fitment to the exterior of a vehicle ormarine craft. The downlead from theaerial is plugged in to the coaxial socketcontained within a small ( 2 x 2in) plasticbox with a weatherproof snap hinge lid.Extending from the rear of the box is athree -metre coaxial cable which ispassed through a hole drilled in the sideof the vehicle and so to the television.When the vehicle moves on to anothersite the external aerial is unpluggedfrom this weatherproof socket and,preferably, dismantled for safety intransit. At the next stop the aerial maybe re -erected and the downlead pluggedin once more to the Maxviewweatherproof socket.

The Cara amplifier is listed at £1 3.50and the Weatherproof Aerial SocketAssembly at £4.95, both including VAT.Although these products have a specialappeal in the mobile market they have

PLPTF

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FOR ALL POURING VEHICLES.CARAVANS, MOTOR HOMES.BOATS, COACHES ETC

8 Hobby Electronics, July 1984

MONITORapplications in the domestic enviorn-ment as well.

Enquiries to Maxview Aerials Ltd.,Maxview Works, Setchy, Kings Lynn,Norfolk PE33 OAT.

Painting The Town LiveElectrolube have introduced a silverconductive paint which can be used onwide range of materials, includingplastic, paper, wood textiles, glass andceramics, and metal. The paint can beapplied by brush, dip spray or even apencil and takes about ten minutes todry, giving a thin, flexible film of highconductivity. Some of the possible useswhich Electrolube list are the designand repair of PCBs, repairing rearscreen heater tracks, screening plasticcases against HF fields, earthing strips,connection with non-solderable sur-faces, etc., etc. - anywhere where anelectrical connection is needed whichcan't be provided by solder or a cable.

Details of stockists, etc. can beobtained from Electrolube Ltd., BlakesRd., Wargrave, Berkshire RG10 8AW.Tel: (073 522) 3014. We don't have aprice for this SPG, but it's never acheap commodity, so we advise againstattempting to lay out entire PCBs with it.

Modular Burglar SystemBattery operated modular burglaralarms are easy to fit and offer a simplesolution to the problem of warningfamily or neighbours if doors orwindows are forced open. A new systemon the market uses plugs and socketsfor main wiring connections, making itsimple to install. This system alsoeliminates problems with lost keys as itis push-button controlled using a secretcode which can be altered if necessary.

Pulling out the plugs or the wiringactivates the alarm.

Battery operation provides a safe-guard against thieves cutting the powersupply and allows the system to be leftactive when the occupier is away onholiday and has switched off hiselectricity at the mains. The basic kitcomes complete with wiring and willprotect four doors or windows, making itideal for flats or high risk isolated areassuch as garages or workshops. Itincludes a 100 dB siren which stops andresets after three minutes. Further reedswitches and wiring and extra sirens,each with its own battery, can beplugged into the system, allowing it tobe extended on a modular basis. Theground floor of the average three -bedroom house could be protected forwell under £50, including a siren in aneighbour's house.

Further details from SemiconductorSupplies International, DawsonHouse, 128/130 Carshalton Rd.,Sutton, Surrey SM1 4RS. Tel: 01 6431126. The Starter Kit costs £29 inc.VAT and p&p.

One In The EyeThe Optical Information Council wanthobbyists and DlYers to take better careof their eyes, and accordingly havecirculated some recommendations forbetter eye care to us.

In the case of electronics construct-ion, the hazards boil down to flyingdebris inadvertantly caused by explod-ing triacs, unpredictable solder -suckers, or stubborn component leads(resistance to the clipping short of). Thetrouble with these is that, unlessyou choose to wear eye -protectors allthe time, they are unpredictableoccurences. Fallout from cuttingoperations, particularly cutting facedchipboard or metal with a power -saw, ismore predictable. Wearing even a cheappair of plastic protective specs can avoidsuch tedious operations as twenty-fiveminutes trying to remove a slap of chipfrom your eye with a piece of wet tissueor worse.

The OIC recommends plastic lensesinstead of glass for spectacle wearerswhen doing DIY, as glass can splinter.Preferred are industrial -standardpolycarbonate lenses, which can beobtained both as simple eye -defendersand also as prescription lenses, and aresaid to be virtually unbreakable.

More information, and leaflets onvarious eyecare subjects, are availablefrom Celia Hewitt at the OpticalInformation Council, Walter House,418 Strand, London WC2R OPB. Tel:01 836 2323.

Go Forth And MultitaskUsers who want FORTH for their BBCMicros will now find it on a 16KEPROM type 27128 from Skywave

Software, going under the name ofMulti -FORTH 83. This version of FORTHhas been specially written for the BBC.

The EPROM can be plugged into themicro's sideways ROM area so that ithas a higher priority than the BASICROM. It is multi -tasking, so that the usercan have several FORTH programs onthe go at once; compatible with theMOS so that the Disc Directory andother DFS commands can be used, andMOS commands can be used fromwithin the FORTH, capable of maintain-ing files of more than 32K which can bestored on disc alongside non -FORTHfiles; vectored so that the more powefulfeatures can be user -redefined; exten-sively documented, and with a numberof other special features.

Multi -FORTH 83 costs £40 plus p&pand VAT from Skywave Software, 73Curzon Rd., Boscombe, Bourne-mouth BH1 4PW. Tel: (0202)302385.

BBC Second ProcessorUpgrade Technology in conjunctionwith Rade Systems Ltd. have produced anew second Z80 processor the BBCModels A and B. Connecting via theserial port of the BBC, the unit has itsown integral power supply and floppydisc controller, making it independent ofthe micro's own systems. The unitsupports the true CP/M or Turbo DOSand the disc controller will handle twodrives taking 3in, 5in or 8in discs, singleor double sided and density, forty oreighty track.

The unit also allows up to three RADEadd on boards to be plugged in. Unitsinclude a RAM expansion to 256K,adding serial, parallel or IEEE inter-faces, hard disc storage or stereo soundsynthesis.

The unit will sell at £299 + VAT underthe name of "Upgrade" through a

network of dealers. Enquiries toUpgrade Technology, 290a HighRd., London NW10 2EU. Tel: 01 4514414.

JVC CourseJVC (UK) Ltd. are now running an in-house course to train a small number ofstudents as service engineers for thevideo and hifi industry. It is expectedthat the trainees, once qualified, will beworking at retail outlet level as after -sales technicians, and with this in mindsome students are being partly fundedby retailers.

The scheme is being set up as a jointventure with the Manpower ServicesCommission and is hoped to be the firstin a series of schemes wherebyprospective employers take an initiate intraining people to service the trade,especially in specialised consumer areasuch as video and hifi.

Which can only be a good thing if itraises the number and standard of after -sales service engineers.

Hobby Electronics, July 1984 9

MONITOR41/2 Digit LCD'The latest addition to the low costinstrumentation range of ThandarElectronics is the 41/2 digit liquid crystaldisplay digit multimeter. This bench/portable instrument has a basic ac-curacy of 0.03% and features full autobench/portable instrument has a basicaccuracy of 0.03% and features full autoand manual ranging as standard. It hasfull measurement capability of DC andAC voltage, DC and AC current plusresistance and diode check in twenty-one ranges over five modes. A samplehold facility is also provided as isa continuity buzzer which also indicatesover -range conditions in a differenttone.

The TM451 is powered by a standard9V PP3 battery, or via a mains adaptoras required. Battery life is considerabledue to the CMOS LS1 technologyincorporated. The TM451 is suppliedcomplete with battery and probes at aprice of £160 plus VAT.

For further details please contactThandar Electronics Ltd., London Rd.,St. Ives, Huntingdon, Cambs PE174HJ. Tel: (0480) 64646.

I/O BureauA warning to home computer owners,especially those doing a bit ofprogramming or reviewing on the side,has come from the Insurance Om-budsman Bureau, a body set up fouryears ago by a group of major insurancecompanies to investigate queries andcomplaints from policyholders.

The two points which concern homeowners are: are you adequatelycovered? and is your householdinsurance valid for your computerequipment if you are using it forbusiness?

If you buy a computer and any amountof software or add-on equipment, checkthat the amount on your insurancepolicy is increased to cover it. Likewise,check with your insurers whether yourpolicy covers your equipment if you areusing it for any commercial purpose, orwhether you need to have it insuredseparately under a commercial policy.Insurance companies are legitimatelyentitled not to pay up if the terms of apolicy are not met by the householder,and lack of cover, or the wrong type ofcover, are two of the commonestreasons for refusal to meet a claim infull or partially.

Read the small print! On a good policyit is there to explain, not mislead. If indoubt, talk to your insurance office orbroker on the phone and then write tothem confirming your understanding ofthe information they have given you.Then you have something in writing ifthere are any queries later.

Organ IntervalsThe Electronic Organ ConstuctorsSociety, which is a non-profit makingsociety which aims to promote thedesign and construction of organs and

other electronic instruments byamateurs, tell us that their Septembermeeting will be on September 8th, andwill be on the subject of Amplifiers AndSpeakers; another meeting on Nov-ember 17th will be on the theme of PCBManufacture And UV Box Construction.

The EOCS publishes five magazines ayear for members, and holds fivemeetings a year in the London area.Enquiries to the Publicity Secretary,Mr. P. Vickery, 5 Cringle Avenue,Southbourne, Bournemouth, BH64HX. Their magazine is always full ofspecific practical advice and circuits.

What's In A Name?National Panasonic (UK) Ltd. haveannounced that, from April 1984 theywill change their name to Panasonic UKLtd. The practical upshot of this is thatall radio and hifi equipment currentlyidentified by the name "National" willgradually be altered to read "Panasonic"this year, and the National Name willvanish from Europe altogether. Nationalowners need need not be concerned iftheir brand name is no longer in theshops - it doesn't mean that themanufacturers have ceased trading.The parent manufacturing company,Matsushita Electric in Japan, areunifying all their products under thePanasonic name.

New from Panasonic is the RQ-8100program cassette recorder, specificallydesigned for use with personalcomputers. The recorder connects byremote jack, and can be stopped andstarted from the computer keyboard.Data accumulation is at a rate of1200bits/s and storage is 500KB on aC60 cassette. A phase selector correctserrors while loading commercialsoftware, and monitor capabilityconfirms signal transmission duringloading and saving. Cue and review canbe used to locate programs on the tape.

Running from mains (an AC adaptor isoptional) or four R6 batteries, the RQ-

8100's RRP is £44.50 from the usualoutlets.

So Much Hot AirA range of hot air nozzles for specialapplications, possibly the first to beavailable in the UK, are being suppliedby Steinel (UK) Ltd., as well as a rangeof nozzles for glue guns.

The four nozzles for the Steinel hot Airgun comprise a fan -shaped air flownozzle for flat surfaces, a concentratedflow for spot temperatures, one forconcentrating hot air flow for thesoldering of pipes, and, possibly of mostinterest to hobbyists a paint -strippingnozzle which directs hot air flow, forinstance, onto a window frame andaway from the glass.

Hot air guns of various kinds seem tobetaking over from more lethal methodsof paint -stripping like caustics andblowtorches. The first person to adaptone to provide a home flow -solderingtechnique will be on to a good thing.Eagerly, we wait . . .

The Steinel Hot -Air Gun is designedfor professional use, but Steindel saythat it is ideal for enthusiasts andhobbyists. There are two models,a single -speed, 500° model and a dual -speed model giving a choice of 300° and500°, as well as two speeds of airflow.For enquiries about the Hot -Air Gun andother tools and test equipment, contactSteinel UK Ltd., 17 Reddicap TradingEstate, Sutton Coldfield, WestMidlands B75 8BU. Tel: 021 3782820.

Clamp, ClipA. Levermore & Co. are stockingminiature, USA -made Vice -Grip lock-ing pliers. The two models, one witha long nose and the other with arounded beak, are said to "crimp, clamp,clip, snip, grip and lock tight just like

10 Hobby Electronics, July 1984

their big brothers." I forsee a rash onenquiries from hairdressers around thecountry . . .

The pocket-size pliers are only 4inlong and will be available from specialistretail outlets. Enquiries to A. Lever -more & Co. Ltd., 24 Endeavour Way,Wimbledon Park, London SW19 81JH.Tel: 01 946 9882.

Redefine Your PersonalSpaceTimedata Ltd. have produced a newsoftware package for the Spectrum,called "HI -T" (piece of cake, ay?), whichgives the lucky user up to 32 lines of 64characters each, user input to any partof the screen without disturbing otherdata, print windows, where printing andscrolling can be confined to anyrectangular area out of the screen,offset printing (figures can be moved upor down by one to five pixels) andredefinable print comma spacing, forflexible tabulation.

HI -T has the same standard characterset as the Spectrum, and HI -T andstandard characters can be mixed onthe same screen. The program can beused on a 16K or 48K machine with orwithout microdrives, and costs £5.95 allinclusive.

Enquiries and orders to TimedataLtd., 16 Hemmells, High Rd., Laindon,Basildon, Essex SS15 6ED. Tel:(0268) 418121.

A Controlled ChargeA new development in the control ofbattery charging by S & W BatteryCharging Systems has been launched.The Sentinel controller is a fourterminal encapsulated electronic plug-in module designed to control ACcurrent and voltage to safe batterycharging levels. The controller is simplyinserted between the AC supply and thebattery, and will allow whatevercurrent is required to keep the battery inprime condition to pass without over orunder -charge, reducing maintenanceand energy waste.

The Sentinel may be incorporatedas original equipment or added later toan existing system. It cannot, claim S &W, be incorrectly installed, and isdesigned to give users the full batterylife that the manufacturer intended.

Enquiries to S & W Battery ChargingSystems Ltd., Nailsea Trading Estate,Southfield Rd., Nailsea, Bristol. Tel:(0272) 855161.

Shoot OutA test instrument for trouble -shootingprinted circuit boards is now availablefrom Antron Electronics Ltd. TheT1200 isolates faults down to com-ponent level. On an unpowered an ACtest voltage can be selected across a

MONITORpair of hand held test probes and, byplotting the current/voltage character-istics of a component in -circuit, willdisplay the resulting impedancesignature on the unit's built-in CRT.Each range is current limited andsafe to use on devices including diodes,transistors, voltage regulators, op amps,integrated circuits and many passivedevices.

The T1200 also has a curve tracingfacility for transistors and FETs, whileits comparator feature allows the userto work on a PCB without a detailedknowledge of the circuit's action.

This rugged, portable unit weighs2.5Kg and measures 252x 262x60mm.More information from Antron Elect-ronics Ltd., Hamilton House, 39 KingsRd., Haslemere, Surrey GU27 2QA.Tel: (0428) 54541.

On The MattQuicker tape and pad application duringPCB design is one of the benefitsclaimed by Universal Grids for theirprecision layout grids.

The grid material, made from stablematt polyester film with camera -invisible blue grid rulings in eitherimperial or metric rulings, allowsgreater accuracy than unruled or lessstable bases, and this is especiallyimportant where reduction or enlarge-ment is involved.

The material also doubles as draftingfilm for technical drawing, with thesame advantages.

For a leaflet and stockists' list, contactUniversal (Electronics) Grids Ltd., POBox 3, Liskeard, Cornwall PL14 6YZ.Tel: (0579) 20878.

Hobby Electronics, July 1984 11

MONITORThree -Way StripNew products from OK Industries: co-ax wire strippers, revolved around thecable, mak two- or three -layered strips.The cutting blades will removeddielectric, braid and external insulationeither simultaneously or in anycombination, by changing the blade"cassettes" which are colour coded forquick identification.

A PCB track repair kit comes in threepackages, economy, standard and deluxe. The kits include master frameswith tracks, fingers, pads, elbows andflatpack pads, eyelets and funneletsplus setting tools. The standard and de-luxe kits have epoxy, flux, cleaner,spatulas, abrasive sticks, tweezers,clamps and knives as well as otheritems. The de -luxe version evenincludes a soldering iron and a range ofpliers. All the separate items can bepurchased alone.

Speaking of de -luxe, for the con-structor who is looking for the best indesoldering comfort, OK's electricdesoldering iron offers one -handdesoldering, combining heat andsuction in one. The vacuum chamberremoves for cleaning, and replacementtip are available with 1.5mm and1.77mm hole diameters. Versions for115 or 230VAC 50/60Hz are offered.

For further information refer to OKIndustries UK Ltd., Dutton Lane,Eastleigh, Hants S05 4AA. Tel:(0703) 619841.

The Reel Thing?TEAC, best known for their taperecorders, is moving into the cassettetape market with two 'models'.

The MR60 is a 'reel to reel' typecassette, ie the tape within the chassisruns on two small metal spools. "Looks

great - what more could you say?" saythe company. Quite a lot, I dare say -the tape itself is Type 1 (Fe) rather thanone of the fussier grades of tape, and thetapes are sixty minutes long.

The MDX Series of tapes come in C90,C60 and C46 lengths. TEAC claim thatthis series, which uses a newlydeveloped metal powder with anadvanced binder to provide a denser andmore even distribution, has "broken themajor objection with metal - price".We have not actually been quoted retailprices, but there is one to keep an eyeopen for, doubtless.

Further enquiries to TEAC, Harmon(Audio) UK Ltd., Mill St., Slough,Berks SL2 500.

abx DiscsA so -far little known system in hifi is the

dbx-enclosed analogue disc system,which boasts that it is the onlyanalogue -recorded format that canreproduce the full dynamics of digitalrecordings. Unlike digital discs, dbxdiscs can be played on an ordinarystereo system, with the addition of aspecial dbx decoder unit.

A list of new additions to the dbxrecords and tapes catalogue has justcome in, and includes records from theBee Gees, Joe Cocker,Jeffery Osborne, as well as severalcassettes by various pop, jazz andclassical artists. The list overall is fairlyrestricted, with about forty rock/poptitles available, and rather more in theclassical department, as well as jazz,easy listening and other titles.

Anybody interested should contactHarman (Audio) UK Ltd., Mill St.,Slough, Berks SL2 5DD. Tel: (0753)76911. HE

12 Hobby Electronics, July 1984

ELECTRONICS

"NiCAD Batteries"We can supply, from stock, quality batteries from one or more of the following companies: Ever Ready,

Safi and Hitachi, at unbelievable prices and a complete range of chargers.

ALL THESE PRODUCTS CARRY A FULL YEAR'S GUARANTEE

NiCAD BatteriesFormat Capacity

(AH)Height(mm)

Diameter(mm)

Prices1-9 10-24 25-99

AAA 0.18 45.0 10.5 1.34 1.27 1.22'/IAA* 0.10 18.0 14.3 1.58 1.50 1.44'/IAA* 0.24 28.1 14.3 1.45 1.37 1.32AA 0.50 50.2 14.3 0.90 0.85 0.82AM 0.50 50.2 14.3 0.96 0.91 0.88I/2A* 0.45 28.1 17.3 1.53 1.45 1.38RR* 1.20 42.1 22.6 1.70 1.61 1.52C 2.20 49.7 25.9 2.40 2.30 2.20D (sub) 1.20 60.5 32.9 2.40 2.30 2.20D 4.00 60.5 32.9 3.50 3.32 3.15D* 4.00 60.5 32.9 3.59 3.41 3.24F* 7.00 91.3 32.9 6.85 6.50 6.20SP 10.00 91.3 41.7 10.50 9.50 8.90PP3 0.11 49 . 26.5 . 17.5 4.35 4.10 3.85

* Denotes cell fitted with solder tags

NiCAD ChargersAC.1 SAFT MAZDA AA charger, charges Ito 4 AA cells £5.75 PC.3 SAFT MAZDA PP3 charger, charges I or 2 PP3 cells £5.75 MC.4 JECKSON

MULTICHARGER, charges 2 or 4 AA, C or D cells £7.00 MC.6 SAFT MAZDA MULTICHARGER, charges I to 4 AA, C or D cells, or I or 2 PP3 cells £8.75

=ME

BNOS Electronics (Dept HE) Bigods Hall, Great Dunmow, Essex CM6 3BETelephone (0371) 4677

AI/ prices include VAT, Postage is free on all UK orders sent with cash over .C.5, 16r UK orders under C5, please add 60p to order total.Trade enquiries welcomed

TOROIDALSThe toroidal transformer is now accepted as the standard in industry,overtaking the obsolete laminated type. Industry has been quick torecognise the advantages toroidals offer in size, weight, lower radiatedfield and, thanks to I.L.P., PRICE.

Our large standard range is complemented by our SPECIAL DESIGNsection which can offer a prototype service within 14 DAYS togetherwith a short lead time on quantity orders which can be programmed toyour requirements with no price penalty.

STEEL DISHEDWASHER

OUTERINSULATION

SECONDARYWINDING

INSULATION

PRIMARYWINDING

CORE

END CAPS

NEOPRENEWASHERS

15 VA62 x 34mm 0.35Kg

Regulation 19%

SERIES SECONDARY RMSNo Volts Current

0,010 6.6 12504011 9+9 0830,012 12+12 0630,013 15.15 0 5004014 18+18 0 420,015 22+22 0 340x016 25+25 0.300,017 30+30 0 25

(encased in ABS plastic)

30 VA70 x 3Ornm 0.45Kg

Regulation 18%

1,0101011101210131.014IxO151,0161017

6+69+9

12+1215.1518+1822+2225+2530+30

2501661251000830.680 600 50

50 VA80 x 35mrn 0.9Kg

Regulation 13%

2,010 6+62x011 9+92x012 12+122,013 15+152,014 18+182,015 22+222,016 25.252,017 30+302x028 1102,029 22024030 240

80 VA90 x 30mm 1Kg

Regulation 12%

3x0103x0I13x0I23x0I33x01430153,0163,0173,0283x0293,030

6.69+9

12+1215+1518.1822+2225+2530+30

110220240

4.162 772 081 661 381 13

000 830450 220 20

6644443 332 662 221 811 601 330 720 36033

120 VA90 x 40mm 1.2Kg

Regulation 11%

4,0104,01140124,0134,0444,0154,40164,0174,0184x028

6+69+9

12+1215+1518+1822+2225+2530+3035+35

1104,029 2204,030 240

160 VA110 x 40mm 1.8Kg

Regulation 8%5,011 9+9 8895,012 12+12 6 665x013 15+15 5335,014 18+18 4.445x0I5 22+22 3.635x0I6 25+25 3.205,017 30+30 2.665x018 35+35 2285,026 40+40 2005,028 110 1 4554029 220 0 725,030 240 0 66

10 006 665 004003 332 722 402001711 090 540 50

225 VA110 x 45mm 2.2Kg

Regulation 7%6x012 12+12 9.386x013 15+15 7.506x014 18+18 6.256,015 22+22 5116,016 25+25 a 506.017 30+30 3 756,018 35+35 3.216.026 40+40 2 816x025 45+45 2506x033 50+50 2 256x028 110 2 046x029 220 1 026x030 240 0 93

300 VA110 x 50mm 2.6Kg

Regulation 6%7,013 15+15 10 007,014 18+18 8 3374015 22+22 6827x016 25+25 6 DO7x017 30+30 5.007,018 35+35 4.287,026 40+40 3757,025 45+45 33374033 50+50 3 007,028 110 2 727,029 220 1 367x030 240 1 25

500 VA140 x 60mm 4Kg

Regulation 4%

8416 25+25 10 008x017 30+30 8 3384018 35+35 7 148x026 40+40 6 258x025 45+45 5 558033 50+50 5 008,042 55+55 4 548x028 110 4 548x029 220 2 278x030 240 2 08

625 VA140 x 75mm 5Kg

Regulation 4%

9x0I7940189,0269x0259033940429x0289x0299,030

30+3035+3540+4045+4550+5055+55

110220240

10 418 927816946 255 685 682 842 60

Why a Toroid7Smaller size & weight to meet

modern 'slimline' requirements." Low electrically inducednoise demanded by compactequipment.

High efficiency enablingconservative rating whilst main-taining size advantages.

Lower operating temperature.

Why I LP?* Ex -stock delivery for smallquantities.

Gold service available. 21 daysmanufacture for urgent deliveries.

5 year no quibble guarantee.Realistic delivery for volume

orders.No price penalty for call off

orders.

Prices including P&P and VAT

VA Size15 030 1

50 280 3

120 4

Mail Order - Plea e make your crossedVA Size cheques or postal orders payable to I LP

7.43 160 5 12.90 Electronics Ltd.8.08 225 6 16.30 Trade - We will open your credit account

10.10 200 7 18.55 immediately upon receipt of your first10.8111.73

500625

89

25.7331.63

order.

For 110V primary insert "0" in place of "X" in type number.For 220V primary (Europe) insert "1" in place of "X" in type number.For 240V primary IUKI insert "2" in place of "X" in type number.IMPORTANT: Regulation - All voltages quoted are FULL LOAD.Please add regulation figure to secondary voltage to obtain off load voltage.

VISA

Post to: I LP Electronics Ltd., Dept. 2Graham Bell House, Roper Close,Canterbury, Kent. CT2 7EPTel: (0227) 54778 Telex: 965780

IL IF'ELECTRONICS LTD..

Hobby Electronics, July 1984 13

Maplight Dimmer

Map Lightimmer

. uf.,A guiding light can be too bright, even in thedarkest night. But not with the help of this

simple in -car gadget.

LEADING, as I do, an excessively busylife, I sometimes find myself needingto work on writing in the car whilesomeone else drives. For this purposethe maplight in the car is invaluable.However, though it is designed not todazzle the driver, on a dark road it canstill be a nuisance.

A much dimmer light would besuitable to check a neatly drawncircuit diagram, or to see thecalculator. As I was part way througha much larger project and wished tomake the best progress possible, Iresolved to fit a dimmer to themaplight to enable me to use it all thetime with out the danger of distractingthe driver.

Those who know me have oftenregiailf.ekph,py extreme dislike ofeleretreihic bbliiponents getting -fingerlickin" hot, so at least for thesecognoscenti (that's Itrnetrrter SmartAlec - Ed.) it is no surprise thatinstead of using a hefty variableresistor, and maybe melting theplastic dashboard, I used an electroniccontroller.

The Principles Of OperationThe principle of operation of thecircuit relies on pers. of eyevision. The lamp is s on andoff too fast for the eye ect with avariable mark to spacd whichcan be adjusted to conbrightness.

In fact the switching rate is highenough that the filament does notcool down much between cycles -the lamp just dims slightly betweencycles rather than going offaltogether.

This particular system dissipatesligle power, since with the switch ONafriftra pthillOpower is transferred tothe l4pp, while with the switch OFFno power is drawn. The little powerthat is dissipated is due totpir vcoltitagedrop in the switching device, -'A4-*switching losses, and the power usedto run the circuit.

Of these effects, the greatest isvoltage drop in the switching device.

A. Armstrong

The CircuitStarting from the ot theswitching device chosen is a VMOSFET,type VN46AF. A VMOS FET doesriot require a continuous currentsupply to maintain conduction, sothe power consumption of the rest ofthe circuit can be reasonably low.Also, in most circumstances, apower FET is less destructible than apower transistor.

The particular device chosen has amaximum ON resistance of 3 ohms,so with the load to be used, a six wattlamp, the maximum voltage dropwould be about 1V5in the ON state.

This would result in a powerdissipation of OW75 maximum - well,within the capabilities of the devicewithout a heatsink. Most devices willdo better than this - the prototype

was measured at OV8 drop in the ONstate.

Surge CurrentA lamp load exhibits a large surgecurrent when switched on from cold.This is because the cold resistance ofthe filament is much larger than itshot resistance.

This surge current can be up to fivetimes the steady running current.

This does not pose a problem to thiscircuit, because the'fairly highswitching speed keeps the lampfilament at an almost constantteMperature so there is not a hewsurge each cycle.

The resistive nature of the FETprevents damage at the initial switchon, and reduces the thermal shock to

14' Hobby Electronics, July 1984

Maplight Dimmer

D1 rA- Cl9V1 AIL 47u

NOTES:IC1 = 55501 = VN46AFD1 = BZY88C9V1

BRIGHTNESSRV1

4it10k

4 8

C2100n

RESET +VE

DISCHARGE

TRIGGERCONTROL

THRESHOLD

IC1 OUT555

OV

6

1

3

R1

1 47k

4k7

R2

C3100n

+12VR3

330R

Q1

VN46AF

MAPLIGHT

0 OV

Figure 1. The circuit. The dimming is obtained by a rapid switching of the lamp, controlled by the 555 timer.

the filament by preventing such aheavy surge of current as wouldotherwise occur.

TimerThe IC which controls the switching isthe well known 555 timer, which isintended for monostable or oscillatorapplications.

Its main internal functions comprisea flip-flop, and two comparators,which can set the flip-flop (and hencethe output) into either state. Thecomparators switch at one third andtwo thirds of the supply voltage, butthis can be modified by the controlvoltage input, and thus in thisapplication can change the mark tospace ratio.

It can in fact be varied from full onto completely off - through being onfor two thirds of the time seems to bea typical setting required.

Gate Turn -onThe FET used requires less than OV8on its gate to guarantee to turn off -no problem for the 555 IC which isguaranteed to pull down to OV25.

It also requires about 10V to reachits three ohm ON resistance, which isslightly more of a problem, since the

555 is not specified to get to closer to itspositive supply than two volts. Aten volt Zener supply is used, so theworst case FET ON gate voltage iseight volts.

This in fact poses no problems -the worst case ON voltage drop wouldnot exceed two volts, and it would besurprising if in practice any units builtwere anywhere near that voltage.

Parts List

FROM CARELECTR ICS

Other UsesThis project can of course be used todim other lamps than maplights. Itcould form a very good way ofprolonging the life of torch batteries iffull brightness is not always needed.

In this kind of application theZener could normally be ommitted,and a wire link substituted for R3. If,in a low voltage torch, the voltagedrop in the FET is too great, then asecond FET can be connected inparallel, due to the resistive nature ofand positive temperature coefficient ofthe device.

WARNING. this is not true of bipolartransistors, e.g. 2N3055.

Experimentors CircuitThere is also another possible use

for which this circuit can be adapted;-- "dim dip" for car headlights.

Apparently someone has realisedthat encouraging everyone to drivearound with their headlights on all thtime at night defeats it own object ofimproving road safety, since the effectof being dazzled easily makes up forreduced change of anyone failing tonotice a vehicle.

In order to achieve the aim ofimproving road safety, cars made from1986 onwards will be fitted (I think)

RESISTORS CAPACITOR ZD1 BZY88C9V1(All 1/4W 5% carbon) C1 47u 9V1 400mW ZenerR1 4k7 16V radial electroR2 47k C2, 3 100nR3 330R polyester or ceramic MISCELLANEOUS

POTENTIOMETER

SEMICONDUCTORSIC1 555

timer

Printed circuit board; maplight;knob; connectors; case if required;wire etc.

RV1 10k Q1 VN46AFlinear pot VMOS field effect transistor BUYLINES page 26

Hobby Electronics, July 1984 15

Maplight Dimmer

+12V TODIMMER °

FROMDIMMER 0PCB(01 DRAIN)

47 R

220R1W

BD140

2R2YAV

2N3055

0

47 R

0 TO LEFTHEADLIGHT

BD140

ALL TRANSISTORS ON A HEATSINK

220R1W

2R2

2N3055

0

+12V FROM0 DIPPEDHEADLIGHT

SWITCH

OTO RIGHTHEADLIGHT

Figure 2. An experimentor's 'ircuit for those wishing to try other applications for the circuit, including possible headlightdimming. with something which can dim

the headlights if required, in the dipposition.

Seemingly, this circuit with a morepowerful output stage would carry outthis function, though without furtherinformation as to the exact lightingregulations one cannot be absolutelycertain. For those who wish toexperiment with this, a suggestedoutput stage is shown in Figure 2.

The output stage shown should bewired up on a heatsink, and caretaken to avoid the insulatedconnections to avoid the risk offailure.

d g s

BEND UP 90°(SEE TEXT)

BULLETCONNECTORS

MAPLIGHT

RV1

c-1-", -I R1 I --

IC1 ) R2 1--

a

R3 I- LINKZD1

0.25" SHROUDEDRECEPTACLETO OV

0.25" BLADETO +12V(FUSED ACCESSORYCIRCUIT)

Figure 3. The PCB layout. Apart from the normal anti -static precautions, theonly point to note is the careful bending -up of the heatsink tab on 01.

ConstructionThe construction of the Map Light onthe PCB is quite straightforward, thereare only two points to note. One isthat to save space there is not enoughroom for the heatsink tab of Q1 toclear one of the fixing bolts. Thismeans that the tab has to be bent asshown in Figure 3.

Carry out this operation verycarefully, with the pliers near theplastic body of the FET.

The other point is that as Q1 is aMOS device, care should be taken notto "zap" it with static.

Continue to connect up the unit asshown, taking care that the polarity ofthe power connections is correct. It isrecommended that a suitableselection of blade and bulletconnectors be used, with female forsupply and male for ground, toprevent misconnection.

TestingSwitch on. If the lamp will not light atall, at any setting of RV1, thensuspect a broken connection. If it willnot dim, check the power supplypolarity, and check that Q1 is installedthe right way round.

As part of its internal structure,most VMOS FETS have an internaldiode between drain and source. Thismeans that the device conducts allthe time if the power is reversed.

You should now have a working dimmaplight (for a dim navigator).

Happy driving!

16 Hobby Electronics, July 1984

Metal CabinetsFrom £1.85

Beautifully manufactured cabinets, with an aluminiumbase and 18 -gauge steel covers. Theycome completewith rubber feet. The cabinets are louvred for ventila-tion, and have an attractive two-tone finish. These areexcellent cabinets for power supplies, remote controlunits and kitsSIZE 1 102(d) x 56 (h) x 83(w) £1.85pSIZE 2 150(d) x 61(h) x 103(w) £2.20p

.SIZE 3 150(d) x 76(h) x 134(w) £2.55pSIZE 4 184(d) x 70(h) x 160(w) £3.15pAll dimensions in mm. Prices include Postage, Packingand VAT.

Send Cheque/Postal Order to:VAN GELDER (UK) LIMITED

Unit 1, South Road, Southend AirportSouthend-on-Sea, Essex SS2 6YG

Tel: (0702) 548681Barclaycard/Access accepted

MICRORANGE ELECTRONICSUNIT 258, STRATFORD WORKSHOPS, BURFORD ROAD (near Stratford Centre)LONDON E15 2SP. TEL: 01-536 1415

Recently openedcomponent shop in the heart of Stratford, we have lotsof special offersuntil the end of June. (You will find us on the 2nd Floor.)

We specialize in the manufac-ture ofPrinted Circuit BoardsNo quantity is too small.We also supplyPhoto Board and associatedchem ica Is at very keen prices.See below:5x4" Single sided 1.808x5" Single sided 2.106x4" Double sided 2.008x5" Double sided 2.40

Other sizes available

ALL PRICES INCLUDE VATPlease add 50p for P&P

SOME SPECIAL OFFERS(Many others in stock)

781 2 12V 1A Reg 30p each78P05 5V 10A Reg 5.50 eachVN67AF Power Fet 65pBF 258 30pTIP 41 35pMJE 340 45pTO5 H/sinks 10p eachH/duty TO3 H/sinks 25p each60W spot bulbs various colours 70p each100W spot bulbs various colours 1.25 each1 Metre Sq. Quality SPK Cloth 2.9520W Car Spks 10.00 pair3 way 700W Sound to Lite Unit 15.00150W Power Amp Module 10.0010x12" Fibreglass Board 2.00

Please come and see our range

MASTER ELECTRONICSNOW!

The PRACTICAL way!

You will do the following: Build a modern oscilloscope Recognise and handle current

electronic components Read, draw and understand

circuit diagrams Carry out 40 experiments on

basic electronic circuits used inmodern equipment

Build and use digital electroniccircuits and current solid state'chips'

Learn how to test and service every type of electronic deviceused in industry and commerce today. Servicing of Radio, T.V.,Hi-Fi and microprocessor/computer equipment.

NewJob?NewCareer?NewHobby?Get into Electronics Now!

el v..Please send your brochure without any obligation tlNAMEADDRESS

HE/7/822 BLOCK CAPS PLEASE IPOST NOW TO:

British NationalI Radio &Electronics School

Readmg,Berks. RG1. 1BR

I am interested in:COURSE IN ELECTRONICSas described aboveRADIO AMATEUR LICENCEMICROPROCESSORSLOGIC COURSE

OTHER SUBJECTS

MODEL COVERS

J

All sizes catered for with the base of your choiceand colour. Let us help you keep your pride andjoy in good condition. Trade or Retail enquirieswelcome.6mm rebate base for 3mm clear perspex cover4" high x 12" long x 6" wide = 12.00p. + pp.

TELEPHONE OR WRITEALL ENQUIRIES ANSWERED

John Wise Limited5 Alpha Road, West GreenCrawley, Sussex RH1 1 7DH

Tel: Crawley 542889

Affordable Accuracy Low Cost Multimeters from ArmonSPECIFICATION MODELSHC -8010 & HC -7030 DIGITAL* 10 amp AC/DC* Battery: Single 9V drycell. Life: 200 hrs.* Dimensions: 170 x 89 x 38mm* Weight: 400g inc battery* Mode Select: Push Button* AC DC Current: 200µ A to 1 OA* AC Voltage: 200mV to 750V* DC Voltage: 200mV to 1000V* Restance: 2000 to 20M0* Input impedance: 10M0* Display. 31/2 Digit 13mm LCD* 0/load Protection: All ranges

ARMON ELECTRONICS LTD.

SPECIFICATION HM 102R ANALOGUE* DC Voltage: 0-25, 1, 2.5, 10, 25 100, 250,

1000 volts20,000 ohms/volt

* AC Voltage: 0-10,25,100,250,1000 volts10,000 ohms/volt

* Decibels: -20 to +22dB.* DC Current: 0-50, soon A, 0-5, 50. 500mA.* Ohmmeter 0-6 Megaohms in 4 ranges

30 ohms Centre Scale.Power Supply. One 1.5 V Size 'A' battery

(incl)* Size & Weight: 135 x 91 x 39mm, 280gr.HC 102 BZ WITH BUZZERBATTERY SCALE, 10A DC RANGE

Dept. E, Cottrell House, 53-63 Wembley Hill Road, Wembley, Middlesex HA9 8BHTelephone 01-902 4321 (3 lines). Telex 923985

Please add 15% to your order for VAT. P&P free of charge. Payment by cheque with order.Offer applicable to mainland UK only. Please allow 15 days for delivery. ol

Hobby Electronics, July 1984 17

COMING SOON TO . . .

0

INFRA -RED LINKA very simple and compact IR link kit which can be used for remote control projects, burglar alarms etc. The

sensitivity of the receiver can be adjusted to suit different applications as required.

TEMPERATURE CONTROLLED SWITCHThermistor-controlled switching device to operate any mains equipment drawing up to 5A. The design is

straightforward, but has a choice of accurately adjustable ranges.

AUDIO FUNCTION GENERATORThis waveform generator can be used for amplifier tests, digital modules, switching circuits etc, and it can be

built into existing test equipment or housed in its own case. The generator provides square, sine and triangularwaves, and has a wide frequency range with good stability throughout.

CIRKIT PROJECTSThree highly functional projects designed by CirKit for their Electronic Construction Kit range, published

exclusively in Hobby Electronics.

THE NEXT MOVE IN MICROSWe take a first look at the new micro which many are saying will dramatically change the face of the micromarket, the all-inclusive Amstrad CPC464. With a built-in cassette recorder (or disk drive) and a choice ofmonitors, this "computing centre" may set the pattern for consumer computers for the future. Or will it?

DIGITAL TEST SETThe HE Digitester has a 5V power supply, a six -frequency pulser, and a three -state logic level indicator. An

indispensible piece of digital test equipment for under a tenner.

SOFT OPTIONSThis month Soft Options looks at the 'pop' face of computing: computer games. Are they time -wasting trivia, or a

genuine computing challenge? If you can't ignore them, how can you make use of them?Also, Soft Options talks to a software company who have already found their answer to some of these questions,

as well as others, and are providing unusually refreshing results. Plus news, views, reviews.

Please reserve me copies of the August issue of11- -I-V V001

forName

Address

August issue on saleat your newsagent

from 13th July.Place your order

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

18 Hobby Electronics, July 1984

Hifi Control Amp

Hifi ControAmplifier

The second in an occasional series of hifiamplifier building blocks, the hifi controlamp features an unusually wide choice of

tone controls, and a circuit designed to thehighest audio standards.

THIS project, which is designed to runfrom the hifi power supply publishedsome months earlier, (HE February'84) is intended to be used as abuilding block from which the readercan construct preamplifiers, completeamplifiers, etc.

The output signal is suitable to feedinto any normal power amplifier, be ita Quad 405 or a pair of poweramplifier modules built from thepages of this magazine, and aseparate output is provided to drive aheadphone amplifier.

No input switch is shown in thisproject. However, with the addition ofa simple selector switch, it could beused as a complete preamplifier withthe qualification that there is no discinput. It would be suitablefor tape, tuner, or laser disc playerinputs.

The circuitry is designed throughoutfor minimum distortion and low noise,so this particular project is suitableeven for those with extremelydiscerning ears.

Tone ControlsSome of the controls are slightlyunusual. For example, as well as theconventional Baxandall bass andtreble controls, a middle (presence)control is provided.

This permits the words of a song tobe made more audible when thecontrol is turned up or, when it isturned down, tailors the frequencyresponse for listening at very lowvolumes, when the ear wouldnormally lose touch with the extremesof bass and treble before the middleranges.

Andrew Armstrong

Insensitive EarThis characteristic of the ear is notlimited to variations in the perceivedloudness of extremes of bass andtreble. In fact, as shown in thegraphical representation of the ear'sresponse known as the "Fletcher-Munsen curves", the threshold ofpain is lower at the extremes offrequency. Thus the dynamic range ofthe ear is reduced outside thefrequency band required most forintelligible speech.

In some forms of deafness, thethreshold of audibility in the middlefrequency band most required for

1

there is little range between a soundwhich is too quiet to be heard, andone so loud as to cause pain.

A project making use of thisinformation is already a gleam in thedesigners eye.

Stereo And FilterA stereo width control has also beenincorporated. This would be anadvantage when listening onheadphones, when the stereo effect ofmost records can be a little extreme,or, alternatively, when listening on

Hobby Electronics, July 1984 19

Hifi Control Ampspeakers which are too close together,or listening to records which soundalmost like mono.

The effective stereo width can beenhanced by advancing the control,thus providing an improved soundquality.

A second order low pass filter isprovided as a scratch or hiss filter,suitable for example, for use with FMstations where the signal strength isnot as high as required for noise freestereo reception. The filter is aconventional circuit, but is switchedby analogue gates, allowing electroniccontrol to be used.

A slightly unusual feature in thisarea is that the balance control isincorporated into the filter circuitry.Another feature of the project is thatthe output to the power amplifier canbe muted by switching an analoguegate. This would permit the use ofheadphones while the speakers areconveniently muted.

The Circuit In BriefReferring to the block diagram shownin Figure 1:

The signal is fed first of all into thevolume control. For this reason, allthe components used must be chosenfor low noise level, since at lowvolume control settings the entirenoise of the preamplifier will still befed to the power amplifier. Thismeans that large input signals can behandled without overload.

An alternative position for thevolume control is provided, for use insituations where the input signallevels from different sources areknown to be similar.

The buffer stage following thevolume control may be chosen at thetime of construction to have somegain, to permit the use of low levelsignal sources, or to provide an extrahigh level output should the poweramplifier chosen require it.

The output of this buffer feeds intothe low impedance of the input of themiddle control, which in turn feedsinto the fairly low input impedance ofthe Baxandall bass and treble control.

FilterFollowing the tone controls is theswitched low pass filter. Since thebalance control is included with thefilter, and since this control is oftenrequired to adjust for unequalstrengths of signal in the left andright channels, the width control hadto come after, rather than before, thispart of the circuit.

The output from the width control isavailable to feed to a headphoneamplifier, and a separate bufferedoutput is provided to feed the poweramplifier. This output is buffered,because, in order to achieve theminimum distortion due to non-linearities in an analogue gate, it isdesirable to feed the output of thegate into a high impedance, and noguarantee can be made about theinput impedance of the poweramplifier chosen to be used with thisproject.

The Circuit In DetailFirst, a note on the componentnumbering. In the left hand channel,component numbers start with "l-eg; R1, R2. In the right hand channelhowever, component numbers startwith a "101". Thus, R1 and R101have equivalent circuit functions inthe left and right channelsrespectively.

For the sake of clarity only the lefthand channel is shown in Figure 2,and component numbers in thischannel are referred to in alldescriptions.

The chosen value for the volumecontrol, 47k, is quite a

usual impedance value to findon an input. This value, with thecoupling capacitor used, gives a lowfrequency roll off to -3dB at about1 5Hz. This should not cause anyaudible effect.

Input BufferThe buffer stage following the volumecontrol is required in order to feed thelow input impedance of the middlecontrol. It is not possible to have avery high impedance at the input of thiscontrol without having extremely highimpedances and possible noise pickupat points in this stage.

The input buffer has resistors laidout on the PCB to enable gain to beset, though of course the best signalto noise ratio will be obtained fromthe circuit if sufficient signal can beprovided to the volume control so thatunity gain can be used. In this case,R1 should be omitted and R2 shouldbe replaced with a wire link.

Buffer GainIf gain is required in the input bufferstage, this can be calculated as:

gain = R1 + R2 + R2

If a very high gain is used, the signalto noise ratio will be degraded, andop -amp distortion may become asignificant factor. If IC1 is required tohave a significant gain, ie input signallevels are very low, the use of a 5532is recommended, as this is anexceptionally low noise device. In thiscase the use of metal oxide resistorsaround this op -amp is also suggested.For most applications, the LF353 orTL082 are sufficiently low noisedevices.

Should there be any difficulty inobtaining the LF347 Quad FET op -

Figure 1. The block diagram, showino details of the left hand channel. An alternative volume control position is shown sothat the control amplifier can be adapated for different requirements/power amps if required.

LEFT MIDDLE TREBLE AND SW ITCHEDINPUTCONTROL BASS CONTROLS SCRATCH

VOLUME FILTER STEREOCONTROL WIDTH

CONTROL

INPUTBUFFER

BALANCECONTROL

ANALOGUESWITCHES

OUTPUTBUFFER

POSITIONALTERNATIVEFORVOLUME CONTROL

20 Hobby Electronics, July 1984

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Hifi Control Ampamp, the LM324 can be used at theexpense of a tiny increase indistortion. Gains in excess of fiveshould be avoided.

The middle control can provide avoltage gain or attenuation ofapproximately 5.6 over the middlerange of frequencies. It achieves thisby having two feedback networksconnected in reverse, and a pot, RV2which can vary the proportions ofnegative feedback the op -amp actuallyreceives from either network.

The range of frequency responsesavailable from this is illustrated inFigure 3.

Level ResponseThe frequency at which the responsewould start rising with the control inthe middle boost position is set by C2and R4, and is about 130Hz. Thefrequency at which the responsestarts to level off is set by C2 and R3and is approximately 723Hz.

The response starts to fall at thefrequency set by C4 and R8, and isabout 1.3kHz while the frequency atwhich it starts to flatten off again, ieback to unity again, is 5.6 times this,at 7.224kHz.

Middle Control FrequencyResponseThis frequency response diagram wasdrawn up by plotting just the pointsringed. This is a simple method toobtain a close approximation to thefrequency response of an RC circuit.To show how it is done, take as anexample the maximum boostcondition.

At very low frequencies, theimpedances of capacitors C2 and C4are much higher than resistances R4and R8, so these resistors are thedominant factor in determining thegain, which is therefore unity.

The frequency at which theimpedance of C2 equals that of R4 is

GAINDECIBELS,

10

10kHz FREQUENCY

Figure 3. This diagram shows the boost and cut over the middle range offrequencies given by the middle tone control of the amplifier.

20

10

5

GAINIDECIBELS) 0

-5

-10

-15

MAX TREBLE

10kHz FREQUENCY

MIN TREBLE

Figure 4. This diagram shows the boost and cut available over the bass and treblefrequencies by the conventional Baxandall bass/treble tone controls.

said to be the first breakpoint, ie thefrequency a which the change inresponse becomes noticeable. At firstglance, it would seem that the gainwould be almost two, with only R3reducing it slightly below this point.

The signal passing through C2 is inquadrature (90 degree phase shift), sothe effect of R3 is less than might beimagined, but the signals via C2 andR4 add vectorially thus producing again of 2 rather than two. ( 2corresponds to about 3dB.)

The next breakpoint, involving C2and R3, is calculated in a similarmanner. The only difference here isthat this breakpoint is at a gain of 3dBless than the maximum that couldoccur if C2 were shorted. Similarreasoning applies to the rest of thegraphical representation of thefrequency response.

The frequency scale is logarithmic,since this is a reasonable

representation of the way the earperceives different frequencies.

This kind of technique, making useof reasonable approximations, iswidely used in electronics to avoid thenecessity for equations which will notconveniently fit on the paper (or in thebrain of the designer).

Tone ControlsThe next stage of the circuit is theBaxandall tone control. This isconventional in design and typicalcharacteristics available from it areshown in Figure 4.

About 15dB of boost or cut isavailable from these controls at theextremes of frequency. Put quitesimply, RV3 adjusts the amount ofnegative feedback or alternativelysignal input at high frequencies, andRV4 performs a similar adjustment at

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22 Hobby Electronics, July 1984

Hifi Control Amp low frequencies. Thus a boost or cutat treble or bass can be provided.

Scratch FilterThe next stage of the circuit is the lowpass filter for reducing the sound ofscratches on the record or hiss on FMreception.

The form of the filter used is knownas "voltage controlled voltagesource", (a standard form). To realisethis particular filter form, a non -inverting unity gain buffer with a lowoutput impedance is required. In orderto serve as a balance control as well,this circuit is also required to have anadjustable amount of gain.

To meet these seemingly conflictingneeds, the signal on the invertinginput of the op -amp is used as theunity gain output. So long as the op -amp does not clip, and is not asked toproduce enormous amounts of gain,the signal on this inverting input willfaithfully reproduce the signalimposed on the non -inverting input,but at a much lower impedance.

The filter roll off frequency is set byR16, R17, C9, and C10. In order toobtain the optimum shape of filterresponse, ie maximally flat, the valueof C10 should be double the value ofC9. This gives a damping factor of0.7071.

Balance ControlThe controllable gain in this circuit isused to provide the balance controlfunction. Each channel, left and right,is connected to one half of a dualganged pot RV5, in such a way thatwhen the resistance on the left handchannel increases, the resistance onthe right hand channel decreases.

When the pot is in its centreposition, the gain of this stage is 1.5in each channel. With the control ineither extreme position, the gain ofone of the channels is reduced to one,

while the gain of the other isincreased to two.

Thus, this balance control cannotdirect all the sound to oneloudspeaker or the other, but it doesprovide a useful range of balanceadjustment, over the ranges ofimbalance liable to be encountered inpractice.

Should a wider range of control berequired, the circuit should be set togive a higher gain by reducing R18and of course R118.

The capacitors in the filter part ofthis circuit may be switched out byswitching off the analogue gates inseries with them. In this case, nofiltering action takes place, and thestage is simply a buffer and balancecontrol.

Width ControlThe following stage is the widthor stereo enhanced control. Thefunctioning of this is at first sightrather complicated, but the principleon which it works is straightforward.What it actually does is subtract aportion of the left hand channel fromthe right hand channel, and viceversa.

This subtraction is carried out byadding some of the input of onechannel into the non -inverting inputof the other. The action of the circuit,overall, is inverting, so the output ofthe left channel op -amp is the leftinput signal inverted plus a proportionof the (non -inverted) right inputsignal.

This therefore gives an output onwhich is superimposed aproportion of the other channel of thestereo, but inverted. This fools the earinto perceiving the loudspeakers asbeing farther apart than they reallyare.

Fine, but what happens if you preferthe sound the way it was on therecord, you may ask. To allow this, aproportion of non -inverted signal is

subtracted, by means of a resistancebetween the inverting inputs of eachchannel. This relies on the sameaspect of op -amp functioning as thefilters, namely that the signal on theinverting input of the op -ampaccurately reproduces that imposedon the non -inverting input, assumingthat the op -amp is operating on alinear mode.

The proportion of non -invertedsignal subtracted can be varied byadjustment of RV6, either to leave theeffective stereo width wider thanstandard, or to adjust it through anunaltered condition, almost to mono.This may be slightly difficult tounderstand at first, but the circuitused is possibly the simplest andcheapest means to produce thiseffect.

The width control feeds theheadphone amplifier output, via aresistor, whose value may be chosento limit the maximum headphonevolume is non-destructive level.

OutputThe width control also feeds, via acapacitor, the analogue gate used tomute the loudspeaker output. Thisanalogue gate feeds to the secondpossible volume control position, andthe wiper of the volume control feedsthe output buffer. Since the signal iscoupled via a capacitor, any offsetbuilt up in the rest of the circuit willnot be transferred to the output.

The 1 k resistor in series with thepower amplifier output reduces thelikelihood of damage being caused ifvoltages are fed back into the output,due, for example, to a severe amplifierfault.

ConstructionThis is a moderately complicatedproject, so it is strongly recommendedthat the printed circuit board shouldbe used, rather than a Veroboardlayout. It is also preferable, if possibleto use a temperature controlledsoldering iron. (No, I don't represent acompany that makes them.)

The use of such an iron can avoidhours of annoyance finding the onebad joint preventing the project fromworking.

Volume ControlWhen the PCB is assembled, it is firstnecessary to decide which of thealternative volume control positions touse.

If the preamplifier is intended toform part of a permanent or semi-permanent system, then it is apractical proposition to use potentialdividers or extra buffers with gain onthe inputs to adjust them all to thesame signal level.

Hobby Electronics, July 1984 23

Hifi Control Amp

INPUTFROM

SOURCE

o<

4111,,o, 11I

RV1 or R27/R127

ALTERNATIVEPOSITION FOR RV1(or R27/127)

SEE TEXT

NOT USED

x o o r -m < <

SW2 OUTPUTTO POWER

AMP

TO POWERSUPPLY

0THROUGHBOARDCONNECTIONS

HEADPHONEOUTPUT TOAMPLIFIER

RH

ovoVLH

Parts ListLeft hand channel numbers

given onlyRESISTORSAll 1/4W 5% carbonR1, 2, 16, 17, 19, 22, 23 22kR3, 5, 7, 9, 25, 26 1k0R4, 6, 8, 10 5k6R11, 14 3k3R12, 15, 18 10kR13 33.kR20, 24 4k7R21, 27 47kTwo of each of the above is re-quired for stereo.

POTENTIOMETERSRV1 47k

dual gang logRV2, 3, 4 100k

dual gang linRV5 10k

dual gang linRV6 10k

single gang linOne of each is required for stereo.

CAPACITORSCl, 2, 5, 11 220n

polyesterC3, 4 22n

polyesterC6 560p

ceramic plateC7, 8 47n

polyesterC9 1n

polystyreneC10 470p

polystyreneTwo of each required for stereo.C12, 13 47u 16V

radial electro

SEMICONDUCTORSIC1, 2, 3, 5 LF353

dual J-FET op -amp (4 off)IC4, 7 DG308

quad analogue switch (2 off)IC6 LF347

quad J-FET op -amp (1 off)

MISCELLANEOUSSW1, 2 SPDT

min toggleDouble sided printed circuit board;IC sockets; screened cable; AudioSupply Power Module (see text);wire; solder etc.BUYLINES page 26

Figure 5. Thje PCB layout. This is amoderately complicated double -sidedboard. Detailed instructions are givenin the text, but we will note here theauthors point that it is preferable toinsert the pin-throughs, marked bysmall rings on the overlay, beforeplacing the components, followed bythe IC sockets if you wish to use them.Otherwise, construction is straight-forward. The photo opposite will actas a guide - there are one or twominor differencies, as the photo wastaken at the penultimate prototypestage.

24 Hobby Electronics, July 1984

Hifi Control Amp

This project has a double sidedprinted circuit board, Figure 5, andconnections must be made from topand bottom in various places. In someplaces this is done by top soldering aresistor lead, but in many places(marked on the overlay), theconnection should be made usingtrack pins, or failing that, pieces oftinned copper wire (ie clipped resistorlead).

Owing to the difficult positioning ofsome of the pin-throughs, theseshould be inserted first.

No top soldering of ICs is needed,so that sockets may be used ifdesired. If sockets are to be used,these may be inserted first to helplocate the rest of the components.Otherwise, it is better to insert theresistors first and the ICs last, as innormal procedure.

Headphone AmpIn this case, better performances willbe available with thevolume control at the output of thecircuit. This also means that themaster volume control does not affectthe headphone volume which canthen remain set at the required levelas the loudspeaker volume isadjusted. A signal level of about three

TUNER °INPUT

TAPEINPUT RA 33

r1

R, 22k

R2747k 3k

10

AUDIO PRE AMP

ALTERNATIVEVOLUME CONTROL

POSITION USED

1

J

OU T

Figure 6. One possible application of the control amp: using the alternativevolume control position, for recording say from a VCR and radio tuner at the sametime.

volts peak to peak is a reasonablelevel to aim for.

If on the other hand, thepreamplifier is to be used with avarying selection of signal sources, itis probably better to use the volumecontrol at the beginning of the circuit,in order to avoid the possibility of thecircuit overloading on a strong signalsource.

Whichever volume control positionis not used should have a fixedresistor of the value of the volumecontrol inserted, and the non -invertinginput of the op -amp should beconnected to the upper end of theresistor.

Once the volume control has beenconnected, all the other controlsshould be wired up, as shown. Thepower supply lead should be solderedto the pads on the PCB, and ideally aMolex connector should be used atthe other end to connect to the powersupply unit.

Take care to connect the powersupply leads correctly, since thepower supply unit's connections donot all correspond to connections onthe preamplifier unit.

TestingThe preamplifier should now be readyto test.

First of all, in order to avoid damageto the power amplifier or speakers,switch on and check each op -ampoutput to make sure that there is nosignificant offset. If there is thensuspect a solder blob shorting aninput.

Assuming there are no problemsthen set the volume to minimum, andconnect a signal source, eg tuner anda power amplifier. Slowly advancethe volume until the sound is at asuitable level, and then test all theother controls to make sure theywork in the right direction.

Assuming all is well so far, the unitcan be built into a case and theknobs fitted. The one control requiringspecial attention is the width control.In order to find the "normal" position,feed a signal into one channel only,and adjust the width control so thatthe signal is audible only on thechannel it is fed into. Carry out the

test in reverse to make sure there isno significant difference in therequired control positions. Centre theknob. The preamp is now ready touse.

Should it by any chance not work, agood way to isolate the area of thetrouble is to connect a probe,consisting of a capacitor feeding avolume control, to the poweramplifier. Use this probe to check forthe presence of signal on each op -amp output from the input onwards,and where the signal disappears orbecomes distorted the fault is not faraway.

Further NotesThere are two associated projectswhich are more than merely a gleamin the designers eye. The next itemunder consideration is a matchingheadphone amplifier with enoughpower to drive a small pair ofloudspeakers for low level monitoringif required.

To follow this, an input switchingsystem is already on the drawingboard. It is intended to provideadequate facilities to cope with themany recording and replay devicesnow available, and will havecontrol of recordingsignal sources separate fromlistening selection.

Thus, for example, one could recordonto the soundtrack of the videorecorder from the radio while listeningto an LP. Figure 6 shows just onesimple application of the pre -amp.Here IC1 is used with its gain set bythe 10k and 33k resistors. Thealternative volume control position isused, as the input signals are so lowas not to need the attenuation of avolume control. Resistors Ra and Rbare used to attenuate the tape signalso that the volume levels for both theinputs are similar. The values for Raand Rb should be determined byexperiment as should the amount ofgain required.

All this and more in future issues ofHE!

Hobby Electronics, July 1984 25

Buylines

Maplight DimmerA components list for theexperimenters circuit is not given inthis article as a few of thecomponents depend on the wattagerating of the load, ie. the lights usedin your car.

No case is specified as the housingdepends on your own ideas. A smallplastic case about 3" x 3" x 11/2" willtake the printed circuit board quitecomfortably if desired.

If not already fitted to your car, amaplight can be purchased in almostany car accessory place. There aresome maplights which have aninternal switch, and this may be usedwith slight changes to the circuit toswitch off the 12V supply to thedimmer.

The one possible difficult item is theVN46AF. This can be obtained fromRapid Electronics.

Estimated cost for this project isf2.50 excluding the maplight andPCB. The PCB is available fromour PCB Service.

± DC VoltmeterNo real buying problem here. Themost expensive item is the panelmeter, and it is advisable to shoparound for this item. A 50-0-50uAmeter is generally available althoughit is not widely advertised.

Our advice here is to collect a fewcatalogues (as we are currentlydoing!).

A metal case is advisable, as thecircuit is rather sensitive and will bemore stable if it is screened. Cost isapproximately £5.00, and thisexcludes the panel meter and case.

Audio Pre -Amp ModuleFirst the cost. We estimate this to beabout f16 and this excludes the PCBand the power supply mentioned inthe article. The most expensive itemhere is the double sided printed circuitboard, and because of its complexity itis not advisable to make your own.

The LF . ICs are common enoughto be found most everywhere,whereas the DG308 analogueswitches are not. The author hassuggested they can be obtained froma number of sources but we havebeen unable so far to find anywhereexcept RS Components.

Your best bet here is to order theICs through your local componentshop, or alternatively you can try: S &R Brewster, 86-88 Union Street,Plymouth, Devon. Tel: 0752665011. The RS order number is303-551.

No case description or size hasbeen given, as the case will dependon how many modules you wish toinclude. For those who intend to usethePre -amp "as is", a small ali box with lidlarge enough to take the controls, thePCB and the power supply will sufficefor the time being.

HE

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SOFTOPTIONS

ContentsComputers On Camera 2Combining the entertainment value oftelevision with the popular appeal of themicrocomputer offers possibilities for morethan just fun and games.

Soft Talk 6Plain language reviews of software forlearning.

School Report:Stanford -in -the -Vale 10Experiments with microcomputers at aprimary school in the heart of thecountryside.

Programmable Learning System . . 14Tandberg's computer -controlled cassettedeck assessed as a tool for computer -assisted learning.

Editor: Ron KeeleyAssociate Editor: Mary Sargent BANews Editor: Helen Armstrong BA

EditorialIt is now official. The home computer industry has failed toachieve useful objectives and this could "seriously affectfuture growth of the market". A Gallup poll says so, and we allknow what jolly useful things opinion polls are.

This one is based on research among "middle-class parentswho have observed little educational benefit from homecomputers bought for their children", and the study says, "Weknow that what actually happens is the child, usually a boy,ends up using it solely for playing games" instead of doinghomework on it, or learning to program.

There follows an interesting section on statistics: so manymachines bought at a cost per unit of under £170 (why don'tthey just say Spectrums and be done with it?); numbers boughtat Christmas; total in UK, etc; then the really good bit, wherethe document sets out its thoroughly researched conclusion:

"We have now potentially 2.5 million homes in which theparents are realising, perhaps only now, the error of theirdecision."

Lest you feel this is all too arbitrary to be taken seriously, Imust say that I read about it in the Times; and at least onesoftware house has mentioned the poll in its recent publicityhandout, which indicates that it's well on the way to passingfrom the realms of opinion into established fact.

I wonder if Christopher's parents know how disillusioned theyare? Christopher is ten, and when he and a friend came in frombob -a -jobbing during the Easter holidays, they tried to workout the finances of their endeavours on the calculator. Theyfailed.

So they sat down and wrote a short program so that the homecomputer could do it for them. The program worked.

And I must remember to explain to Mike that his nine year oldis not really interested in doing maths with his computer -he must just be playing games on it, because that's what thesurvey says. As for Hazel, Kate, Josephine, Nicholas, et al, theirinterest is a mere micro -illusion. The people of Gallup know .

What nonsense it all is! Of course there are a number ofdisillusioned people around. New technologies are susceptibleto impulse buying by consumers who subsequently discoverit's not what they expected.

Someone I know fell for the advertising hype surrounding thelatest hi-fi system during the seventies boom, only to discoverfor the first time that he was deaf in one ear and couldn'tbenefit from its highly balanced twin -speaker, ultra -fidelitycapacity.

And doubtless the home -micro industry has suffered similarcasualties.

Nevertheless, I suspect the computer business will survivethese devastating findings. After all, even in this day and age,not everybody either can, or wants to, drive a car, but nobody'spredicting bankruptcy for the Ford Corporation.

Soft Options, july 19R4 S1

ComputersOn

Camera

Glitter, spangles, musicand laughter. These are notthe usual surroundings for acomputer, you might think,but to the team on ITV'spopular children's magazineprogramme, the SaturdayShow, they are at least asnatural as the classroom orthe family TV set. Whilecomputers are not yetendowed with the glamour ofa pop star or a formula oneracer, presenter TommyBoyd and producer GlynEdwards felt strongly thatthe microcomputer'stechnocratic image could bebrought down to earth toprovide entertainment andpractical information fortheir young audience.

This conviction led to theshow's researcher, RobinEastwood, to track downcomputer journalist ChrisPalmer to act as the show'sconsultant on all matterscomputerate. An expert atthe age of 20, Chris was amember of the youngcomputer generation, whilebeing experienced enough totake a broad view of thesubject. Chris resents beingcalled a whizz -kid. As hepoints out, the real "whizz -kids" are around 14 - oryounger - falling into theage bracket of the SaturdayShow's audience.

Too many people are bewildered by computers, evenfrightened of them, says the Saturday Show's computerexpert. That's why, although their job is to entertain a

young audience, they aim to enlighten as well. Ifparents benefit as well as kids, so much the better . .

by Helen Armstrong

But the computer corner isnot aimed at the elite of theyoungsters to whomprogramming a computerseems to be as natural astalking. They are concernedwith the other 98 percent,the ones who are curious, orwho haven't yet seen enoughto be curious, or who haveseen just enough to beintimidated, baffled or boredstiff by the whole idea.Perhaps unsurprisingly, thegerm of the curiosity which

the show's staff detected hadarisen from what must bethe most glamorous aspect ofcomputing to most teenagers.No, not space invaders, butthe wealth and fameachieved by the invader'sinventors, the freelanceprogram writers, sometimesonly 15 or 16 years old.

The production team becameaware of this interest aftera spate of news items in1983. As a result, they asked

Chris at first to organise acouple of general-intrerestitems on computers. Thesewere a success, and Chriswas asked to supervise aregular computer slot,thereafter known asInterface. The task, as hesaw it, was to present micro-computers to the school -ageaudience without preachingonly to the converted. To do

"We have done some prettyrevolutionary things" says

52 Soft Options, July 1984

Chris. "We were the first totransmit an actual computerprogram, live on the air, sothat people could record itin their homes, take it to acomputer, and run it. Allthey needed was a taperecorder, or a videorecorder."

Not that this first incomputing and broadcastingwas trouble -free. Theprogram broadcast was agame for the Spectrum, andviewers were invited to sendthe solution to the game tothe programme. When noresponse came, the teamchecked a recording of theirown broadcast, and foundthat electrical noise from thestudio had destroyed theprogram as it was sent out.They re -broadcast it in asubsequent programme, andpresto! three hundred repliesarrived. The over -the -airsoftware was a success,showing how computer datacould be sent simultaneouslyto every home in the countryand stored for future use.

This is just one example ofChris's policy of takingordinary domesticmicrocomputers and doingunusual things with them.Computer graphics areinviting because they can bealtered in colour and form tosuit the user, and can beprinted out - in differentcoloured versions - andkept. A computer -controlledrobot, too, went down well,not least because it showedthe experts having their ownproblems as the little robotstubbornly refused to do asit was told.

Definitely for theinitiated was the show'scompetition, co -sponsored byCommodore, to write aprogram. The response,amounting to severalhundred programs, wasremarkably good, especiallyas this could only includeyoungsters already owningand programming theircomputers. "It took us twoweeks to work through themall" recalls Chris.

During his time workingwith computers, Chris has

been impressed by theunusual relationship betweenhumans - especially, butnot exclusively, youngsters- and their computers,which seems to exceed theintimacy between some malepersons (typically) and theirmotor vehicles.

"They talk to them" explainsChris. "And, unlike anyother piece of machinery, thecomputer answers back. I'mnot talking about speechsynthesisers, although thatcould come! But BASIC, orany computer code, is acomplete language which canpass information about whatis going on inside thecomputer, in response toinstructions from the user. Alanguage like BASIC is notso very different fromstandard English."

The complete absorption inthe computer experienced bysome users is not merelybecause they can conversewith them. "Kids want tohave fun" says Chris, "andonce they know how to useit, the computer offersalmost infinite fun andamusement. It engages theirsense of fantasy. It can betheir plane, their space ship,their jungle, their gamesboard. It's a window intoanother world." It's thesoftware which is important tothem. It's malleable andintangible, like magic. Oncethey have learned to writeand modify their ownsoftware, they can conjureup whatever scenario theywant."

This special relationshipwith computers has,apparently, both positive andnegative results. Shy peopleare often drawn out by theirenthusiasm and becomecommunicative, but othersbecome so absorbed thatthey are only concerned withtheir machines and otherenthusiasts, giving rise to thelittle clusters of "computerbuffs" who huddle togethertalking an incomprehensiblejargon.

Fortunately this excessmystique will become a thingof the past, as more people

Let's not get too serious. This is a Saturday morning variety show,and everyone's in it to have some fun. Presenter Tommy Boyd, in hisSaturday Best, prepares to count in a competitor on Up For Grabs.

become acquainted with howthey actually work. "Manyparents find them scary"says Chris. "They've heardthat the computer is themost powerful tool everinvented, something that cantake over the world. On amore practical level, they areafraid that the computer willreplace them in some way.Then they see that their kidscan control computers almostnaturally. They're afraid thattheir kids are moreknowledgeable than they are,and terribly different. Thishappens when the kids arevery young, and it worriesthe parents. But all that ishappening is that childrenpick up new languages fasterthan adults, and learningcomputing is learning a newlanguage.

"Computers very rarely getused for practicalapplications in peoples'homes. How many people doyou know who actually keeptheir accounts on a

' computer? That tends to belimited to the salesmen'sschpiel. They mostly getused for playing games.Interested kids gradually getbored with playing games,buy some add-ons and startprogramming. They start bywriting their own simple

games, they read the manual,and gradually find out justwhat the machine can do.

But Chris is keen to promotethe very realistic view thatlearning how to program isnot the only route tounderstanding computers.Far from it: programming isa specialised task. Mostcomputer users don't needany knowledge ofprogramming at all: thesoftware is already wittenand packaged. The majorityof professional users don'teven have contact with thesoftware.

But I wonder, does the sightof Chris's computercomplex, roped together withcables and not alwaysresponding on cue,contribute anything to theconfidence of the uninitiatedchild, let alone its parents?Chris reiterates that childrenwant to be entertained, theylike a challenge, and theywant to know that they canget their hands on thesepieces of machinery and dothings with them, that itdoesn't matter if they don'talways get results first time.Once they know that theycan experiment, that they canmake mistakes withoutbreaking anything, and that

Soft Options, July 1984 53

S

the results are there as theyhunt for them, the barriersare down.

The next step is to get"hands on" the machinery.Inspired by the traditional"grab a gobstopper" seasidegame, Chris devised "Up forGrabs". Like the originalgame, this involved onemechanical grabbing arm,operated by remote control,which the players use tofish for prizes. The differencewas that the player in thiscase could be five hundredmiles away.

The motorised arm would becontrolled by a computer inthe television studio, butwould be connected viaanother computer to ajoystick controller in thehome of a volunteer viewersomewhere around thecountry. The signals wouldbe passed from the viewer'sliving room, to the televisionstudio in Birmingham, downthe telephoe lines. Theplayer would watch therobot arm on television, liveas it happened, and attemptto manipulate it to collect atrophy from the array ofprizes.

However, linking the joystickto the robot arms - notoriginally designed to bejoystick controlled - andfeeding the real-time signalsfrom the distant joystick viathe telephone to thetelevision studio so that theplayer could see what washappening needed acompletely new piece ofsoftware, which Chris wrotehimself. As it wasexperimental software, hedesigned it so that he couldrecompile the program in themorning before the showbegan, using PET speedcompiler software, if he sawa way of improving it.

The robot arm itself,Armdroid I, was contributedby Colne Robotics, who alsomade some modifications toit to make it easier tocontrol. In the studio, thearm was given an orangelivery with fluorescent greengrabs, the better to tone inwith the show's sparklydecor, mounted on arevolving rostrum, and itwas ready to go. Meanwhile,the computer corner's ManOn The Spot, SimonRockman, was standing by to

travel to a distant place,armed with joystick, modemand computer, to set up thecontrols needed to operatethe arm.

"We had a good response tothis" says Chris. "We wouldprobably have had an evenbetter response if we hadmade it clear that the kidsdidn't have to have theirown computer, or the rightsort of computer. Weprovided all the equipment.It would be impossible if wehad to adapt a whole lot ofdifferent set-ups." Chrisprefers to work with theCommodore 64, which heknows well and findsexcellent for control work.On the strength of this,Commodore provided amodem and other equipmentfor Up For Grabs.

Once everything is linkedup, making the grab is not aseasy as A -B -C. Real-timemachine control bytelephone is not acommonplace requirement,and ordinary modem linksare not designed to encodeand decode signals quicklyenough for a mechanicalgadget to respond smoothly.

"The Rick Wakeman of the computer keyboard" - Mr. Palmer co-ordinates micro, modem and a string ofback-up systems to put a viewer in charge of the Armdroid.

4

The movements of the armare more complex than thenormal up -down -left -right -fire of joystick commands,giving the player a differentset of responses to becomeaccustomed to before thegame. Chris got around thislast factor, largely, byorganising the controlsoftware so that the armmirrored the movement ofthe joystick as much aspossible - but there wasstill the grab to manipulate.Nonetheless the movementsof the arm occasionallyappeared eccentric to say theleast. And the player hadexactly one minute andtwenty seconds to grab theprize. A minute is a longtime on television.

Watching the robot armperform live, the catch in thegrab become apparent -literally. Chris contacts theplayer of the week bytelephone and puts him intouch with the arm. As thecountdown begins, he standsby with a spare joystick -they even have an"understudy" playerstanding by in case of linefailure - and callsinstructions to the player.The arm begins to move, inresponse to the joystick onthe other side of the country.It moves uncertainly at first,peering around. Then itbegins to home on one of thepackages. The player canonly follow its progress viathe television. On the TVscreen, the robot's grab isclearly linked up to a prize, butseen from another angle, it'sa good six inches to the left.The player can't see this."Right, go right" calls Chris.Eventually the player of theweek manages to lift oneprize away and drag offanother, blundering into afew more on the way. "Thisis the best one we've had sofar" Chris enthuses."Usually they just knockthem over. We give them allthe help we can, but thetwo-dimensional TV picturedoesn't give enoughinformation. There's noparallax to guide them. Westopped using the rotatingrostrum after the first couple

Soft Options, July 1984

of attempts."

Nevertheless the studioaudience are cheering thearm, apparently moving ofits own accord. The player isup in North Wales, and isthe last contestant. Theexperiment has run itscourse, the series is ending,and when it returns therewill be something differentbut, if Chris has his way, noless experimental.

What about the entrants, Iasked. Computer freaks tendto be male. Are they allboys? "Mostly, but we'vehad about twenty per centgirls replying, which isn'tbad." I asked why hethought girls seemed lessinterested in computing thanboys. He gave the opinionthat they weren't encouragedenough, and that theywanted to see somethinguseful that they could dowith computers. He does notsee cookery software as ananswer.

Chris doesn't see theSaturday Show's computercorner as overtly educational."It's a Saturday morningkids' programme, we don'twant to be seen as directlytrying to educate the kids.But we try to educate themsubtly." So why attempt toeducate at all? "There are alot of people who are veryconfused about computers.Any hints and tips they canget are a help.

Chris also has his views oneducational aspects ofcomputers, especially aboutteaching computeracy. Thecomputer as a window on amagic world where anythingis possible is a view whichhas impressed him."Educational programs canencourge kids to play, andtherefore to learn" he says- reinforcing a view whichis developing here at SoftOptions. "You can get theirattention by playing up thefantasy element; when theyget the questions right,especially. This is primarilyfor younger kids. The olderones are better at just

Soft Options, July 1984

Tommy Boyd demonstrates the "parallax problem": the two-dimensional TV screen gives a flattened viewof the arm and its targets, so that it is very hard to judge where the arm is pointing.

working through theexamples, using thecomputer as a personalteacher. There isn't a greatdeal of this happening yet."

"Schools don't have enoughmachines. A school tends tohave "a computer". Youneed one per child. That's apurely an economicproblem."How does he rate software asopposed to textbooks as theeducational medium?"That's hard to say, butgood software could be easierto index because thecomputer can search veryquickly through the material.There's not much softwareof that kind."

As to teaching computing,he doesn't like to see toomuch on the schoolcurriculum, believing thatformal teaching can putyoungsters off programming,which they often teachthemselves out ofenthusiasm. He thinks theyshould be told to "go awayand play with thecomputers" to see what theycan get out of them."What should be done" hesays "Is to teach people

how to use computers,instead of how to program,which is specialised. Thetime would be better spentin teaching them how toextract information from adatabase, how to use thesystem, how to use thepower of computers to accessinformation. This is what ismeant by InformationTechnology. I think that theteaching of computing isbeing formalised in thewrong direction."

Talking after the show toTommy Boyd - who refersto Chris as "the new BarnesWallace" - I learnedanother angle of theSaturday Show'sinvolvement with computers.According to Tommy, bothhe and the show's producer,Glyn Edwards, are"converted computerites".Tommy's father was acomputer engineer on thejuggernaut -sized mainframecomputers of the fifties"where you had to work allweek to get the thing readyto operate for two hours on aSaturday, and it could doless than a Spectrum" -these machines didn'tcapture his imagination.

Microcomputers did,however. "They looked likefun and they are fun" hesays. "I play with mycomputer." Tommy reckonsthat youngsters presentedwith computers start off byplaying with them, andgradually progress to writingprograms. He claims that hecan't write programs himself- the furthest he has got is

around 100 lines - becausehe doesn't have the largeamount of free time needed tobecome familiar with the art."After doing about ninety-sixhours in one week, you beginto develop a relationship withthe computer" he says.

Having begun with a gamethat mimicked an old-fashioned seaside game,Tommy would now like tomove on to somethingfuturistic "With fantasticvisuals, like a videodisc game- say finding the way out ofa maze". The next seriesof the Saturday Show willhave a new producer,Graham Mole, and a new setof attractions including, wehope, another contribution tothe cause of making the homecomputer so familiar that"techno-fear" is in theforgotten past.

55

oftTat

This month's reviews have been written by primaryand secondary teachers, and by parents with children

of the ages catered for by the particular programs on test.

Words, Words,Words(A.S.K. Software)BBC ComputerRecommended for ages 5 to 8Price: £9.95

Reviewed by Roger Battley

The program comes on acassette together with a small,twelve page booklet. This iswholly adequate document-ation, and the quality of thepaper and layout are designedto give the impression fromthe outset that no effort hasbeen spared to create a good,usable program.

And this initial impressionproved to be extremelyaccurate; a good, usableprogram is precisely whatA .S .K. have produced.

It is aimed at the 5 to 8 year agegroup, with the degree ofassistance decreasing for theolder child.

The booklet is divided intosections, one of which gives avery full explanation on how toload the program and copewith possible problems.

This sort of information is

always welcome, both to homeusers and to harrassed teachersworking under pressure inclassrooms, and it is a pitymore programs are not as wellintroduced as this one.

Another indication that

$6

A.S.K. knows what it is doinglies in the educational notes,which give some helpful hints,probably for the home userrather than the teacher, whocould very easily introduce theprogram as part of the classactivities.

The particular point whichimpressed me concernedupper and lower case letters.Displayed letters are always inlower case, regardless ofwhether the CAPS lock is onor off, and this, as thehandbook points out, couldcause confusion because theletters on the keyboard areupper case.

The booklet suggests usingstickers printed with lowercase letters when youngerchildren are using the pro-gram, which indicates that thewriter really has thought aboutcomputers vis a vis children.

Perhaps some enterprisingmanufacturer might consideroffering a lower case keyboardfor use in infant and primaryschools.

At the end of the booklet, alist of words used in theprogram is given, withalternatives in some cses.

For example, a drawing of abus can be identified either assuch, or as a coach.

I found one error, when theword "ant" was not listed, butsince my daughter was able to

Oltr.

Words Words WordsFor the BBC Microcomputer Model Band Acorn Electron

identify it and the computeraccepted her input, that ishardly significant.

As for the program itself,this has been equally wellthought out. Since I consist-ently forget to rewind a tapeafter loading, the fact that thisone was recorded on both sidesprejudiced me in its favour.

I also felt that it was verythoughtful of them to printclearly on the cassette the timeneeded to load the program. Ifa teacher knows it will take 4minutes 25 seconds to load, ithelps with lesson planning.And as it happened I had nodifficulties with loading, at all.

The object of the program

is to build up a scenario bycorrectly spelling the names ofthings drawn by the computer.The really captivating aspect isthat when the game has beensuccessfully completed, thefinished picture is animated asa reward. The children whoplayed the game enjoyed thisvery much.

A menu gives a choice of eightplaces which can be visitedduring the "writing" of thepicture story. You can visitthem in any order, with thelimitation that the castlealways leads to the end of theprogram.

The "sound track" volume isadjustable and it is worthdoing this before you select the

Soft Options, July 1984

first loction; this is done bytyping in the name of the scenerequired.

Once the location is chosen, aseries of objects such arepresented for identificationand their names must becorrectly spelt.

Two attempts at each answerare allowed, and if the word isproperly spelt the object is re-drawn as part of the scene to bebuilt up.

If the answer is wrong, thecomputer gives the right one,but the object is not includedin the finished picture.

When the picture is fullycomplete, the animationstarts.

A duck swims across a pond, acar drives into its garage, aballoon floats away and burstsor a girl posts a letter.

The animation was sufficientlywell done to hold my sevenyear old daughter's attentioneven after several demonstrat-ions of the same sequence, andit certainly encouraged her totry other locations to see whatwould happen.

The final venue is a suitablecastle scene and involves a

ghost and a wise (BBC?) oldowl, which were particularlyenjoyed by my children.

The program ends by generat-ing most of the charactersfeatured along the way,and moving them slowly andrandomly around the screen.This, in itself, the childrenfound entertaining as they

Soft Options, July 1984

"spotted" the different creat-ures.

In my opinion, this is a mostsuccessful program, and couldwell be used with successiveclasses in schools. The wordsit uses formed a good basicvocabulary of object nameslikely to be frequently en-countered, and the programworked well on a black andwhite screen. In colour,however, it really came to life.

Did I have any criticisms? Atthe risk of being petty, I feltthat some of the soundsproduced by the objects, whenanimated, could have beenmore realistic.

The duck for example, spokea language entirely un-ducklike to the conniseur of

quackish, but this seemed toworry me more than it worriedthe children.

I would like to see, as a futuredevelopment of this program,possibly on disc, a facility forcreating characters and scenesoneself, and so expanding theword list to make a highlyuseful program even better.

Having nit-picked, I mustnow say that I can thoroughly

recommend Words, WordsWords for use in any primaryschool and I am equally surethat parents using it forchildren at home would bepleased with it.

A.S.K. programs are availablemail order from A.S.K., atLondon House, 68 RichmondRoad, London SW15, or fromthe same high street outlets asAcornsoft, who are marketingtheir software priced £9.95.

Pathfinder(Widgit Software)16/48K SpectrumPrice: £5.95Reviewed by GeraldLockyerPathfinder is an attractive setof four programs appropriatefor infants or pre-schoolchildren. The instructions tellus that the programs areintended to "help childrenthink in spatial terms and planmoves ahead", and I thinkthey will succeed.

They also demonstrate someimportant computing con-cepts for beginners, such asautomatic execution of a list ofinstructions. The programsare quick to load, can be listedand will run on either the 16Kor 48K Spectrum.

In the first program,Rabbit,four cursor control keys move

PATHF

16/48k SPECTRUM

Software Ltd

FOR CHILDREN

ahead

a rabbit through a maze. Themaze is created by a randomprocedure at the start ofeach turn, and takes a fewseconds.

The final maze always,miraculously, allows for onlyone pathway through it!However, since even the blindalleys are paved with carrots,which the rabbit system-atically chomps as he advanceshe'll probably want to eat thelot before leaving.

Kangaroo is also a mazegame, with the added attract-ion that a sequence of movescan be entered before they areexecuted. If, for example, youenter 5 followed by 1 andthen press G for GO, theprogrammed kangaroo jumpsfive squares up and one along- unless he hits a wall, due toa miscalculation.

PATHFINDER INSTRUCTIONS

TO RETURN TO t NSTRUC It° Qst ex,t the phArath type 0 Aga",

tht. compute( but wo hav-°ROE TT 0 RF n?Jti

MAZES RABBIT and KANSA

Firkeea rat '

am for

Tritediffic;,Ity

one QC'

$7

THE

HUMPTY DUMPTYMYSTERY.

&WHO KILLED COCK ROBIN?

48k SPECTRUM

widgitS wa d

FOR CHILDREN

You have the option ofentering and executing onemove at a time, or of plottinghis entire route in advance. Allthe moves are clearly listedbeside the maze for checking,and are flagged as they areexecuted.

In the third program, Pic-nic, the grid is still present butwithout maze partitions. Thetask here is to steer a monsterround four sites, so that it maypick up fruit.

The game calls for foresightand planning skill, since themonster must not cross its owntrail, and the player has theoption of giving up andrestarting with the samelayout, which is friendly.The final program, Frogs, testssimilar skills, with more sitesto visit and with obstacles toavoid. The frog must cross apond, picking up as many aspossible of his six friends onthe way, whilst avoiding waterlilies and his own trail.

Judged purely as games, allfour programs share a weak-ness: there are no prizes forspeed or success, and I thinkthis might discourage somechildren who need suchmotivation. The one specialreward promised for a fullypre-programmed kangaroowas merely a series of hot

fNSTRUCTtONS

SIDE A, "The Humpty Dumpty Mystery"LOAD mpty" CAPS LOCK must be oft during

these programs.Game 1L. Find out who pushed Humpty ott the wag by

asking questions and making guesses.VOCABULARY' blue hat

red badgepurple eyesgreen mouthyellow jacketwhiteblack a

Mode I For early readers who are not yet good atspelling. Enter colours using the colour keyson the spectrum.Enter nouns and names by initial letter,

Mode 2 Whole words must be typed in,This program develops skills in logical thinking.

Game 2. Is loaded from an option from Game 1 Yougel a glimpse of the culprit, but can youremember well enough to describe him

Uses the same vocabulary and modes as Game 1This program develops memory skills.

SIDE 8:LOAD "robin"

"Who killed cock robin"CAPS LOCK must be oil during thisprogram.

Can sparrow's confession be believed'?Find out WHO killed cock robin. WHERE and WHEN.Use clues and logic to help you.Needs some reading ability. 4 skill levels.Develops logical thinking and memory skills.PRESS CAPS SHIFT 8 Z together to leave any of theseprograms and return to the start.

WIDGIT SOFTWARE LTD.,48 DURHAM ROAD, LONDON N2 9DT.

flushes as he retraced his path.Adult supervision is needed,both to get the children startedand to applaud their skill. Thisputs the emphasis on fosteringparent teacher involvement, agood component of softwarefor early learning.

The programs are robust andvery simple to use, employinga minimal set of keys, and aredistinguished by imaginativescreen designs and motifs,which use cheerful, well -contracted colours.

On the whole, Pathfinder is askillfully designed package,well suited to its aim and at aprice which makes it a veryreal alternative to toys andbooks.

The Humpty DumptyMystery(Widgit Software)16/48K SpectrumPrice: £6.25Reviewed by AudreyVerdin

The tape consists of threegames, each involving at leasttwo skill levels. The HumptyDumpty game has two re-sponse modes: single key orthe typing in of whole words,which constitute a challengefor older children.

The first game is the "Humpty

Dumpty Mystery" itself.Humpty Dumpty has beenpushed off his wall with maliceaforethought, by one of theKing's Men, and the playersmust determine the culprit bya series of questions designedto establish the colour of hishat, badge, eyes, mouth andjacket.

If it is established that thefelon's hat is not red, forexample, then pictures of allred -hatted suspects are re-moved from the screen. Aninformed guess is possible,when the field has beensufficiently narrowed.

This is a game for one player,similar to the board game,Guess Who, by Milton Brad-ley. Young children found itdifficult to sort out the men'snames in the initial line-up oftwelve suspects, since thereare no spaces between themand they are written in capitalletters.

However, they enjoyed thepictures and loved it whenHumpty Dumpty winked atthem when they had solved themystery. From a learningpoint of view, the value of thegame lies in teaching childrento recognise sets, and evolve alogical strategy in questioning.

Game Two involves identi-

fying the unfortunate Egg'sattacker by dint of remember-ing his colour scheme, brieflyglimpsed as he gloats over hisvillainy. Questions and an-swers develop a description ofthe man and points areawarded for accuracy.

The younger children foundthat the mechanics of thisgame easier, and it is a verygood program for developingvisual memory and visualdiscrimination, which areessential skills in learning toread.

The third game is WhoKilled Cock Robin, whichuses logic in the same way asMastermind by Invicta. Spar-row has confessed to thedastardly deed, but we areinvited to query his guilt.

Detective work is required todiscover the murderer, thetime of the crime and where itwas carried out.

There are four skill levels, andfrom three to six suspects,times and locations may beselected. The answers aredetermined by logical ded-uction and the occasionalclue, if requested. The cluesthemselves need to be ap-proached logically.

The program uses goodgraphics, is well presented andprovides an interesting exer-cise in logical thinking. It isadvertised as "One of a rangeof programs for pre-schooland primary aged children",but the children at the lowerend of the age range play thegames intuitively rather thanlogically, and do not easilydevelop a systematic approachuntil they are about seven.There is no doubt that theseprograms represent a step inthe right direction. Widgithave produced a truly educat-ional tape, in the best sense ofthe word. It is entertaining,attractive and appeals to awide age range. At £6.25, itrepresents excellent value formoney and is the sort ofpackage needed in primaryschools.

It will be also give pleasureand value to children using itat home.

S 8 Soft Options, July 1984

All Fingers Go(Micro Trust Software)BBC Model BPrice £14.95

Reviewed by Roger Battley

All Fingers Go (Ultra FastTouch Typing) from theNational Extension Collegecomes in a moulded plasticcase which holds the instruct-ion booklet and two cassettes.The booklet gives an intro-duction to the programs,together with a summary ofthe commands available to theuser.

It also gives instructions onloading and running the tape,and the warning that if youhave the disc interface fitted,you must first reset the pageto &E00.

This being done, the tapeloaded first time, every time. Acolour set is an advantagewhen using this program, andthere is a facility for alteringthe colours originally pro-grammed. This has its ownsub -menu and the functionkeys are used to change thesettings.

It is worth adapting thecolour to suit your ownprejudices and to find theparticular combinations whichshow best if you are using ablack and white set.

There is a "beep" used tosignal a typing error, but thevolume of this is adjustable tosuit your mood, your state ofnerves or the time of day("You musn't disturb thechildren while they're sleep-ing").

As a confirmed beeperphobe,I was grateful for this verythoughtful touch!

The program, when loaded,displays a menu from whichyou make your lesson select-ion. The screen display is split,with the keyboard layout ofthe micro in the lower half andthe instructions in the upper.The pictured keyboard has theoutline of a pair of hands overthe keys and this is used toshow the correct finger neededfor each key.

Soft Options, July 1984

These phantom append-ages hover over what we -in -the -learning -to -touch-typebusiness quickly come to rec-ognise as the "home keys", abase from which to make allmoves to the rest of the keys.

The first program is anintroduction to the keys, andsubsequent lessons followed ina similar format to lesson 1.

At first, the keys to be struckchange colour on the screen,which assists indentification.The same sequence of letters isthen presented as a line to becopied, and the screen fingersmove to the next key as you hitthe right ones, but there is nocolour change.

Each line has to be typedthree times before you maymove one.

In the second part of theprogram, you have the sameletter sequence, but must nowtype with no errors before youprogress.

As your fingers leave thehome keys, the diagrammaticdigits also move, indicatingwhich finger to use and wherethe key you need is located. itquickly becomes fairly easy totype the right keys byfollowing the screen fingers,and not looking at thekeyboard.

With each ensuing lesson, newkeys are introduced, and bylesson seventeen, you will haveused every key, alwaysassuming that you haven'tindulged in any short-cuts,otherwise called cheating!

There are eighteen lessons inall, which take you through allthe processes of learning totype.

Each lesson begins with amenu detailing additionalfeatures useful to the partic-ular lesson. Lessons are loadedseparately and if you leave oneuncompleted, you can returnto the point at which you leftoff.You can also check progressand obtain a speed and erroranalysis for each letter typed.

In later exercises, thesentances are automatically

Ultra Fast Touch TypingAlan Mackie

MEP T V UI0

BBC Micro Model B

MICROTRUST SOFTWARENATIONAL EXTENSION COLLEGE, CAMBRIDGE

adapted so that words youhave found difficult occurfrequently, which ensures thatyou get the necessary practice.

The features found in eachlesson are very concisely listedin the handbook.

The program has been writtenwith the beginner in mind.The emphasis throughout ison accuracy, not speed, whilstthe division into eighteenlessons enables the moreadvanced student to join theprogram at a level appropriateto his standard.

I am very much a two -fingeredtypist at the moment, but theearly lessons have convicedme that touch typing is withinthe reach of the patient andself-disciplined user. Theprogram has a very friendlyapproach which helps make apainstaking process as painlessas possible.

It might have been useful tohave a printout facility so thatthe speed and error analyses

could have been saved andcompared with subsequentattempts, but this is a veryminor point of contention.

If you need or wish to learnbasic keyboard skill, includingcorrect fingering and the like,then this program shouldprove invaluable. I certainlyhave no hesitation in recom-mending it, and if you feel theinitial cost is high, I can onlysay that the more one uses it(and practice in plenty paysdividends), the better theinvestment becomes.

Just one other thing. Doesanyone where I can get aprogram teaching patienceand self-discipline?

All Fingers Go is available fromcomputer departments in W.H. Smith's or by mail orderfrom Microtrust Software.

Microtrust Software,National Extension College,18, Brooklands Avenue,Cambridge, CB2 2HN0223-316644

59

School Report

Stanford -In -The -ValeThere are enormous practical difficulties in introducing computers

into schools, but two teachers in rural Oxfordshire managed itwith energy, enthusiasm, and the active assistance

of a Parent's Association.

Stanford -in -the -vale is asmall rural village with a fewshops, a garage, a village greenand a primary school whichboasts 142 pupils between theages of five and 11 years, andfive members of staff.

It is not a wealthy communityand the school buildingsreflect that fact. But if thebuildings are out of date and inneed of renovation, thestandard of education beingdispensed within the greystone walls is emphatically ofthe 1980s, for Standford-in-the-Vale is in the process ofachieving what many largerand more sophisticated estab-lishments only aspire to intheory.

With only one RML 480Z anda couple of Sinclair ZXmachines, the school hasproduced such a degree ofcomputer literacy among thechildren that the difficulty itnow faces is, what to do next?

But how has this odd situationcome about? The first thingthat must be said is that itcould not have happenedwithout two specific factors:one is Terry Rothwell, whohas been at the school for 17

years, first as deputy head andfor the last six years asheadmaster; the other is BobLoader, who met up withmainframe computers as a

physicist at the governmentresearch establishment atHarwell and decided to takehis enthusiasm and expertiseinto education in 1968.

He arrived at the school in

10

by Mary Sargent

1971, and when Sinclairlaunched his first computer,the two men together set aboutharnessing the micro -revolut-ion for the children's benefitwith an impressive dedication.

They started with a ZX80 bought from school funds,and without active under-standing or support fromeither Stanford or the CountyEducation Authority.

"One could see straightaway," says Terry Rothwell,"that computers were comingin so quickly. They had such alot to offer education ifeducation could take advant-age of it, not only in basiclearning skills but in theinteractive programs, makingchildren more aware. Whenwe first started we werebasically thinking in terms ofchildren being aware of

computers, so that they wouldnot be frightened of them.This was to be their future. Icould see it coming into somany fields, credit cardsystems, paying in shops -it's all there in an embryoform. In education, whilst weare trying to educate them forthe present world, we mustalso educate them for thefuture they will be living in."

Initially, Mr. Rothwell usedhis status as a familiar andtrusted figure in the com-munity to persuade par-ents that his ideas should begiven a chance. Today, nosuch persuasion is necessary.He has the active help of aParents' Association whichnow raises around £1,000 ayear, which is largely used tosupplement the hard andsoftware support for the RMLsystem, partially funded by

the Government'sscheme.

MEP

As further proof of the successof the school's computingenterprise, some twenty of theolder children now have theirown microcomputers at home.In an area where money is notin vast supply, that sort ofdomestic expenditure is a clearindication that the Stanfordparents still have faith in theheadmaster's vision.

It is just as well, for the schoolfaces two major problems. Thefirst is hardware.

"I'm very pleased with ourcomputer. My only criticismof RLM, indeed of all thesefirms, apart frcm Sinclair, isthat they're all trying to maketheir fortunes in one year. Thebasic cost of the 480Z with amonitor and so on is around

Soft Options, July 1984

£800. These sorts of figuresare way beyond any normalprimary school.

As teachers, we're delighted toknow that the RML networkexists, but there's no way inthe present economic climatethat anybody's going to be ableto afford one. I feel thatschools should be leading theway as regards equipment andnot be behind homes. Takecolour televisions. 80% of mychildren had colour televisionbefore the school had one! Itshould be the other wayround, but inadequate fund-ing is a part of our lives.

I'm not criticising Oxfordshire. They've done theirwhack as far as they're able toin the sense of the governmentscheme, but we really needabout five government sche-mes. And the other aspect ofthis problem is that, whilstSinclair's prices are steadilycoming down, Acorn's BBCmachine and others haveactually gone up! As a non -business man that doesn'tmake sense to me."

The second major problemthe school has to contendwith is a lack of good software.A lot of the programs aremaths based, since these arethe easiest type of program towrite, but the need at primarylevel is for introductoryprograms in English, Rem-edial Reading and other

With one RML and a couple of Spectrums in the school, interaction between children is inevitably encouraged.

subjects in which the primaryteacher feels confident.

Mr. Rothwell believes that ateacher should be able to say,"This is what I want to do andI would like some programs tosupplement the work andteaching I am doing." There isno doubt in his mind that theteachers must be dominant indeciding the content of thesoftware.

It is not an area for thecomputer experts or thecommercial firms and he isdepressed about the lack ofliason between the softwarehouses and in-service teachers.

He feels that four years ago,the Government should have

Uninterruped use of a computer at home allows more concentrated activity.

set up a team of 50 people towrite educational software tospecific briefings, whichwould have afforded somekind of basis for educationaldevelopment, but he admitsthere is no easy solution to theproblem.

A good teacher cannotalways define why he operatesin a particular way, andtherefore may well not be ableto communicate to a thirdparty precisely what he needsin the software line, or why.

As far as Stanford itself isconcerned, there is onemember of staff who canpartially mitigate that part-icular problem. Bob Loaderhas just spent some 300 hourswriting a program, usable oneither the 480Z or thesecondary schools' 380Z,which demonstrates factor-isation in a colourful andgraphic form infinitely super-ior to many of the commericalprograms available.

It is an unrealistic amount oftime on top of a teacher'salready demanding work -loadand in any event, few teacherscould work to Mr. Loader'sexceptionally high programm-ing standards. His personalcommitment to computing inthe school is total, but he is nofanatic.

"I'm cautiously optimisticabout the future. We have aproblem with the number ofmachines available and what

software is available. I don'tknow what the limits are as tohow far you can go withcomputing in schools. It's likeso many other things, tele-vision for example.

It's a novelty to begin with andthen later on the childrenbecome insensitive to outsidestimulus. When we have tele-vision programmes, I enjoythem sometimes more than thechildren do. They watch tele-vision and immediately it'sfinished, sometimes before theend, they want to go on tosomething else. And I thinkthe same thing will happenwith the computer if we're notvery careful.

In some ways, you can neverwin. If the programs becomemore attractive, then childrenmay become blind to softwarewhich is less colourful but hasa lot in it. But we've just got towait and see."

This problem equates witha dilemma familiar to manyteachers - if a reading bookis designed with colourfulcartoons and speech bubbles,is the child better motivated toread or seduced in to merelyenjoying the presentation andavoiding the learning process?

At the moment, as TerryRothwell says, "There's nodoubt about the terrificmotivation from the child-ren," but they agree that, inBob Loader's words, "It's gotto be handled in the right sort

Soft Options, July 1984

Some participants in a co-operative session lose interest occasionally!

of way, and it varies from timeto time as to how you're goingto use it."

Because Stanford was the firstprimary school in the area toshow interest in computing,there has never been anyquestion of facilities beingdelayed or withheld. What theCounty has been able to offerunder the MEP scheme, it hasoffered, and Messrs Bothwelland Loader have done the restwith funds and support fromthe Parents association."We're better off as a smallvillage school than a largecomprehensive. Even thoughwe only have one computer,it's much more available to allthe childrencomprehensive,are still onlymachines andchildren.

than in awhere thereone or twomany more

We're using it as a tool foreducation, not to teachprogramming. In a secondaryschool they're trying toprepare children for exam-inations in computer studiesand so on. We haven't got thatproblem."

But what of the future?The men agree that they arenot interested in forcingprogramming into pupils. Ifindividual children decide topursue that angle, that is abonus, but as a subject forthe classroom, it is outside the

scope of primary education.Terry Bothwell believes that afuture based on half -dayschooling, with childrenworking from home usingcomputers as electronic bookswould be a very poorsubstitute for the personalcontact and interaction whichhappens at school betweenteacher and child and betweenthe children themselves. He ishopeful that that particularvision will founder on thebuilt-in social factor ofthe need most parent have fortheir children to be out of thehouse from nine to four.So where does education ingeneral and Stanford in

particular look for futuredevelopments?

Terry Bothwell is sure thatrobotics provides an immed-iate answer. But like everyother aspect it must behandled with care. The latestin technology is not auto-matically the best in allsituations.

"Floor turtles, I think, areexaggerated. In our situation,you can achieve the sameattitudes and thinking withBig Trak. At Primary schoollevel, floor turtles are tooprecise.

To have a Turtle drawing youa little triangle, that doesn'tmean anything to the children.To have a Big Trak goingthrough some chairs, nowthat's a different situationcompletely. Turtle is absol-utely superb for older children,a possible development for myolder children, 11 year olds.Big Trak - best toy out.But the things which are goingto come in over the next fewyears are the robots. No doubtabout it. Tandy have a superblittle robot at £30 and I can seegreat potential there in aprimary school situation

5 5

. .

It would appear that Stand -ford -in -the -Vale has littlecause to worry about develop-ments in its own village schoolcoming to a halt for lackofideas,

"And if she presses these keys it plays Rhapsody In Blue".

but how does Mr. Rothwell seethe situation in education as awhole?"If it hadn't been for teachersmoving along with Sinclair,who was the one who broke themarket open in education, Ireally don't see that we wouldever have had any movementfrom the top, particularly inprimary schools.

What we really need in theeducational world is for someof the passion and the dramawhich is found on the arts sideof teaching to be applied tocomputing. We need a sense ofurgency and enthusiasm, notclinical detachment andscientific caution."

The underlying drive andrationale of both men'scommitment to the micro -revolution in schools isperhaps best summed up inBob Loader's assesment of thecomputer's usefulness tochildren.

"It's got an immediate appealand gets an immediate re-sponse. The important thing isit carries a person on,whoever they are, a child or anadult, and I think it is

universal in that it applies toall ages and all abilities. It hasthis ability to draw you on tothe next step. I find this myselfwith programming - youdon't want to stop. It is soenjoyable to get on a bitfurther.

I don't think it's good to fixany limits on it at the moment.We don't know enough yet tosay, don't use a computer forthis or that. You've got to bevery open about it and use itwhen you feel it's the thing touse."

There is little doubt that theschool in Stanford -in -the -Vale not only feels it is thething to use, but is using it in avery effective way.

"We would like to continue"School Report" as a regular

feature in Soft Options. Pleasewrite and tell us of yourexperiences and experimentswith computers at your school.Contributions from teachers,pupils or parents are equallywelcome!

S12 Soft Options, July 1984

SellingEducationalSoftware?

Software Options reachesthe parents, teachers and

pupils you need.

To Advertise

Contact:Jo James

01-437 0626extn 290

NEC SOFTWARE

CROSSWORD PUZZLERBBC B' AND SPECTRUM

A cassette of programs which allow you tocreate, store and play your own crosswordpuzzles. I ncludesthree demonstration data filesand instructional booklet. An ideal method ofimproving juniorand infant spelling, helping withrevision facts, foreign language vocabulary etc.

£6.90 inc VAT

ALL FINGERS GO!BBC 13'

Ultra fast touch typing course with a completelynew approach to learning to type- users followthe computer's moving fingers on the micro'skeyboard. Eighteen lessons from beginners'standard to full keyboard typing, including errorchecking and speed measurement. Superb useof the BBC's colour and graphics.

Set of two cassettes £14.95 inc VAT40 and 80 track Disk £28.75 inc VAT

From bookshops or direct from NECNATIONAL EXTENSION COLLEGE

18 Brooklands AvenueCambridge CB2 2H N

(prices include post and packing)

1 SOFTWARE FROM FLITE:

CARTESIANcan graph the simplest of functionsOr the most complicated. It then goes on to do an awfullot more. Like drawing the differential curve and findingthe definite integral. Like extracting roots whereverthey exist, even when the function has multiple roots.Like solving complex equations. Like allowing for manygraphs to be overlaid one on the other. Like letting theuser animate the scales and axes in order to reach anypart of the curve, and to magnify segments.

Naturally if CARTESIAN can handle the functions above,then it can also take care of quadratics, cubics, trig.functions, polynomials, circles and elipses.

CARTESIAN is available for the BBC'B', Acorn Electron, Apple 11e andApple Europlus.

PRICE:

Cassette: £24.90Disc: £27.75

Cartesian is fun to use, whichshould go a long way towardsensuring that it is used, and itis both powerful and flexibleenough to be of real benefit toany serious student of mathe-matics.

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Use it in the home, club, office or school. It's veryversatile.

1. Records are designed by the user.

2. May be used with one disc drive.

3. Allows selective label/envelope addressing or full

record recall.

4. Search using ANY field.

5. Random access for fast operation.

6. Very user friendly.

7. 40 or 80 track versions. A 40

track disc will hold up to 400

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supports professional standard

features.

price:£15.90Disc only. Please specify whether

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software Mail Order (074) 22286 & (074) 22025rders

welcome.

rd rSoft Options looks at a computer -controlled cassette recorder

designed to make waves in computer assisted learning.Reviewed by Margaret Curtis

The Tandberg TCCR, iscapable of being used, on itsown, as a high -quality con-ventional tape recorder and, inconjunction with a micro withRS232 interface, as a highlysophisticated computer -con-trolled machine.

It has its own internal microcomputer which performs avariety of tasks like windingand speed control, scanningits own keyboard, computingthe linear tape counter valuesand displaying the results onseven -segment LED digits,and communicating with thehost computer.

What this all means to theuser is that the machine iscapable of winding the tape athigh speed, forwards orbackwards, and stoppingprecisely at a predeterminedpoint.

The motor is controlled tosuch an extent that gradualacceleration and decelerationis possible and the usualabrupt stop/start action of astandard recorder is prevent-ed. Tape slippage is thusavoided and precise position-ing of the record/playbackhead on any part of the tape ispossible.

The overall effect is to givethe ordinary cassette theappearance of being random-ly -accessed, although ofcourse the mechanics of thesituation are such that it is

merely being wound back-wards and forwards with ahigh degree of precision.

The operation is very quietand providing that there issomething on the computerscreen to hold the user'sattention, the time taken towind through a C60 cassette isnot noticed.

The "something" on thecomputer screen is what theTandberg system is all about.You could use the recorderas a very efficient storagemedium for your computerprograms, your data banks or(dare it be said) for yourfavourite arcade game, butthat would be under -using the

capabilities of the machine.The Tandberg is an interactivesystem. Together with thecontrolling computer it pro-vides the facility to have audiomaterial linked with text andgraphics displayed on thecomputer monitor.

After loading a programfrom the TCCR530, the com-puter instructs it to present thefirst sequence of audiomaterial. At the end of thesequence control passes backto the computer whichpresents a commentary orquestion to test the student'sunderstanding.

The student's response mightbe an input on the computerkeyboard or a spoken phrase orsentence to the cassette. Thiswill trigger off an appropriatereaction, leading either torepetition of one or moresequences, or to the nextsection of material.

All the techniques of com-puter -based learning may beapplied, involving tutorial,practice, testing, simulationetc, and the computer can beprografnmed to collect andanalyse student performanceand print out appropriaterecords.

S 14 Soft Options, July 1984

Some examples of possibleuses are . . .

In the Language Laborat-ory: the computer could dis-ply a sentence and switch theTCCR530 into record modewhile the student reads thesentence aloud. A variety offeatures could be developedincluding comprisons of thestudent's pronounciation witha pre-recorded version pro-vided by the teacher.

Problem solving (questionand answer exercises): one ofthe limitations of theseactivities in a conventionalcomputer -aided learning sit-utation is the restrictedamount of material which canbe displayed on the monitor.It is sometimes necessary toerase the student's input inorder to explain why it waswrong.

With the TCCR530 it is pos-sible to maintain necessary in-formation on the computermonitor, wind on the tape in

the TCCR530 in a pre -deter-mined position and play an ex-planation of the student'serror, with some reassuringmessages that encourge some-one who is making the samemistake time and time again totry a different approach.

Music Tuition: music lessonsmight be adapted to thesystem, with the possibility ofplaying extracts from, forexample, actual orchestralperformances, whilst explain-ing about the work or theinstruments in text, graphicsand manuscript form on thecomputer monitor. Themicro's own sound capabilitycould also be used to illustrate,simply, certain musicalphrases, or they could beincluded on the cassette tape.The computer software whichallows these complex tasks isprovided by an "authoringpackage", and the creation ofmultiple-choice branchingprograms is made quick andefficient with their use.However, there is much that

ato."" 4, fro. ,0 4... 400OW* *VS 4 9,

.....

RF

GT0122

PL TO+002

RT

GT1441

PL TO+004

GTxxx

Table 1

Rewind fast - make sure the tape is fullyrewound and the tape counter zeroed.

Wind tape until counter reads 0122.

Play the tape until 2 seconds of silence aredetected and stop.

(computer, then displays relevent material,poses questions etc).

Read tape counter (xxxx) into computerso that it can be used later if necessary.

(Suppose user's input was a "wrong answer")

Tape forward to position 1441.

Play tape until 4 seconds of silence detected,then stop. While the tape was finding 1441the monitor could have explained the errorand the audio information from the tapecould have been supplementary detail.(Then, while waiting for user response maybejust any keypress . . . )

Go back to the stored location where theuser error was detected, and continue.

can be achieved solely by usingBASIC.The Tandberg has a com-mand language which is wellexplained in the manual, andwhich is easy to use. Themanual contains hints onpreparing programs and, bestof all, a short example of aBASIC program showing howto send commands to theTCCR530. The complete setof commands will not bedescribed here but a typicalsequence is shown in Table 1.

To provide greatest flexibilityin use, the logic functions ofthe computer-TCCR530 in-terface are software defined.As a result the operatinginstruction manual can init-ially appear a rather dauntingdocument to those of usunfamiliar with electronics.

However, the Tandberg staffwill be able to advise on cables,connections, and variousparameter settings to cover thelimited number of situationsthat the TCCR530 is likely tomeet in any one educationalenvironment.

The review model wasconnected to a BBC Model B

computer, and worked verywell.

A demonstration program wasprovided, in which the usertook the role of a noviceleading seaman/yatchspersonabout to be instructed on thepractice and proper way togive an International DistressSignal in the event of the vesselcapsizing! If you have alwaysassociated controlled tape -recorders with language labsand "la plume de ma tante"then obviously you mtA thinkagain.

In fact the TCCR530 hasbeen designed to cope withmany applications other thancomputer -based learning, andsome of these applicationscould also be used in schoolsand colleges.

For instance, it can be used torecord data from a computer -monitored experiment, withthe computer reading ana-louge values (temperature,pressure, velocity etc) andconverting them to digitalinformation which would bedownloade to tape wheneverthe compute'rs's memorybegan to fill up.

Soft Options, July 1984 S15

With the addition of asimple unit, it could besynchonised with a slideprojector and be used either togive a straight forward slidepresentation with musical and

spoken sound track or, with aback -projection box, anaudio-visual learning program- which brings us back tointeractive systems again.To make the TCCR530/Com-

puter configuration reallyuseful either software -plus -audio packages should beavailable (and this, as far as weknow, is not presently thecase), or, perhaps more

importantly, an authoringpackage which will enable thenaive user to create his or herown course material easily.Such authoring packagesare just becoming availableand it is hoped to review oneof them in the future issue.With a school interested inaudio-visual teaching tech-niques, and with departmentsactually creating source mat-erial (slides and tapes) as partof their own courses, it wouldnot be difficult to envisage thatsufficient computer -assistedlearning material could begenerated in a co-ordinatedeffort across several depart-ments to justify the cost of thisvery excellent machine.Two versions of the TandbergTCCR 530 are available fromTandberg. The single channelversion is priced at £425.53,while the dual channel model is£473.57. Prices to educationalestablishments are substantiallylower.Tandberg Limited,Revie Road, Elland Road,Leeds,LS11 8,7G0532-774 844

SOFT OPTIONS COMPUTING DIRECTORY

ED -SOFTWARE

E d.s a rEDUCATIONAL SOFTWARE

76 Woodville Road, Exmouth EX81SWTel: (0395) 275741

Cassette based Educational Software. forBBC nnic,ro. Suitable for all from 7 to 18.Programs from £4.95 include: Whatsit(20 questions type garnet.Wordflashdo aid in the increase of read-ing ages). MMaths/Placeval (add, sub-tract, divide. multiply and check placevalues). Progo (S.95 LOG style includesDRAWN, MOVE, TURN and a manual).Also TRANSforrnatton goemetry.ANAGRAM and BASICALLY BBC BASICBooklet 02118 others.

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APPLE COMPUTER OWN-ERS: Super bargains on all yourfavourite business, word pro-cessing, applications, educa-tional and games software ondisk. Send addressed envelopefor detailed list to: Zytek Soft-ware, P.O. Box 51138, Kifissia14510, Athens, Greece.

COMPUTER REPAIR SERVICES

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SPELECTRONICS

Specialists in BBCComputers, Disc Drives,Printers and extensive

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Why not upgrade your 48K Sinclair ZX Spectrum to 128Kwith our special add on self contained board. For full par-ticulars, & price please write with your SAE.

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We undertake repair work for home computers. Charge verymoderate. Charges are as follows:Spectrum & ZX 81Power Supplies for Spectrum & Z81BBC MicrosAny other Micros

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16 Soft Options, July 1984

U Forward Bias . . .

Questions, answers and errata from readers and writers.

Conductance Meter(HE June '84)A small miscalculation: in the text onpage 25, we state that 5n/mhos isthe equivalent of 50MR. This shouldread 200MR.

Mains Touch Switch(HE May '84)In Figure 4, on page 15, the transistorQ1 has been omitted from thecomponent layout.

See the details below.Additionally, the component just to

COLLECTED BOOBS

the right of C4, which is unlabelled, isD2.

We are unable to show theposition of the missing resistor in adiagram this month, but will send acopy of the revised diagram to anyonerequesting it.

Continuing excerpts from the Hobby Electronics Errata BoxWindscreen WiperController(HE March '81)In Figure 2, the Veroboard tracksbetween the IC pins should be cut, ie atD11, Ell, Flt and G11.

Pre -Amplifier (HE April '81)In Figure 4, SW2 out -lead should be

connected to the top of RV1,bottom. C7 can be increased toreduce 'thumps'.

not the100u to

Super Siren Project(HE April '81)In the Parts List, C2, 3 and 4 should be10u not 10n, and C5 should be 100u,not 100n

Russian Roulette(HE April '81)In Figure 1, pin 1 on IC2 should be pin 3.

In Figure 2, make sure that SW2 is a'biased up' switch (ie momentary action).Break connections on PCB to pin 1 andconnect to pin 3.

HE

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Instrumentation Protect;The BBC Model EtTransistor Curve Tracer

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Hobby Electronics, July 1984 43

All About Electronics

ALL ABOUTELECTRONICS

Our Beginner's Series tells you all you'd like to knowabout electronics. From start to finish. All about

components and circuits, all the theory you need to getstarted in the world of electronics.

THROUGHOUT this series of All AboutElectronics, we have studied variousaspects of electronics. First, we lookedat the individual hardware items whichcollectively make up the family ofelectronic components fundamental toall electronic circuits: resistors,capacitors, inductors - passivecomponents - and the active semi-conductor components, transistors,operational amplifiers, logic gates etc.

Using these components we wereable to understand and learn how to usethe basic laws of electronics, and seehow the components can be combinedto produce electronic circuits. We sawhow transistors, resistors and capacit-ors may be connected to produceamplifiers, flip-flops, filters, countersetc. - all circuits which are the buildingblocks of electronic systems.

Next, building-block circuits werecombined to give an appreciation of thetheory behind the two main concepts ofelectronics: analogue and digitalsystems. We looked at telecommunica-tions, and how many telephone speechchannels are multiplexed onto singletrunks. Generally, in this analogueexample, frequency division multiplex-ing is used to combine the many speechchannels, each of which is single side -band modulated to a higher frequency.Then we looked at microprocessors andcomputer architecture to see howcomplex problems must be broken upinto many basic and simple digitaloperations which the central processingunit of a computer performs sequenti-ally.

We may summarise what we haveobserved, in Figure 1, with a "familytree" of topics, showing how therelationships between areas of studydefine their position in the family.

Keith Brindley

A Vs. DThroughout the series, the concepts ofanalogue and digital electronics havebeen shown as separate, and withlittle or no overlap. The basic differencebetween circuits is the way individualcomponents are used. In analoguecircuits, for example, transistors areoperated in their linear regime, ie, theysmoothly control the flow of currentthrough them. In digital circuits on theother hand, transistors are merelyturned on or off, switching the currentfrom maximum to minimum.

RESISTOR

CAPACITOR

INDUCTOR

PASSIVE COMPONENTS

ANALOGUE

AMPLIFIER

I

However, this is not always the case.There are many instances whereanalogue and digital circuits jointogether in one system. We did see anexample of such an analogue and digitalsystem when we considered timedivision multiplexing of telephonespeech channels in telecommunicat-ions systems. In a TDM system eachchannel is regularly sampled, andvalves or codes corresponding to thesampled signal are transmitted. In thisway values or codes of many differentspeech control signals are transmitted

ACTIVE COMPONENTS

DIGITAL

FILTERS GATES

DIODE

TRANSISTOR

FEEDBACK FL IP-FLOPS COUNTERS REGISTERS

OSCILLATOR CPU

e.g. TELECOMMUNICATION e.g. COMPUTERS

Figure 1. A 'family tree' of topics in electronics, all of which have been covered inpast instalments of All About Electronics.

INPUT 1

ELECTRONIC ELECTRONICSWITCHING

DEVICESWITCHING

DEVICEOUTPUTSIINPUT 2 2

(MULTIPLEXER) (DEMULT IPL E XE R3

INPUT 3

Figure 2. The principle of Time Division Multiplexing.

44 Hobby Electronics, July 1984

All About Electronics 1111

1110

1101

1100

1011

1010

1001

1000

(a) 0111

0110

0101

0100

0011

0010

0001

0000

( c )

ANALOGUE SIGNAL

AIL Mg

IF "(6) 1100 1010 0000 1001 0100 1100

00 0 0 0 0 0 0

Figure 3. Pulse code modulations onan analogue signal, showing samplingand analogue -to -digital conversion.

Figure 4. The stages in digitising andrecreating an analogue signal:

a) The signal.b) Six samples taken from the

signal.c) The rounded digital codewords.d) The digital signal.e The recreated analogue signal with

distortion due to quantizationerrors.

( a )

b)

1111 -1110 -1101 -1100 -1011 -1010 -1001 -10000111 -0110 -0101 -0100 -0011 -0010 -0001 -0000 -

TH IS SAMPLE ISROUNDED DOWN

ROUNDEDDOWN

ROUNDED UP

( c ) 1101 1001 0011 0101 1100 1011

d)

1 1 0 1 1 0 0 1 0 0 1 1 0 1 0 1 1 0 0 1 0 1 1

1 1 1 1 1

SAMPLES

0 0 0 0 0 0 0

over single telephone trunks. Theprinciple of TDM systems is repeated inFigure 2.

In the national telephone network,the time division multiplexed signals aretransmitted as a pulse code modulatedsignal, ie each sample value isconverted to a corresponding binarynumber before transmission. Figure 3shows an example where a possibleanalogue signal is sampled, eachsample value is converted to a four -bitbinary number, and each binary numberis combined to form a single, pulsecode modulated, digital signal.

This example shows two things whichI want to consider now. First, the rate atwhich the digital signal must betransmitted - the bit rate - dependsprimarily on the original analoguesignal. The important factor concerningthe analogue signal is its maximumfrequency, f max. If, say, the analoguesignal is a typical speech channel signalwhich contains a variety of frequencycomponents in the range of 200Hz to4kHz then we can define f max as 4kHz.We know from the sampling theoremthe samples must be taken at a rate oftwice f max ie at 8000 samples persecond, and so the bit rate of the four -bitdigital signal is four times this - 32kbitss-1 - just to transmit a single speechchannel signal. Every such speechchannel analogue signal requires thesame bit rate so, if eight similar speechchannel signals, are to be pulse codemodulated, time division multiplexedonto a single trunk, a bit rate of at least256kbits s-1 is required.

What Do You Quant?Second, this analogue -to -digital con-version relies on the fact that a digitalsignal consisting of discrete steps can

adequately represent a continuousanalogue signal. The four -bit digitalsignal of this example only has 24 =sixteen discrete steps, known asquantization steps so, inevitably, in theconversion of an analogue signal to afour -bit digital signal some rounding -upor rounding -down of the continuoussignal to match the sixteen quantizationsteps must occur. Figure 4a shows ananalogue signal which is to be sampledsix times (Figure 4b) and the samplevalues converted to corresponding four -bit digital words by rounding -up orrounding -down to the nearest quant-ization step (Figure 4c). The digitalsignal corresponding to the analoguesignal is shown in Figure 4d, and theeventual analogue signal, after con-version back from digital -to -analogue,is shown in Figure 4e. The distortiondue to the discrete quantization steps isclearly seen, and is classed as an error- quantization error - which in thisexample is one part in fifteen (becausethere are fifteen quantization intervalsbetween the sixteen quantizationsteps). As a percentage, the quantizat-ion error is 6.67% of the full output andif the output voltage range is say, 1 OV,the quantization error voltage is OV67.

Quantization error will fall as thenumber of bits in the digital wordincreases, so an eight -bit digitalcodeword range will introduce aquantization error of only one part in255, a mere 0.04% of full output. Usinga larger number of bits per codewordobviously increases the minimum bitrate required to transmit the analogueinformation in a digital way, but greateraccuracy and less distortion is theresult. Eight -bit codewords are adequ-ate for low -quality transmissions ofanalogue signals such as telephonespeech signals but even the associatedlow quantization error of eight -bitcodewords can be detected in the trans-mission of high quality music (forexample, high fidelity reproduction) andfrequently twelve -bit, fourteen -bit andsixteen -bit codewords are used. We willsee an example later.

The circuits used to convert analoguesignals into digital codewords anddigital codewords into analoguesignals are known as analogue -to -digital convertors (ADCs) and digital -to -analogue convertors (DACs). Often theprinciples used in DACs are also used inADCs, so we'll look at DACs first.

Digital To AnalogueOne of the simplest types of DACs isshown in Figure 5. It is based on abinary weighted resistor network, inwhich the resistor connected to themost significant bit of the appliedcodeword can have any suitable value,R. The resistor connected to the nextmost significant bit has the value of 2R,the next - 4R etc. In this way, thevoltage produced at the output of theresistor network is proportional to thedigital codeword applied to the input.

Although this DAC is simple andtheoretically can be used to convert

Hobby Electronics, July 1984 45

All About ElectronicsMOST

SIGNIFICANTBIT

DIGITALCODEWORDINPUT

LEASTSIGNIFICANT

BIT

C7UTPUTVOLTAGE

(ANALOGUE)

Figure 5. A binary weighted resistornetwork. This forms the basis of one ofthe simplest types of DAC.

digital codewords of any number of bitsinto an analogue signal, it does haveone disadvantage - the doubling ofresistor value for every bit means that awide range of accurate value resistorswill be required for anything other thanconversion of digital codewords withless than, say, six bits.

Another type of DAC is based on thecircuit of Figure 6 which is an R -2Rresistor ladder network. In this DAC onlytwo values of resistor are used anddigital codewords of any number of bitslength may be converted, simply byextending the ladder.

Output voltages of both of thesecircuits may be amplified by suitableamplifiers; buffering the circuit andincreasing the analogue voltage rangeto any desired level.

Analogue To DigitalMost DACs rely on one of the twoprinciples outlined here. ADCs, on theother hand, can rely on a number ofprinciples and tend to be much morecomplex. Two of the more commontypes of ADC are shown in Figures 7and 8. The first type, a successiveapproximation convertor uses a DAC (ofeither variety previously discussed) inthe circuit. A comparator compares theoutput is high. If the analogue voltage isinput voltage. If the analogue inputvoltage is greater than the outputvoltage of the DAC the comparatoroutput is high. If the analouge voltage islow. The logic block in the successiveapproximation converter decodes thelogic states of the comparator andinstructs the four bit register to act asfollows:

assume that the four -bit register isinitially zeroed ie all bits are set tologic 0. The applied analogue inputvoltage must be greater than the DACoutput so the comparator output ishigh. This sets the most significant bitof the four -bit register to logic 1. Thisis known as the first approximation.

if the analogue input voltage is stillgreater than the DAC output the logicblock sets the most significant bit ofthe four -bit register to logic one, in asecond approximation. A third andfourth approximation are then under-taken.

if after any approximation theanalogue input voltage is less than

DIGITAL CODEWORD INPUT

LEASTSIGNIFICANT

BIT

/7777

MOSTSIGNIFICANT

BIT

Figure 6. The R -2R resistor ladder type of DAC network.

ANALOGUEINPUT

VOLTAGE

COMPARATOR

DAC

LOGIC BLOCK

MIINOMINCIAMI

DIGITAL

CODEWORDOUTPUT

Figure 7. The successive approximat-ion type of ADC.

REFERENCEVOLTAGE

ANALOGUEINPUTVOLTAGE

CODERNETWORK

DIGITALCODEWORD

OUTPUT

Figure 8. The parallel, or flash ADCwhich uses 2"-1 comparators.

the DAC output, the output of thecomparator is logic 0 and the logicblock resets the previous set bit of theregister to logic 0, and sets the nextmost significant bit to logic 1.

In this way four successive approx-imations of the applied analogue inputvoltage at each sample value areundertaken in the analogue -to -digitalconversion process to four -bit digitalcodewords. If six -bit codewords are

O

ANALOGUEOUTPUT

VOLTAGE

required a six -bit register should beused and the conversion process takessix approximations; eight -bit codewordstake eight approximations, etc.

Successive approximation ADCs areideal for conversion of low frequencyanalogue signals such as telephonespeech channels, but the finiteconversion time does not allow their usewith high frequency analogue signals,say, radar frequency signals - becausethere is just not enough time betweensamples to fit in the required number ofapproximations. An alternative type ofADC, known as the parallel converter, isoften used in such situations. Its basis isshown in Figure 8 and consists of abank of comparators, each of whichcompares the applied voltage with areference voltage. The referencevoltage for each comparator is differentand is generated by the bank ofresistors in the potential divider chain.The analogue voltage may be convertedto digital codewords of any number ofbits simply by using sufficient comp-arators and resistors - but here's thecrunch.

The circuit shown would convert ananalogue voltage to a three -bit digitalcodeword and uses seven (ie 23 -1)comparators. An eight -bit parallelconverter, which is the minimumrequired for reasonable quality, wouldneed 28 -1, that is 255 comparators!Such conveters are relatively expen-sive, but nevertheless are regularlyused because of their fast conversiontimes. Parallel converters are, in fact,so fast and can be used to convertanalogue signals of such high fre-quency that they are often referred to aflash converters.

MOD And DEModMany electronic systems use ADCs andDACs and their use is becoming moreand more common with time. Thereason for this lies in the fact that theadvent of small cheap computers hasled to an enormous increase in digitalsystems, which need to be interfacedsomehow to the 'outside world'. Allsignals in the 'outside world' arenaturally of an analogue form, soanywhere a digital system requires ananalogue intput or output, an ADC orDAC must be used.

A form of ADC/DAC combinationcalled a modem is often used where it isrequired to connect two digital systemover a single telephone -type channel.

46 Hobby Electronics, July 1984

All About Electronics

MODEM SYSTEM B

COMPACT DISCROTATES

PRISM ALLOWS LASER BEAM TOPASS THROUGH ON ITS WAY UPTO THE COMPACT DISC, BUT AFTERREFLECTION FROM THE DISC, THERETURNING BEAM IS REFRACTEDOUT TO THE DETECTOR

LASER BEAM GENERATOR

LASER AND DETECTOR ARE ON ASWIVEL ARM ALLOWING THE 1.ASERBEAM TO TRACK THE DIGITALINFORMATION ON THE COMPACT DISC

16 -BIT DAC

SYSTEM A MODEM

TONES TRANSMITTED OVERTELEPHONE LINES CORRESPONDTO LOGIC 0 AND LOGIC 1GENERATED BY SYSTEM A AND SYSTEM

LASER BEAM IS FOCUSED TO ADIAMETER OF APPROXIMATELY -1 MICROMETRE

LASER DETECTOR GENERATESA VOLTAGE PROPORTIONAL TOTHE DIGITAL INFORMATION ONTHE COMPACT DISC

LASERGENERATOR

LASERDETECTOR

HIGHFREQUENCY

AMP

MICROWAVE114/11 GHz)

TORONTO

INTELSAT VSATELLITE

TORONTO FIRSTCANADIAN PLACE

AUDIO

NTSC VIDEO

MODEM

CODEC

STUDIO

16 -BIT DAC

LOW PASSFILTER

LEFT-0 OUTPUT

LOW-PASSFILTER

16 -BIT DIG TAL INFORMATIONFROM COMPACT DISC

GOONHILLY

DIGITAL'LINK

LONDON

RIGHTOUTPUT

CODEC

PALVIDEO AUDIO

LONDON STUDIO

Figure 9. The use of a modem at eachend of a telephone line allows digitalsystems to communicate in ananalogue fashion.

Figure 10. A low -power laser tracksthe bottom surface of a digitallyrecorded compact disc.

The basis of such a modem connectionis shown in Figure 9. "Modem" is anabbreviation for modular/demodulator,and this gives a clue to its operation.When one digital system, say System A,wishes to transmit information toSystem B, the digital codewords arebroken down into individual bits, andinformation corresponding to each bitis sent over the telephone line. Beingbinary, a bit is either logic 0 or logic 1and so it is a simple job for the modem tomodulate a tone onto the telephone line,of one or two frequencies, depending onthe bit. At the other end of the telephoneline, System B's modem demodulateseach tone received into a digital bit.

Modems are two-way communicat-ion devices and, whenever System A isnot transmitting data to System B,System B can transmit data to SystemA. Thus, a single analogue telephoneline may be used for two-way digitalcommunication.

Integration and hybridization of ADCsand DACs has meant that what used tobe quite complex and expensive circuitsare now comparatively cheap. They arein fact becoming so cheap and readilyavailable that they are now being usedin areas of electronics which werepreviously considered to be the domainof analogue. One of the best examplesof the invasion of analogue/digitalconversion into analogue system is thecompact disc high fidelity audio playersrecently developed and introduced.The compact discs such players play aresmall (41/2in) plastic discs with digitalinformation corresponding to analoguemusic information recorded onto them.

Bits Of MusicAt the recording studios, ADCs convertthe analogue music into 16 -bit digitalcodewords which, at the compact discfactory, are transposed onto the disc.

A laser pickup, shown in Figure 10tracks the disc and picks -up the digitalinformation, ready for conversion backto the analogue signal which may thenbe amplified to drive loudspeakers in theusual way. The laser is a low -voltage,semiconductor device, which radiatesinfra -red light of a single frequency.

The lens focuses the laser beam to awidth of about 1 micrometre, within thedisc. Reflected light from the disc

Figure 11. A block diagram of themain sections of a compact discplayer.

Figure 12. A "block diagram" ofBritish Telecom's new conferencetelevision system (see overleaf).

Hobby Electronics, July 1984 47

All About Electronics

passes back through the lens, backtowards the laser source, but isrefracted onwards by the prism so that itfalls on the infra -red detector. Thisoutput voltage of the detector, aftersuitable amplification, and processingforms the digital input to the DAC. Ablock diagram of the basic parts ofcompact disc player are shown in Figure11.

Although, currently, these playersand the discs themselves are quiteexpensive (they are about the samesort of price as top -of -the -range recordplayer decks and supercut LP records)they do, according to the specifications,produce sound of a much higher qualitythan their analogue counterparts, withadded advantage that the compactdiscs are not easily damaged.

Digitisation of audio frequencyanalogue signals is not the only type ofanalogue -to -digital conversion current-ly in progress. British Telecom hasrecently announced details of its newtransatlantic colour video conferencingservice between the UK and Canada, inwhich customers in both countries cansee and hear each other over a high-speed digital transmission link (Figure12). The service is the first of its kind,and further services, with links to theUSA, are in progress.

A special kind of ADC, named a codec,(coder/decoder) converts the analoguevideo and audio information into serialdigital information, ie a string of bits.Simultaneously the codec compressesthe original picture signal so that areduced transmission capacity isrequired.

A Bit Above UsOf course, satellite television communi-cations will not be restricted to only

businessmen's conferences in thefuture. Within the next two or threeyears, a satellite, similar to that used forBT's transatlantic video conferencingservice, will be used to relay broadcasttelevision pictures across the UK. Infact, the satellite's footprint (ie the areaof the earth's surface it covers - shownin Figure 13) will cover parts of westernEurope, too. The satellite will begeostationary, ie it traverses its orbitonce every twenty-four hours, and thusappears to be fixed in position whenviewed from the ground. You can

Figure 13. Footprint of the DirectBroadcast Satellite Service, whichwill be launched as a new televisionsystem.

observe its position in the sky -although you will not see the satellitebecause it will be 22,300 miles up! -if you check the position of the sun atthree o'clock in the afternoon (Britishsummer time) in mid -October. At thistime the sun is directly in line with thesatellite's position. The aerial requiredto receive the satellite's transmissionsmay be sited at any point which is not inshadow at this time, and must pointaccurately at the satellite.

The satellite service, called DirectBroadcasting by Satellite (DBS), will bemore effective than the existingbroadcast television service and will bereceivable at most if not all homeswithin the UK. The existing transmitternetwork, by comparison, only coversabout 90% of homes.

Five television channels will bebroadcast by the satellite within therange 11.7 to 12.1GHz (GHz = 1 x1012Hz). At these sorts of frequenciesthe conventional television aerial is notusable and a parabolic dish -type aerialmust be used the diameter of this dish isabout 60 to 90cm to provide goodreception, and obviously, to pointaccurately at the geostationary satellitethe dish must be solidly sited.

Existing television receivers may befitted with converter -circuits allowingreception of the DBS televisiontransmissions. Picture quality in thiscase will, however, be no better thanthat at present. New televisionreceivers, specifically for DBS receptionwill, on the other hand, produce a muchimproved picture quality. This isbecause the DBS system will use a

An artist's impression of a DBX-type satellite.

48 Hobby Electronics, July 1984

All About Electronics Figure 14. The contents of a C -MACtype Time Division Multiplexed Signalto be used in the DBS televisionservice.

different method of transmission thanthe existing PAL colour system whichwe saw last month. DBS transmissions,in fact, are an ideal example of howdigital and analogue concepts can becombined within a communicationssystem. We shall look at DBStransmissions in detail.

DBS transmissions will be based on acolour picture system known as C -MAC(an acronym for C -type sound,Multiplexed Analogue Component).Three types of possible sound trans-mission within the DBS channels havebeen considered, all using digitisedaudio information:

A -type, in which the audio signals areall carried on a sub -carrier within thechannel. This (apart from the fact thatdigitised audio signals will be used inDBS) is similar in principle to the ex-isting PAL television broadcasts, inwhich a sub -carrier, 6MHz above thevision carrier, carries the audio trans-mission.

B -type, in which the audio signals aretransmitted during television linesynchronisation pulses.

C -type, (the chosen type) in whichthe audio signals directly modulate thesame radio frequency carrier modu-lated by the vision signals. DBS trans-missions of C -type allow a maximumof eight digital high-fidelity soundchannels. Two of these will be usedfor stereo sound transmissions withthe television picture, the remaindermay be used for other musictransmissions or perhaps datatransmissions.

Time -division multiplexing of sound andvision signals (a digitising process) willbe used, the 64us time slot betweentelevision lines sync pulses beingdivided up as shown in Figure 14.Chrominance (colour) and luminance(brightness) signals are transmitted asanalogue signals and, unlike theexisting PAL colour systems wherechrominance is transmitted merely asan extension of the luminance signal, acompletely separate chrominancecomponent is multiplexed and trans-mitted in the DBS signal. This separatetransmission of the chrominancecomponent is one of the main reasonswhy a DBS television receiver willproduce pictures of much higher qualitythan those of PAL receivers.

More A Than DIt is interesting to note the fact that theauthorities have opted for analoguetransmission of the chrominance andluminance signal. This is mainlybecause of the fact that digitaltransmission of an analogue signaltakes up much more of the transmission

DIGITALAUDIO/DATA9.58uS

SYNC

CHROMINANCE17.53uS

LUMINANCE35.06uS

channel capacity than does theanalogue signal itself. We saw this inour earlier example of pulse codemodulated telephone speech channelswhere an analogue signal of 200 to400kHz requires a bit rate of 64Kbits persecond for adequate quality. Thisdoesn't, of course, matter if anunlimited amount of transmissionchannel is available, as in thetelephone system where extra cablescan be laid as and were required. In abroadcast radio system, on the otherhand, the transmission channel islimited. The satellite only has a definedfrequency range in which to transmit,and few frequencies in the whole radiospectrum are not already used for radiotransmissions of some description.Because of this, broadcast televisionchrominance and luminance signals arelikely always to be transmitted asanalogue signals.

Eventually, of course, even thoughtransmitted signals may always be

circuits within television receivers willbe digital, with a high degree ofintegration into IC form. A move hasalready begun in that area with at leastone digital TV receiver being marketedin Europe. At this time however, suchdigital television receivers are expen-sive, although the trend towardscheaper and cheaper digital circuits willobviously close the price gap betweendigital and analogue television.

An End To It AllSo, where does all this leave us? Howwill our electronic future (because it willbe, undoubtedly, electronic) affect us?And where do we go from now?

64uS

Well, one sure fact is that there will bea great use of computers. As more andmore components and facilities arereduced in size and built into single ICs,the more these ICs will be used in themost unlikely of places. The telephonesystem which we have considered indetail is an ideal example. For years,since their introduction, telephone setshave remained virtually unalteredapart from minor aesthetic changes.Within only a few years, however, everytelephone set in the country is likely tohave its own microprocessor inside it.Voice signals will be converted withinthe telephone to digital codewordswhich will be passed down the digitaltrunks to the exchange.

In short, digital circuits will be foundin almost every gadget, tool, toy,entertainment etc. available, withappropriate analogue -to -digital anddigital -to -analogue convertors acting asinterfaces between them and us.Fortunately, no matter how cleverthese digital circuits are, they have tointerface with the analogue world -mainly us.

Thankfully, we can't be digitised,(we're working on it - Ed.) so there isalways the hope that analogue will sur-vive the onslaught of dig ital.lhave to go,my batteries are running down.GoodbClick.

The staff and readers of HobbyElectronics would like to thank KeithBrindley for a series which has taken usfrom the first principles of electronicsthrough to an appreciation of some of itsmost complex applications. We will bestarting anew and very special series onelectronics for beginners in the autumn,so watch out for that round aboutOctober.

Hobby Electronics, July 1984 49

Points Of View

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

What A MetterDear Sir,Re your comments on Woods Metal inyour May issue. I would suggest toyou that the Low Melt Solder used forModel Rail White Metal Loco Kits.It melts easily in water which isalmost boiling. Use a spoon dipped inthe water at the same time. I enclosea piece for your perusal. Any modelrail shop which sells Loco Kits willsupply. Try W&H (Models) Ltd., 14New Cavendish St., London W1 (01-837 5551) or Hobby Time, 5Ravenswood Crescent, WestWickham, Kent (01-777 3510). Thecost is about 75p to £1, this should bemore than enough for Mr. Simmonds.

I hope this will help.Yours sincerely,H. J. Woodman,Brighton,Sussex.

We carried out the followingexperiment on the nugget of whitish -grey metal which Mr. Woodmanenclosed:

Equipment: one kettle; oneteaspoon; four or five plastic coffeecups (beaker style); one plastic"swizzle stick" of type provided withhot drinks dispensers; kitchen sink;water.

The water was placed in the kettleand the kettle powered up. In themeanwhile, three of the plasticbeakers were stacked one inside theother (to prevent the application ofboiling water from eating a holethrough to the experimenter's hand)and the sample of metal placed in oron the teaspoon.

When the boiling water was ready,the top beaker of the triple stack wasfilled with the water. The teaspoonbowl was then floated as deeply intothe boiling water as possible withoutactually admitting the water to theteaspoon: (note to experimenters: holdonto the teaspoon at this point).Within about twenty seconds, themetal had begun to liquify at itsextremities, and before a minute wasup it was completely liquid.

At this point, the metal was pouredfrom the teaspoon into the fourth(separate) beaker and encouraged tocool by holding beneath a stream ofcold water. When the initialcrystallisation was observed, the

plastic swizzle stick was implanted inthe cooling metal and held.uprightuntil the metal set hard. The plasticbeaker (that is, the one with the metalin it) was inverted at this point, and itwas observed that the swizzle stickdid not fall out of the beaker.

From this we deduced that the LowMelt Solder would do the job ofWoods Metal adequately. In fact, aftertaking expert advice, we decided thatit probably was Woods Metal, underanother name, or at least a verysimilar substance.

On a more serious note, we hadbetter point out that this is notordinarly low melt solder. It is veryunusual for any metal to melt belowthe boiling point of water, ashappened here - a fact borne out byastonishment of other members of thecompany who happened to drop intothe kitchen during the experiment.This astonishment also lends point tothe scarcity of Woods Metal, whichmost had heard of but few had everseen.

However, Woods Metal is still theprescribed method of mountingcrystals in some radio sets, we arevery grateful to Mr. Woodman for histimely information.

Back IssuesDear Sirs,Having just read your July '82 issue, Iwas very interested in the HEMicrotrainer, as a first computerproject, but I noticed it as a secondpart and now wish to obtain the firstpart in the June '82 issue. Could youplease give me details of orderingyour back numbers?Yours,R. I. Powis,Swanscombe,Kent.

Now that our Backnumbersdepartment has moved and settleddown, we are running a newBackissues advert, with all the details.You will find it in most issues, possiblyeven in this one; if not, then the nextone.

Electronics By ComputerDear Sir,Would it be possible to incorporate

in your excellent magazine a series ofcomputer programs to show:

(1) How with moving graphics OhmsLaw works, how current flows in acircuit.

(2) Resistors and capacitors, inseries and parallel.

(3) Set number of questionsrequiring an input answer, and if theanswer is wrong, a routine that willexplain the question/answer in detail.

In fact, a program on the wholeaspect of Electronics.

I am sure, because of myconversations with people of all ages,especially young hobbyists, that thiswould be a very popular series. Thereare thousands of people withcomputers in their homes, that with awell -written series of programs couldbe given the chance to see how thisotherwise invisible force works.

Why not be the first to give themthis chance?Yours truly,F. J. Chappell,Ha yes,Middx.

We ourselves are unable to devote theattention needed to write a reallygood educational electronics package(which is not as simple as it mightlook), but we are aware that programsare soon to appear which cover thisgeneral subject area. If you keep aneye on Soft Options, you should seesome of these mentioned before long,and we hope there will be programsthat we can recommend.

Solid InducementsDear Editor,I am writing several letters toyour mag - well, three to be exact.One is to your backnumbers sectionfor a photocopy of the Dig FreqCounter project - please could you letme know if there are any faults withthe diagrams or project (misprints, ofcourse). SAE enclosed.

Excuse the slight sarcasm there!You produce a very good mag. I'vestayed with it for three years now andwill continue to do so. Your mag isgenerally simple enough forbeginners, and some excellentprojects for the not -so -beginners. I've

50 Hobby Electronics, July 1984

Points Of View designed my own frequency meter(digital) so I want to see what HE'slooks like.

A suggestion for projects: whatabout more test equipment? Yourcapacitance meter (April 1982) wasgood. To make mine more accurate Iadded a third digit.

A question: I have a problem withETI project (Soldering Iron page 24May 1981). As your mags areaffiliated and you have the sameaddress, could you let me know whoto write to, or be so kind as to give mesome help. My 20-0-20 transformerand 1A bridge rectifier blows up. Theonly substitution I have made is thetoroidal core which I used a standardcore of about 2x2x11/4in.

I also read and experimented withyour Switched Mode PSU, but howdo I work out the inductance of a core,given its size?Yours,Dave Van Rooyen,Queensburgh,S. Africa.

First off, yes, there was an error inthe DFC project: C1 was listed asceramic; it should read carbonate.

Like you, we are always keen ontest equipment projects. They are notthe easiest of projects, though,because of the problem of alignmentand calibration. Almost always, youneed test equiment to calibrate testequipment! Accuracy is a problem,because very reliable and preciseinstruments are always complicatedand expensive, both factors which putthem beyond the range of the averageconstructor.

That said, we remain dedicated tothe idea of producing cheap,reasonably accurate and useful testequipment, and in fact we have oneor two such projects lined up for thenear future. And of course, if anyonehappens to have a circuit for aspectrum analyser costing around £20we'd love to hear from them....

You can't work out the inductanceof a core. A core has no inductance.It may even have no substance, as it canbe empty air. You can work out theinductance of a coil, but the mathsused are tedious and involved. In theirsimplest form they look somethinglike this:

Ln urAT21

where L is the length of the coil, A isthe cross sectional area of the coil, Tis number of turns and u is thepermeability of the former (whichmust be calculated separately). 1 isthe answer. For further information,consult the Coil Design AndConstruction Manual by B. B.Babani, £1.95 from Bernard Babani(publishing) Ltd., The Grampians,Shepherds Bush Rd., London W67NF.

We can't offer any help with the ETIproject, I'm afraid. The gentleman totalk to is Phil Walker, Project Editor,ETI, at this address. Just don't tell himwhere you got his name from!

Telephone Hang -UpDear Sir,I'm a student of electronics and Ipractice different electronics circuitsby designing some myself; with thehelp of guide books, magazines andsometimes with the help of seniors.Recently, I designed a circuit to recorda telephone conversation. This circuitproved to work alright, except the factthat the telephone line is blockedwhen the system is attached to theline, so that dialling of a number isnot possible.

Could you please help me bysuggesting some circuit diagramswhich could perform the telephonerecording with the help of an ordinarycassette player such that the recordingtakes place only when the speech ismade, with no effect on theperformance of the telephone. It isalso intended that such a device couldbe attachable to the live wires ofthe telephone line in any place beforethe set, and unexposed.

I would be very much thankful forthis act of assistance and kindness.Yours truly,M. Arshad H. Alvi,Riyadh,Saudi Arabia.

We're always glad to be of assistance,and happy to be kind, but we regretthat in this case we can't help you.First, we haven't got the time or themanpower to design circuits foreveryone who would like them, so wemake it as fair as possible by notdesigning any at all. This is especiallyfair to Terry, who already has a full-time job designing and testing circuitsfor Hobby.

Additionally, in this country it ishighly illegal to attach to thetelephone lines any device which hasnot been strictly approved by BritishTelecom. I suspect it is also highlyillegal to record telephoneconversations without the knowledgeof the parties concerned, at leastwithout the proper authorisation,which isn't usually granted to popularmagazines. At any rate, we have noexperience in this specialised field.

(On the otherhand, what couldprovide more security and privacythan a device which phone calls beingmade? Mr. Alvi may be ontosomething here ...).

It's Dead AgainDear Sir,I have recently come into contact witha publication of yours called Into

Electronics Plus, published by HE inthe summer of 1979, priced f 1. / ammost interested in obtaining a copy ofthis publication as it appears to be byfar the best book on basic electronicsfrom an introductory point of view.

I would therefore be very interestedin your being able to tell me if it isstill in print and its current price.Yours faithfully,D. T. Ellis,Saltash,Cornwall.

Sorry to disappoint you. IEP hasbeen out of print for a number ofyears, although it was a popularpublication in its time. Our otherreprints collection, Electronics - It'sEasy, has also now succumbed torecession economics and gone o/pafter several years' popular run.

The department which deals withall our special publications is now inthe process of arranging refunds forthose people who have ordered EIEduring the time when they were stilldeciding whether or not to revive it.This is not to say that it will neverreturn in the future. If it does, this iswhere you will read about it.

Scope For A 'ScopeDear Sir,I have bought your magazine for aboutfour months now and find it a verygood publication.

Recently, I have noticed an advertfor an oscilloscope kit that uses anordinary TV set, and wondered if youhave tried this type of project;alternatively, are there any plans forHE to publish such a project?

The reason I ask is that I haverecently acquired the parts for yourdigital thermometer, and I noticed inthe plans that an oscilloscope isuseful, and thought that it may be ahandy tool for the future. As you mayhave guessed, a commercial -typescope is beyond my budget.Yours faithfully,P. Humphries,Newcastle-upon-Tyne.

Indeed, we have tried several times toproduce an oscilloscope for thehobbyist. Our last attempt ground to ahalt, fortunately before we got to thestage of issuing a parts list, when theauthor declined to continue theproject.

However, a reasonably cheaposcilloscope project (one that uses anordinary black and white TV set) ison line for another of our magazines,Digital and Micro Electronics, andwill appear when we have tied up allthe loose ends - possibly beginningwith D&ME 5 later in the summer. Isuggest that you check that out whenit appears on your newsstands andsee if it will fulfill your requirements.

Hobby Electronics, July 1984 51

Short Circuits

1_FL

L

Circuit ideas from Hobby Electronics readers.Hobby Electronics cannot undertake to answer queries on Short Circuits.

J

18W Alarm GeneratorAn oscillator design to cause the maximumalarm.

THIS CIRCUIT is a logical developmentof the Morse Oscillator circuit.It uses the same basic designbut has a power amplifier connectedto provide a louder output suitable foruse in say, burglar alarm systems

The oscillator section consisting ofIC1, has already been described andneed not be gone into here. Theimportant point to note is that themorse key has been removed and pin1 is permanently connected to thenegative supply.

The first transistor, Q1 is used as abuffer instead of the extra gate usedin the previous design, as the outputof the gate is insufficient to drive thepower transistor. The buffer transistorthen drives the pre -driver Q2, whichin turn drives the output device Q3.

The alarm can be used in anysituation and will provide a good loudoutput whenever the supplyconnection is made. Because of thehigh power, Q3 will dissipate a large

R2820k

IC1PIN 14

IC1b

R310k

ICI PINSt7,8,9,12,13

R42209

amount of heat and so should ideallybe mounted on a small heatsink.Similarly, it is advisable to use

Morse OscillatorA one -IC circuit for morse code practice.THE SIMPLE circuit here uses justone IC as the active component toproduce an audio signal suitable forbudding radio operators to get somemorse code practice. The circuit usesa CMOS IC connected in a ratherunusual manner to that normallyfound around digital IC's. Theindividual gates of the IC are in factused as inverting amplifiers withtheir inputs connected together toproduce the inverting effect.

The circuit operates in the followingmanlier.

Assume for the moment that themorse key is made and pin 1 isconnected to ground. Without goinginto the why's and wherefore's, pin 1is effectively connected to pin 2, (takeour word for this - please!).

When the supply is first madethe output of one of the gates will gohigh. Due to the varyingcharacteristics of each gate it isimpossible to say which one will gohigh first. Assume for the moment itis gate IC1 a output which goes highwith ICI b output low.

01

R522R3W

Q2

LS1OR

R61k

ID1

NOTES:01 = 2N3702Q2 = 2N305403 = 2N3055IC1 = CD4001D1 = 1N5401

OA -15V

0 OV

heatsinks for the other twotransistors.

Mark Stone,Essex.

The capacitor now charges up fromthe high level of the output of IC1a viaR2 and RV1. After a time which isdetermined by time constant of thecapacitor and two resistor's, thevoltage across the capacitor willreach the transfer voltage ofICI a. This results in theoutput of IC1 a going low thus causingthe input of IC1 b also to go low. Thischanges the previously low output ofIC1 b to high. At this time thecapacitor discharges into the invertorsas the capacitor is effectively

52 Hobby Electronics, July 1984

Short Circuits IIIreverse -connected. That is, previously,the right-hand end had a (logical) low,and the left-hand end had a high (viathe resistors).

Once discharged the next cyclebegins.

Now the capacitor beings to chargeup from the negative supply via thetwo resistors, which are noweffectively connected to the negativesupply by virtue of the fact that theinput of IC1 b is low. As the capacitorcharges up, the voltage at the input ofIC1 a will gradually fall, and after atime the transfer voltage of the gatewill be reached. When this voltage isreached, the input will become lowcausing the output to go high - this inturn causes the output of IC1 b to golow.

The capacitor is now once againreverse connected and begins todischarge through the invertors. Thecircuit operation then returns to thebeginning with the capacitor chargingup from the high output of IC1 a.

The circuit thus continuallyoscillates producing a square waveoutput from both the outputs of thegates. All this takes place far quicker

MORSEKEY

R2100kR1

100k

ClII

4n7

RV1 IC1PIN 14

IC1PINS 7,8,9

0 O

than it takes to explain!The remainder of the circuit

consists of IC1 c used in this design asa buffer to feed the signal to thevolume control and headphones. Thepreset is used to vary the frequency.The circuit is simple to construct andcan be built on a small piece ofVeroboard. Any supply can be used in

Protected PSUA short circuit whichTHE PROTECTED PSU is conventionalin design, using Q1 with its base tied toeach of the Zener voltages to providethe regulated outputs of 6 and 9 volts.The circuit differs in respect to theshort circuit protection componentsconsisting of SCR1, R1 and C1.

When a short circuit occurs, thecurrent passing through R1 increasesto such a point that the gate turn onvoltage of the thyristor is exceeded.Once this point has been exceededthe thyristor turns on, and in so doing,pulls the base of Q1 to ground,effectively turning the transistor off.With the transistor turned off, theexternal short circuit is effectivelyremoved from the regulating circuit.However, becuse the thyristor is stillturned on the current from theunregulated supply will still flow.

It in fact flows through the thyristorvia R2, hence the need for a largepower rating for this resistor. Becausethe regulating transistor is nowturned off, there will be no supply tothe LED, which of course goes out.This provides the user with anindication that a short circuit hasoccured and must be rectifiedimmediately.

Once the short circuit has beenremoved, the circuit may be reset bypressing SW1. This puts a shortacross the thyristor which thus turnsoff. With the thyristor turned off thecircuit returns to normal operation.The large value capacitor, C1 isincluded to prevent spurious operation

avoids short circuits.

12-15V DCMAX 1AUNREG-ULATEDINPUT

SW1RESET

SCR1

R2200R

4W

NOTES.01 = 2N3055SCR1 = ANY 1A 50V

BT149E/ZD1 = BZX61C3V3ZD2 = BZX61C6V8LED1 = TIL209

CI1000u

16V

of the thyristor in the case of thelarge (but short) surge currents thatmay occur when the power supply isconnected to circuits with a largecapacitance across its own supplylines.

The value of R1 is calculated fromthe equation:

Value of R1 =

gate trigger voltage (VG)required cut-out current

The value of VG can be found fromthe data sheet of the particular deviceyou are using. So for example if youare using the example given in thecircuit then the calculation is:

NOTE.ICI = CD4001

RV210k

VOLUME

0 +510V

HIGHIMPEDANCE(>200R)HEADPHONES

V

the range 5-10 volts, but note thefrequency changes as the voltagechanges. To provide a good audiooutput it is essential. to use highimpedance headphones, and thosewith an impedance of greater than200R will work very well.

Mark Stone,Essex.

R31kOW5 ,y OUTPUT

+9V or +6V

ti LEO1

Value of R1 =OV8

800mA= 1 ohm

Note that, for this particular circuitthe maximum cut-out current that youcan safely use is one amp. Althoughany current value smaller than this isquite safe. It is not possible to use avariable potentiometer instead of R1as the values encounted are verysmall, and in most cases the value ofR1 needs to be made up from lengthsof enamelled copper wire.

Paul Mulvey,H EIreland.

Hobby Electronics, July 1984 53

DC Voltmeter

1:10CVoltmeter

A large ranges for a low cost: this voltmeteruses a centre -zero meter to give readings

from plus/minus 500V to plus/minus 5mV,as well as unusually good protection against

overload.

HERE is the experimentors' answer toDC voltage metering. An accurate,easily read, very high impedancemeter that costs only a couple ofpounds more than the metermovement.

We choose a centre zero meter notonly for the great convenience itprovides but also because with thisdesign it's virtually impossible todestruct it.

The CircuitAs you can see from Figure 1, a FETinput op -amp is used as animpedance transformer and we haveswitched the feedback resistors in anunusual way to virtually eliminatezero null adjustment and to givethe meter a truly wide range ofvoltage reading, from plus and minus500 volts to plus and minus fivemillivolts.

All this selective switching is donewith a simple one pole six way rotaryswitch. Resistor, R10 sufficientlyprotects the meter movement fromoverload, as the maximum outputof the op -amp is probably around ±8Vwhen driven from nine volt batteries,only about 100uA maximum could bepushed through the meter. Since thisis only twice the full scale current noother meter protection is needed.

The feedback resistors should behigh tolerance precision resistors asthese values effect the accuracy of themeter.

Op AmpWith negative feedback applied by R2-7 to IC1, the output will try to keepboth inputs, pins two and three at

J. E. Aman

the same voltage. Since the non -inverting input, pin three is connecteddirectly to earth (the referencevoltage), the inverting input, pin two,assumes a "virtual earth".

Any voltage introduced across theinput sockets tend to upset thisbalance and the output voltage willchange proportionally according to thevalue of this input voltage. By varyingthe value of the feedback resistors,we can achieve any voltage gain wewant within the limits of the IC andthe power supply rails.

For the higher ranges, 500, 50 and5 volts, no voltage gain is required,and the combination of R1 and R2-4

attenuates the input voltage andprovides gains of less than unity.

For the lower ranges, OV5, 50mV and5mV, voltage gain is required,and R1 together with R5-7 and thevoltage divider network R8/9 providesgain greater than unity according tothe selected range.

The zero null adjustment of IC1could have been made accessibleexternally to the case. However this isnot really necessary as once it hasbeen set it is rarely adjusted. Thecircuit also includes a low batterywarning indicator which lights anLED when sufficient volts havedisappeared from the batteries.

54 Hobby Electronics, July 1984

DC Voltmeter

SW1

RANGENOTES:IC1 = CA314001,2 = BC549BLED1 = TIL209

R110M

2SK1

C1 -1-+ 100n

SK2 0

t9V

7

IC1CA3140

45

±500V

+5mV

RV10kZEROADJUST

R8100k

R9100R

+9V

Q1

LED1

R112k2

R12 R13220k 470k

Q2

R1068k

RV247kSCALEADJUST

M150-0-50uA

C2220u

R1424k

SW2aOFF

0ON

C3'-220u

SW2b

B19V

B29V

Figure 1. The circuit. All the switching is done via the six -pole switch SW1, while R10 protects the meter from overload. Thered LED1 is a low battery warning indicator.

Low VoltsWith fresh batteries the low batterycircuit usually has 18 volts across it.This gives approximately OV9 atthe base of Q2. This transistor thusturns on, and in so doing pulls thebase of Q1 down to ground. The LEDthus does not light.

When the supply voltage drops to

say, 9V, the voltage on the base of Q2falls to approximately OV4, Q2thus switches off. As it does so, thebase of Q1 is no longer tied to groundand the voltage on the lower end ofR12 presents sufficient voltage on thebase of this transistor to turn it on.Thus the LED lights and gives anindication that the battery voltage istoo low for reliable operation.

RESISTORS(All 74W carbon except wherestated)R1, 4, 7 10M

1',) metal filmR2, 5, 8 100k

1% metal filmH3, 6 11V1

metal filmR9 100R

1`%. metal filmR10 68kR11 2k2R12 220kR13 470kH14 24k

POTENTIOMETERSiiV1 10k

horiz preset

Parts List

It is often found that digital metersare marvellously accurate and easy touse. However, their sample rates attimes can be less than optimum andthey give no indication of any smallbrief surges which might occur. Thesecriticisms seem minute but there aremany situations where the addition ofan analogue meter to one's workshopcan be of greatest advantage.

FiV2 47k MISCELLANEOUShoriz preset

CAPACITORSCl 100n

polyesterC2, 3 220u

25V axial electro

SEMICONDUCTORSIC1 CA3140

CMOS op -amp01, 2 BC549B

NPN siliconLED1 TIL209

red LED

M1 50-0-50uAcentre zero panel meter

Bl, 2 9V PP3batteries

SW1 1 pole 6 wayrotary switch

SW2 DPDTmin toggle

SK1, 2 4mm socket

Veroboard; metal case; controlknob; battery connectos; IC socket;test leads; connecting wire, etc.

BUYLINES page 26

Hobby Electronics, July 1984 55

DC Voltmeter

SW2

LED1SK2 SKI

000

+

B2 0 0{

SVV2t,

C2

1116.----11.

SW 1WIPER

1{7F4111

--1 R8 1-- ----

C3

R2-4

R5-7

--F1101-

Figure 2. The PCB layout. If the CA 3140 is used, an IC socket is recommended.Note that resistors 2 to 7 are mounted on SW1 - see Figure 3.

Figure 3. A recommended layout for the front panel (seen from inside). R 2 -7 areshown "flattened out" for clarity, but would normally be mounted perpendicularto SW1

FRONT PANEL APPROX 5" x 3"

LED1

M1

LSK2 SK1

M1

ConstructionThe construction of the Voltmeter isvery simple and easily built onVeroboard. The feedback resistors,R2-7 are mounted on the switch andthis eliminates the requirement of alarge number of connecting wires toand from the board.

The actual Veroboard layout isshown in Figure 2.

An IC socket is recommended forIC1 as this particular IC is sensitive tostatic. However, if a TL061 is used,this is not so sensitive and does notreally require a socket.

A recomended front panel layoutis shown in Figure 3, and this showsthe reverse side. Notice how theresistors on the range switch havebeen shown opened out for clarity. Inpractice, they are usually mountedhorizontally to the switch.

Figure 4 shows a meter scale if therecommended type of meter cannot beobtained. Remember though thatwhatever type of meter is used, itmust be a centre zero type.

The scale is drawn full size and maybe cut out or traced and stuck on themeter's existing scale. The scaleshould be suitable for most meters,but if not, the proportions can easilybe gauged.

2 1 0 1 24 \ I / 4

5 5

DC Volts

C 0

Figure 4. Cut out, or photocopy, thismeter scale if you cannot obtain asuitable centre -zero meter.

CalibrationConnect the sockets together andadjust RV1 for a zero reading.Remember that this is a centre zeroreading.

Select the OV5 range and connecta known voltage source between OV1and OV5. Next, adjust RV2 for thecorrect reading on M1 according tothe applied voltage. As a check,reverse the test leads and see if acorresponding reading only this timenegative shows on the meter.

As a final check, apply knownvoltages of the correct value andcheck the other ranges. They should,within reason be accurate ifprecision resistors are used. Becauseof the wide tolerance (comparitivelyspeaking) of the ten megohmresistors, slightly more inaccuracymay be noticed on these ranges thanothers.

56 Hobby Electronics, July 1984

All About Batteries

All AboutBatteries

HE takes the lid off - or at least, a slice out of thehumble battery, and gets direct to the source of

the power

EVERYONE KNOWS what a battery is:it's one of those little tubes you bunginside your tranny radio, torch orcassette player so that you can havelight and music wherever you go.

But aren't they expensive? And whyare some of them even more expensivethan others? And is it really true whatthey say about this sort lasting twice aslong as that sort, and does it reallymatter what sort of battery you putinside your torch because you use thetorch so rarely the batteries are alwaysflat anyway?

Well, this article aims, to dispel all themyths surrounding batteries with somehard scientific facts and figures whichwill allow you to choose between thedifferent types and prices available.

First, a battery isn't "one of thoselittle tubes" - one of those little tubes isa cell. Strictly speaking a battery in theelectrical sense of the word is a

collection of a number of cells. Four ofthe most common cells are shown inFigures 1, 2, 3 and 4, along withapproximate sizes.

Figure 1 shows an AAA -size cell,about 44.5mm high and 10.5mm indiameter. Figure 2, AA -size, is about50mm high and 14mm in diameter,and is one of the most popular sizes forsmall torches and radios, personalstereos, etc.

Keith BrindleyAlthough there may be many different

types and makes of these cell sizes (andeach different manufacturer mayproduce two, three or more varieties ofeach cell size) we are going to classifythem here as AAA -size, AA -size, C -sizeand D -size in ascending order. We'll seelater that many more cell sizes areavilable.

Cells In SeriesOne of the most popular size of battery- note the word, battery - is the PP3-size, shown in Figure 5. The PP3-size isan actual "battery" because its consistsof six small cells in series with the case,as shown in Figure 6. Each cell is ratedat 1 V5, so the PP -3 size battery is ratedat 9V. Other batteries in the PP -rangeare the PP1, PP6, PP9 etc. which are allconstructed in similar ways.

Figure 3 shows a C -size cell, about49mm in height and 25mm in dia-meter. Figure 4 shows a D -size cell,about 60mm high and 33.2 in dia-meter. This is the popular size forlarger portable appliances, which may

use from two to eightof them, typically.

But let's not forget another commonbattery, the car battery, which alsoconsists of six cells in series, thedifference being that they are a

completely different type of cell, rated at2V, so that the battery is rated at 1 2V.There's something else different abouta car battery. It stores a substantialamount of electricity (far more than thecells and batteries we have looked at,enough to start a car. Once the engine isrunning, however, the generator oralternator gradually recharges, iereplenishes, the battery.

The car battery allows this rechargeof electricity because it is constructed ina form we know as secondary cells.A secondary cell is any cell which allowsrecharge. The cells above, the AAA -size, AA -size, C -size, D -size, and all thePP -sizes are generally constructed ofprimary cells and cannot be recharged.We have used the word 'generally'because ranges of secondary recharge-able cells of these sizes are available,known as nickel -cadmium ("Nicad")cells.

Figure 5 shows a PP3-size battery,well known because of its hobby appli-cations. The PP3 is a true "battery",made up of a set of cells, unlike the

preceding four examples.

Hobby Electronics, July 1984 57

All About BatteriesIn a following article we will look

closely at the secondary cells andbatteries of Nicad and car types, butthis article will concentrate purely onthe primary types available, how theyare made, how they work, and theirmain uses.

How Does A Basic CellWork?Essentially an electric cell is formed byinserting two conducting electrodesinto a substance known as an electro-lyte, as shown in Figure 7. One elect-rode, called the anode, is usually madeof metal; the other, the cathode, isgenerally a metallic oxide material.

Metal oxides are formed when metalatoms combine with oxygen. A verycommon form of metal oxide, iron oxide,commonly known as rust, forms on ironor its derivatives when exposed to air.We all know too well the problemswhich rusting can create in car bodies,due to this combination of iron andoxygen. Most metals oxidise, and whena metal oxide is used in a cell it is used ina constructive way - unlike destructiverust.

The electrolyte can be made of anumber of different materials, speciallychosen for use with the particularelectrodes in the cell. Different cellswith different electrodes requiredifferent eletrolytes. Whatever sub-stance the electrolyte is, it is an elect-rical conductor which conducts in aspecial way, which we shall look at now.

A metal used for an anode is alwayschosen because it has a much higheraffinity for oxygen than does the metal(which is oxidised) of the cathode. Thus,if the anode and the cathode weremixed together the anode would take

Figure 6. A possible internal con-struction for a PP3 battery, showinghow six 1V5 cells are connected inseries.

ANODEGENERALLY

MADE OF METAL

CC

0

111

-J

-o

Ui

CC

U

ANODE

ELECTROLYTE

I0U

0UH

wII0 -4*

CATHODE

Figure 7. A basic cell, showing anode, cathode, and electrolyte.

BULBCURRENT FLOWSTHROUGH WIRE,LIGHTING BULB

I0U

_J

0U

LUICC

0U

ANODE

ELECTROLYTE

NEGATIVE IONS OFOXYGEN FLOW THROUGHTHE ELECTROLYTE FROMCATHODE TO THE ANODE

CATHODE

CATHODEGENERALLY

MADE OFMETAL OXIDE

Figure 8. A basic cell in operation, in this case used to illuminate an electric lightbulb.

away the oxygen from the metal oxidecathode, leaving the cathode's metalbehind. In this case we say the anodehas been oxidised and the cathode hasbeen reduced.

Electrolytes are the special sub-stances which allow this 'mixing' ofanode and cathode to take place -without the necessity of the anode andthe cathode touching. Under certainconditions the electrolyte containsparticles of oxygen (charged withelectrons) which originate at thecathode and move over to the anode, sothat the cathode is reduced and theanode oxidised. These conditions donot, however, occur if the cell is as inFigure 7,although we say they have thepotential. (This, incidentally is how theword potential, meaning voltage, isderived). In order for the charged oxygenparticles to combine with the metal ofthe anode, each particle has to give upits electron charge. And in order for theoxygen particles to leave the cathodeand enter the electrolyte they must gaina charge.

We can use this potential if weconnect an electric circuit to theterminals on the anode and cathode, asshown in Figure 8. In this way theelectrons, give off by the combination ofcharged oxygen particles with theanode, can flow from the anode into thecircuit, through the bulb (causing it tolight up) and back to the cathode where

they can charge more oxygen particles.This stream of electrons, an electriccurrent, will flow in a connected circuitfor as long as the cathode has oxygenparticles, or until the anode has beenfully oxidised. At this point, we say thecell is discharged.

The charged particles flowingthrough the electrolyte are called ions.They can be of many varieties - not justoxygen - depending on the cell and theelectrolyte used, but the principle is thesame.

Different electrolytes, and differentanodes and cathodes, produce cells ofvarying cost and performances. We'lllook at the different parameters of allcells which are of most importance sothat we may compare the different typesas we meet them.

Voltage And ResistanceThe potential voltage output of a cell isknown as its electromotive force (EMF).The exact figure (usually around 1V5)depends particularly on the nature ofthe anode and cathode and theelectrolyte, but also depends on thetemperature and age of the cell. For afresh cell, the EMF is usually slightlyhigher than its rated EMF, say about1V6, falling to a lower figure, say 1V2,when old and discharged.

This variation in cell voltage, although

58 Hobby Electronics, July 1984

All About Batteries IN

T

INTERNALRESISTANCE

1V5VOLTAGE

GENERATOR

(a)

INTERNALRESISTANCE

1V5

R1 I

10RI

R21k5

( b ) ( c)

Figure 9a, b and c show the equivalent circuit (to Figure 8) of a 1 V5 cell, showinginternal resistance. For details see text.

important, if often not critical becausemany electronic circuits do not need afixed and steady voltage to operate.

Much more important, however, is acell's internal resistance. This is theeffective resistance within the cellitself, caused by the very structure andmaterials used. It cannot be eliminated,but may be very low depending on thetype of cell.

We can look at the effects of internalresistance if we consider the diagram inFigure 9a which we may imagine to bethe equivalent circuit of a cell. It consistsof a voltage generator together with aseries resistance: the voltage generatorrepresents the potential EMF of theanode/cathode/electrolyte combin-ation while the resistance representsthe internal cell resistance.

Figure 9b shows a cell, with a voltagegenerator of 1V5 and an internal seriesresistor R1, of value 10R, connected to aresistor which represents a circuitwith an overall resistance of 1 k5. Acurrent will flow which you may haveexpected to be (from Ohm's law).

1V5I -

1500= 1 mA

However, the series internal res-istance has an effect on the current andmust be taken into account. The circuithas been redrawn in Figure 9c wherewe can see that the two resistorsform a voltage divider network. Thus thevoltage across the connected resistor(which we had previously taken to be1V5) is

VR2 =R1

R+2

R2x 1 5

150010 + 1500

= 1V49

x 1.5

slightly lower than we thought. And thecurrent through the connected resistoris

I

1V491500 = 0.99mA

also slightly lower. The lower voltageand current is not, fortunately,sufficient to affect operation.

Let us now look however, at thecircuit in Figure 10 where theconnected circuit has an overallresistance of 5R. As before, we mightexpect the current to be

5.I =

1--g--= 300 mA

However, due to the cell's internalresistance, the voltage actually acrossthe connected resistor is

VR2- 1055 x 1V5 = OV5+

and the actual current is

OV51= -5

= 10mA

The significantly lower voltage andcurrent will be sufficient to seriouslyaffect operation of the connectedcircuit.

Not only does a cell's internalresistance reduce the potential currentwhich may be delivered by the cell, but italso wastes energy. In the aboveexample, the voltage dropped across theinternal resistance, ie, 1V5 - OV5 =1V.causes a power dissipation of

VP= - = - = OW110

1

to be lost as heat from the internalresistance. The cell will get warm,which increases the internal resistancewhich, in turn, increases the voltagedrop, thus increasing the power thusincreasing the voltage drop etc in avicious circle. In the worst case theconnected circuit will not have enoughcurrent to work at all, and even if it does,the wasted energy will reduce thetime the cell would otherwise be able tosupply current.

So, as we see, internal resistance of acell becomes more important thegreater the current required from thecell. By reducing the value of theinternal resistance the effect islessened, but can never actually beeliminated.

Power For HoursOne of the last cell characteristicswhich we need to study before movingon to cell types is cell capacity, ie theamount of electricity which a cell

R11OR

R21k5

R11OR

R25R

Figure 10. This shows how internalresistance affects operation in highcurrent applications.

actually holds. This is often specified asthe amount of current which a cell cansupply for a given period of time. Forexample, a cell may have a capacity of1000 milliampere -hours (mAh). Thismeans that (ignoring internal resist-ance) the cell may provide 1000mA ofcurrent for one hour, or 100mA ofcurrent for ten hours, or 20mA for fiftyhours etc.

But, describing a cell's currentcapacity in terms of mAh alone doesnot define the cell's total capability.Somewhere along the line we need toconsider a cell's voltage as part of itscapacity. This is easily done bymultiplying the cell's current capacity inmAh by its voltage. So, if our examplecell's voltage is 1V5 it has a total energycapacity in milliwatt-hours (mWh) of

1000 x 1V5 = 1500mWh

Zinc Carbon CellThe existing zinc carbon cells availableare all based on the original celldeveloped by the French engineerGeorges Leclanche in 1866. It wasassembled in a glass jar inside whichwas the cathode in the form ofmanganese dioxide paste, contained ina porous pot. The pot was surroundedwith an ammonium chloride electrolytesolution, into which the zinc anodestood. A connection was made to themanganese dioxide cathode with a

carbon rod. Modern zinc carbon cellshave come a long way since the days ofthe Leclanche cell, known as a wet cellbecause of the electrolyte solution.

The outside can of the modern dry cellis made of zinc metal and forms theanode. Just inside of the zinc is a thinlining which separates the anode fromthe cathode and is saturated withelectrolyte. The electrolyte is a mixtureof ammonium chloride and zincchloride, which is slightly acidic. Thecathode of manganese dioxide is mixedwith carbon powder and electrolyte toform a paste and inside this is insertedthe carbon rod, which acts as a currentcollector. Various bits of paper are usedfor isolation and a thin plastic filmcovers the outside jacket.

By varying the electrolyte mixture,different types of zinc carbon cells can

Hobby Electronics, July 1984 59

All About Batteriesbe made, suitable for different Figure 11. The in -applications. For example an electrolyte ternal constructionof zinc chloride alone produces a cell of a zinc carbon cellwith a lower internal resistance and is (see previous page).therefore more suited to heavier dutyapplictions. A higher quality blend ofmanganese dioxide cathode producesthe same effect.

Alkaline Manganese CellIn the alkaline manganese cell, theanode and cathode materials, zinc andmanganese dioxide, are the same as inthe zinc carbon cell. The anode,however, consists of powdered zincwhich allows the formation of a largesurface area, formed into a paste withthe electrolyte.

The manganese dioxide cathode ofalkaline manganese cells is made froma much purer form of material known aselectrolytic manganese dioxide, pro-duced synthetically to have a muchgreater oxygen content. A solution ofpotassium hydroxide, an alkaline (hencethe name) which is highly conductive, isused as the electrolyte. The use of thiselectrolyte, and the higher quality anodeand cathode materials, results in a

heavy duty, high quality cell with areasonably low internal resistance andhigh energy capacity.

When compared with the construct-ion of a zinc carbon cell the alkalinemanganese cell (Figure 12) is 'inside -out', because the anode is on the insideand the cathode on the outside. A steel

ALKALINE MANGANESE CELL

CATHODE CAP(Positive Terminal)

INSULATING WASHER

OUTER STEEL JACKET

SEPARATOR

ANODEPowdered zinc

ELECTROLYTEPotassium hydroxide solutionabsorbed into separator,anode material and cathodematerial

CATHODECompressed mix ofelectrolitic manganesedioxide and graphite

CATHODE COLLECTORSteel cell case

PLASTIC SLEEVESeparates steel casefrom outer steel jacket

ANODE COLLECTORMetal 'nail'

PLASTIC GROMMET

VENT

INSULATOR

ANODE CAP(negative Terminal)Prolusion in contactwith collector 'nail'

Figure 12. The in-ternal constructionof an alkaline man-ganese cell.

METAL COVER(Positive Terminal)In contact with carbon rod

WASHER

AIR SPACEAids escape of gas

SEAL

WASHER

-41- JACKET

ZINC CARBON CELL

CATHODEMixture of powderedmanganese dioxide,carbon black andelectrolyte

CATHODE CURRENTCOLLECTORCarbon rod

ANODE+4_ Zincas asenrdv both

at cellcontainer

ELECTROLYTESolution of ammoniumchloride and zinc chlorideabsorbed in separator andin cathode (but not in anode)

SEPARATORSaturated with electrolyte

INSULATING CUP

METAL BOTTOM(Negative terminal)Tin plated steel, incontact with zinc can

container is used which, unlike the zinccontainer of the zinc carbon cell, doesnot take part in the chemical process ofproducing current, so does not tend toperforate in use. It also provides a

stronger and more leak -proof container.A metal central current collector - thenail - is in direct contact with theanode.

Cell EMF, because the same metaland oxide are used as anode andcathode, is the same as that of a zinccarbon cell - nominally 1V5.

Button CellsSome of the smallest and lightest cells,measured against capacity, are thebutton cells used to provide power indigital watches, hearing aids, calculat-ors and photographic equipment.A number of different types areavailable and we shall consider themain types.

The mercury cell, shown in Figure13, has an aqueous solution ofpotassium hydroxide as electrolyte. Theinner surface of the cell's top is copper,which is electrochemically compatiblewith zinc, so wasteful corrosion isminimised. The cell is of a nickel -plated steel which is highly resistant toelectrolyte corrosion.

Mercuric oxide, a material with a highoxygen content is the cathode which,although expensive, offers manyadvantages due to the possibility of ahigh ratio of energy to weight and

60 Hobby Electronics, July 1984

All About Batteries

SLEEVE

CELL TOP(Negative Terminal)

CELL CAN

ANODEPowdered zinc togetherwith electrolyte

ABSORBENTSEPARATOR

(Positive Terminal)

MERCURY BUTTON CELL

CATHODEMercuric oxidewith graphite

volume. Nominal cell voltage is 1V35,and internal resistance is very stableand low.

Silver Oxide CellAnother button cell cathode substance,silver oxide, is used in very similar cellconstruction to produce a cell with ahigher nominal voltage of about 1V55.Internal resistance is again low and thecell is thus ideally suited for highcurrent rates in applications such asdevices with LED displays etc.

The combination of a high ratio ofenergy to weight and volume, excellentsealing, and long storage life (like themercury cell) make the silver oxidebutton cell an ideal choice where spaceis at a premium. Silver oxide is,however, a very expensive substance.

CELL SYSTEM

ZINC CARBON

ALKALINE MANGANESE

ZINC CARBON(ZINC CHLORIDE TYPE)

MERCURY

SILVER

ZINC AIR

LITHIUM

CELL SYSTEM

WATT-HOURS PER KILOGRAM

80

100

101

123

136

GROMMET

ELECTROLYTEAlkaline solutionIn anode, cathodeand separators

BARRIERSEPARATOR

Figure 13. The con-struction of a mer-cury button cell.The silver buttoncell, and the zinccell, are of similarconstruction.

Zinc Air CellThe zinc air cell has a similarconstruction and appearance to silveroxide and mercury cells with theaddition of air access holes in the base.

Oxygen, from the air around the cell isused to oxidise a zinc powder plusalkaline electrolyte anode, through asynthetic membrane. The fact that theoxygen particles are taken from the air,and not from a cathode means that morespace inside the cell may be used tocontain the anode, so the cell has nearlytwice the electrical capacity of mercuryand silver oxide cells.

Zinc air cells can have an exception-ally long storage life if they are sealedbefore shipment, with a sealing tabwhich prevents air from reaching theinside of the cell. The tab is removedimmediately prior to use.

1 310

L_

WATT HOURS PER CUBIC CENTIMETRE

ZINC CARBON L 1016

ZINC CARBONIZINC CHLORIDE TYPEI

ALKALINE MANGANESE

MERCURY

ZINC AIR

LITHIUM

0.19

0 23

04

0.49

SILVER

0.54

57

330

Figure 15. A graphshowing a com-parison of the cap-acities of variouscell types with re-gard to their weight.

Figure 16. A graphshowing a compar-ison of the capacit-ies of various celltypes with regard totheir volume.

TOP(Positive Terminal/

CAN(Negative Terminal)

GROMMET

CATHODE

\SOLID ELECTROLYTE

LITHIUM ANODE

LITHIUM CELL

Figure 14. The construction of alithium button cell.

Size and number of air holes candetermine the amount of air access andthus cells may be manufactured forspecific application. For example, in anapplication where a large current isrequired, large and plentiful air holesare needed. An application of lowcurrent drain but long life, on the otherhand will require a limited number ofsmall holes.

Nominal cell voltage is 1V45.

Lithium CellsThe construction of a lithium -mangan-ese dioxide cell is shown in Figure 14. Itis similar to that of other button cells butwith a lithium anode together witha manganese dioxide cathode.

Lithium is a highly reactive metal andthis makes it an attractive material touse as a cell anode but this also makes ita most tricky material to deal with.Lithium must be handled and fabricatedin an airless, moisture free environ-ment.

This higher reactivity allows a cell ofgreater nominal voltage to be made -up to 3V6 ideal for use in heavy-dutyhigher -voltage requirements.

Many different electrolytes can beused within a lithium cell, producingcells with various specifications. Onesystem used a solid electrolyte which isvery stable but has a high internalresistance thus can only supply lowcurrents, and has a nominal voltage ofonly 1V9.

Another electrolyte used in lithiumcells is sulphur dioxide in liquid form,which allows a cell voltage of 3V. Yetanother electrolyte, thionyl chloride,also a liquid, gives a cell with a nominalvoltage of 3V6. These higher cellvoltages are possible because theelectrolytes act as combined electrolytecathode materials to create higherpotentials.

All types of lithium cells with liquidelectrolyte allows a much lower internalresistance to be obtained and so canprovide much higher currents.

Comparing The DifferentCellsWe have seen enough now to make aqualified judgement on the perform-ance of the various cell -types and weshall make this judgement in terms ofweight, size and finally performance ofthe two main types of cells - zinccarbon and alkaline manganese. Figure

Hobby Electronics, July 1984 61

All About Batteries

PHOTOGRAPHIC

RELATIVECOST

CALCULATORSAND WATCHES

ZINC CARBON

0.75 -

0.5 -

HEAVY DUTYZINC CARBON

0 25 -I

ALKALINEMANGANESE

LED

LCD

HEARING AIDS

ciriE

FLASH

EXPOSUREMETER

RADIOS

TAPERECORDERS

TORCHES

TOYS

100 300

CURRENT CONSUMPTION ImAl

= NOMINAL MINIMUM

= NOMINAL MAXIMUM

100 200 300 400 500 600 700 800 900 1000

CURRENT CONSUMPTION ,rnAI

Figure 17. An inter-esting graph show-ing the relativecosts of alkalinemanganese, zinccarbon and heavyduty zinc carboncells as a functionof their currentconsumption.

Figure 18. Thisgraph shows thecurrent consumpt-ion of some typicalbattery -powereddevices. Typically,the more heat thatis generated (as inthe photographicflash) and the moremoving parts thedevice has (as in thedrive mechanism ofa tine or tape re-corder) the moreexpensive it is torun.

Zinc air cells (seeprevious page).Batteries tend todecay if they arestored for a longtime without use.Zinc air cells aresealed until use,which gives themvery long storagetime. The seal isbroken by pullingthe tabs shown inthe picture.

15 shows a block chart comparing theseven types of cell we have looked at,with regard to weight. The exceptionallylightweight characteristics of zinc airand lithium cells are obvious.

A block chart showing cell -typesagainst volume, however, shown inFigure 16, is more evenly spread withsilver cells giving the best performancein terms of physical size.

But the most important comparisonwe can make, and also the one which isvery different to accurately undertake, isin terms of efficiency regarding cost perunit time. The difficulty arises becauseof the wide variety of retail pricesbetween cells at different retail outlets.Nevertheless, the following gives a

reasonable guidance.Generally speaking, the button cell

varieties are used in specific situations,in which other types of cell are notuseable. Little point is therefore gainedby including them in an efficiencysurvey. The three cell -types ofimportance, therefore, are the zinccarbon, the heavy duty zinc carbon andthe alkaline manganese, which are allproduced in similar ranges of size andare thus interchangeable. The questionto be asked, then, must be, it is better touse zinc carbon or heavy duty zinccarbon or alkaline manganese cells inany specific application? Figure 17shows a graph of relative cost of cellsagainst supplied current and illustratesthat at fairly high current rates (about100 mA or more) alkaline manganesecells are most cost effective.

However, below this figure heavyduty zinc carbon cells become a moreviable form of portable power source.

Finally at low current levels, less than20 mA or so, or even ordinary zinccarbon cells compare favourably withalkaline manganese cells.

Obviously, alkaline manganese cellsare superior in terms of containedpower and quality - the zinc case of thezinc carbon cell enters into theelectrochemical reaction and the cellmay leak its acid contents; the alkalinemanganese cell's steel case should notleak. In all situations an alkalinemanganese cell will outlast a zinccarbon cell, ie it will provide the sameamount of current for a longer period oftime. But in low current, or medium-intermittant current applications, theymight not be the economically sensiblechoice.

Figure 18 shows a chart of battery -powered devices along with typicalminimum and maxium current con-sumptions. You may find this of interestif you wish to know which type of cell ismost economic for your battery -powered devices.

ReferencesUse has been made in this article of thefollowing booklets: Modern PortableElectricity (issued by the Every ReadyCompany (Great Britain) Ltd.); PackagedPower (issued by Duracell InternationalInc.).

62 Hobby Electronics, July 1984

rb,HE pcg SERV I C El (For Peelsecle)ileadv

% Readers( IPRINTED CIRCUIT BOARDS (PCBs) for HE projects have often represented anobstacle for our readers. Some of you, no doubt, make your own . ,.......,....-but 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 82 February 83 November 83HE/8206/3 Auto Greenhouse HE/8302/1 Incremental Timer £8.20 HE'8311/1 Wiper Delay f3 22

Sprinkler £3.97 HE/8302/2 DigiTester PSU £7.71 HE. 8311,2 Light Delay £3 21HE/8206/4&5 Telephone Timer

(Set of two) E7.48 March 83 December 83July 82HE/8207/1HE/8207/2HE/8207/3

Tanover £2.45TVI Filter £2.05Computer PSU £8.83

HE/8303/1

HE/8303/2

April 83

LoudspeakerProtector

Overvolt Cutout£2.89£2.59

HE/8312/1HE/8312/2HE/8312/3HE/8312/4

Damp MeterContinuity TesterLight MeterBassman

£3.32£1.39£3.63£2.75

HE/8207/4 Solar Radio £2.28 HE/8304/1 6502 EPROMMER £8.26 January 84August 82 HE/8304/2&3 Ducker HE/8401/1 Power Reducer £3.69HE/.8208/1&2 Digital Millivoltmeter Main Board £4.09 HE/8401/2 Lap Counter £7.00

(Set of two) £4.99 Preamp Board £2.66 HE/8401/3 Quizmaster £3 23HE/8208/3&4 Audio -Analyser HE/8304/4 Power Down £2.42

(Set of two) £13.28 February 84September 82HE/8209/1 &2

HE/8209/3HE/8209/4

Signal lightsMain Module £2.25

Junction Module f1.96ZX Interface £3.84Slot Car Controller £2.28

May 83HE/8203/1HE/8305/3HE/8305/4

June 83HE/8306/1

BBC InterfaceStall ThiefAuto -Test

Sinclair Sound

£5.54£2.88£2.88

HE/8402/1HE/8402/2HE/8402/3

HE/8402/4

Audio PSUField MemoryCamera Remote

TransmitterReceiver

Timing Strobe

£5.62£3.23

£2.67£3.48£3.61

October 82 Board £3.22 March 84HE/8210/1 Flash Point Alarm £2.45 HE/8306/2 CB Rap Latch £1 90 HE/8403/1 Offbeat Metronome £3.46HE/8210/2 Negative Voltage HE/8306/3 Bat Light HE/8403/2 Sinewave

Generator £1.71 (Car battery Generator £3.31HE/8210/3 Squelch Unit £2.90 monitor) £2.59 HE/8403/3 Lightning Timer £3.35

HE/8306/4 Traffic Light Toy £2.94November 82HE/8211/1 Pedometer/

Odometer £2.45July 83HE/8307/1 Soft Fuzz £3.19

April 84HE/8404/1HE/8404/2

Analogue Test SetTime Out

£4.31£3.54

December 82HE/8212/1HE/8212/2HE/8212/3&4

HE/8212/5

Phase Four f3.25Microlog £4.58Tape/Slide

(Set of Two) £6.05TV Amp £6.56

August 83HE/8308/1HE/8308/2HE/8308/3HE/8308/4

Whistle SwitchAce InterfaceEnlarger TimerAuto -Winder

£5.06£4.05£3.36£3.43

May 84HE 8405/1HE 8405/2HE/8405/3

Spring ReverbTouch SwitchTouch Switch(Double sided touchplate)

£3.70£3.11

£5.49

HE/8212/6HE/8212/7HE/8212/8

Lofty £3.00Noise Gate £4.14Low Cost Alarm £2.65

September 83HE/8309/1HE/8309/2

TremolekoSPL Meter

£3.61£4.85

June 84HE/8406/1HE/8406/2

ZX81 TapeMains Intercom

£3.81£3.78

January 83 October 83 HE/8406/3 Millivoltmeter £3.33HE/8301/1 Chip Probe £2.09 HE/8310/1 Ultrasonic Alarm £3.67 July 84HE/8301/2 Switched Mode HE/8310/2 Audio Level Meter £3.55 HE/8407/1 Audio Preamplifier £7.20

Regulator £2.25 HE/8310/3 High Voltage Meter £399 HE/8407/2 Map Light Dimmer £2.12

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.

->11HE PCB Service, Argus Specialist Publications Ltd., No. 1, Golden Square, London W1R 3AB.I enclose a cheque/Postal Order made payable to ASP Ltd,for the amount shown below Price.ORI wish to pay by Barclaycard. Please charge my account number

VISAOR

I wish to pay by Access. Please charge to my account number

SIGNATURE

NAME(BLOCK CAPITALS)

ADDRESS(BLOCK CAPITALS)

Please allow 21 days for delivery

Boards Required Price

Add45ppflp

Total Enclosed £

0.45

Hobby Electronics, July 1984 63

PCB Print Out

PCB FOILPATTERNS

eo

T

esHE 8407 1 AUDIO PREAMP 0.

tHE 8407 2 MAPLIGHT DIVMER

0 0

HE 8407 2 MAPLIGHT DIMMER

I

HE 8407 1di)AUDIO 0t'REAMP

COPPER SIDE

Above: The two foil patterns required for the Audio Amplifier. Ignore the fancycompass -like circles, these are only needed for registration purposes and are notlikely to be needed for the home constructor.

Left: The foil pattern for the Map Light Dimmer. This is a simple board and can bemade easily using for example a Dalo pen.

64

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PARAPHYSICS JOURNAL(Russian translations). Psy-chotronics, Kirlianography,heliphonic music telekinetics.Computer software. SAE 4 x9":- Paralab, Downton Wilts.

COMPONENTS

BRITISH TELECOM plug soc-kets and leads, etc. Tel: C.W.A.S(0274) 731532. Or visit ourshowroom opposite OdsalStadium, Bradford.

WE SUPPLY a wide range ofelectronic components andservice parts. Also new tele-phone plugs and sockets, joy-stick interfaces and leads formost computers. Burglar alarmequipment including sensorsirens, bells, buzzers all at com-petitive prices. Write or phonefor details. Shudehill Supply Co.Ltd., 53 Shudehill, ManchesterM4 4AW. 061-834 1449.

FOR SALE

KIA RETURN AN. AD No.16 ...FREE... OualityCapacitor Pack...Simplyreturn+121/2pS.AE-KIA-8, LS29 9DZ ... SummerBonanza 1000 Amplifiers &Offers.

STEREOAMPS 120 Watt(60+60) ... Case - D.I.N. soc-kets and controls . . . 9-40v/Smoothing .. . protected out-puts 3/15 -0.H.M. tested anddiagrams £10/inc . . . KIA-8Cunliffe Rd., Ilkley.

6116 CMOS RAM 150ns. FullSpec Devices available now at£6.50 each whilst stocks last.Tel: 0734 760109.

66 Hobby Electronics, July 1984

PREVIOUSLY ADVERTISEDSTILL AVAILABLETape punch and reader ..... £22.50Bench isolating transformer 250 watt E7.75BOAC in-flight stereo unit £1.50Drill assortment 4 each 25 sizes between .25mm & 2.5mm E11.50Battery condition tester, less box E1.75N iced chargers, mains £0 75Flourescent inventor 13 watt front 12v £3 50

Ten digit stitch pad-pb phone etc. £1 95Uniselector 2 pole 25 way £4 60Water valve mains operatedCounter 6 digit mains operatedditto 12v resettableDouble glazing clear PVC sheet, 231/2" wide -per running ft.Locking mechanism with 2 keysMagnetic ClutchMouth operated suck or blow switchSolenoid with slug 8- 12v battery op.ditto 230v mainsTimer Ontron STP NH 110v AC CoilKey switch with 2 keys dp mainsAir valve mains operatedLatching relay mains operatedDry film lubricant aerosol canCoin op switch, cased with coin tray

fip or?,, 4;#.

legeComplete kit of parts for a three channel sound to light unitcontrolling over 2000 watts of lighting. Use this at home if youwish but it is plenty rugged enough for disco work. The unit ishoused in an attractive two tone metal case and has controls foreach channel, and a master on/off. The audio input and outputare by Y." sockets and three panel mounting fuse holders providethyristor protection. A four pin plug and socket facilitate ease ofconnecting lamps. Special price is £14.95 in kit form or £25.00assembled and tested.

£250El 15£345£0.15El 15E4 50E2 30El 82E2 30£6 90£1 75£3 75£3 50£0 65£4 60

8 POWERFUL MODELMOTORS(all different)for robots, meccanos, drills,remote control planes, boats,etc. £2.95.

12 volt MOTOR BY SMITHSMade for use in cars, etc. these are serieswound and they become morepowerful as load increases. Size31/2" long by 3" dia. They havea good length of '1/2" spindle -Price £3.45.Ditto, but double ended £4.25.Ditto, but permanent magnet E3.75.

I a

EXTRA POWERFUL 12v MOTORProbably develops up to h.p. so it could be used to power ago-kart or to drive a compressor, etc. £7.95 + £1.50 post.

THERMOSTAT ASSORTMENTio different thermostats. 7 bi-metal types and 3 liquid types.There are the current stats which will open the switch to protecdevices against overload, short circuits, etc., or when fitted sayin front of the element of a blow heater, the heat would tripthe stet if the blower fuses; appliance stats, one for high temp.eratures, others adjustable over a range of temperatures whichcould include 0 - 100°C. There is also a thermostatic pod whichcan be immersed, en oven stet, a calibrated boiler stat, finally anice stet which, fitted to our waterproof heater element, up in theloft could protect your pipes from freezing. Separately, thesethermostats could cost around £15.00 - - however, you can havethe parcel for E2.50.

MINI MONO AMP on p.c.b., size 4"x 2" (app.)Fitted volume control and a hole for a tone con-trol should you require it. The amplifierhas three transistors and we estim-ate the output to be 3W rms.More technical data will be includ-ed with the amp. Brand new,perfect condition, offered at the verylow price of £1.15 each, or 10 for £10.00.

- BARGAIN OF THE YEAR -The AMSTRAD Stereo Tuner.This ready assembled unit is the ideal tuner for a musiccentre or an amplifier, it can also be quickly made into apersonal stereo radio - easy to carry about and which willgive you superb reception.

Other uses are as a "get you to sleep radio", you could eventake it with you to use in the lounge when the rest of thefamily want to view programmes in which you are notinterested. You can listen to some music instead.

Some of the features are: long wave band 115 - 270 KHz,medium wave band 525 - 1650KHz, FM band 87 -108MHz, mono, stereo & AFC switchable, tuning meterto give you spot on stereo tuning, optional LED wave bandindicator, fully assembled and fully aligned. Full wiringup data showing you how to connect to amplifier or head-phones and details of suitable FM aerial (note ferrite rodaerial is included for medium and long wave bands. Allmade up on very compact board.

Offered at a fraction of its cost: only £6.001.50 post insurance.

THIS MONTH'S SNIPHi Fi sound from your Spectrum 1 watt amppm speaker & instructions £2.45

REVERSIBLE MOTOR with control gear Made by thefamous Framco Company this robust motor is approx 71/2" long, 3'4"dia. 3/8" shaft. Very powerful, almost impossible to stop. Ideal foroperating stage curtains, doors, ventilators, etc. Even garage doors if,properly balanced. Offered complete with control gear as follows:1 Framco motor with gear box 1 push to start switch1 manual reversing & on/off switch 2 limit stop switches1 circuit diag. of connections ONLY £19.50 + postage £2.50.

FOR SOMEONE SPECIALWhy not make your greeting card play a tune? It could play'Happy Birthday'. 'Merry Christmas', 'Wedding March', etc, or'Home Sweet Home', etc. Wafer thin 3 part assemblies, formaking cards musical. Mini microchip speaker and battery withswitch that operates as the card is opened. Please state tune whenordering. Complete, ready to work E1.25.

JOYSTICKWHY PAY £10 OR MORE - Make yourself a Joystick -full details were given in Dec/Jan 'Sinclair Projects'. We willsupply complete kit for £2.30. Although designed for theSpectrum or Z X81 it is equally suitable for any home computer.

TELEPHONE ITEMSPlug and Wall socket -4 pin or 5 pin E3 45Plugs only 4 pin or 5 pin El 15Modern desk telephone £7 50Heavy black old type E5 50External bell unit .E6.50Bell ringing power unit £4 50Pick up coil £1 15

STABILISED POWER SUPPLY (Mains Input)By LAMDA (USA) - Ideal for computer add-ons, d.c. output.Regulated for line volts and load current. Voltage regulation .1%with input variations up to 20% - load regulation 1% front noload to full load - or full load to no load. Complete in heavy dutycase Models available: 5v - 9A £23. 12v - 1.5A£13.25. 15v 1.2A £13.25. 24v - 2A £23.

PRESTEL UNIT - brand new and complete except for 7plug in IC's - Price: £19.75+ £2.00 p&p.Note: British Tele-com may notconnect this equip-ment as there is nomanufacturer toguarantee it. howeverit is well worth buyingfor its immense breakdownvalue - sold originally at over £150.

25A ELECTRICAL PROGRAMMERLearn in your sleep: Have radio playing andkettle boiling as you wake - switch on lights toward off intruders - have a warm house to comehome to. You can do all these and more. By afamous maker with 25 amp on/off switch.Independent 60 minute memory logger.A beautiful unit at E2.50.

BELLS & ALARMSHooter/Siren 6v - 12vLoud, med & soft buzzerOpen buzzer ex G.P.O.12" Gong cast iron cased ALARM BELL 12v do6" Gong 12v dc6" Gong mains

69p75p50p

£19.50E7.50E8.50

50 THINGS YOU CAN MAKEThings you can make include Multi range meter, Lowohms tester, A.C. amps meter, Alarm clock, Solderingiron minder, Two way telephone, Memory logger, Liveline tester, Continuity checker, etc. etc,, and you will stillhave hundreds of parts for future projects. Our 10KgParcel contains not less than 1,000 items - panel meters,timers, thermal trips, relays, switches, motors, drills, taps,and dies, tools, thermostats, coils, condensers, resistors,neon, earphone/microphones, nicad charger, power unit,multi -turn pots and notes on the 50 Projects.

YOURS FOR ONLY £11.50 plus £3.00 post.

TELEPHONE & INTERCOM CABLES15 conductors colour coded 200mt coil £59.0010 conductors colour coded 200mt coil £39.00Flex extension lead twin rubber.5rnin ideal grass cutters etc .250mtn coil 025.0050 meter coil E6.75

MAINS TRANSFORMERS4 volt 4 amp £1.756 volt 1 amp £1.15

12 volt 15 amp £1.1512 volt '/.amp £1.5512 volt 1 amp £1.7515 volt 2 amp £3.4515 volt 4 amp £4.6018 volt 1 amp £1.9520 volt 1 amp £2.3024 volt 2 amp £3.45

24 volt 4 amp25 volt 1 amp35 volt 2 amp38 volt 21/2 amp26 volt 10 amp50 volt 2 amp25.0.25 Ys amp12.0.12 2 amp115v 100w auto115v 250w auto

£4.85E2.25£3.95£4.95£9.95E5.50E3.95£4.95E3.95£5.75

J.BULL(Electrical) Ltd.(Dept. HE), 34 - 36 AMERICA LANE,

HAYWARDS HEATH, SUSSEX RH16 3QU.Established30 YEARS

MAIL ORDER TERMS: Cash, P.O. or cheque with order. Orders under£12 add 60p service charge. Monthly account orders accepted fromschools and public companies. Access & B/card orders accepted day ornight. Haywards Heath 104441 454563. Bulk orders: phone for quote.Shop open 9.00 - 5.30, mon to Fri, not Saturday.

STORE CLOSING SALEAll stocks must go from one of our big warehouses. 10,000,000items, everything from AERIALS to ZENER will be cleared atfantastically low prices if you are a manufacturer you can saveyourself a fortune - send for our Sale List, not for small buyers asminimum order £100.

EXTRACTOR FANS - MAINS OPERATEDWoods extractor.

5" - £5.75, Post f 1.25.6" - £6.95, Post E1.25.

5" Plannair extractor£6.50. Post £1.25.

4"x4" Muffin 115v.£4.50. Post 75p.

4"x4" Muffin 230v.£5.75. Post 75p.

All the above ex -computer,those below are unused.4" x 4" £8.50. Post 75p.9" American made

£11.50. post £2.00.Tangential Blower 10x3air outlet, dual speed

£4.60. Post £1.50.

LIGHTING & POWER CABLES

Made by Volex to BRITISH STANDARDSPECIFICATIONSP.V.C. sheathed outer -copper clad conductors1.5mm flat twin 100 metres £4.501.5mm flat 3 core 8E metres £11.00

6mm flat 3 core metres £54.0016mm flat twin 8E metres £115.00

MINIATURE WAFER SWITCHES2 pole, 2 way -4 pole, 2 way - 3 pole, 3 way4 pole, 3 way -2 pole, 4 way -3 pole, 4 way2 pole, 6 way - 1 pole, 12 way.All at 25p each or 10 for E2.00

OTHER TYPES IN STOCK - PLEASE ENQUIRE

BLEEP TON E These work off 12v and have an unusual andpleasant bleep hey each.

CONNECTING WIRE PACK 96 lengths of connectingwire, each 1 metre long and differently colour coded, a must forthose difficult interconnecting jobs. 85p the lot.

RED LEDS 10 for 69p. 100 for £5.75. 1000 for £52.

IN LINE SIMMERSTAT Ideal heat controller for solderingiron and many other hand-held appliances. £2.30. 10 for £17.25.

VENNER TIME SWITCHMains operated with 20 amp switch, oneon and one off per 24 hrs. repeats dailyautomatically correcting for the lengthening or shortening day. An expensive timeswitch but you can have it for only £2.95.These are without case but we can supplya plastic case . £1.75 or metal case - £2.95.Also available is adaptor kit to convertthis into a normal 24 hr. time switchbut with the added advantage of up to12 on/offs per 24 hrs. This makes an

ideal controller for the immersion heater.Price of adaptor kit is £2.30.

IONISER KITRefresh your home, office, shop, work room, etc. with anegative ION generator. Makes you feel better and workharder - a complete mains operated kit, case included.

£11.95 plus £2.00 post.

OTHER POPULAR PROJECTSShort Wave Set - covers all the short wave bands usingplug-in coils. Kit complete £14 50

R C Bridge Kit £9 953 Channel Sound to Light - with fully prepared metal case. E14.95

Ditto - made up £25 00Big Ear, listen through walls £9 50Robot controller - receiver/transmitter £9 50Ignition kit - helps starting, saves petrol, improvesperformance . . . . . . ........ £13.95Silent sentinel Ultra Sonic Transmitter and receiver . . £9.50Car Light 'left on' alarmSecret switch - fools friends and enemies alike . . .

3 - 30v Variable Power Supply2 Short & Medium wave Crystal Radio3v to 16v Mains Power Supply KitLight Chaser . . . - three modes .

Mullard Unilex HiFi stereo amplifier with speakersRadio stethoscope - fault finding aidMug stop - emits piercing squarkMorse Trainer - complete with keyDrill control kitDrill control kit - made upInterrupted beam kitTransmitter surveillance kitRadio MikeFM receiver kit - for surveillance or normal FMSeat Belt reminderCar Starter Charger KitSoil heater for plants and seedsInsulation Tester - electronic meggerBattery shaver or fluorescent from 12vMatchbox Radio - receives Medium WaveMixer Pre -amp - disco special with caseAerial Rotator - mains operatedAerial direction indicator40 watt amp - hifi 20hz - 20kHzMicrovolt multiplier - measure very low currents withordinary multitesterPure Sine Wave Generator

£3 50£1.95

E13 80£3 99Et 95

£17.50E16.75

£4 80E2 50£299E3 95E6 95£2 50£230£6 90E3.50£3 00

£15 50E16 50

£7.95£6 90E2 95

£16 00£29 50£550E9 50

Linear Power output meter115 Watt Amplifier 5Hz 25kHzPower supply for 115 watt ampsStereo Bass Booster, most items

E3 95

E£151 5705

E138 50

£8 95

Gt

21-PAK BARGAINSMINIATURE TOOLS FOR HOBBYISTS

Miniature round nose side cutters - insula-ted handles 44inch length. Order No: Y043.

Miniature long nose pliers - insulatedhandles 54inch length. Order No: Y044.

Miniature bend nose pliers -

insulated handles 54inchlength. Order No: Y045.

Miniature end nippers -insulatedhandles 44inch length.Order No: Y046,

Miniature snipe nose pliers with sidecutter and serrated jaws - insulatedhandles 5inch length. Order No.Y042

FLEKEY DRIVER

A flexible shaft screwdriver for those awkwardto get at screws. Overall length 134inch. OrderNo: FS -1 Rat blade 4mm FS -2 Cross, point no. 1

E1.75 each.

GRIP -DRIVER

8inch long screwdriver with spring loadedgrip on end to hold screws in positionwhile reaching into those difficult places.

Order No. SD -1 Flat blade 4mm SO -2ALL AT £1.25 each Cross point no.O. E95p each.

13 PIECE TOOL KIT AND CASE

7'itd 1

ONLY £7.50 ORDER No VP102

13 -piece tool set housed inattractive moulded plasticcase with clear sliding cover 1 off 5" snipe nose "radio"pliers with side cutters 1off 44" side cutters 1 off44" end cutters 2 off hexAllen" key drivers 2mm and

2.5mm; 2 off cross -point"Phillips" drivers No. 0 andNo. 1 (with tommy bar) 6off precision screwdrivers.Sizes from 1mm to 3.5mm

PRECISIONJEWELLERS' TOOLS

Rustproof, Tempered Handles and BladesChrome Plated Handles. Swivel Heads for useon Precision Work.

5721 SCREWDRIVER SET6 precision screwdrivers in hinged plasticcase. Sizes - 0.8, 1.4, 2, 2.4, 19 and 3.8mm f1.75

5731 NUT DRIVER SET5 precision nut drivers in hinged plastic case.With turning rod. Sizes - 3, 3.5. 4, 4.5 and5mm E1.75

5741 TOOL SET5 precision instruments in hinged plastic case.Crosspoint (Philips) screwdrivers - HO and HIHex key wrenches. Sizes - 1.5. 2 and2.5mm f1.75

5751 WRENCH SET5 precision wrenches in hinged plastic caseSizes - 4, 45, 5. 55 and 6mm E1.15

MULTITESTER1,000 opv including test leads &

Battery

AC volts - 0-15-150-500-1,003

DC volts - 0-15-150-5001,000

DC currents 0 lma-150ma

Resistance - 0 25 K ohms 103 K

ohms

Dims - 90 x 61 x 30mm0/No. 1322 OUR PRICE £6.50 ONLY

BRAND NEW LCDDISPLAY MULTITESTERRE 188m

LCD 10 MEGOHM INPUT IMPEDANCE.3; digit '16 ranges plus hFE test facility forPNP and NPN transistors 'Auto zero, autopolarity 'Single-handed, pushbutton operation"Over range indication '12.5mm (4 -inch) largeLCD readout Diode check "Fast circuitprotection "Test leads, battery and instructionsincluded.Max indication 1999 or -1999Polarity indication Negative only

Positive readings appearwithout + sign

Input Impedance 10 MegohmsZero adjust AutomaticSampling time 250 millisecondsTemperature range -5°C to 50°CPower Supply 1 x PP3 or equivalent 9V

battery20mW

155x88x31mm

Consumption

Size

RANGES

DC Voltage 0-200mV0-2-20-200-1000V. Acc. 0.8%

AC Voltage 0-200-1000V

Acc. 1.2% DC Current 0-200uA ;0 2 20 200mA, 0-10A. Acc, 12% rResistance 0-2-20-200K ohms02 Megohms. Acc. 1%BI.PAK VERY LOWEST PRICE

£45.00 eachLeather Case for 188m £2.50 EACH

SPEAKER PROTECTORLimits voltage to speaker orto the permissible max., byautomatically introducing aresistor in series with speak-ers. When excessive voltage is re-duced the unit resets itself. Electronicvoltage -sensing relay circuit. Spring terminals. Cut-offlevel adjustable from 10W -120W. Full instructions includ-ed. Dims: 85 x 74 x 25mm.0/No, VP 118 £9.95

ANTENNA SWITCH 2 and 3 WAYCo -axial switch for one transceiverto two antennae or one antenna totwo transceivers. Dims: 86 x 55 x32mm (Body).0/No. VP 113As above but 3 -way.0.No. VP 114

£4.50£4.75

SIGNAL INJECTOR

Simple push button operation. Oscillates at 700- 1k Hz with harmonics to 30MHz. 1.4V p/poutput. Impedance 1041 Ideal for troubleshooting with audio equipment. One "AA,"penlight battery supplied. 0/No VP96 £2.50

LOGIC PROBE

Automatic levelling. White LED indication,Minimum width of measuring pulse 30milfisecs.Maximum input frequency 10M Hz.Input impedance: 100kf1Power consumption: 40mA maximumPower supply: 4.5 - 18 V d.c.

ORD R N.. VP97 £10.50

Heavy duty test prods with built-in indicatorsfor testing polarity: indicates whether ac. ord C 3.5V to 400V. 0/No. VP98 £2.50

0/No VP 10795p

()°.

0/No VP 108El 15

PIE20Miniature round piezo-electronicbuzzer. White plastic. Lowconsumption.Frequency 4kliz approx.

Output 70dB AlI @ I. typPower 12Vdc 4m9Dims. 22 Idia) x 11.5mm.Fixing Centres. 26.5mm

P1820hem buzzer. White plastic 90mm

leads. For use on ac mains.Frequency. 35kHz approxOutput 85dB IA/ @ 1m typPower, 240Vac 5mADims 32 Idia I x 14mmFixing centres 38mm

ELECTRONICMiniature elettronicSolid state Ivory plasticleads Frequency 500

approx.

D ins 22 x 16 x I 5-rnm

o tput 82dB (Al @ m typmg centres 26mm

3V 25mA 0/No VP 829V 25mA 0/No. VP 84 I2V 25mA VP 86

130p each

TESTER

Universal tester with ceramic buzzer. Testsdiodes, transistors, resistors, capacitors andcontinuity. One "AA" penlight battery included.Test current: Max 2y.ATest voltage: 12VResponse range: 100M11Max voltage: 500VInternal resistance 390M1Len th: 135mm 0/No. VP99

CIRCUITC TESTER

D.C. continuity tester for circuit checking on alllow voltage equipment and components. Diodechecking also possible. Takes two M batteries90cm lead -has crocodile clip. Body length145mm 0/No. VP100 75.

Red plastic case with adjustable fixingbracket. Emits high-pitched wailing note ofvarying pitch - 100 cycles per minute. Dims -90mm (dia.) 60mm (depth). Power - 12v DC,0/P 90dBA lm type.

Our Price:.£5.50 0/No. VP79

TAPE RECORDER SWITCHUnit to control motor of tape recorder.1 8m cord and 2.5mm plug attached.On/Off switch. Dims: 55 x 20 x 20mm.0/No. VP 127 £1.00

POWER SUPPLY OUR PRICE £4.25Power supply fits directly into 13 amp socketFused for safety. Polarity reversing socket.Voltage switch, Lead with multi plugInput - 240V AC 50HZ, Output - 3, 4. 5, 6.

7b. 9 & 12V DC Rating - 300 ma VP109.

ET C EWDRIVER KITComprises 2 standard screwdriver blades 5 &7mm size. 2 cross point size 4 & 6. 1 Ratchethandle. 5 -in -1 Kit. f1.45 each. 0/No 3298

HIGH PASS FILTER/SUPRESSORCB/TV. High pass filter. Reducesunwanted signals picked up byantenna. Dims: 45 x 25 x 17mm0/No. VP 115 45p

LOW PASS FILTERDesigned to reduce harmonics onthe VHS and TV band. Cut-offfrequency: 30MHz. V.S.W.R.: Lessthan 1.2 to 1. Insertion loss:-0.2dB @ 27MHz. Impedance:50 ohms. Dims: 8) x 55 x 40mm,0/No. VP116 £2.75

glxll

LOW-PASS FILTERLP -30

AEC

DC -DC POWER SUPPLYDC to DC adaptor. Plugs into car cigar lighter aperture.Output 3, 4.5, 6, 7.5, 9, 12V @ 800mA Has universal outputspider plug, also 9V battery snap and polarity reversing

0/No. VP 119 £2.45

BI-PAK

£5.00

ANTENNA COUPLERTransceiver/car radioantenna coupler. With co -axialcables. One co -axialterminates in antenna plugand the other in PL259plug. Dims: 67 x 46 x 33rnm0/No. VP 117 £2.00

Send your orders to Dept HE 7 BI-PAK PO BOX 6 WARE, HERTSSHOP AT 3 BALDOCK ST. WARE, HERTS

TERMS CASH WITH ORDER, SAME DAY DESPATCH, ACCESS,BARCLAYCARD ALSO ACCEPTED. TH.. 10920) 3182, GIRO KM 1006

ADD 15% VAT AND 75p PER ORDER POSTAGE AND PACKING

SUB -BOXA neat swivelling disc providesclose tolerance substitution re-sistors of 36 preferred valuesfrom Sohms to 1Kohm. Simplyfix clips into circuit and swiveluntil optimum result is

achieved.0/No. VP 112 E4.75

6V 25mA VP 83

MINIATURE VICEMiniature plastic and metalvice with strong suction basefor portability. Single action tosecure or release suction.Plastic jaws with rubber pads20mm wide, open out to40mm. Dim, 85 x 6560mm approx.

FANTASTIC VALUE0/No. VP 95 ONLY E7.60

LEARN A UNGO!PILLOW SPEAKERSlim under pillow unit. Bohms2" speaker. 1.5m lead with3.5mm mono jack plug. BlackDims. 65 (dial x 17mm.0/No. VP 88 E1.25

METRIC &BRITISHMEASURES

Steel tapes in sturdy ABsplastic case. Silk wrist strap Theseyellow coated convex tapes have inchand metric graduations. Automatic pushbutton return2m long x I3mm wide 0/No VP 89 E7.003n long x 13nm wide 0/No. VP 90 f1.505th long x 16mrn wide 0/No. VP 91 f2.00

--11711TIVTIVIUTests all types of batten/ including

standard, NICAO, Alkaline etc Takesall standard sues including 6V lairtern batteries and watch/heanngaid cells Also tests fuses andlamps by means of ,nternai 9VIPP3/ battery. Can also be usedto recharge NICAD batteriesby means of external 312Vd c

Power supply Inot included)Full instructions provided. Dims 185 . 103 x 30mm0/No. VP 101 f7.00 )approx

FM MONITORFM monitor for 2 metre band Allmetal. Attached earphone PL259/50239 connectors 144MHr IOWmaximum. Dims (Body) 55 - 30

23rtun

0/No VP 120 E4.20

DUMMY LOAD50 ohms 30WUHF co -axial plugfitting IPL259/0/No VP 121 £5.20

0/No VP 87

PICK-UP COILLarge telephone pickup coil for /nutsensitivity Suction pad to stick to

telephone 90cm lead to 35 lack plugConnects direct to cassette recorderDims 32 (die I a 17mm /body/ 36mm(dial sucker E1.00

Use your credit card king us on Ware 3182NOW and get your order even faster Goodsnormally sent 2nd Class MailRemember you must add VAT at 19% to yourTotal orderPostage add 75p pen Total order