issn 0142-6192 march 80 45p - world radio history

Short Wave RadioFull Coverage Receiver

mt.) ler dulesSounds Good

Bits And Pieces

ISSN 0142-6192

March 8045p

Touch Switch PSU ModuleDigitally Controlled Transformer Offer

IT'S HA

ambit

PPE1111E11 nounTHE PART THREE CA

WE HAVE MOVEDTALOGUE 15PTO BIGGER

UBLISHEDPREMISE5.

Yes. it's here at last - the all new Part Three Catalogue. hot for all the family. and the usual update on all that is new. worthwhile andexciting in the world of Radio and Communications. A frig section on frequencl synthesis techniques covering broadcast tuner. to communic,iniiiiquality transmitter systems. More new products than ever - RADIO CONTROL parts. crystal filters, ceramic filter, for 455kH/ and tire- new rangeof TOKO CFSH low temperature coefficient types for 10.7M1-1/. Details on new radio ICs. including the new HAI1225. the C.131 )19f. lirokalikewith ti4d13 signal to noise. and adjustable muting threshold. Radio control ICs - and an updated version of the RCATIVI s channel FM receiver -

noss alai an Ambit designed screened front end, with 27MH, ceramic bandpass filter. LCD panel clock timer modules - the neatest and best LCI)panel DVM vet tinily £19.45 each + VAT,. the new 5 decade resolution DFAll for LW HE VHF with LCD readout. The DEMO with fluoresceindisplay to 10kHz resolution run VHF, 1kHz on SM. .)) IkH, HF synthesiser with Core - the list is endless. Get your copy of the catalogue now.Post publication price is 60p fine PP etc). The previous Iwo sections are also required for a complete picture: Parts I & 2 LI theydr. AllEI.50.And don't miss our spot the gibbon contest. together u Oh a quiz to see if s Call Spill file differences between a nerilithic cave drawing antescircuit diagram of one of our competitor's tuners. * Yes. we still hasen't learnt how to spell

Updated RCME FM radio control RX kit

8 Channel RC receiver IFM)Single IC RF/IF/DetectorSingle IC decoder27MHz ceramic filter inputFET RF stage with doubletuned bandpass filterDual ceramic filter IFBased on RCM&E FM systemBest quality SLM servoconnector blockONLY £16.10 inc VAT (kit)

(includes new SLM case)

New series of radio modules in fully screened cans'

There is a danger when advertizing in somemagazines that because we, do not findspace to list everything we sell in every ad.,that some readers forget about half the rangeswe stock. So to summarize the general ranges:TOKO Chokes, coils for AM/FM/SW/

MPX, Audio filters etcFilters: Ceramic for AM/FM,LC for FM, MPX etc.PolyvariconsICs for radio, clock LSI, radiocontrol MPX decoders etc

Micrometals Dust iron cores for toroidsfor resonant arid EMI filtersToroid mounts

Hitachi Radio/audio/mom linear ICs100W MOSFETs, small signalFETs, MOSFETs and bipolar

DOES YOUR ONE GLOW GREEN IN THE DARK ??Our DFM4 does, since it uses a vacuum fluorescent display for direct readoutof MW/LW/FM. Basically the same as the DFM2, (LCD Version). £24.45 kit (Inc VAT)Transformer with all necessary windings for DFM4 - £2.50 inc VAT.

_ .

Not illustrated here - but also now available is the DFM6. This is a vacuum fluorescent displayversion of our immensely popular DFM3 (LCD). Resolution is 100Hz to 3.9999MHz, 1kHz to39.999MHz, and 10kHz to 200.00MHz-; all standard IF offsets (inc. 10.7MHz on shortwave)are available via diode programming.

UM1181 VHF band 2 VARICAP TUNERHEAD5 tuned circuit, with image/spurit better than -80dB, buffered LOoutput, MOSFET RF stage, FET IF preamp, tunes with only 1Y, to 8v,-9dBm 3rd order intercept. loft price E12.00 Inc VAT. 1100off/ OAI

911225 FM IF strip with all mod cons for the HiFi tuner:All types use 80.dB S/N Hitachi IC, with muting, AFC, AGC, meteroutputs for signal level and centre zero. IF preamp stage.'A' Dual linear phase ceramic filter, with MOSFET IAGC'ell IF

preamp and a 3rd narrow filter with DC filter selection. Dualtuned FM detector stage. E23.95 Inc VAT Ibuilt)

'B' Dual ceramic filters, single tuned detector stage E14.95 Inc VATlall 'A' series units are set up with a spectrum analyzer for best THDI

91072 AM RADIO TUNER MODULES - DC TUNEDand DC SWITCHED Available February '80An include buffered LO output. mechanical IF filter ITOKO CFMOI1.10v tuning bias, switching by a single pole to earthA MW/LW 1150 t0 350kHz LW range) with ferrite rod antennaB As 'A' but also including SW1 or SW2 (seecifY I

5551 , 1.8 to 4MHz SW2 5 to 10MHzC With both SW rangesPrices one off INC VAT'A' E14.43 'B' f15 90 'C' E17.50 (Custom types OA)

And the following groups of products from abroad range of sources:Semiconductors -specializing in radio devices,Plessey SL1600, EUROPE's best selection ofAM/FM and communications devices. PowerMOSFETs, WORLD's LOWEST NOISE AUDIOsmall signal transistors, BAR graph LED driversfor linear and log.CD4000 series CMOS, TTL/LPSNTTL, standardlinears (741, 301, 3080 etc). MPUs, memories.Small signal transistors from AEG BC237/8/9families etc. (1000 off BC239C : 5.2p ea)LEDs: AEG 3mm/5mm round, 2.5x5mm flat,red, greem, orange, yellow. The best pricesyou will find for quality products.MOSFETs for RF signal processing includingthe BF960 UHF device, and 3SK51 for VHF.Varicap diodes for 17:1 capacity ratio tuning

FREQUENCY READOUT LSI from OKI witha one -chip answer to most digital frequencydisplay needs (and various modules)..crystal and ceramic ladder filters from leadingmanufacturers, ferrite rods, various ferrite beadsand a range of crystals for 'standard frequenciesand both AM and FM radio control at 27MHz.Trimmer capacitors.METERS - a new range of linear movementtypes, plus many 'indicator' types for VU, alltypes of tuning indicators etc.SOCKETS a new range that are better qualitythan Texas low profile, yet better priced.Modules for AM/ FM/STE REQ complete kitsfor tuners, audio amplifiers from Larsholt.SWITCHES - complete low cost DIY systemsfor push button arrays, keyboard switches.DOUBLE BALANCED MIXERS - MCL SBL1,replacement for MD108 etc. And cheaper,

OUR LATEST MOVING EXPERIENCE :: At last, we have moved to the address below. There is car parking for customers approaching viaNorth Service Road Ian extension of North Road Avenue, entrance opposite the Brentwood Fire Station.) Pedestrian access from the High Street(alongside 117 High Street). The new building is six times bigger than our Gresham Road offices, and we will be installing a much expanded salescounter in the fullness of time. NEW TELEPHONE NUMBER 102771 230909. TELEX NUMBER las before) 995194 AMBIT G. See you there !

200 forth Seruice Road, Brentwood/Essex.

YR/9,PM]. ,W.MWAIWM,

Vol. 2, No. 5 March 1980

PROJECTS FEATURES NEWS ANDINFORMATION

25 Watt Module

Sounds excellent

11 Clever DickOverseas edition

PSU Module 19

Cheap deal

Touch Switch 44

Do it digitally

Miniboard Siren 55

Loud enough?

Short Wave Radio 57

Hobby Electronics145 Charing Cross Road,London WC2H OEE01-437 1002 (4 lines)Published by Modmags Ltd,Distributed by Argus Distribution Ltd,Printed by QB Ltd, ColchesterHobby Electronics is normally publishedon the second Friday of the month priorto the cover date.

17

Short Circuits 23, 33, 36, 52, 72

More novelties

PETting it Together 24

They have the technology

Kit ReviewCheap stereo

Electronics on Wheels

)s

29

MonitorNews, news, news

Books

Great reads

Transformer OfferOur primary offer

Market Place38 Cheaper still

Roadworthy resistors

Chit -ChatMore practical circuits

Breaker One -FourMike review

BindersWrap up well

Next Month's HEAnother blockbuster

ETI Coming SoonBig stuff!

Hobbyprintsriubbing down

Back NumbersStill some left

SubsrciptionsWhy miss out?

T -Shirts49 Adorn yourself

63Complete your set

Into Electronics Construction 67

Part two

Editor: Halvor MoorsheadAssistant Editor: Rick MayburyProject Team: Ray Marston, Steve Ramsa-hadeo, John FitzGerald, Keith BrindleyProduction: Diego Rincon, Dee CamilleriPhil Gerring (Photography)Technical Artists: Paul Edwards, TonyStrakas, Joanne BarseghianAdvertising: Chris Surgenor, Steve Rowe,Sandie Neville, Kate SmithAdmin. Staff: Margaret Hewitt, Bren Good-win, Tim Salmon, Tracey Campbell, LoraineRadmore, Lorraine Stout, Halina Di-Lallo,JoanBrimm

Specials

Mini AdsIt "s all here

22

23

34

36

37

48

53

54

54

55

66

73

Copyright: All material in this publication is

subject to world-wide copyright protection.Permission to reproduce printed circuit boardpatterns commercially or marketing kits of theprojects must be sought from the Editor. Allreasonable care is taken in the preparation of '

the magazine to ensure accuracy but Mod-mags cannot be held responsible for it legally.

ABC

Simply ahead . .ILPS NEW GENERATION OF HIGH

I.L.P. modular units comprisefive power amplifiers,pre -amp which iscompatible with thewhole range, and thenecessary powersupply units. Theamplifiers are housedand sealed withinheatsinks all of whichwill stand up toprolonged workingunder maximumoperating conditions.

With I.L.P. performance standards andquality already so well established,

any advances in I.L.P. design arebound to be of outstanding importance

- and this is exactly what wehave achieved in our new

generation of modularunits. I.L.P. professionaldesign principles remain

- the completelyadequate heatsinks,

protected sealed circuitry,rugged construction

and excellent performance.These have stood the

test of time far longerthan normallyexpected from

ordinary commercialmodules. So we have

concentrated onimprovements whereby our

products will meet evenmore stringent demands

such, for example, asthose revealed by vastly

improved pick-ups, tuners,loudspeakers, etc., all of

which can prove merciless toan indifferent amplifier system.

I.L.P. modules are for laboratory andother specialised applications too.

PRODUCTS OF THE WORLD'S FOREMOST SPECIALISTSIN ELECTRONIC MODULAR DESIGN

ALSO AVAILABLE FROM A NUMBER OF SELECTED APPOINTED STOCKISTS

4 Hobby Electronics, March 1980

and staying therePERFORMANCE MODULAR UNITSHY5 PRE -AMPLIFIER

VALUES OF COMPONENTS FOR CONNECTING TO HY5Volume - 101c -n- log.Bass/Treble - 100K t2 linear. Balance - 5K n linear.

The HY5 pre -amp is compatible withall I.L.P. amplifiers and P.S.U.'s, It iscontained within a single pack 50 x40 x 15 mm. and provides multi-function equalisation for Magnetic/Ceramic/Tuner/Mic and Aux (Tape)inputs, all with high overload margins.Active tone control circuits; 500 mVout. Distortion at 1KHz-0.01%.Special strips are provided for connec-ting external pots and switchingsystems as required. Two HY5'sconnect easily in stereo. With easy tofollow instructions.

£4.64 + 74p VAT

THE POWER AMPLIFIERSF.1KHzLOAD- art ON ALLEXCEPT HY400AT4n.

START OF WAVE IFORM CLIPPING /0,

R.

5 10 20OUTPUT PONER - WATTS RMS

50 700 250

THE POWER SUPPLY UNITS

I.L.P. Power Supply Units aredesigned specifically for usewith our power amplifiers andare in two basic forms - onewith circuit panel mounted onconventionally styled trans-former, the other with toroidaltransformer, having half theweight and height of con-ventional laminated types.

ModelOut pPowerutR.M.S.

Dis-tortionTypicalat 1 KHz

MinimumSignal/NoiseRatio

PowerSupplyVoltage

Sizein mm

Weightin gms

Price +V.A.T.

HY30 15 W 0.02% 80dB -20 -0- +20 105x50x25 155 £6.34into 8 1-2 + 95p

HY50 30 W 0.02% 90dB -25 -0 +25 105x50x25 155 £7.24into 8 E2 + £1.09

HY120 60 W 0.01% 100dB -35 -0-+35 114x50x85 575 £15.20into 8 l + £2.28

HY200 120 W 0.01% 100dB -45 -0-+45 114x50x85 575 £18.44into 8 E2 + £2.77

HY400 240 W 0.01% 100dB -45 -0-+45 114x100x85 1.15Kg £27.68into 4 2 + £4.15

Load impedance - all models 4 - 16_n_Input sensitivity - all models 500 mVInput impedance - all models 100K -n -Frequency response - all models 10Hz - 45Hz - 3dB

PSU 30

PSU 36PSU 50PSU 70

PSU 90

PSU180

±15V at 100ma to drive up tofive HY5 pre -amps £4.50 + £0.68 VATfor 1 or 2 HY30's £8.10 + £1.22 VATfor 1 or 2 HY50's £8.10 + £1.22 VATwith toroidal transformer for 1 or2 HY120's £13.61 + £2.04 VATwith toroidal transformer for1 HY200 £13.61 + £2.04 VATwith toroidal transformer for1 HY400 or 2 x HY200

£23.02 + £3.45 VAT

* ALL U.K. ORDERS DESPATCHED POST PAIDHOW TO ORDER, USING FREEPOST SYSTEMSimply fill in order coupon with payment orcredit card instructions. Post to address asbelow but do not stamp envelope - we paypostage on all letters sent to us by readers ofthis journal.

IILELECTRONICS LTD.FREEPOST 4 Graham Bell House, Roper Close,Canterbury, Kent CT2 7EP.Telephone (0227) 54778 Telex 965780

r

NO QUIBBLE5 YEAR GUARANTEE

7 -DAY DESPATCH ONALL ORDERS

INTEGRALHEATSINKS

BRITISH DESIGN ANDMANUFACTURE

FREEPOST SERVICE-see below

Please supply

Total purchase price £

I enclose Cheque 0 Postal Orders 0 International Money Order El

Please debit my Account/Barclaycard Account No.

NAME

ADDRESS

Signature

Hobby Electronics, March 1980El OM Ell - MI ME NM 1

5

MonitorWHATEVER NEXT?Ignoring for a moment the young lady (if youcan) let us describe to you the object of herobvious affection. It is a TR-1200G (as if youdidn't know) Tele-Casseiver. (If that soundedlike a new word to you, stay tuned). Panasonic,the people who make the TR etc have made upanother word for your. More of that later.

The unit contains, deep breath, a 12 inchmonochrome TV, FM stereo radio that will alsocover MW, SW, and LW, and of course a stereotape recorder thrown in for good measure. Asyou would expect the permutations of recor-dings are such that you can record somethingwhilst doing something else, confusing, isn't it?

Now for new word number two, themanufacturers say that the TR etc isideal for making the most of 'Simulcast' pro-ductions when the TV soundtrack is additionallytransmitted on FM stereo radio. Repeat afterme, Tele-casseiver, Simulcast, now on yourown. Remember them because we may comeround your house to test you.

Usually at this point we get to the painful bit,the price. This time, just to be different, the TR .. . etc seems quite reasonably priced. Con-sidering what you get, a full stereo system (5Wper channel) plus a telly, £225 doesn't seemtoo bad. On the other hand if you're like us itcould be £25 and you still couldn't afford it. Ahwell, we can all dream.

By the way the young lady is not included inthe price, she's an optional extra.

HALVOR GOES WESTThis is the last issue for Hobby Electronics to beedited by Halvor Moorshead. Next month he'llbe in ten feet of snow publishing his ownmagazine in Toronto: the Canadian editionElectronics Today International.

Halvor has been with ETI (HE's big brother)in England since the days when it was astruggling one -year -old. As Editor andPublisher he has been responsible for thephenomenal growth of the magazine and thecompany. As well as starting the Canadianedition of ETI, back in England Halvor startedHobby Electronics and Computing Today.

6

Halvor's contribution to the hobby of elec-tronics has been enormous, as any reader ofHE, ETI or CT will realise. On behalf of all hisfriends I wish him success and happiness inNorth America.

HE's new Editor will be me, SteveBraidwood, currently Assistant Publisher atModmags. I worked with Halvor on ETI in theold days, and kept in close contact as I did mybit for the colonies on the Australian andCanadian editions of ETI. I returned to Londonlast year and was delighted to work for Halvoronce again. So its goodbye Halvorand Hello HEmen.

ROBOTS, ROBOTSAND MORE ROBOTS

The long-awaited Robot revolution seems to befinally taking off. First the latest news onHEBOT.

Sales of HEBOT chassis have been phe-nominal, several hundred so far are runningabout, schools and colleges seem to be taking aparticular interest. Lansing Bagnall, the fork-lifttruck people, are considering using HEBOT todemonstrate their control systems. Our Germanand Canadian editions of ETI will be featuringHEBOT, orders for chassis are already comingin. On the home front, Nationwide, the BBC TVcurrent affairs programme, are filming HEBOTfor a feature that should be transmitted in earlyFebruary, HEBOT is now a TV star. One of themore surprising aspects of HEBOT sales hasbeen the number of Microdrives sold, almosttwice as many drive units as chassis pans. Howabout sending us some pictures of your HEBOTand any improvements or adaptations you havemade. Best pictures and suggestions will befeatured in the coming months.

On a more sinister note, we've just heardthat Mullard, the TV tubemakers, are to lay off850 workers over the next two years, guesswhat will be replacing them? You've got it -Robots. If HEBOT gets any cleverer the nextEditor of HE might just be a HEBOT, watch outSteve Braidwood.

PROJECTS SPECIALDotted around the mag you will see referencesto our latest special. Don't miss next month'sissue of HE for the full unexpurgated details!

Hobby Electronics, March 1980

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MonitorNews from the Electronics World

BASICALLY ATARI

wart.. .1

er=rr s'ite!or ou.,

41=iksimeitentimp

TOY CHIPS

Hot on the heels of a couple of other telly gamemanufacturers Atari have announced theirversion of the personal computer.

The Atari 400 / 800 series has been de-signed with expansion in mind. It will happilyconnect up to all manner of cassette decks,floppy disc and bubble memory devices. Thecomputer comes complete with a full colourdisplay on your own telly, four sound 'voices'and the capability for working light pens andhigh speed printers.

The 400 model has 8k RAM, expandable upto 48k when it becomes the 800 series. Simi-larly the standard 8k ROM will go up to the 40kof the 800 series given time, inclination andmoney. The machine works in something calledAtari Basic and is based on the 6502 Micro-processor IC.

Price wise it looks most attractive, just £400for the 400 series model and £750 for the 800.Launch date should be in June 1980. Impatientpeople should contact Ingersoll Electronics Ltd(the importers at 202 New North Road, LondonN1 7BL.

By the way, it will play games if fed with the.appropriate programmes.

Considering the delays we're having gettingour single IC radio control system off theground it was understandably annoying to hearof these new offerings from Plessey.

The pair of ICs in question, (SL490 trans-mitter and ML928 receiver) were originallydeveloped for remote control systems in TVsets. Much of Plesseys output now ends up inR /C toys, the example shown here is made by aFrench company, Joustra, who have just ord-ered half a million of the ICs from Plessey.

These ICs, unlike our proposed system, stillneed quite a bit of external circuitry, in thisrespect they are quite versatile, finding a goodhome in remote control systems using anythingfrom ultrasonics to Infra red.

We have no details of prices as yet but if youwould like some more information contactPlessey at: Plessey Semiconductors Ltd,Cheney Manor, Swindon, Wiltshire.

8

THIMPLETHERMOMETERGone are the days when you were required tosquint at a near -invisible line of mercury in athin, fragile glass tube. By that we mean theelectronic thermometer has arrived in all itsglory. Latest model to blink its LEDs comes fromSimwood Ltd. The SM1 covers the range -55degrees C to + 1250°C. The hand-held unit hasa three digit display with an accuracy of±0.15% and a resolution of 1.0°C.

A switch on the side of the unit is operatedeverytime a measurement is to be made,battery life is expected to ensure around 2000operations. In the event of a low battery thedisplay will flash.

The SM 1 comes complete with a carryingstrap and case. Further details from SimwoodLtd., Garrett's Hall, Shalford Green, Essex.

BOOK REVIEWStill puzzled by integrated circuits? Youshouldn't be, not after reading HE all thesemonths. If on the other hand this is your firstexcursion into the world of micro -electronicsthen you would be well advised to read a new(ish) book called Integrated Circuits, Questionsand Answers. It comes from the pen of R GHibberd and is published by Butterworth, price£1.55 (ISBN 0408004665).

This little book is probably one of the easiestto follow as it is based on a series of questionsand answers. You can literally just.pick it up andstart anywhere. In the past Q and A books havesuffered from poor indexing, a maddeningaspect of any book. This one seems to haveovercome this problem, making it quite suitablefor quick reference. A handy book to havearound.

JAWS THE JOB

Have you noticed our new Binders ad? Thewording has been changed from the originalbecause of the efforts of one D Bryant. In theoriginal ad we said, (quite lightheartedly)

'Send your cheques, postal order's, goldsovereigns, false teeth or anything negotiableto'

You guessed it, D Bryant sent us his upperset. In return we have sent D Bryant an HEbinder, and to discourage anyone else fromtrying to do the same we have kept his teeth. Soif you see a man in the Britsol area walkinground with an HE binder in his mouth you'llknow why. No more false teeth please, justmoney (Gold Sovereigns are still OK).

TV EXHIBITION50 years ago this March Logi Baird's 'Televisor'was finally on sale. The Science Museum inLondon are celebrating by holding an exhibitioncalled 'The Great Optical Illusion'. It opens inMarch 1980. Don't miss it. (Look out for ourfeature on Narrow Bandwidth TV next month).

ERRATANow pay attention to this one as it is a bitnaughty. On page 32 (Feb HE) Infra RedRemote Control, last paragraph, second col-umn should read: -(1 ) The EARTHS of the mains input and output

Not Neutrals, this would be most inadvisable,not to say dangerous. Sorry.


cos40014002400740094011401240134015401640174018

13p13p13p30p13p13p28p50p28p47p551;

4020402240'3402440254026402740284029404040414042404340464049

50p50p13p40p13p90p28p45p50p55p551755p50P901;25p

405040604066406840694070407140724081409345104511451845204528

25p80P30P13p1317

13p13p13p131,36p60);60P6517

60p601;

FULL DETAILS IN CATALOGUE!

LINEAR

THIS IS ONLYA SELECTION,70974174774871067107CA3046CA3080CA3130

35p16p451130p

85017900P

551,70);90);

LF 356 80pLM301AN 26pLM308 601)LM318N 751)LM324 45pLM339 45pLM378 2301;LM379S 4101;LM380 75pLM3900 50PLM3909 65pLM3911 100p

NE531 98PNE555 23pNE556 60pNE567 lOOPRC4136 100PSN76477 2301;TBA800 70PTBA810S 100PTDA1022 620PT1081 45pT L084 125PZN414 80p

MC1458 32); ZN425E 39017

MM57160 590); ZN1034E 20017

TTL74007401740274 047406740874107413741474207427743074327442744774487454

101;10p101,12p22p1217

1017

22p39»121,201;1217

18p38p45p5017

121;

74 73 201,7474 22p7475 25,,7476 20p7485 55p7486 20p7489 135p7490 25p7492 30p7493 25p7494 451;7495 35);7496 45p74121 251,74172 35,,74123 38p74125 35p74126 35p74132 45p

741417414574148741507415174154741577416474165741 70741747417774190/41917419274193741967419774199

551;55p90p551;40p65p40p55p55p

100p55p50p50p50p50p50p50p50p90p

°PioLED's 0.125in 0.2in

ed TI L209 TI L.220Green TIL211 TIL221Yellow TIL213 TIL223Cbps 3p 3p

(SPLAYSL704 0 3 tr, CCL707 0 3 in CAND500 0.5 in CC

each 100.9p

13p13p

7.5p12p12p

130p 1201,130p 120p10011 8017

TRANSISTORSAC127AC128AC176AD161AD162BC107BC108BC108CBC109BC109CBC147BC148BC177BC178BC179BC1828C182LBC184BC 184 LBC212BC212LBC214BC214LBC477BC478BC548BCY 70BCY71

17p16p181,38p38p

8p8);

10p8p

10p717

7);14p14p14p101,101;

10p101,101;10p10p10p19p19p10p141;

14);

BCY 7260131130132BD139BD140BF Y50BF Y51BF Y52MJ2955MPSA0bMPSA56TIP -29CTIP30CTIP31CTIP32CT1P2955T1P3055ZTX107ZTX108ZTX300

14p35p351;35);35p15p15p15p98p20p201,60t;70p65p80p651;55p14p14p16p

ZTX 5002N6972N30532N30542N30552N34422N37022N37032N37042N37052N37062N37072N37082N38192N38202N39042N39052N39062N40582N54572N54592N5777

1601217

181;

50;;501;

135PBP81,81;

9P91;91)

8p151;44p8p8p8p

121,32p32p50p

DIODES1N914 31; 1N4006 61,1N4001 4p 1N5401 131;

1N4002 4p BZYBBsi i 8;

ITT r .1, product1N4148 1 40 1130

SKIS

Low profileby Texas

8pin 8p 18pIn 1417 24pin14pin 10p 20pin 16p 28Pii,16pin 11p 22pin 170 40p,11

3 lead TO18 or TO5 socket. 10p eachSoldercon pins. 100,50p 1000,3700

181,

22p32,'

PCBsVEROBOARD

IZP in 0 lin 0 15in.5 x 1 14p - Cott,' 801,.5 x 3.75 45p 45p.5 x 5 54p 54p Pin

3.75 x 5 64p 6417 to,3.75 x 17 205p 185pSingle sided

Ins per 100 40); 40Pop quality fibre glass cam],tded. Svd 203 x 95inu1 60P

alo' pens 75p eachFlee mixed sheets of NIA: 14517 II' he.

RESISTORSCarbon film resist-ors. High stability,low noise 5%.

612 series. 4.7 ohms to 10M. Any mix.each 100+ 1000+

0.25W 1p 0.9p 0.8p0.5W 1.5p 1.2p 1p

Special development packs consisting of10 of each value from 4.7 ohms to 1 Meg -ohm 1650 rest 0.5W £7.50. 0.25W £5.70.METAL FILM RESISTORSVery high stability, low noise rated at1%. Available from 51 ohms to 330k in£24 series. Any mix.

each 100+ 1000*0.25W 4p 3.5p 3.2p

CAPACITORSTANTALUM BEAD0.1, 0.15, 0.22, 0.33, 0.47, 0.68,1 & 2.2uF @ 35V4.7, 6.8, 10uF @ 25V22@ 16V, 47 @ 6V, 100 @ 3V

MYLAR FILM0.001, 0.01, 0.022, 0.033, 0.047 .

0.068, 0.1

POLYESTERMallard C280 series0.01, 0.015, 0.022, 0.033, 0.047, 0.068, 0.1. 5p0.15, 0 22 7p0.33, 0.47 ......... 10p0.68 14p1 OuF 17p

CERAMICPlate type 50V. Available in E12 series from22pF to 1000pF and E6 series from 1500pF to0.047uF ...... .. 2P

RADIAL LEAD ELECTROLYTIC63V 0.47 __1.0 2.2 4.7 10 5p

22 33 47 7p100 1317

220 2017

25V 10 22 33 47

each

100220

1000470

8P13p16p

3p4p

5p8p_

10p15p23p

PLEASE WRITEFOR YOURFREE COPY OFOUR 80 PAGECATALOGUEOF COMPON-ENTS.OVER 2500ITEMS LISTED.

CONNECTORS

JACK PLUGS AND SOCKETSunscreened screened socket

2.5inm 90 13p 7p3.5mm 9p 14p 8pStandard 16p 30p 15pStereo 23p 36p 18p

DIN PLUGS AND SOCKETSplug chassis

socket7p 7p

3pin lip 9pSpin 180° 11p 10p5pin 240° 13p 10p

lmm PLUGS AND SOCKETSSuitable for low voltage circuits, Red & black.Plugs 6p each Sockets 7p each

4mm PLUGS AND SOCKETSAvailable in blue, black, green, brown, red, whiteand yellow. Plugs lip each Sockets' 1217 each

PHONO PLUGS AND SOCKETSInsulated plug in red or blackScreened plugSingle socket 7p Double socket

linesocket

7p14p14p16P

9I13p10P

STEVENSONElectronic Components

SPECIAL OFFERSA range of special offer items validduring February. All orders placedfor these items must be receivedduring February.

Pack of 3 x LM380 2 200pPack of 30 x 1N4001 12ff.tri 100pPack of 4 x FND500 4.000 350pPack of 15 x 2N3702 120b 100pPack of 15 x BC107 120p 100p

Special pack of nuts + bolts containingover 600 4BA + 6BA nuts, bolts andwashers 330p 250p

Pack of 4 red + 4 black crocodile clips -64p 50p

Mixer control knobs, per 100 (mixed)colours to suit 1400p 1300p

MULTIMETERSA really smart looking multimeter withan impressive specification for such a smallsize. The very clean scale in white andgreen on a black background makes thismeter very easy to read. The D.C. Imped-ance of this meter is 4K ohms per voltwhich is exceptionally good comparedwith the vast majority of multimeters ofa similar size. £5.95 each.SPECIFICATIONDC VoltsAC VoltsDC CurrentResistance

5V 25V 250V 500V ziff ohms/V)10V 50V 500V 1000V (2K ohms/V)250uA 250mA0 - 600K 17K ohms centre)

PANEL METERSr--

High quality 2" wide view meters.Zero adjustment. Back illuminationwiring.Available in 50 uA, 100 uA, 500 uA,lmA, 100mA, 500mA, 1A. £4.95 ea.VU meter similar style. £1.50 ea.

SLIDE POTENTIOMETERSGood quality 60mmtravel slider with80mm fixing centres.Available from 5k - 500Kin log and linear. 55p each.Suitable black knobs 6p ea. Coloured knobs 10p ea.

We now offer one of the widest ranges of components atthe most competitive prices in the U.K. See catalogue forfull details. We welcome callers at our shop in College Rd,Bromley, from Mon-Sat, 9am-6pm (8pm on Weds andFridays). Special offers always available.We also provide an express telephone order service.Orders received before 5pm are shipped same day.Contact our sales office now with your requirements.TELEPHONE: 01-464 2951/5770.

Quantity discounts on any mix TTL, CMOS,74LS and Linear circuits: 100+ 10%, 1000+ 15%.Prices VAT inclusive. Please add 50p for P & P,no charge for orders over £15. Official orderswelcome. All prices valid to April 1980.

=1=111VISA BARCLAYCARD

& ACCESS WELCOME.

ORDERSDESPATCHED

BY RETURNPOST

Mail orders to: STEVENSON (Dept HE)

76 College Road, Bromley, Kent BR1 IDE.

Veinal

VERO ELECTRONICS LTD RETAIL DEPT.Industrial Estate, Chandler's Ford,

Hampshire SO5 3ZRTel: (04215) 62829 Yen

Wiring Accessories

The Vero range of wiringaccessories are all highest quality

`professional' products, carefully selected to easeyour interconnection problems. There's a full rangeof pins and DIP sockets (including low -profile) forsolder or wire wrapping techniques and the popularVerowire prototype wiring system.Add these to our established range of boards, boxes,frames and cases and you've got all you need foryour project. It's all in our catalogue - just send40p. and it's yours by return.

10

FASTER THAN A SCOPESAFER THAN A VOLTMETER

Instant - simultaneousmonitoring of the logic stateof all IC nodes

ONLY £2870plus 15% VAT, plus post and packing

Total £34.44 including box andinstruction manual.

iONT1Nf NtAk SPKIA,Lts ,oppoq.0,4=0=C.S.C. (UK) iirmted

Dept 14S Unit 1, Shire Hill Industrial EstateSaffron Walden, Essex CB11 3A0

te.iphone Saffron Walden (0799) 21682Telex 817477

Just clip it over your IC.LM -1 Instantly and accurately shows both static

and dynamic logic states on a bright 16 LEDdisplay.

LM -1 finds its own power.LM -1 cuts out guesswork, saves time, and eliminates

the risk of short circuits.LM -1 is suitable for all dual -in -line logic ICs.LED on = logic state 1 (high), LED off = logic state0 (low), and each LED is clearly numbered 1 to 16in the conventional IC pattern.

CONTINENTAL SPECIALTIES CORPORATION. DEPT.',:,Unit 1, Shire Hill Industrial Estate, Saffron Walden, Essex.

Name

II

AddressQUANTITYREQUIRED

LM1. £34.44inc. p & p and VAT

FREE catalogueTick box I enclose cheque/PO for

E

Phone your order with Access, Barclaycard or American ExpressLCard No Expiry date

1E111 I=M MIM Mill INN OMNI MEN =IN

II


System 5080AHE introduces a brand new amplifier system beginning with the 5080APOWER AMPLIFIER module.

THE HE 5080A POWER AMPLIFIER MODULE is thefirst part of an exciting new system in modularamplifiers, which on completion will provide the builderwith a first rate stereo amplifier of 25 watts per channelinto a speaker impedance of 8 ohms. Elsewhere in thisissue is the 5080 PSU - the second part of the systemand finally, in a couple of months' time the design will becompleted with the pre -amplifier module.

The main advantage of a modular amplifier is thateach module can be built separately. This suits thebuilder who cannot afford a complete kit of componentsall at once, or the builder who is not too sure of hisconstructional capabilities and who wishes to test eachstage as he progresses. An important secondary advan-tage of such a method of manufacture is the reduction ofinterference (causing mains hum) from one device toanother. The pre -amplifier in any amplifier system isparticularly susceptible to pickup from the poweramplifier and power supply and the only real way toeliminate this is to separate them - the HE 5080 doesthis.

A fine pair, the 5080 Power Amplifier and PSU modules.


The overall objectives of the 5080 are that eachmodule, be self-contained, be easy to construct and lookgood. These aims do not, however, override the qualityof the amplifier as a whole, the specifications andperformance being within the criteria of "High Fidelity"audio systems.

To this end, distortion (an amount of which is inevit-able in any amplifier) in the 5080A power amp moduleis so low as to be inaudible and the frequency responseof it is well above and below the human hearing range.

To any experienced amplifier constructor, the circuitwill look fairly conventional, ie the power stage is a ClassAB type and the pre -driver stage is a common collectortype to provide a higher input impedance to the source.This is not to say that modern techniques have not beenutilised in its design. For example, "state of the art"output stage protection is provided by FS 1, whichprevents excessive current flow due to faults or shortcircuits in the speaker connections. In the past, there hasbeen a tendency to use semiconductor type currentlimits which resume normal operation after the fault has

11

C147u

C2100n

T/7777

I/P

v0

C322u

FS1

NOTES:01 IS BC182L02,3 ARE BD131Q4 IS TIP33A

R1 05 IS TIP34A1k2 D1,D2 ARE 1194002

ZD1 IS 30V, 1.3W

30V 11500n

R368k

Q3,4,5 ARE MOUNTED ONSAME HEATSINK'

R2330k

Q1

IC7470u

R6270R2.5W

RV1100R

C10680p

03

C1210u

RV2 R74k7 1k8

C112n2

C6 R4 R5 C95n0 100R 82R C8 680P

1n0

Fig. 1. Circuit diagram of the 5080A Power Amplifier

How it WorksTHE 5080A power amp consists of a Class A inputstage followed by a Class AB output stage. A classA transistor amplifier is shown in figure 2. As canbe seen, a similar configuration is used in thecircuitry around QI in the 5080A. The transistor isbiased permanently half on so that the outputwaveform is identical to that at the input. Class Aamplification is, however, very wasteful of powerbecause the transistor is always conducting acertain amount of current even when there is noI/P signal, ie, under quiescent conditions. This isnot normally important except in power amps,where a large amount of power stands to be lost.So, in the power 0/P stage we must turn to a moreefficient method of amplification.

LARGER SIGNAL UP

ALLER SIGNAL I/P

LARGER SIGNAL 0 P

SMALLER SIGNAL O'PDISTORTION

In a Class B amplifier the transistors are biasedto their cut-off point so that they conduct only overone half of the signal waveform. Therefore, with-out an I/P signal the power loss is zero (meaninggreater efficiency). Obviously one transistor is

R8OR332.5W

R9OR332.5W

Q4

05

D1

C13+ 1000u

02

C14100n

R1010R

LS1

needed for each half of the waveform, as in figure 3.But, a transistor's characteristic is not linear

near the cut-off point, resulting in crossoverdistortion where the changeover occurs betweeneach transistor. Moreover because the distortionstays the same size irrespective of the signal size,the relative percentage of distortion increases witha smaller signal.

The answer to the problem is to introduce en-ough bias to eliminate this distortion. The overalleffect is a mixture of Class A and Class Bamplifications (called Class AB).

The HE 5080A power amplifier does this bymeans of a simple voltage regulator around Q3 andRV I. Class AB operation does mean that a certainamount of quiescent current is necessary. This isnot, however, enough to represent a great heat lossand therefore this mode still maintains a highefficiency.


System 5080A

Above: PCB foil pattern for the 5080 PA

Fl3W09q MA

UP

L'SPKR

42 V DC

04 Q3 05

MID POINTVOLTAGE

UIESCENTCURRENT

SET MIDPOINTVOLTAGE

QUIESCENTCURRENT

Above: Overlay diagram of the 5080A

been rectified, but consequently the circuit becomesincreasingly more complicated. Most amplifier de-signers are now turning towards fuse protection as thebetter method.

Another ultra -modern protection technique is in theuse of D1 and D2 - included to protect both the output

BuylinesFirst off, let's get the case out of the way. It isavailable from West Hyde Developments and is their"Sink Box" of length 100 mm. Their telephonenumber is Aylesbury (0296) 20441.

PCB mounting electrolytic capacitors are availablefrom Electrovalue.

We cannot foresee any more problems with com-ponent supply.

transistors and the speaker against sharp transients. Theloudspeaker being partially a reactive load can causelarge back EM Fs to occur around the output stage area,which these diodes eliminate.

Also, our designers' minds turned to the problem ofappearance - well, what's the use of a, gadget if itdoesn't look good? You can't show it off to the neigh-bours if it looks like a tobacco tin radio, can you? And,it has got to be neat - as few wires and cables aspossible hanging all over the place, tripping you up andbring the specifications down. No - a compact, goodlooking module is required, as good as or better thanthose that can be bought.

The case which we used is just the job, constructed ofmetal it can be used to shield the amplifier from pickupand also be used as the amplifier's own heatsink. Theprinted circuit board was, in fact, designed specificallyfor this case and it does provide the amplifier with verysmart and functional protection, although it is by nomeans essential that the same case is used.

Parts ListRESISTORS (All 1/4W, 5% except where stated)

R1

R2R3R4R5R6R7R8,9R10

CAPACITORS

C1C2,5,14C3C4C6C7C8C9,10C11C12C13

SEMICONDUCTORS

Q1Q2,3Q4Q5D1,2ZD1

1K2330K68K100R82R270R1K8OR331OR

2.5W

2.5W1W

47 II F 63V PCB elect100n polyester22p 25V elect47 µ 40V PCB elect5n polystyrene47Oµ 10V elect1 n polystyrene680p polystyrene2n2 polystyrene10µ 16V Tantalum1000p 40V elect (see text)

BC 182LBD 131TIP 33ATIP 34A1N400230V 1 3W

MISCELLANEOUSHeatsinkPCB fuseholder + 1 amp quick blow fusePhono socket2mm sockets - 1 black, 1 redRubber grommetCase - see Buylines.

Hobby Electronics, March 1980 13

System 50 WACONSTRUCTIONUsing our design of printed circuit board, construction isstraightforward. Consultation of the layout will tell youthat the whole effect is one of neatness. C1 and C4 arePC mounting capacitors - if you have trouble obtainingthem a suitable source is mentioned in Buylines. C13 isspecified as 100 µ F 40 volt electrolytic, but it does needto be quite small (a maximum of 40mm in length).Various miniature types are available, eg ITT, Plesseyetc, but if you cannot obtain one small enough then buya smaller capacitance value - 680 µ F or 470 µ F - donot be tempted to use a capacitor of lower workingvoltage than 40 volts. By using a smaller capacitancevalue the only effect will be to slightly diminish the bass.response, it will probably not even be noticeable.

Q2 is mounted on its own heatsink (plastic packagetransistor type - see photographs).

Q3,4,5 are all mounted on a large heatsink. If you usethe same type case as you will find that the case can beused as the heatsink and does make for a good looking,neat module.

Whatever heatsink is used the transistors must bemounted using mica washers so that each transistor iselectrically isolated from each other and also from thecase. It is worth checking with a resistance meter that noelectrical connections occur before switch on. The PCBcan be bracketed to the end panel of the box and I /Pphono, speaker 0 / P plugs and power lead can be madethrough this panel. Note that all external connections tothe board are made from this end, meaning that all leadsare kept very short, minimising the possibility of untidyflying leads and pickup. The power supply connectioncan be made with a small plug and socket as in our

keep cost down via a long lead with arubber grommet in the case.

We used a PCB mounting finger release fuse -holderin order that, when the module is cased, the fuse can be

-k

3 POWER

HEP System 5080

Two 5080 Amplifier modules removed from their cases.

Close-up of the rear panel of one of the amplifier modules.

14

Inside the 5080 PSU module. For constructional details seepage 19.

removed or inserted easily. Ordinary PCB types can beused but these make the removal of fuses moreawkward. Alternatively a panel mounting fuseholder canbe used, connected to the board with flying leads.

SETTING UPDo not attempt to use the amplifier without heatsinks! Aheatsink of some description must be fitted before poweris applied, either the module case or any ordinaryheatsink.

Turn both presets fully anti clockwise, looking fromthe end away from the connection panel. Insert a 1 ampquick blow fuse in the fuse holder.

Next, connect the quiescent current test points usinga short wire link. There are now two measurements to betaken:

1) The output voltage should be at about half thepower supply potential. This is adjustable by RV2 andshould be the first test, using a voltmeter connected tothe appropriate test points.

2) The quiescent current, adjustable by RV1 andmeasured using an ammeter connected to the biascurrent test points (taking the link off first) should be setso that crossover distortion is eliminated. The currentwith RV1 turned fully anti -clockwise should be no morethan 100 mA and is the current through the biassingchain R6, RV1, Q3 and Q2. About 50 mA of quiescentcurrent should be added to the bias current and the finalreading should therefore be about 140 to 150 mA,adjusted by RV1.

Finally resolder the link across the test points. If anyaudible crossover distortion occurs when an audio I /Pand a loudspeaker is connected, then turn RV1 a shadefurther clockwise. But bear in mind that the more thequiescent current is increased the hotter the amplifierwill run even with no input signal.

All of these measurements can be made with theboard in its case and only the end panel taken off. HE


Greer 1980SaleSUPER SOUND SAVING!DINDY LOW NOISE CASSETTES

SJ30 10 C30 15 min per sideS.155 10 C46 23 min per side (LP)5131 10 C90 45 min per sideSJ32 10 CI 20 40 min per side

£2.00£2.50E3.50£4.50

ALL REDUCED!CAPACITOR PAKS

16201 18 electrolytKs 4 781-108116202 18 electrolytics 10u1-1008116203 18 electrolytics I DOuf 680u1

ALL 3 sr SPECIAL PRICE of £1.3016160 24 ceramic caps 220-82p116161 24 ceramic caps 100pf-390p116162 24 ceramic caps 470pf-3300pf16163 24 cerarrac caps 4700p1-0 047pf

ALL 4 at SPECIAL PRICE of 01.80

RESISTOR PAKS16213 60 'Aw resistors 100ohm820ohnx16214 60 1/4w resistors 16-8.2K16215 60'4w resistors 106-82K16216 60 1/4w resistors 100K -820K

ALL 4 at SPECIAL PRICE of E1.5016217 40 15w resistors 100ohm-820ohn)16218 40'/.w resistors 1K-8 2K16219 40 V.rw resistors 106-82616220 40'/,w resistors 100K 820K

ALL 4 at SPECIAL PRICE of £1.80

IC SOCKET PAKSSJ36 14 8 ponSJ37 12 14 pinSJ38 11 16 pinSJ39 8 18 pinSJ40 7 20 pinSJ41 6 22 pinSJ42 5 24 pinSJ43 4 28 pin5144 3 40 pin

ALL at ONLY E1.00 EACH

F.E.T.s753819295458254220254860

£0.17£0.18£0.28£0.25

(PROGRAMMABLEUNIJUNCTION)

256027 E0.2588/56 £0.25

VOLTAGE REGULATORSPr8,81,

u47805dA7812uA7815u47818uA7824o4723 14 pin OILLM3096 T03

Case T0220£0.55 uA 7905E0.55 uA7912E0.55 uA7915£0.85 uA7918£0.85 uA7924E0.35£1.10

Negative£0.70£0.70£0.70£0.70£0.70

OPTOELECTRONICS1510 707 LED display1511 747 LED Display1512 727 LED Display

DISPLAYSPrice eachPrice eachPrice each (dual)

£0.70£1.50E1.55

SJ78SJ795120S12115021505

115031506SJ80SJ82SJ83

L.E.D.s125 LED Diffused2 LED Diffused125 LED Bright2 LED Bright125 LED Diffused2 LED Diffused125 LED Diffused2 LED Diffused2 LED Bright2 LED Clear illuminating125 LED Clear illuminating

REDREDREDREDGREENGREENYELLOWYELLOWYELLOWREDRED

Price each£0.08£0.08£0.09£0.09£0.11£0.11E0.11£0.11£0.14£0.10£0.10

2nd QUALITY L.E.D. PAKS1507 10 assorted colours & sire E0.65S122 10 125 RED £0.505123 10 2 RED £0,50

L.E.D. CLIPS1508/ 125 125 5 for 60.101508/ 2 2 5 for £0.12

SJ81 1

SJ98 5

ORPI2SJ99 4

Infra RED emitter - Fairchild FP100Photo Detector MEL11 DataNORP12 Cad CellITT 5870 ST Nixie Tubes

£0.25E1.00£0.45£1.00,

5J29 Texas NPN silicon transistors 25503= BC 108 TO 18metal can - perfect & coded50 off E2.50 - 100 off E4.00 - 1.000 off E35.00

SPECIAL OFFERSJ 100 12v Electric Drill 7.500 RPM for all your PCB drilling

complete with 2 drills 1 & 15 £5.50

SUPER DUPER COMPONENT BOXMin 3 lbs in weight consisting of a fantastic assortment ofElectronic Components- Pots Resistors. Condensers. SwitchesRelays.Board -Semiconductors. wire. hardware, etc. etc. etc

'This is a large box and is sent separate to your order'5140 £2.50 including PAP

CALCULATOR CHIPGOM2 C500 24 pin MOS £0.50

IC INSERTION /EXTRACTION TOOL1015 £0.35 each

BI -KITS AUDIOMODULESAT

PRE -INCREASE PRICES!AMPLIFIERS

ALIO 3 watt Audio Amplifier Module 22-32v supply £2.67AL20 5 wag Audio Amplifier Module 22.32v supply E3.74AL30A 7-10 watt Audio Amplifier Module 22.32v supply

£4.36AL60 15-25 watt Audio Amplifier Module 30-50v soppy

£5.39AL80 35 watt Audio Amplifier Module 40-60v supply E8.44AL120 50 watt Audio Amplifier Module 50-705 supply

£13.74AL250 125 watt Audio Amplifier Module 50.80v supply....

STEREO PRE -AMPLIFIER' PA 12 Supply voltage 22-32 volts _input sensitivity 300rny

suit ALIO /AL20 /AL30 £7.76PA 100 Supply voltage 24-36 volts inputs: Tape. Tuner, May

P U , suit AL60 /AL80 £16.05PS200 Supply voltage 35-70 volts inputs Tape. Tuner, May

P.U. suit. AL80 /AL120 /AL250 £16.55

MONO PRE -AMPLIFIERSMM100 Supply voltage 40.65 volts inputs Mag. P U

Microphone Max output 500mv £11.30MM 100G Supply voltage 40-65 volts inputs 2 Guitars

Microphones. Max. output 500my £11.30

POWER SUPPLIESPS12

SPM80

SPM120 /45

SPM1201 55SPM 120 / 65

SG30

24v upply suit 2 X AL10, 2 x AL20 2 X AL30 &PA12/5.450 E1.50

33v Stabilised supply - suit 2 x 6160. PA100 to 15watts £4.40

45v Stabilised supply - suit 2 X AL60. PA100 to 25watts £5.110

55v Stabilised supply - suit 2 x ALM PA200 £6.8065v Stabilised supply - suit 2 x AL120. PA200, I x

AL250 PA200 £5.6015-0-15 Stabilised power supply for 1 x GE100MKII

£3.50

MISCELLANEOUSMPA30

S 450

STEREO 30

BPI 24GE100MK11

VPS3O

PS250

Stereo Magnetic Cartridge Pre -Amplifier - input 3Output 100rny 62.98

Stereo FM Tuner supply voltage 20-30v - Varicaptuned £23.24

Complete 7 watt per Channel Stereo Amplifier Board -includes amps. pre -amp, power supply. front panelknobs etc - requires 2050 Transformer £16.18

5 watt 12 volt max - Siren Alarm Module E3.5010 channel mono -graphic equaliser complete with

sliders and knobs E23.00Variable regulated stabilised power supply 2-30 volts

0-2 amps £7.60Consists - 1 capacitor & 4 diodes for constructing

unstabilised power supply for AL250 to 125 wartsE3.76

5m

TRANSFORMERS2034 1 7 amp 35v suit SPM80 £8.40 P&P El .212035 2 amp 55v £6.35 P&P El 472036 750mA 17v suit PS12

. £3.202040 1 5 amp 0-45,55v Suit SPM120 / 45. SPm120/ 55v

£5.20 PAP El 212041 2amp 0 -55v -65v suit SPM120/ 55. SPA/120;65v

£6.80 P&P El 472050 1 amp 0-20v suit Stereo 30 £3.25 P&P ED 751725 150mA 15-0-15v suit SG30 £1.77

ACCESSORIES139 Teak Cabinet suit Stereo 30. 320 X 23 X 81 mm

£8.49140 Teak Cabinet suit STA15 425 x 290 x 95mm E7.60FP100 Front Panel for PA100 & PA200 E1.50BP100 Back Panel for PA100 & PA200 £1.80GE 1 OOFP Front Panel for one GEl 0GMKII £1.752240 Kit of parts including Teak Cabinet chassis sockets

knobs to build 15 watt stereo amplifier £16.66

DIODESTypeAA119BA I 00BA14BBA173BAX13BAX160420004202B1100131126BYI270447

Price£0.08£0.08£0.13£0.13£0.05E0.08£0.06E0.07£0.18E0.12£0.14£0.06

Type0470047904810A9004910495934N605414854001N4002N4003

PriceC0.05£0.08£0.08£0,08£0.08£0.08£0.06E0.07£0.05£0.04£0.04£0.05

Type PriceN4004 E13.06N4005 £0.07N4006 £0.0854007 £0.09N5400 £0.1255401 £0.1355402 £0.14N5404 E0.15155406 £0.19N5407 £0.23N5408 £0.28S44 E0.03

LINEARTypeCA270CA3089CA3090LM380I.M381LM3900MCI 310PNE555NE556

Prins£0.95E1.70E3.00£0.80E1.35£0.50£0.85£0.18£0.55

TypeSL4144SN76013N55760235SN 76115TAA550TAA621ATBA120BTBA6414TBA800

Price[1.75£1.65£1.60E1.60£0.30El .80£0.60£1.10£0.75

Type Price184810 E0.85164820 £0.85JA703 £0.20((A 709C £0.25u4710 £0.25u8711 £0.28741P £0.18144661 E1.25TAA661B E1.25

SPECIAL OFFER

COMPONENT PAKS0/NO fluantity E pSJ 1 200 Resistors mixed values 0.50SJ2 200 Carbon resistor s1/4 -'h watt preformed 0.50SJ 3 100 'A watt resistors mixed values 0.50SJ4 60 1/2 watt resistors mixed values 0.50SJ 5 50 1-2 watt resistors mixed pot values 0.50SJ 6 50 Precision resistors 1-2' col. mixed 0.50SJ7 30 5-10 watt wirewound resistors mixed 0.50SJ1I 150 Capacitors mixed types & values 0.50SJI2 60 Electrolytics all sorts mixed 0.505113 50 Polyester / polystyrene capacitors mixed 0.50S114 50 C280 type capacitors mixed 1.00SJ15 40 High quality electrolytics 100-470mf 1.00SJ 16 40 Low volts electrolytics mixed up to 10v 0.50S.117 20 Electrolytics transistor types mixed 0.505118 20 Tantalum bead capacitors mixed 0.50SJ20 2 Large croc clips 25A rated 0.30SJ21 Large 71/2 Mains Neon Tester screwdriver 0.85SJ22 Small pocket sue Mains Neon Tester 0.55S.J23 Siemens 220v AC Relay DPDT contacts 10amp rating

- housed in plastic case 1.005124 Black PVC tape 1%) 15mm 025w - strong tape for

electrical & household use0.35 par roH 1.50 5 rolls

SJ25 100 Silicon NPN transistors all perfect & coded - mixedtypes with data & equivalent sheet 2.50

SJ26 100 Silicon PNP transistors all perfect & coded - mixedtypes and cases data and equivalent 2.50

SJ27 50 Assorted pieces of SCR s diodes & rectifiers incl studtypes all perfect - no reiecls fully coded - data Ind

2.60SJ28 20 TTL 74 series gates - assorted 7401 - 7460 1.005133 PC Board - mixed bundle PCB fibreglass paper single &

double sided - super value, 0.75SJ34 200 sq ins (approx) copper clad paper board 0.80SJ36 100 sq. ins. Ism.) copper clad fibre glass 0.50SJ49 8 Dual gang carbon pots log & fin mixed values 1.00SJ 50 20 Assorted slider knobs - chrome/black 1.00SJ 51 1 Switchbank 5 way incl silver knobs 0.505152 1 Pak of vero board approx 50 sq ins mixed 1.00SJ 53 1 Mammoth IC Pack approx 200 200pcs assorted

fall -out integrated circuits including logic 74 serieslinear -audio and DTL many coded devices but someunmarked - you to identify 1.00

SJ54 20 Slider pots mixed values & saes 1.00SJ 56 6 100K lin 40mm slider pots 0.505157 6 100K log 40mm slider pots 0.50SJ58 6 16 lin 40mw slider pots 0.5051 59 6 5K lin 40rnrn slider pots 0.50SJ 60 4 5K log 60mm single 0.505161 4 100)6 log 60mm single 0.50SJ62 5 15mm chrome knobs standard push fit 0.50S.163 1 Instrument knob - black winged (29 x20rnm) with

pointer 1/41' standard screw fit 0.15SJ 64 1 Instrument knob - black /silver aluminium top

(1 7 x 15mm) 'A'. standard screw fit 0.12METAL CASE DUAL SLIDER POTS: 45mm travelSJ65 106 log 0.25 roachSJ66 1006 lin 0.25 each'5167 Chrome slider knobs to fit 0.10 eachSJ68 30 21X300 type transistor NPN pre -formed for P/c Board

colour coded blue - all perfect 1.00SJ69 30 ZTX500 type transistor PNP pre -formed for P/c Board

colour coded white - all perfect 1.00SJ70 25 BC107 NPN to 106 case perfect transistors code

01359 1.00SJ 71 25 BC 177 PNP 10106 case perfect transistors code

01395 1.001SJ72 4 ZN3055 silicon power NPN transistors 103 1.00SJ73 6 TO64 SCRs 5 amp assorted 50v -400v all coded 1.00''SJ74 8 Way ribbon cable - colour coded individually PVC

insulated solid tinned copper conduction 0.2 metroSJ75 FM coax cable - plain copper conduction cellular

polythene insulated and plain copper braided P00:sheath - Impedance 75 ohms 0.10 Instr..

SJ76 1 Board containing 2 X 5 pin DIN sockets 180' 02-2 pinDIN loudspeaker sockets 0.30

SJ 77 A5 pin DIN 180' chassis/normal socket Inc' DPDTswitch 0.20

' SJ83 5 Germ. OCP71 type photo transistors 1.00SJ84 10 BD131 NPN transistors low Hfe rejects 0.50SJ85 6 PNP Darlington Power Transistors TO -126 0.505166 5 PNP T0-3 germ Power Transistors at VLTS 10-20CVC8

0.50SJ87 20 Asst heat sinks T01/5/18/92 0.505188 2 Post Office relays 0.60SJ89 20 Mixed values 400mW rener diodes 3-10v 1.00SJ90 20 Mixed values 400rnW zener diodes 11-33v 1.005191 10 Mixed values 1W renal' diodes 3.10v 0.505192 10 Mixed values 1W caner diodes 11-31v 0.50SJ95 8 Silicon Bridge Rectifiers up to 4Amp 200v -c Data

1.50SJ96 1 Battery holder to take E0HP7 s 0.1016168 5 Assorted ferrite rods 0.5016169 2 Tuning gangs MW / LW 0.5016170 50 Meters asst colours single strand wire 0.5016171 0 Reed switches 0.5016172 3 Micro switches 0.5016173 15 Assorted pots 0.5016177 1 Pack assorted hardware 0.5016178 5 Main slider switches assorted 0.5016179 1 Pack assorted tag strips 0.5016180 15 Assorted control knobs 0.5016181 3 Rotary wave change switches 0.50

16182 2 Relay 6-24v16184 25 Assorted fuses 100mA-5A16185 An assortment PVC sleeving markers16186 25 Presets assorted types and values16187 30 meters stranded wire mixed colours

0.500.500.500.500.50

HI 'Send your orders to DEPT. HE3, BI-PAK PO BOX 6 WARE HERTS.SHOP AT: 3 BALDOCK ST. WARE HERTS.-PAK TERMS: CASH WITH ORDER,

TESAMEDAY DESPATCH,CCESS.

BARCLAYCARD ALSO ACCEPD. TEL: (0920) 3182. GIRO 388 7006ADD 15% VAT AND 50p PER ORDER POSTAGE AND PACKING'APPX. COUNT BY WEIGHT


I

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16

Super10

.o press

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Clever DickQuestions from abroad thismonth. A prize for the correcttranslation. At the other end ofthe scale a problem concerningnoisy woodworm. Where will itall end?

RIG HTY-HO, brains in top gear, eyes down for anotherin our series of answers to burning questions. JonathanHill is first away this month.

Dear CD,As issues 1, 2, 3, 6 and 7 of HE are now unobtainable

why don't you start a photocopying service for readers.Your sister magazine ETI runs such a service for around50p per article. If you would consider this idea I am suremany readers would take advantage of this service.

Jonathan Hill,Northampton

Actually we were considering offering a photoco-pying service but this was planned for next year. Wehave been genuinely surprised at the speed at whichback numbers have sold out. In response to your requestwe will be offering photocopies of articles. More detailsnext month.

A quick one from Gavin Cawley now.

Dear Dick,Is it possible to put the Multi -Siren and R2D2 radio in

the same case, sharing the same power supply andspeaker?

Gavin CawleyCoventry

A quick answer for you Gavin, yes. There will have to bea double changeover switch (DP changeover) to switchfrom one circuit to the other but apart from that it shouldbe OK. By the way, it won't fit into the original R2D2case, you'll have to find a larger model for that.

Now for something slightly different. Copies of HE reachall over the world, even Belgium. A gentleman called 0.Lecoq wrote to us the other day. This is his letter, as hewrote it.

Dear Dick Clever,In the issue HE of January p.22, you announce

projects of negativ ion generators. I made one and I feelno well being, only a weight on the chest when I let itfunction during a night in my bedroom . .

I think you will be interested by the article "TheInvisible Enemy" I join. It was published in the Luxem-burgisch newspaper "LUXEMBURGER WORT- of the20.11.79.

0. Lecoq,Arlon-Frassem, Belgique


Att.

S.,14%*- T,

Now to the problem. Mr Lecoq writes English muchbetter than we read Luxemburgish. In fact none of usread this or any other language for that matter. (We evenhave difficulty with English.) The copy of the article isprinted below, can any of your read it, if so could yousupply us with a translation. First correct entry receives abrand new HE binder.

Incidentally, we are hoping to review a Negative IonGenerator kit in the next month or two. We'll let youknow if we feel any well being . .

Deeirrare Feind

Ozon ist kein Gesundbrunnentinter dem Tate] Ozon ist kein Ge-

suodbn.mnen" vered fentlichte die be-kannte ' Siiddeutsche Zeitung". am 6Oktober 1976 emen aufschluareichenBericht iaber ein Syrnposion. das in Dia-.Idorf 250 Wis.nschaftler und Exper-ten aus 10 Staaten abhielten, urn dieGesundheitarisiken des' zone zu untersuchen und Schutzma0nahmen auszu-arbeiten.

War lesen: Ozon gilt manchen Men-schen noch im rner als ,Gesundbrunnen'.Ware dem so, so gabe es fur Ozon keinenMAK-Wert (rnaximale Arbeatsplatzkon-zentration wahrend einds achtstilndigenArbeitstages: 0.2 Milligramm am Kubik -meter Luft) und keinen MIKWert: Men -gee von 0,15 Milligramm Won je Kubik -meter Luft durfen ale halbstundiger Mit-telwert nicht Uberschritten werden."

Natiirlich stellen diese Grenzwerte,vom Gesetzgeber festgelegt, keine wain-schenswerten Ozonkonzentrationen dar,sondern geben an, welche Ozonmengenden Arbeitendcra Ubcrhaupti nignnutctwerden kOnnen.

Wir lesen welter: Ozon beeintrachtigtunmittelbar Mensch, Tier und Pftanze".

Da Ozon mit an der Luft enthaltenenKohlenwasserstof fen reagiert, entstehenneue Folgeprodukte. Oxidantien genannt War erfahren:

tinter diesen (Oxidantien) sand be-sonders zu nennen die toxischen StuffsPAN (Peroxyazethylnitrat) und PPN(Peroxypropionylnitrat), die unter ande-rem AktivitatsstOrungen bei Enzymenbewirken, das heilh das Blutbild andernkonnen. (...) Nur 0,028 Milligramm PANim Kubikmeter (ingicbm) Luft genugenum Pflanzen nach zweistaindiger Ein-wirkung zu zersteren, PPN ist fUnfrnalso wirksam."

Gefahrlicher aber ist die umnittelba-re biologische Wirkung von Ozon, da esgenerell schon lenge vor den Oxidantienin hohen Konzentrationen auftretenkann und zu 90 Prozent corn menschli-churl Organismus aufgenornmen wird:0,16 Milligramm lc Kubikmeter schwa.chen bereits die Infektionsabwehr, beivorbelasteten Bronchien schadigenOzon plus Oxidantien bereits im MIK-Wert-Bereich (= 0,15 mg/cbm) das Lun-gengewebe und die Lungenfunktion."

Uber die Einwirkung auf gesunde Er.wachsene erfahren wir Akute Ozon-

wirkungen zeigen rich allerdings beimgesunden Erwachsenen spatestens beiMengen von 0.4 Milligramm je Kubik.meter. ,trockener' Mund und Rachen,Atembeschwerden, Asthma und hart-nackage Krapfschmerzen sand Folgen."

Ozon ist nicht nur ganger als PAN,sondern im Gegensatz zu PAN greats esvor allem die tie/en Atemwege an.'

Interpssant ist es, zu erfahren, dab dieRiesenstadt Los Angeles (USA( einenOzonwarnplan fur die Bevolkerungpraktanert. Bei einer Konzentrationvon 0,2 mg/cbm (in der AuBenluft) sinddie Fenster zu schhellen und Kinder amHaus zu behalten."

Soweit aus diesem Fachbericht.

Uber Ozon erfahren wir welter urnBuch von Prof. Dr. med.Lucas: DasNeue Grin. Gesundheitsbuch", VerlagSiadwest", Ausgabe 1979. Seite 73, un-ter dem Kapitel WetterfUhligkeit."

Dem Ozongehalt der Luft (Gehalt anverdkhtetern Sauerstofft besonders inBodennahe, soil can entscheidender Ein-flu0 zukommen."

Die Encyclopaedia Univairsalis be.zeichnet Ozon als giftig. sclbst beischwachen Konzentrationen (Band 19,Seale 1434.1

SchlulHolgernd kann gesagt werden.dall Ozooprodulitaon in geschlossenenRaumen, besonders aber in kleinen Rau -men wie Kiiche und Badezimmervermeiden ist. da es hier besondersschrrell zu hohen toxaschen Konzentrabonen kommen kann

Wo Ozon unvermeidlich ist, z.B. beimelektrischen BogenichweiBen, ist (Ur ei-ne gute Beluftung zu sorgen. G.

The article from Luxemburger Wort

17

To say we get some unusual requests would besomething of an understatement. Take this one fromCliff Robertson for instance.

Dear Dick,Some time ago I heard about the grubs of woodworm

beetles gnawing their way through furniture until theywere fat enough to emerge and start on the next lot. Onecan see the exit holes of the beetles on affected furni-ture, but there may or may not be younger members ofthe family still munching away inside. Could you devise amicrophone / amplifier / headphone set which wouldenable a doubtful purchaser of a genuine antique to listento the ravages of the creatures within? Using my taperecorder microphone and stereo headset, possibly withan adaptor to transfer the sound from the Sheraton to themicrophone, or perhaps one of the advertisers in HEmight like to adopt the idea!

Cliff Robinson,Isle of Wight

What a brilliant idea! This was put to the project teamwho shook their wise heads in disbelief. After pickingthem up from the floor it transpired there may be one ortwo practical problems. The first would be calibration,how noisy are woodworm? Would they oblige by holdingthe microphone? Would they eat the microphone? Wehave decided to throw this knotty problem over to you.Best suggestions will be published in a month or two.

Our last letter this month comes from one J. F.

Button. Getting extremely good value for money hasasks three questions. This just goes to prove flattery willget you everywhere.

Dear Dick,I am writing for three reasons.'

1) To suggest that every now and then you print thenames and photos of various members of the staff at HEand ETI.2) That you design several projects which would all fitonto one big PCB and all use LEDs. (Really just a minioptical effects unit).3) To congratulate you on running the best electronicmagazines there are, namely HE and ETI, which I readand enjoy very much. Keep up the good work.

J. F. ButtonWinchester

PS: I thought your stand at Breadboard '79 was the best- congratulations.

Letters of this calibre are always given priority treatment.Who can argue with the truth? Seriously though, yourfirst request has to be denied, most of the staff at HE andETI are either too ugly or are camera shy. You'll just haveto be content with the odd pix that creep into articles andprojects now and again. Number two is a little easier, wehave published several projects along the lines yousuggest and will be designing many more in the monthsto come. Although we have no definite plans for com-bining them all onto one PCB it is quite possible that it'ssomething we shall consider.

Lastly, thank you very much for number three and thePS. What more can we say . . . HE

18

All theseadvantages...

Instant all-weather starting Smoother running Continual peak performance Longer battery & plug life Improved fuel consumption Improved acceleration/top speed Extended energy storage

..in kit formSPAR KRITE X5 is a high pert or mance lop quality imitii.tivedischarge electronic ignition system designed to! the elect r (rowsD I Y world. It has been tried tested and proven in 1)1. Lain(reliable. Assembly only takes 1 2 hours and installat 'ofeven less due to the patented easy fittuul

The superb technical design of theSparkratecircuit eliminates problems of thecontact breaker There is no misfire due tocontact breaker bounce which iseliminatedelectronically by a pulse suppressioncircuit which prevents the unit firing if thepoints bounce open at high R P MContact breaker burn is eliminated byreducing the current by 95% of the norm

There is also a unique extended dwellcircuit which allows the coil a longerperiod of time to store its energy beforedischarging to the plugs The unit inclur e,.built in static timing light systems functionlight. and security changeover switchWill work all rev counters

Fits all 12v negative -earth vehicleswith coil/distributor ignition up to 8 cylinders.THE KIT COMPRISES EVERYT HI NV NEEDEDDie pressed case Ready drilled aluminium extrudedbase and heat sink, coil mounting clips and accessories All kitcomponents are guaranteed for a per :3(1 of 2 years from date ofpurchase Fully illustrated assembly and installation instructions areincluded

Roger Clark the world famous rally driversays "Sparkrite electronic ignition systemsare the best you can buy"

SINIAiritaHIGH PERFORMANCE

.616\ %oaf ELECTRONIC IGNITION

Electronics Design Associates, Dept. HE/382 Bath Street, Walsall, WS1 3DE. Phone: 109221 614791

Name

Address

Phone your order with Access or Barclaycard

Inc V A 1 and P P QUANTITY REO'D

X5 KIT f16.95

LACCESS OR BARCLAY CARO No.

I enclose cheque PO's for

Cheque No.

Send SAE II brochure only required.


PSU ModuleIf you haven't already got a supply for your 5080A power amp modules thenyou will need one! The 5080 PS is designed for the job.

THERE IS NOT AN AWFUL LOT one can say about apower supply unit. It is a pretty boring project really. Yetmost electronic gadgetry just will not work without one.It actually is the work -horse of any mains poweredequipment, but is generally forgotten about by mostpeople. The HE 5080 PSU power supply, we hope, willbe no exception to the rule. Designed to be trouble free

OFS11 AMP

N

T1(SEE TEXT)

Fig. 1. Circuit diagram of the system 5080 PSU module.Photographs of the module are featured in the 8080 PowerAmplifier project on page 11

and easy to build, the supply can be built, tested andused without much fuss.

The 5080 PSU features a dual regulated voltageoutput of 42 volts DC and 24 volts DC so that it canpower two of the 5080A power amplifier modules alongwith the 5080 Pre -Amplifier module which is still indesign stages and will follow in a couple of months time.

How it WorksThe circuit can be divided into two main parts -the 45 volt DC supply, which is a fairly standardtransistorised voltage regulator providing a stablesupply for up to two 5080A Power Amplifiermodules - and the 24 volt DC supply providing avery stable supply for the future pre -amplifiermodule in the 5080 system.

The 42 volt supply consists of the usual bridgerectifier and smoothing capacitor. A stable 43 voltsis given by the series combination of ZD1 and ZD2.Q1 and 2 form a Darlington pair in a series passregulator configuration to allow the high current

FS22 AMP

R347k

NOTESICI IS 78L2401 IS 2N305302 IS 2N3055BR1 IS 4 AMP 200VZD1 IS 30V 1.3WZD2 IS 13V 1.3W01.2 ARE 1N4001

24 V DC

output necessary with power amps.The 24 volt supply is somewhat more unusual in

that a voltage doubler rectifying stage is usedaround D1, 2 and C3, 4 so that over 24 volts DC isavailable from 12 volts AC.ICI is a 24 volt regulatorproviding up to 100 mA at that voltage - quiteample for most pre -amplifier applications.

FS2 is quoted as a 2 amp fuse - this is essentialwhen the PSU is to supply two power amplifiermodules of the 5080A type. If only one poweramplifier is to be run, then lower the fuse rating ofthe power supply to 1 amp.


PSU Module0e 1Jg9U2. v,:og -.3H

Fig. 2. Component overlay

Parts List

24 V DC

B Q2

RESISTORS (All 1/4W, 5% unless otherwise stated)R1R2R3R4

1K0 1/2W100R47K12K

CAPACITORSC1 2200 u 63 volt Elect.C2 47 u 63 volt PCB Elect.C3, 4 220 u 25 volt PCB Elect.C5 1000 u 40 volt Elect.C6 220 n polyesterC7 100 n polyesterSEMICONDUCTORSIC1 78L24BR 1 4Amp 200V bridge rectifierQ1 2N3053Q2 2N3055ZD1 30 V 1.3Watt zenerZD2 13 V 1.3Watt zenerD1,2 1N4001MISCELLANEOUSPanel mounting fuseholder + 1 amp fusePCB mounting fuseholder + 2 amp fuseNeon mains indicatorRadiating fin heatsink for TO5 transistorCase (see Buylines)T1 50 VA or 100 VA mains transformer with 40 volt ACand 12 volt AC windings. (See buylines).

no HE POWER SUPPLY 5080

Fig. 3. PCB foil pattern for PSU Module.

71

CONSTRUCTIONThe main construction work concerns the building up ofthe circuit board, which is fairly spacious and thereforeshouldn't be too difficult. C2, 3 and 4 are P.C.B.mounting capacitors and a suitable source in case ofdifficulty is given in Buylines.

Q1 heatsink is a radiating fin type, to fit a TO5transistor.

Q2 is mounted on to the metal chassis of the caseusing the usual mica washer and heat sink compound toprovide electrical isolation - check that this is so beforeyou wsitch on.

SW2 is mounted on the circuit board in fuse clips FS 1however, should be panel mounted on the case, alongwith SW1 and the neon indicator.

Finally as with any mains powered device, make surethat the chassis case of the power supply is taken tomains earth, with bolt on connection. This is a safetymeasure in case of any fault. HE

BuylinesIf printed circuit board mounting capacitors are hardto come by, you might try Electrovalue. All othercomponents should be easy to obtain.

Our case was type FP 1 B. This is available fromWatford Electronics. This case was found to be idealwhen a 50 VA transformer was used. If a 100 VAtransformer is used, the next case up in the rangemight be necessary.

Transformer T1, although easily obtainable, may

present some cost problems to your pocket. If this isthe case (and even if this is not the case) look at the adon page 23 of this issue of Hobby Electronics, wherelo and behold you will come across the answer to yourdreams. Either of these transformers can be used inthe 5080 PSU. It would appear that these trans-formers were purpose-built for the power supply (thetruth is that we designed the PSU to suit the trans-formers).


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S9'3116

.mature PresetsH. Vert 1009 1M 12pCarbon Track Pots

5K 1 M Log or OnSingle 30pSingle weft Switch 60pDual 72p

SLIDER POTS 60mm TrackLIN 5K 10K 50K 100K

60pLOG 104 60p

CRYSTALS100Kliz 300p111AM, 3709I 008MHz 370p3 2768MHz 350p3 579545MHz 200p4MHz 350p8 867237MHz 400910 7We 350p18MHz 300p26 690MHz 210p77145519, 210p

VEROBOAR DSDIP Breadboard4 15 x 6 15 270p(Surtable for 20 x 14 pm or

16 x 16 pn DIL ICs) DIPBreadboard as above with tracksfor 31 way connector 340pV0 Boards for ICs 105p(No track cutting)

CONNECTOR PLUGS31 way Plug31 way Socket5,100 Busboard

110p110pE12

EDOESOARD CONNECTORS 0.159. PITCH2 10 oto S5P . 22 4ey 13592 15 611Y 1009 2 . 25 way 1110p2.18 nay 1209

COUNTERS74092574C928105172168ICM7217A251040E

47Sp1100p

E20II50p700p

TTL 5 ECLMC4024MC40441011610231

325p370p

350,

SPECIAL OFFERS TO 31.1.805557412114L327082716 (Plus 5V onlyl

E18 100£16 100

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£5/10£5/10£6/10E6/10

VAT RATE. Please add VAT at1 5% on total order valueAccess and Barclaycard acceptedPlease send SAE for list

OREADSOARDS PROTOSOARD (R) SOLDE SSSSS BRE AD-EXP150 3 6" x 2 I E3.15 BOARDS(Up to 3 x 14 pn ICs) Socket Strips Bus Strips Binthng Posts mountedEXP650 3 6" x 2 4" OM on sturdy base plate(Up to 1 x 40 pin ICI P66 6 n 14 DIL ICsEXP300 6" 11" E5.75 P8100 10 it 14 DIL ICs

(Uto 6 x 14 pn ICS) P8102 12 x 14 DIL ICsEXP600 6" . 2 4" E6.30 P8103 24 x 14 DIL ICs

tUp to 1 x 40 pin DCsl P6104 32 . 14 OIL ICs1The above boards are suitable for all DIL ICs I

IC TEST CLIPS

14 pn E2.60

[9.20E11.80E22.115E34.45CM 95

16 KEY KEYPAD(Reed Switches)UHF ModulatorsReed Switches 112VAILOGIC PROBEMULTIMETERSSUPE RT ESTER 6808MICROTEST 809TMK 500Pocket multimmer

E4.00 COMPUTER KITSMEMORY MAPPED VDU INTERFACE KIT

E3.75 £45.00E0.25 SERIAL I P VDU INTERFACE KIT E56.00

E18.00 ELF II MICROCOMPUTER KIT E79.95ELF II WIRED AND TESTED E99.95

E33.00 GIANT MONITOR BOARD KIT FOR ELF II E3S.00E17.00 4K STATIC RAM BOARD FOR ELF II E69.44E22.00 ASCII KEYBOARD KIT E50.50

E4.75 I Please add 75p p&p to all above dents /

L240 We carry a large stock of 74 and 74LS TTLs. CMOS ',nears Memories etc and can normally offer16 pin E2.75 4U pin E2.90 ex stock deliveries We welcome inquiries for volume quantities both from local and overseas buyers

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TECHNOMATIC LTD.17 Burnley Road, London NW10(2 minutes Doll's Hill tune station) (ample Street parking)Tel: 01452 1500 Telex: 92 800

21

HobbyElectronicsBook ServicePOPULAR ELECTRONICS BOOKS

Sinclair, I. R., Introducing Electronic SystemsSinclair. I. R.. Introducing Amateur Electronics

£1.80£1.55

QUESTIONS AND ANSWERS

SIMPLE AND CONCISE ANSWERS TO MANY QUESTIONS WHICH PUZZLE THEBEGINNER.

Sinclair, I. R., Electronic Fault Diagnosis £3.45 Coker. A. J.. 0 & A On Electric Motors £1.90Sinclair, I. R.. Repairing Pocket Transistor Radios £2.50 Hellyer. H.. 0 & A On Radios and T.V. £1.90Sinclair. I. R., Oscilloscope In Use £3.00 Hibberd, R.. 0 & A On Integrated Circuits £1.90Sinclair. I. R.. Understanding Electronic Components £4.00 Jackson, K.. Q & A On Electricity £1.90Sinclair, I. R.. Understanding Electronic Circuits £4.00 Brown. C., 0 & A On Hi-Fi £1.90Kitchen, H. T.. Handtools For Electronic Workshop £2.75 Brown, C.. Q & A On Transistors £1.90Kitchen. H. T., Electronic Test Equipment £5.00 Brown. C.. Q & A On Electronics £1.90Capel, V.. How To Build Electronic Kits £2.20 Reddihough. J.. Q & A On Colour T.V. £1.90Darr, J., How to test almost everything electronic £3.50 Miller. H., Q & A On Electric Wiring £1.90Brown, R. M.. How to read electronic circuit diagrams £4.10

CONSTRUCTOR GUIDESAUDIO

Graham, P.. Simple Circuit Building £2.60

Earl. J.. Audio Technicians Bench ManualEarl, J.. Pickups and Loud SpeakersEarl, J.. Tuners and AmplifiersEarl. J., Cassette Tape RecordersEarl. J., ABC of Hi-Fi

£3.50£3.50£3.00£5.25£4.25

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£2.60£2.60£2.60£2.60£2.60

Capel, V.. Microphones In Action £3.00Capel. V.. Improving Your Hi-Fi £3.50Capel, V., Creative Tape Recording £4.00 BEGINNER'S GUIDEHellyer, H. W.. Tape Recorders £4.25Sinclair. I. R.. Audio Amplifiers For Home Construction £2.75 Sinclair. I. R.. Beginner's Guide To Tape Recording £3.35

Sinclair. I. R.. Beginner's Guide To Integrated Circuits £3.35Sinclair, I. R., Beginner's Guide To Audio £3.35King, G. J.. Beginner's Guide To Radio £3.35

RADIO CONTROL King. G. J.. Beginner's Guide To Television £3.35King. G. J., Beginner's Guide To Colour T.V. £3.35

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Short CircuitZN1034E TIMER

Long timing periods are difficult oreven impossible to obtain usingmost simple timing circuits, suchas those using the well-known 555timer IC. The problem is that suchcircuits usually provide a timingperiod of only about 1CR seconds,and times of more than a very fewminutes require unrealistically highvalues for the time resistor andcapacitor. The ZN1034E device isspecifically intended for aplicationswhere long times are required, andusing an oscillator, a 14 stagebinary divider (divide by 4,096circuit), and a logic control section,an output time of between about2,700 and 7,500CR seconds canbe attained! This enables ti mes ofhours or even days to be obtained,and times of a few minutes to a fewhours can be obtained withouthaving to use an electrolytic timingcapacitor, giving excellentreliability and accuracy.

R1 TO R6 ALL 820k 1%

-L.

220n

10 14

This simple timer circuit pro-vides an audible alarm at the end ofthe timing period which can bevaried from 10 to 60 minutes in 10minute increments. C1 is thetiming capacitor, and the timingresistance is formed by whicheverof the series of resistors (R 1 to R6)is switched into circuit using SW1.The timing resistors all have thesame value, and so if one resistorgives a time of 10 minutes, twoproduce a time of 20 minutes,three give 30 minutes, and so on.The timing period can be varied

47k

ICIZN1034E

7

C2

R8470R

R9100k

C347n

R10390R

02BC179

4k7

01BC109

from about 2,700CR to 4,100CRseconds using R7, and in practicethis is adjusted by trial and error togive a suitability high level of timeaccuracy.

The ZN1034E has an internal5 V. shunt regulator, and R8 is theload resistor for this. The triggerinput (pin 1) is connected to thenegative supply so that circuit istriggered at switch on. The not Qoutput at pin 2 goes low during thetiming period, cutting off both Q1and Q2. These two devices, whichform the basis of an audio oscillator

SW2ON/OFF

C4100u10V

c( LS150 -80R

BY19VPP7

driving LS , are biased into opera-tion at the end of the timing periodwhen pin 2 goes high, causing thealarm to sound.

The circuit consumes about 8mA under quiescent conditions,rising to about 16 mA when thealarm is operating. The times pro-vided by the unit can be varied tosuit individual requirements bychanging the timing componentvalues, but the timing resistanceshould be no more than about 10megohms, and the timing capacit-ance should not be less than 3.3nf.

TRANSFORMER OFFER (PSU)If you are contemplating building the 25 watt ampliferand PSU modules in this month's HE (page 1 9) then youmay be interested in our special Readers Offer thismonth. We have a fairly limited supply of transformerssuitable for the PSU module. These are the same typesas used on our prototype. We have two types on offer,the larger of the two is a 100 VA device, it has two 12 Vwindings and one 40 V winding. The primaries are bothrated at 240 V AC. (The smaller model also has a 220 Vtapping on the primary).Both types are available for just £6, that includes VATand postage and packing. (Postage on the larger one .isnearly £1.50!) so as you can see it is a very good dealindeed.

When ordering please specify which type you need (S orL). As stocks may be limited we reserve the right to sendyou the alternative model, so order early.

Personal callers to the HE offices can purchase thetransformers for just £4.50 (inc VAT)

Send cheques, postal orders or gold (not less than1oz please) to:HE TRANSFORMER OFFER.Hobby Electronics,145 Charing Cross Road,London WC2H OEE.


If you think PETs are small furry animals, then read on. Rick Maybury hasbeen looking around the Commodore factory in California where PETs aremade.

'SILICON VALLEY: that conjures up all sorts of images.What the papers and TV programmes fail to tell you isthat it is an area some 200 miles long. To locate oneparticular place requires a little more than a vague mapand a tentative invitation.

Heedless of these 'minor' problems HE went insearch of the Mecca of microcomputers, that well knownmanufacturer of watches, calculators and of course PETcomputers, Commodore.

Commodore, or at least, the place where they makePET are to be found in what might be called the heart ofSilicon Valley, Santa Clara. Santa Clara, and particularlythe Commodore complex is about as easy to find as aproper English chip (potato that is) in the USA.

Having finally arrived we were greeted by our genialhost Neil McElwee who conducted our visit.

Before we launch into graphic descriptions of howPETs get put together some information on other Com-modore products. The watch and calculators bearingCommodore badges are mostly built in the Far East,however, LCD displays for which Commodore are justlyrenowned are put together in their Texas plant. Right,back to sunny California.

PET, or Personal Electronic Transactor, (not sure whatit means either) has become synonomous with homecomputing. They first sprang upon the unsuspecting

world during 1977, bringing computing in real terms'into the home. During these past two or three yearsCommodore have managed to knock out something like80,000 PETs, surpassed only by the amazing RadioShack (Tandy to us limeys) who claim an impressive100,000 TRS 80s on the streets.

SOLAR POWEREDThe PET is a rather unholy mixture of modern and''ancient' technology. On the one hand we have therelatively old fashioned monitor, the telly bit on the topcoupled up to the very latest (well, pretty new con-sidering) IC microprocessor technology. Just to compli-cate matters, a mechanical tape deck is thrown in forgood measure. To date the PET is still the only all -in -onecomputer system on the market. This curious combina-tion is reflected in the factory complex.

The Commodore factory boast one of the mostadvanced solar heating and air conditioning systems inthe world. (Why they should need any kind of heating inCalifornia must remain a mystery). Within this ultra-modern complex the PET computers are virtuallyassembled by hand. In fairness though they hope to beusing automatic insertion machines for the main PCBs in


the very near future.From beginning to end a PET takes about three days

to come together, a bit slow when you consider theaverage family car is built in just a few hours. Much ofthe three days period is taken up by what the Americanscall 'burn time'. We call it 'soaking', it involves puttingthe various assembled PCBs through a continuous testcycle for up to 36 -hours.

BIG SCREENLooking round the factory it's surprising to see how,many varieties of PET there are. Apart from the variouspermutations of memory size, 8k, 1 6k and 32k they alsohave an intruiging machine called Teachers PET. Farfrom being designed for whiskey manufacturers it isspecifically intended for schools and colleges. To look atit is pretty much the same as a standard PET. Though'we're told it has a couple of features that will maketeaching the intricacies of computer programming a lot:easier. (Classrooms full of sceptical students, we wishthem luck). Most of the PETs under construction nowsport the green screen, this is the 9 inch, 40 columnitem. Commodore are currently introducing a 12 inchscreen model, capable of displaying 80 columns andsupporting up to 64k of memory. That means it will be:Seven smarter. Fascinating as this doubtless is, we tend,only to be interested in how good the games are.

Apart from the PET, Commodore also assemble anoisy device called a line printer. In reality they onlymanufacture the electronics, the mechanics are off -the -shelf items. The same goes for the Floppy Disk units,only the electronics are assembled on -site.

It was interesting to see the PETs undergoing theirfinal checks before packing. A test involves a pro-gramme being loaded into the machine from a floppydisk and a trained operator looking at the results on thescreen. This must be one of the most boring jobsimaginable, peering day in, day out at rows ofmeaningless alphanumeric and graphic charactersflashing on the screen. Boring or not, their rejection rateand after sales failure rates are impressively low. There isa chance for us humans yet.

The entire factory (the Americans call it a 'facility') isstaffed by only 300 people, most of them concernedwith PET manufacture. Whilst we were there a lorryloadof PETs was being packed up for the UK market, thoughinformed sources at Commodore now predict the next.big market to be in Germany.

Commodore are basically a hardware manufacturer,that is to say they have very little interest in the softwareside, the programmes written for PET. However, at thetime of our visit the Gentlemen at the facility were takinggreat pains to impress us with their new Word Processor'package, and most interesting it sounded too. This

Below. The Commodore factory. The sloping roof acts as a solar collector. Inside much of the air-conditioning and heating is alsosolar -powered. The entire complex is staffed by only 300 employees, most of the component parts of the PET. i.e. metal work isfabricated in other plants.


preoccupation with business use emphasised the cur-rent US trends in microcomputing and doubtless theway, we in Europe will be going in the next year or so.

BUSINESS USERSWhen PET first came onto the scene most of themwent to what we would call the hobbyist market. That isthe chap (and probably a good few ladies too) who sit athome writing and running programmes purely forpersonal use. Today we have the situation where themajority of machines are being brought for business use.Many small companies unable to justify spendingthousands of dollars on time sharing or a mainframesystem are turning to devices like PET to solve all theirpaperwork and financial problems. For a very modestoutlay a small company can buy a complete package ofhardware and software capable of dealing with suchdiverse subjects as payroll, stock control and invoicingyet still play a creditable game of Star Trek, all at the flipof a cassette tape or floppy disk. Commodore confidentlypredict this will be the way of minicomputers in the nextfew years. To this end they are preparing to tool up forthe CBM Business system a somewhat serious version ofthe ordinary PET.

Naturally everyone at Commodore were a littlereticent (to say the least) to discussing the future butone helpful gentleman steered us towards a shinybooklet, Commodore's annual report. Without commit-ting himself too heavily he pointed out three very

Above. The sloping roof ofthe factory acts as a solarcollector.

Left. Inside the receptionarea. The area is space -heated and air-conditionedby the solar system.

Right. Inside one of theassembly shops. The PET'sare built on an assembly -linethough much of the work isstill completed by hand.

26

interesting paragraphs which he assured us mightanswer one or two burning questions. The first states;

". . . and work is moving forward on a large area LCD(Liquid Crystal Display) to be employed in computers andselected consumer products".

Could this be a thin screen TV?The second paragraph is a little more down to earth.

"Other computer enhancements under developmentduring fiscal 1980 will expand the capability of PETsystems to a point where they will be able to talk, listenand draw. Development of a next generation computer isscheduled for completion during 1979-80 and intro-duction by the end of the fiscal year".

Whatever next? A talking PET. Our office PET couldtell a tale or two.

Our last clue to the future is a little more concrete,PET owners will be delighted /frustrated to know that;

". . . a low cost colour controller to be introduced infiscal 1980 with the PET system and available for sale tooutside customers by the Electronic Components Divi-sion".

We are tempted to ask whether combining all of thesefeatures, speech, etc, will produce a PET with an LCDdisplay and some very colourful language. Watch thisspace.


PETting It Together

Inside a typical PET. The main processor board can be seen on the right hand side of the cabinet. The rows of ICs at the front are theRAMs. The hefty power supply can be seen on the rear, right hand side. The large smoothing capacitor is just below the mainstransformer.

All of the current range of PETs share a commonchassis. The case is fabricated from mild steel, makingit very robust and unfortunately quite heavy.

The electronics are divided into three sections. Themain board, that does all of the clever stuff. It sits inthe bottom part of the case. This board holds all of thedigital bits, an array of large and small ICs in neatrows just beneath the keyboard.

Sitting next to this is the mains power transformer.The incoming mains is stepped down to the varioussupply levels needed to drive the electronics. Thesupply for the monitor circuitry also originates here,so it is a pretty hefty device.

The final section is the monitor. This is housedwell away from delicate ICs in the top sectionof the case. It gives an interesting contrast to the neatdigital stuff below, looking .somewhat similar to a.birds nest, made by a blind bird.

We were interested to ask why Commodore optedfor the all -in -one concept. The answer came assomething of a surprise. In the US the controls overusing UHF modulators are very strict. So rather than

running foul of the all powerful FCC they decided tosupply a monitor built in. Incidentally this has anumber benefits. Fewer problems arise as a result ofpoor interconnections between computer and displayand the character definition is much better.

As it turned out the in-built monitor was a wisechoice. Texas lost several months in getting theircomputer on the market, purely as a result of havingto obtain FCC approval for their modulator.

Another aspect of this unconventional design is theease of service. Literally everything is readily acces-sible. The top half of the cabinet tips up into theservice position, a very good idea.

It is difficult to comment upon the PETs design,after all 80',000 people can't be wrong. Many lessercomputer companies have gone bust buildingmachines with extravagant claims.

The durability of PET is unquestionable though thismay work to Commodre's detriment. Newer designsappear almost daily, hopefully PET will also movewith the times and a new model should be appearingsoon.


10+ 10AMPLIFIER KITAn opponunity to buy a 10 watts per channel stereo amplifier kit whichis suitable for use with a ceramic cartridge The antplitier utilises provenMullard modules and is available at a very competitive price The amplifierkit comes complete with instructions and includes a Mullard LP1183stereo preamplifier module, two LPI 173 power amplifiers with integralhealsinks, a power supply. Zobel networks, front and back mountingpanels, a finished lascra panel, all contol potentiometers (bass, treble,volume and balance) switches, input, output and headphone sockets, wireand an easily assembled wrap atound cabinet to house the finished unit

Size approximately91/4" x Brit. x 4" p.,f 12.25

50 WATT MONODISCO AMP

f30.60p&p £2.70

Size approx. 131/4" x 51/4" x 61/4"50 watts rms 100 watts peak output Big features includetwo disc inputs, both for ceramic cartridges, tape inputand microphone input. Level mixing controls fitted withintegral push-pull switches Independent bass and treblecontrols and master volume.

I"a f.) (, (,) 1 ,, r) 0 c 4REINIORNBewrAen

20 x 20 WATT STEREO AMPLIFIERViscoumNunitinteaksimuWecabmetSilverlimhrmiymtiolsandpushbuttons with matching fascta red mains indicator and stem tack socketFunctions snatch for mit magnetic and crystal pickups, tape tuner and auxiliaryRear panel features fuse holder. OIN speaker and input sockets 20 x 20 wattsRMS 40 a 40 wens peak for use with 8 to 15 ohm speakers j. 31.90Site e 3" s 10" enema NEW feature -units mwincludes a built in four channel stereo sound facility [3 00 p&p

MullardAUDIO MODULES INBARGAIN PACKS

CURRENT

CATALOGUE

PRICE

AT OVER

ACCESSORIES ARE °OttAvADMIEE TO THOSECUSTOMERS WHEN BUYINGnue BARGAIN PACIIS

RPACK SEE OUR PRICESPACK I 2 x LP1I 73 I Ow RMS output power audio amp modules.r 1 LP1 t82/2 Stereo pre amp for ceramic And auxiliary input

OUR PRICE f5 00pop il 00.

2 PACK 2 2 x LP1173 I Ow RMS output power audio amp modulesa I LPI184/2 Stereo pre amp for magnetic ceraminc and auxiliaryinputs

illus. OUR PRICE f7 65 pop tioo

ACCESSORIES Suitable mains power supply pans. consisting ofmains transformer, bridge rectifier, smoothing capacitor and set of rotarystereo controls for treble, bass,volume and balance f 3.00 PI" El 50 P&P

Two Way Speaker Kit Composing of two 8" x 5" approx 4 ohmbass and two SrI" 15 ohm midrange tweeter with two cross -over capacitors

AVAILABLE ALSO TO PURCHASERS Per stereo pair 1.A neOF THE 10 o 10 AMPLIFIER KIT plus El 55 I. U

R323 EDGWARE ROAD, LONDON W221E HIGH STREET, ACTON W3 6NG

ACTON. Mail Order only. No callersALL PRICES INCLUDE VAT AT 15./

All items >unrest to availability Price correct atand subject to change without notice

All enquires Stamped Addressed Envelope.NOTE. Persons under 16 years not served without parent's authonsahon

30x30 WATT AMPLIFIERIN KIT FORMfor the experienced constructor complate in every detail, same facilitiesas Viscount IV. but with 3000 output 0.60.60 watts peak For use with 41015 ri441:,ohms

speakers f31 50 14P"444"/3 00

EMI SPEAKER BARGAINStereo pair 350 kit System consists 0,13" x 8" approx woofer with rolledsurround. 2'," approx Audas tweeter,crossover components and circuitdiagram frequency response 20 Hr

to 20 KHc Power handling 15 wattsAMS20 watts max8 ohm impedance

f18.25Per stereo pairf3 65 p&p

BSR P200Belt drive chassis turntable f25.50unit semi-au!omatic, cueing device p&p 12 60Shure M75 6 Magnetic Cartridge

'10 suit

0 f7.95n, Manual single play

,ecord deck with autoreturn and cueing lever lined with stereoceramic cartridge 2 speeds with 45 r pspindle adaptor ideally suited for home

or disco use P&PON PRICE f12.25 /2 75

BARGAIN OFFER,e,Ariston pick-up armmanufactured in Japan.

Complete with headshell.Listed price over f30.00.

OURPRICE

f11.95

MayPersonal Shoppers EDGWARE ROAD LONDON W2 Tel, 01-123 0432. 9.30am-5.30pla Closed all day Thursday ACTON. Mail Order only. No callers coons DESPATCHED TO MAINLAND ANON IRELAND ONLY

I

ii -y-IL

-electronics 56 FORTIS GREEN ROAD

TELEPHONE 01-883 3705 01-883 2289 MUSWELL HILL LONDON N10 3HNyour soundest connection in the world of components

NOW AVAILABLELow cost computer in kit form

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INCLUDED FREESample tape with extended machine

code moditor and disassemblerPrice includes RF modulator and

power supplyABSOLUTELY NO EXTRAS NEEDED

Also available ready assembled, testedand ready to goonly E249 + VAT

Build, understand, and programyour own computer for only asmall outlay

AVAILABLE SOON - COLOUR ADD-ON CARDEnables you to choose your foreground, the becir7ground colour anywhere on the screen. Flash any character on the screen at will. Full

ctocumentation and parts in kit form. Phone for details.STOP PRESS:- The latest edition of our 'STOP PRESS' is now available, and contains an up-to-date price list showing all the items that we stock.Just send an SA.E or phone for your FREE copy. Our catalogue is still available and if you're one of the few who haven't gota copy, order yourFREE copy today.

AR prices are EXCLUSIVE of VAT. Postage and pecking 30p (computers charged at cost). CALLERS WELCOME. Hours 5.00 ern -6.00 pen (enterthrough stationers). TRADE and EXPORT inquiries WINC011141. Phone your orders through our ONDER-R1140 line quoting your Aceees orBarclaycard number (AM. tel order C6).

Extra 4KMemory 8 x 2114only a8.00 + VAT

PLUSSuperboard II

onlyE1811.00 + VAT

8 x 4116only

f.49.90 + VAT

16 x 21L02only

E14.50 + VAT

2708only

E6.29 + VAT

Dynamic RAMS

4027 3.0140501200ns) 2.504050 (350ns ) 2.364080 (30Onsi 2.394116 6.74Static RAMS2102A 1.162102A-2 1.162111A-1 1.702112A-2 1.1321102 1.162114 5.174035 (1000nal

1074046 (260ne) 6.165257 (17.464044)

8810ROMS2513 (U.C.)2513 (LC.)MM5230CPU

808099002806602E -PROMS1702A027082716

6-M6.254.62

6.016.011

26.065.009.60

6.166.26

24.M

TV_ Controller6E698384 14.59Buffers74385 0.5274388 0.5274387 0.5274388 0.5281L995 0.5681L696 0.7081LS97 0.M81LS98 0.708T26 1408128 1,108195 1.578196 1.578197 1.5781913 1.57Interface8205 3.008212 2.608216 2.M8224 2.778228 4.138251 5.1168263 6.838256 5.1111

Maid RaeGeneratorsMC14411 5.67MM5307 11-311

UARTSAY -5-1013 0,...rsMM6303 5.64TIAS1301 INC 4.30

lbw INSTRvCCIONS coRs...h.kw -(01:p SA rtif- Egf..)/T OE

COrriPt.rff.tk ROTA

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sq(c-ocAT_ENJEA^10


Kit ReviewINTEGREX 2020 TAWithout doubt the most ambitious and one -of the most expensive kitswe've ever reviewed. Was it worth it? Read on and find out.

QUITE POSSIBLY the most rewarding kit we've everbuilt, extravagant claims? We think not, after solderingup some two hundred or so components and to have saidkit work first time, how satisfying can you get?

The kit in question is the Integrex S2020 TA StereoAmplifier Tuner. Integrex are past masters at audio kits.specialising in designs published in a certain 'venerable'electronics journal. Our kit was chosen carefully fromtheir range, taking into consideration cost, specificationsand apparent ease of construction. Obviously we had toavoid any previously published designs so we settled forthe 2020. The kit will arrive on your doorstep for just£59.95, not bad at all.

BEGINNER BEWAREFrom the outset it must be said this kit is not for thefaint-hearted or clumsy solderers. It is a kit on the grandscale. The instructions assume a basic familiarity withelectronics, quite the opposite philosophy to Heathkit

who reckon that if you can read you can build their kits.(And rightly so for their instruction manuals are the bestwe've ever seen.)

Now for the gripes, the kit arrives carefully boxed, allof the electronic components neatly packaged in theobligatory plastic bag. Unfortunately none of the dozenor so bags bore any identification labels, confusionreigned. Worse was to come. Having warmed up the HEsoldering iron and selecting what seemed to be theappropriate plastic bag, construction commenced.About half way through the first hundred or so resistors itappeared that the bag being used had more bits thanwas necessary for the first stage, indeed several bits didnot seem to belong anywhere. We still have a couple ofresistors, three transistors and good few nuts, bolts andround things left over. We've often discovered thingsmissing in the past but never a surplus, even allowing forthe modifications Integrex suggest for the unit they stillremain a mystery. Perhaps they are spares, if this is sothen this is a trend we shall encourage.

As it arrives. Unfortunately none of the plastic bags bear any labels, confusing isn't it?


THE ELECTRONICSBack to business, the electronics are all built up onto twoglass fibre PCBs, one for the main amplifier and a muchsmaller one for the tuner. (Incidentally the amplifier isavailable as a kit on its own). The PCBs deserve amention, they are plated, screened and a componentlegent printed on the topside. All this makes them apositive delight to work with. Construction of theelectronics is to work with. Construction of the elec-tronics is the longest job, allow two or three evenings forthis and don't forget to tick the bits off as you go along.

The PCB with the first batch of resistors soldered down. Notethe excellent component legend.

One or two comments about the electronics before weget to the metal work. The toroidal transformer, asplendidly made device, was just a touch too big,probably this was only the thickness of the coveringmaterial but it did necessitate making the mounting holea shade larger. Secondly, lntegrex would be well ad-vised to supply some IC holders in the kit, they wouldadd pennies to the cost but might save hours fault-finding. Lastly the holes for the PCB mounting pots weretoo small, they had to be opened out at quite a late stagemaking life a bit difficult. Small points but they are soeasily remedied.

The mains supply area. The toroidial transformer was a slightly'snug' fit.

BOLT UPOn the home stretch now, the well made aluminiumchassis pan accepts all of the various bits and pieces.The channel selector assembly is a trifle fiddly to bolt up

30

and align with the front panel. Apart from that every-thing just falls together. Integrex suggest that whenmounting the pots the front panel should be used toensure that everything lines up properly, we didn't, andsuffered the consequences accordingly.

Once assembled, and before the tuner section isconnected the amplifier is set up. This could not beeasier, consisting of about four current and voltagereadings and two preset pot twiddlings. Everythingchecked out OK first time. How about a fault check -listfor the not -so -fortunate I ntegrex?

Next, the tuner section is connected, this is based ona pre -aligned tuner head, the only adjustments to bemade are for AFC and background noise. Both are madeby ear so no problems here, again a first time success.

All that remains is to bolt up the front panel and slidethe whole unit into its attractive solid mahogany case.Our front panel was just a little too long for a comfortablefit, a couple of strokes with a file soon cured that.

The tuner area. The pre -aligned tuner head saves a lot oftrouble.

VALUE FOR MONEYSo, to the important bit. It works extremely well,concensus in the office was most favourable, theclaimed 20 watts per channel all seemed to be doingtheir stuff. Generally it seemed to live up to its

The completed amplifier/ tuner prior to sliding into its case.

specifications and produced a very pleasing sound. Thetuner section was comparable with any other set wehave heard, costing up to three or four times as much.The use of a varicap tuner makes it very convenient touse. How about a little light behind the tuning scaleIntegrex?


Kit ReviewConclusion? The kit represents very good value for

money, if you are in the market for a stereo tuneramplifier look no further. One or two little things outlinedearlier need to be looked at by the manufacturers butapart from that we have no hesitation in recommendingit. Remember though, it is not for the absolute beginneryou at least need to know how to solder. All of thecomponents supplied are of the highest quality andshould give years of trouble -free service. In case ofproblems Integrex offer a repair service. The amplifierspecifications are given below. Integrex can be found at:Portwood Industrial Estate, Church Gresley, Burton onTrent.

SPECIFICATIONSAmplifier SpecificationSensitivity to give 20 watts into 80

Magnetic pick up 2.5mVTape input 1 30mVRadio 1 30mV

Input impedance 47k @ 1 kHz

Tape output (low level output) 1 30mV viaunaffected by tone or volume controls

Tone controlsTreble + 10-1 2dB at 1 5kHzBass ± 1 6dB at 30Hz

Balance ± 8dB one channel relative to other

Unweighted signal-to-noise of complete amplifierwith full amplifier bandwidth-60dB magnetic pickup-72dB radio

Power Output (both channels)>20+ 20 watts into 80 intermittent sine wave16 4- 1 6 watts into 80 continuous sine wave1 5+ 1 5 watts into 1 50 continuous sine wave

Harmonic distortion1 5 watts into 1 50 0.05% at 1 kHz20 watts into 80 0.09% at 1 kHz

Low level distortion0.16% at 1 kHz 50mW into 1 500.07% at 1 kHz 50mW into 80

Frequency response (16 + 16 watts into 80)-1dB14Hz to 22kHz-3dB less than 7Hz to 35kHz

4. 7 k0 Stability - will drive electrostatic loudspeakers

Output impedance less than 1 milli ohm

Dimensions (sleeve)Width 391mm 1 5.4inHeight 69mm 2.7inDepth 170mm 6.7in HE

20Hz to 100MHz - £7755

It's an incredible price for a very credible frequencycounter ... Continental's MAX -100.

It comes to you from a major American corporatilmand has one operating range, and one only: 20Hz to100MHz, minimum. (Guaranteed.)

So we've pensioned off the range selector, and fittedthe sharpest of LED displays. (Sheer brilliance.)

We've also designed the MAX -100 around the latestin LSI technology; and built-in high sensitivity, with a30mV trigger level; protection against high transients;and an outstanding accuracy of 3ppm. (What performance!)

But, most importantly, the MAX -100 is totallyautomatic and available now. In fact, you could have onetomorrow.

Hesitating? Just take a look at the spec. Then, if you'reready to order immediately, call us on (0799)21682. And

1+ VAT 15% & P & P. £90.91) Export + 10%

your MAX -100 could be on its way, today! (Continentalare great performers, too.)

For data, please use our enquiry number.Specification * Frequency range 20Hz to 100MHz Inputimpedance 1 megohm shunted by 56pF Sensitivity 30mV to300mV r.m.s., from 20Hz to 100MHz Timebase accuracy 3ppm"Temperature stability 0.2ppm per °C Max. ageing rate 10ppmper year Overfrequency indication Low battery power alarm Operates from a.c. mains, dry or rechargeable cells, or 12Vd.c.auto battery Dimensions 45 x 187 x 143 mm. Options: 12Vauto. cigar lighter adaptor; battery eliminator/charger; r.f. antenna;low -loss r.f. tap; and carrying case.

Quality. At a low, low, price.

CSC C S C (UK)

) H, ',A..(0799)21682


The NEWA/larshall's 79/80 catalogueis just full of componentsand that's not all .

. our new catalogue is bigger and better than ever. Within its60 pages are details and prices of the complete range ofcomponents and accessories available from Marshall's. ""'These include Audio Amps. Connectors, Boxes, Cases, BridgeRectifiers, Cables, Capacitors, Crystals Diacs. Diodes. Dis-plays, Heatsinks, I Cs. Knobs. LEDs, Multimeters, Plugs,Sockets, Pots, Publications, Relays, Resistors, SolderingEquipment, Thyrtstors, Transistors. Transformers VoltageRegulators, etc., etc.Plus details of the NEW Marshall s 'budget Credit Card. Weare the first UK component retailer to offer our customers ourown credit card facilityPlus - Twin postage paid order forms to facilitate speedyordering.

Plus - Many new products and data.Plus 100s of prices cut on our popular lines including ICs.Transistors, Resistors and many more.If you need components you need the new Marshall "sCatalogueAvailable by post 65p post paid from Marshall's, Kingsgate,House, Kingsgate Place, London NW6 4TA. Also availablefrom any branch to callers 50p.

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iarshalltter tweets ateettsete componentstirter80

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Retail Sales: London: 40 Crinklewood Broadway, NW2 3ET. Tel: 01-452 0161/2. Also 325 Edgware Road, W2. Tel: 01.723 4242. Glasgow: 85 WestRegent Street, G2 2Q0. Tel: 041-332 4133. And Bristol: 108A Stokes Croft, Bristol. Tel: 0272 426801/2.

S-2020TA STEREO TUNER AMPLIFIER KITSOLID MAHOGANY

CABINET

A high -qualitypush-button FMVaricap Stereo Tunercombined with a 24Wr.m.s. per channelStereo Amplifier.As reviewed in this issue.Brief Spec. Amplifier Low field Toroidal transformer, Mag, input, Tape In /Out facility (for noisereduction unit, etc.), THD less than 0.1 % at 20W into 8 ohms. Power on /off FET transient protection.All sockets, fuses, etc., are PC mounted for ease of assembly. Tuner section uses 3302 FET modulerequiring no RF alignment, ceramic IF, INTERSTATION MUTE, and phase -locked IC stereo decoder.LED tuning and stereo indicators. Tuning range 88-104MHz. 30dB mono S / N @ 1.2 1\/. THD 0.3%.Pre -decoder 'birdy' filter.

PRICE: £59.95 + VATWe guarantee full after -sales technical and servicing facilities * High performance Amps, Tuners and Dolby units available.

repave for B.B.C. Quadrophonic Broadcasts - Send for details of our Ambisonic H.J. decoder

'Please send SAE for complete lists and specificationsINTEGREX ura. Portwood Industrial Estate, Church Gresley,

Burton -on -Trent, Staffs DE11 9PTBurton -on -Trent (0283) 215432 Telex 377106

WIN:LAMM


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SOUNDOPERATEDSWITCH

Sound activated switches are usedin many applications, some typicalexamples being voice operatedtape recorders, baby alarms, burg-lar alarm systems, and VOX ,,voiceoperated switching) systems ofradio transmitting / receiving in-stallations. The simple circuitshown here will operate at a dis-tance of up to about 2 or 3 metres

Short circuits

from a voice of average volumeslightly less if the xtal microphoneinsert is replaced by a medium orhigh impedance dynamic type).

Signals produced by themicrophone are amplified by a highgain amplifier which uses twostages of common emitteramplification. These two stages arebased on Q1 and Q2 and use astraight forward capacitively coup-led arrangement. Both transistorsare operated at low collector cur-rents in order to give a low noiselevel and quiescent current con-sumption. C3 rolls off the highfrequency response of the circuitand aids good stability.

The output from Q2 is coupled

04BC179

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to a thi d common emitter stage byC5. This third stage is based onQ3, and is biased by R6 and R7 toa point where Q3 is virtually cut off.There is thus very little voltagedeveloped across load resistor R8,and the input voltage fed to Q4 viaD1 is insufficient to switch on thisdevice and activate the relay whichforms its collector load. However,when sounds are received by themicrophone, a strong signal isreceived at Q3's base, causing it toconduct heavily on positive goinginput half cycles. This produces aseries of strong negative pulsesacross C4, charging up this com-ponent to an adequate level toswitch on Q4 and the relay. A pair

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of relay contacts are used to controlthe supply to the slave equiptnent.

C4 charges via the fairly lowimpedance of Q3 and R9, givingthe circuit a fairly fast attack time.C4's discharge path is through therelatively high impedance of Q4'sbase emitter junction giving a de-cay time of a second or two. Thusthe circuit responds rapidly when asignal is initially received, but therelay does not cut out during thebrief pauses that occur during nor-mal speech.

The quiescent current con-sumption of the circuit is onlyabout 250 µA, but this rises toabout 35 mA when the relay is'activated.

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rent is fed into the base terminal of With SW1 in the "10" position, a current is reduced to 100 uA andthe test device. This causes a larger nominal base current of 1 mA is fed 10 uA respectively, giving the cor-current to flow in the collector to the test device, and it must have respondingly higher full scale gaincircuit of the transistor, and the a current gain of 10 in order to values.current gain is equal to the collec- produce a collector current of 10 PNP and NPN transistorstor current divided by the base mA and give full scale deflection of require opposite supply polarities,current. If SW2 is depressed, a ME1. Lower levels of current gain and SW3 is used to switch thebase current will be provided to the give a proportionately lower meter supply polarity to suit the typetest device by whichever resistor reading. With SW1 in the "100" being tested and to connect ME 1

leakage testing, except that a cur- R 1 to R3) is selected by SW1. and "1,000" positions, the base with the correct polarity.111111111111111 lllllll 111111 lllllllllllllllll 111111111111111111111111111111111111111111111111111111 lllll III lllll 11111 llllllll 1111111111111111111 llllll 11111111 lllllll II llllll 11111?

This very simple transistor testermeasures DC current gain in threeranges, with full scale values of 10,100 and 1,000. It will also showwhether or not the device undertest has a high leakage current.

The basic tests for a transistorare very simple and in order to testfor high leakage, it is merelynecessary to connect a voltageacross the emitter and collectorterminals of the test device, andthen measure the current flow. Inthis circuit BY1 is the voltagesource, and ME1 registers the cur-rent flow. R4 is a current limitingresistor which protects ME1 andthe test device from passing anexcessive current.

Silicon devices have extremelylow leakage currents, and if there isany deflection of ME1 when testinga silicon transistor it certainlymeans that device is not functionalor is connected incorrectly). Ger-manium devices have somewhathigher leakage currents, and a verysmall deflection of ME1 is accept-able when testing this type of tran-sistor.

The test for DC current gain,Hfe) is basically the same as for


LCD CHRONO

EsoNo CALENOAF4STAR T STOPSET

MIN SEC 1/100

TIME LIGHTL A P RESET

MARTEN

We feel we've got to tell you carefully about this offer. Why?Because our price is so enormously lower than anywhereelse you may suspect the quality.

The display is LCD and shows the seconds as well as thehours - and minutes - press a button and you'll get thedate and the day of the week.

Press another button for a couple of seconds and youhave a highly accurate stopwatch and hundredths of asecond displayed and giving the time up to an hour. There isa lap time facility as well - and of course a back light.

Our Chrono comes complete with a high grade adjustablemetal strap and is fully guaranteed.

£11.95

ALARM-CHRONO LCDZETRON

QUARTZ

ALARM -CHRONOGRAPH START/STOPDATE

LIGHT DUAL TIME A L S T

MODE SELECT1 IMF SET/RESET

This new addition to our unbeatable selection of bargains isno ordinary LCD watch. It's a slim, multi -function, dual timechronograph alarm watch, no less.

This model will show hours, minutes, seconds, date, dayof the week, stop watch, split time, alarm and alternate dualtime zone - not all at once, of course. There is also a nightlight.

Hours, minutes, seconds and day of the week aredisplayed continuously, while'the date will appear at thetouch of a button. The day of the week is indicated by a flag.When used as a stopwatch, the maximum count is 0.1 secs.short of thirteen hours.

E19.95

To:LCD Watch OfferHE Magazine145 Charing Cross RoadLondon WC2H OEEPlease find enclosed my cheque / PO' for £11.95 (payableto HE Magazine) for my LCD Chronograph.

Name

Address

To:ALARM /CHRONO LCD WATCH OfferHE Magazine145 Charing Cross RoadLondon WC2H OEE

Please find enclosed my cheque /PO for £1 9.95 (payable toHE Magazine) for my Alarm /Chrono LCD watch.

Name

Address

Please allow 28 days for delivery


owe comm.

DIGITAL ALARM

(

THIS IS THE THIRD digital alarm clock thatwe are offering (we regret the earlier versionsare no longer available). We have sold thou-sands and thousands of these and our buyingpower enables us to offer a first rate brandedproduct at a really excellent price.

The Hanimex HC -1100 is designed formains operation only (240V / 50Hz) with a 12hour display, AM/PM and Alarm Set indica-tors incorporated in the large display. Aswitch on the top controls a Dim -Brightdisplay function.

Setting up both the time and alarm issimplicity itself as buttons are provided forboth fast and slow setting and there's noproblem about knocking these accidentally asa 'locking' switch is provided under the clock.A 9 -minute 'snooze' switch is located at thetop.

An example of this clock can be seen andexamined at our Charing Cross Roadoffices.

E10.60

CLOCK RADIO

Lmmisi '77

You probably won't believe us as we're sellingthe goods but we're going to tell you anyway'We have rejected eight clock radios for Mar-ketplace, they were all cheap enough but thequality was so poor that we couldn't have lentour name to them. However, we are now ableto offer another portable LCD Clock Radio toyou which meets our standards.

The clock is a 1 2 -hour one with AM / PMindicated and a back light. The radio isMedium Wave with very nice quality for asmall speaker. The alarm can be either abeep -beep type or the radio, there's also asnooze facility.

The cylindrical construction is in keepingwith the very modern styling. The tuning dialis actually incorporated into one of the endcaps!

We won't even mention the RRP - butjust check on comparable prices - you'll findours a bargain.An example of this Clock Radio can beseen and examined at our Charing CrossRoad offices.

£17.95

To: Hanimex Alarm OfferHE Magazine145 Charing Cross RoadLondon WC2H OEEPlease find enclosed my cheque/PO for£10.60 (payable to HE Magazine) for aHanimex Digital Alarm Clock.

Name

Address

To:CLOCK RADIO OfferHE Magazine145 Charing Cross RoadLondon WC2H OEEPlease find enclosed my cheque/PO for£17.95 (payable to HE Magazine) for myClock Radio.

Name

Address

All offers inclusive of 15% VAT and Postage


Car AudioManualMW/LWFull medium and long wave tuning. Com-plete with speaker and mountings. Suitablefor positive or negative chassis. Latestmodel.

1.00£10.25 + Post

Push -Button

MW/LW

T.

One LW. four MW buttons plus manualtuning. Complete with speaker and moun-tings Latest model, negative chassis only

£15.95 £1.00-T- Post

Stereo FM/Cassette+ MWStandard cassettes and FM in stereo plusmedium wave. Tone and balance controls.Fast forward facility on tape. Adjustableshafts. Suitable for 4 or 8 ohm speakers (notsupplied). This model is discounted else-where at £50 up.

1.00£40.95 +

£Post

Stereo

Speaker SetSuitable for above £4.00stereo unit. Good qualityin surface mounted (pair)casing, 5W nominal, + 70p Post8W peak.

Telescopic Car AntennaMulti -section standard type, suitable forangled mounting with locking key.

£1.60 + 30p Post

Metal Detector* Induction Balance Model

Built with sensitivity up to 10in onsingle coin; fitted with speaker andmeter; PP3 battery; 7in dia. searchhead. Telescopic stem. Excellentpin -pointing, positive reaction tonon-ferrous, negative reaction toiron. This model's normal price is£39.95!

£24.50 + £1.00 Post

All goods guaranteed one year10 -day money -back offer. Goodsex -stock at time of going to pressCallers by appointment only pleaseSend s.a.e. for illustrated leaflet.

Minikits Electronics Ltd.88H Hainault Road

LeytonstoneLondon, E.11

35

28 Tested Transistor Pro-ject £1.55Richard Torrens. The projectscan be split down into simplebuilding blocks which can berecombined for ideas of yourown.

Books fromthe HE BookService

Electronic Projects for Be-ginners £1.85F. G. Rayer. Divided into 'NoSoldering Projects,' Radio andAudi.° Frequency, Power Sup-plies and Miscellaneous.

Practical Electronic Calcula-tions and Formulae . £2.55F. A. Wilson. A valuablereference for the home andlaboratory, containing all themost frequently used, andsome of the less well knownelectronic formulae and calcu-lations.

Popular Electronic Projects£1.75

R. A. Penfold. A collection ofthe most popular types ofcircuits and projects usingmodern, inexpensive and freelyavailable components.

Digital IC Equivalents andPin Connections . . £2.85Adrian Michaels. Covers mostpopular types and gives detailsof packaging, families, func-tions, country of origin andmanufacturer.

Radio Stations Guide £1.75B. Babani and M. Jay. An inva-luable aid to everyone with aradio receiver helping them toobtain maximum entertain-ment, value and enjoymentfrom their set.

Linear IC Equivalents andPin Connections £3.10Adrian Michaels. Gives mostessential data for popular de-vices.Electronic Security Devices

£1.75R. A. Penfold. Full of construc-tional circuits covering the mostbasic security systems to theUltrasonic and Doppler Shiftsystems.How To Build Your OwnSolid State Oscilloscope .

£1.80F. G. Rayer. The book containsconcise practical instructions sothat even an inexperiencedhobbyist can construct a fairlysophisticated instrument withthe minimum of difficulty andexpense..50 FET (Field Effect Tran-sistor) Project £1.55F. G. Bayer. Contains some-thing of interest for every classof enthusiast. Short Wave Lis-tener, Radio Amateur, Experi-menter or audio devotee.50 Circuits Using 7400Series ICs £1.65R. N. Soar. The author hasmanaged to compile no lessthan 50 interesting and usefulcircuits using this range of de-vices, covering many differentaspects of electronics.

Essential Theory for theElectronics Hobbyist £1.55G. T. Rubaroe gives the hob-byist a background knowledgetailored to meet his specifitneeds.

Beginners Guide to BuildingElectronic Projects . £1,65R. A. Penfold. Covers com-ponent identification, tools,soldering, constructionalmethods and examples ofsimple projects are given.

50 Projects using IC CA3130£1.25

R. A. Penfold. Describes audioprojects, RF project, TestEquipment, Household andmiscellaneous circuits.

IC 555 Project .. £2.05E. A. Parr. Circuits are given forthe car, model railways, alarmsand noise makers. Also coversthe related devices 556, 558and 559.

Second Book of CMOS ICProjects £1.80R. A. Penfold. Following in thesuccess of the original CMOS,projects book we present thesecond volume covering allaspects of CMOS technologyfrom multivibrators to trig-gering devices.

Note that all prices include postage and packing. Please makecheques etc. payable to Hobby Electronics Book Service (inSterling only please) and send to:

Hobby Electronics Book Service, P.O. Box 79Maidenhead, Berks.

HE BindersNow that Hobby Electronics is in to itssecond volume the need for a good strongbinder is greater than ever.

In line with our policy of value formoney, we will outline some of the altern-ative uses an HE binder can be put to.

(1) Blocking cat -flaps to prevent straycats from entering your kitchen.(2) Blocking off car radiators during coldweather.(3) Temporary bridges for model trainlayouts.(4) Emergency umbrellas.(5) A hat for HEBOT.

Of course, you could use them for keeping thosevaluable copies of HE in pristine condition, but that's upto you.

To become the proud owner of these blue bound, goldembossed works of art just send us £3.20 without delay.

Send your cheque, postal order, pools win or goldfillings (to the value of £3.20) to;

Hobby Electronics Binders,145 Charing Cross Road,London WC2H OEE.


HobbyElectronics

DIGITAL FREQUENCYMETER

HDF"Arl

The most sophisticated piece of test gear toappear in HE so far! Don't let that put you off,our main project next month will be very simpleto build and will cost a fraction of a commer-.cially made unit. Once calibrated (that's adoddle too) it will accurately measure frequen-cies up to 10 MHz in a series of switchedranges. Now you will be able to measure theoutput of those oscillators, calibrate test gear,even use it to indicate frequency on Long Waveand Medium Wave radios. Why wait anylonger? This one is for you.

INTERCOMUntil CB gets legalised you will have to contentyourself with this really superb intercom. Prac-tise your 10 code, try some slang, we gauranteeit will not contravene any Post Office regula-tions. Seriously though, a really good two -wiredesign that will not leave you so poor trhat youcan't afford the batteries. It features a callingfacility and a massive 2 watt audio output.Perhaps we should have called it a PA system!

RADIO CONTROLSPEED CONTROLLERDon't worry. The radio control system is com-ing, meanwhile, how about this neat and simplesolid-state motor speed controller for existingsystems. If you've got an R /C car with electricmotor drive this will be just what you're waitingfor.

PROJECTS SPECIALNext month we hope to bring you news of theHobby Electronics Projects Special - Volume1. After months of research we have come upwith what we believe will be the last word inspecials, and all for just £1.25.

SLOW SCAN TV

Almost exactly 50 years ago a new inventionwas demonstrated for the first time. It consistedof an unweildy mixture of bits and pieces thatwould not have looked out of place in a scra-pyard.

This invention was called a 'Televisor' andby now you may have guessed the inventor'sname, Logi Baird. His system for transmittingmoving pictures unfortunately lost the race forcommercial success to the all -electronic sys-tem, the forerunner of our present system.

If you thought the Baird system is now littlemore than a historical curiosity you would besadly wrong. Unbeknown to most of us deve-lopment of the Baird system has been ploddingalong steadily these past fifty years. Theimprovement in available technology has madefurther investigation very worthwhile and we'resure you'll find next month's feature on SlowScan Television very interesting. It is one of thefew fields where the amateur can still make animportant contribution.

ELECTRONIC IGNITION

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After this month's feature on automotive elec-tronics we are following it up with a reallyprofessional design for an electronic ignitionsystem. We won't make any extravagant claimsfor this unit, we don't have to, it will speak foritself.

NEGATIVE IONSNext month we go into the health business,with a review of a kit that will change your life.

We've had a steady stream of inquiries aboutnegative ion generators in recent months. So,by popular request, before your very eyes, wewill review the latest in personal negativeionisers. Called the 'Fusion', the ioniser isavailable both in kit form and ready built. It's acompact (41/2 inx21/2 inx1 V4 in), battery operated -unit complete with a magnetic fixing pad, soyou can even use it in your car.

The claims of the effects of negative ions aremany and various. Once we've got our sol-dering iron out of hock and built the box oftricks, we'll see how many of these claims wecan verify.

It's well known that increasing the density ofnegative ions hurtling around your ears canmake you feel more awake and alert and dispel!the gloom of a smoky atmosphere. They have tobe negative, mind you. Positive ions have theopposite effect.

It is also claimed that negative ions can, insome cases, alleviate asthma, allergies andmigraine. We have our doubts, but we're goingto try it out anyway. By inhibiting the growth ofbacteria, they are also supposed to cut downinfections caused by air -borne germs. Well,that's a lot to live up to, but watch this spacenext month (give or take a few' pages) for ourfindings on this new kit.

The April issue will be on sale March 14th'The items mentioned here are those planned but circumstances may affect the actual contents


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AS AN INDUSTRY, the world's car manufacturers havealways been a pretty conservative bunch. That's not tosay that they don't expend a great deal of money andeffort on research and development, but the fact is thatthe nature of their market makes them extremely reluct-ant to take any risks in terms of putting untried innova-tions into production. Mud sticks in the automotivebusiness, and a reputation for unreliability due tomalfunction of some insufficiently tested piece ofequipment would be as easy to acquire as it would behard to shake off. With very few exceptions, then, themotor industry prefers to tread a safe path and use onlytechnology that has been proven in practice over a longperiod.

The potential for the utilisation of electronics in motorvehicles is enormous. In all probability, but for thecaution and reticence of the major auto makers, many ofthe possibilities could have been realised in practical usesooner than they have been. Both specialist electronicscompanies and 'in-house' research departments of thecar firms have devised numerous auto -related applica-tions for microprocessors and other types of electroniccomponents, in some instances replacing conventionalsystems but in others creating entirely new functions.Only in the last few years have these ideas filteredthrough on to the production line, and then mainly dueto outside influences.

Taking a broad view, development has been going onin all three of the world's main motor production centres- the USA, Europe and Japan - but local conditionsand pressures have tended to concentrate efforts indiffering directions. For instance, due to more congestedroads and higher fuel prices, European and Japanese

cars have always been designed in a way which makesthem much more fuel -efficient than their Americancounterparts. Oil shortages and ever tightening engineemission controls in the last few years have left theStateside giants frantically scrabbling for radical altern-atives to keep their own products viable in the face ofcompetition from the imports. Along with lighter, smal-ler, aerodynamically cleaner bodies and advances inmechanical engine design, electronic ignition and fuelcontrol systems offer them salvation. In Japan, evenmore stringent emissions regulations have preoccupiedthe local manufacturers. In Europe, by comparison,much less outside pressure has been brought to bear,certainly in terms of governmental legislation, althoughof course the overall energy situation has been just asprominent in the designers' minds. Consequently,implementation of electronic options has been moreselective and deliberate. A further difference betweenEurope and the US is that few European car companieshave extensive in-house electrical and electronics de-partments, unlike their American counterparts, thoughmajor independent electronics firms have divisionsspecifically given over to automotive work.

HISTORYThe history of electronics in cars goes back to the lateFifties, when the old DC dynamo -type generator beganto be replaced by the alternator, which incorporated atleast a semiconductor rectifier, if not at first an integralelectronic voltage regulator. Alternators caught on in anincreasingly big way, but nothing else of note happeneduntil 1967 when the first electronically controlled fuel


injection system went into mass production. Bendix inAmerica had patented the idea in the mid -Fifties but itwas the German company Bosch who put theory intopractice.

Electronic ignition was the next major development.Transistor ignition systems using an induction pulsegenerator had been introduced as early as 1959 but itwas the end of the next decade before any entered seriesproduction, and then to begin with only 'transistor -assisted' types retaining the mechanical contact -breakerpoints. Contactless designs came next and many kindsof both inductive and capacitive discharge variantsproliferated on the accessory market. As original equip-ment, contactless transistor ignition became almostuniversal on the US scene by 1975 but is still onlyslowly infiltrating the European assembly lines.

Alongside the primary components in the late Sixtiesand early Seventies came a sprinkling of ancillarydevices - electronic turn signal flasher units, wind-screen wiper intermittent switching systems and quartzclocks, for instance - but the widely predicted elec-tronic revolution did not materialise. There was a steadytrickle of electronic gadgetry on to the accessorysidelines but, until very recently, no large-scale break-through in the OE field.

ENVIRONMENTAL PRESSUREThe last couple of years have brought far-reaching anddramatic changes, particularly on the other side of theAtlantic. Environmentalist pressures, and those ofrapidly increasing petrol scarcity and price, have madeelectronically governed fuel injection systems such asBosch's several 'Jetronic' variations more and moreattractive to designers of spark -ignition engines. Suchset-ups enable very precise and effective control of apetrol engine's fuel supply. In conjunction with deviceswhich monitor exhaust gas content, closed -loop feed-back can be established so that an engine's fuel /airmixture can continuously be regulated at the optimum

Fuel pump

Fuel fitter

Auxiliary -airvalve

Air -flowsensor

Cold -startInjector

Pressure regulator

Injector High-tensiondistributor

QThrottle -switch n'Thermo -time

switch

Airtemperature

TT

Temperature sensor

Rotational -speedsensor

Referencemarksensor

Electroniccontrol unit

Ignitioncoil

Starting switch

Simplified diagram of the Bosch "Motronic' system.

point for emissions and economy. On the ignition front,too, a major transition is in progress - from merelycontactless ignition to a much more sophisticated typewhich, as well as creating and supplying a powerfulspark, replaces conventional mechanical timing adjust-ment by a fully self-governing electronic timing system.

ENGINE MANAGEMENTPartly thanks to technology derived from the US spaceprogramme, there is now a sufficiently strong electronicarmoury to deal with the difficulties of in -car service. The

The prototype display for ALI. It shows both directional instructions andpictorial warnings of potential road hazards.


The control box for the Lucas electronic Fuel Injection system.

motor vehicle environment puts relatively tough de-mands on semiconductors, and perhaps one reason forthe delay in introduction of major systems was theformer dearth of reasonably -priced and dependableparts. Such components are now available and, togetherwith the perfection of LSI (large-scale integration)circuitry, they have made viable the installation of anon -board microprocessor, so designed as to regulateboth the fuel /air and ignition systems simultaneouslyand in complementary fashion. This is the 'electronicengine management system' or 'integrated enginecontrol', which will be seen on increasing numbers ofEuropean cars in the next few years.

If a vehicle has engine management plus other,subsidiary electronic components, the idea of combiningall together in a 'central electronic system' is attractive,for reasons of both cost-effectiveness and function.Where a number of information inputs from variouspoints on the engine and running gear of a vehicle arerequired by different systems, feeding them all into acentral electronic processor obviates the need for waste-ful duplication of individual sensors and connections.For example, an input for engine speed is required notonly for ignition timing but also for fuel injection, as wellas automatic transmission if the vehicle is so equipped.

Taking the idea a step further, intermediate informa-tion from the electronic data-processing of one sub-system may be utilised as the input for others. Dividingthe inlet airflow by the engine speed, for instance, givesdata about engine load, which may be usefullyemployed as an input signal for electronic ignition andan electronically -controlled automatic transmission. Thecentral electronic system will enable many functions tobe dealt with in more sophisticated ways than at present.Common use of housings, connectors and even com-plete functional 'blocks' will yield not only cost reduc-tions but increased reliability.

The possibilities are exciting. A variety of separatefunctions (e.g. anti -lock braking, cruise control) can behandled by a central system. So too can all the informa-tion currently given by conventional instrumentation,plus additional computations outside the scope ofnormal gauges. Vehicle speed, engine speed, watertemperature, oil pressure and temperature, distancetravelled and so on can easily be derived and displayed,

40

and only simple computations are necessary to producefurther data such as ETA at a given destination, fuelconsumption at any instant or projected quantity of fuelnecessary to complete a journey. Additional sensors canadd warning capability for things like incorrect level offuel, oil, coolant, brake fluid, etc, brake lining wear andeven tyre pressure; monitoring operation of all bulbs andlamps is equally simple. A check can be fed into a centralelectronic system of virtually every sub -system andfunction on the vehicle. To avoid baffling the driver withtoo much information at once, a single panel display cangroup the various items of feedback according to relativesignificance or potential danger and suppress those notwanted for normal driving, only displaying them when amalfunction arises in the relevant area or when re-quested to do by the driver.

COMPUTER CONTROLUntil recently, the circuitry used in car electronics waslargely analogue type. Increasing use will be made ofdigital circuits, as in modern computer equipment,facilitated by LSI. Currently, two distinct methods ofrealising the central electronic system concept are beingexplored, termed a) 'single purpose computer' and b)'microprocessor' systems. Both consist of MOS (metaloxide semiconductor) based LSI components and so-called 'peripherals' (pick-ups, sensors, etc).

In the single purpose computer system, each in-dividual function has a separate computer circuit, whilea central storage element holds only the data for thespecific vehicle along with certain fundamental func-tions which bring about effective interaction of thevarious individual data processors. The whole systemcan be built from standardised parts and be expandedwithout difficulty.

The microprocessor system uses one central com-puter for all its range of component systems: this holdsnot just the vehicle data but programmes for each of theindividual functions. The main benefit of this type ofdesign is one of economy both of cost and space when alarge number of sub -systems are required; it is alsohighly flexible, as the programme can be altered by asimple change in the central element.

HERE TODA YThere you have an overall view of trends and likelydevelopments. Much has already been achieved, andsome of the specific points mentioned deserve a closerlook. The name 'Bosch' has already cropped up once ortwice, and certainly this firm is in the forefront of theEuropean, if not world, scene. Two of their most in-teresting projects that have reached production are'Motronic' and 'ABS'.

Motronic is already in service on the BMW 723i. It isan integrated engine control system consisting of amicroprocessor, data and programme memory andinput/output circuit. Sensors provide it with informationon inlet airflow, engine speed, crankshaft position, andengine and intake air temperatures: it then interpretsthese data and continually, at minute intervals, regulatesthe quantity of fuel being injected and the point in thecombustion cycle at which ignition is taking place, by;reference to predetermined programmes. In other wordsit provides highly accurate and stable management of

,the two essential engine processes.Advantages to the driver stem from Motronic's ability


Electronics On Wheelsto distinguish particular engine conditions - idling,cold -running, over -running and accelerating - from'normal' running, and compensate accordingly. In,practice this means instant starting and totally smoothrunning during warm-up, regardless of changes in load,circumstances or ambient conditions, the engineoperates without any 'flat spots' or hesitationimmediately it is set in motion, in winter and summer.'Advantages to everyone include impressive reductionsin fuel consumption and pollution.

The Motronic system is designed to match the life ofthe engine, and needs no servicing whatsoever. In factthe only maintenance requirement left on the electricalside of the engine is routine renewal of spark plugs.Motronic additionally makes it possible to adapt enginecontrol to deal with possible future requirements, suchas use of alternative fuels or compliance with revisedexhaust emission standards.

ABS means, if you untangle the German initials,anti-skid braking. Under development since 1970 inconjunction with BMW and Mercedes-Benz, it _utilisessensors to measure the speed of wheel revolutions andsend signals to an electronic control unit, which dis-tinguishes whether the wheels are tending to lock as thebrakes are applied or are still turning. In the light of thisinformation, the appropriate amount of braking force isthen applied or removed from the relevant wheels by ahydraulic unit.

On the road, ABS shows to greatest advantage underwet conditions, when stopping distances are oftengreatly improved. The system is especially useful incompensating for clumsy or unskilled driving, as it helpsmaintain directional stability even if the brakes areapplied whilst cornering. Technically the circuitry isfail-safe: if a fault in the electronics should by somechance occur this is detected before the brakes areapplied, a warning light is activated and the brakesrevert to full normal operation. Bosch claim that, insafety terms, ABS is 'the most important developmentsince the seat belt'.

ALIAnother Bosch project which is still at the research stagebut could rapidly be put into operation if given the nodby government is known as ALI. Don't ask what theinitials stand for this time, but the concept is of a driveraid that gives up-to-the-minute traffic reports and infor-mation about weather conditions on the roads ahead.The computers this time are not in the car but are linkedto series of inductive loops set into the surfaces of majorroads. As an ALI-equipped car passes over each of theseloops, a bleep from its information receiver alerts thedriver and reminds him to check his ALI screen forupdated information - it may, for instance, advise himto turn off at the next junction. All the driver has to do toget continual route guidance is, when commencing histrip, to switch on the device and key in numberscorresponding with his destination.

Installation of ALI would, its makers estimate, costabout £30,000 per mile on the current motorway andmajor road network, or about 1% of the cost of road -building (only a fraction of which would be accounted forby the actual electronic hardware). The on -vehicleequipment should cost between £70-100 on a mass:produced basis, and in view of impressive -sounding.estimates of an up to 10% overall fuel saving on amotorway network, plus a reduction in both driver


frustration and accidents, the whole system ought to payfor itself within a few years.

HOME GROWNThe leading British auto -electrical company is, without adoubt, Lucas. They, too, have extensive past experiencewith electronic ignition and petrol injection systemsincluding a joint project with Bosch, the L-Jetronic fuelinjection. Foremost among their own current develop-ments is their latest microprocessor controlled injectionsystem which is based on digital circuitry of the typementioned earlier, rather than analogue as on previousvariants. The control unit incorporates the latest LSItechniques, using just two chips to contain all the mainfuelling functions. The digital design, Lucas claim, pro-vides more precise control of the fuel supplied to eachengine cylinder than was previously attainable. The newsystem is already in production for Jaguar XJ 1 2 andXJS models, in which applications it has met with awarm reception from the motoring press, and is alsobeing fitted to SD 1 Rovers for the US market.

In the near future Lucas propose their own version of.the total 'engine management' package, combiningignition control with the injection on one microproces-sor. They point out the comprehensive diagnostic facilitythis will allow, and make the bold prediction of fuelconsumption gains of as much as 25%. They emphasisethat to make optimum use of the instantaneous logicavailable, adjustments based on it must be made asquickly as possible - to this end, they have developed asolenoid with an operation time of well under half amillisecond, which they expect to play a big part inactuating engine control functions in the future.

STILL TO COMEA couple of more mundane applications of electronicsare also just around the corner. Lucas are at presentworking on electronic control of conventional carburet-tors to bring some of the benefits of the more sophisti-cated fuel systems to cheaper cars. Vehicle ConditionMonitoring ('VCM') will be available for smaller carswithin the next year or so; this will provide an illuminatedreadout for such things as fluid levels and brake liningwear, and give a check on correct operation of bulbs.

.o\1LInterior shot of the Aston Martin Lagonda instrument panel.Most of the secondary controls am operated by the labelledtouch pads on the console.

41

Electronics On WheelsASTON MARTINAside from the work being performed by the big auto -electronics specialists, some car firms in Europe havealready taken an initiative by buying -in electronic sys-tems from elsewhere. First, and most brave, were AstonMartin Lagonda. Their unique Lagonda - the world'smost sporting limousine or most luxurious sports car,depending on which way you look at it - has featured afully electronic instrumentation system right from thestart. (When the car was initially announced it wasintended to incorporate a trip information computer too,but problems in those early days with electromagneticinterference caused that idea to be shelved; now, withthe available improved technology, it could be rein-stated.)

The Lagonda's instrumentation package was de-signed exclusively for AML by a small firm in the USA. Ituses a single PCB mounting all instruments and warninglights: these include speedometer, tachometer, clock,total and trip odometers, along with readouts for batteryvoltage, fuel level, water temperature, oil pressure, oiltemperature, plus both internal and external air temper-ature. The speedometer and odometer readings may beselected in miles or kilometres per hour at will. Twobinnacles house touch -sensitive switchgear.

The display panel is blank when'switched off, lightingup with red LEDs when in operation. Instead of facingthe whole gamut of data all the time, the driver can toucha switch to select 'essential instruments' only, reducingthe information in front of him/her to speed, time andfuel tank contents. In this mode, the rest of the displayonly makes itself visible if a problem arises, in the eventof which the relevant readout flashes to attract attention.

AML use Lucas Opus electronic ignition at the mo-ment, and, regarding integrated engine control systemsand the like, take the view that they will adopt what theirsuppliers develop. One thing they do predict is the use ofLCDs in instrumentation.

EUROPEAN ELECTRONICSTalbot (ex -Chrysler Europe) were in a good position whilethey were still a subsidiary of the American parentChrysler Corporation to keep tabs on what was going onin the Stateside industry. Their Alpine models wereamong the first in the popular mass market to featurecontactless ignition as standard, and now the SX ver-sions of Horizons and Alpines are equipped with elec-tronic trip computers which, at the touch of a button,give readouts for journey time elapsed, distance cov-ered, fuel consumed, average speed and average rate offuel consumption.

By contrast, Citroen had no transatlantic connectiori.The totally electronic completely distributorless ignitionsystem fitted to the downmarket Visa and LN twin -cylinder models was conceived entirely within France, incollaboration with the Thomson company. It consistsmerely of two proximity detectors, a vacuum sensor, acoil and - the important bit - a computer. This prox-imity detectors respond to the passing of a metallic'slug' attached to the engine flywheel, sending a pulseto the microprocessor with each revolution. The vacuumsensor signals the varying state of engine load. Theelectronic control centre then chooses the appropriatetiming, according to engine speed and inlet manifolddepression, for the coil to send HT current to the spark

plugs, at the same time ensuring that it (the coil) is fedsufficient primary current to produce the desired secon-dary voltage. The system is cheap, absolutelymaintenance -free, and produces improvements inalmost all aspects of engine behaviour: fuel consump-tion, exhaust pollution, low -speed torque and accelera-tion, and cold starting (even with a partially dischargedbattery for it needs to be cranked at only 20rpm toproduce a spark). Work is continuing on versions forlarger engines.

CRYSTAL CONTROLOther ideas being muttered about on the Europeanscene at the moment include piezo-electric actuation ofthe injector valves in fuel injection systems, andreplacement of the conventional wiring harness or loomwith a single feeder wire, multiplexed signals and adecoder at each 'service' point. For instrument displays,electroluminescence seems likely to be the in -voguemedium, with digital circuitry but analogue -type visualpresentation. Talking gauges will surely come - TexasInstruments are already developing them in the States.

As repeatedly hinted at, the Americans are aheadof us at least in implementation of a

number of the possibilities. Right now a wide range ofelectronic add-on toys is available for fitment to theircars. If you happen to live on this side of the big pond butfind the lure of accessories such as electronic combinedanalogue /digital display instruments and trip com-puters irresistable, don't despair. At least one Britishconcern is importing them: Hatton Enterprises, ofLangwood House, Epsom Road, Ashtead, Surrey, whohandle 'Avatar' instruments and 'Prince On -BoardComputers'. Thanks to the conservation -orientatedpressures existing in the USA, virtually every car emer-ging from Detroit in 1980 has (as well as transistorignition) some kind of electronic fuel metering device,from a basic 'feedback' carburettor system to fullanalogue or digital electronic fuel injection. Otherelectronics applications proliferate - electronic levelcontrol, electronically tuned radios, electronic speedo-meters, electronically coded door and boot locks are justa selection of the stock and optional equipment availableon vehicles in dealer showrooms this year. Ford give thevalue of all the electronic components on a 1980 LincolnContinental Mark VI as around $1800 or nearly 10% ofits retail price.

The trend can only continue upwards. Anotherauthoritative American source estimates that the worldautomotive industry will use about $600 million -worthof semiconductor devices in the 1 981 model year, risingto $1 billion -worth per year by 1985 - a compoundannual growth rate of close to 30%. European crystal -gazers are hardly more cautious: Volkswagen, for in-stance, talk in terms of electronics constituting about7% of the average car's manufacturing cost by 1988,compared to around 2% today.

I started this article by talking about the car industry'searly reluctance to accept electronics. I'll finish bysaying that today it couldn't do without them. Com-puters are now extensively used in designing newmodels. They're even running the assembly lines (youmust have seen Fiat's brilliant 'Hand -built by Robots'advertising campaign). If there's any way to solve theautomotive problems of the next two or three decades,electronics will be the key. HE


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43

Touch SwitchBet you'll think this project's a touch of genius. Ten sequential outputs, orbuild it like a bistable. All under perfect, personal, fingertip control.

TOUCH SWITCHES have begun to appear in all kinds ofplaces . . . lifts have them, TVs have them; evenpersonal computers have them. Well, now you can haveone too, for the price of a couple of chips and a handfulof discrete components.

Now is your chance to get the world under yourthumb. Featuring up to ten sequentially selected outputsand an overiding reset input, the project is a cinch tobuild. Make one for fun or control your radio, Hi-Fi,goldfish, etc.

Many commercial touch sensors rely on the electricalmains for an energising field. This circuit can be pow-ered from a single nine volt battery, a PP3 will do, haslow current consumption, uses only a few cheap com-ponents and is simple to construct. Also, above all, it issafe.

CONSTRUCTIONTo avoid the introduction of stray circuit capacitancesand ensure reliable and repeatable operation, westrongly recommend that our PCB design is used. It isvery small and should be quite easy to make or cheap tobuy. There is only one link to make on the board. Makesure you get the diode and electrolytic capacitor the rightway round. That goes for the integrated circuits too. It isquite okay to use sockets, in fact we would recommendit. That way you can always use the chips again andanyway, sockets make substitution easy if (horror ofhorrors!) the project fails to work first time.

You can try different layouts for the touch sensors.We made up a special board. At its simplest, a touchsensor could consists of a piece of unetched PCB split

-iouchcontact'RESET'

R2

12

it' to,

-NAM- g

Rs

D1g LET

I 6

MR

C34 7OF


NOTES:ClI IS 4093B

IC2 IS 40179Q1 IS BC107D1 IS 1N4148

ICla

R110N1

C1100n

TOUCHCONTACT'RESET' rt, /nip

R2100k

M"12

IC1d

TOUCHCONTACT'COUNT'

R3100k

0

/

/7)77

IC1c

IC1b

RV1 R4

220k 22k

0p

R5

110k

D1

Q'AUTORESET'

15

0 4-9V C3+ i 470u

16

14

Fig. 1. circuit diagram of the HE Touch Switch.

13

MR

IC2

CPO

CP1

11

9 '8'6 0 '7'

5 0 '5'

1 Q'S'

10 0 '4'

7 0 '3'

4 0 '2'

2 0 I'

0 '9' -

3 '0'

How it WorksThe circuit operates by using the hand as part of acapacitor in a critical timing circuit. When thedetector contacts are touched, the extra capacit-ance introduced has the effect of delaying thetransmission of a clock edge. The circuitry isdriven by one single phase clock generated by IClawhose output consists of a continuous stream ofpulses at about one Hertz with a nominal fiftypercent duty cycle. A delayed and inverted clock isgenerated from this signal by IC lb whose outputdrives one of the clock inputs of decade counter -decoder IC2.

This chip does all the work of decoding the clocksignals and provides a reset input which can becontrolled from the touch circuitry or drivendirectly by one of the outputs of the chip. Forexample, to reset to zero after the 'fifth' count hasbeen reached, just connect output 'six' (pin 5, IC2)to the 'auto reset' input at the anode of DI. If noconnection is made to D1 then the circuit will cyclethrough all ten outputs. By connecting output`two' (pin 4, IC2) to 'auto reset' and taking anoutput from 'one' or 'zero' (pins 2, 3 IC2), thecircuit will operate as a bistable: one touch turningthe output on; another touch resetting the outputto off. The 'reset' touch contact may be left dis-connected in this case.

A certain delay will always be introduced byIC lc, d owing to stray capacitance from the circuitboard and connecting leads. This may be nulled outby adjustment of RV1 which should be set to

0 OV

- OUTPUTS

minimum resistance consistent with reliableoperation.

Two suggested output circuits are shown. Thefirst lights a LED when the appropriate output isselected, the other circuit will drive a small relaywhose contacts may be used to switch more power.

The touch 'reset' circuit operates in a similarmanner to the 'count' circuit. A glance at thetiming diagram should make things clear.

FROM OUTPUT BC107

OF 4017

10k

FROM OUTPUTOF 4017

820R

OV

RELAY OUTPUTFOR TOUCH SWITCH

LED OUTPUT FORTOUCH SWITCH

ti


Touch Switchinto two copper lands by scoring or filing a line down themiddle breaking the copper, but leaving the insulatingboard intact. Make sure no copper whiskers remain tobridge the copper lands as these would prevent thecircuit from working at all. Sensitivity will depend to anextent on the physical size of the touch contacts and thearea covered by, for example, the thumb or palm.Reliable operation was obtained using the prototypewith the touch contacts covered by a layer of adhesive

tA

It ft/,J°isra t

Fig. 2. PCB for the Touch Switch

The assembled board, clean and compact

Good soldering pays off. Practice makes perfect

Use of a PCB makes construction a snap!

plastic film. Use of a coloured film like the sort used tocover books could make an attractive addition to theproject. Use your imagination and do not be afraid toexperiment. Finally, a word of caution to anyonethinking of controlling mains powered equipment. Thisis okay so long as you make sure you use a relay whosecontacts are rated for the job and keep all mains wiringaway from the rest of the project. Build one now and giveyour projects a little touch of class!

'AUTORESET'

'COUNT' 'RESET'

Fig. 3. Overlay diagram for the Touch Switch.

Parts ListRESISTORS (All 1/4W, 5%)

R1R2, 3R4R5R6R7

POTENTIOMETER

RV1

CAPACITORS

10M100k22k10k47k1 5k

220k submin. horiz. preset

Cl 1 OOn polyesterC2 10p polystyreneC3 470i1 electrolytic

SEMICONDUCTORS

Q1IC1IC2

BC107409364017B

BuylinesAll the components for this project should be readilyavailable from the larger mail-order suppliers.


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-eiiimzi.®O8E100OS

- . nhi.(7, ,=,

Cffl m'ID C:I

CI © al,0 ..E1 El

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MASTER PACKAGE DEAL. Programmables.FX-501 P + FA1 + Master Pack software kit(usually £1 7.95) for only £5 £79.90FX-502P + FA -1 MP £99.90REMEMBER we are never knowinglyundersold and will try and beat any adver-tised priceOur 1980 catalogue of Casio, Seiko etc will beavailable Feb/ March. Price 25p. Price includesVAT, P&P Send cheques, PO or phone yourACCESS or B'CARD No to. -

IDept HE Beaumont Centre 164-167 EastRd., Cambridge CB1 1DB Tel: 0223 312866

B.K. ELECTRONICS

AM/FM STEREOTUNER AMPLIFIER

CHASSISOriginally designed for installation into a music centre)

Rezdy-buill and lusted tuner/ preamp hoard and power supply andpower amp board. Easily wired together.

Note: literconnection wiring diagram supplied.Rotary Controls: Tuning. on/ott volume. balance. treble. bass.Push-button Controls: Mom, Tape. Disc. A.F.C.. F.M. )VHF). LW.MW. SW.Power Output: 7 watts FINS per channel. at better than 2%190 intoB ohms. 10 watts speech and music.Frequency Response: 50112-20Kliz within 3dB.

Tape Sensitivity: Output - typically 150 me. Input - 300 my forrated output.Disc Sensitivity: MO my [ceramic cardrirlgelRadio: FM (VHF) 87.5M112-1013MHz 'Stereo Beacon.Long Wee 145Kitz-255KHz.Medium Wave 520Kliz-16201(Hz.Short Ware 5.8Milzi1 6MHz.Size Tuner - e I Sin. x 71Hn. Awes Power Amp - 2in. x7':in. x 4' ,in approx.2443 roll AC operation. Complete with circuit diagram.Price - E22.00 + E2.50 PIP.

LOUDSPEAKERSHigh quality lull range 8 inch loudspeakers. 10 watts RMS. 80. Rolledsurround with aluminium centre cones.E9.50 per paw + EI.50 PIP.

MAIL ORDER ONLY

Dept. HE, BK ELECTRONICS37 WHITEHOUSE MEADOWS, EASTWOOD

LEIGH -ON -SEA, ESSEX

ALL. 1.C.'s ARE.

LAseLLEI, 'hi LAN

47

R12

electronics todayWhat to look for in the April issue: on sale March 7th

CIRCUIT SUPPLEMENT

Next months ETI carries something really special - a SIXTEENPAGE circuit supplement for the experimenter. All the circuitshave been tried and tested by us, making this the most reliablereference yet. If there is anything you need a circuit for or anycircuits you need something for this is the place to find it. Noless than 50 in all. Half a hundred of the best you'll find any-where.

Well worth keeping for that inevitable future time whenyou'll NEED ONE or more of the priceless little gems lying amidthese pages.

TESTEDCIRCUITSTO BUILD

R2 +R1

R3

R4

INFRA-RED CONTROL SYSTEM

Most of the human race is lazy. Any-one who says he isn't is lazy anddishonest. This means that most ofthe human race should buy ETI nextmonth. Why you may ask. Thereagain you could be too lazy tobother. We'd understand completely.

Reason is that we are printing aproject for a 32 channel IR controlsystem which will allow you tolounge back and do everythingwithout moving more than a finger.

01

C2

IC1a

R5

D1

03

C4

I[D2

rIC2

A I the articles here are inan advanced state of prep-aration, but circumstancesmay dictate slight changesin the final issue.

R13

Q4

ANALOGUE SWITCHES

As if it isn't enough topresent fifty circuits inone issue, we've goneone better yet and talkedTim Orr - the man ofone thousand and onenodes - into producingone of his amazinglydetailed features. Thistime his subject is switch-ing analogue signals -how to, when to andwith what.

R/C PROTECTOR

How do you know whenyour radio control air-craft has flown outsidethe transmitter range orwhen one or more ofyour channels fails? Atworst, it's when you tellit to come back and itignores you, winging itsway into the distantsunset.

If you'd built theETI R/C Protector, itwould have been a differ-ent story. Should youlose control of any sur-face (aileron, rudder,etc.), the servo concern-ed will set itself to apreset position, bringingyour personal plane pilot -wards.

R10 R11

TOUCH DIMMERThis touching projectis a dimmer with a

difference - it has amemory.lt can be acti-vated by touch padsor conventional swit-ches.

=AAAA-4,-111-oR14

/////


HobbyChitawChatAs a follow-up to last month's 'Chit -Chat, we look now at alarm -callgenerator circuits and methods of connecting them up to self -latchingburglar alarms.

IF YOU BUILT or intend to build any of the relay -outputburglar alarm circuits described in last month's 'Chit -Chat' feature, you'll need to couple your circuit up to asuitable alarm -call generator (a bell, siren or electronicsiren) in order to make a working burglar alarm system.This month's 'Chit -Chat' tells you how to make thoseconnections and describes some practical 'electronicsiren' circuits that you can build.

An alarm -call generator may use the same batterysupply as the actual burglar alarm (see Fig 1 a) or may bepowered from it's own supply battery (Fig 1 b). The rulesfor deciding which alternative to use are quite simple.First, if the burglar alarm and the generator voltages arenot the same, you must obviously use individual sup-plies for each. Second, if the burglar alarm is NOTself -latching via a pair of relay circuits, you should useseparate supplies: the reason for this is that the alarm -call generator impresses a lot of 'noise' on it's batterysupply and this noise may cause malfunctioning of a nonrelay -latching burglar alarm that uses the same supply.

kt ALARM -CALL

GENERATOR

Fig. 1. Interfac ng a direct -action alarm call generator (bell,siren etc) to a self -latching burgular alarm using (a) common or(b) individual supply batteries.

Thus, you can safely use a common supply only if theburglar alarm is self -latching via a relay contacts and if it

has the same voltage rating as the alarm -call generator.Four of the burglar alarm circuits described in lastmonth's 'Chit -Chat' were of the self -latching 'relay' type,so from this point on we'll confine the discussion to thistype of alarm circuit.

AUTO -TURN-OFF ALARM ACTION.Once a self -latching alarm has been activated it soundsthe generator until the systems batteries run flat if theconnections of Fig 1 are used. An alternative action, inwhich the generator sounds for only a pre-set period(typically 5 to 15 minutes) can be obtained by inter-posing an auto -turn-off unit between the burglar alarmand the alarm -call generator, as shown in Fig 2. This unitincorporates a relay that closes and completes thegenerator circuit as soon as the burglar alarm activates,but then automatically turns off and disables thegenerator after some pre-set period. Fig 2 shows altern-ative ways of interconnecting the three units when (a)common or (b) dual supply batteries are used.

SELF AUTO -LATCHINGLATCHING TURN -OFF

Bt OUT UNITOUT

BURGLARALARM

ALARM -CALL

GENERATOR.'

OUT

-rB2

ALARM -CALL

GENERATORT

Fig. 2. Interfacing an alarm call generator to a self -latchingburgular alarm via an auto -turn-off unit, using (a) common or (b)individual batteries.


Figure 3 shows the practical circuit of an auto -turn-offunit that gives a basic timing period of 8 minutes: theperiod is proportional to the CI value and can be doubled(for example) by giving CI a value of 200n.

The operating principle of the Fig 3 circuit is quitesimple. ICI is a 555 'clock' generator and IC2 is a

14 -stage binary counter which changes state on thearrival of each 8192nd clock pulse. When power is firstapplied to the circuit the output of IC2 is set to the low'state via C2. As the output goes low the relay is driven onvia Q1 and contacts RLA / 1 close and complete the

NOTES:ICI IS 555 TIMERIC2 IS CD4020BCI1 IS BC214LD1 D3 ARE 1N4001

IC1

1C1

R115k

R2470k

100n

0RLA

1

oscillator on and off. The resulting pulsed tone signal isamplified by Q1 and Q2 and reproduced at a level ofseveral watts in the speaker. The available power outputof this circuit is limited by the '18 volts maximum' of thesupply line.

The permissable maximum voltage (and thus theavailable power output) of the above circuit can beincreased by modifying the circuit so that the supply toIC 1 is limited to 12 volts by a resistor and zener diode, asshown by R4 and ZD 1 in Fig 5. This particular circuitgenerates a 'dee-dah' warble -tone alarm, similar to a

R36k8AA"

1C2

16

11

10

C2100n

R4

C3100u

Q1

RLA12V

>120R

D1

02

D3

R5470R

O +12V

v--° OUT

RLA

2

LED 1

INTRUSIONRECORDER

0 OV

Fig. 3. A practical auto -turn-off unit giving a delay of about 8 minutes. The delay can be increased by using a larger value for Cl.

supply connections to the IC1 clock generator, whichthen starts operating. On the arrival of the 81 92nd clockpulse (after roughly 8 minutes with the componentvalues shown) the output of IC2 flips high and turns therelay off via Q1, thereby opening contacts RLA / 1 andbreaking the supply connections to the clock generator.The operating sequence is then complete.

Note in this circuit that LED1 illuminates so long as avoltage supply is connected from the output of theself -latching burglar alarm. The LED thus acts as a visual'Intrusion Recorder' which continues to glow even whenthe alarm -call generator has switched off.

ELECTRONIC SIREN CIRCUITSAn alarm -call generator can take the form of an electro-mechanical bell or siren or of an electronic siren or soundgenerator. In some cases it may be an advantage to usetwo types of generator, either operating directly inparallel or operated simultaneously via a multi -contactrelay. An electronic siren may, for example, be used tosound inside a house while an alarm bell sounds outside.

Electronic 'sirens' can take a number of differentforms and may be designed to generate quite distinctivesounds. Figures 4 to 8 show five useful designs that caneasily be built by the electronics hobbyist.

The Fig 4 circuit generates a 'bleep -pause -bleep -pause' pulsed tone signal. 1Cla-IC1b form a 1 Hz astablemultivibrator which alternately gates the IC1c-IC1d 1 kHz

IC1a IC1b

6

R16M8

C11122_0n

C2100u 4.

-I

NOTES:IC1 IS CD4011801 IS BFY5002 IS 2N305501-D3 ARE 1N4001

12 TO 18V +V.

68k

C3

SPKR8RO

®02

D2

D3

Fig 4. Higher power pulsed -tone alarm call generator.

British police car siren. The circuit is similar to that of Fig4, except that the 1 hz astable is used to frequency -shiftthe IC1c-ICld oscillator.

The frequency -shift 'symmetry' of the circuit


Chit -ChatNOTES:IC1 IS CD4011B01 IS BEY50

C21000 +

,\AA/' D1

R102 IS 2N3055D1-D3 ARE 1N4001 /2Z1 ZD1

IK 0

12V

0112 KS

Fig. 5. High -power warble -tone alarm call generator.

R110k

R268k

Cl10u

IC1

10

13

R388k

iCid

C3

TC2 R4470u 10k

R310k

R5220k IC2

NOTES:IC1 AND IC2 ARE 555Q1 IS 2N305501 D3 ARE 1N4001

Fig. 6. Alternative warble -tone alarm call generator simulates aBritish police car siren.

10n

1

R6

SPKR8R0

D2 12 TO 30V +Ve

120R

SPKR8R0

D3

02

OV0

012 TO15V +Ve

102

01

D3

OV

R14k7

B247k

I+100u

IC1

C2470u

R34k7

R410k

R5100k

R62k7

01

Fig. 7. 'Wailing' alarm call generator simulates an Americanpolice siren.


10n

IC2 3

2

R7120R

SPKR8R0

Q2

0

0

12 TO 15V +Ve

D2

D3

I

NOTES:IC1-1C2 ARE 55501 IS BC214L02 IS 2N3055D1-D3 ARE 1N4001

OV

0

51

Chit -Chat

R110k

D1

33kR2

T147u

IC1

6

/12470u

R312k

R44k7

R510k

R6100k

C310n

R72k7

IC2

2

Fig. 8. 'Red -Alert' alarm call generator simulates 'Star Trek' alarm signal.

depends somewhat on the characteristics of the in-dividual chip that is used in the IC1 position. Figure 6shows an alternative warble -tone generator that does notsuffer from this defect. The modulation frequency of thiscircuit can be varied via R2 and the 'tone' frequency can.be varied via R5.

Figure 7 shows a variation of the above circuit. Thisparticular design generates a "wailing' or alternately

THERMOSTAT

This simple thermostat will stabil-ise temperatures to within a frac-tion of one degree Centigrade. Itcovers a range which extends froma few degrees C to over 35 degreesC, and is therefore suitable for useas a room thermostat, a thermostatfor photographic solutions, etc. .

The circuit uses IC operationalamplifier IC1 as a voltage compa-rator. If the voltage at its non -inverting (+) input is higher thanthat at the inverting (-) input, theoutput goes to vitrually the fullpositive supply voltage. If thecomparative input states arereversed, the output assumes avery low voltage. The invertinginput is fed with a reference voltagewhich is taken from the slider ofRV1; the latter acting as the tem-perature control. The non -invertinginput is fed a potential dividerwhich consists of R1 and Th 1.

Th 1 is a negative temperaturecoefficient thermistor, and its res-istance varies according to its tem-perature, With increased tempera-ture causing decreased resistance.If the voltage produced by Th 1 andAl is less than that set at RV1'sslider, IC1 's output will go high,

L

E

R812OR

SPKRIY8R0

0

Q3

12 TO 15V +Ve

D3

NOTES:IC1-1C2 ARE 555Q1 IS 8C214LQ2 IS BC184LQ3 IS 2N3055131 IS 1N4148D2-D4 ARE 1N4001

D4

f

OV

0

rising and falling tone, similar to that of an Americanpolice car siren.

Finally, the Fig 8 circuit generates a "zeep-zeep"sound that is similar to the 'Red Alert' alarm signal usedin the 'Star Trek' programme. The period or interval ofthis signal can be varied via R2 and the tone can bevaried via R6. This circuit is an ideal project for theexperimenter. HE

Short Circuits

switching on the relay which iscontrolled from this output via anemitter follower buffer stage whichutilizes Q1 Power is then con-nected to the heater by R LA1 , andthe room temperature (or what-ever) starts to rise. This causes areduction in the resistance of Thl,and the voltage fed to IC1's non -inverting input. This voltage soon

D11 N4002

101

D21 N4002

0"I

TH1VA1056

Ti000p

RI47k

RV11khn

R21k2

C22u2

falls below that fed to the invertinginput, causing IC1 's output to golow, the relay to de -energise, andthe heater to be switched off. Thetemperature then falls, causingThl's resistance to increase, and ahigher voltage to be fed to thenon -inverting input of IC1. Thissoon results in IC1 's output goinghigh again, and the heater being

IC1LF351

C11

BC108

D31 N4148

RLA185

switched on. In this way the re-quired temperature stabilisation isobtained.

Make sure that the relay con-tacts are capable of handling thecurrents involved (which will prob-ably be quite high). The thermistormust be fitted in a watertight probeif it is to be used in photographicsolutions.

I


Hobbyprints

We're just etching to tell you about HOBBYPRINTS, we,know you won't be able to resist them.They're so goodwe've even patented the idea (1445171 and 1445172).If you're board with all those untidy strip boards orsemi -permanent bread boards then read on.

After many months of extensive research we thinkwe've come up with the ideal solution (Ferric Chlo-ride?) to all of those problems people have with:making really professional PCBs. (Puns come at noextra charge).

Seriously though, the HOBBYPRINT rub -downtransfer, (very similar to the rub -down lettering) is theanswer to the project builders prayer. PCBs take up adisproportionate amount of time, using HOBBYPRINTSa typical PCB can be finished in under half an hour.Because HOBBYPRINTS are produced from our originalartwork there's no likelihood of making a mistake.They can even be used as photographic masks forultra -violet PCB production.

Please notethat HOBBYPRINT L is £1.20. Print N(Dec HE) is intwo parts Part (b) contains the Hebot print and is available for40p. Print (a) is still 80. The HOBBYPRINTS for Jan 80 are intwo parts. (a) has the Cap Counter and PSU, (b) has Digi-Die,Hebot Loop Drive and Crosshatch generator. Each costs 80pence.

ORDER TODAYSend cheque or postal order (payable to HobbyElectronics) to:

HOBBYPRINTS,HOBBY ELECTRONICS,145 CHARING CROSS ROADLONDON WC2H OEE.

80p INCLUSIVE OF VAT AND POSTAGE

Please note that Hobbyprint 'L' is £1.20 in-cluding VAT, as it consists of two sheets.

Please mark the letter(s) of the HOBBYPRINTS on.the outside of the envelope.


First the EuroBreadBoardNow the EuroSolderBoard

Indispensiblefor the professional

Ideal

for the beginner

Design on a EuroBreadBoard - Instal on a EuroSolderBoard

First the EuroBreadBoardWill accept 0.3" and 0.6" pitch DIL IC's, Capacitors, Resistors,LED's, Transistors and components with up to .85mm dia leads.500 individual connections PLUS 4 integral Power Bus Strips alongall edges for minimum inter -connection lengths.All rows and columns numbered or lettered for exact locationindexing (ideal for educational projects)Long life, low resistance (<10m ohms) nickel silver contacts£6.20 each or £11.70 for 2 including 1 or 2 EuroSolderBoards FREE

Now the EuroSolderBoardNew 100mm square, 1.6mm thick printed circuit board with pre -tinned tracks identically laid out, numbered and lettered to Euro-BreadBoard pattern.Four 2.5mm dia fixing holes.£2.00 for set of three ESB's or FREE with every EuroBreadBoard)

And don't forget the EuroSolderSuckerIdeal for tidying up messy solder joints or freeing multi -pin IC's, this195mm long, all metal, high suction desoldering tool has replaceableTeflon tip and enables removal of molten solder from all sizes ofpcb pads and track. Primed and released by thumb, it costs only£7.25 including VAT & PP

Snip out and post to David George Sales,Unit 7, Higgs Industrial Estate, 2 Herne Hill Road, London SE24 OAUNoma seismisom

David George Sales, HE 3Unit 7, Higgs Ind. Est., 2 Herne Hill Rd., London SE24 OAU.Please send me: -

1 EuroBreadBoard(plus 1 free EuroSolderBoard)

or 2 EuroBreadBoards(plus 2 free EuroSolderBoards)

or 3 EuroSolderBoardsor 1 EuroSolderSucker

@ £ 6.20 0

@£11.70 0@ £ 2.00 0@ £ 7.25 0

Please

Tick

All prices are applicable from Jan. 1st 1980 and include VAT& PP but add 15% for overseas orders.Name

CompanyAddress

Tel. NoPlease make cheques/P.O. payable to David George Salesand allow 10 days for cheque clearance and order processing

53

Miniboards6 WATT SIREN

A state-of-the-art project to terrify intruders and pussy cats. A police -like"de-dah" alarm that produces a 6 -watt output in an 8 ohm speaker whenpowered from a 12 -volt battery supply.

THIS NIFTY LITTLE DESIGN uses the very latest ad-vances in semiconductor technology to implement avery compact, inexpensive, yet exceptionally powerful,alarm -sound generator unit that can easily be incorpo-,rated into an existing burglar alarm system or similar"security" device. The alarm produces a police -like"dee-dah" signal at levels up to 6 -watts in an 8 ohmspeaker when powered from a 1 2 -volt battery supplyand incorporates a number of unusual features.

The alarm circuit incorporates a basic alarm -signalgenerator, followed by a power amplifier stage. Thealarm -signal section of the unit is designed around aninexpensive CMOS integrated circuit that consumesvirtually zero "standby" power. The power amplifierstage is a real state-of-the-art device, a low-cost VMOSpower FET which also consumes virtually zero currentwhen in the "standby- mode. Consequently, the unit,does not need a separate on /off switch and can be leftpermanently connected to a 1 2 -volt battery supply. The

alarm can be activated either by closing push-buttonswitch PB 1, or by applying + 1 2 volts to the junction ofR1 and R2 (the low end of PB 1).

CONSTRUCTION AND USEThe unit uses relatively few components and can be builtin less than one hour. The components are assembled ona standard 1 inch X 21/2 inch strip of Veroboard, asshown in the photos. Start construction by breaking thecopper strips as indicated and then solder the nine wirelinks into place. Next, solder a suitable IC holder intoposition and then assemble the rest of the components,taking care to observe the polarities of Cl, D1, IC1 andQ1 .

When construction is complete, double-check allwiring and then connect the unit to a suitable 8R0speaker and a 12 volt battery supply, connect PB1 inplace and give the unit a functional check by closing theswitch, The unit should produce an ear-splitting "dee-

114 D1 +12V

I+0at

C110u SPKR

8R0PB1PRESSON OUTLINE OF THE iTft7VN67AF

Fig. 1. Circuit diagram of the 6 watt siren.

How It WorksICla and .1C1b are wired as a slow astable mul-tivibrator and IC1c-ICld are wired as a fast astable.Both these astables are "gated" types, which canbe turned on and off via PB1. The output of theICa-IBlb slow astable is used to modulate thefrequency of the IC1c-ICld fast astable, and theoutput of the fast astable is fed to the externalspeaker via the Q1 VMOS power FET amplifierstage.

Normally, with PB1 open, both astables and Ql

OV

NOTES:131 IS 1N400101 IS VN67AFIC1 IS CD40118

are inoperative and the circuit consumes virtuallyzero standby current. When PB1 is closed bothastables operate and the frequency of the fastastable is modulated by the slow astable to pro-duce a "dee-dah" signal, which is passed to thespeaker via the Ql power amplifier stage. DI andCl are used to ensure that the astable actions arenot adversely influenced by voltage transientsinduced into the battery supply leads via thespeaker.


dah" alarm sound. Note that the speaker used in thesystem must be an 8R0 type with a power rating greaterthan 6 watts.

If you want to use this unit in conjunction with anexisting burglar alarm system, you can either replace

Parts ListMINIBOARD No. 7RESISTORS (All 1/4w,R1, 2R3R4R5

CAPACITORSC1

C2C3

SEMI -CONDUCTORSD1Q1IC1

MISCELLANEOUSSPKRPB1

5%)12k6M8220K68K

10p 1 6V Electrolytic100n Polyester10n Polyester

1N4001VN67AFCD4011B

8RO, 10 wattPush button switch

BuylinesThe only component that is difficult to find is Ql, theVN67AF VMOS power FET. It can be obtained fromJ. W. RIMMER, 367 GREEN LANES, LONDON N41DY. For price, phone 01-800 6667.

PB1 with a set of relay contacts that are activated via theburglar alarm system, or possibly can use the burglaralarm to activate the generator directly by applying 12volts to the R1 -R2 junction under the -alarm"' condi-tion, HE

ABCDE

F

GH

J

cxi '4 XXX: "AA 2311010011LS; 4110111at'Ern IrirW,3 it iLIIIMJIMAL ' car *.., `41C, 5 '*"' *Tit."'" IN/

Pk, - Air drICIC IriLIE1'4 ,018A1CCirit cit.- iir.:11rIt

EXXAC38.111.11 *41LX-31,11.2k1101110831-2"' rt XX i , - 'Hi .ranicartir

11211U1OnlIC" -°"4,),-* k1/1%, mararinr1no At imar...ium manor dont. c.wriorzitr.a..1IIEMIL7.11.).*111tir>.-rtNrr 0-0*- -1r

r- C4 01 et Ul r. co Ch C) r- Cs! CI et MI 611 r. co en CD 9I N NC4r- 91 CI et

91

Above. Component insertion layout. Note the orientation of01.

Below. Underside of the Miniboard 6 watt siren. Ensure thatcuts in the track are made in the correct places.

J

H

F

E

DCBA

" NM et en co P. co cm 44 Cl Tr ID (0 r. Do en epN NNNrsi en itN

HAND-HELD GAMESElec. Mastermind £12.90

KITSPinball Wizard £28.90

CHESS COMPUTERSStar Chess TV Game

Digits £14.95 Play 7 games on your tv. Boo £63.35Zap £11.95 Set for P. W. E6.50 Chess Champion E54.95Amaze-a-Tron £18.95 Mains Adaptor £3.90 Challenger 7 £99.00U. F 0 Master Blaster

Enterprise 4 or 1

£24.95£24.95

C E H 202.1 £18.90Versatile car alarm

Challenger 10Voice ChallengerChessnpte 181

£180.00£230.00

£59.95Space Alert £15.90 CHROMA-CHIME

Bridge Challenger £290.00Auto Race £15.90 24 -tune door chiniesSoccer £21.50 Kit £10.50 Backgammon £90.00Atari Touch Me £26.95 Built Et 5.90 Checkers 4 £90.00Destroyer £16.95

FIRE -SMOKE ALARM£15.90 Database

Atari V C SE89.95

£159.001Football 12 player) £24.95

Commodore WatchesLCD Snooze Alarm.1.26-99 Our Price £14.90

1 -year guarantee

CB -CB C B. C BDisguised Aerials, S W RR F Pre -Amp. Connectors.etC

ZODIACAstrology Computer

£34.95

N .1 .0 .61 Broad Lane, London, N.15

Day -Tel. 01-808 0377 Evg.. 01-889 9736

OHIO SCIENTIFIC Su perboard 2 Assembled5011z model £158 -0- 15% vet, post free***************IK Special offer: If bought with superboard

there items are Cr the reduced price shown *,ir,iosoidseparatysrthebra.d

IR prices. Add 15% vat. Modulator and power *, supply kit E1.00 (E7.95). 4K extra ram id,

E25.74 (E31.95). Cassette recorder1E £12.13 (E14.74).41**************SINCLAIR PRODUCTS New 10MHz scope E145.pf rn200 £51.55, case E3.40, adaptor E4.03,connector kit E11.27. Mtcrovision tv E91, adaptor0.55. pchn35 134.23. adaptor E4.03. case E3.40.dm350 08.70. dm450 £102.17, dm235 E55.55,rechargeable beets E7.1111, adaptor £4.03. case E9.Enterprise prog calculator + accessories £11.15.COMPUTER GAMES chess champion 6 E49.95.Chess challenger 7 E114. Phillips G7000 homecomputer E149. Videopaks E12.95. Atari video -computer E147. Cartridges £14.55.COMPONENTS 1N4148 0.9p. 1N4002 2.9p.741 18p. bc109, bc182, bc184, bc212, bc214.be 548 5.5p. Resistors 1/2W 5% 612 1OR to 10M 1 p,0.Ip for 50+ of one value 16V electrolyttcs .5, I, 2,5,10, 22111F Sp, 100mf Sp. 1000mf 10p. 1 lb FeCIE1.30. dalo pen/140.40 sq ins pcb 45p. Polystyrenecapacitors Er 2 63V 10 to 1000pf 3p, 1n2 to 10n4p. Ceramic capacitors 50V E6 22pf to 47n 2p.Zeners 400mW E24 2v7 to 331/ 7p.

TV GAMES AY -3-8500 + kit E7.28. Rifle kitE5.27. AY -3-8600 + kit E17.28. Stunt cycle chip +kit E18.118. AY -3-8603 chip E13.53.TRANSFORMERS 6-0-6V 11/2A £2.80. 9-0.9V75ma 75p, 1A £2.22. 2A 131.114, 12-0-I2V 100ma92p, I A E2.80.IC AUDIO AMPS with pcb. JCI 2 6W E2.08. JC2010VV E3.14.BATTERY ELIMINATORS 3 -way type 6/71/2 /9V300rna E3.14. 100ma radio type with press -studs9V £3.57. 9+9V E4.79. Car convertor 12V input,output 41/2 /6/71/2 / 9V 800ma E2.85.BATTERY ELIMINATOR KITS 100ma radio typeswith press -studs 41/2V E1.49, 6V 11.49, 9V E1.49,41/2+41/2V E1.92, 6+6V 11.92, 9+9V E1.92.Stabilized 8 -way types 3/41/2 /6 /Ph / 9/12 / 15/18V 100ma £2.50, IA E5.30. Stabilized power kits2-18V 100ma E2.1111, I 30V IA £5.20, 1-30V 2AE11.24. 12V car convertor 6 /71/2/9V IA £1.35.T -DEC AND CSC BREADBOARDS s-dec £3.78,t-dec £4.55. u -dace E4.89, u -deck E7.111, aap41312.84. atip300 £8.81, exp350 E3.112, exp325ELM.111-PAK AUDIO MODULES s450 E25.08. ALSO

pet 00 £17.33. sprn80 E4.74. brnt80£5.05. Stereo 30 £21.57. AL30A E4.05. pa 1 2ES.38. pit 2 E1.55. rna60 £31.27.

SWANLEY ELECTRONICSDam HE. 32 Cloldaal Rd., Swanlay, Kant

Post 30p extra. Prices include VAT unless stated.Official and overseas orders welcome. Lists 24p, postfree. Mail order only


TEE SHIRTSWe won't guarantee HE Tee -Shirts will make your sol-dering any better, we won't even claim it will make yourprojects work first time. What we will say is that it willprotect your body from harmful Ultra -Violet radiation fromthe sun, embarrassing Tomato Ketchup stains on your hairychest and overweight wallets (if bought as directed insufficient quantity).

Yes folks, for just £2all inclusive you can bethe first kid on your blockto own a brand new HETee -Shirt. If you buymore than one your torsoneed never be left unpro-tected whilst your otherone is in the wash.

Send yourcheque, PO oranythingnegotiable to:HE TEESHIRTS, 145Charing CrossRd, London

'WC2H OEE.

55

HOBBY ELECTRONICS PROJECT SPECIAL -VOLUME 1From deep inside the HE specials department comes this once -in -a -lifetime opportunity. You could be one of the first to own a copy ofthis special re -publication containing 25 of Hobby Electronic's mostpopular projects. Cover price will be just El .25 If you missed themfirst time around then this is your big chance.

More details next month.

HEWHIT NO it IT

'T

tic (4111CRUITI

COMING SOON/DISPLAY LIGHTING

Each unit has 4 channels (rated at 1KWchannel) which switch lamps to provideeffects, controlled manually or by anisolated audio inputDL 1000KThis kit features a bi-directionalsequence, speed of sequence andfrequency of direction changebeing variable by means ofpotentiometers, Incorporatesmaster dimming control. E14.6013L21000KA lower cost version of the above.featuring undiractional channelsequence with speed variable bymeans of a preset pot. Outputsswitched only at mains zero cros-sing points to reduce radio inter-Terence to minimum. £8.00Optional Opts Input0 LA1 60p

KITSat 240V persequencing

optional opto

DIGITAL VOLTMETER/THERMOMETER KIT

24 HOUR CLOCK/APPLIANCETIMER KIT

MINI KITSThese KITS form useful subsystems which may beincorporated into larger designs or used alone. Kitsinclude PCB short instructions and all components.

TEMPERATURE CONTROLLER /THERMOSTATUses LM 3911 IC to sense temperature (80°C max.)and mac to switch heater. PCB (4 cm sq.) poten-uorneter, plus all other components included withinstructions.500W EL 20 1KW E3.50

SAID STATE RELAYIdeal for switching motors, lights, heaters etc. fromlogic. Opts isolated with zero voltage switchingSupplied without triac. Select the required mac fromour range. E2.60

OAR/DOT DISPLAYDisplays an analogue voltage on a linear 10 -elementLED display as a bar or single dot. Ideal forthermometers, level indicators etc. May be stacked toobtain 20 to 100 element displays. Requires 5-20V

supply £4.75BURST FIRE/PROPORTIONAL TEMPERATURE CON-

TROLLERBased on the TDM 024 Zero Voltage Switch this kiicontains all the components required to make a"burst fire" power controller or a "proportionaltemperature' ' controller enabling the temperature ofan enclosure to be maintained to within 0.5 C1 5KW £5.26 3KW 05.55

Switches any appliance upA to 1kW on and off at preset

times once per day. Kit.. contains AY5-1230 IC,i 0.5" LED display, mains,. supply, display drivers,

.,... tc hes. LEDs. triac, PCBs

., N I

t

as the sensor. Requires(PPS battery)

Based on the ICL7106. This kitcontains a PCB, resistor, pre-sets, capacitors, diodes. IC and0.5" liquid crystal display.ComponenN are also includedto enable the basic DVM kit tob modified to a Digital Ther-mometer, using a single Mode

a 3mA 9V supplyE20.75

'

wigwam .,...r,,' & full instructions.

CT1000K Basic Kit £14.90CT 1000KB with whitebox (56 x 131 x 71mm) £17.40Ready Built £22.50

LEDs CAPACITORSLEDS0.1" Red 9p0.1" Green 12p0.1" Yellow 12p0 2" Red Bp0.2" Green 12p0 2" Yellow 12p0.2" clips 3pRectangular Red 1BpRectangular Green

20pRectangular Yellow

21p

DISPLAYS

r1 OL304 Red 0.3" c c. pin com-p atible with DL704 70p

1 1DL307 Red 0.3" c.a. pm compDL707 70p

Polyester00o033000.10.15

Electrolytic.

63V

25V

Tantalums35V

25V

250V01 OP 0.22 12p002 Sp 0.33 12p

7p 0.47 15p047 7p 0.68 18p068 7p 1.0 24p

7p 1,5 27p11p 2.2 31p

A Axial R Radial

1.0 3P 16V 10 R 3p2 R 3p 22 R 3p

4,7 R 4p 33 R 3p10 R Op 47 R 4p47 R Bp 100 R 5p22 Bp 220 R Bp47 A Bp 470 R Op

100 A 1000 R 15p110 A Op lOy 47- A Bp470 A 16p 100 A 8p

1000 A 20p 220 A 6p

(bead)0.1 7p 101/ 22 12p0.22 21. 6.3V 33 140. 47 1447 7p p

1.0 7P 3V 100 14p2,2 SP4.7 9P10 12p

VOLTAGE REGULATORS

ii Available in 5V, 12V & I5)/versions.IR 78L series 100mA pos. 26p79L series 100mA neg. 60p78 series to pos. 52p

( M3171 adjustable 1.2V37V 1.5A E1.80

INTEGRATED CIRCUITS

41101.11°. /55 Timer 21p741 Op. Amp 19pAY -5-1224 Clock E2.60

AY -5-1230/2 Clock/Timer E4.20AY -3-1270 Thermometer E8.20ICL7106 DVM (LCD drive) E7.00LM 377 Dual 2W Arno £1.45LM 379S Dual 6W Amp £3.50LM380 2VV Audio Amp 80pLM382 Dual low noise pre-arnp E1.00LM386 250mW low voltage amp 75pLM 1830 Fluid Level Detector E1.50LM2907 f -v Converter E1.40LM3909 LED Flasher/Oscillator 65pLM 3911 Thermometer E1.20LM3914 Dot/ Bar Driver E2.10MM 57160 (star) Timer E5.90MM74C9 I 1 4 -digit display controller £6.50MM74C915 7.segment.BCD converter 96pMM74C926 4 -digit counter with 7.segoutputs £4.5055668 Touchdirnmer £2.5059263 Touchswitch 16 -way E4.85IBA BOO 5W Audio Amp SipTBA810AS 7W Audio Amp 85p1041024 Zero Voltage Switch E1.00TDA2020 20W Audio Amp £2.85ZN1034E Timer £1.50All ICs supplied with data and circuits. Data sheetsonly 5p.

BOXESMoulded in high impact ABS. Suppliedwith lids and screws. Black or white.

1 I. itu..8295 x71 x 35rnrn 86p(33115X95X 37mm 78p

...

-L01847 Red 0.8'. (pin comp. DL747) c.c. £1.80DLB50 Red 0.8" c.c. (pin comp. 01.350) E1.80DL727 Dual 0,5" c.a. Red £1.50 RESISTORS

ZENER DIODES YeW 22ohrn-10MPack of 10

400mW3.3V.30V Bp rune value) 10p

1.3W 7.5-27V 15p 10 Packs(10 values) 80p

TRIACS400V Plastic Case (Texas)

3A 49p 16A 90p8A 58p 20A 165p

12A 70p 25A 190p6A with trigger 80p8A isolated tab 65p

DIOC 18p

.MINI TRANSFORMERS

Standard mainsprimaries 240V a.c100mA secondaries6.0-6V 80p9-0-9V 85p

12-0-12V 90p

_OIL. LC. SOCKETS8 pin SP 18 pin lip

14 p 2Bin 12p pm 24p16 pin 14p 40 pin 36p

Soldercon Pins 50p. 100-- - .

-ALL COMPONENTS ARE BRAND NEW AND TO SPECIFICATION. ADD VAT AT CURRENT RATE TO ABOVE PRICES PLUS 35p P&P_ MAIL ORDER CALLERS WELCOMEBY APPOINTMENT.

(WE.), 106 STUDLEY GRANGE ROAD L.,.. t-,....1 TK Electronics LONDON W7 2LX. TEL. 01-579 9794........,...._


Short WaveRadioFar away places with strange sounding names . . . Eavesdrop on the etherwith this great project. 1 to 30 MHz in three sensitive and selective ranges.

IN THE BAD OLD DAYS OF RADIO, sometime after theappearance of crystal sets but before the superhetbecame a practical proposition a breed of radio receiverbecame popular called a TRF. The letters stand for'Tuned Radio Frequency' and the circuits usually con-tained several tuned (that is highly selective) stages ofradio amplification. As superhet (short for superhetero-dyne) receivers were developed the humble TRF becameless popular. Superhets mix a local oscillator signalgenerated inside the receiver with the received signal toconvert all signals to an arbitrary intermediate frequencybefore amplifying and detecting them. The advantage ofthis arrangement is that the IF amplifier can beoptimised for one particular frequency giving a narrow"passband" and good selectivity. The vast majority of

The HE short wave radio spans the world.


modern radio receivers now use superhet circuits, eventhe cheap transistor pocket portables. Over the years,the radio spectrum has become increasingly crowded;especially the Short Wave bands and this has led to thedevelopment of a number of different modes of trans-mission. Amplitude modulation (AM) where the carrierwave is modulated in strength by the audio signal, isstill used universally by commercial broadcasting sta-tions at frequencies below VHF and very simplereceivers, even a crystal set, can detect transmissions inthis mode. However, many radio amateurs use con-tinuous wave (CW) for morse code and single sideband(SSB) for speech. These signals are best resolvedthrough the use of special detectors or with a directconversion receiver. Many commercial short wave

57

ce

C1

10n

RF

C47

0uH

/7M

R4 15

0R

176p

208p

C4 10

n

C5 15

0p

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10M

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d

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RE

2N

3819

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IS B

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LM

380

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1000

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210

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Fig

. 1. C

ircui

t dia

gram

for

the

HE

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rt W

ave

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or c

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rage

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he S

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and

you

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nee

d th

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ree

rang

eco

ils (

L), s

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list.

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it W

orks

Q1

and

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form

a b

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rad

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freq

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y,am

plif

ier

who

se o

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d by

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the

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C14

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the

sele

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put o

f au

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side

IC 1

is d

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by

C15

and

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of s

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pro

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s.

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use

of o

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eally

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w

Par

ts L

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TO

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(A

ll 1/

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%)

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210

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31k

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415

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10M

R6

3k9

R7

150k

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18k

R9

1k5

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10k

R11

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R12

2k2

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PA

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3, 4

, 12

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Fig

. 3. O

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lines

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this

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you

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OV

LS1

SW Radioreceivers incorporate two or three detection systems andcan cope with most modes of transmission. They mayalso feature a digital frequency readout covering 0.5 to30MHz. Sounds great doesn't it? Of course, such areceiver might cost several hundred pounds.

This version drives a crystal earphone directly. Even cheaper!

CHEAP AND CHIRPYBy contrast, you can listen to the wonderful world ofsquawk, crackle and pop (music) with the Hobby shortwave radio for about a 'tenner'. If you are happy withearphone reception or have your home Hi-Fi handy it willcost even less! You should be able to tune the wholeShort Wave band from about 1.5 to 30 MHz using threeplug-in coils. Use of a TR F circuit means that noalignment is needed and though there is only one tunedcircuit, the receiver is made quite sensitive and selectiveby applying variable positive feedback: 'reaction' or'regeneration'. By increasing the feedback until thecircuit is just oscillating, it is possible to resolve CWmorse transmissions and with care SSB.

Our chart shows what you are likely to find on theshort wavebands and where. Although it looks rathersparse, you will probably find that there is not an emptyspot on the dial until about 15 or 20 MHz. By far themost interesting reception is providecrby the range 4 coilcovering about 5 to 15 MHz. You should be able toreceive broadcast tranmissions from many foreignstations throughout the range. Using the prototype, wereceived English language transmissions for Cuba,Israel, Moscow, America, Vatican City, Canada and, ofcourse, the BBC World Service to name but a few. Moststations identify themselves on the hour. Reception willvary during the day and according to the time of year butit is always possible to pick up something and there arenumerous beacons and code transmissions scatteredaround the dial.

CONSTRUCTIONUse of the specified components and our PCB is essen-tial to ensure stability. Radio frequency waves areawkward little things and find their way into everything.Indeed, at very high frequencies they will not even traveldown a wire, preferring instead to run along the outsideof a conductor.

PRINCIPAL 1

BROADCASTBANDS I

AMATEURBANDS

MHz1

MHz9 01 8-2 0

'TOP BAND' '80 METRES'160 METRES

7 -7 3MHz

The variable capacitor and two potentiometers aremounted on the PCB supported by stiff pieces of wire. Allthe other components with the exception of the loud-speaker mount directly on the board, keeping the com-ponent legs as short as possible. Our photo's should giveyou the general idea.

A mixture of capacitor types is specified. They arechosen both for their physical size and electrical charac-teristics and you should try to obtain the right types.None of the components are very out of the ordinary.Q1, 2, 3 are conventional junction FETs and no specialhandling precautions are required.

The coils plug into a modified B9A PCB mountvalveholder. Simply remove the centre spigot and theconnectors for all the pins except 1, 6 and 7. A short wirelink can be soldered between pins 6 and 7 on the range3 (low frequency) coil effectively connecting bothsections of VC1 to the coil when range 3 is selected. Inthis way, a greater tuning range is obtained. Do not worrythat there are no connections to pins 8 and 9; this coil isnot used. To change range, simply plug in the appro-priate coil. VC1 should be the slow motion drive com-ponent. Although it costs a little more, it is worth theextra expense and obviates the need for a bandspreadcontrol.

Three plug-in coils cover all your favourite bands.

If you do not need the audio amplifier stage, theoutput from the negative side of C13 will drive anexternal amplifier or a crystal earpiece directly. Thecheaper 8 Ohm magnetic earphones will not work here.Connect the ground or shield of your amplifier input toOV and the other wire to C 3. A hole is provided on theboard for this connection.

In use, the regeneration control RV1 should beadvanced until just before the circuit begins to oscillate(stations will be received as whistles when the set isoscillating); this is the most sensitive state. The setting ofthe 'regen' control will vary over the tuning range andaccording to the coil in use. To receive morse code CWand SSB, advance RV1 just past the point of oscillation.The SSB transmissions sound like Donald Duck voicesand considerable care is needed to resolve them.

The Hobby SW radio offers an economical and simplesolution to the problem of getting your ears on the worldout there. Build it now and happy listening!

15 0

I1

14 14.35MHz

21-2145MHz

'20 METRES '15 METRES'

Our chart shows the principal broadcast and 'ham' bands, but thre's more out there than you think.

'40 METRES

28-29.7MHz

'10 METRES'


WE DID

WARN YOU!Nobody likes to gloat, but nearly sixmonths ago we warned you about ourdiminishing stocks of backnumbers. Theones shown here are all that are left! Hob-byprints are still available.

JUNE 79 (Hobbyprint H)Projects: GSR Monitor, Envelope Generator, DrillSpeed Controller.Features: Citizen Banned, Display Techniques, MovingCoil Meter, Electronics in Music Pt 2, etc.

JULY 79 (Hobbyprint I)Projects: Shark, Baby Alarm, Point Controller, LinearScale Ohmeter.Features: Cassette Decks and Tapes, Binary Numbers,Fixed Resistors, Short Circuits Special, etc.

AUGUST 79 (Hobbyprint J)Projects: Home Security Sound System, LEDTachometer, Injector/Tracer, Constant VolumeAmplifier.Features: Security Installation, Variable Resistors,Tools, Satellite Power etc.

SEPTEMBER 79 (Hobbyprint K)Projects: Combination lock, Light dimmer, Starburst,Ultrasonic Switch.Features: Electronic Timekeeping, Thyristors, RadioControl, FET Special.

L

Shown here are all of the backnumbers still available. They are£1.00 each inc. P&P. When ordering please quote the issuenumber, i.e. Nov. 78 is issue 1 Vol. 1. Next to each issue is therelevant Hobbyprint code letter, please note that Hobbyprints arestill available for every issue.

Please send me the following back issues Nos

Cheque/P.0. enclosed £

Hobby Electronics Backnumbers Dept.145 Charing Cross Road, London WC2H OEE

Name

Address

OCTOBER 79 (Hobbyprint L see Hobbyprint Ad)Projects: Tantrum, Hobbytune, Analogue FrequencyMeter, Multi Siren.Features: Home Computing, Electronic Games, Micro-wave Cooking, Breaker One -Four.

DECEMBER 79 (Hobbyprint N)Projects: Scalextric Controller, Ring Modulator, Bar -graph Voltmeter, Hebot II.Features: TV Receivers, Project Fault Finding, DataSupplement.

JANUARY 80 (Hobbyprint 0)Projects: Hebot Ill, La / p Counter, Crosshatch Genera-tor, Digi-Die.Features: Mini TV Survey, CMOS Spread, Spacelab.

FEBRUARY 80 (Hobbyprint P)Projects: Passionmeter, Infra -Red Control, Win Indica-tor.Features: Short Circuit Special, Kezy Does It, Power tothe People.

SUBSCRIPTIONS

WHYMISSOUT?

I To: SubscriptionsI Hobby Electronics

P.O. Box 35Bridge Street

Hemel HempsteadHerts

II

I

II

Name . .

Address

E N MN

I would like a postal subscription to HE start-ing with theissue. I enclose payment (£6.50 for UK andEire, £7.50 elsewhere, £11.50 air mail).

N MI MIK IM MMM=M==MMM INN ME EN INN


VARI WIPEWIPER DELAY CONTROLThe Vari Wipe provides intermittentoperation of the windscreen wipers withadjustable control to delay each wipe between 3 and 60 seconds.Set the control to suit the conditions to clear light drizzle, fog,snow, sleet or spray. Easily fitted to British, Continental &Japanese cars with 12 volt self park wipers. Complete kit containsall components, including timer chip, PCB, case, mounting panelwire, etc., withfull instructions.

oi

VARI WIPE KIT £6.75 inc. P & P IASSEMBLED £9.25 inc. P & P,....._ir or send large s.a.e. for details -1,','".

P/NM DEVELOPMENTS

Dept HE IFREEPOST Thornton Cleveleys, Blackpool FY5 2BR

Card HoldersPhone

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ale `toy VIOR Cow( -fuE I R1SN

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NEW FROM MAGNUMDIGITAL INDICATION of RADIO FREQUENCY using a uniquecombination of FUTABA FLUORESCENT DISPLAY (the 'GreenOne') and OKI COUNTER/DRIVER.

Combination 1OKI MSM 5524RSOLI MSL 2318FUTABA 6 -LT -09Crystal

Special Price Offer £21.38AM, FM, SWPre -Scaler5 digits + MHz, KHz3.2768 MHz

Combination 2 Special Price Offer £18.32OKI MSM 5525RS AM, FMOKI MSL 2318 Pre -ScalerFUTABA 6 -LT -06 31/2 digits + MHz, KHz + AM,

FMCrystal 6.5536 MHz

Combination 3 Special Price Offer £24.57OKI MSM 55271 AM, FM, SWOKI MSL 2318 Pre -ScalerFUTABA 7 -LT -02 5 digits + MHz, KHz + AM,

FMCrystal 6.5536 MHz

Send today for your Combination (suggested circuit details andFREE I /C Socket are included) and enjoy "spot on" visualtuning.

OUR NEW CATALOGUE IS NOW READY. Send S.A.E.

MAGI-WM AUDIO Ltd.DEPT. E.T.I. 1, 13 HAZELBURY CRESCENT

LUTON, BEDS. LU1 1DFTEL: 0582 2887

K40SUPEREX CBAUVICO CBTURNER CBHYGAIN

RETAIL&TRADE CB

ACCESSORIESSPEECH PROCESSORS

(inc. K40, Telex)POWER MIKESMAGIC MIKE

(without cord)SPEECH COMPRESSORSVOICE OPERATED MIKES

SWR METERSSWR /POWER METERSSWR / POWER/MODULATION

METERSSWR/POWER/

K40 BASE LOADDV 27- all typesDX 27 - inc.S' typeDK 27 - with or without

Splitter BoxELECTRIC AM/FM/CB

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HAM K40INTERNATIONAL CB

H.M.P. & E.A.ANTENNASTELEX CB

DISGUISED ANTENNASBASE ANTENNAS

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ANTENNA ACCESSORIES(inc. Splitter, Cable, PL259,Plugs etc.)

POWER SUPPLIESLINEAR AMPLIFIERS

(up to 200W)

MODULATION/ COMMUNICATIONS EQUIPMENT DISTRIBUTORSFIELD STRENGTH 103 High Street, Tel: Walton -on -Thames 48145METERS Shepperton, Middlesex

*until Rigs become legal we will be unable to supply them*

MOTORCYCLE CBACCESSORIES

JRA62 Hobby Electronics, March 1980

BreakerOne Four

Send any news. comments, orinformation you may have to:Breaker One Four,Hobby Electronics,145 Charing Cross Road,London WC2 H OE E.

At last, the winners of the Tape Competition and the famous K 40 review.Plus, some more clubs for your notebook.

NCLCBRThat stands for the National Committee for the Legalisa-tion of CB. It was set up at the meeting last December asreported in BOF. The committee held its first meetingearly in January. The members of the committee havenot wasted any time in setting the ball rolling. Ademonstration is planned for April the 27 the venue isunclear at the moment but probably around TrafalgarSquare London. The next meeting of the committee isplanned for Saturday the 9th February. Contact yourlocal club chairman for details.The demonstration planned for the 26th of Januaryappears to have been a hoax, unfortunately HE goes topress a few days prior to this so we won't know until it'stoo late. If anyone has got details of CB events pleaseby all means tell us but please no more wind ups.

CHANNEL CONFUSIONHave you ever wondered why this feature is calledBreaker One Four? Simple, or least so we thought.Channel 14 has been the English breaker channel forabout a long as we can remember, except in areas where14 is unusable due to local interference. It now trans-pires that most areas north of Birmingham have beenusing channel 19. Sorry to all concerned but it's a littletoo late to change the title.

CLUB NEWSNews of clubs is still trickling in. Just. Remember if youwant a mention in BOF just drop us a line giving detailsof your club and where you meet if possible. On to thismonth's offerings.

CBA-SWChairman D J Bennet7 Wookey Hole Road,Wells,Somerset. Tel. 75306.

Harrow and Wembley Citizens Band GroupSecretary, Bill Ridgeway7 Sandringham Crescent,Harrow,

,Middlesex. HA2 9BW.Meeting place: Queens Arms High St Harrow 7.30pm1st and 3rd Wednesdays each month.

CALIFORNIA TEAMINGAfter BOFs recent jaunt to the USA last year we weresurprised to hear from an American Breaker that we

spoke to in the 'States. As we were using CB quite legallywe did not mind giving out details of our address inEngland. A postcard from the 'States arrived just beforeChristmas giving details of our chat. This is almost thesame as the Ham QSL in fact many European countriesdo send QSL cards for CB contacts.

This set us thinking, we know HE does get around theworld, most countries in Europe can buy HE on thebookstalls. So, if we have any CBers in other countrieswho would like to send us an example of their QSL cardwe will reciprocate. As it's not illegal to listen to foreignCB we may get some special HE QSL cards made up sowe can reply to any overseas stations. Well, how aboutit.

TAPE COMPETITIONThe entries for the competition were a little disap-pointing, not from the quality but the number. Theanswers to the questions are as follows:(1) Channel 14 is 27.125 MHz(2) SWR stands for Standing Wave Ratio.(3) A 'Firestick' is a make of CB antenna.The suggestions for new slang for (a) a production linecar, (b) the police and (c) the Home Office were quitegood. Alongside the name of each winner we haveprinted their best suggestion.

K Bareham, Surrey. The Home Office -Wave Rovers.Lance Brake -Whitley, Croydon. Production line car -RoadBeater.M D Barson, Whitstable. Home Office -Desk Jockeys.

M. Jay London. Home Office -Gear Grabbers.T. Jenkins Devon. Car -Breaker TakerDave Finch Southampton. Police -Charlie Clore(Rhyming slang -Law)E. Peters Dulwich, Home Office -EarwigsM. Dilton Newcatle. Car-Mouthmobile.Peter Raines London Police - BluesJ. Wilson Glasgow. Car -voice box

K 40 REVIEWBet you're thinking 'How can they test a CB mike whenCBs are illegal.' Well, it just so happens we can, almost.Here at HE we have a licensed radio amateur, he comescomplete with a transceiver. Problem solved, a genuine


'on air' test. We decided to hook up the K 40 to the rigand try it out on the 11 metre amateur band. (27 MHz isaround 10 metres so we're pretty close.)

Before we get to the test proper a few words on whatis supposed to happen. You may be familiar with powermikes, they usually incorporate an audio amplifier to'boost' the level of audio to the rig's input and driverstages. This would hopefully increase the level ofmodulation giving a stronger signal, in theory at least.The trouble arises when these are coupled up to modernrigs that incorporate compression circuits, designed toreduce the level of strong peaks from the microphone.Result, the signal from the power mike often getsseverely clipped and distorted making it worse thanever.

The K40 opened up for inspection

The K 40 works on a different principle. Within themike case lurks a purpose designed op -amp IC. This'looks' at the output from the microphone and amplifiesthe portions of the signal that are below a pre-determined level. This increases the amount of signalthat reaches the modulator stage resulting in a stronger(though not louder) signal.

The really clever bit of the K 40 design is the FETcontrolled charging circuit. The K 40 circuitry does notrequire batteries, instead an electrolytic capacitor ischarged from the rigs existing mike leads. When themike is keyed the IC is powered from the internalcapacitor. When the rig is in the receive mode thecapacitor re -charges. The current consumption is so lowthat a two second period of receive will power the mikein the transmit mode for around three minutes.

As an added bonus the K 40 has a 'Hi Lo' switch thatincreases the treble content (Hi) for operation in crowdedcities. The higher frequencies stand a better chance ofpunching through the mush. Limiter circuits in the mikealso maintain a constant input to the rig whether themike is half an inch or two feet from the mouth. This, is itclaimed is especially useful to truckers who have a highlevel of background noise in their cabs. They just holdthe mike as close to the mouth as possible and thebackground noise is cancelled out.

Finally, the mike has a permanent magnet built intothe rear of the case, no hooks or clips needed, just stick itto any metal surface when not in use.

So, does all this fancy stuff live up to the manufac-turers claims? In short yes. Our Ham friend reported

64

excellent 'copies' from as far away as Germany. Acomparison test involving the standard mike and the K40 was favourably reported from the other end. We willcontinue to review the K 40, this time on a mobile 2metre rig under noisy conditions. In the meantime wewould like to thank Wintjoy for the opportunity to testthe K 40 and say that for around 40 quid it's a touchpricey but well worth looking into.

15 PENCE = LEGAL CB?Our penultimate item this month comes from that wellknown personality of the Airwaves (Rumour has it he's alicensed amateur) 'Mack The Hack'. He writes to us witha very worthwhile suggestion.

Would you spend 15p to help get CB legalised? I'msure you are all scr earning 10-4 for sure.

In the recent Commons debate on CB. It was statedthat 'The Minister (Home Office) has received 3,300letters on the subject since May. That will be a drop in theocean compared to the number of letters he will receiveduring the next few months'.

It has been suggested that all interested persons sendpost cards, (No not OSL cards), to the Minister.

The one I sent with views and greetings from Londonhad this message. 7th Jan. 1980. 1140am GMT.10-20 Victoria embankment, in 10-33.Dear William,10-50 (accident) Blackfriars underpass, traffic tailbackto your works 10-20 (Parliament Square) wish you'dbeen there. If Citizens Band Radio was legal I wouldhave been forewarned and able to have taken alternativeroute.

Yours faithfully, Mack the Hack.CB4 UK NOW (please).This postcard cost 7p and the stamp 8p (2nd class)

and was serft to Mr William Whitelaw, House of Com-mons London.

Whenever I see a situation where CB could havehelped I think that I'll send the Rt Hon William Whitelawanother postcard.

Now why don't you do the same. It will only cost you15p and less time to write than it takes you to read this.Mack the Hack.We can see nothing wrong with that idea. How aboutsending a postcard. It might just make the difference.

AND FINALLY . . . .

Lastly a couple of items from Wintjoy Ltd who seem to bejust about the biggest dealers of CB accessories in theUK at the moment. They are compiling a map of GreatBritain showing each town with its calling channel. Ifyou would like to drop them a line giving details of yourlocal 10.20 they would be most grateful. (This is not assinister as it sounds, more about this next month).Finally, they would like to apologise for the breakdownof their phones earlier last month. Phone bill has beenpaid and they've now got their ears on.

LATE NEWSJust managed to get this in, in the nick of time. A majordemo is planned for Sunday, February 23rd. Venueshould be Hyde Park, Speakers Corner again. The marchshould commence around 11 am. See you there.

HE


GREENWELD443F Millbrook Road,

All prices include VAT at

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COMPONENT CABINETIDEAL FOR THENEWCOMER TOELECTRONICSContains hundreds of brand new resistors

Southampton SO1 OHX15% - Just add 30p post

THE NEW 1980

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FEATURES INCLUDE 60p Discount Vouchers Quantity prices for bulk buyers Bargain List Supplement Reply Paid Envelope Priority Order Form VAT inclusive prices

AN for only 40p + 20p post

capacitors, transistors, diodes and i.c.s Alluseful values, carefully chosen to help thenew constructor pursue his hobby withoutfinding himself short of some vital parts!All parts contained in clearly marked bags ina plastic storage cabinet 232 Y 121 Y.185mm with 9 drawers into which all parts

1000 RESISTORS £2.50!!New stock just arrived - Carbon Film 2% &5%, 1/2 & 1/2W, all brand new, but havePre -formed leads, ideal for PC rnnta -' Enor-mous range of popular mixed values for just£2.50/1.000; C1115,000; 00/25,000

can be neatly located.If bought individually parts plus case wouldcost over £45 but we are offering this forONLY £31.95 + El P&P. Simply send acheque or PO for E32.95 for immediatedespatch.

CONTENTS

--INVERTER

Prepare for the Power Cuts! Ready builtinverter, 290x55x37rnm 24V DC in, willpower 6 x 8W flourescent tubes. Circuitsupplied. Only E2.90

200 1/2 wan resistors20 Wire wound resistors70 Ceramic Capacitors70 Mylor Capacitors50 Polyester Capacitors56 Electrolytic Capacitors61 Transistors12 I .0 s

SCR PANEL & REED PANELSZ525 Contains 11 800mA 60V 2N5061SCR's, 11 6V8 zeners, 11 1 N4004 diodes+ Rs, Cs etc. Only £1.00.

_

Z527 2 x 6V reed relays, 6x2S030 or25230 6x400V rests, + Rs. Only 50p.

20 LE.D.s55 Diodes and rectifiers

Altogether 614 components

Price includes current catalogue and Green-weld pen for reordering supplies. Plus freesurprise gift.

WIRE AND FLEXSolid core - ideal for breadboards etc 50 x2m lengths many assorted colours, total100m for £1.30.Flex packs - 5 x Sin lengths of multi -strandthin flex, ideal for wiring up circuits. Only35p.

EX -COMPUTER PANELSZ528 Pack of boards containing 100s Rs. Csdiodes, including at least 50 transistors.Only £1.20.2529 TTL pack - Panels with 74 series on,together with code sheet. From simple gatesto complex counters 20 ICs El. 100 ICs £4.

' VEROBLOC BREADBOARDNew from Vero. this versatile aid for buildingand testing circuits can accommodate anyeze of IC. Blocks can be joined together. Busstrips on X & Y axis - total 360 connectionpoints fa just £3.70.

VERO OFFCUTSPacks of 100 sq ins of good size pieces about4x2in. in the following types:K541 0.1 in. copper clad £1.50K54-4 0.1in. plain £1.50Also pieces 21/2xlin. - 10/£1.20 100/29.17x3aAirtx0.1in. sheets, 10/ £16.50

,

3W Amp ModuleReady built and tested, this handy amplifierwill prove very useful around the workshopJust requires 1 7V ac source (and 8R spkr) asbridge rest and smoothing cap are mountedon the PCB. The 4 transistor circuit provides

Large range of Standard Veroboard andboxes/cases in stock. Details in Catalogue.

SCOOP!!! Verobox type 2522, unused buthas 31/2in. holes in one end and 11/2 in. holein the other, so instead of £3.96, we areselling these at £1.85;

enough sensitivity for most applicationsSupplied complete with circuit diagram andwiring details.Only £1.75. Suitable transformer. E2.20.

BUZZERS. MOTORS & RELAYSZ401 Powerful 6V DC Buzzer, all metalconstruction, 50mm dia. x 20mm 70p.

Miniature Buzzer, 6, 9 12V,DISC CERAMIC PACK

Amazing variety of values and voltages froma few pF to 2.2uF1 3V to 3kV I 200 E1 500£2.25 1000 £4.00.

Z402. type, oronly 22x15x16mnt. VeryZ450 Miniature 6V DCmotor,

neat,high quality55p.

type, 32rnm dia x 25mm high, with 12mmspindle. El.W892 Heavy duty 12V relay, ideal for car

DIODE SCOOP!!!We have been fortunate to obtain a largequantity of untested, mostly unmarked glasssilicon diodes. Testing a sample batch

use - single 15A make contact. Coil 25R85p.W890 DIL reed relay SPCO 2.4-10V 200Rcoil, Only E2.20.

revealed about 70% useable devices -signal diodes, high voltage rests and zenersmay all be included. These are being offeredat the incredibly low price of £1.25/ 1,000- or a bag of 2.500 for £2.25. Bag of10,000 £8. Box of 25,000 217.50.

VU METERSV002 Twin type. 2 metres 40x4Omm anddriver board, supplied with circuit andconnexion data E3.50.V003 New type, lust in. Twin type moulded

AERIALSX901 Telescopic 8 section 970mm long

in one piece, 80x4Omm (no driver board butsuitable circuit supplied) £2.50.

extended. 175mm collapsed. Swivel joint.2E1A fixing hole in base. 75p.X904 Ferrite rod 140mm x 9mm LW/MW/coupling coils, each independentlymoveable 64p.X905 As above, but LW/coupling coiltogether on moveable former 65p.

CLOCK CASE BARGAIN2472 Oval format, overall size130x68x87mm deep, with built in stand.Rear panel drilled to accept 4 switches +alarm 60p.


TorrlGOTTACOPY

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Abe: for the more technically melded -'"THE BEST ON C.B. RADIO" and "GOOD BUDDIES' ... Cer Miter.

IAl THE C.B. BIBLE - Discusses mewl aspects of C.B. £3.75 o 70p P&P.

send me copies of "BIG DUMMYS GUIDE" at £2.59 each + 45p P. + P.And/or ... copies of "THE C.B. BIBLE" at £3.75 each + 70p P. & P.And/or . copies of "THE BEST BOOK" at £3.95 each + 70p P. + P.And/or ... car stickers at 75p each + 15p P. + P.

I I enclose £ Cheques or postal orders only.Name, Mr./Miss/Mrs.

KWide range of L.B. Accessories available. Send for catalogue.

ONA PUBLICATIONS LTD. CITY RD., LONDON EC IIsm - Inn NM MINI MEI 11111 =111

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We stock a full range of everything you arelikely to require and more. If not, we can

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Duff Rig?? Then why not take advantage ofour repair service - absolute confidence

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REMEMBER!! Until C.B. becomes legal weDO NOT sell rigs

65

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66

HOBBY ELECTRONICSPROJECTS SPECIAL.

Contains twenty five ofthe very best projectsfrom Volume 1 ofHobby Electronics. Itwill be available inabout six weeks andshould be on your new-sagents shelves for just£1.25.

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ROM HEHobby Electronics, March 1980

Into ElectronicsConstructionPart 2 BY IAN SINCLAIR

The most fundamental device in electronic construction - the transistor.This month Ian Sinclair takes a close look at this and other importantcomponents.

YOU ENDED UP LAST MONTH with a working circuit,which flashed a couple of LEDs on and off. What makesthis circuit electronic as distinct from just electrical is thefact that there are no moving parts in the circuit to causethe flashing, it's all done by these remarkable transistorsalong with the capacitors, resistors and LEDs.

This month we're going to spend some time findingout what a transistor does, and learning a bit about howit does what it does. One way of learning would be toread every book about transistors you could lay yourhands on - but the HE way is easier, just stay with us.What we'll do is to build a circuit that helps to explainwhat the transistor is doing in the circuit, then we'll takeit from there.

To work then. Take the components off the board,gently pulling the leads out of the Eurobreadboard holes.Don't pull the leads out violently, because we want to beable to use these components over and over again.Providing you don't get the leadout wires too badlykinked at the ends, they should last out this course andstill be useful to you for years to come. I find that a pair oftweezers is very useful for taking components off, andalso for inserting the leadwires into the holes. Unlikepliers, tweezers can be used in one hand, and they're notso heavy to hold either.

SIMPLE STARTERSThe first circuit is a very simple one. The table ofconnections is shown in Fig. 2.1, it's just a LED with itscathode connected to the negative (-) lead of thebattery - the part of the circuit we usually call earth -and its anode connected to a 1 K5 resistor. There's noconnection between the other end of the 1 K5 and thebattery positive (+) lead. Now if you clip the battery on,but leave the + lead free, not plugged anywhere into theboard, nothing happens. If you now plug the battery +lead into the board at XI, the LED lights. What does thistell us? The LED lights when an electric current flowsthrough it and current flows only when there is acomplete circuit. All familiar stuff, you say? Yes, but weneed to bear it in mind when we make the next step.

The next step is to see if enough current will flowthrough you - yes, you. Touch the lead of the 1 K5resistor which is plugged into XI, and with the other

X1

REDGREEN

BROWN

1A

BATTERY 1-1 TO 5A

CATHODEI I ANODE

5A 1A

TABLE 1X1: 1K5to 1A1 A: LED Anode; 1 K 5 from 1A5A: LED Cathode; B (-)

Fig. 2.1 A simple LED and resistor circuit.

hand hold the battery + connection. Does the LED lightnow?Why not? It's because your resistance is too high. A 6 V

battery simply won't pass enough current through youto light the LED. The voltage of a battery measures howmuch push it can give to an electric current, and 6 voltsisn't much of a push. It's just as well, in fact. If a 6 Vbattery could push enough current through you tooperate the LED, you wouldn't feel very comfortable. Tobe precise, you would suffer electric shock, which iswhat happens if you touch a high voltage which can passquite a lot of current through you.

OK, so you have a lot of electrical resistance, and a 6 V.battery doesn't pass enough current through you tolight an LED. Now set up the circuit which uses the tableof connections shown in Fig. 2.2. This time we've used atransistor, the 1 K5 resistor, and the LED in the circuit.

TABLE 2X1: 1K5 to 1A; B(+)1A: LED Anode; 1 K5 from 1A5A: LED Cathode; Transistor collector7A: Transistor base1 OA: Transistor emitter; B (-)

Fig. 2.2 Using a transistor to control the LED.


The battery + connects to one end of the 1 K5 resistor atline XI, and the battery negative connects to the emitterof the transistor at line 10A. At the moment, the base ofthe transistor isn't connected anywhere, just pluggedinto line 7A. Now there's an electrical circuit presenthere. Current could flow from the battery + through the1 K5 resistor, through the LED, through the transistorcollector and emitter leads and so back to the battery.Why doesn't it? We know that current can pass throughthe resistor and the LED, so it must be the transistorwhich stops the current. The transistor works in thiscircuit like a large resistance - it won't allow enoughcurrent to flow to light the LED.

Watch this now. Plug a piece of wire into line 7A, sothat it connects with the base leadout wire of thetransistor. Remember you don't have to force both wiresinto one hole, any hole in line 7A will do. Hold a bit ofthis bare wire in one hand (don't let it come against anyother part of the circuit) and touch the battery + terminalwith the other hand. What happens? What's moreimportant, why does it happen?

RESISTANCEThe glowing LED indicates that there is current flowingbetween the collector and the emitter leads of thetransistor. This didn't happen before, and we reckonedthen that the transistor must have a high resistancebetween its collector lead and its emitter lead. Now itlooks as if it has a low resistance between these twoleads. Stop touching the wires - and the LED goes outagain.

It looks as if a connection to the base lead of thetransistor can make the difference between a transistorbeing a high resistance and being a low resistance.We've found already that we have a high resistancebetween our hands - we can't pass enough current tolight an LED. That small amount of current which passesfrom one hand to the other seems to be enough,however, to make the transistor change over from beinga high resistance to being a low resistance. All it has todo is to flow into the base leadout wire.

Try moistening your fingers, then hold them on thewires again. The LED glows a bit more brightly this time.You don't feel any current flowing through you, though,so you can only be passing a very small amount ofcurrent, much less than the transistor allows to passthrough the LED.

Stop to gather breath and ideas. A circuit whichincludes connections to a transistor collector and emitterdoesn't pass current unless there's a small amount ofcurrent flowing into the base terminal from a positivevoltage. That's the way these particular transistors work- they're all of a type called NPN which conducts whenboth the base and the collector are connected to positivevoltages. What this little lot has shown is that thetransistor acts as a tap for electric current. A smallamount of current flowing through you has caused thetransistor to pass a much greater current through theLED. You can think of the base lead of a transistor asacting like a tap which controls the flow of currentbetween the collector and the emitter.

TRANSISTOR TAPThere's an important difference, though. The transistor,unlike a tap, is controlled electrically. The amount ofcurrent which flows into the base controls the amount of

current which flows between the collector and theemitter. The name 'transistor' comes from the originalname 'transfer resistor', because the discoverers oftransistor action noticed that the resistance between thecollector and the emitter changed when the amount ofcurrent flowing into the base changed. The word 'con-trols' doesn't just mean that the current can be switchedon and off, either. Let's look for a moment at anexperiment that we can't do (without a lot of expensiveequipment) but whose results are important. Fig. 2.3shows what's involved. A transistor is connected with itscollector and emitter in one circuit, complete with ameter to measure the current (a milliammeter) whichflows through the transistor from collector to emitter.There's another meter too, a current meter of the typecalled a microammeter, which can measure very smallcurrents. This meter is connected to the base of thetransistor, and to a current regulator which can controlthe amount of current which passes.

METER (MILLIAMMETER)

TRANSISTOR

Fig. 2.3 The arrangement which shows how a transistorcontrols current. You don't need to do this one, but you shouldknow about it.

What happens? Well, as you'd expect, passing somecurrent into the base of the transistor causes current toflow between the collector and the emitter. That muchwe knew already. What is new is how these currentschange when we alter the regulator. We'll find that, forexample, doubling the amount of current into the baseterminal causes the other current, the current betweenthe collector and the emitter, to double also. In fact, anychange we make to the base current causes an exactlyproportional change to the collector -emitter current.Mathematically, this is simple proportion, so that thecollector -emitter current is directly proportional to thebase current. If we drew a graph, plotting collector -emitter current in one direction and base current alongthe other direction, the graph would be a straight line.

That's very convenient, because it means that theratio:-

collector-emitter currentbase current

is constant. Suppose, for example, that the ratio hap-pens to be 100. A ratio of 100 means that thecollector -emitter current is one hundred times the basecurrent - always. If the base current happens to be 10microamps, for example, then the collector -emittercurrent is 10 X 100 microamps, which is 1000microamps (equal to one milliamp). Can we work this theother way around? Yes, if the collector -emitter current is10 milliamps, then the base current has to be onehundredth of this,

10

100 milliamps, or 0.1 mA.


Into Electronics ConstructionVARIABLE VOLTAGESOK so far? The action of the transistor is sometimescalled current amplification, because a small amount ofcurrent into the base controls a larger current betweenthe collector and the emitter. Notice one very importantpoint - amplification of this sort doesn't mean makingcurrent greater - it means using a small current tocontrol a large one, like making a large-scale copy.

So far, we've been working with just one electricalquantity, current, and we've been relying on the voltageof a battery to keep the current flowing. Will the currentflow at any voltage, or do we need a certain amount ofvoltage to keep current flowing through a transistor?Once again, we can discover this by experiment only ifwe have suitable measuring instruments, so we'll de-scribe what happens.

Suppose we set up voltage measuring instruments,called voltmeters, to measure the voltage between thebase and the emitter and also between the collector andthe emitter of a transistor, as in Fig. 2.4. We'll keep thecurrent measuring meters in place also, so that we knowwhen there is a current flowing, and we'll regulate thevoltages, not the currents. What would we expect toread from these meters?

COLLECTOR

EMITTER

MILLIAMMETER

VOLTMETER

MICROAMMETER

Fig. 2.4 Another one you don't need to do for yourself - itshows how the voltage between the base and the emitter of atransistor controls the current.

Well, the first thing we would notice with this smallfortune in measuring instruments is that no current flowsat all when the voltage reading at the base is only arounda quarter of a volt (0.25 V). The meter is connectedbetween the base and the emitter, so that this is thebase -to -emitter voltage. That's one important differencebetween a transistor and a resistor, because a resistorpasses current when any voltage is placed across it. Thetransistor behaves as if there's some sort of switchinside, preventing current flowing.

If we jack up the voltage, slowly and steadily, we seethe current start to flow at somewhere around half a volt,between 0.5 V and 0.55 V. Can't we be more precise?No, we can't, because the voltage at which the transistorstarts to conduct varies - it depends on the temperatureof the transistor for one thing, and also on the transistoritself. That doesn't just mean what type of transistor, butwhich individual transistor you use. They're not as alikeas peas in a pod as far as this is concerned, and eventransistors which were made on the same productionline and at the same time from the same materials showthese differences. It's just something we have to livewith.


CURRENTWhen current starts to flow in the base -to -emitter circuit,current will also flow in the collector -to -emitter circuit,just as we have now come to expect. Now for anothermeasurement. Let's suppose that the current whichflows into the base is a small quantity, ten microamps(written as 10 NA), and that we needed a voltage of 0.5V to make this amount of current flow. How muchvoltage do we need to make 100 NA, ten times as much,flow? If we were dealing with a resistor, the answerwould be simple - ten times as much, 5 V would beneeded. How much voltage does the transistor need?Just 0.06 V more, that's all. In our example, that's a riseof voltage from 0.5 V to 0.56 V.

Far from making life difficult, this makes transistorelectronics rather simpler. When a small transistor isconducting, its base to emitter voltage woll be some-where between 0.5 and 0.6 V, whether the current islarge or small. We've said 'small', because some largepower transistors may need a volt or so between the baseand the emitter if they are to pass really large currents;we shan't be using that size of transistor in this series.

There's one more trick left up the sleeve. Suppose themeasuring circuit is changed to the arrangement shownin Fig. 2.5. The new variable resistor RV2 lets us controlthe voltage at the collector. Up till now we've left thatvoltage at 6 V, because the battery supplies 6 V. Whathappens if we set the transistor conducting, and thenstart winding this voltage down? The answer, sur-prisingly, is practically nothing! Once we set the currentflowing, using RV2 to regulate the current in thebase -emitter circuit, the collector voltage has very littleeffect, until the voltage drops right down to about 0.2 V.

COLLECTOR

BASE

EMITTER

MILLIAMMETER

VOLTMETER

MICROAMMETER

VOLTMETER

RV1

HATTERY

Fig. 2.5 This is the last of 'em! It shows how the voltagebetween the collector and the emitter of the transistor affects(or doesn't affect) the current.

Only when the voltage drops this low (the figure of 0.2 Vis called the saturation voltage) does the current sud-denly start to drop. What do we make of the show so far?Let's list what the transistor does.

1. The current that flows between the collector andthe emitter is always a fixed amount times the currentthat flows between base and emitter. This 'fixed amount'varies from transistor to transistor.

2. The voltage between the base and the emitter hasto be around 0.5 to 0.6 V to keep the transistorconducting.

3. The amount of current isn't affected much by thevoltage at the collector, unless this drops to about 0.2 Vor less.

69

LIGHT LEDNow let's try a circuit. Fig. 2.6 is the table of connectionson the Eurobreadboard, which should result in a circuitwhich lights the LED. The transistor collector is con-nected to +6 V, and the emitter connects to the 2K2resistor and then to the LED. When current flows, then, itflows through the transistor, the 2K2 resistor, and theLED, causing the LED to light.

YELLOW, PURPLE. RED

4k7

X1 2A

BA

ANODE

6A

CATHODE

2A

RED, RED, RED

dk 7 2k2

TABLE 6X1 : B(+); 4K7 to 2A; Transistor collector2A: Transistor base; 4K7 to 6A; 4K7 from X14A: Transistor emitter; 2K2 to 8A6A: B(-); 4K7 from 2A; LED cathode8A: 2K2 from 4A: LED Anode

Fig. 2.6 How the components are connected for an "emitterfollower" circuit.

All right? The LED lights when it's connected to theemitter of the transistor. Now change the connections,by taking the end of the 2K2 resistor which was pluggedinto 4A and now plugging it into 2A. This is theconnection to the base of the transistor. Does the LEDlight here too?

It does, and the experiment shows that the voltage atthe base must be about the same as the voltage at theemitter. This is a different type of transistor circuit, calledan emitter -follower, in which we connect the collector ofthe transistor to the + supply voltage, but we don'tconnect the emitter of the transistor to the negativesupply voltage. Instead, the emitter is connected to a'load', the resistor, LED or whatever it is we're control-ling with the transistor. We'll look at these differentconnections again in the next part when we learn a bitmore about circuit diagrams. The emitter -follower circuitmakes use of the fact that the voltage between theemitter and the base of a transistor is always low, about0.5 to 0.6 V.

WET CURRENTSNow for this month's project circuit, which makes use ofall that we've learned about transistors so far. The circuitis for a moisture detector, useful for showing when yourplants are well watered, or if the washing -machine isdripping water, unseen, on the floor underneath. Theprinciple is very simple, it makes use of the first experi-ment you tried out this month. A very small current intothe base circuit of a transistor will cause a much greatercurrent to flow between the collector and the emitter ofthe transistor. Now water doesn't conduct electriccurrent very well, but it conducts a lot better than air ormost dry materials. If we have a couple of wires, one

connected to the positive of the battery and the other tothe base of a transistor any slight current which passesfrom the positive terminal to the base will cause a muchlarger current to flow through the transistor between thecollector and the emitter. The 'slight current' can becaused by water touching both wires, so that the wiresact as a sensor or detector of water or steam. One usefulway of making this more sensitive is to use two of thecopper strips in a sheet of Veroboard (Fig. 2.7) with thewires soldered to the strips, and a piece of cottonfastened across the board. Cotton retains moisture, sothat current leaks quite happily from one track to anotherif any water falls on the detector.

DETECTORWIRES

SOLDERED

SOLDERED

STRIP OF COTTONSECURED BYELASTIC BAND

Fig. 2.7 One form of the water detector board.

If you're not too happy with soldering yet (wait untilPart 5) then try the scheme shown in Fig. 2.8. This usesa wood or hardboard base with aluminium cooking foilglued to it. The foil is cut with a modeller's knife so that

BOLTS/WASHERS /NUTS

HOLDING WIRE COOKING

HARDBOARD

Fig. 2.8 A version of the water -detector board which doesn'tneed any soldering.

it's in two separate pieces, with a thin wooden trackbetween them. Electrical connections are made from thealuminium foil into our circuit by bolting the connectingwires to the foil, using small -gauge nuts and bolts andlarge diameter washers. Remember that only single -coilwire should be plugged into the Eurobreadboard.

That settles the detecting part of it, which can be along distance from the rest of the circuit if you like. Theelectronics part of it all consists of two transistors, threefixed -value resistors, an LED, a silicon diode and acomponent you haven't met before - a 10K poten-tiometer. The potentiometer, usually referred to as a potis a type of resistor with an extra contact whose positioncan be varied. The one we've used is called a 10K potbecause there's a resistance of 10K (more about theseunits later) between the two end connections, and this'value of resistance is fixed. There's another connection,though, to a contact which can slide over the resistor


Into Electronics ConstructionCONNECTS TOHIGHER VOLTAGE(LIKE B+)

CONNECTS TO POINT WHOSEVOLTAGE IS TO BE CONTROLLED

CONNECTS TOLOWER VOLTAGE(LIKE B-)

Fig. 2.9 The potentiometer.

materials, and the position of this contact can be setanywhere between one fixed contact and the other byturning the shaft of the pot. Suppose, for example, weconnect this pot to +6 V at one end and to zero at theother. We can move the sliding contact to the zero end,making the voltage at the middle contact equal to zero.We could set the contact to the +6 V end, making thevoltage at the middle contact equal to + 6 V. We can alsoset the contact half -way, which makes the voltage of themiddle terminal equal to +3 V, and we can set thecontact so that the voltage of the middle terminal can beany value between 0 and +6 V.

CONNECTIONSIt's a very useful device, and we'll be using it again laterin the series. The connections are always the same onthese rotary They are set in a row, andwhen you're looking from the front, looking down theshaft of the potentiometer, then the end which connectsto the higher voltage is on your left and the end whichconnects to the lower voltage is on your right. Themoving contact is between them in the middle. That'sthe way it's going to be connected in this circuit, andthat's the way it's connected in most circuits.

The connections can be made by stripping the insu-lation from an inch or so of single -core wire, andwrapping this bare end several times tightly round one ofthe potentiometer terminals. This doesn't give as good aconnection as soldering, but it'll do for experimentingwith provided you don't allow it to loosen too much bymoving the whole potentiometer around too much. Fig.2.10 shows these leads labelled, so that you can seewhere they plug into the board.

Fig. 2.10 Making the connections to the potentiometer for thewater -detector circuit.

The rest of the connections are shown in the table ofFig. 2.11. Remember that the transistors must beconnected the right way round - you should know bynow how to identify the emitter lead of this type oftransistor by its metal tab. The LED also has to be the


right way round - though the circuit will still work withthe LED connected the wrong way round, there's achance of damaging the LED. The diode also has to beconnected the right way round, otherwise the LED willnever light and may possibly be damaged.

BROWN, BLACK, OR ANGI RED, RED, BROWN

6A

LEEE

ANODE

10k 220R

CATHODE

4A 6B

BI41- - -X1 RI I

1st TRANSISTOR(011

BAND

YELLOW, PURPLE, BRO1

4 RIP

4A 68

CATHODE

xl2A

4A

DIODE

D1

YI

v1

DETECTOR WIRES IRA

2nd TRANSISTOR(02)

X1

2B

48

TABLE 11X1 : 10K to 6A; Collector Q, Collector Q; PotentiometerP; B (+)2A: Base of Q; Detector wire 14A: Emitter of Q; Anode of LED; Cathode of Dl; 220R toY16A: 10K from X1; detection wire 2Yl: 220R from 4A, Potentiometer R; B (-)6B: Cathode of LED: 470R to 4B4B: 470R from 6B: Anode of Dl; Emitter of Q2B: Base of Q; Potentiometer Q

Fig. 2.11 The connections for the water -detector circuit.

SETTING UPHow do we use it? The pot adjusts the sensitivity of thecircuit for detecting water. You can, for example, placethe detector where you want to detect water and turn thepotentiometer shaft fully clockwise. If you've connectedit the right way round, the circuit should now be at itsmaximum sensitivity, and a drop of water on the detectorplate bridging across the contacts should cause the LEDto glow.

Sometimes you don't need so much sensitivity. Youcan use two bare wire leads in a plant pot, for example,and adjust the potentiometer so that the LED justswitches off when the soil is damp enough. Now if youadd too much water, the LED glows to warn you!

Suppose you want to use the unit to warn of dryness?It's easy, you just reverse the LED and the diode .^-e

71

Into Electronics Constructionconnections as shown in Fig. 2.12. Now you set thepotentiometer so that the LED just switches off when themoisture around the detector is getting a bit low, and theLED will shine a warning to you when things are too dry.It would never light in my local!

CATHODE

ANODE CATHODE

68 4A 4A

D1

48

Fig. 2.12 How to plug in the LED and the diode so that the unitwarns of dryness.

Next month - circuit diagrams, and a big stepforward in circuit construction.

ADDITIONAL SHOPPING LISTPart 2

These are the extra components which you'll needto add to last month's list for the new work thismonth.Resistors: 1 x 220R

1 x 470R1 x 2K22 x 4K71 x 10K

Potentiometer: 10K miniature typeHardware: small strip of Veroboard or hardboard(see details in text).

,HE

u.........................................,........,...sor ircui .......................................................

RI22k

Cl1n0

SW1PLAY

L

1 14

2 13

123 ICI4 4047 11

10

9

C2220,,10y

8 8 15

IC24026 5

10 12 13 9 11 6 7

eelm C3100n

b c

DISPLAYFND500

8 8 15

IC31 54026

10 12 13 9 11 6

SW2ON/OFF

DISPLAY 2FND500

6 8 15

IC44026

10 12 13 1 6

DISPLAYFND500

0-1-9V

-Ve0

game is to score as many points as needs to be reasonably high. observer to perceive. When SW1 isONE ARMED possible in an agreed number of The display section uses three released, the display is "frozen" at

attempts, say 25 or 30. CMOS 4026 decade counter/ whatever number it happened toBANDIT The circuit consists basically of a seven segment decoders, which be displaying when ICI ceasedclock oscillator using ICI and a can be used to directly drive high oscillation. There is, of course, no

= This circuit is designed to give an three stage counter which uses IC2 efficiency common cathode dis- way of operating SW1 to definiately= approximate simulation of a one to IC4. The 4047 CMOS device plays such as the FND500, obtain one of the winning= armed bandit fruit machine, and is used in the IC 1 position is a DL704, etc. The three display numbers, and it is purely a matterE only intended for home- monostable/astable device which circuits are connected in series, in of chance whether or not one of= entertainment purposes. The unit is used here in the true gating the normal way, so that one thou- these is displayed, as is the case: has three seven segment LED dis- astable mode. Under quiescent sand clock pulses take the display with a real one armed banditE plays, and when a pushbutton is conditions R2 takes the gating through every number from machine.

depressed, all display segments input (pin 5) low, and prevents the "000" to "999", and then back to IC1 to IC4 are all CMOS de -E. appear to light up. When the but- circuit from oscillating. Depressing "000" again. vices, and normal CMOS handling: ton is released, a random number SW1 takes the gating input high, Thus, when SW1 is operated precautions should be observed

is displayed. The idea of the game and starts the circuit oscillating at a the display cycles through every when dealing with these. The cur-= is to obtain a row of three identical frequency which is controlled by number about ten times per rent consumption of the unit can be= numbers in the display, with (say) 1 R1 and Cl. The specified values second, with all the display seg- over 50 mA when certain numbers= point being scored for "000", two give an operating frequency of ments appearing to switch on con- are displayed, and a large battery

points for "Ill", etc., up to 10 about 10kHZ, although the exact tinuously as the action of the dis- such as a PP9 should be used as apoints for "999". The object of the frequency is unimportant, it just play is too fast for a human power source.


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VISIT OUR ELECTRONIC TIME CENTRESAND SEE ONE OF THE MOST IMPRESSIVE QUARTZ WATCH

RANGES IN BRITAINDAVENTRY

67 High StreetDaventry, N'hants

Telephone: 03272 76545/77659

NORTHAMPTONSt Giles Square,Northampton

(Open 1st Feb. 1980)

QUARTZ MELODYAlarm Chronograph(incredible watch)

Count -down Timer

8.50Alarm

[ e?18 16}

Time Zone

nit fin nnlithuuuuChronograph

5 independent workingmodes, day of week inEnglish, French or GermanOust select the one you like).Hours, mins, secs, clay, date, countdownalarm, dual time zone, 1 / 100th sec.stopwatch. Lap/split time, 1st and 2ndplace times. Melody test function.34 Functions

M 30

Price only£19.95

Same day despatchPrice includes

POST & PACKING

CASIO CHRONO9505-3213

Stainless steel case.water resistant to 66 feet.Hours, mins, secs, am /pm,year, month, date, day.Auto -calendarpre-programmeduntil the year 2029.12/ 24 hour. Stopwatch function.Range .7 hours. 1/ 100 sec.(Mode) Net time/lap-time/1st -2nd place times.Dual time function.Accuracy 15 secs per month.Battery life approx 4 years.

M22

CASIO ALARMCHRONO81 CS -36BHours, mins, secs, day,and also day, month and yearperpetual automatic calendar.100th sec chronograph to7 hours.Net time /lap /time /1stand 2nd place times. Useroptional 12/ 24 hr display. 24hourly chime.Alarm. User optional,Backlight, mineral glass,stainless steel.Water resistant to100k.Battery life approx 4 years.

M25

Same daydespatch

Price only

£23.95including POST & PACKING

Price only Same daydespatch

including POST & PACKING

CASIO F-200Sports ChronoAttractive Man's watchin black resin withmineral glass.Hours. mins, secs, am /pmMonth, date,alpha -numeric day.Auto -calendar set28th Feb.Stopwatch workingrange 1 hour,units 1/ 100 sec. Mode.Net Time/lap/time/1st -2nd place times.Accuracy approx 15 secsper month.Battery 12 months.

M24

Price only£15.95Same daydespatch

. including POST & PACKING

CASIO F -8C3 Year Battery LifeHours, mins, secs,am/pm, date, day.Auto calendar set28th Feb.Accuracy 1 5 secs permonth. Battery lifeapprox 3 years.

Same day despatch

M36

Price only


SEIKOCHRONOGRAPHNEW STYLE

Hours, mins, secsand day of the week.Month date andday of the week.Stopwatch display -Hours, mins, secsup to 12 hours(mins, secs, 1/ 100 secsup to 20 minutes).Lap timing.Continuous timemeasurement of twocompetitors.Stainless steel,mineral glass.

Same day despatch

M 33

Price only


=NM

SEIKO AlarmChronograph

With WEEKLY Alarm.Hours, mins, secs, monthdate, day. am /pm.Weekly alarm - can be setfor every day at designatedtime e.g. 6.30 am on Mon,Wed and Friday.Alarm set time displayedabove time of day.Full stopwatch functions,laptime, split etc.

Same day despatch

M10

Price only£79.95

including POST & PACKING

SEIKO DIGI-ANACHRONOGRAPHTime and Calendar functionAnalog pan display; hr, min, sec.Digital pan display; hr, min, sec,date. day and colon.Calendar -month, date. day.Stopwatch - hr. min, sec, 1/100 sec.Lap /stop and stop marks.Counter function.Time and calendar settingfunction.

Price only

£79.95

Same day despatchincluding POST & PACKING

M62

POST COUPON TO: METAC (24 -hour despatch centre) FREEPOST (No stamp required), 47a High Street, Daventry. Northants

Please send me

I enclose PO/Cheque value

Barclaycard/Access No.

Name

Address

POST. PACKING AND VAT included in price

Please complete both coupons

From: METAC Electronics & Time Centre, (ETI)47a High Street, Daventry, Northants.

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Post this 004coupon now for your'.

A es. copy of our 1979-80 ncatalogue price 70p.

Please send me a copy of your 280 pagecatalogue. I enclose 70p (plus 37p p&p).

-7 If I am not completely satisfied I may return thecatalogue to you and have my money refunded.rl If you live outside the U.K. send £1.35 or ten r)

International Reply Coupons.I enclose £1.07.

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A wide range of disco accessories atmarvellous prices. Our catalogue hasall the details.

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A very high quality 40W per channelstereo amplifier with a superbspecification and lots of extras.Full construction details in ourcatalogue.

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Telephone: Southend (0702) 554155.Shop: 284 London Road, Westcliff-on-Sea, Essex.(Closed on Monday).Telephone: Southend (0702) 554000.

issn 0142-6192 march 80 45p - world radio history

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