105
January 1984
95 pup-to-date electronics for lab and leisure I:31.0570P incIVAT)
How accurate isyour watch?Find out with our opto-
coupled timepiece timer.
A gyrophoneto make your
stereo wander.PLUS: audio embellisher address decoding weather vane
universal active filter audio sleuth Z80 EPROM programmer programmable crystal oscillator digital cassette tucording
TIlla LINEAR 1 Cs CPU's MEMORIES @ROOM CRYSTALS INTERFACE ICS
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MAIL ORDERS TO: 17 BURNLEY ROAD, LONDON NWIO IEDSHOPS AT: 17 BURNLEY ROAD, LONDON NWIO
(Tel: 01-452 1500, 01-450 6597. Telex: 922800)305 EDGWARE ROAD, LONDON W2
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TELETEXT
DECODER6445070644557335445011
ACIS
CS
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LOGIC PROBE KIT E12
ELEKTERMINAL KIT £50 7013170417
HOUSEKEEPER
Full 106 as described in May Deltic),Sockets for all I C.5 2K Prog EPROIA
E55 -E1p&p
Power Supply 1 8.5 8Vsuaabte f Or the Housc-keepe,
E7 El 1090.0
JUNIOR COMPUTER KIT E86 plus Et p &All Junior Computer Extension Boards availableJUNIOR COMPUTER BOOK: 1 £4 2.3 & 4 £4.50 ea to & book 70p,1V Games Extension boards available.ELEKTERMINAL KIT £50 (plus El p & galTELETEXT DECODER KIT £85 (plus £1 p & p)(Decoding Board and Keyboard Elektor Nov. 81)Reprint of Teletext articles 1125 (plus large SAE)
PROGRAMMED EPROMSJunior Computer 2 . 2716 Intelekt Chess ea 682708 Basic £8 2716 TV Games E82716 Tape Management £8 71301 Elekterminal E72716 Prog. Management ES 2716 Disco Lights £882523 Interface £5 82523 Freq. Counter IIC3C4) ea ES2716 Housekeeper £8 2716 Talking Dice E8
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111:11:1211:1175A
elektor january 1984
gyrophoneWith this unit connected to your stereo system you can produce an effectvery like that of a Lesley rotating speaker system.
how accurate is your watch?'Clockwork' watches can be very accurate provided they are adjustedproperly. The circuit described here quickly calculates the error in amechanical ticker so that it can be set correctly.
digital cassette recorderCassette tape is often used as memory storage in personal computersUnfortunately, the quality of the computer's cassette interface usuallyleaves a lot to be desired. The present circuit improves matters consider-ably without affecting the audio performance of the cassette recorder.
audio signal embellisherA three part modular system that can increase your listening pleasure ifyou are forced to connect mono and stereo equipment together.
universal active filterAn IC that can act as a universal active filter with a minimum of externalcomponents is certainly worth having a look at.
from thermometer to thermostatAdding a single IC and a handful of other components to the LCD ther-mometer featured in our October 1982 issue permits it to be used as athermostat.
1-20
1-22
1-29
1-34
1-42
1-44
missing link 1-45
PC board pages 1-46
audio sleuth at work 1-49When something goes wrong (and it often does) this article can help youfind the root of the problem.
wind direction indicatorMany lament the passing of the weathercock, but our electronic versionhas at least one distinct advantage in that you no longer have to see theactual weather vane to know which direction the wind is blowing.
Z80 EPROM programmerA small circuit consisting of just a few components is all that is needed toenable any Z80 system to program 2716 EP ROMs in situ.
home-made low-cost wiring probeWiring prototype circuits is greatly simplified by keeping the wire tidilyon a spool.
address decodingOne of the least understood aspects of computing is address decodingThis article is intended to throw some light onto the subject.
applicatorNew programmable crystal oscillators in which the oscillator, dividers,and selector circuits are housed together with the quartz crystal in a 16 -pin DI L package.
1-52
1-60
1-62
1-64
1-69
market 1-71
switchboard 1-77
EPS service 1-88
advertisers index 1-90
A gyroptorao make your
Ouse watefteswi, aerl SI.,aledl =DIM pragpurr-T34,.i.*0-.#1.01 nesinftg
At the beginning of a newyear it is quite appropriatethat our cover item deals withtime. It enables the error ofa mechanical watch to bemeasured so that the watchcan be set correctly. The titlesof the rest of this month'sarticles more or less speak forthemselves, except maybewhat do we mean by 'agyrophone to make yourstereo wander'? Some of themore musical of gyrophonistssuggest that it is like a crossbetween a moose and a setof bagpipes! Well, we're nottoo sure. Suffice it to say thatthe effect has to be heard tobe appreciated. We must warnyou- to beware of maskedtypes appearing at your doorclaiming to be gyrophones,they are likely to make morethan your stereo 'wander?
A selection fromnext month's issue: capacitance meter video combiner video syncbox constant -light source disco control unit tachometer for diesels
1-03
Elektor Publishers Ltd., Elektor House,10 Longport, Canterbury CT1 1PE, Kent, U.K.Tel.: Canterbury (0227) 54430. Telex: 965504.Office hour: 8.30 - 1230 and 13.30 - 16.30.
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P.E.L. Kersemakers, R.P. Krings,P. v.d. Linden, D.R.S. Meyer,G.C.P. Raederscforf, J.F. van Rooij,G.O.H. Scheil, M.J. Wijffels
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40-16-11, arc 11014587Giro a/c no. 315-4254
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misted for publication etc,) EPS = Elektor printedcircuit board service
The circuits are for domestic use only. The submission of designsor articles to Elektor implies permission to the publishers to alterand translate the text and design, and to use the contents in otherElektor publications and activities. The publishers cannot guaran-tee to return any material submitted to them. All drawings,photographs, printed circuit boards and articles published inElektor are copyright and may not be reproduced or transmittedin any form or by any means, including photocopying andrecording, in whole or in part without prior written permissionof the publishers. Such written permission must also be obtainedbefore any part of these publications is stored in a retrievalsystem of any nature.
Patent protection may exist in respect of circuits, devices, com-ponents etc. described in this magazine.The publishers do not accept responsibility for failing to identifysuch patent or other protection.Dutch edition: Elektuur B.V.,
6190 AB Beek (L), the Netherlands.German edition: Elektor Verlag GmbH,
5133 Gangelt, W -Germany.French edition: Elektor Sarl, Le Seau, 59270 Bailleul, France.Italian edition: Elektor, 20092 Cinisello B., Italy.Spanish edition: Elektor, Av. Alfonso XIII, 141, Madrid 16.Greek edition: Elektor, Karaiskaki 14, Voula, Athens.Turkish edition: Elektor A.S., Refik Saydam cad. 89, Aslan,
Han kat 4, Sishane Istanbul.Indian edition: Elektor Electronics PVT Ltd., 3 Chunam Lane,
Bombay 400 007.Australian Elektor Australia Pty Ltd.,edition: 11-174 Military Road, Neutral Bay, Sydney.
Volume 10 - Number 1
What is 10 n?What is the EPS service?What is the TQ service?What is a missing link?
Semiconductor typesA large number of equivalentsemiconductors and ICs existswith different type numbers.For this reason, 'universal'type numbers are used inElektor wherever possible:for instance, '741' stands forpA741, LM 741, MC741,MIC 741, RM 741, SN 72741,and so on.
Type numbers 'BC 107B','BC 2378', 'BC 547B' allrefer to the same 'family'of almost identical good -quality silicon transistors.In general, all membersof the same family can beinterchanged.
BC 107 (-8, -9) families (NPN):BC 107 1-8, -9 I,BC 147 1-8, -91,BC 207 1.8, -91,BC 237 1-8, -9),BC 317 1-8, -9I,BC 347 1.8, -91,BC 547 1-8, -9 i,BC 171 1-2, -3),BC 182 (-3, -41,BC 382 1-3, -4),BC 437 1-8, -91,BC 414
BC 177 (-8, -9) families (PNP):BC 177 1.8, -9),BC 157 (-8, -9),BC 204 1-5, -6I,BC 307 1-8, -9),BC 320 (-1, -2),BC 350 1-1, -2),BC 557 (-8, -9),BC 251 (-2, -3),BC 212 1-3, -41,BC 512 (-3, -4),BC 261 (-2, -3),BC 416.
Resistance and capacitancevaluesDecimal points and largenumbers of zeros are avoidedin values of resistors andcapacitors wherever possible.Instead, the following prefixesare used:p (pico-) =
(nano-) = 10/'(micro-) =
m (milli-) = 10'3k (kilo-) = 103M (mega-)G (aloe-) = 10'
A few examples of resistancevalues:2k7 = 2700 2; 3M3 =3,300,000 2; 820 = 820 P.Resistors used are 'J.: wart,5% carbon types, unlessotherwise stated.
Distribution in U.K.: A few, examples of capaci-Seymour Press Ltd., 334 Brixton Road, London W49 7AG. tance values:
4p7 = 4.7 pF=Copyright (c..2% 1984 Elektor Publishers Ltd., Canterbury . 0.000 000 000 004 7 F;Printed in the Netherlands. ABC IlOn= 0.01 pF = 10"! F =
10,000 pF
eiektor januar; 1984
ISSN 0308-308X
The DC working voltage ofcapacitors (other than elec-trolytic or tantalum types)is normally assumed to be atleast 60 V. As a rule of thumb,a safe value is usually ap-proximately twice the DCsupply voltage.
Test voltagesDC :est voltages shown aremeasured with a 20 kniv in-strument, unless otherwisespecified.
U, not VNormally, the internationalletter symbol 'U' instead ofthe ambiguous 'V' is usedfor voltage. 'V' is reservedas an abbreviation for 'volts'.For instance, Ub = 10 V,not Vb = 10 V
Mains voltageMains (power line) voltages arenot given on Elektor circuitsas it is assumed that ourreaders know what voltageis standard in their part ofthe world!Readers living in areas whichuse 60 Hz supplies should notethat Elektor circuits aredesigned for operation from50 Hz supplies. This will nor-mally not be a problem, butin cases where the mains fre-quency is used for synchron-isation, some modification tothe circuit may be required.
Technical services to readers. EPS: Elektor printed -circuit
board serviceMany Elektor articles in-clude a layout for a printed -circuit board. Most, but notall, of these boards areavailable ready -etched andpre -drilled. The EPS in thecurrent issue gives a list ofavailable boards, front panels,and software cassettes.
Technical queriesTechnical queries relating toarticles published in Elektormay be submitted by tele-phone (Tel. 0227-534741on Mondays between 13.30and 16.15, or in writing.The telephone service doesnot operate during July/August. Letters should beaddressed to Dept. TQ Pleaseenclose a stamped self-addressed envelope or, ifyou live outside the UnitedKingdom, an InternationalReply Coupon.
Missing linksAny important modifi-cations to. additions to, im-provements to, or correctionsin, Elektor circuits are gen-erally published under 'MissingLinks' at the earliest oppor-tunity.
-04
advertisement elektor january 19 84
RESI & TRANS!A series of strip cartoons in book form inwhich two enterprising characters explorethe field of electronics in then own inimi-table way. Their adventures are full oftension, because they often go against thecurrent - whereby they encounter muchresistance - before they reach their goal.These books familiasize the reader witheiectionics in an unusual way: exciting.playful, yet thorough. Part I comes com-plete with a printed -anon board and rest -materPart I. Banish the Mysteries
of Electronics E 5.75Pan II: Hands oil my Bike! . . E 450
TV GAMES COMPUTERThis book, pomades a different - and, inmany ways, easter - approach to micro-processors.. The TV games computer isdedicated is one specific task, as thename suggesn. This provides an almostPhase opportunity to have fun whileleaning!Price E 6.75
DIGIBOOKProvides a simple step-bystep introduc-non to the basic theory and applicationof digital electronics and gives dearexplanations of the fundamentals ofdigital circuitry, backed up 0y expe,iments designed to reinforce this newlyacquired knowledge. Supplied with anexperimenter's PCB.Price
300 CIRCUITS
E6.00
For the home constructor - 300 projectsrangng from the basic to the very sophismatedPrice E. 5.50
MICROPROCESSOR HARDWAREThis book describes a range of peripheralequipment that can be connected andused with an assortment of personalcomputers viMich use the 6502,6809,280or the 8080 CPU.Price E 7.50
JUNIOR PAPERWARE 1Modifications of the PMIPME EPROM:Source listings, Hex dump of the Softwarecrunches and punches fElektor 85, May1982)Ps ice £2.00JUNIOR PAPERWARE 2Source listing of the bootstrap loaderfor Ohio Scientific Floppys: Hex dumpof the EPROM IESS 5151Price £2.00
DATA SHEET BOOKHere at lass is the book that designers havebeen waiting for the ['elm:it Data SheetBook_ In 240 pages it gives you a CMOS,a Linear, Special Function and Audio DataBook: extensive information on 269 ofthe most important IC's. A very usefuland economical reference book!Price 8.00
JUNIOR COMPUTER VIA 6522
This book deals with the well-knownVersatile Interface Adapter (VIA) type6522. Although it is an inckspensable ad-dition to the four books already devotedto the Junior Computer, it is not aimedsolely at Junior users, but at anybody whohas a system with one or more 6522s. Itaffords a complete familiarization withthis flexible and effective component.Price E 3.25
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JUNIOR COMPUTER BOOK 1For anyone washing to become familiarwith bnicrokomputers, this book givesthe opportunity to build and program apersonal computer at a very reasonablecost.Price E 6.50
JUNIOR COMPUTER BOOK 2Follows in a logical continuation ofBook I. aid contains a detailed appraisalof the software. Three major programmingtools, the monitor, an assembler and aneditor. ore discussed together with pratical proposals for input and peripherals.Price E 6.50
JUNIOR COMPUTER BOOK 3The next, transforming the baste. singleboard Junior Computer into a completepersonal computer system.Pnce E 6.50
JUNIOR COMPUTER BOOK 4Book 4, the last in the series, describes allthe software requited to operate the corn'plete system. A number of peripheraldevices, such as a printer and a videoterminal, may be 'hooked up' to thecomputer. During the final stage in its'growth', the machine is able to extendits linguistic skills, fora special version ofBASIC is now available on cassettePace 6.50
301 CIRCUITSThe book is a continuation of our popularand very successful 300circuits publi-cation. It is composed of 301 assortedcircuits ranging from simple to morecomplex designs. described and en:darnedin straightforward language.Price £5.50
33:
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SC/MPUTER (1)Describes how to build and operate yourown microprocessor system - the firstbook of a series - further books willshow how the system may be extended tomeet various requirements.Price E 5.50
SC/MPUTER (2)The second book in series. An updatedversion of the monitor program lElbug IIIis intnicluced together with a number ofexpansion possibilities. By adding theElektemiin.al to the system described inBook 1 the microcomputer becomes evenmore versatile.Price E 5.50
FORMANTComplete constructional detals of theElektor Formant Synthesiser comeswith a FREE cassette of sounds thatthe Formant is capable of producingtogether with advice on how to achievethem.Price E 6.00
33 ELECTRONIC GAMESA selection of circuits which give as mudsenjoyment in building them as actuallyplaying the games. The circuits are fasci-nating although the electronics Involvedare not complex and therefore anyonewith a good soldering iron will find thisbook satisfying. These are electronic gamesthat do not need a TV screen, and as aresult can be played just about anywhere.Price . . E 4.50
To order please use the postage paid ordercard in this issue.ADD 50p P 8 P U.K. (OVERSEAS 1.00)
sc/mputer (1) utter (2)txsid ycta- own tuict yet: cFM1
micciycces-scr system 7000mci,,tet System
xr vhf cars Lu
gyrophoneelektor january 1984
. . . to makeyour stereowander
Figure 1. Block schematicof the gyrophone. Thesignal and control paths(the latter in dashedlines) are shown separatelyto clarify the operationof the gyrophone.
Most of us have heard the stereo effect of an express train, a gale force wind, orperhaps an artificially created sound transferring from the right-hand to theleft-hand speaker. It's just as impressive when the sound returns from the left-hand to the right-hand speaker, as when, for instance, a train from the oppositedirection passes by. The circuit described in this article makes it possible forboth effects to happen simultaneously: creating a sound very much like that ofa Lesley rotating speaker system.
gyrophonBefore we go any further, there is one thingto be borne in mind: the contents of thetwo stereo channels must be quite distinctfrom one another if the effect is to berealized. A short listening test will soonshow which type of recording is suitable:listen to it and then turn one of the speakersoff. If half of the sound just 'dies', therecording is usable. Stereo records producedten years or more ago are particularlysuitable.The circuit is not really an electronic versionof a Lesley because phase shifts are notcatered for, but its action is none the lessremarkable. Briefly, the right-hand signal'wanders' to the left-hand channel, and viceversa. Shortly afterwards, the two soundsrevert to their original channel. This effectis achieved by periodically inverting the twochannels.The block diagram in figure 1 shows that thesignals from the two channels are split andapplied to four operational transconduc-tance amplifiers (OTAs). However, althoughboth OTA1 and OTA3 are fed with the left-hand signal (and OTA2 and OTA4 with theright-hand signal), they are not controlled bythe same sawtooth voltage. The low -frequency oscillator (LFO) drives OTAs 1and 4 directly and OTAs 2 and 3 via aninverter. This means that OTAs fed with the
0 same stereo signal have opposing controlsignals. The left-hand information is there-fore amplified in OTA1 but attenuated inOTA3 and consequently appears in theleft-hand but not in the right-hand output.From time to time, however, the controlsignals are such that the left-hand infor-mation appears in the right-hand but not inthe left-hand output. The right-hand input
gnal is treated in an identical manner. Thewhole process is continuous and thereforecauses the characteristic swelling and fadingof the loudspeaker outputs. In contrast toa real Lesley. our circuit creates the effectonly by differences in volume in eachindividual channel.A low -frequency oscillator consisting ofintegrator Al and trigger A2 (see figure 2)generates a sawtooth voltage. This voltageshould not go negative because that wouldblock the OTAs, and a diode. DI, is there-fore included in the feedback path of A2.The sawtooth voltage is fed to A3 and toinverter IC2. The output of IC2 is appliedto the inverting input of A4. Opamps A3and A4 drive transistors T1 and T2 andthese in turn feed the four OTAs.As already explained, the signals from thetwo channels are split and the parts areamplified in different OTAs. Outputchannel L contains a mixture of the signals
1
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1-20
2 gyrophoneelektor january 1984
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fed to OTAs 1 and 2 and, similarly, outputchannel R a mixture from OTAs 3 and 4.The mixing elements are formed by tworesistors and a capacitor (for instance,R27/R28/C2).The buffers contained in 1C3 and IC4(pins 7, 8 and 9, 10 respectively) mustnot be used in this application.
Construction and calibrationThe design has been kept as simple andinexpensive as possible and its constructionon a prototyping (Vero)board should notpresent any trouble to the hobbyist withsome experience.Preset P1 enables the frequency of thesawtooth generator to be set to yourown individual taste. The frequency, f, isgiven by f = 1/[C1(P1 R1)11 -1z. With valuesshown, the frequency can be set anywherebetween 0.2 Hz and 4 Hz, corresponding toperiods of 5 s and 250 ms respectively.Because IC2 inverts the sawtooth waveform,its output would normally be mostly nega-tive. As stated, this cannot be tolerated as itwould block the OTAs. Therefore, the
inverted sawtooth voltage is superimposedon a d.c. voltage, the level of which is presetby P2. If an oscilloscope is not available, thepresetting can be done by ear. Apply a signalto one of the input channels and set theLFO to a low -frequency output. If P2 hasbeen set correctly, the loudspeaker volumeshould gradually fade away and then grad-ually swell again. If not, limiting is takingplace and this is indicated by an absenceof sound for some time followed by asudden burst of volume.The audio input signals to the circuit maylie between 0.7 V and 10 V. However, whenyou use inputs of just about 0.7 V and havea powerful main amplifier connected to theoutput of the gyrophone, it may happenthat the maximum and minimum values ofthe sawtooth voltage become audible in theloudspeakers. This can be prevented byincreasing the signal input by, for instance,inserting an additional amplifier betweenthe signal source and the inputs to thegyrophone.We shall be very brief about the requiredmains supply: the current consumptionof the gyrophone is around 50 mA perchannel at ± 15 V. 14
C2
15 V 47"__10 L
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470 n
R30
R32
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170n
134009-2
Figure 2. It is dear fromthis circuit diagram thatonly inexpensive andeasily available com-ponents have been used.Only the setting of P2may test your patience(and your hearing!).
1-21
how accurate is yourwatch?elektor january 1984
quartzprecision formechanicalwatches
INC fine mechanical craftsmanship that goes into a clock-work watch. That regular tick, coming from so many
carefully made parts, tirelessly assembled to make one whole unit, is some-thing completely different from the invisible, silent shuffling of electronsin a quartz controlled watch.The 'watch tester' described in this article is a crystal controlled circuit that isused as an aid to set a mechanical watch accurately. A crystal is used as areference to determine, within a few seconds, how much time the watch gainsor loses, and this is shown on a display as a certain number of minutes perday. Knowing the error is essential to be able to set the watch accurately.
Even though quartz watches seemto have almost completely sup-
planted their mechanical counterparts, for manypeople there is still nothing to compare with the
how accurateis your watch?Man has always tried to measure time in oneway or another. Sundials, water clocks, oillamps, candles and hour glasses are just someof the things that have been used to measuretime down through the ages. Then came themechanical clock. Nobody knows for certainexactly when this first came into existencebut they have been made at least since thefourteenth century. Since then, mechanicalclocks have been consistently improved andrefined.Watches have been made since about the endof the fifteenth century, but it took a longtime before the `portable clock' was im-proved enough so that it worked reasonablyaccurately. The best clocks in the seven-teenth century had an error of about aminute per day. With an average watch an
error of a quarter of an hour a week couldbe expected.Until the beginning of this century watcheswere normally carried on a chain and it wasonly around the year 1900 that somebodycame up with the idea of a wrist watch.Since then watches developed very quickly.In 1924 the automatic wrist watch arrivedand after the second World war the 'electric'watch. In 1957 a watch appeared on themarket that used an electromagnetic systemto drive the balance weight. Four yearslater the firm of Bulova produced a muchmore interesting idea, using an electronicallydriven tuning fork instead of the balanceweight. This tuning fork watch was guaran-teed to be accurate to within one minuteper year!
1-22
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The modern watch is the final stage (so far)and uses a quartz crystal as the time base.The accuracy of this design is such that theerror per year is neglegible.A mechanical watch always has much morecharm than its 'cold' electronic counterpart.It is a testament to the skill of the craftsmanwho made it, and this alone is a great pointin its favour. Clockwork watches do haveone undeniable advantage, of course: theyhave no batteries to fail at the most unex-pected and inconvenient moment.There are, of course, still a lot of mechanicalwatches in circulation and several firmscurrently sell clockwork watches at the'expensive' end of the market. Mechanical'tickers', it seems, are always in fashion.Adjusting a mechanical watch is a lengthyprocess because changing the effective lengthof the balance spring does not give animmediately noticeable change. A goodwatchmaker, certainly, has expensive equip-ment that can measure the error fairlyquickly, but anybody else simply could notafford one. With the watch meter hereanybody can quickly adjust almost anyclockwork watch accurately.
The block diagramThis circuit uses an optical pick-up. An
acoustic pick-up should also be possiblebut in practice that seemed to be moresusceptible to problems with ambient noise.With this optical pick-up we use a small lampto shine light on the spokes of the balancewheel and the reflections are received by aphoto transistor. The pulses given by thephoto transistor are processed and comparedwith a 'standard' frequency, and the error isthen shown on a display.The block diagram of figure 1 is a bit morecomplex than our usual circuits, but thissimply makes the circuit easier to under-stand. The photo transistor pulses areconverted to 'proper' digital signals in the
how accurate is yourwatch?elektor january 1984
Figure 1. The blockdiagram of the circuit. Thepulses picked up at thebalance wheel of the watchcan be converted to ameasuring signal with atime of 2 or 20 seconds.This signal is compared toa reference time and theerror is shown on a display.
1 -23
how accurate is yourwatch?elektor january 1984
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first block. These pulses then go to amonostable multivibrator. The monostabletime can be set to three different valueswith switch S la. These values are < 400 ms,< 333 ms and < 200 ms, and they require ashort explanation.Almost every mechanical watch falls intoone of two standard tick frequencies,namely 18000 ticks per hour (= 5 ticks persecond) or 21600 ticks per hour (= 6 ticks
per second). The first generally applies toolder watches. There are also some clocksthat beat with 36000 ticks per hour(10 ticks/s). One complete swing of thebalance (from the middle to one side, backto the other side and to the middle again)consists of two ticks. Five ticks then consistof 2.5 swings. Because we want to measureswing times with this circuit the MMV timemust be chosen so that only every second
1-24
tick is registered. In other words thetime must be about 5 .. . 10% less thanthe time for two ticks. For 5 ticks persecond the I.ih1V time must be relative to2 x 200 ms = 400 ms. This drops to 333 msfor 6 ticks and 200 ms for 10 ticks.The l.lI.IV is followed by a divider that,depending on the position of Si, divides by5, 6 or 10. A signal with a period of2 seconds now appears at the wiper of Slb(provided that S1 is in the correct positionfor the watch under test). If the period isnot 2 seconds. this means that the watch isnot keeping time. A period of less than2 seconds means that the watch is runningfast, and more than 2 seconds means it isrunning slow.This signal then goes to switch S2a whichenables us to select the 2 second signal orone ten times as long. The 20 second signal'contains' a greater number of ticks and istherefore better than the shorter time formeasuring the error of a watch. The signalchosen with S2a then goes to I.II.IV3 and
which drive the counter and thelatch. The latch with a seven segmentdecoder is driven by a pulse supplied by1.1I.IV3, while LliriV4 presets the counterafter the count has been stored in the latch(and shown on the display).Finally, the counter. Because we want thedisplay to show the error in minutes per day,the counter has to be a bit special. It mustbe able to count positively and negatively aswe can have an error in either direction. Theclock frequency of the counter must becarefully chosen to enable the read out to bein minutes per day. Furthermore the countermust be capable of being preset, so that itsoutput is exactly zero if the watch is work-ing accurately. To enable all this to be done,an eight -bit BCD up/down counter is used.Now to the clock frequency. There are1440 minutes in a day (except Monday,which has at least twice as many). If ameasuring time of two seconds is used, thecounter must receive 1440 clock pulses inthese two seconds. The error measured bythe counter relative to this 1440 is then
the error in minutes per day. If a time of20 seconds is used the counter must count14400 clock pulses. This means that theclock frequency for the counter must be1440/2 (or 1400/20) = 720 Hz. This refer-ence frequency is supplied by a crystal anda few dividers.With a measuring time of 2 seconds thepreset value of the counter must be -1440so that the count is exactly zero if the watchis running correctly. The counter can actu-ally only count from -99 to -99. so a presetvalue of -1440 is impossible. Because theread out only shows two figures, we set thepreset CO -40 (the last two digits of -1440).The counter will then be at zero after twoseconds. This 'trick' works here because anormal watch will never have an error ofmore than 99 minutes a day. The counterstarts by counting from -40 to zero thenfrom zero to 99 and six times from -99 to,-99 and finally from -99 to zero making1440. Note that there is a delay of one clockcycle every time the count crosses zero onits 'jump' from -99 to -99. Without this ourarithmetic would not be correct. If 20seconds is used as the measuring time thecounter is preset to zero (the last two digitsof 14400).In practice the counter cannot itself workout if its count is positive or negative, so the-' or '-' sign is stored by a flip-flop. Thisflips (or flops) every time the counter is atzero, and drives the = sign in the display.Finally there is a reset circuit whereby allcounters can be reset simply by pressing onebutton. The circuit is then ready to beginmeasuring anew.
The practical layoutAs we have spent quite a long time talkingabout the block diagram, we do not reallyneed to say much about the actual circuit -diagram of figure 2. The block diagram alsosimplifies matters by stating which com-ponents make up each block.We will have a look at the input stageseparately. The d.c. voltage setting of photo
how accurate is yourwatch?elektor january 1984
1-25
how accurate is yourwatch?elektor january 1984
Parts listResistors:
R1 = 120 nR2,R3*:R10 = 2M2R4,R14,R16,R21,R27,
R28,R44 = 1 kR5,R17= 1M2R6,R12,R25,R26 = 56 kR7 = 100 f?R8,R19,R22 = 10kR9 = 1 MR11 = 47 kR13,R15= 10MR18,R20,R23,R24 = 100 kR29 = 680 !-1R30 ... R43 = 820P1 = 1 M preset
Capacitors:
C1,C15,C18,C23 = 100 nC2,C17 = 220nC3,C6,C22 = 10 ;2:16 VC4 = 1C1Ou 16 VC5,C10 = 680 nC7,C14,C20,C21 = 10 pC8 = 4 ... 40 p trimmerC9 = 56 pC11 = 560 nC12 = 330 nC13 = 1 nC16= 1000u 25VC19 = 100 pC24 = 560 p
Semiconductors:D1 ... D4 = 1N4001D5,D6 = LEDLD1 = 7756 universaloverilov: 7 1 display
LD2,LD3 = 7760 commoncathode seven segmentdisplay
T1 = BS 250. BC 516'T2 =TIL 81T3 = BC 549CT4 = BC 547ICI = 3140IC2 = 4060IC3 = 4518IC4 = 4017IC5,1C9 = 4098IC6,1C7.1C15 = 40131C8 = 7812IC10,1C11 = 4511IC12,1C13 = 4510IC14 = 4078
Figure 3. This is theprinted circuit boarddesign for the measuringsection of the circuit.
3
transistor T2 is handled by FET T1. For lowfrequencies and d.c., T1 acts as a voltagesource: its drain voltage is then fed back tothe gate via R2. The low-pass filter con-sisting of R3 and Cl ensures that TI actsas a current source at higher frequencies.Slow variations in the light picked up(from ambient conditions for example)are therefore compensated by the FET.while fast changes in light cause a largechange in the voltage on the collector ofthe photo transistor. This is exactly whatwe need to detect the moving spokes of thebalance wheel. These voltage changes aretransmitted via C2 to T3 where the pulsesare rectified. The voltage on C4 is the sameas the maximum value of the pulses. This
voltage goes via voltage divider R9/R10 toIC1 where it acts as the trigger -level settingfor this schmitt trigger. The other input ofthe schmitt trigger is fed the voltage changesfrom the photo transistor via C3. This set-up allows the circuit to adapt itself to thestrength of the input signal. If the phototransistor provides a strong input signal thenthe triggering threshold is high. The strengthof the input signal is indicated by the meterconnected parallel to C4. If switch S4 isclosed the output of ICI is heard throughthe buzzer. An LED, D5. at the Q output ofFF1 flashes in time with the tick pulses. Themeasuring time is shown by means of LEDD6 at the output of FF4.The supply for the whole circuit is handled
1 -26
4 how accurate is yourwatch?elektor january 1984
by the same 7812 regulator IC. The currentconsumption is about 250 mA.
Constructing the circuitThe circuit has been divided between twoprinted circuit boards that are shown infigures 3 and 4. The 'measuring' section islocated on the board shown in figure 3 andcontains all the components shown in theleft half of the circuit diagram, with theexception of R21 and D5. The second boardconsists of two sections which may beseparated if desired. These are the countersection and the read-out (the right half ofthe circuit diagram with the exception ofFF4). The numbered points on the two
boards must be connected to each other.The supply for the display must be takenfrom points 1 and 2. Trying to tap a supplyfrom anywhere else will probably causeproblems.It is quite possible that the BS 250 FET mayprove difficult for some people to get theirhands on. If this is the case, a BC 516 maybe substituted for T1, but R3 must then be3M9. Fortunately this transistor can befitted to the board exactly the same as theFET.When all the electronics is assembled we canturn our attention to building the sensor.The photo transistor and the lamp aremounted next to each other, but in such away that the light from the bulb does not
Miscellaneous:Bz = buzzer, Toko 2720Fl = 100 mA slow blow
fuse and holderheatsink for IC8La1 6 V/50 mA
miniature lamp"M1 = moving coil meter
100 µA FSDS1 = 2 pole 3 way switchS2 = 4 pole 2 way switchS3 = push buttonS4 = single pole toggle
switchS5 = double pole mains
switchTr1= mains transformer.
15 V/500 mAX1 = crystal, 1.8432 MHz
(13 pF)
If T1 is BC 516,R3 = 3M9
Reflection sensorOPB 730 can be usedinstead of a lamp andphoto transistor; thenIR 1 = 560 n
Figure 4. The printedcircuit board for thecounter section and theread-out, which can, ifdesired, be separated toenable the display to bemounted away from thecounter.
1-27
fall directly on the photo transistor. This iseasily done with a piece of black paperbetween the two. The emitter of the transis-tor can now be soldered directly to thecollar of the lamp. This leaves three connec-tions which can be linked to the printedcircuit board with a piece of screened stereocable. The collar of the lamp (which can bea miniature type) must be connected to thescreen. This unit can then be fitted intosomething like a big felt tip pen. A clip canbe made up to hold this 'pen' steady duringa measurement. The photos and the frontcover show how our prototype was built.A nicer (but also more expensive) possibilityis to use a reflection sensor, such as theOPB 730, which contains a LED and aphotodarlington. If this is done the sensormust be well screened from ambient light,and the value of resistor R1 must be in-creased to 560 a
Adjustment and useAdjustment is very easy. The frequency ofthe crystal can be set to the exact valuerequired with trimmer C8. To do this afrequency meter with a maximum error of0.005% is needed. A frequency of 115200Hz must be measured at test point TP.If you cannot get hold of a good frequencymeter then simply put C8 in mid position.In most cases the frequency will then bereasonably accurate.Next, MMV1 must be set, preferably with anoscilloscope. Potentiometer P1 is set so thatthe monostable time is 360... 380 ms withSla in position A. If you do not have anoscilloscope, this MMV can also be adjustedwith the aid of a watch that is known to beaccurate. Place the watch under the sensorand turn the sensor until the meter shows astrong signal and the buzzer ticks regularly.Turn the preset to maximum, set switch S2to position A (2 s measuring time) andadjust the preset by turning it backwards alittle at a time. After each adjustment waituntil the measuring time has passed and seewhat the read-out shows. At some stage anerror of about zero minutes will be dis-played. Turn the preset a little bit furtherand then leave it at that.A few words about using this circuit willcertainly not go astray. First we mustknow the tick frequency of the watch to betested. Older gents watches generally have5 ticks per second, whereas modern gentswatches and ladies watches usually have 6.After a bit of practice this can even beheard from the ticking of the watch. Lay thewatch under the sensor and point the phototransistor towards the spokes of the balancewheel. Move the watch carefully until themeter reading is as large as possible. If S4is closed the pulses from the phototransistorcan be heard from the buzzer. This shouldbe a regular tick. If it sounds more like'sawing' then the transistor is pointingat the adjusting screws and must be movedslightly.The COUNT LED, D5, should flash regularlyto show that the circuit is receiving thepulses. The correct ticking frequency (5, 6,or 10 ticks per second) must be set with Si.
A measuring time of 2 seconds is selectedusing S2. Press the RESET and after2 seconds LED D6 (GATE TIME) 'changes'.What we mean is that the LED lights if itwas out and it goes out if it was lit. Thedisplay now shows the error in minutes perday. Whenever D6 changes the measurementhas been taken and the result is shown onthe display.If the error of the watch is less than tenminutes, S5 can be moved to position B(20 s measuring time). First press theRESET again and after 20 seconds LED D3changes and the error is shown on the dis-play in tenths of minutes.With a pocket watch the photo transistorcan also be focused on the balance screwsand this usually gives good results. In thiscase, however, it is important to reduce thelevel of ambient light as much as possible.Incandescent lamps and fluorescent tubes inparticular can cause problems.A period counter could also be used inthe circuit in place of the counter sectionand read-out. It is simply connected to thewiper of switch S2a. However, IC2, IC7,Xl, C7, C8, C9, C13, R15, R16 and R18can then be removed and point 4 of themeasuring board and pin 1 of IC3 must beconnected to earth. The read-out on themeter will not, of course, be in minutes perday any more. It is a simple matter toconvert the output to minutes per day usingthe formula 60 x 24 x (2 - T)/T, where Tis the period measured in seconds. If T is1.986 seconds the error of the watch is60 x 24 x (2 - 1.986)/1.986 = +10 minutesper day.
how accurate is yourwatch?elektor january 1984
A mechanical watchworks with almostincredible accuracy con-sidering that it has totick nearly a half milliontimes per day
A mechanical chronometerhas an error of one minuteper month at most; with anautomatic watch that isabout one minute perweek.
S1 position: A = 5 ticks/sB = 6 ticks/sC = 10 ticks/s
S2 position: A = 2 secondgate time
B = 20 secondgate time
1-28
digitacassette recorder
digital cassette recorder ...elektor january 1984
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Cassette recordings are still the most popular memory for home computersbecause they offer the cheapest method available. Unfortunately, it is not themost reliable method because a cassette recorder is, after all, intended forprocessing audio rather than digital signals. The present circuit converts anormal cassette recorder into a digital one with vastly improved data transfercapability without the loss of the audio facility.
Most home computers have a cassetterecorder interface which usually obeys asimple rule: the cheaper and simpler thecomputer, the worse the data transfer tothe recorder. This only becomes evident, ofcourse, when you 'read' a newly loadedprogram and find that all is not what it'ssupposed to be. Why is that? And cananything be done about it?In most computers, a signal is deliveredto the interface which is not really suitablefor an audio cassette recorder. The ampli-tude of the signal is normally limited toprevent the overloading of the recorder,while a transfer speed is chosen which,according to the computer manufacturers,is 'safe'. In other words, the computer isadapted to the cassette recorder without toomuch thought to the fact that the recorderwas designed for a different purpose.We have tackled the problem from theopposite direction by matching the recorderto the computer. A 'read' (playback) and a'write' (recording) amplifier are added whichimproves the data transfer to the extent thatbaud rates of 4800 may be used! When youconsider that the baud rate in most, if notall, home computers cannot exceed a three -
figure number, you realize what a consider-able improvement our circuit offers.
Analogue and digital recordingThe (analogue) recording of audio signalsonto magnetic tape requires special circuitsto ensure that the playback signal is afaithful reproduction of the original. Afterall, Dolby and DBX did not come about byaccident! One of the important designconsiderations, for instance, is to preventsaturation of the magnetic tape (as satu-ration would cause distortion).A square -wave pulse, as generated by mostcomputers, consists of a large number ofsinusoidal voltages. As the recording/play-back amplifier of a recorder is optimized foraudio signals, it will suppress a number ofconstituents of such a pulse. The result isthat what's recorded is no longer a square -wave signal. Further disintegration of thepulse takes place during playback, there isthe tape noise, and ... The consequence ofit all is that the Schmitt trigger normallyfound in the input stages of a cassetteinterface is not presented with one properpulse, but several distorted ones.
SOW 2
. . . ensuresyour bits stayon the tape
1.29
digital cassette recorder ...elektor january 1984
Figure 1. The only modification to the recorder is inthe cable to the tape head.The existing amplifierremains untouched andfully usable for audiooperation.
The process in a digital recorder is muchsimpler: the magnetic tape is driven intosaturation. This is, without any doubt, thebest method for recording data onto tape,particularly if the tape is positively magnet-ized during logic 'high' signals and negativelyduring `low' signals.Before we analyze the circuit diagram, areassurance about the cassette recorder: itneeds only one modification. The screenedcable to the tape head needs to be cut andthe digital read/write amplifier insertedbetween the cut ends as shown in figure 2.The audio recording/playback amplifier isnot touched at all so that the recorder re-mains fully usable for normal audio oper-ation.
The circuitThe write/read (recording/playback) ampli-fier consists of two functional units separ-ated by the switch -over unit (see figure 1).The read amplifier is constructed in twoparts to which we'll come back in the circuitdescription. Other items shown in figure 1are the write and read indicator LEDs.
Write (recording) amplifier
As explained in 'switching' below, we'llassume that ES1 and ES2 (see figure 2) areclosed and that contacts Rel and Re2 areopen.The square -wave pulses from the computerare applied across preset P1 and from therefed to the inverting input of opamp IC1 viaR1 and Cl. Diodes D1 and D2 limit thesignal to ± 0.7 V. The gain of ICI is fixedat about 100 by voltage divider R2/R3.Anti -parallel connected diodes D3 and D4in the feedback loop limit the output of theopamp to ± 0.7 V. Plus or minus? you mayask. Surely the supply voltage is +12 V only?
True, but the non -inverting input of ICIdoes not lie at earth potential but at +6 Vbecause of voltage divider R12/R13. Thesignal output of IC1 is therefore super-imposed onto +6 V. This arrangementis also used in other parts of the circuit.Figure 3 shows how a sinusoidal (FSK) inputsignal is converted by this method: thefrequency remains unchanged, but the wave-form becomes rectangular. You can wellimagine that if a sine wave is so converted, adistorted rectangular pulse will certainly befully resorted to its original shape. We havetaken an FSK signal as an example becausethat shows the operation of the circuit mostclearly. In general, our digital recorder is notrequired with computers which have anFSK output, but as this example shows: younever know .The rectangular output of IC1 is invertedagain by trigger Al and increased to themaximum possible level of 12 Vpp (waveshape 4, figure 3).The output of Al is split: one part is appliedto terminal 'A' of the tape head via R32 andES1; a second is again inverted by trigger A2and then fed to the earth terminal 'B' of thetape head via R33 and ES2. The signal at thetape head is therefore the difference inoutputs of the two opamps Al and A2: notethat the tape head is not connected to earth.This method not only saves some couplingcapacitors (which might distort the signalslightly) but, what's far more important,the tape magnetization for a logic low signalis the opposite of that for a high signal.
SwitchingA third part of the output of Al is appliedto the electronic switching circuit via C3.This circuit consists of electronic switchesES1 and ES2, relays Rel and Re2, diodesD7 and D8, and a few resistors and capaci-tors.
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1-30
2 digital cassette recorder ...elektor january 1984
A1... A4 = IC3 = TL 084
ES1,ES2 'AIC4 = 40668
12 V
-2:1N4148
2:IN4148
1.24x14841
1144148
The non -inverting input of comparator A3is at a level of about +6 V via voltage dividerR12/R13. Under no -signal conditions, theinverting input is at about +4.4 V via voltagedivider R30/R31. The output of A3 istherefore at +12 V and relays Rel and Re2are actuated. The voltage at the invertinginput also exists at the inputs of electronicswitches ES1 and ES2, but is not sufficientto close the switches: a voltage close to thesupply voltage is required to do that. Sum-marizing: under no -signal conditions, ES1and ES2 are open and the contacts of Reland Re2 closed. The circuit is then in the'read' condition.When a signal arrives from the computer, theoutput of Al is applied to the control inputsof ES1 and ES2, and to the inverting inputof A3 via C3 and D7. The output of A3 goeslow, the relays open, and ES1 and ES2 close.The circuit is then in the 'write' condition.Capacitor C4 charges and continues to do soas long as there is a signal coming in fromthe computer. As the input current of A3,ES1, and ES2 is very small, the charge on C4is sufficient to keep the switching circuits
in the same state even during the pausesbetween the pulses. When the computersignal ceases, C4 discharges through R10 andthe circuit reverts to the 'read' condition.
Read (playback) amplifier
In the 'read' condition, Re2 connects theearth terminal of the tape head to the circuitearth (0 V). The tape signal is connectedvia Rel to the gate of FET T4. This small -signal amplifier is followed by a secondconsisting of T1 and T2, and a third formedby IC2. To ensure that the maximum signalis available at the output of IC2, its input is'raised' to about 6 V, derived from thevoltage divider R12/R13. The total gain ofthe three stages is around 80 dB, of whichhalf is contributed by IC2. This is ample formany computers and the output of IC2 istherefore available at terminal 'AN'. Theoutput level can be matched to the com-puter input requirement by preset P3.For those situations where more gain isrequired, a fourth amplifier, A4, has beenprovided. The gain of this amplifier can be
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Figure 2. The new amplifierconsists of three parts:a recording (write) andplayback (read) amplifierand a switching circuitwhich separates the twoamplifiers.
1-31
digital cassette recorder ...elektor january 1984
1V2 1V4
6
3
Figure 3. The variousphases of signal con-version are clearly seen inthis representation. Theoperation of the circuitcan be checked with theaid of this figure and anoscilloscope.
Figure 4. The printed -circuit board is double -sided, and the componentlayout side takes the formof an earth -plane.
83134-3
condition. It is possible that it continues tolight faintly during the 'read' condition; ifyou find this disturbing, the only solution isto replace Dll by a cheaper LED (giving lesslight).Then there is LED D12. This diode lightsduring the 'read' condition. Capacitor C12keeps T3 conducting so that this does notswitch on and off in time with the inputsignal. Resistor R25 prevents the indicatorcircuit affecting the output signal.Finally, diode D10. This component appearsto be located in a somewhat strange pos-ition, but a good look at the circuit willshow that it functions as a protection diodefor relays Rel and Re2.
Construction and calibrationAssembling the printed circuit board shouldnot present any difficulties: figure 4 andthe parts list give all the information re-quired. One point needs watching, however.Although we are dealing with a double -sidedboard, the two points 'B' must be connectedby means of a short length of screenedcable. The reason for this is that during'read' operation the signal from the tape
4
set between 17 dB and 37 dB by preset P2.As A4 is driven into saturation, its outputis virtually identical with signal 4 in figure 3.The output is raised to TTL-level via voltagedivider R26/D13/D14 and made available atterminal 'DIG'.
A few further points
To avoid confusion, some aspects of thecircuit have been ignored so far. To startwith: LED D11. This lights when the outputof A3 is low, that is, during the 'write'
head is very small (remember the 80 dBgain!). For the same reason, the screenedcable between 'A' and the head must be keptas short as possible. In contrast to audiocircuits, there is no central earth point here,so that the earths at both sides of the cablemust be connected with one another.The circuit is very simple to set up. Thecorrect positions of P1 ... P3 are dependentupon the type of computer and on thebaud rate. If you start at the centre positionof these presets and have checked that thed.c. levels shown in the circuit diagram are
1-32
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OK (no -signal conditions), the right settingsshould soon be apparent.Final rip: load a not -too -small memoryregion of the tape with a fixed hex -valueand program a loop. It is then possible withthe aid of an oscilloscope to check theconversion of the signal (with reference tofigure 3) at various test points. During'write' operation simply run the tape withthis fixed hex -value. It is, by the way,not necessary to press the 'record' buttonduring 'write' operations to erase anymaterial already present on the tape because
the signal now fed to the tape head isconsiderably stronger than the previousrecording.Current consumption of the circuit is around50 mA and it may therefore just be possibleto draw this from the existing recorderpower supply.
digital cassette recorder ...elektor january 1984
Parts list
Resistors:
R1,R15= 2k2R2,R14,R17= 10 kR3,R10 = 1 MR4,R5,R22,R30 = 6k8R6 = 33 kR7 = 47 kR8,R9 = 5k6R11,R26,R29 = 470 ki-2R12,R13 = 4k7R16 = 47 k or 47k5,
metal film, 1%R18 = 3k3R19,R23,R24,R34 = 22 kR20,R28 = 1 kR21,R25= 100 kR27 = 330 knR31 = 3k9R32,R33 = 15 kP1,P3 = 5 k presetP2 = 500 k preset
Capacitors:
Ci,C2,C3 = 220 n ceramicC4,C8 = 470 n ceramicC5,C14 = 47 pr10 V
electrolyticC6,C10 = 820 n ceramicC7 = 100 p/16 V
electrolyticC9 = 1 p16 V electrolyticC11 = 47 gil6 V
el ectroly ticC12,C13=1p/10V
electrolytic
Semiconductors:Di ... D10= 1N4148Di1,D12 = LEDD13 = zener diode 2V7,
400 mVii014 = zener diode 4V7,
400 mi.."Ti = BF 494-12,T3 = BC 6478T4 = BF 256CIC1,1C2 = LF 356IC3 = TL 084IC4 = 4066B
Miscellaneous:Rel,Re2 = DI L relay,
e.g. ERNI 10L34 14.5.... 5.0 V '1 Al
PC Board 83134
1 -33
audio signal embellisherelektor january 1984
audiosignal embellisher
from an idea byJ.F. Brange
signalrestorationwith stereosimulation
It is often unavoidable to have toconnect an item of mono equipmentthat is rather less than hi-fi to amodern stereo installation. Althoughthis may give some improvement inthe resulting sound quality, thereproduction remains monaural(mono) invariably with a level of humand noise which by present-daystandards is unacceptable. We havedesigned a circuit which by humsuppression, stereo simulation, anddynamic noise limiting (DNL) givesa greatly enhanced performance. Thestereo effect is created by splitting theaudio spectrum into sixteen frequencybands which are fed alternately to theleft and right-hand channels.
Ever since the arrival of hi-fi audio equip-ment and the introduction of stereo, ouraural senses have been spoilt to the pointof addiction. Nowadays when we listento ordinary monaural music, we soonfeel there's something missing. If in ad-dition the sound is accompanied by humand noise, this feeling soon becomes oneof disappointment or even annoyance.However, sometimes there is no alternativeto the poor sound source, if only for the
simple reason that we don't want to throwaway perfectly good equipment. Thiscould, for instance, take the form of simplecassette recorders, AM receivers, soundprojectors, and TV sets or video recorders.The last three are particularly prone to beingneglected by audio designers. While thepicture quality is praised (often deservedlyso) as hi-bri (high brilliance), more oftenthan not the sound is a disgrace by modernstandards.
Spatial soundWe are aware of depth in sound becausewe have two ears. As the sound waves reacheach ear at a slightly different time and witha slightly different amplitude, the brainreceives two separate signals. It is able todeduce the relative position of the soundsource from the differences: our ears forma true stereo receiver! The shape of the earalso plays a role: if you want to know moreabout this, we refer you to 'our remarkablesense of pitch' in the May 1979 issue ofElektor.What can we do with a mono sound? It isimpossible to convert it into true stereo,because the subtle differences between theleft and right-hand channels just cannot beadded afterwards. What we can do is tocreate artificial differences by splitting thesound into a number of frequency bandsand then feed these selectively to the leftor right-hand channel of the stereo instal-lation. This is, by the way, the method
1.34
1audio signal embellisherelektor January 1984
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used in the TDA 3810 stereo -IC featuredin 'pseudo stereo' in our November 1983issue. The present design is rather moreradical and effective: the audio spectrumis split into sixteen bands by means ofactive filters. If the filter outputs are num-bered 1 . .. 16 in order of ascending centrefrequency, all odd -numbered frequencybands are fed to the left-hand channel, andall the even ones to the right-hand channel.The result is truly remarkable: the sound,which at first seemed to come from betweenthe speakers, now seems to 'hang in space'around the speakers.
The block schematicThe block schematic in figure 1 clearlyshows that the design consists of threedistinct main parts: each of these is housedon a separate printed -circuit board.The input of the circuit is a pre -amplifier(with variable sensitivity), followed by a100 Hz and a 50 Hz band -stop filter (some-times called a 'notch' filter). These filtersrespectively reject the 100 Hz fundamentalfrequency of a double -phase rectifiedvoltage and the 50 Hz fundamental of asingle-phase rectified voltage. Both filterscan be switched out.The next element is a level indicator whichis useful when the input sensitivity is set.Nothing sophisticated, just a simple ampli-fier and LED which blinks away quietlywhen the sensitivity is set correctly.Next, we come to the heart of the design:the sixteen active band-pass filters. Theoutputs of the odd -numbered filters, andthose of the even -numbered ones, areseparately combined and are then, in prin-ciple, suitable for processing in a stereoinstallation.
We have, however, added dynamic noiselimiting (DNL) stages which, if required, canbe switched off or be omitted altogether.Some of you may even use this part ofthe design only.
The circuit diagramsThere is a circuit diagram for each of thethree mains parts of the design: the pre-amplifier, band -stop filters, and powersupply (figure 2), the sixteen -element activeband-pass filter (figure 3), and the DNLstages (figure 7).
The pre -amplifier, band -stop filters, and powersupply
The input sensitivity is preset by means ofP1. Pre -amplifier Al has a gain of about10 dB and is followed by active band -stopfilters A2 (100 Hz) and A3 (50 Hz). Theoutput of A3 is fed to the band-pass filterson the second printed -circuit board (seefigure 3), and also to the level indicatorstage. After amplification in A4, the signalis applied to the base of T1 via C13. Whenit exceeds a certain level, T1 conducts tolight LED D1.The power supply for the entire designconsists of the customary mains transformer,bridge rectifier, voltage regulators, andsmoothing capacitors. The output is sym-metrical: = 12 V at 85 mA.
The band-pass filters
The sixteen band-pass filters (see figure 3)are identical in construction. The basicdiagram of one of them is shown in figure4: a common filter circuit with an opampas the active element and RC combinationsto give the required frequency response andQ factor. As you can see from the formulas
Figure 1. Block schematicof the entire circuit. Thethree separate modulesare shown in dashed lines.
1-35
audio signal embellisherelektor january 1984 2
CI
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in figure 4, if a fixed value is chosen forR1 and R2, the centre frequency becomesinversely proportional with the value ofcapacitance C. By appropriate values of C inthe sixteen filters, the centre frequencies arevaried, but the Q factor and gain Ao, remainthe same.
The DNL stages
For those of you who are not completelyfamiliar with the operation of a dynamicnoise limiter, here is a short description.The simplest noise limiter is a low-passfilter. Unfortunately, its action is somewhatradical and affects the audio signal. Adynamic noise limiter is a low-pass filterwith variable cut-off profile which onlyfunctions during soft passages (when thenoise is most audible) by suppressing thosefrequencies to which the ear has the highestsensitivity, that is, about 1 . .. 10 kHz.The amount of suppression is thereforedependent upon the level of the inputsignal. During loud passages, the cut-offfrequency is shifted upwards so that theentire audio range is passed, including thenoise, but this is then, of course, maskedby the audio signal. At lower levels of signalinput, the cut-off frequency is lowered, sothat a relatively larger amount of noise issuppressed. The action of a DNL is illus-strated by the graphs in figure 5: for aninput signal, Ui, of 2.0 mV, the attenuationwith respect to the output level at 1 kHz
is 10 dB at 7.5 kHz and 20 dB at 10 kHz.The slope is then approximately -18 dB/octave. With input signals above about8 mV, the response is virtually flat to 20kHz!The input stage, A, (see figure 6) ensurescorrect impedance matching between theband-pass filter and the DNL. From here,the signal is fed to two channels: the upperone consists of a high-pass filter (B), ampli-fier (D), variable attenuator (E), and fixedattenuator (G), while the lower one com-prises a phase shifter (C) and a fixed attenu-ator (F). The output of the DNL is thesum of the outputs of the two channelswhich are, of course, in anti -phase.For low levels of input, Ui, the output,U1, of the phase shifter is, apart from thephase shift, identical with Ui. The output,U2, of the high-pass filter contains onlythe high -frequency content of Ui. SignalsU1 and U2 are, as already stated, in anti -phase so that if they are summed the high -frequency content of Ili is cancelled out.The net result is therefore that of a low-passfilter. When the level of input signal rises,the variable attenuator in the upper channelcomes into operation and reduces thecontribution of U2 to the output signal, Uo.The high -frequency portion of Ui is then nolonger (or to a lesser degree) suppressed andU0 will tend to resemble Ui more and more.Turning to the circuit diagram (see figure 7),the input amplifier, transistor T2, in con -
1 -36
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audio signal embellisherelektor january 1984 4
Figure 4. Basic circuit of aband-pass filter showingthe formulas for calculat-ing the various filtercharacteristics.
Figure 5. Transfer charac-teristic of the DNL: thefilter action is dependentupon the level of the inputsignal.
Figure 6. Simplified blockschematic of the DNL.
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es1n-7
junction with C52 and R70, forms thephase shifter. The output of the phaseshifter is taken to the DNL output via fixedattenuator R70/R79.The active high-pass filter, formed by C53,C54, T3, and R72 ... 76, is followed byamplifier T4 and a variable attenuatorconsisting of T5 and associated components.The collector as well as the emitter of T5feed a signal to the diode bridge D8 . . . D11.Capacitors C58 and C59 are charged to theemitter voltage via R83/D8 and R84/D11respectively. If the audio signal level liesbelow the forward voltage of the diodes,these will not conduct. The signal from T5is then taken directly to the DNL outputwhere it is summed with the signal fromthe phase shifter. As the two signals arein anti -phase, the cut-off frequency isabout 6 .. . 7 kHz and filter action is at amaximum.When the audio signal is greater than thediode forward voltage, the diodes conductand present a low impedance to audiofrequencies. A low-pass filter is then formedby R84, C58, C59, which causes the higherfrequencies to be attenuated. The endresult will be that fewer (or hardly any)high frequencies are removed from the finaloutput signal, which shows up as a flatteningof the overall frequency response.
ConstructionAs stated before, the design is built up fromthree modules: pre -amplifier plus powersupply plus band -stop filters, the sixteen -element band-pass filter, and the DNLstages. This type of construction makes itpossible for everyone to choose whichpart(s) of the design he needs: some of youmay not want the stereo effect, in whichcase all you have to do is omit the sixteen -element band-pass filter. If the DNL unitonly is built, it is, of course, necessary toadd a suitable power supply.When the printed -circuit boards shown infigures 8 . .. 10 are used, no particularproblems should be encountered in theconstruction. During the building of thepower supply, make sure that one voltageregulator IC is turned 180- with respectto the other. In view of the small currentconsumption, these ICs do not need heatsinks.The band-pass filter board is best com-menced by wiring in the four wire bridgeswhich are to be located under IC2 ... IC5:this will make things a lot easier later on.The DNL board consists of two absolutelysymmetrical halves: it is possible to cutit into two and have two independent monoDNLs! In contrast to the remainder of the
audio signal embellisherelektor january 1984
Figure 7. The circuit dia-gram of the DNL: twosuch circuits are required,one for each channel.
Parts list (DNL)Circuit: figure 7PC board: figure 10Resistors:
R67,R67' = 270 kR68,R68' = 150 kR69,R69',R71,R71' = 1k5R70,R70',R80,R80' = 5k6R72,R72' = 15 kR73,R73' = 2k2R74,R74' = 180 kR75,R75' = 680 kR76,R76' = 3k9R77,R77' = 330 kR78,R78',R84,F184' = 22 kR79,R79' = 6k8R81,R81',R82,R82'
680 12R83, R83' = 120 kR85,R85' = 220 kP2,P2' = 47 k (50 Id preset
Capacitors:C51,C51',C61,C61' = 4p7/
16 VC52,C52',C60,060' = 4n7C53,C53' = 1n8C54,C54' = 270 pC55,C55' = 1n5C56,C56' = 680 pC57,C57' = 2n2C58,C58',C59,C59' = 22 nC62,C62' = 10 p/16 V
Semiconductors:08 ... D11' =
1N4148T2 ... T5.T2' ... T5' =
BC 5478
Miscellaneous:
S4 = DPST switch
Figure 8. Layout andcomponent side of theprinted -circuit boardfor the pre -amplifier,band -stop filters andpower supply.
1 -39
audio signal embellisherelektor January 1984
Parts list (filters and powersupply)Circuits: figures 2 and 3;PC boards: figures 8 and 9
Resistors:R1 = 47 kR2= 100kR3,R4 = 18 k85,811 = 8k2R6,R12 = 820 2R7,R13 = 470 288,814 = 100c89,810= 18 kR15 = 12 kR16 = 220 kR17 = 3k9818 = 2k2R19 ... R34 = 1k2835 . . . R50 = 330 kR51 ... R66 = 1 kP1 = 47 k 150 k) preset
Capacitors:Cl = 220 nC2,C9,C10 = 180 nC3,C5 = 82 nC4,C6 = 8n2C7,C27,C28 = 33 nC8 = 330 nC11 = 2µ2.25 V tantalumC12,C13= 10 µ 25 VC14= 10 µ.16 VC15,C17 = 1000 µ/25 VC16,C18 = 10 gi16 V
tantalumC19,C20 = 150 nC21,C22 = 100 nC23,C24 = 68 nC25,C26 = 47 nC29.C30 = 22 nC31,C32 = 15nC33,C34 = 10 nC35,C36 = 6n8C37,C38 = 4n7C39,C40 = 3n3C41,C42 = 2n2C43,C44 = 1n5C45,C46 = 1 nC47,C48 = 680 pC49,C50 = 470 pC63 ... C66 = 10 µ 16 V
Semiconductors:D1 = LEDD2,D3 = 1N418D4 . . . D7 = 1N4001T1 = BC 5478IC1 ... IC5 = TL 084IC6 7812IC7 = 7912
Miscellaneous:51,52 = SPST switchS3 = DPST switch (mains)Tr1 = supply transformer
2x 12 V.300 mAF1 = fuse, delayed action,
500 mAfuse carrierprinted -circuit boards
83133-1 and 83133-2
Figure 9. Layout andcomponent side of theprinted -circuit for thesixteen -stage bandpassfilter.
1 -40
10
design, the DNL needs only a single supplyline: -12 V and earth.
CalibrationWith the output of a tuner or record playerconnected to the input of the pre -amplifierboard. adjust the overall sensitivity by meansof P1 until LED DI quietly blinks in rhythmwith the incoming audio signal.Because the DNL is a variable filter, theaction of which is dependent upon the signallevel at the base of T2, preset P2 should beadjusted carefully. Connect an a.c. voltmeter(input impedance at least 100 kE2) betweenthe wiper of P2 and earth, and inject a signalof about 1 V into the input terminals of theDNL. Adjust P2 for a reading 775 mV onthe voltmeter. If the input signal was derivedfrom a tuner. or record player. it may benecessary to re -adjust P1 slightly.
If you have no access to a suitable a.c.voltmeter. adjust the preset(s) by ear. Ivlakesure that with a reasonably large inputsignal the high frequencies are not cut.If that happens, the input signal is too smalland must be adjusted with P2. If this hasalready been set for maximum sensitivity,adjust P1 also. If this still does not give asatisfactory result, the output from thesignal source (tuner, record player, taperecorder) is too low, in which case an extraamplifier has to be added.
Final note:
The DNL can be inserted almost anywhereinto the audio chain, but as its 0 dB inputlevel must correspond to 775 mV it mustbe located before the volume control. N
audio signal embellisherelektor January 1984
Figure 10. Layout andcomponent side of theDNL board: as the DNLshould be suitable forstereo, the board consistsof two symmetrical halves.
In audio technique, allvoltages are referred tothe 'normal level'. This is1 mi.': into 600 1-21= 775 mV across 600 n)and is conventionallydesignated 0 dBm,
1.41
universal active filterelektor january 1984
Not so very long ago, active -filter ICs would have seemed about as likely aspocket washing machines but today they are, if not exactly commonplace,certainly readily available. With the aid of very few extra components theReticon R5620 can form the basis of a versatile active filter for use in audioor synthesiser applications - or as an extra piece of test equipment for usein the workshop. All this - and not a single coil in sight!
universal active filterfive filtermodes fromone IC
Figure 1. The R5620active filter IC formsthe basis of the universalfilter circuit shown here.The binary coding forprogramming the filterparameters is derived fromthe two counters 1C2 andIC3.
The full title of the Reticon R5620 is 'asecond order switched capacitor filternetwork'. It is able to implement the fivebasic filter modes: low pass, band pass,high pass, all pass, and notch. One further,very useful, function of this IC is that ofa programmable sine -wave oscillator.One could be forgiven for expecting tofind all this in a large IC of the LSI variety.In fact, it is all contained in an 18 -pinpackage thanks to one further feature of theR5620: all functions of the IC are fullyprogrammable. This includes the filter centrefrequency and the Q factor both of whichare independently programmable by meansof two five -bit binary codes. For example,to program the filter for a given Q factor,table 1 provides the bi
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