INDIA AF WAVEFORM GENERATO NEW! datalek nside for details Selective calling in CB radio Autoranging DMM Printed resistors READ THIS AD SLOWLY... jr XT' TTTTTTTTYTTmTTTTtT Discover the speed and power of sci. <;r>02 Microprocessor It's last Pipeline Architecture enables thi9 Microprocessor to execute an instruction as it (etches the next one. saving tew cycles, every time in the process Easy to handle instruction set A simple sot ot 56 instruction when mixed SCL6500 FAMILY COURSEWARF with 13 addressing modes provides a versatile language tor your programming needs Other prominent features. * T rue indexing capacity * Programmable stack pointer * Addressable memory up to 64K * Choice between external and on chip clock * 8 bit parallel processing * 8 bit bidirectional databus * Expandable, using support chips through interlaces Documentation Extensive documentation, dealing with every bit ol the chip thoroughly, helps you to integrate your imagination with the potential ot the chip Support There is a team ot live-wire engineers, who can help you to realise the possibilities the chip otters In every (acet generating the concept, conceiving and implementing the design, mapping your needs, etc. — They will be there guiding and working with you. SCL the matchless chip! ■I Semiconductor Hi Complex Ltd. Rogd Office Semiconductor Comple* Ltd (A Govt of India Enterprise) Phase VIII. S A S Nagar-160 059 (Near Chandigarh) Punjab Phones 87585 87265. 87397. 87409. 87310. 87443 Tele* 0395-270 LSI IN Gram CHALSI Delhi Office 12 48 Malcha Marg. 1st Floor. Chanakyapun New Delhi- 110 021 Phones 30144554.3010426. Tele* 031-65 H8 Stocks available with: WEST: Sales Industrials. Bombay. Ph: 2872169, General Electronics. Bombay. Ph: 4946422/ 897953/4946553. 5 International Electronics, Pune. Ph: 65253. Hari Electronics. Ahmedabad, Ph: 342563/344697 NORTH: Mohan Radios. “5 Delhi, Ph: 234578/2518675. U P Electronics, Saharanpur. Ph: 7318 Bharat Radio Centre, Lucknow, Ph: 45808 e> SOUTH: S.P E.E.D.(P) Ltd.. Madras, Ph: 452931/454810. Micro Electronics Incorporated. Madras Ph: 450217, Namtech P Consultants Pvt. Ltd.. Bangalore. Ph: 561234. Safeguard Micro System. Bangalore, Ph: 568324. Shilba Electronics Secunderabad, Ph: 73792 Marketing Engineers & Consultants. Hyderabad. Ph :221293 EAST: Sham Electronics. Calcutua. Ph: 274867/269879 Premier Micro Systems Pvt. Ltd., Calcutta, Ph: 359039. India International Patna Ph 52616 7.04 elektoc mdta |uly 1987 Publisher: C.R Chandarana Editor: Surandra Iyer Editorial Assistance: Aahok Oongre Circulation: J. Dhaa Advertising: 8 M Mehta Production: C.N. Mithagari Address: ELEKTOR ELECTRONICS PVT. LTD. 52, C Proctor Road Bombay - 400 007 INDIA Telex. (Oil) 76661 ELEK IN Overseas editions Elektor Electronics Standfast House Bath Place High Street. Barnet Herts EN5 5XE U K Editor: Len Seymour Publitron Publicacoes Tecmcas Ltda Av Ipiranga 1100. 9° andar CEP 01040 Sao Paulo - Brazil Editor: Juliano Barsali Elektor sari Route National®; Le Seau; B P 53 59270 Bailleul — France Editors: D R S Meyer, G C P Raedersdorf Elektor Verlag GmbH Susterfeld-StraBe 25 100 Aachen - West Germany Editor: E J A Krempelsauer Elektor EPE Karatskaki 14 16673 Voula - Athens - Greece Editor: E Xanthoulis tlektuur BY Peter Treckpoelstraat 2 4 6191 VK Beek - the Netherlands Editor: PEL Kersemakers Ferreira b Bento Ida R.D. Estefama. 32-1° 1000 Lisboa Portugal Editor Jorge Goncalves Ingelek S.A Av Alfonso XIII. 141 Madrid 16 Spam Editor A M Ferrer In part: Kedhorn Holdings PTY Ltd Cnr pox Valley Road b Kiogle Street Wahroonga NSW 2076 Australia Editor: Roger Harrison Volume-5 Number-7 July- 1987 Electronics Technology The magnetic way to painless brain stimulation 7.22 Design abstracts 7.45 Projects Electronic weathercock 7.23 Selective calling in CB radios 7.24 Eight-channel multiplexer 7.26 AF Waveform generator 7.27 Printed resistors 7.31 Spot sine wave generator -2 7.33 Intercom for motor cyclists 7.39 Autoranging digital multimeter 7.42 Information Electronic Press AB Box 63 182 11 Danderyd Sweden Editor: Bill Cedrum The Circuits are for domestic usa only. The submission of designs of snides of Elektor Indie implies permission to the publishers to alter and translate the text and designend to use the contents in other Elektor publications and activities. The publishers cannot guarantee to return any material submitted to them. All drawings, photographs, printed cirucit boards and snides published in Elektor Jndia ere copyright and may not be reproduced or imitated in whole or part without prior written permission of the publishers. Patent protection may exist in respect of circuits, devices, components etc. described in this magazine. The publishers do not accept responsibility for failing to identify such patent or other protection. Distribution/ Subscription For Singapore. Malaysia and Brunei C.R DASARATHA RAJ PRIVATE LIMITED 126. Race Course Road. Singapore 0821 Tel 2931422 Printed At: Trupli Offset Bombay • 400 013 Ph 4923261, 4921354 Copyright © 1987 EMituur B.V. The Netherlands Editorial 7.07 News • News • News • 7.19 New products 7.56 Info/Data Sheets 7.73 Guide lines Switch board 7.67 Datalek 7.69 Classified ads 7.72 Index of advertisers 7.72 Corrections 7.72 Sal«x-25 Inside view - of a low frequency amplifier stage 7.48 Amplifier variations 7.50 Valves „ 7.52 The push pull amplifier 7.53 elektor mdia iuly 1987 7.05 WORLD ELECTRONICS MARKET EXPANDING AT 6-7 PER CENT WORLD ELECTRONICS MARKET ET71 USA JAPAN V77> EUROPE E3S3 Row The World electronics market is forecast to expand at 6.9% in real terms in 1987 according to Benn Electronics in their new Yearbook of Electronics Data. The Benn Electronics Yearbook is published in two volumes, comprising West Europe (Vol- ume 1) and America, Japan & Asia-Pacific (Volume 2), to- gether covering 30 countries representing over 95% of the Free World electronics market. The total market for electronic equipment and components is forecast to reach US$413 billion in 1987 compared with US$387 billion in 1986 and US$373 billion in 1985 at constant 1985 values and exchange rates. Growth during the remainder of the 1980’s is expected to be similar to that in 1987 at an average annual rate of 6.6% to reach US$500 billion in 1990. The US market growth was only 0.9% in 1986 but is forecast to in- crease to 5.7% in 1987. However, this is significantly slower than Japan with growth of 3.8% in 1986 and 8.2% in 1987 and Europe with growth of 8.4% in 1986 and 7.5% in 1987. Overall growth for the remaining countries is estimated as 5.5% in 1986 and nearly 9% in 1987 with India having the highest growth of around 18% for both years. The appreciation of the yen severely restricted Japanese exports in 1986 and resulted in a drop in production of 1.2%. With the home market improv- ing in 1987 and the yen stabil- ising, a growth in production of 5% is forecast, but this will still be well below overall home market growth as exports will remain depressed. In the USA and Europe, pro- duction growth is forecast as being marginally higher than market growth but it is mainly the Far East countries that are benefiting from Japan's difficult- ies. Growth in production in 1987 is forecast to exceed 20% in South Korea, Singapore, In- donesia, Malaysia and Philip- pines. India’s production is also growing strongly, but this is almost entirely to supply its own burgeoning market with very few exports. The Electronic Data Pro- cessing sector is expected to return to high growth in 1987 fol- lowing a poor performance in 1986 when the US market con- tracted by an estimated 4.5%. A real growth of around 10% per annum will be maintained for the remainder of the decade to give a World market of US$140 billion in 1990 at constant 1985 values. The consumer equipment market improved significantly in 1986 with a total estimated real growth of 3.9% as con- sumer expenditure in most countries increased. A similar growth rate is forecast for 1987, with growth slowing to an average 1.4% per annum for 1988-90 as previously high growth products such as video cassette recorders, compact disc players and camcorders approach maturity. The market for telecommuni- cations equipment will con- tinue to grow at around 6% per annum overall but at a higher rate of 8 to 10% per annum in the less industrialised countries as equipment is updated and systems extented. Growth in the communications and military sector will average around 4.5% per an- num for 1987-90, being de- pressed by limited defence and space expenditure in the US. Only in Japan, where military expenditure is negligible, will the sector exhibit more robust growth, forecast as 6.6% per an- num for 1987-90. Following the recession in the semiconductor industry in 1985 the market for active compo- nents improved in 1986 with a growth of 4.6% increasing to around 10% per annum for 1987-1990. The market for passive and audio components is also expected to grow more strongly in response to in- creased production of equip- ment and the total World market for electronic components is forecast to reach US$121 billion in 1990 at constant 1985 values, an annual growth averaging 6.8% for the period 1986-1990. The Yearbook of World Elec- tronics Data 1987 is available in two volumes for West Europe (14th Edition) and America, Japan & Asia-Pacific (4th Edition). Together they survey the markets and production of electronics equipment and components in 30 countries with details of over 100 products in the EDP, Office Equipment, Control & Instrument, Industrial & Medical, Communications & Military, Telecommunications and Consumer Equipment sec- tors (Video, Audio, Other); and Active, Passive and Audio Com- ponents. In addition, there is a full review of developments in the electronics industry and economic prospects in each country. The Yearbook of World Elec- tronics Data 1987 is priced at US$1295, prices for individual volumes on application. Benn Electronics Publications Ltd Chiltem House 146 Midland Road LUTON LU2 0BL elektor mdia |uly 1987 7.21 THE MAGNETIC WAY TO PAINLESS BRAIN STIMULATION by Anthony T Barker, BEng PhD CEng MIEE (Department of Medical Physics & Clinical Engineering • Royal Hallamshire Hospital • Sheffield) The prototype magnetic stimulator in use. Ever since the work of Galvani and Volta in the 1790s it has been known that nerves and muscles can be stimulated by electric currents. Indeed, the whole neuromuscular system of the body is an intricate elec- trical signalling network. Sensory nerves transmit im- pulses from the extremities of the body to the brain and cen- tral nervous system to pass on information such as tempera- ture, force, pressure, texture and vibration. Motor nerves transmit signals in the opposite direction, from the brain to the muscles, to control bodily movement. Electrical stimulation is a widespread and standard clinical tool for the investigation of disorders of the nervous system. Perhaps its most com- mon application is to measure the speed at which signals travel along nerves. If a nerve is stimulated, by ap- plying a brief pulse of current via surface electrodes such as strips of metal or conducting rubber in contact with the skin, or needles inserted into the body, impulses will travel along the particular nerve. These im- pulses, known as action poten- tials, may be detected further along the nerve using similar electrodes connected to re- cording amplifiers, and the transit time or latency from stimulating to recording site can be measured. Slowing allows detection Diseases of the nervous system in general slow down the con- duction velocity of the nerves, which can be up to 80 m/s in normal subjects, and so can be detected by such measure- ments. While conventional electrical stimulation provides a valuable clinical tool in many appli- cations, it does have some limitations. In particular, it is dif- ficult to stimulate deep struc- 7.22 elektor mdia iulv 1987 tures using surface electrodes without causing considerable pain, and the human brain is also virtually inaccessible because the high electrical re- sistance of the skull makes it difficult to pass current from the scalp to the brain. The ability to stimulate the human brain would allow the measurement of transit times through the central motor pathways of the brain and spine, and it is known that these pathways are seriously affected in diseases such as multiple sclerosis. Research started in 1975 in the Department of Medical Physics and Clinical Engineering at Sheffield University into a novel method of stimulating human nerves with pulsed magnetic fields. The stimulation of superficial nerves was reported in 1982, and in 1985 the first magnetic stimulation of the human brain and deep nerves throughout the body was described™. Practical technique Magnetic stimulation is now a practical clinical technique and the stimulators are to be manufactured in Britain by Physiological Instrumentation Ltd* under licence from Shef- field University. The technique has excited considerable worldwide attention because of its ability to measure the per- formance of previously inac- cessible parts of the human nervous system. The basic concept of magnetic stimulation is simple. By pass- ing a brief duration (typically several hundred microseconds) very high amplitude pulse of current through a coil a corre- sponding pulse of magnetic field is produced. By the basic laws of electromagnetism this pulse of magnetic field will in- duce electrical currents in any conductor through which it passes, including the human body. If the induced currents are of sufficient amplitude and dur- ation they will stimulate nerves by exactly the same mechanism as if the currents had been ap- plied via electrodes in contact with the body. Advantages and disadvantages Magnetic stimulation has ad- vantages and disadvantages compared to conventional elec- trical stimulation. Its disadvan- tages are twofold. First, the equipment is rela- tively bulky and costly because of the high current, high voltage technology involved. Commer- cial versions will be consider- ably smaller than the proto- type but will still weigh ten to 20 kilograms and initially be limited to one stimulus every three seconds. The equivalent technology for electrical stimulators is very simple and they can be made both small and lightweight. Second, the precise site under the stimulating coil at which the nerve is stimulated is not well defined. In theory, stimulation is most likely to occur around a loop of diameter approximately the same as the median diam- eter of the coil winding which is typically 70-100 mm. In practice, however, the uncertainty is usually considerably less than this because of the anatomy in- volved. i The equivalent uncertainty of stimulation site with electrical stimulation is determined by the electrode spacing which is typically 10-50 mm. Magnetic stimulation has, how- ever, several important advan- tages. Magnetic fields of this type pass through all body structures— bone, fat or muscle —without attenuation. Hence, currents can readily be in- duced inside structures such as the skull allowing the brain to be stimulated with ease. Painless Magnetic stimulation is painless. Because the magnetic I fields do not decrease rapidly with distance from the coil (fields 40 mm into the body will be typically one quarter of those at the surface) it is poss- ible to reach deep structures without having very high fields at the surface of the body where most of the pain sensing structures lie. These sense organs have high thresholds to electrical stimulation compared with the structures to be stimu- lated and hence are not stimu- lated by fields only four times greater than those applied to the deep nerve. The corresponding fall-off in i field with depth for electrical stimulation would be some 30 times greater and the resultant high surface fields that occur while attempting to stimulate deep nerves can cause con- siderable pain. Magnetic stimulation is ex- tremely easy to use in the clinic. Because the magnetic fields will pass unattenuated through clothing it is not necessary for the patient to undress. Similarly, it is not necessary to make elec- trical contact with the patient, as has to be done with conven- tional stimulation. Indeed, it is not even necessary to make mechanical contact with the patient. Stimulation can be achieved with the coil held some tens of millimetres away from the skin, a feature which may be valuable in the assess- ment of seriously damaged areas of tissue such as head in- juries. Clinical applications The first clinical study® car- ried out using magnetic stimulation has shown the ease | with which slowing of nerve conduction within the brain and spine of patients suffering from multiple sclerosis can be detected and that, as would be expected, no slowing occurs in 1 patients having motor neurone j disease. Evidence is beginning to ac- cumulate that slowing, which has not yet caused clinical symptoms, can be detected. Because of the lack of discom- fort associated with magnetic stimulation of the brain it is now | possible, for the first time, to ; carry out repeated measure- ; ments on patients to quantify the effectiveness of new therapies for central nervous system disorders. Other applications at present under investigation include the monitoring of central pathways during surgery to detect damage before it becomes ir- reversible and the assessment of deep and previously inac- cessible peripheral nerves. At present, six magnetic stimulators, all constructed by Sheffield University, are in clinical use in England and the United States of America. *Physiological Instrumentation Ltd, (Subsidiary of Novametrix Medical Systems), Whitland Ab- bey, Whitland, Dyfed, Wales, SA34 0L6. Bibliography A. Barker, A T., Jalinous, R. and Freeston, I.L. "Non-invasive magnetic stimulation of the human motor cortex”. Lancet, 1985, 1:1106-1107. B. Barker, A.T., Jalinous, R., Freeston I.L. and Jarrat, J.A. "Clinical evaluation of conduction time measure- ments in central motor pathways using magnetic stimulation of human brain". Lancet, 1986, 1:1325-1326. electronic weathercock Until recently, finding out which way the wind is blowing has always necessitated putting on one’s shoes and stepping outside the door, thereby exposing oneself to the vagaries of the British climate. However with a little technical ingenuity, it is possible nowadays to know the precise direction of the wind without leaving the comfort of one’s fireside. The electronic weathercock functions by connecting the vane to a potentiometer which turns with the vane. The voltage at the slider of the potentio- meter is then proportional to the angle through which the vane is turned by the wind. The size of this voltage (and hence the direction of the wind) may be displayed in digital form using a UAA 170 and 16 LEDs. The circuit is designed so that there is a smooth interchange between the LEDs. Potentiometer PI controls the brightness of the LEDs, whilst P2 is set such that, when the voltage at the slider of P3 (which is connected to the vane) is at a maximum, then D16 lights up. Further details regarding the UAA 170 may be found in Elektor 12, April 1976. Potentiometer P3 may present a slight problem, in that it must be of a type which can be adjusted through 360° If such a potentiometer proves difficult to find, then one solution is to use sixteen reed relays, each of which is enabled whenever a magnet connected to the vane passes over the relay. In this case a resistance divider replaces the potentiometer. Readers who are adept at making very small printed circuit boards, may like to replace the carbon track of a conventional potentiometer by a small 16-segment circuit board and connect each segment to the resistance divider. The supply does not need to be stabilised, since the It has an internal reference voltage output I pin 14) which is (gratefully) utilised. The maximum current through an LED is approx. 50 mA. thus a suitable supply would be a transformer producing 100 mA with a voltage of 9 or 12 V. The circuit is completed by a bridge rectifier and a 470 p 25 V electrolytic capacitor. elekior india July 1987 7.23 SELECTIVE CALLING IN CB RADIOS by R Spengler This simple to build unit enables CB operators to send and receive selective calls amidst all the hectic traffic on mostly overcrowded channels. Base CB radio sets equipped with the present tone call unit can be left switched on all day without producing noise or conversations between other CB users, even if the signals trip the set squelch threshold. The receiver’s AF amplifier is only enabled when a specific tone call is received from another station, which may be fixed or mobile. It is also possible to have the selective tone decoder automatically tum on the transmitter in the base station to acknowledge ad- equate reception of the caller (auto-answer facility). The block diagram of the selec- tive tone call system appears in Fig. 1 . The upper blocks repre- sent the tone transmitter, the lower the receiver, while those in the centre and to the right form the interface to the CB radio. Circuit description The circuit diagram of the tone transmitter section is shown in Fig. 2 . The main blocks in this circuit are a Schmitt-trigger based clock oscillator, N2, a ; counter, IC2, and an astable multivibrator set up around TfTj. When the tone call system is switched on with St, IC2 receives a brief reset pulse, and all outputs On are conse- quently made logic low. Relay Ret is not activated, so that the CB radio can receive calls. When push-button Ss is briefly operated, electrolytic capacitor C4 is charged via Ri, the clock oscillator is enabled, and Ret is energized, so that the output of AMV T2-T3 is fed to the micro- phone input of the transceiver (point 1 ), which is switched to transmission at the same time because the PTT (push-to-talk) contact is grounded (point 2 ). Output O2 of decimal counter IC2 goes high on the third clock pulse from N2. Each further Fig. 1. Block diagram of the selective tone call system for CB radios. 7.24 elektor india july 1987 clock pulse switches on the next output, so that the voltage at junction R?-Re steps in four levels, according to the adjust- ment of the preset at each of the counter outputs. The AMV can thus output a sequence of four pre-programmed frequencies. The seventh clock pulse from N 2 causes 06 to go high, and the counter is disabled via its CE in- put. The output of N< goes low, so that Rei is de-activated, and the receiver is enabled again. Immediately after pressing S3, R 2 slowly discharges C», down to a voltage that is recognized as logic low by Schmitt-trigger N 2 . The oscillator is disabled 5 to 7 seconds after depressing S3, and can not be re-started to output a new tone sequence before this interval has lapsed. The circuit diagram of the tone receiver appears in Fig. 3. The AF signal from the CB receiver is amplified in ICa, and fed to four identical PLL tone de- coders Type NE567. The tone sequence is evaluated in IC 10 , and Re 2 turns on the alarm cir- cuit around Rea. A three-tone chime is sounded by the loud- speaker connected to the out- put of IC 11 The AF signal from the CB transceiver is applied to the tone decoder circuit via an unused pin, 3, on the micro- phone/PTT socket. This in- volves connecting the AF signal at the input side of the volume potentiometer in the transceiver to pin 3 of the M/PTT socket with the aid of a short length of shielded wire. When it is preferred not to carry out this modification in the transceiver, the AF signal from the external loudspeaker connection is a suitable alternative. Since this is generally a low-impedance sig- nal, ICa in the tone decoder can be omitted, and the signal is ap- plied direct to the junction of capacitors Cte-C2t. Note, how- ever, that the operation of the tone decoder then depends on the volume setting of the transceiver; generally the best results are obtained when this is set to about */» of its travel, the squelch being turned off. A second modification to the CB radio has to do with the PTT switch on the (handheld) micro- phone. The switch contacts be- tween microphone element and microphone wire (from pin 1 on the M/PTT socket) are con- nected, so that the PTT switch only enables the transmitter, and Re3 switches between the signal from the microphone and that from the tone transmitter. The operation of the selective tone decoder is fairly simple. When pin 3 on the M/PTT socket is utilized as set out above, C13 feeds the AF signal to IC4, which ensures the rela- tively low impedance for driv- ing four PLL decoders in paral- lel. The centre frequency of each tone decoder ICs-iCa is adjustable with an associated preset. When the PLL locks onto the incoming tone, pin 8 goes low, and the relevant LED lights. After a brief delay in- troduced with an R-C network (R 1 5-C34 — R18-C37) the output of the respective NAND gate goes Fig. 3. Circuit diagram of the tone receiver and the interface to the CB radio set. elpktor India July 1987 7.25 high. The inputs of code lock chip ICio must go high in suc- cession to produce a logic high pulse at pin 13. The period of this pulse is determined with the value of C 44 . Driver Ts activates Re?, the transmitter is switched on, and the chime is sounded. At the same time, Re3 switches the chime signal to the AF input of the transmitter, and the "call acknowledged" signal is auto- matically transmitted to the call- ing station. Components R 20 and C40 prevent the chime from sounding any time the radio is turned on. The mobile station Although a three-tone chime is a fairly exclusive alarm in a car, a buzzer is more effective. This can be connected to a contact on Re 2 as shown in Fig. 3. the circuit around Re4 is also in- tended for mobile CB oper- ators. Since Re4 is connected in a self-retaining circuit, LED Dio, which is preferably a blinking type, is turned on when a valid tone call is received, and re- mains on until the car driver presses S 2 . Any call to the mobile station is thus "re- tained” until the operator is available to answer it. The tone call system is fed from the CB radio, because the positive line in the vehicle gen- erally carries considerable noise from the ignition system and the alternator. Setting up Connect either an AF amplifier or the input of a signal tracer to the output of the tone transmit- ter. Adjust presets P 2 -P 5 such that a sequence of four clearly distinct tones is audible after pressing S3. The speed of the clock generator is adjustable with Pi, whose alignment will be reverted to. Use a SOK preset to temporarily feed the tone call to Co in the receiver. Set a relatively low clock speed with Pi, and adjust the PLL centre frequencies (P 7 -P 10 ) until LEDs D 6 -D 9 light in sequence after pressing S3. When the "slowest” setting of Pi is still too fast, R 2 can be re- moved temporarily. Note that C 4 must be discharged before a new tone call can be sent. When the adjustment of the tone decoders is complete, the transmitter clock speed is in- creased until the tone se- quence takes about one second. When it is desired to equip more than two stations with this selective tone call system, all decoders must, of course, be set to the appropriate tone fre- quencies. A new tone se- quence is readily made by swapping tones with the aid of a switch at the output of IC 2 . At the receiver side, the relevant tone code can be selected with a switch connected to the in- puts of ICm The use of two regulators to feed the circuits effectively precludes mutual disturbance in the operation. Frequency determining parts, notably capacitors Ce. C?, C& C 10 and C22-C25, must have a low tem- perature coefficient: NPO types are preferred here, but good MKT capacitors should also give adequate results. The need for high stability compo- nents is best accounted for by the fact that the tone decoders are so selective that a fre- quency drift of about 100 Hz at the transmitter side already makes it impossible to call up the other station. R Note: the Type LS7270 code lock is available from Criclewood Electronics Limited • 40 Criclewood Broadway • London NW2 3ET. Telephone: 01 450 0995. The Type SAB0600 three-tone chime is available from Univer- sal Semiconductor Devices Ltd, whose address and telephone number appear elsewhere in this magazine. eight-channel multiplexer When testing logic circuits it is often necess- ary to examine several different pulse trains simultaneously to check that the time- relationships between them are correct. This is difficult when only a single-channel-, or at best a two-channel oscilloscope is available. Fortunately a simple eight-channel multi- plexer can be constructed using only three TTL IC's. It will display up to eight pulse trains on a single-channel oscilloscope. The heart of the circuit is a 74151. one-of- eight data selector. A BC D input from 0 to 7 applied to the data select inputs allows the data on the corresponding" input 1 to 8 to appear at the output. The input codes are generated sequentially by a 7493 counter which is clocked at 16 MHz by a multi- vibrator comprising N I toN3. In order that the outputs should appear one above the other on the oscilloscope each output must have a different DC offset volt- age added to it, otherwise the outputs would all appear intermingled in a single trace. This offset voltage is generated by a simple D/A converter circuit consisting of N4 to N6 and Rll to RI5. This generates a DC voltage proportional to the binary count of IC2, which is added to the output at the junction of R9 and RI6. The value of ‘R’ is not critical and can be anywhere between 1 k and 10 k. However, fairly close tolerance resistors should be used (1% or 2%), other- wise the eight traces may not be uniformly spaced on the screen. Switch SI selects the number of channels which are displayed. In position 1 all eight channels are displayed. In position 2 the ■(" input of the multiplexer is held high by RIO. so channels 5-8 are displayed. In position 3 the ‘C’ input is held low and channels 1-4 are displayed. The circuit can be used with input fre- quencies up to a few hundred kilohertz. 7.26 elektor tndia july 1987 AF WAVEFORM GENERATOR The AF waveform generator is intended primarily for use in an electrophonic synthesizer. It produces a number of waveforms without the use of filters. The transition from one waveform to another is continuous. A sound consists of a number of discrete tones, which are known as harmonics. The lowest of these, or fundamental, is called the first harmonic, the next lowest the second har- monic, and so on. The tone- colour, also called timbre, of a sound is determined by the number of harmonics present in it. It follows that the tone- colour can be altered by add- ing or removing harmonics from the sound. Harmonics are normally re- moved from a sound by means of passive filters. Unfortunately, these have the disadvantage of attenuating the whole sound, so that additional amplification becomes necessary. Active filters give much better results with a number of musical instru- ments, but not with, for in- stance, the guitar. The frequency spectrum of a guitar contains only very weak high harmonics. The only way of changing the tone-colour of such a signal is the introduction of non-linear distortion. This consist of adding higher har- monics by electronic means. The present generator can pro- duce sine-wave, pulse, square- wave, and triangular waveforms. There are a number of ways in which sounds can be produced in a synthesizer. The most im- portant of these are subtractive synthesis; additive synthesis; direct synthesis; and enrich- ment synthesis. In subtractive synthesis, a number of waveforms, each with a different composition of fundamental and harmonic fre- quencies, is used. The desired tone-colour is obtained by filter- ing the unwanted higher har- monics. In additive synthesis, a great number of separate sine-wave generators is used, each of which has its own frequency and amplitude. The number of generators required makes this an expensive method. In direct synthesis, a number of separate voltages is stored in a memory. When the memory is read in a certain sequence, a predetermined waveform is ob- tained. In enrichment synthesis, as used in the present generator, a number of higher harmonics is added to the fundamental (sine wave) signal. The great advan- tage of this method is the un- broken transition from one waveform to another (i.e., with- out the need of switches). Block schematic In Fig. 1, the VCO— voltage- controlled oscillator— provides the basic waveform for the gen- erator. The fundamental operating frequency is set via inputs Fi and F 2 (coarse and fine respectively). Steps of an octave are selected via input Fa . The VCO generates a triangular waveform which is fed to a voltage-controlled amplifier— VCAi. The output waveform of this amplifier depends on the level of the control voltages at inputs K and L. A number of possible waveforms is shown in Fig. 2: note that potentiometer Pi determines control voltage Uk, while P? controls Ul. Note also that the control voltages may be derived from an exter- nal source. The signal is then taken to a double limiter, which gives it an upper and a lower level. The limiter is shunted by a toggle amplifier— VCA 2 — which doubles or trebles the fun- damental frequency as deter- mined by the control voltages at M and N. Fig. 3 gives some idea of the effect the control voltages have on the signal- note that ?•> determines control voltage Um, while Ps controls Um. Note also that the control voltages may be derived from an external source Finally, the signal is passed to a third voltage-controlled ampli- fier— VCAi— the output of which can be connected to any ordi- nary audio amplifier. The con- trol voltage, Up, at input P is derived from a keyboard, while Uo is intended for amplitude modulation, for instance to pro- duce tremolo. Circuit description The VCO shown in Fig. 4 is fully temperature-compensated and its output is short-circuit-proot Fig. 2. Illustrating the effect of the presets in the waveform amplifier on the triangular 1 waveform output of the VCO. elektor india |uhr 1987 7,27 N ▼ Fig. 1. Block schematic of the waveform generator. 3 position of P9 P8 at centre P8 not at centre O A puls* 3 ,10 Hz). The turn-off instant of the CHOP signal is fixed with MMVi reverting to its inactive state. Briefly recapitulating the characteristics of the BURST signal: pause and burst duration are variable, and the entire signal can be phase-shifted over 10 to 360° to suit particular measurements. The signal at output Q of MMVz is attenuated in divider R4-P6, and fed to the sync output for triggering an oscilloscope. Out- put 0 of the same monostable turns on LED Di via driver Ti. This makes it possible to see the burst activity from the in- strument’s front panel. The power supply for the spot sine wave generator and its built-in burst adaptor is a con- ventional design based on a pair of integrated voltage regulators Type 7808 and 7908. The unregulated ±22 V output is connected to the regulators on the main busboard. LED Da is the power indicator of the spot sine wave generator. The low pass filters for the burst and sine wave outputs are shown in Fig. 9, while Table 2 summarizes their technical characterists. Presets Pi and P 2 enable nulling the offset voltage at burst and sine out, re- spectively. Construction and setting up Commence the construction of the instrument with fitting all parts on the main busboard shown in Fig. 10. It is possible to fit potentiometers instead of multitum presets for P 4 and Ps. When this is opted for, soldering pins and wires are re- quired to make the necessary connections. The low pass filters are also fitted onto the busboard with the aid of soldering pins (8 off per filter), Fig. 8. Circuit diagram of the CHOP generator, and the power supply. I but it is also possible to use elektor india July 1987 7.35 8 St : PHASE (Input Frequency) t Burst oft 2 10Hz 3 33Hz 4 100Hz S3: BURST P3 : BURST 0 1ms 1 25ms 2 500ms Ft MMV3, MMV4 = IC3 = 4538 87036 -11-3 Fig. 9. The continuous sine wave and the sine wave burst are filtered prior to being output. Table 2 Bessel low-pass; 2nd-order with multiple feedback. 70 kHz (LP5a) 35 kHz (LPsto) A1 = 1.3617 B1 =0.618 LP5a: At = Ao=— 1 (ftest<, Pi and C10. Stereo amplifier IC4 functions as a double mono amplifier in this circuit. Its out- 1 put signal is fed to the head- phone set of the passenger. The intercom has a built-in auto- matic mute facility, so that it is only operative when either the driver or the passenger starts to speak. The speech signal from opamp Ai is applied to the — in- put of comparator A3, whose threshold is defined with preset P3 (mute b). Monostable MMVi is thus triggered by the peaks in the speech signal, and reverts to its inactive state when the speech pause is longer than about a second. Transistor T2 then short-circuits the input of the headphone driver, IC*. When a long enough speech signal is available, the collector- i emitter junction of Ti forms a elektor India July 1987 7.39 Seen here is one of the designers working on a prototype. high resistance, and the AF Safety first signal can reach the input of Figure 2 shows the preferred IC». arrangement of the micro- The supply for the intercom is phones and the loudspeakers taken from the motorcycle’s (headphones) inside the safety 12 V battery with the aid of a helmets. The flat electret 10 V series regulator, ICi. Filter microphones are fitted components Li and C23 are re- underneath the lining inside quired for suppressing alter- the helmet to preclude head nator and other noise on the injuries. In this context, it is supply lines to the intercom, strongly suggested not to fit Fig. 2. This shows the preferred locations for the microphones while Di affords protection jack sockets in the helmet. A and headphones inside the helmets. against negative voltage surges. Walkman® headphone set is 7.40 elektor india |uly 1987 Fig. 3. The printed circuit board for making the intercom. Parts list Resistors (±5%): Semiconductors: Ri;Rj;R*;Rio= 1K8 Dt = 1N4001 Ri. . Re incl . ; Ti;Tj=BC547 Rn;Ri2,Ri3;Ri6 -47K ICi — 7810 R7;R#;Ri4,Ri5 = 1K5 IC 2 = CD4538 R 17 ; R is — 1K0 ICj = LM324 Ris;R2o-10K R2i;R22;R2s;R2» = 6K8 ICa = TEA2025 (ITT. Thomsonl R2j;R24 = 3M3 Miscellaneous: R2?;R2« = 100R Li = 50 pH; 1 A; toroidal Rr.;Rjo = 2K2 suppressor choke. Pi;P 2 = 10K preset for horizontal Ft = 100 mA delayed action fuse mounting. with PCB mount holder. Pj;P 4= 1K0 preset for horizontal MCi . . MC 4 = electret condenser mounting. microphone. PCB Type 87024 (see Readers Capacitors: Services page). Ci . . . C 4 incl.;C22;C24 = lUOn Suitable ABS enclosure Cs. . .Cb incl.;Cio;Ci 2 = 330n (waterproof). C*;Cn = 470p LS 1 .LS 2 and LSb;LS4 = Cu;Ci»;Cit = 100p; 16 V; radial Walkman • lightweight Ci«;Ci5 = 22p; 16 V; radial Ci7;C20 = 150n Cis;C 2 t =470p; 16 V; radial C 2 J = 100p; 25 V; radial headphones. eminently suited for this inter- com, since it has a sufficiently long cord fitted with a small plug at the end. A similar cord and plug combination shoud be used for the microphone con- nections. In case of an accident, cord and plug will break instan- taneously and can not inflict injuries on the wearer of the helmet. Construction The circuit board for the inter- com is very compact in view of the limited space for mounting it onto a motorcycle. Fig. 3 shows that many resistors are mounted upright, while all elec- trolytic capacitors are radial types for PCB mounting. The completed board is best cased in a strong, waterproof ABS enclosure with a built-in battery compartment to enable fitting the sockets. The cables to the helmets can be fed through small holes drilled into the associated lid. The presets on the intercom board can be operated with the aid of short, home-made, shafts which are secured onto the central part of the wiper by means of two-component glue. When the adjustment is com- plete, the 4 holes in the inter- com enclosure must each be sealed with a piece of water- proof adhesive tape. St From an idea by W vh Klooster & R Baltissen. elektor India July 1987 7.41 AUTORANGING DIGITAL MULTIMETER An accurate, fully protected, 3% digit meter that can be made with an absolute minimum number of components. Digital multimeters are now- adays offered in many different styles and at very competitive prices. In spite of this, many enthusiasts remain convinced that building good quality test equipment for use in their workshop is a very rewarding pastime. The digital multimeter pro- posed in this article is a ver- satile and remarkably user- friendly test instrument that has some features not commonly found in its price bracket. Circuit description The Type ICL7139 from GE- Intersil is a recently introduced, high performance, low power, autoranging digital multimeter IC, whose main technical data are summarised in Table 1. When used as a DC voltmeter, the ICL7139 always displays the result of a conversion on the correct range. As can be seen from the front panel for the multimeter, shown in Fig. 3, the mode selector has but a single position for DC and AC voltage measurements. When set to DC voltage, the ICL7139 automati- cally selects one of four ranges to ensure optimum accuracy of the readout. For AC voltage measurement, the chip has one range: 400 V. The mode switch has a high (H) and a low (L) pos- ition for resistance and current measurements, and the ICL7139 automatically selects one of two ranges within these groups. Four features of this design deserve attention. Firstly, the RMS (root-mean-square) value of 50 Hz sinusoidal input signals can be accurately measured in the 400 V AC range. Secondly, the use of a 3% digit LCD readout for the measuring 7 42 elektor india july 1987 Auto ranging DMM ICL7139 Technical characteristics: • 13 ranges: 4 DC voltage: 400 mV: 4 V; 40 V: 400 V I AC voltage: 400 V 4 DC current: 4 mA; 40 mA; 400 mA; 4 A 4 Resistance: 4KQ, 40KQ, 400KQ; 4 MQ • Autoranging— first reading is always on correct range. • On-chip duplex LCD driver includes 3 decimal points and II annunciators. • No additional active components required. • Low power dissipation: <20 mW. • Battery life typically 1,000 hours. • Average responding converter for sinewave inputs. - • Display hold input. • Continuity output drives piezoelectric beeper. • Low battery annunciator with on-chip detection. • Guaranteed zero reading for 0 V input on all ranges. • Accuracy: 400 Voc: 1% of reading + 1. all other Voc ranges: 0.2% of reading +1. 4KQ; 400KQ: 0.5% of reading +8. 40KQ; 4MQ; 1% of reading +9. 4 mA: 400 mA: 0.5% of reading +1. 40 mA: 4 A: 0.2% of reading +1. 400 V/50 Hz: 0.2% of reading. - • Overvoltage protection with varistor or surge arrestor. • Current overload protection with fast fuse and diodes. Principal data taken from manufacturer's preliminary data sheet. ranges and associated display symbols. Thirdly, an on-chip supply level detector automati- cally warns of a flat battery by activating the lo bat symbol on the display. Lastly, the proposed DMM has a built-in continuity tester that produces an audible signal when the measured re- sistance is less than IKS. Also included is a hold function that enables "freezing" display readings. With reference to the circuit diagram shown in Fig. 1, a few components require elaborat- ing. Capacitor C 3 at the Cint in- put of the DMM chip must be a high stability type with a toler- ance of not more than 2.5%. The ratio (R 3 + R.)/Rr must be kept at 10:1 within 0.05%; the absolute values of the resistors are less important here. Resistors Ri +R 2 and R3+R4 can be matched with the aid of preset Pi. The value of Rs and Re must be cor- rect within 0.5% for optimum accuracy on the resistance measurement ranges. Precision resistors Rs+Rg and Rio deter- mine the accuracy of the cur- rent measurements: both their absolute value and the 10 6 :10 ratio to R? must be correct within 0.5%. An autoranging voltmeter can not work reliably without proper protection against input overvoltages. Although a varis- tor would be capable of ad- equate surge suppression with a response of the order of 25 ns, its equivalent capacitance of about 200 pF makes it less suitable for the present appli- cation. A gas-filled surge ar- rester has a slightly longer response time, but a very low parasitic capacitance: in the Type B2B600 used here it is only 2 pF while the device gives very good protection of Kii vinl mAVViA- Arl = BZB600 DtO = ICL8069 CCZR D3...D9 = 7 1N4148 Fig. 1. Circuit diagram of the autoranging digital multimeter. Fig. 2. The circuit board for the DMM fits in a standard Vero enclosure. Semiconductors: Di;Dz = 1N4001 Di D»incl. = 1N4148 Dio = ICL8069CCZR (GE-IntersillY 1 C. = ICL7139 (GE-lntersil)Y Ti - BC547B Miscellaneous: Si;Sa = miniature SPST slide switch. So = double pole. 6 way rotary switch for PCB mounting. F> = fast 4 A fuse with PCB mount holder. T Available from Universal Semiconductor Devices Ltd. • Telephone 01 348 9420. • See text. Parts list Resistors (±5%): Ri . . R« incl. = 5M0 Rs = 10K; 5 W R«;Rr = 1M0; 0.1% Rs = 1R24F Ro-8R66F (R. + R» = 9R9; 0.5%l Rio = 0R1; 2 W Rn = 100K Ru = 47K R.3 = 22K Pi = 20K multitum preset Capacitors: Ci = 180p Cz;C«;Cs = 100n Cj = 3n9G polystyrene or silver-mica C< = 10p; 16 V; axial Xi = 100 kHz miniature quartz crystal. * Bz = piezoelectric beeper PB2720 (TOKO).* * Surge arrester B2B600 (Siemens). * 9 V PP3 battery with clip-on leads. 3 off insulated 4 mm wander sockets. Enclosure Vero Type 65-2996H. Display Type 38D8R02H (LXDI.A PCB Type 87099 (see Readers Services page). We regret that the front panel foil for this project is not available through the Readers Services. # Available from 2D Electronics • Wellington House • 2 Kent- wood Hill • Reading. Tele- phone: (07341 420440. ♦ Available from ElectroValue • Telephone: (0784) 33603. ♦ * Available from Cirkit PLC • Telephone: (09921 444111. E i kn mo I mAVuA elektor India July 1987 7.43 HOLD V/Q ZfA COM 4A I fused I ELEKTOR AUTO RANGING DIGITAL MULTIMETER Fig. 3. Drilling template and suggested front panel foil for the DDM the sensitive inputs on the ICL7139. Diode Dio is a temperature-compensated, pre- cision, 1.2 V reference. As already stated, the function of preset Pi is not to set the voltage at the REF input of the DMM chip, but to compensate for the tolerance on the 5 MQ resistors. Its adjustment is simply carried out with the aid of a sufficiently accurate digital multimeter, borrowed from a friend or a helpful electronics shopkeeper. Rotary switch S 3 selects one of six measurements modes plus associated symbol on the LC display. Slide switch Sj selects the hold mode. The multimeter is fed from a 9 V battery, and is switched on and off with Si. Since crystal Xi clocks the RMS converter internal to the DMM chip, the stated value of 100 kHz is only valid for measuring 50 Hz input signals. For 60 Hz measurements, Xi must be changed to a 120 kHz type. PCB. The stated Vero enclosure has a battery compartment whose inside should be lined with expanded polystyrene. As shown on the accompanying photographs, a piece of alu- minium foil is cut to size and in- sulated at both sides with self adhesive transparent foil. Great care should be exercised to avoid electrical contact be- tween the aluminium foil and any component on the circuit board. A small area around the hole for the threaded part of the switch shaft should be left unin- sulated. The screening foil is carefully secured by inserting it between a washer with a solder tag and the nut on the shaft of the rotary switch. A short wire is then run from the solder tag to point shield on the printed cir- cuit board. Construction The autoranging DMM is built on PC board Type 87099— see Fig. 2. The LC display is fitted into a wire-wrap socket or two sets of stacked terminal strips to ensure the required height above the circuit board. The three sockets for connecting the test leads are preferably mounted onto the enclosure lid to avoid excessive strain on the L is t — * 25 * J \i— 36 ' ' M M H DESIGN ABSTRACTS The contents of this column are based on information obtained from manufacturers in the electronics industry, or their representatives, and do not imply practical experience by Elektor Electronics or its consultants. Driver 1C for Class D amplifiers The driver IC Type TDA7260 from SGS-Ates offers a new con- cept for the output stages in car hi-fi systems. Driving four bridge-connected SGS-Ates Type 321 MOSFETs, it delivers 25 W (sinusoidal) into 2Q. At up to 80% efficiency heat sinks are not required. Pulse-duration modulation— PDM— has been of practical im- portance in switch-mode power supplies for some time. Switched audio amplifiers are generally only found in AM broadcast transmitters. Sony’s hi-fi PDM amplifier Type TA- N88, introduced in the late 1970s, had not really overcome the problems associated with this type of operation and was, therefore, withdrawn from the market within a very short time. In the TDA7260, SGS-Ates has succeeded in overcoming the problems associated with PDM, even under the exacting re- quirements of car hi-fi equipment. The most serious problem in PDM is the stability of the modulator that has to provide a rectangular pulse with a width that is proportional to the ampli- tude of the AF signal. To achieve maximum power at a given voltage, duty factors of between 5% and 95% are necessary, but at the same time overmodulation must be prevented. Owing to their— relatively— poor dynamic per- formance and distortion factor, PDM systems with fixed clock frequencies are not often found in high-quality audio equip- ment. Freely oscillating PDM amplifiers are much more suitable, but their frequency tends to decrease at high amplitudes. Where high switching frequencies are used (as, for instance, the 500 kHz in the TA-N88), the efficiency, therefore, drops, while HF radiated noise increases. SGS-Ates has solved these prob- lems by stabilizing the fre- quency: depending on the amplitude, the hysteresis of the comparator is arranged in a manner that ensures optimum switching frequencies— see | Fig. 2. [ Unfortunately, frequency stabilizing can not prevent over- modulation and the consequent possibility of damage to the switching transistors. Because of that, the input opamp in Fig. 4 incorporates a limiter Table 1 Technical specification Maximum ratings Supply voltage, Ub Input voltage Floating input voltage Peak output current Dissipation at Tambiem = 70°C Max 30 V Max 10 V ±6 V 300 mA Max 1 W Electrical characteristics IUb = 14.4 V; T« = 25°CI Power output into 2 ohms at 1 kHz 25 W Distortion factor at 1 W into 2 ohms at 1 kHz 0.001 Voltage gain 12 dB Switching frequency 120 kHz Common-mode rejection 70 dB Noise output voltage 15 mV Efficiency at 25 W output into 2 ohms 85% which comes into action when the peak value of the input signal reaches 3 V. The limiter also provides a warning signal to pin 7 when the input signal approaches a peak value of 3 V. This warning signal drives an OTA— operational transconduc- tance amplifier— in the TDA7232 in a manner that in- itially makes limiting un- necessary, thereby preventing an increase of the noise factor. Because of the small current density in PMOS FETs (higher ON resistance), a complemen- tary push-pull switched output Fig. 1. Block schematic of the TDA7260 Fig. 2. Frequency stabilization in the TDA7260 prevents the sharp reduction in switching frequencies at high signal levels. PEAK OUTPUT VOLTS (20 resistive toad) 870B8 • 2 elektor mdia july 1987 7.45 Fig. 3. The drivers at the out- put of the TDA7260 use bootstrapping. Fig. 4. Circuit proposed by SGS-Ates for a 25 W car hi-fi amplifier with an efficiency of over 80% at the rated power output. Fig. 5. Distortion vs frequency characteristic at 25 W into 2 Q or 50 W into 1 Q. stage with NMOS FETs— SGS- Ates Type P321 — is used. These FETs switch 60 V at 12 A with an ON resistance of typically 0.07 ohms. They are driven by a special stage in the 7260. To ensure correct drive levels for the two upper FETs in the bridge, the gate voltage must be some 9 V higher than the supply voltage. The driver stage, therefore, contains two bootstrap stages that are capacitively coupled to the bridge outputs via pins 13 and 16. In theory, therefore, twice the supply voltage is available at pins 14 and 17 for the control of the FETs. The switching times of the driver stages are carefully arranged to prevent an 7.46 ulektor mdia July 1987 overlap with the corresponding conduction times of the FETs in one of the bridge halves. The transition delay of the drivers is smaller than 100 ns. The outputs of the driver stage can provide up to 300 mA at a maximum capacitive loading of 1800 pF. This means that even FETs with much greater power output can be driven effectively. Another interesting feature is the facility for sub-sonic modulation of the switching fre- quency. An internally generated, very-low-frequency triangular signal varies the hysteresis of the comparator, and consequently the fre- quency of the rectangular signal, to reduce interference 6 * z S i ■■ in - m l i 20 M 5 5 1 ‘ 2 1 i H / / 1 / / T i mm / 7 5 0.2 ■ -i - ii rjp H II ■in 0.1 — _ — 1 I 8 during radio reception. Such in- terference is further decreased by a low-resistance 150 pH toroidal choke in the positive supply line. The 0.025-ohm re- sistance, decoupled by a 1000 pF capacitor, serves as cur- rent sensor for the short-circuit protection stages at pin 18. The TDA7260 contains voltage regulators that provide an inter- nal supply voltage of 10 V and a 4.5 V reference potential for the opamps. The RC network at pin 20 pro- vides an effective switch-on delay which ensures that the amplifier is not actuated until the internal supply voltage reaches 10 V. If that voltage ex- ceed 18 V or drops below 9 V, the muting stage is actuated and renders the output stage in- operative. Since the driver IC has a power dissipation of 900 mW at 100 °C, an integrated thermal protec- tion circuit is indispensable. When the IC overheats, it is completely switched off: once the temperature has dropped to a tolerable level, it is switched on again automatically. The input opamp in Fig. 4 has been arranged as a (floating) symmetrical difference ampli- fier. The bridge-connected output ; amplifier is terminated into two parallel-connected 4-ohm loudspeakers via 15 pH low- resistance toroidal chokes. Distortion, power output, and efficiency characteristics of the circuit in Fig. 4 are given in Fig. 5, Fig. 6, and Fig. 7 re- spectively. At 80% efficiency and a driver output of about 1 W (corre- sponding to 25 W power output into 2 ohms), the FETs dissipate not more than 1 W each, so that a heat sink only becomes necessary at output powers above 25 W. In view of the low load impedance, the loud- speaker connexions must be kept short and be made of thick cable. A combination of the TDA7260 and TDA7232 is ideal for use in an active loudspeaker system: a schematic representation of this set-up is shown in Fig. 8. Fig. 6. Noise factor vs power output characteristic at 1 kHz. Fig. 7. Efficiency vs power out- put characteristic. Fig. 8. Block schematic of an active loudspeaker system based on the TDA7232-TDA7260 combination. Literature: TDA7260 Product Preview, SGS-Ates, May 1985. A high-performance, high- efficiency audio subsystem for car radios by Casini, et al, IEEE Transactions on Consumer Electronics, Vol. CE-31, No. 3, August 1985. Low-noise amplifier Type TDA7232, Elektor Electronics, June 1987. SGS-Ates (UK) Limited Planar House Walton Street AYLESBURY HP21 7QJ elektor india (Uly 1987 7.47 selex 25 INSIDE VIEW of a low frequency amplifier stage It is not very difficult to see how a transistor, a capacitor or a resistor works individually. The explanations are quite simple and a few examples and comparisons can make the points clear. However, in case of circuits, where all the three types of components are interconnected and fed with a single battery pack, it becomes a bit difficult to visualise how the currents will flow in different paths and what voltages will appear at different points. The problem becomes still more complex when such a circuit is supplied with an AC signal at the input. How does this AC signal affect the currents and voltages in the circuit? In short, how does one manage to understand a complex circuit? For instance, the amplifier circuit shown in figure 1 amplifies the AC signal presented at the input and gives an output signal which is almost ten times the input signal. Let us use this low frequency amplifier circuit to see how a circuit can be analysed to understand its operation. DC Conditions Let us first simplify the circuit and assume that no AC signal is present. Only DC conditions are present initially and the power supply causes only DC currents to flow through various parts of the circuit. As we know that capacitors do not allow DC currents to flow through, we shall neglect them for the time being. What remains is one transistor and four resistors as shown in figure 2 R1 and R2 form a voltage divider which divides the supply voltage and the ratio is 2.7 : 1, so the voltage at the junction is approximately 2-4 V This point is directly connected to the base of the transistor and hence the voltage on base of the transistor is naturally 2.4 V. This calculation is not very accurate because we have not considered the base current which flows also through R1. However, this is very small and can be neglected. The current through (R 1 + R2) voltage divider is about 0.24 mA which is much greater than the base current. The next point to observe is the base voltage, which we have already seen to be about 2.4 Volts This is greater than the threshold voltage (0.6 to 0.7 V), and a collector current must flow This current also flows through the emitter and thus there will be a voltage drop on R3 as well as R4 and R5. The emitter voltage must be less than the base voltage by 0.6 V, i.e. 1.8 V. Because the base-emitter junction drops about 0.6V. The Ohm's law now gives us the emitter current as follows 1,8 V _ 1. 22 kfl ” 1 ,5 mA Once again, neglecting the base current which also flows through the emitter, we can say that the collector current is also 1 .5 mA. Now, multiply this collector current by the collector resistance 2.2 KA and we get the voltage drop of 3.3 V. This leaves us with a voltage of 5.7 V on the collector terminal. If we know the current gain of the particular transistor, 2 Figure 1 : A commonly used low frequency amplifier. Figure 2: During operation without any AC input signal, only DC currents flow in the circuit. They are caused by the DC supply voltage. Figure 3: When we consider only AC conditions, the capacitors behave like short circuited paths and can be replaced by direct connections to simplify the circuit. 7.48 elektor mdia july 1987 selex Photographs a. The input voltage is a pure AC voltage with a frequency of 100 Hz. b The input AC voltage superimposed on the DC voltage at the base. Tne DC voltage ensures that the transistor always remains conductive. we can find out the base current. Assuming a value of 300 for the current gain, we get a base current of only 5 micro amperes. This is indeed negligible compared to the current through the voltage divider and that through the emitter. The calculated voltages are shown in the figure 2 at the base, emitter and collector of the transistor. AC Conditions So far we have seen the DC conditions only. Now let us visualise what happens when an AC signal is present at the input of the circuit. For analysing the AC conditions, we must consider the capacitors, because they are known to be conductors of AC currents. To simplify the matter, let us assume that the capacitors have a very low impedance so that they can be effectively replaced with short circuited conducting paths for the AC currents. The result of this is shown in figure 3. Let us now give an AC voltage of 100 mV (peak to peak) at the base of the transistor. The base voltage is thus superimposed by an AC voltage which alternates between +50 mV and -50 mV. As the emitter voltage must be less by about 0.6 V than the base voltage, it also goes up and down by 50 mV for each cycle. The difference remains constant at 0.6V between the base and emitter voltage. Note that for the AC conditions only R4 must be considered As the voltage across R4 fluctuates, the current must also fluctuate, i.e. the emitter current must also fluctuate by: 220 n (peak to peak). The collector current is also same as the emitter current and thus it must also c. The emitter voltage is always less than the base voltage by 0.6 V. So the AC waveform remains same, but shifted down by 0.6 V, compared to that in photograph b. d. The voltage on R5 is a DC voltage because C2 behaves as a short circuit to the AC voltage across • R5. fluctuate by 0.45 mA peak to peak. The collector resistance converts this fluctuation in to an AC voltage of 2.2 KA x 0.45mA s* IV peak to peak. If we compare this AC voltage at the output with that at the input we can see that the output AC Voltage is 10 times larger than the input AC Voltage. Please note that this is just an overall picture of how the circuit functions. The assumptions that we have made during our discussion may not be valid in case of a more complex practical circuit. Also, the DC and AC conditions can never be seperately analysed as we have done, because both types of currents and voltages exist simultaneously in the circuit and they are superimposed on each other. We have assumed that the capacitors behave like short circuited paths for AC currents. This is not true in a practical Figure 4: AC and DC conditions occur simultaneously in practical circuits. Various waveforms in the circuit are shown to explain how the input signal gets amplified and inverted at the output. The various waveforms marked as a. b, c g are also photographed from the oscilloscope and given seperately. The negative terminal of the battery was also connected to one of the oscilloscope channel continuously to show the relation between various waveforms and the negative ground line. circuit. The capacitors behave like frequency dependant resistors for AC currents and the analysis becomes much more complex. The DC and AC analysis that we have done here is purely an imaginary thought process based on various assumptions and approximations. This has been used only for the purpose of understanding the basic operation of the circuit and to provide you with a guide line for studying similar circuits. The output at the collector is not a pure AC voltage, but a combination of both DC and AC, and that is why the coupling capacitor C 3 must be used to pass on only the AC part to the next stage for further amplification. For the sake of completeness, let us see the polarities of the input and output Voltages. During the positive half of the input voltage, the emitter voltage also goes through the positive half to maintain the difference of 0.6V. However, as the collector current goes through the positive half, the voltage drop on collector resistance increases and thus effectively the voltage on the collector goes through its negative half cycle. The amplifier thus inverts the input waveform during amplification. This is also called a 180° phase shift between input and output. eleklor rndta July 1987 7.49 /V\AAA e. The collector voltage is formed by substracting the drop across collector resistance from the supply voltage. As the collector current contains a DC as well as AC part, the collector voltage is also made up of DC and AC. Note that the collector AC voltage goes through its positive half cycle when the base AC voltage is going through its negative half cycle. AAAA A f. The coupling capacitor allows only the AC voltage to pass through. Thus the output voltage is purely an AC voltage, which is an amplified and inverted replica of the input. AMPLIFIER VARIATIONS g. The DC supply voltage provides the energy required for amplification. "Matching problem!", says the specialist, when somebody connects a record player to an amplifier — and the sound output is no good. This "matching problem” can be frequently solved with a simple, single stage amplifier One such circuit is shown in figure 1. It has four variations,, A, B,C,D, which differ only in their input impedance and amplification. The amplification factors and other data are listed in table 1 . The distortion factor with a value of 0.3% is quite acceptable and lies with in the limits of Hi-Fi DIN standard 45 500. Another variation which can give a distortion value of 0% is shown in figure 1 (E). Unfortunately the amplification factor is just 1 . 1 . EKSSjI I 83770-1-3 83770-1-5 Construction The circuit is quite simple and small. Two such amplifier stages for a stereo can be easily accommodated on a single SELEX PCB The circuit can be selected from the four given variations depending on the required amplification. If the requirement is unknown, R4 and R5 can be temporarily soldered from the track side to try out which combination works best. Power supply can be derived from the amplifier or a seperate battery pack can also be provided if the voltage of the amplifier power supply is not suitable. Any value between Component List R1 - 27 Kfl R2 = 10 Kll R3 = 2.2 K R4, R5 As per Cl - 2.2 ,iF/10V C2 - 100 jiF/IOV C3 = 10 pF/IOV T1 = BC 547 B 1 Standard SELEX PCB (Size 40x100 mm) Figure 1 : Different variations of the matching amplifier stage. Figure 2: The smallest size of SELEX PCB has enough space for two amplifier stages of a stereo system. Figure 3: All four variations A.B.C.D assembled on a double size SELEX PCB for testing in the Elektor Laboratory. The last variation of figure 1 (E) obviously needs no PCB or components ! I elektor mdia july 1987 7.51 selex 6 and 24 V is acceptable The values given in table 1 are valid for a 9V supply. A plug in type 9V supply. A plug in type 9V adapter can also be used, however, in this case a 1 00 pF electrolytic capacitor must be soldered on the PCB between plus and minus lines to eliminate noise and hum. The PCB must be installed inside the amplifier casing for proper shielding. If this is not possible, it can be installed inside a small independent metallic enclosure. Shielded wires must be used for connections between the different units. The metallic casing is not to be connected with the earthing point. If the record player or the cassette recorder has sufficient space, the PCB can be fitted inside the enclosure. Table 1 Variation A B c D R4 1.5 Kll 56 n 220 11 680 11 R5 1.2 Kll 1.2 Kll 1 Kll 470 11 Amplification Factor 100 30 10 3 Input Impedance 3.5 Kll 4 Kll 6 Kll 7 Kll Output Impedance 2 Kll 2 Kll 2 Kll 2 Kll VALVES •• is it really true that once again some stereo systems are being constructed using valves?" "Yes, however, these are only a very few exotic amplifier systems". "But why this prehistoric technology is being revived? Aren't they really happy to have finally got rid of the old fashioned valves?" "The valves are not as bad as you think. Even they have their plus points!" "Well, just look at the heat they produce Isn't it a shear waste of energy?" "Indeed, it is true, but there are some people who are ready to accept this. "And then who would buy an amplifier that takes so much time to heat up and start functioning?" "Not me However as I have said, there are quite a few enthusiasts, who do not mind waiting for a minute before the amplifier starts functioning. Because, they are convinced that the valve system does sound better than a transistor amplifier." "But even from the technical point of view, the transistor amplifiers are clearly superior" "The technical problem with the valve systems is that they require a transformer ." "How come this is a problem? the transistor amplifiers also have a mains transformer." "Yes, that is right, but I was refering to the output transformer and not the mains transformer. The valve system does have a mains transformer, but in addition to that, it also requires an outpout transformer to feed the loudspeakers." "You mean a transformer can also transform music?" "The music and speech appear in the amplifier as a mixture of various AC signals with frequencies of individual sounds, and a transformer can transform AC voltages. You already know this!" 7.52 etoktor India july 1987 "Seems logical .... but, in that case why do we need an amplifier at all? We can just use a transformer to step up the voltage from the record player or cassette player directly and feed it to the loudspeaker. This would indeed be much simpler than a complicated amplifier, and we would need neither the valves nor the transistors" "This would indeed be much simpler, only if it were to function! The record player and cassette player, unfortunately, supply very little voltage and very little current. When you step up the voltage with a transformer, the current is reduced in the same proportion. Because the transformer does not supply any energy. This reduced current would never be able to drive a loudspeaker. As against this, amplifier adds energy to the signals, which it draws from the mains. "How does it add energy to the signal?" "It is not very simple. In the amplifier, first the AC voltage is transformed and converted into DC voltage. Then depending on the incoming signal voltage, the amplifier provides a porportionally higher voltage to the loudspeakers, drawn from the DC supply voltage." "This means that the amplifier is not an amplifier, but rather a controller which draws power from the supply voltage in a manner controlled by the input signal and gives it to the loudspeaker." "Strictly speaking, yes, it is a controller. However, I was telling you about the transformers. You know that the loudspeaker has a low resistance "... four Ohms or eight Ohms " "So, they do not require a very high voltage but require a high current. Transistor amplifiers can supply high current without any problem and do not always need the output transformers to feed loudspeakers." "And Valves?" "Valves require very high voltages compared to transistors, but they can supply very low currents. Therefore, the valve amplifiers require output transformers to step down the voltage and step up the current. Technically it is quite difficult to design a good output transformer which can reproduce all the audio frequencies true to life." "Then why do people still prefer valve amplifiers?" "As I said, it is difficult to design a good output transformer, but not impossible. Incidentally, some of the valve amplifiers are constructed with several valves, which can together supply the required current. The output transformer is not necessary in these amplifiers. Most of the Hi-Fi enthusiasts buy these amplifiers simply because they like the sound better.” THE PUSH-PULL AMPLIFIER The principle of the "Push- Pull" Amplifier has a similarity with the woodcutters saw which has handles at both the ends. These handles are held by two woodcutters. When one is pulling the saw other is pushing .... the advantage is obvious, the saw cuts in both the direction. The transistors in a push-pull amplifier work in a somewhat similar manner. One transistor amplifies the positive half of the AC signal, and the other amplifies the negative half. One such circuit is shown in figure 1 . Emitters of both the transistors are connected together and the voltage at this point is about half of the supply voltage. During operation, when Ce passes a positive half wave, Ta becomes conductive and more or less connects Ca to the positive pole of the supply voltage. Tb is blocked at the same time because it is a PNP transistor and Ce has connected the positive half cycle of the input signal to its base. When the negative half cycle of the input signal arrives, it is passed on by Ce again to the bases of the transistors. This time the conditions are reversed and Tb becomes conductive, more or less connecting the capacitor Ca to the negative pole of the supply voltage. •Simultaneously, Ta is blocked due to a negative voltage on its base, because it is an NPN trnasistor. In this manner, the voltage on capacitor can swing between the plus pole and minus pole of the supply voltage. Steady state voltage being half the supply voltage value. Due to the presence of capacitor Ca, the loudspeaker receives a true AC voltage which is controlled by the input voltage. Even though AC voltage amplification is possible with a single transistor, it is not very eifficient because of the power losses in the collector and emitter resistors. In a push-pull circuit these resistors are absent, so there is no question of these extra Figure 1 : The basic principle of a push- pull amplifier, Ta amplifies positive half cycles and Tb amplifies negative half cycles of the AC input voltage. Ce is the coupling capacitor for the input AC signal and Ca is the coupling capacitor for the output AC signal Figure 2: A practical amplifier circuit with a push-pull output stage. Figure 3: Details of the practical push- pull output stage. Two diodes are used between the bases to produce 1-5 V difference between them. This eliminates the disadvantage of the basic circuit, that the input voltage must be more than ± 0.6 V to have any effect on the circuit. elektor india July 1987 7.53 selex power losses. The basic circuit diagram in figure 1 is very -simple compared to the circuit shown in figure 2. Even the circuit in figure 2 is very simple compared to the sophisticated Hi-Fi amplifiers. Therefore, it does not give a very high quality of sound but represents a practical easily realisable push-pull output stage for 8A loudspeakers It can be operated from a 4.5V battery, and gives a peak power of about 250 mW for sine wave inputs. What more can one expect from a simple circuit and a supply voltage as low as 4.5V? CIRCUIT If we compare the circuits of figure 1 and 2, there is nothing in common excepj for the operating principle. The input circuit has completely changed as shown in figure 3. The two diodes between the base terminals carry current through R5 and T2. Their threshold voltages add up to 1.5V and appear between the bases. This modification is necessary to overcome the disadvantage of the original circuit that Ta conducts only when the positive halfwave is greater than + 0.6V, and Tb conducts only when the negative halfwave goes below — 0.6V; in between these limits, practically nothing happens to the circuit. Because of the two diodes, both the bases are at 0.6V each, compared to the emitters. The diodes also prevent excessive transistor currents. The push pull stage can be compared to an emitter follower circuit. It has the characteristic features of emitter follower. The collectors are connected to the supply voltage poles and the output load is connected in the emmitter circuit. In this case the load is formed by C3 and LS. Like the emitter follower, it does not amplify the input voltage but provides relatively high current at the output, without loading the input voltage. As we are also interested in voltage amplification, we use two more transistors in addition to the push-pull output stage. These are T1 and T2 5 which form the so called ' driver'' stage. This stage is seperately shown in figure 4 also, for more clarity. R1 and R2 decide the base bias voltage of T1 . The collector current flows into the base of T2 and gets further amplified by T2. The output voltage on the collector of T2 is them fed to the push- pull output stage. R5 functions as the collector resistance for T2. R3 is shown in figure 4 as connected tothe plus pole of the supply for the sake of simplicity. The emitter current of T1 flows through R3 and depends upon the voltage on R3. This voltage (as seen from figure 2) is the difference between the output voltage of the amplifier and the input voltage, deducting 0.6 V base-emitter drop of T1. Thus the input stage is controlled by the input voltage but is also dependant on the output voltage through R3. Let us take an example to see how this happens. Assume that a rapidly rising positve half wave lies at the input. Because of some reason, if T3 does not conduct rapidly enough, anc Figure 4: Details of the practical driver stage. The negative feed back is not shown here for the sake of simplicity. Figure 5: Component layout for circuit of figure 2. Component list R1 =2.2 Mil R2 = 820 Kit R3 = 22 KI1 R4 = 1 KI1 R5 = 470 11 R6. R7 = 2-2 II PI =1 Mil (Log) Cl =470 nF C2 = 10 mF/ 10 V C3 = 100 /rF/10 V D1 , D2 IN 4148 T1 = BC 557 B T2 = BC 547 B T3 = BD 139 T4 = BD 140 LS = Loudspeaker (8 11/0.5 W) 1 SELEX Board (40 x 100 mm| 1 Battery 4-5V. the output voltage rises too slowly. Consequently the voltage drop on R3 reduces, emitter current of T1 falls, and collector current of T2 (through R5) also falls, this causes the voltage drop on R5 to reduce and thus increase the basecurrent of T3. The collector current of T3 thus rises more rapdily and the error which was assumed initially gets corrected. This method of control is called negative feedback. The quality of the reproduction by the Hi-Fi output amplifiers depends on how cleverly the negative feedback circuit is designed. A detail which we have still not touched is the R4/C2 combination. If we carefully observe the connections, we can see that R4 and R3 form an AC voltage divider. As C2 blocks the passage of DC currents, R4 and R3 work as a voltage divider only for AC Voltages. The reason for using a voltage divider in the negative feedback circuit is quite obvious. If the negative feeback voltage is given directly, it will throttle its own input signal and the circuit will stop amplifying completely. As the capacitor C2 makes the voltage divider ineffective for DC Voltages, the input DC Voltage given by the voltage divider R1/R2 appears at the output increased by the threshold voltage of T1 and by the drop on R3. Cl couples the input AC to the base of T1 but prevents the Dc base voltage of T1 from reaching the volume control potentiometer. C3 keeps away the DC Voltage from the loudspeaker. Component layout is shown in figure 5 for those who would like to construct and test the circuit. Those who are interested in experimenting further, can vary R1 and R2, and R3 and R4 to observe the effect. Battery voltage can be increased to 9 V to get more power output. But in that case the output transistors must be provided with heat sinks. 7.54 elektor mdia July 1987 EW PRODUCTS • NEW PRODUCTS • NEVi ACCSYS-1 Multipoint Temperature Scanner 'ACCSYS-1' is a unit that can monitor, control and log the temperature of 128 channels in its maximum configuration. The Scanner architecture is based on Intel's 8085 Microproccessor. Its's features are: 1) Auto or Manual operation. 2) The type of sensor for every channel is field programmable. It supports R,S,J,K & RTD's. 3) Software linearisation for all types and through out the measuring range of 0-1760 C ensuring ± 1 C accuracy. 4) Temperatures as low as -150°C can be measured, logged and controlled by the system. 5) The system has a CPU Module, Display & Key-board Module and an Analog Module. Other options are Printer Module and Control Annunciator Module. 6) The battery back-up contains rechargeable ni-cad cells for preserving the set point and other programs in RAM. The recharging of these cells on power-resumption is automatic and would take 6 hours to attain full charge. For further details contact: MICRO CONTROLS 1, Srinivasa Avenue Road Ramakrishna Nagar Mandaveli Madras 600 028 I BATTERY MONITORS EQUILAB introduces new electronic auto battery monitors to know the exact condition of batteries under dynamic condition viz. below normal, normal, charging condition fully charged and over charged condition with the help of coloured LEDs. These monitors are also helpful in giving battery replacement warning signal as well as a fault in the charging mechanism. These are available in three models. BM3 gives three states of the battery viz. POOR, NORMAL & CHARGING. BM4 gives POOR, NORMAL, CHARGING & OVER CHARGING state of battery and BM5 gives five conditions such as POOR, NORMAL, CHARGING, FULLY CHARGED AND OVER- CHARGED. For further details contact: ELECTRONIC INSTRUMENT LABORATORIES B-69/004, Anand Nagar Chh.Shivaji Road Dahisar (East) Bombay 400 068 CHIP RESISTORS & NETWORKS Yokohama Electric Components Co. (YEC) Japan offers Thick and Thin film Resistors. Thin film Resistors are available in plate type. Chip and SIP Networks. Thick Film Resistors are Chip Networks. These resistors are available with very low tolerances and T.C.R. upto ± 5 ppm/°C. * S S - s a H k id a; a a .e S n a * "EJ 1 1 nn For further details contact: HI TECH RESISTORS PVT LTD. 1003/04 Maker Chamber 5 Nariman Point Bombay 400 021 LUXMETER OPTO India has introduced a very sensitive, portable Compact Luxmeter for measurement of light levels. This is suitable for all photometric measurement in Science & Research as well as quality testing labs. 'h Contact: AGRAWAL SALES ENTERPRISES 34 Ganesh Bazar Jhansi 284 002. OPHIR's LASER POWER/ ENERGY MONITORS OPHIR OPTICS LIMITED offer a very wide range of Power/Energy Monitors from 30 to 3000 Watts full scale. All the monitors incorporate a specially designed Thermopile Absorber Disc which ensures accuracy and linearity, independent of beam shape/position, combined with a rapid response time. A complete range of volume and surface absorbers are available both for broad band general purpose use and custom- tailored to a specific laser type. The Disc’s high sensitivity and up-to-date electronic design of the display unit allows an unusually large dynamic range extending over 4 decades in all models. All ranges are measured directly without beam attenuators, range extenders or reflection attachments. Three different display options— Analog, Digital and Hand-Held Digital Displays are available giving the user utmost flexibility in configuring his monitor to his specific needs. For Further details please contact: TOSHNI-TEK INTERNATIONAL 267 Kilpauk Garden Road Madras 600 010 Him nmi nun mm Mint mm 7.56 eiektor india july 1987 classified ads adi/ertisers index 8085 MICROPROCESSOR TRAINER built in EPROM programmer, power supply. 2K CMOS/RAM with dry cell back up expandable to 8 K, 12 K user EPROM installed Rs. 2975/- All inclusive. EPROM Eraser Rs 500/- Contact NEW AGE ELECTRONICS. Third Floor. Laxmi Mahal, Near Vandana Cinema, Agra Road, Thane - 400 602 KITS — Radio remote control call bell Rs. 150/-, Radio remote control music light Rs. 1 50/-. Ask projects list with 60 paise stsmps. SUPER ELECTRONICS, Shivaji nagar, Barsi-41341 1 Water level indicatbr with alarm' 1 ) With feather touch control system for Rs. 180/-, 2) Automatic Controller with probe Rs. 600/-. 3) Telephone amp Rs. 300/-. (Send 50% advance for V.P.P.) Dealers Solicited Contact: MINI MAX ELECTRONICS Alto-Porvorim Bardez Goa-403 521 CORRECTIONS Computerscope Nov 1986 P. 11-18 The following amendments apply to the circuit diagram in Fig. 2: Ri7=10K; Rjs=2K2; Cis=10p. High power AF amplifier July 1986 P. 7-18 The parts list should be modified to read: Cu=100n. ABC ELECTRONIC 7 14 ACE COMPONENTS 7.62 ADVANCE VIDEO LAB 7.66 ADVANI OERLIKON 7.06 APEX ELECTORNICS 7.63 BHARAT BIJLEE 7.63 CENTURY PERIPHERALS 7.55 CHAMPION ELECTRONICS 7.17 CHIP CHIP 7.71 COMTECH 7.10 CYCLO COMPUTERS 7.14 DEVICE ELECTRONICS 7.15 DONAU ELECTRONS 7.64 DYNATRON ELECTRONICS 7.66 ECONOMY ELECTRONICS 7.66 ELCOT 7 08 ELECTRONICA SALES 7.14 EXCEL 7.66 G.S. ELECTRONICS 7.64 HITECH 7.58 IEAP 7.12 INDIAN ENGINEERING 7.65 INDUSTRIAL RADIO HOUSE 7.65 ION ELECTRICALS 7,58 JR. COMPURTER KIT 7.68 KLAS ELECTRONICS 7.64 LEADER ELECTRONICS 7.62 LOGIC PROBE 7.64 MECO INSTRUMENTS 7.59 MELTRON 7.57 MURUGAPPA ELECTRONICS 713 NCS ELECTRONICS 7 63 PAREKH MARKETING 7.18 PECTRON 7.68 PHILIPS INDIA 7.11 PIONEER ELECTRONICS 7.16 PRECIOUS BOOKS 7.60 PRECIOUS KITS 7.03 PROFESSIONAL ELECTRONICS 7.68 ROCHER ELECTRONICS 7.10 SAINI ELECTRONICS 7.18 SELPAGES 7.16 SEMICONDUCTOR COMPLEX 7.04 SIEMENS 7.09 SMJ ELECTRONICS 7.02 SOLDRON 7.65 TESTICA 7 12 TEXONIC INSTRUMENTS 7.59 TRIMURTI ELECTRONICS 7.16 UNLIMITED ELECTRONICS 7.59 VASAVI ELECTRONICS 7.18 VISHA ELECTRONICS 7.75 7.72 elektor mdia july 1987 Elektor Electronics Datasheet-33 Transistors Types BUX80 & BUX81 The collector of these transistors is connected to the case. Thermal resistance. Re (junction to case): 1.1 K/W Turn-on time, ton: <0.5 \i s (typ 0.35 ^s) Turn off time, toff: <3.5 ^ s (typ 2.5 ps) Fall time, tf: typ 0.3 ps All times measured with Icion) - 5 A; iBiom 1 A. iBioffj - 2 A. Dimensions in mm Subscription to elekt©? is accepted from the current issue INDIA: 1 Year Rs.75/- 2 Year Rs.140/- 3 Years Rs.200/- OVERSEAS: 1 Year ONLY BY AIRMAIL Rs. 350/- ( SOUTHEAST & SOUTWEST ASIA OWIY) Enter details on both sides of this form N EW/ R|NEWAL II PER|0D YR/S II RS CHEQUE/D D /M O No DATE Add. Rs.S/- for outstation cheques Payments to: Elektor Electronics Pvt. Ltd., Chhotam Building 52C, Proctor Road Grant Road (E), Bombay-400 007 elektor ind.a july 1987 7.73 Elektor Electronics lnfosheet-502 Semiconductor manufacturers and their UK distributors Manufacturer: ADVANCE MICRO DEVICES Manufacturer: AMERICAN»MICROS (AMI) IAMDI Distributors Telephone Distributors Telephone Active Electronics (0494 ) 441129 Active Electronics (0494) 441129 Aviquipo of Britain (06281 34555 Aviquipo of Britain (06281 34555 Consort Electronics (0252) 871717 Consort Electronics (02521 871717 Merlin Electronics (0622 ) 678888 Hawke Electronics 01 979 7799 Polar Electronics (0525) 377093 Merlin Electronics (06221 678888 Regisbrook (0734) 665955 Micromark Electronics (06281 72631 VSI Electronics (0279) 35477 Polar Electronics (05251 377093 Solid State Scientific 01-748 3143 Manufacturer ANALOG DEVICES Thame Components 084 421 4561 Distributors Telephone Active Electronics 10494 ) 441129 Aviquipo of Britain (06281 34555 Merlin Electronics (06221 678888 Polar Electronics (05251 377093 Elektor Electronics Transistors Datasheet-33 | Types BUX80 & BUX81 Type Characteristics Limits The BUX80 b BUX81 are n-p n transistors for fast switching and motor control Collector cut off current, ICES < 1 mA (UCES - max.UBF 0 V) Collector emitter saturation voltage. UCE(sat) (IB 1 A; lc 5 A) S 1.5 V (IB 2.5 A; lc 8 A) <3.0 V Base emitter saturation voltage. UCEisati (IB = 1 A. lc = 5 A) 4 v llB 2.5 A. lc 8 A) < 1.8 V DC current gain, hFE typ 30 Current gain bandwidth product. fT typ 6 MHz BUX80 BUX81 UCEO 400 V 450 V UCER 500 V 500 V UCES 800 V * 1000 V 4 1C 10 A 10 A ICM 15 A 15 A IB 4 A 4 A IBM 6 A 6 A Pe 100 W * 4 100 W 4 * h 150°C 150 °C with Rbe 50ft ' t«-a ir value B E shorted * up to Tc 40 n C Data are valid only for conditions stated R N No 39881/83 Allowed to Post without prepayment LIC No 91 MH BY WEST -228 LIC No 9 1 NEW ■ ■ — Includes information on: • Home work -Table. • Hardware & Components • Checklists • Soldering • Component data & codes Please send amount by MJv.DJY.OJ only to: eIektor ElECTROINiCS PVT lid. 59-C Proctor Road Grant Road (E) Bombay • 400 007 Phones: 3674591/369478 Telex No. (01 1 ) 76661 ELEK IN Send a 3 year Subscription for elektor India masazine and get this book free. Existing subscribers can order this book @ 30% discount. Please mention Subscription number (or send latest address label from magazine envelope) This offer is valid to payments received from 9.06.87 to 30.09.87 Damle Printer &: Publisher - C.R. Chandarana, 2, Koumari, 14th A Road, Khar. Bombay 400 052. Printed at Trupti Offset, 103 Yasan Udyog Bhavan, Tulsi Pipe Road. Lower Parel, Bombay 400 01 3.