You couldn’t ask for anything more complete! SCR 2065 is the only multi-featured ampli deck in India with Dolby® NR. A top seller for so many reasons Only Sonodyne audio engineering is advanced enough to design a stereo cassette tape recorder incorporating Dolby NR - a noise reduction system that completely eliminates hiss - and a host of wonder-working features as well. There's the Tape Selector Switch for instance. Letting loose electrifying sound from your normal, chrome or metal tape. While the Noise Filter Switch filters outtape hiss, scratches and high frequency noises. The soft touch, heavy duty tape mechanism with cue and review lets you indulge in the magic of music day after day, year after year. You can also connect the SCR 2065 to external inputs such as a record player, a tuner or an external tape deck. Even direct recording is a cinch. Just depress the Recording Switch. The LED VU-meters instantaneously display tape signal levels during recording and playback. Allowing you to precision hone recording levels to capture sound as live as the original. Sound which is precisely reproduced by speakers protected by a hybrid power module with built-in short circuit and overload protection. A complete stereo system with upgraded SX 505 speakers Put together, these exceptional features make the SCR 2065 a complete stereo system : stereo cassette tape recorder with a built-in 80 watt amplifier and matching SX 505 speakers. All in one compact, power packed assembly at an affordable price. Proof that you don't have to compromise on quality for economy. ® Dolby is the registered trademark of Dolby Laboratories Licensing Corporation SONODYNE SCR 2065 Music for your ears, eyes and... wallet! SCR 2065 stereo cassette recorder with matching SX 505 speaker system. Dattaram-SE 68G/80 Publisher: C.R. Chandarana Editor: Surendra Iyer Editorial Assistance: Ashok Dongre General Manager: J Dhas Advertising: B 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 Tecnicas Ltda Av Ipiranga 1100, 9° andar CEP 01040 Sao Paulo - Brazil Editor: Juliano Barsali Elektor sari Route Nationale; Le Seau; B P. 53 59270 Bailleul - France Editors: D R S Meyer; G C P Raedersdorf Elektor Verlag GmbH Susterfeld Strafte 25 100 Aachen West Germany Editor: E J A Krempelsauer Elektor EPE Karaiskaki 14 16673 Voula — Athens Greece Editor E Xanthoulis blektuur B V. Peter Treckpoelstraat 2 4 6191 VK Beek - the Netherlands Editor PEL Kersemakers Ferreira B Bento Lda. R D Estefama, 32-1° 1000 Lisboa Portugal Editor: Jorge Goncalves Ingelek S.A Av Alfonso XIII, 141 Madrid 16 Spain Editor: A M Ferrer In part: Kedhorn Holdings PTY Ltd Cnr c ox Valley Road & Kiogle Street Wahroonga NSW 2076 Australia Editor: Roger Harrison Electronic Press AB Box 63 182 11 Da ideryd - Sweden Editor: Bill Cedrum The Circuits are for domestic use only The submission of designs of articles of Elektor India implies permission to the publishers to alter and translate the text and designand 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 articles published m Elektor India are 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 Printed At: Trupti Offset Bombay 400 01 3 Ph 4923261.4921354 Copyright c 1986 Elektuur B.V. The Netherlands Volume-5 Number 1 January 1987 J u Communications security 1.24 New rival to the world's fastest computers 1 .42 Atlas. Minerva, Carmlnat 1 -49 Noise at high frequencies 1-57 (an important factor) Projects Digital-to-analogue converter for I/O bus : 1 21 Electronic balance 1.26 True-RMS meter 1.30 Analogue wattmeter 1.39 Top-of-the-range preamplifier-2 1.44 Temperature proble for DMM 1-51 MW receiver 1.53 Information News and views 1.17 New products 1.64 Licences & letters of intent 1.70 Year Index-1 986 1.80 Corrections 1.82 Guide-lines Switchboard 1 T5 Classified ads 1.82 Index of advertisers 1 -82 Selex-9 Dimmers 1.58 Field strength 1 .59 Measuring range extension 1.61 Continuity tester 1.62 elektor mdia January 1987 1-03 V/ AS AVI DIGITAL METER NS RANGE BOTH FOR VALUE S TAN DELTA for details write to: VASAVI ELECTRONICS 630, Alkarim Trade Centre Ranigunj (opposite to Bus Stand) SECUNDERABAD-500 003. ph: 70995 gms: VELSCOPE Telex: 0 1 55-6834 Hirktor india January 1987 1 -05 9188/rilBO PHILIPS ^0 Philips PM 2518. It’s got more aces up its sleeve than any other multimeter Extremely sturdy and reliable, it’s the ideal choice for manufacturing and servicing workshops, and quality control and R&D labs. Furthermore, the PM 2518 comes fully backed by the nationwide service network of Philips. An assurance of prompt service anytime, anywhere in India. For further information contact Philips India Industrial & Electro-Acoustics Systems Division Calcutta: 7. Justice Chandra Madhab Road, Calcutta 700 020. New Delhi: 68. Shivaji Marg, New Delhi 1 10 015. Bombay: Band Box House. 254-D, A.B. Road. Worli, Bombay 400 025. Madras: No. 3 Haddows Road, Madras 600 006. Bangalore: 73/1 , St. Mark's Road, Bangalore 560 001 technology. Philips PM 251 8 starts where the others stop. Compact and portable, this new digital meter has all the basic features and performance you’d expect from no-compromise test-bench meters. And more. □ Annunciation of units, parameters, measurement mode on LCD. □ Temperature measurements with special probe □ Guaranteed safety and reliability □ Meets IEC specifications □ Uses two batteries - low power consumption Fully developed at the totally integrated modern professional electronics factory in India, the PM 2518 incorporates all the advantages of Philips’ advanced Philips -the trusted Indian household name for over fifty years olcfctor india January >987 1-07 SC SOCKETS. HIGHLY RELIABLE— —CONSISTENT SUPPLY AT AFFORDABLE PRICES I Socket all your Id’s with CHAMPION 1C Sockets and MULTIPLY* your PROFITS ! ! Flats of Spnng Contacts ore Oriented to Flats of 1C Leods. Dual Leaf Spring Contacts. Phosphor bronz or beryllium copper contact material - for total cost vs. performance capability. Dutiable end-to-end and side-to-side on 2,54 mounting grid. Kapton 1M solder wickmg barrier - meets Class 1 requirements of EIA standard RS-486. Kapton barrier also prevents 1C leads from shorting to PC traces beneath socket. Kopton IM 40 r«gql*r«d l»odr«Oi* O* 0 Dual inverted leaf face- wipe contacts - for reli- able connections and easy insertion/extraction of IG Anti -moisture bosses - 'to assist flux removal after soldering. Black glass-reinforced polyster body meets UL 94 V-O requirements for flame retardoncy. Low profile — 3,94 mox. overall height. \ Ladder frame body con- struction - for improved oirflow around 1C and Tin Plating or visibility of circuit traces Gold plating on pcB. for total cost vs. performance capability. * For details write to us CORP USA elektor india January 1987 1-11 The Motwane 3 V? Digit: L R-204 and 205. developed in our inhouse RSD Laboratory are Exceptional instruments. To begin with, they're a digital series enjoying their inherent advantages at analog prices Cost/ performance bargains in Micro-ohmmeters. because of their excellent accuracy, high reliability and effortless operation ( The L R senes read in 6 ranges each The LR- 204 from 20 milliohms to 2000 onms Cresolution 1 0 micro-ohms) TheLR-205 from as low as 2 milliohms to 200 ohms (resolution 1 micro-ohm). Here is the combination of features that make these micro-ohmmeters uncommon. ■ Special circuit to negate those errors caused by pick-up m inductive components —automatically increasing versatility too. ■ Pulse mode operation that conveniently holds readings and avoids the usual errors resulting fromheatmgof chemternalcircuit/ samples under measurement ■ B C.D. output for systems capability ■ Sleek plastic casing that provides maximum protection and longer lasting good looks, with reduced size and weight. ■ Quality that's exclusive, at a price that's not. A system can be built around these instru- ments with the following optional accessories: ■ A Digital limit comparator for quick go-no-go checks. ■ A D.gital printer for hard copy. ■ A simple quick mate jig for speedy Q.C. tests. When buying a Micro-ohmmeter you really have just 2 options. And they are both great! For further details write to THE MOTWANE MANUFACTURING COMPANY iJsvru/AkJC PVT LTD., at Gyan Baug. Nasik MUlWAWt 422101 Tel 86297/96084 Telex: 752 247 MMPL IN Grams: MOTWANE or Gyan Ghar. Plot 434 A, 14th Road. Khar. Bombay 400 052. Grams: MOTESTEM P'**;*se t>nr>ci literature end Quotation on your LR Series Name _ _ . . . . Designation Company Address . _ Telephone Telex SELL ADS.MMC 1 2.84 ek-ktor india January 1987 1 -1 3 Get your international conference going without winding yourself up. Just contact Air-India’s Congresses & Conventions cell. They’ll offer you all their advice— absolutely free! They’ll work with you right from inception by helping you promote your conference. Advising you how to bid for India as your conference venue. Liaising with your delegates. And transporting them to India on a wide range of low, low group and individual fares. Of course, they’re backed by Air-India’s worldwide network of 145 offices. So that your conference gets all the publicity and promotion it needs. And by Delhi’s superb conference venues. Like the Talkatora Stadium or the Indira Gandhi Stadium. Or, the many new hotels in Delhi, most of which offer excellent conference facilities. Or even the ultra-modem Sher-i-Kashmir International Conference Centre at Srinagar. Attached to the superb 5-star Centaur Lake View Hotel next to Dal Lake. Naturally, with such services, it’s no surprise that Air-India has been closely involved with the 12th International Leprosy Congress, the World Energy Conference, the World Mining Congress and many more. The next time you want to host an international conference, don’t wind yourself tense trying to organise one. Get some help from the professionals in the field. Air-India Congresses & Conventions 6th Floor, ‘Vandhana’ 1 1 , Tolstoy Marg NEW DELHI-110 001 Tel: 3311225 Cable: AIRINDIA You host it. We’ll help promote it. Member International Congress & Convention Association s elefclo* India Januafy 1987 1-15 challenge: That's the name of the game To pit your sirengtns against almost impossible odds, and come out a winner.To work together with a client as a team, and find the right answers that benefit both. Build a lasting relationship, step by step Larsen SToubro, Calcutta required a custombuilt temperature scanner for their NALCO project. On an analysis of their problem, our temperature scanner was modified and a suitable scanner developed Another breakthrough was the Rectifier designed for Electrophoretic Painting. This rectifier is the first of its kind in India. Similar rectifiers have been installed by us at Bajaj Auto, Pune and Wheels India, Madras. OSt®® ADVANI-OERLIKON LIMITED Where Specialists Interact We were l called upon to design a I special DC Motor for F the battery operated 'locomotives of Hindustan Construction Company. The DC motor was such a success that as many as ten motors have now been supplied to them These arejust three of the several customer-specific solutions from a Company committed to innovation and excellence. Each system is designed with the same dedication and expertise that has made Advani- Oerlikon a name to reckon with in a host of other industries. So, if you're looking for customer- specific, hi-precision electronics instrumentation, contact the Specialists. Multimedia Aquarius/AO/29/86 January 1987 1 -1 9 india D/A CONVERTER FOR I/O BUS To further complete the range of plug-in I/O bus extensions, here is a programmable analogue output board. Those many owners of a C64, Cl 28, or MSX micro equipped with the I/O bus board will, no doubt, appreciate the flexibility of the present extension, which is based upon the use of a readily obtainable D/A converter chip. The C64 I/O bus, along with an as- sociated digitizer board, was in- troduced in the June 1985 issue of Elektor India. ' while an 8-bit I/O port appeared in the December 1985 issue. How the universal I/O bus is to be modified to suit operation with the MSX series of computers is detailed in the Elektor India, February 1986. The present D/A converter features 8-bit resolution, buffered outputs, and a presettable output voltage j span. It is, we believe, an extremely | j simple to build module which will J enable programmers to put their I computer into contact with the real j (analogue) world. An 3-bit D/A converter chip \ The proposed D/A board is based ; upon the use of the Type ZN428 8-bit digital-to-analogue converter (DAC), whose internal configuration is shown in Fig. 1. A data latch loads the byte to be con- verted at the high-to-low transition of the latch pulse applied to the ENABLE input of the chip. The data will remain in the latch until a new byte is strobed into the device. Each bit in the latch controls an as- sociated electronic switch, Si-Ss, connected to an R-2R resistor ladder network, which is fed from a stable reference voltage, Uref (see Fig. 2). Depending on the magnitude (bit- configuration) of the latched byte, the switch poles of St-Ss are either at digital ground potential, or at Uref. Writing 255io to the DAC latch, therefore, produces Uref at the analogue output, since 255io= FFhex= 1111 1111 (all switch poles at Uref). Writing 0255 THEN X2 255 350 POKE B,X2 360 REM 400 REM 4=4=4:4:4=4:*4:4=4= DISPLAY VALUE 4=*4:*4:4:4:4:4:4:4: 410 REM 420 PRINT PRINT" VOLTAGE " VO: VOLT":PRINT:PRINT 430 FOR I - 1 TO 1000:NEXT I 440 REM 500 REM 4=4=4:4:4=4:4:4:4:4: LOOP *4=4=4:4=4:4:*4:4:4=4=4:4:4:4:4: 510 REM 520 GOTO 150 530 REM 1000 B 57632:RETURN 1010 B 57636:RETURN 1020 B - 57640:RETURN 1030 B 57644:RETURN 2000 END Fig 4. Track- layout and com- ponent mounting plan of the I/O bus DAC board By virtue of its simple address decoder, the board may be plugged into any slot on the I/O bus-board. Parts list (Note: parts are coded to BS 1852; see Infocard 500) Resistors: (tolerance is ±5% unless otherwise stated) Ri = 390R R 2 ...R 5 incl. = 1K0 ’ R 6 ;R9 ;Rio 10K R/.Rs 47K Pi P 4 incl. 10K multiturn preset * Ps 10K multiturn preset Capacitors: Ci 1fi0; 16 V tantalum C 2 = lOp; 16 V tantalum Semiconductors: Di;Di = 1N4148 ICi - ZN428 (Ferranti) IC 2 - 74HC(T)10 or 74LS10 IC 3 .IC 4 = LF356 Miscellaneous: S 1 . . .S 4 incl. = 4 way DIL switch Ki = 21-way angled busconnector to DIN41617 PCB Type 86312 (see Readers Services) 3 off soldering pins * See text for dimensioning details. Table 1. Simple BASIC program to verify the cor- rect operation of the 8-bit DAC board Observe the I O map ad- dresses at lines 1000-1030. and. if necessary, modify these to suit your com- puter s I/O ad- dress configur- ation. •Moor imMa January ' 987 1 -23 COMMUNICATIONS SECURITY The problem of unauthor- ized access to information in transit is as old as mankind itself. Each ad- vance In the means of transferring information has tended to be ac- companied by more soph- isticated possibilities for compromising that infor- mation. Thus, in 1986, despite the millions of possible frequency hopping sequences it may possess, the integrity of a modern military radio which falls into enemy hands is assumed to be no more than a few hours. However, there has been a fundamental change in one aspect of this sector in recent years. Tradition- ally, interest in secure communications was con- fined to the military and diplomatic communities. Today, because of the in- creased dependence on the continual exchange of information— be it techni- cal, financial, or per- sonal— the problem ap- plies equally to industry, commerce, and public administration. Consequently, an industry dedicated to interfering with communication ter- minals of all sorts has evolved. Products avail- able range from local and remote telephone bugs, through microtrans- mitters on terminal keyboards, to systems that can reconstruct conver- sations from electromag- netic emissions from ter- minals. Illicit access to information takes many forms, from the accidental interception of a conversation (as in the case of a crossed tele- phone line), to the planned electromagnetic attack on a specific com- munication system known to carry data of a sensi- tive nature. Disguising messages In the 20th century, the consequences of com- promising privileged infor- mation vary from personal embarrassment to con- siderable pecuniary loss. Illicit access to personal information— for example, credit rating— can have serious cumulative effects for the individual con- cerned. Unauthorized ac- cess to other information— 1-24 oloktor mdka January 1987 perhaps that relating to impending changes on the stock exchange, pro- prietary processes, or movement of high value cargoes— can result in ob- vious financial loss. Malicious modification of information in transit can also have dramatic results. The science of avoiding such consequences can be divided into two parts— the protection of the media and the de- fence of the message. In practice, the com- prehensive protection of modern communications media is not a practical proposition. Metal com- munication cables, to an extent, act as radiating antennas and the con- fidentiality of traffic can be jeopardised by the use of suitable listening equip- The Plessey Crypto Voicelok 100 secure tele- phone provides complete security for the executive who has to discuss sensi- tive matters on the tele- phone. I ment. The most vulnerable types are the overhead open wire links that are common in some parts of the world. Screened and shielded cables, particu- larly if buried, are a more difficult proposition for the would-be eavesdropper, but physical access to the cable makes interception relatively straightforward. Fibre optic cable, which carries photon instead of j electrical energy, does I not act as a radiating ! aerial. Attempts to tap into fibre should shut the whole link down, although it is believed that con- siderable sums of money j are being invested in systems to surmount this impediment to eavesdrop- ping Radio signals can also be compromised by sensitive receiving systems. As a generalization, the more directional and pre- cise a transmission, the more difficult is the pro- cess of compromising it. Tropospheric scatter and | meteor burst communi- cations score highly for some specialized traffic types. These interception risks have focused increasing attention to disguising the content of messages. ; Voice scrambling involves the partitioning, rear- rangement, and permu- tation of the signal, with the reverse processes be- ing applied at the receiv- ■ ing end. An interesting development in this sector is the FX204 scrambler | from Consumer Microcir- i cuits ", a new monolithic ! implementation for radio application including cellular and cordless telephones. Digital vs analogue I In essence, the FX204 is a two-band frequency inver- sion device that uses switched capacitor filters to split the voice spectrum into high and low fre- quency bands, and bal- anced modulators to invert each frequency i band about its own centre | frequency. The split point frequency is externally programmable , to 32 different points in the range 300 to 3000 Hz and makes the FX204 suitable for both fixed program- mable and roiling code speech scramblers. All filter cut-off frequencies | and inversion carriers are derived from a single reference crystal oscil- lator and facilities are pro- , vided to input and output synchronization tones where required. Con- structed in a 5 V single supply, complementary metal-oxide semiconduc- tor (CMOS) process and available in dual-in-line (DIL) and surface-mounted 24-pin packages, the FX204 is suitable for use in fixed or portable equip- ment. Encryption schemes, which are usually digital, are applied to both voice ! and data signals. They operate by reducing the signal to a bit stream which is then permutated and transposed on a bit- by-bit basis according to the dictates of a key which is applied at the re- ceiving end. A comparison of ana- logue and digital systems reveals that the former provide a more natural voice quality and allow speaker recognition. Digital systems, by syn- thesizing the original signal, are not as com- j petent in this area. In terms of traffic security, it is recognized that digital systems in general operate at higher levels, although some analogue arrange- ments are comparable. Some digital systems re- quire data compression and so are more expens- ive for voice than analogue systems which can transmit over conven- tional speech channels without modification. Analogue signals become | dirtier than digital ones during the course of am- '• plification on long dis- ; tance metal carriers, i A critical difference be- I tween the two lies in the I likelihood that an ana- logue system will be vul- nerable to the engineer and the cryptoanalyst, the sophistication of their equipment, and the com- plexity of the original scrambling technique. Digital systems are more readily dealt with by com- puter facilities; here the concerns are the key algorithm and the signal. Protection standards Advances in technology have made it possible to build complex and sophis- ticated encryption equip- ment for use over the public switched telephone network. Plessey Crypto 21 , for example, has recently introduced the Voicelok 100 secure telephone. Voicelok, which uses a patented, essentially analogue time division technique, has 10 12 poss- ible key settings. It is de- signed for high-level security over telephone networks and is available in either multi-frequency or loop-disconnect signal- ling versions. All encryp- tion circuits are contained on a single module within the telephone Based on the Plessey PBT 100 series, Voicelok has two oper- ating modes— clear and secure. In the clear mode the instrument is a stan- dard duplex telephone link. Switching to secure mode by an illuminated push button initiates a 16 bit key, pseudo randomly generated, and trans- mitted at each trans- mission path reversal. This involves a transmission delay of typically 600 ms. Plessey has also devel- oped Faxlok, a system using similar technology, for facsimile transmission. Widely used inter- nationally is the Data Encryption Standard (DES) developed in the United States of America by IBM. DES uses keys that are periodically changed, either physically or elec- tronically. Due to the American government's restrictions on the export of high technology, there have been periodic short- ages of encryption de- vices embodying the DES algorithm. It has also been reported that the American National Secur- ity Agency (NSA) does not intend to recertify DES when it is reviewed in 1988. These developments have led organizations through- out the world to develop alternative encryption standards. A new encryp- tion chip, developed by British Telecom 31 and called B-crypt, is a device that embodies such a standard. BT says that in some respects its B-crypt devices are superior to DES devices. In particular, data sent over telephone lines contain a lot of repetitive elements such as data address messages or headers DES encrypts these in the same way as the main data, thereby giving clues to the cryp- toanalyst, while B-crypt encodes headers in a dif- ferent way. BT is also working on a telecommunications authorities cryptographic algorithm (TACA). de- signed to protect data sent over satellite circuits. (1) Consumer Microcircuits Ltd; Wheaton Road; In- dustrial Estate East; Witham; Essex CM8 3TD. (2) Plessey Crypto; Waver- tree Boulevard; Wavertree Technology Park, Liverpool; Merseyside L7 9PE. (3) British Telecom Centre; 81 Newgate Street: London, EC1A 7AJ. rrleklor trWta January 1 987 1 -25 by R Ochs ELECTRONIC This accurately operating balance, which is entirety composed of electronic parts, features a 3 Z 2 digit read-out, a tare offset facility, and a weighing capacity of 500 grammes. Based upon the use of a common bass loudspeaker as the weight sensor, this novel household utensil is readily built and extremely useful for a variety of hobby applications, and, of course, for cooking! Like most types of electronic balance, the proposed low-cost ver- sion is based on the underlying prin- ciple of electromagnetic force compensation. Since the force on a conductor placed in a magnetic field is proportional to the coil current causing the field, the voice coil in a loudspeaker can be used as a force sensor, if weight is transferred direct onto the cone and thus onto the voice coil. After measuring the cone displacement, an electronic control circuit arranges for a current to be sent through the voice coil, causing the initial position of the cone to be shifted, i.e. it is pushed outwards. The current necessary to effect the counterbalancing cone displace- ment is directly proportional to the force applied to the voice coil. In the proposed design, the loudspeaker is 1 -26 elektor intiia January 1987 a fairly powerful type with a flexible cone suspension system that ensures adequate repeatability in the stated weight ranges of 0 to 200 and 200 to 500 g. Also, the loudspeaker should be capable of handling considerable dissipation, as its voice coil is fed with a direct, rather than an alter- nating (AF). voltage. The foregoing considerations regarding the re- quisite type of loudspeaker leave vir- tually no other choice than a rugged woofer with a power handling capability of some 100 W. The weight sensor Converting the loudspeaker into an accurate weight sensor is not too dif- ficult, provided the cone, membrane and voice coil are treated with care. A pre-heated knife may be used to loosen and remove the dust cover in the cone centre. Once you have gained access to the magnet and voice coil assembly, great care must be taken to prevent small metal parts or even dust from entering the air gap, since this will have a highly adverse effect on the linearity of the balance. Fig. 1 illustrates how to proceed with the construction. The light barrier is carefully glued onto the magnet, and its three wires to the control circuit are left long enough to allow for the maximum anticipated cone dis- placement, before they are fed through small holes in the cone glued into piace, and connected to a terminal strip fitted onto the loud- speaker chassis Fig. 3. Circuit diagram of the 7106-based digital readout. 5600 1 Parts list isee Fig. 41 Resistors: Ri = 560 Q R 2 = wire link Rj = 22 k R< = not required R$;R9. . Ri? incl. 100 k Re = 47 k R; = 1 M Re = 220 k P« = 2k5 preset Capacitors: C»;Cj = 100 n C* = 100p C« = 470 n C» = 220 n TEST Semiconductors: Di;D* = 4V7;0.4 W zenerdiode »Ci 7106 IC 2 = 4070 II 470 nl lOOn MKT MKT 4V7 400fnW Miscellaneous: LCD = 3% digit liquid crystal display; digit height 13.3 mm le.g. Hamlin Type 3901 or 3902 SE 6902) PCB Type 84012-2 (see Readers Services) Suitable sloping front cabinet adjusting the 7106 gain preset, Pi (see Figs. 3 and 4) for an LCD read- out that tallies with a few standard weights placed onto the platform. Alternatively, but with some loss in accuracy, a number of small weights may be made at home by wrapping sugar lumps into paper and having these weighed at a chemist's. TW should not normally be necessary if the loudspeaker is adequately damped by the enclosure lining. The adjustment screw (see Fig. 1) should be set to produce a slight up- ward cone displacement at power- on; the voice coil quiescent current should then lie between 10 mA and 50 mA. Both weight ranges are calibrated by Most likely, you will find that there is a tendency to oscillate at relatively low weights with Pi adjusted for a high P/I ratio, while increasing the integrated (I) portion promotes oscillation at relatively large weights. If attempts to stabilize the cone movement are unsuccessful, the system may have to be pre-loaded with a small weight; however, this Fig. 4. Track layout and com- ponent mounting plan of the LCD board in the electronic balance. Fit neither link A nor link B. dimensions pertain to Philips loudspeaker Type AD80602WB Fig. 1. Cross- sectional view of the balance enclosure- structure to prevent lilting ol weighing table man - made libre tube to transler weighing table movement direct onto voice coil man • made fibre disc 0 160 x 4 mm screwdriver slot speech coil suspension M3 nut secured with super ■ glue enclosure = epoxy resin 0 22 mm man - made libre disc to hold light barrier It should be borne in mind that the fi- nal accuracy of the balance depends very much on the damping of the loudspeaker: since the control cir- cuit is a proportional integration type (PI, this will be reverted to), the removal of fairly heavy weights from the platform may be counteracted rather slowly, causing forceful cone displacement and oscillation at very low frequencies. Therefore it is strongly suggested to fit the loud- speaker and associated control & supply circuits into an air-tight enclosure so as to improve upon damping, A wooden enclosure is perfectly adequate, both from a tech- nical and an aesthetical point of view. Circuit description The control circuit in the electronic balance is shown in Fig. 2. Light bar- rier IC-, functions as the sensor, since its output voltage is determined by the adjustment screw that interrupts the light beam from the internal LED as the cone sinks deeper due to the weight on the platform. The current-control loop is based upon the use of a PI (proportional in- tegration) circuit, composed of in- tegrator hi and adjustable amplifier As. The former provides a time- averaged output voltage, the latter a proportional output voltage deter- mined with feedback preset Pi. Both A2 and As are driven by input ampli- fier Ai, while P2 enables setting the amount of integrated or amplified signal (P/I ratio) fed to current amplifiers T 1 -T 2 . Potentiometers Pi and P 2 are set to positions where the control loop output signal is free from oscillation. As stated above, fit- ting the balance in a closed cabinet is the best way to go round this problem. Current sense resistor Ris drops a voltage in direct proportion to the current passed through the voice coil. In order to achieve a relatively low temperature-coefficient and hence optimum repeatability of measurements, R19 should be home- made from constantan wire. Differen- tial amplifier As has a gain of 20 dB. Note that R 13 is at +4.7 V relative to the supply ground to ensure correct DC interfacing to the display board. Resistor Rio should be mounted close to the ground connection of R19 so as to prevent erroneous readings owing to contact resistance in the voice coil circuit. The circuit around As is a sample- and-hold arrangement to enable switch-controlled tare subtraction. Pressing S 2 charges C; with the out- put voltage of Aj and at the same time forces a reset of the balance read-out. At power-on, Cs is discharged and the + input of As is therefore at the same potential as junction Ru-Ris, i.e. at +4.7 V with respect to ground, plus 80 mV voltage drop across Ris. The 80 mV drop serves to establish a quiescent output current of about 40 mA if the outputs of Ai and As are at equal potential. The exact amount of 1-28 elektor tndta January 1987 quiescent current can be set with the adjustment screw (see Fig. 1). The tare/reset button, S 2 , is simply pressed after determining the weight of the tray, jar, or any other ; container which is to hold the rel- evant substance for weighing. In a similar fashion, S 2 can be used to reset the display prior to adding a further ingredient to a mixture, ac- cording to the recipe to hand. There are. however, a few important points to observe in the use of the tare fa- * cility. The first concerns the total weight of the load on the platform: this should not exceed 500 g. Sec- ond. there is a specific time limit for pressing S 2 between tare weighings, as C 7 is slowly discharged by its in- ternal resistance and the load presented by An. In the 200 g range, tare weight is retained for about 30 seconds, in the 200-500 g range for a much longer time. At relatively low weights, therefore, readings should be taken rapidly for best accuracy. Switch Ss is used to select the previously mentioned weight ranges. Although the 0-200 g range is more accurate than the 200-500 g range, the former calls for S 2 to be pressed prior to any weighing. The pre-set quiescent current is likely to be slightly instable owing to tem- perature changes in the cabinet, caused by voice coil, current loop, and power supply dissipation, which has a negative effect on the sensi- tivity of the phototransistor. Selection of the higher weight range is accomplished by Ss taking the voltage from divider network R.6-Rir-Ria. At the same time, the decimal point on the LCD is switched to the appropriate position. The digital read-out for the proposed balance is based upon the use of PCB Type 84012-2, incorporated in the Capacitance Meter, published in the March 1984 issue of Elektor India. The circuit diagram is shown in Fig. 3. the component mounting pian in Fig. 4. Note that neither link A nor link B should be fitted on the board to suit operation with the balance control circuit. Also note that D -Dz-R. are in fact the parts shown to belong to the power supply (see Fig. 2); they are most con- veniently fitted onto the LCD board, of course. Functional details of the Type 7106 LCD display driver have been dis- cussed in LCD panel meter Elektor Electronics October 1981. In brief, and with reference to Fig. 3, Ri and Ci determine the internal oscillator frequency of about 45 kHz, which is used to derive the sample and measurement interval. Capacitor Ca functions as the auto-zero capaci- tance. which, correctly dimen- sioned, ensures a reading of 000 on the LCD with both chip inputs at 4.7 V. The maximum indication on the LCD is reached at an input voltage of 2Vref hi; therefore Pi determines the final sensitivity of the display board. The power supply for the proposed balance can source up to 1.5 A and requires adequate cooling. The stated value of Rj gives an output voltage of 14.0 V, which determines to a large extent the voice coil cur- rent at maximum weight, i.e. 500 g. Network Ri-Di-Dr serves to stabilize the LCD board supply voltage, and to create a virtual common rail at + 4.7 V above the circuit ground potential. The +9.5 V potential for sample-hold As is taken from point CDP on the LCD board. The voltage limit prevents the 7106 inputs from being driven in excess of their hand- ling capability. Setting up To begin with, the PI control loop should be adjusted. This may be a little tricky in view of the previously mentioned tendency to oscillation at low frequencies. Moreover, oscil- lation may occur with different weights on the platform. Checking for undesirable oscillation at low frequencies is best done by monitoring the output of Ai with a DC-coupled oscilloscope, while the weight is increased slowly by piling sugar lumps on the weighing table. Technical characteristics Weight ranges: 0 200 g and 200. 500 g. Maximum weight load: 500 g. Linearity: <1% of read out ±1 digit. Accuracy: <0.5% of full scale indication ± 1 digit ( - 0.1 g in 200 g range). Compensation for off centre placed weights: <2% of read out at weighing table diameter of 100 mm. Loudspeaker: 4 200 mm; 60 100 W. 8 ohm. Display: 3 digit, switched decimal point. Fig. 2. Circuit diagram of the balance control and supply sections. Parts list Isee Fig. 2 Resistors: Ri 560 Qr Rz;Rn = 100 Q Rs = 1 k R* - 470 Q Rs; Rs 56 k R? - 220 k R« = 150 k R 9 = 12 k Rio;Rii;R^ 10 k;1% Ri 2 ;Ru - 100 k; 1 % Ri« = 4k7 R 1 7 = 1 k; 1 % Ria 100 Q;l% Rn = 0Q22 * Pi = 100 k Pz = 10 k Capacitors: Ci=3300 M ;40 V C 2 ...C 4 incl. = 100 n Cs = 470 n C& - 680 n C? = 47 n Semiconductors: Di;D? 4V7;0.4 W ▼ Ti = BD135 Tz = 2N3055 ICi = LM324 ICz = CA3140 ICj = CNY36 IC* = LM317T Miscellaneous: $1 = SPST mains switch Sz = push to make button S 3 = miniature DPDT switch Fi =200 niA delayed action LS - bass loudspeaker (woofer): 8 Q; $ 200 mm; Pmin = 60 W (e.g, Philips Type AD80602W8) or Rencforce 60/100 W 8 Q>. B< bridge rectifier; 2 A min.; e.g. B40C2200 Tr - mains transformer 15 V; 2 A. ▼ On display board • See text We regret that no ready made PCB is available for this part of the circuit. elektor india January 1987 1-29 TRUE RMS MET! R Determining the RMS value of a voltage or current hitherto required at least a scope, a textbook of basic electronics, a pocket calculator, and, at times, sheer guesswork regarding the interpretation of resultant figures. This plight has prompted us to design a wideband AF RMS meter featuring technical characteristics to make it suitable for a wide variety of measuring applications. Technical characteristics: id Input ranges'. 20 mV; 0.2 V; 2 V; 20 V 1 40 dB; —20 dB; 0 dB; +20 dB). H Accuracy (U«i= ViUinimaxi): ±(1.5% + 1 digit) 0-100 kHz; ±5% 100-200 kHz. » Bandwidth (Urn - VSUkiimaxi): 300 kHz (-3 dB). ffl Span of variable 0 dB level : + 65 to -30 dB. a® Special features. switch selectable 0 dB reference; AC or DC coupled input (20 mV AC only); 3 digit LC display; optional LIN and LOG outputs to drive external in struments. In electronics literature, both at the hobby and the professional level, the synonyms effective, virtual, and root- mean-square are frequently used to qualify an alternating quantity such as voltage or current. Also compo- nent ratings, maximum permissible dissipation, AF and RF signal levels, to name but a few examples, are fre- quently stated as being rms values. For relatively low-frequency, pure, sinewaves, the rms amplitude can be read with ample accuracy from an analogue or digital AC voltmeter, since these instruments are gener- ally calibrated for the sine wave crest 1-30 elektor mdia January 1987 factor of 1 2. However determining the rms value of other periodical signals, such as ramp voltages, rec- tangular, or triangular waveforms, is not usually possible with the same AC voltmeter for lack of a calibration in accordance with the requisite crest factor, defined as the ratio of the peak value of a periodically varying quantity to the root-mean- square value. Without going into ; mathematical details, Table 1 sum- marizes terms and conversion for- : mulas for some of the most fre- quently encountered waveforms (see also Infocard 114). The proposed meter is based upon the rms-to-DC conversion principle and fulfills a variety of applications as it has been designed to accept many waveforms at wide frequency and in- put voltage ranges, ensuring a high mput impedance. The instrument combines the functions of true-RMS meter and dB (AF input voltage level) meter, offering instantaneous read- j ings on a liquid crystal display. As seen from the introductory photo- j graph to this article, the RMS meter adds to the Elektor range of measuring equipment housed in a standard Verobox enclosure. Ex- tremely straightforward to operate and fairly easy to construct, the latest addition to the series achieves a remarkable degree of precision at moderate cost. Block diagram Fig. 1 shows the functronal organiz- ation of the true-RMS meter. The AC or DC-coupled input voltage is fed to an amplifier/attenuator circuit, which ensures a maximum input level of 200 mV for the rms-to-DC converter. This means that the input | section functions as an amplifier in the 20 mV (AC only) and 200 mV position, the display unit accepts the ranges (A = 10 x and A = 1 x , respect- HI input voltage from a temperature ively), while it functions as an ampli- compensation circuit connected to fier in the 2 V and 20 V input ranges the converter's logarithmic output. (A = — lOx and A = -100x, respect- This compensation circuit is based ively). Selection of the relevant range upon the use of an amplifier whose is accomplished with an electronic gain is temperature-dependent and switch arrangement, which obviates whose output is applied to a voltage the drawbacks associated with long divider to achieve a 1 mV/dB gradient wires at relatively high impedance. with respect to ground. The rms-to-DC converter provides a Provision has been made to select linear as well as a logarithmic direct either a fixed or a variable (offset) output voltage. With Ss set to the V 0 dB threshold (0 dB = 0.775 V = position, the linear output voltage is 1 mW into 600 ohms, see also In- fed direct to the analogue-to-digital focard 501). The taking of linear rms converter comprised in the LCD readings is quite straightforward in read-out circuit. With Ss set to the dB that it merely involves selecting the Fig 1. Block diagram of the true-RMS voltmeter. elektor India January 1987 1 -31 Fig. 2. Internal organization of the Type AD636JH pre- cision RMSto-DC converter. appropriate attenuation or amplifi- cation factor of the input section, plus switching the decimal point on the LC display. There is a snag, how- ever. in the reading of dB levels. Assuming a meter input level of 0 dB (0.775 Vrms). the rms converter chip is fed with 77.5 mV (input attenuation is 10 times in the 2 V/0 dB range) and it can be adjusted to yield the cor- rect LCD reading. However should the meter be switched to its + 20 dB input range, the input voltage is at- tenuated 100 times, and the con- verter input voltage is, therefore, 7.75 mV, which would cause the dis- play to read 201og>o (7.75/77.5) = —20 dB, rather than still 0 dB. This er- ror is corrected by applying —20 mV to the LO input of the LC driver. A similar correction applies to the —20 dB and —40 dB ranges, in which case LO is driven with +20 mV and + 40 mV, respectively. An overfiow/underflow circuit pro- vides users of the meter with infor- mation as to the preferred range for use with a specific input voltage level. Should this exceed the maxi mum displayable value by about 14 dB, the LC display gives an overflow indication. Similarly, an in- put level of 30 dB below the set value is signalled with the underflow sign, prompting the user to switch to the next lower range for optimum accu- racy. However in the —40 dB range of the meter the underflow circuit is disabled to allow carrying out measurements at very low input levels. It should be borne in mind, however, that the meter's accuracy below some —70 dB falls rapidly, as this value approaches the minimum detectable level of the converter chip. Finally, a switch shifts the decimal point as required, while LED drivers arrange for the relevant unit indi- cation (mV. V. or dB) to light on the front panel. RMS-to-DC conversion In essence, there are two methods for converting an rms level to a pro- portional DC level, which can sub- sequently be used to drive a meter indication circuit, whether this be a digital or an analogue type. The first method is based on the use of a ther- mocouple device, which determines the rms value of measured current or voltage by means of the heating ef- fect in a strip or wire composed of two dissimilar metals joined to form a circuit producing an electromotive force. The second method involves 1-32 cl«ktor india January 1987 the use of semiconductor devices output voltage is available at chip which incorporate analogue pro- pin 10. cessing circuits for the calculation of External preset Pa provides the bias a corresponding direct output for the internal squarer/divider, and voltage or output current. hence can be used to effect cali- Figures 2a and 2b show what is in- bration of the AD363 at 0 dB input side the Type AD636JH rms-to-DC level, converter chip. It comprises an input rectifier plus voltage-to-current con- verter, a feedback-current con- trolled squarer circuit based upon CsOnVeFSiOH eTTOTS the use of logaritmic and anti-logar- ithmic amplifiers, which are used to It stands to reason that any type of output the logaritmic DC level. practical rms-to-DC converter in- The squared signal is averaged by evitably produces a small deviation means of a low-pass R-C network, of from the ideal conversion character- which the capacitor, Civ, is connec- istics. The main errors and their ted as an external part. The averaged possible cause will be discussed value is converted to a proportional briefly in the following points, direct current by means of a current- Static error Production tolerances mirror, which passes its output and deviations from the target through an on-chip, high-stability, specifications amount to an accept- 10K resistor. The proportional direct able level of 1 mV in the case of the Volt 1 VOLT rms INPUT l200mV rms INPUT 30mV rms INPUT lOmV rms INPUT ImV rms INPUT n r ' — I — r "1 n » IdB \ is, N \ l\ \ . \ 1] J i t LHz. stated converter chip. Bandwidth. There is, unfortunately, a limitation imposed upon the achiev- able bandwidth of the converter chip. Fig. 3 shows the correlation between input signal frequency and the chip output voltage. Note that the con- verter’s usable bandwidth is strongly dependent on the level of the ap- plied input voltage. It is, therefore, advisable to carry out measurements in the lowest possible meter range. DC error It is readily understood that Cav determines the lowest input signal frequency that produces a faithful direct output voltage; the capacitance of Cav therefore re- quires due consideration in de- signing with the AD6636JH. In the proposed meter, provision has been made to select 'one of two capacitors Cav to achieve an indication response as required by the specific input frequency. Crest factor As already stated in Table 1, the crest factor of a rec- tangular wave is inversely pro- portional to its duty factor. Fig. 4 shows the conversion error percent- age as a function of the crest factor. The cause for this error lies in the fact that, in the case of very low duty factors (needle pulses), Cav has the daunting task of instantaneously "catching" all the energy contained in the pulse, and retain its charge for the averaging process to be com- pleted. Obviously this is very diffi- cult to achieve in practice, whence the relatively small error, which, however, becomes the more mani- fest when added to the previously mentioned errors, especially when reading rms values of signals with a very high crest factor (i.e. low duty factor). A special difficulty may arise if a high crest factor signal causes the meter's input section, and hence the converter chip, to be overdriven, since the resulting waveform distor- tion (clipping) and the generation of harmonics readily leads to er- roneous display readings. It is, therefore, suggested to first measure the peak value of such signals using an oscilloscope, to decide on the correct input range of the true-rms meter. Circuit description Display unit (see Fig. 5). The LC display driver/A-to-D con- verter is a conventional design based on the Type 7106, whose oper- ational details have been covered in Electronic balance, elsewhere in this issue. Fig. 6 shows how circuit Fig. 3. Converter direct output voltage as a function of input signal frequency, with six rms in- put voltage levels as parameters. Fig. 4. Corre- lation between input signal crest factor and con- version error of the Type AD6363JH i inii.a January 1907 1 -33 teH- tSe>’- WO. a 10 1 R 111 R I ® rl IC2 R3 M ? T Tt 0-0 Q -t.Q-.U.U sQ 0°0 0 'io: 0 D O : MKT MKT ?rH-^ 2 I 05 W ° 3 .. 1 _ 06 c ~? K 04 Ml . N4 IC2 4070 < Q'jOwQuOuiQuai ° 1 SX t Fig. 5. Circuit diagram of the universal LC dis- play board. Please note that dotted compo- nents, including wire A or B, should not be used. Parts list (display boardl INote: parts indication is to BS 1852: see Infocard 5001 Resistors: (tolerance is ± 5% unless otherwise stated! Rb --- 820R R j = 22K R* = .1K5 Rsi&.-Rb. . .R 12 -IOOK Re = 47K0F Rb = not required Pi 2K5 multiturn preset Capacitors: Ci=330n Cz = lOOp ceramic Cs-560n MKT Ci - 470n MKT Cs = 220n MKT 1-34 elektor india January board 84012-2 is to be completed to make the LC display unit. Point C should be wired to ground, while the dotted components are not required. Converter board (see Fig. 7). With reference to circuit diagram Fig. 7, the input voltage enters the meter via a AC/DC selector. S 2 /C 1 . Next comes a three-resistor, fre- quency-compensated voltage div- ider, R1-R2-R3. Two pairs of FETs, T1-T2 and Ti-Tr, have been connec- ted to function as ultra-low leakage protective diodes on the 20 mV/ 200 mV and 2 V input lines. Low-noise opamp IC ■ is the 10 x amplifier for the 20 mV (AC only) range. With the range selector set to 2 V or 20 V, Ts takes the non- inverting input of the LF356 to ground so as to prevent noise or cross-talk from being amplified. Also Re: is de-activated to avoid the meter input impedance from falling to about 10 k (Rs). Selection of the relevant input voltage range is accomplished with a dual analogue multiplexer. De- pending on the binary code applied to its channel selection inputs, pins 9 and 10, each section of the IC passes the analogue voltage at the relevant input 0-3 to the chip output. The channel selection code is ob- tained from two-pole range selector Ssa-Seb. It is readily seen that the analogue multiplexer is in fact the semiconductor equivalent of a two- pole, four-way rotary switch. In this design, where signal levels are rela- tively low, conventional switch wir- ing would readily lead to noise being picked up by long cable runs connected to circuits with a high input or output impedance. It was, therefore, deemed practical to leave all signals "on board" and to ac- complish selection with an elec- tronic device ensuring low cross-talk and good reliability. Moreover, it simplifies the construction of the meter to a considerable extent. The upper section of the analogue multiplexer drives buffer IC3, which serves to provide matching of the high-impedance multiplexer output to the converter chip input, which is stated to have an impedance of about 6700 ohms. The lower section of the multiplexer provides selection of the correct compensation voltage ap- plied to the display driver's LO input during dB measurements. The re- quisite compensation voltage is de- rived from a tapped resistor ladder network at the four inputs of the lower section of IC2. Switch S3 selects between a fixed 0 dB level (77S mV rn\s ) and a user-defined level (offset) brought about by turning Pi. During linear rms measurements, the LO input of the display driver is taken to ground by T«; R24 functions to prevent IC2 from being damaged by the virtual short-circuit to ground brought about by the MOSFET. Operational amplifiers A2 and A3 form the overflow and underflow detector, respectively. Should the voltage at the output of Ai be higher than 140 mV (8 V/^/Rbb), A ; - toggles and drives the HI line with about 8 V, causing the overflow sign to appear on the LC display. Similar- ly, A3 signals underflow if the output of Ai drops below —300 mV. Diodes D 3 -D«-Ds constitute an OR gate to disable Aj from detecting underflow in the —40 dB range. Opamp A: has been included to enable the rms converter output to be temperature compensated. To this end, the feedback circuit of A- includes a negative temperature coefficient resistor (NTC), which is arranged to be in thermal contact with the converter chip enclosure. Voltage divider R22-R23 provides the previously mentioned 1 mV/dB gra- dient for the A-D converter con- tained in the LCD driver, ICi ir. Semiconductors: Di = not required D? = 3V3; 400 mW zenerdiode 04. . ,D« incl. = red LED (Dj & D/ not required) ICi = 7106 IC 2 = 4070 LCD = 3ft digit liquid crystal display; digit heigth 13.3 mm le.g. Hamlin Type 3901 or 3902 SE 6902). Miscellaneous: PCB Type 84012-2 Isee Readers Services) Fig. 6. Track layout and com- ponent mounting plan of the dis- play board Fig. 7. Circuit diagram of the mam converter board. SI OH-Off I (AC ONLY) olektof ind- 100k; 0.1% ▼ Ri;R 2 r;Rrr;Rio;Rii - 10K Rs = 1K0; 0.1% ▼ R. = 9K; 0.1% ▼ Rr = 100K R.-560K Rs = 33K Rio= 120K Ru;Ris = 330K Ru;Rn;Ru;Rrj= 1K0F Rie = 1K0 Rir = 10M Rta = 3K3 Ri»=1M0 Rm = 2K7 Rn = 6K8 Rrr = 9K09F Rrs;R2s = 68K R !6 ==1K2 Rzb;Rj2 = 2K2 Rs3 = NTC 500R; -5.9% FC; e.g. Milliard Type 2322 610 12501 ( + 10%) or Type 2322 610 11501 ( ±20%). (STC; (02791 26777) Pi = 100K linear potentiometer; multiturn. P!;Pj = 10OK multiturn preset Pi = 25K multiturn preset o«o 01100# Fig. 5. The meter has two optional outputs, one linear (ICe), and one logarithmic (full output of Ai). The former may be used to drive an analogue meter in order to observe the trend of the measured voltage; the latter is es- pecially useful for swept-frequency measurements, where an oscillo- scope can be used to display curves with amplitude readings given | direct in decibels. Resistors Rx. Ry and Ri (denotation ▲) may be fitted to enhance the meter's response to input fre- quencies in excess of about 100 kHz. Also, R 19 is changed to 220K. Refer- ring back to Fig. 3, it is seen that the converter chip sensitivity begins to fall appreciably at that frequency, when driven with an input signal of the order of 1-10 mV. Where this is considered problematic, IC 3 may be configured as shown to achieve an amplification factor of about ten (10K/2K2). This modification implies that the converter chip is driven with a higher input signal level so as to improve upon its response to rela- tively high signal frequencies. How- ever it should be borne in mind that it also implies overdriving the chip since it receives about 1 Vrmn rather 1-36 elektor nidia January 1987 than 200 mV™*, which is stated to be the level for optimum accuracy of conversion. The 2K2 resistor, Rz, at the LIN OUT line has been included to keep the display from reading a five times too high rms level. Finally, the decimal point selection with S6c, and the three-LED range in- dication, are circuits with a sim- plicity to obviate the need for any further detailing. Construction Constructors wishing to make their own PCB for this project are advised not to use the usual aerosol pc board lacquer, since this material may cause stray resistance in high-im- pedance circuit sections. The use of plastic or poly-urethane spray may be resorted to, but the best solution in all cases is to order the Type 86120 1 ready-made PCB from our Readers Services, since this has a protective film to ensure rapid soldering as well as extremely high electrical isolation i between tracks and ground plane. Fig. 8 shows the location of the various parts on the converter board. All parts are fitted in the normal man- ner; some, however, should have their leads soldered at both PCB sides to effect through-plating, j Capacitors Cn and C« are fitted at the track side. The NTC, Ru, should be fitted on top of the converter chip enclosure, using a small amount of heat conductive paste, and taking j due care to prevent short-circuits be- | tween NTC leads and the IC can. All resistors marked with an asterisk are high-stability, 0.1% tolerance types. Replacing these with more readily available 1% types is feasible at the cost of a corresponding loss of , I accuracy. i PCB holes remaining empty after fit- ting all parts should be through- plated with pieces of left-over com- ponent wire. Do not forget to fit Ry or i a wire jumper. ^ The display board is mounted onto the main converter board by means of four spacers whose length allows the face of the LC display to be level with the enclosure front panel. Use isolating washers or nylon screws and nuts to secure the boards in a sandwich construction. Prior to fit- j ting them onto the board, soldering pins should be cut to a length of 3 mm to preclude short circuits. In the usual manner, the fuseholder, | mains socket, and the linear and I logarithmic outlets are fitted onto the rear panel. The photograph on page 40 of this article further illustrates the construction of the meter. The studs in the lid of the Verobox enclosure should be removed to enable the unit to be closed properly, closed properly. The inside of the enclosure should be lined with aluminium foil to effect screening against stray inductive fields, which would otherwise cause erroneous readings. It is also poss- ible to spray the inside of the box with conductive lacquer. Whichever screening is used, do not forget to connect all surfaces to ground, and beware of short-circuits. In order to preclude earth loops from being made by the use of the mains earth line, this should not be connected to the circuit ground. Pro- J vided due care is taken in the iso- lation of terminals and wires at mains potential, no problems are expected to arise from the absence of an earth connection. P*;P* - 10K multiturn preset P? 5K multiturn preset Capacitors: CA = 33n; 200 V (not mounted on PCBI Ci = 6p8 ceramic Cz - 5p5 foil trimmer tgrey) Cz = 68p NP0 Cr = 40p foil trimmer (violet) Cs = 1n Cv.Cu . . Civ incl. - lOOn Cr = lpO; 25 V tantalum Cs - 4p7; 25 V tantalum Cio = 2 p2; 16 V tantalum Cn;Ci2 = 220p; 40 V Cu=22p; 16 V Semiconductors: Di... Dii incl. -1N4148 Diz...Dis incl. = 1 N4001 Tt. . .T» incl. =’BF2568 Ts = BS170 T?;T« BC557B ICi;ICz;ICi - LF356 ICj - 4052 B IC« = AD636JH I Electromail; (05361 204555) IC* LM324 ICr = 7808 IC* = 7908 Miscellaneous: Fi = 100 mA delayed action Si = DPOT mains switch Sz . . S* incl, - miniature SPOT switch Ss= miniature DPDT switch S* = 3 pole. 4 way rotary switch Tri = 2x12 V; 150 mA Rei = 15 V OIL reed relay Enclosure Verobox Type 75 0141 ID PCB type EPS 86210 (see Readers Servicesl From panel foil Type 86120-F (see Readers Services) Output sockets (LOG and LIN) if required ■ Available from Trafo- Lowe Elektronik, Postfach 2150. Issum 2, Sevelen, West Germany. Telephone: + 49 2835 5012/5013; Telex 08 12 261, ▼ Welwyn RC55 series 0.1%, 15 ppm; or Rhopoint Econistor/Miniohm series I10K; 9K; 100K; 1K0) 3 ppm Both series available from STC Electronic Services, (0279) 26777 (note: Welwyn series only 10+ I). India January 1987 1 *37 ELEKTOR POWER 0 dB LEVEL TRUE RMS METER Fig. 9 Front panel foil for the true-RMS-meter 86120-9 Setting up ICs and set Ss for a display reading of 0 dB. Next, select the +20 dB range (20 V) and set Pj for a display reading of 20.0. Verify that the meter reads —20.0 when set to the —20 dB (0.2 V) range; if necessary, correct the indi- cated value by means of adjusting Pj . Finally, apply a direct voltage of 77.5 mV to the meter input, select the 0 dB range (2 V), and adjust P? for an LCD indication of —20 dB. The input attenuator is preferably aligned using an oscilloscope and a generator capable of supplying a rectangular wave of 1 kHz at 1 V« and 10 Vn. Apply the 1 Vn square wave to the meter input and connect the scope to pin 6 of ICi . Set Ss to the 2 V range, and S 2 to DC. Carefully ad- just trimmer C 2 for optimum edge steepness of the displayed rec- tangular signal; there should be no undershoot or overshoot on the leading or trailing edges. Increase the generator output voltage to 10 Vn and select the 20 V meter range; peak Cl like C 2 . Redo the trimmer adjustments until both meter ranges offer a satisfactory pulse response. In the absence of an oscilloscope, the input attenuator may be aligned using a sine wave oscillator whose output voltage is known to be ac- curate. Set the generator to produce a 10 kHz, 1 Vrms sine wave, and con- nect its output to the meter input. Sel- ect meter range 2 V, DC, and adjust C 2 for a display reading of 1.000 V. Select meter range 20 V, DC, and in- crease the generator output voltage to 10 Vrms. Adjust Cl for a display reading of 10.00 V. Switch between the two ranges and each time care- fully adjust the relevant trimmer until the meter reads the correct rms value of the applied voltage. Fi- nally, the attenuator alignment may checked by varying the generator output frequency to see whether the display indication remains in accord- ance with the set sine wave ampli- tude. Before embarking on the setting up of the instrument, it is suggested to leave it switched on for about 20 minutes so as to ensure sufficient thermal stability. To begin with, the linear (V) func- tions are adjusted as follows. Short- circuit the meter input, set S 2 to DC, and set S6 to the 200 mV range. Adjust Pl for 0 mV with respect to ground, measuring at the output of ICi . Next, adjust Pe for a display reading of 00.0. Apply a direct voltage of 150 mV to the meter input and turn P on the display board for a display indication of 150.0. Proceed with the dB functions of the meter by first setting Ss to the dB pos- ition; S2 is left in the DC position, and Ss is set to the 2 V (0 dB) range. Select the fixed 0 dB level with S3. Apply a direct voltage of 77.5. mV to pin 3 of elektor india January 1987 by C Giorden ANALOGUE WATTMETER This simple meter is primarily intended to establish how much power a mains load consumes and thus how much it adds to the electricity bill. We all know that the power con- sumption of electric appliances is generally stated in watts, and that the cost of using the appliance is roughly proportional to its power drain from the mains. It would ap- pear interesting to investigate the phenomenon "power” a little further, particularly since the simple notion that power is the product of current and voltage (P = I U. whence P=U 2 /R and P=I 3 R) is not directly applicable to alternating voltage. A brief summary of terms may help to shed some light on the operational principle of the proposed wattmeter. Simply measuring the rms values of alternating current and voltage developed across a load R yields the apparent power : P = 1 rms ' Urms (Wl. However this method can only be used where the load R is purely resistive; should it consist of a reac- tive part (capacitance, inductance, or both) and a resistive part, as is the case with most mains loads, the cal- culation becomes more complex, since only that component of the cur- rent which is in phase with the voltage adds to the active power consumed by the load. The greater the phase shift, expressed as an angle, 0 50 1 1 i ' \ 1 1 1 i 20 -■H 30 100 / WATT • • elefclor incl .i January 1987 1 -4 1 by Sandra Smith next year on the basis of its success. The transputer brings nearer the dream of a computer not bigger than a suitcase yet powerful enough to model a nuclear explosion, or to plot a space vehicle's path to distant planets. It can be used to process the massive amounts of in- formation involved in generating and manipu- lating images in the field known as computer Britain staked a large claim In the world of infor- mation technology earlier this year with the launch of a computer to rival the fastest in the world. It is Floating Point Systems's ' new family, the T-series supercomputer. The key to the T-series’s un- questionable superiority is the transputer, popurlarly called the computer on a chip. This invention is the brain-child of Ian Barron, one of the founders of In- mos'* 1 . the semiconductor company set up by the Government in 1978. It was established to secure a place for Britain in the mass market for micropro- cessors and memory chips. In 1984 Inmos was bought by Thorn-EMI 131 . Its transputer could now be- come the world's standard chip for supercomputers and Inmos's market value, it is predicted, could rise to at least £200 million by graphics. Even powerful present-day computers can take hours to process graphic images in, for example, television broad- casts, computer aided design, or film animation. Complex graphics The transputer can pro- duce complex graphics as quickly as the operator r; r: ft rrr: ri n 1 1 ■Hr — -a mrir ' * ftriijtfi.ni ULiru nr , i mr u nr y ::::unru nr y The Inmos IMS T414 transputer— a computer on a chip elekior mdia January 1987 m u u J u U can think. In use in supercomputers— ma- chines with greater speed, accuracy and memory size and speed than lesser computers— the transputer allows the simulation ot ex- periments formerly poss- ible only in laboratories. This ot course makes these processes cheaper than the real thing. The boon to engineers is that they can play "what if?” experi- ments with proposed de- signs. Weather prediction is a classic example ot super- computer application. The idea is to perform the simulation much faster than nature so that one knows the weather before it happens. Even one day torecasts, if sufficiently ac- curate, can save lives by allowing people to pre- pare for hurricanes, flooding, and so on. Another application that "speeds up time” is the simulation of ways to ex- tract oil from proven re- serves. Supercomputers enable constructors to ask ques- tions about complicated structures that require a great deal of planning. The answers enable them to know about stress (ac- tors; the use of more suitable materials; aero- dynamic design in vehicles; heating and vi- bration problems and a whole range of essential facts. Design award I This year, two researchers dt University College Hospital, London, won an award for designing a low cost system tor modelling the effects of facial plastic surgery using four trans- puters to build a graphics processor rigged up to the host computer already at the hospital. It would not be stretching the point to say that the size of projects a country can undertake can be dictated by the maximum speed ot its supercom- puters. This is why the low- cost transputer is a revol- utionary development. The chips cost about £350, and should fall to £50 as production and demand increase. The T-series’s smallest machine, the FPS-264, costs under £350 000— less than a tenth of its nearest rival, the heavyweight Cray ‘ . There are only 12 Cray computers in Britain, costing between £10 million and £20 million each. Up to 1000 linked transputers can perform as well as the most powerful Cray. Comparisons between ! transputer-based ma- chines and Crays are not ‘ reliable, however, as it is not comparing like with like. A yardstick for such comparisons can be the | number of floating point ! operations or arithmetical calculations a supercom- puter completes in a sec- ond. They are counted in thousands of millions (gigaflops). The Cray 2 of- fers one gigaflop and costs between £5.2 million and £14.5 million. The T- series's largest machine, the T'40000. has a top speed of 262 gigaflops, about 200 times more than any comparable machine, and it costs only in the region of £1 million. Concurrent processing I The key to the transputer and the T-series is parallel or concurrent processing, an array of transputers I dealing with information in parallel rather than a j piece at a time, j Conventional computers process data serially— one task at a time. Parallel machines process several different parts of an oper- ation simultaneously, often millions at a time, by link- ing a number of pro- cessing elements together. This speeds up the process but creates complex design and programming difficulties. The patterns for the inter-linking of the pro- cessors determine the | complexity of the arith- I metic and data manipula- I tions that can be carried out. To simplify the pro- gramming of parallel pro- cessors a new program- ming language, Occam, was developed in 1983. According to world transputer expert and co- author of The Inmos Saga, Mick McLean; "Like the transputer, the essence of Occam is its simplicity". Until now the power and versatility of parallel com- l puters has been restricted by the bulkiness of their processors. These are made up of a number of chips, making their ability a trade-off between power and choice of inter-linking pattern. The transputer eliminates these restric- j tions because it is a com- I plete processing element on a single chip. integration techniques Made by very large-scale integration (VLSI) techni- ques, it contains the equivalent of 200 000 tran- sistors on a chip which is less than 9 mm 2 and has a central processor which- j handles 32 bits of data at a time. It also has a built- in memory and high- speed communication links for exchanging data | with other transputers, j Floating Point Systems has 1 chosen a "hypercube" ar- rangement for its pro- cessor inter-linking patterns in which eight | transputers link to form the corners of a cube. The hypercube was found to be the mosl efficient for complex arithmetical calculations. Each hypercube is called a node, two ot which, housed in a filling cabinet-sized container, give as much processing power as a large main- | frame computer. To increase processing power, more hypercubes are simply added, up to a maximum of 2048. A machine called Com- puting Surface, designed by Meiko 5 , of Bristol will not have such size limi- tations. Its design will allow it, in theory, to link a limitless number of transputers together. The company’s founders are ex-lnmos managers who were involved in the development of the transputer chip. Recognition systems Miles Chesney, one of the former managers, says Computing Surface will, for example, be used in "pattern recognition systems for robots and modelling the neural net- works of the brain". The computer has 150 transputers and can handle 1200 million program instructions a second— the sort of per- formance that only the biggest supercomputers can achieve. Yet it costs only about £250 000. fits into a box the size of a microwave oven, and re- ] quires little power. 1. Floating Point Systems ; (UK) Ltd • Apex House • London Road • Bracknell » Berkshire RG12 2TE. 2. Inmos Ltd • Whitefriars • Lewins Mead • Bristol ' BS1 2NP. 3. Thorn-EMI PLC • Upper St Martins Lane • London j WC2 H9ED. 4 Cray Research (UK) Ltd • Cray House • London Road • Bracknell • Berkshire RG12 2SY. 5. Meiko Ltd • Southgate • Whitefriars • Lewins Mead • Bristol BS1 2NP elektor india January 1987 1-43 PART 1-44 TOP-OF-THE- RANGE PRE- AMPLIFIER This month’s instalment of the article deals with the description of the circuits of the phono and line amplifiers. Constructional details will follow in next month’s issue. Initial considerations In essence, there are only two types of good-quality pick-up cartridge in use nowadays: the moving coil— MC— and the magneto-dynamic— MD. The main difference between these is the level of output voltage they provide. The signal provided by a modern MC cartridge is 100-400 ^V, whereas that of a MD type is 2-5 mV. In the design of an IEC (RIAA) equalization circuit that is suitable for use with both types of cartridge, there are two choices: one in which one or more stages of amplification can be switched on or off depending on whether an MC or an MD car- tridge is used; or one with variable I (or switch-selected) gain. In the pres- ent preamplifier, the second choice I has been adopted. This choice makes heavy demands on the input stage, because it is not easy to achieve a good signal-to- noise ratio with MC cartridges owing to the combination of low output voltage and small hum resistance of these elements. At very low hum im- pedances (a few ohms), the noise of | the input stage tends to drown the signal. Fortunately, careful design and the use of specially selected components can reduce the noise factor of the input stage to a very low value. Another requirement of a universal input stage is that its input capacitance and resistance can be varied: some MC cartridges should be terminated into 47R, others into 100R, while MD cartridges need a much higher resistance, around 47k. The input capacitance is particularly important when MD cartridges are used, because it affects the fre- quency response of these elements between 10 kHz and 20 kHz. The IEC de-emphasis characteristic is obtained by a well-tried combi- nation of a passive low-pass filter and an active low-frequency correction section as shown schematically in Fig. 8. Input stage A> raises the level of the signal from the cartridge: its amplification is matched to the type of cartridge and the input voltage by switched resistors. The output of Ai is passed through a passive low-pass section which has a cut-off frequency of 2120 Hz. The signal is then applied to amplifier Az, the negative feedback loop of which j contains a low-frequency equaliz- ation section that has cut-off fre- quencies at 500 Hz; 50 Hz; and 5 Hz. Circuit of the phono amplifier The input capacitance and resist- ance are selected by DIL switch | S 2 — see Fig. 9. Capacitors Cs , Ce , ; and Cz are necessary to prevent any DC from reaching the sensitive MC cartridge. All capacitances in the signal path are formed by parallel combinations of a polypropylene and a polyester capacitor: this will be further gone into in Part 3. The input amplifier consists of three dual transistors Type MAT-02. These are low-noise, carefully matched devices with a low offset voltage drift-see Table 1. Current source T< provides the DC bias for the tran- sistors. The voltage drop across a LED is used as the reference voltage. The three transistors are connected in parallel because the base resist- ance of the input transistor generates most of the thermal noise when the signal source has a very low output impedance: the thermal noise here is, therefore, reduced by nearly 67%. Another type of noise, the so-called Schottky noise, is determined largely by the collector current of the input transistor. Generally, the Schottky noise diminishes when the collector current increases— up to a limit. The collector current here is set at 1 mA per transistor; ideally, it should have been 3 mA (according to the manu- facturers), but this value would give difficulties with the active offset con- trol, which will be discussed later. A value of 1 mA is, however, a good compromise, resulting in excellent signal-to-noise ratios. The value of input capacitors Cs, Cs, and C; also has an effect on the amount of noise. The total value should be of the order of 100 >iF to 200 hF for a negligible contribution to the noise at the lowest fre- quencies. Since electrolytic capaci- tors can not be used in the signal path (because of their poor perform- ance), a compromise was found em- pirically between the dimensions of the capacitors and their noise con- tribution. All the measures to reduce the noise to an absolute minimum are for the benefit of MC cartridge users: if only MD pick-ups are used, one MAT-02 is sufficient. The collector current of that one transistor can then be re- duced to, say, 560 piA by increasing the value of R29. The input stage forms one half of a differential amplifier: the other half is ICi. This opamp raises the level of the difference signal at the collec- tors of the dual transistors. Opamp ICi is a high-quality device elektor mdia January 1987 that is no! cheap but which gives an excellent performance: its electrical characteristics are given in Table 2. The negative feedback loop of this stage— R u-Ru-Ri 2 -Ri 7 — contains two switches, Sia, Sib, with which the in- put sensitivity can be set to 0.1 mV; 0.2 mV; 2 mV; and 4 mV. This arrange- ment enables optimal matching of the dynamic range and the signal-to- noise ratio to the output signal of the cartridge. Note the low values of R 12 and Ri- which enable the noise at the inverting input of ICi to be kept to a minimum. The difference in value between Rs and R 1 2 -R 1 7 results in a relatively large, unwanted offset voltage. This is particularly troublesome when an MC cartridge is used, because the gain of the input stage is then be- tween 40 dB and 46 dB. This problem is resolved by integrator ICs, which provides active offset correction. The output of ICi is first taken through a low-pass filter, R 25 -C 16 , with a cut-off frequency of 0.3 Hz, and then integrated by IC3 . The DC level at the bases of the dual tran- sistors is set by IC3, via Rio or R 16 de- pending on the position of Sib, to a value which results in zero output of ICi. Since the supply voltage to a Type LF41 1 should not exceed 30 V, a 6k8 resistor— R35— has been inserted in the positive supply line to reduce the supply to IC 3 to about + 10 V. This creates no problems, since the out- put of the opamp is always negative when the offset is being adjusted: the output current then flows via the negative supply line The current required from IC 3 is fairly large, mainly because of the low value of Rw (even a small poten- tial difference across this resistor re- quires a fairly large current). The output current must be 6—8 mA to keep the output voltage at zero. This explains why the collector current of the dual transistors is arranged at 1 mA: higher values would necessi- tate an even larger current through R12-R17. Increasing the values of the feedback resistors would result in in- creased noise in the input stage. The passive part of the de-emphasis circuit is formed by Rk-Cs-C’o. the capacitors are 1% polystyrene types. , The output of ICi is fed to the non- inverting input of a second Type OP -27 amplifier. The negative feed- back loop of this stage contains the low-frequency correction section of the de-emphasis circuit. All resist- ances in the loop are formed by two Fig. 8 . The twofold nature of the phono ampli- fier becomes clear from this block diagram. Fig. 9 . The cir- cuit diagram of the phono ampli- fier. Special low- noise transistors are used in the input stage. Great care has been taken 111 the design of the lEC(RIAA) equalization cir- cuit, which is split in a passive and an active section. ©lektor mdia January 1987 1-45 Table 1. Mam electrical characteristics of the MA T-02 dual transistor. Table 1. Vce - 15V, Ic = 10^A, Ta = 25°C, unless otherwise noted PARAMETER MAT 02A/E — MAT 02B/F — SYMBOL CONDITIONS MIN TYP MAX MIN TYP MAX UNITS Ic = 1 mA (Note 1) 500 605 400 605 Current Gain Ic = 100pA 500 590 400 590 hFE Ic = 10pA 400 550 — 300 500 Ic = IpA 300 485 _ 200 485 Current Gain Match AhFE 10^A fo 30Hz (Note 3) _ 3.1 4.5 — 3.1 4.5 - 3.3 5.6 nV/ 1 Hz Voltage Density fo 1000Hz (Note 3) 3.0 3.8 3.0 3.8 ~ 32 4.5 fo - 10Hz (Notes 3.6) 1.7 4.0 _ 1.7 4.0 - 1.7 - Input Noise In fo = 30Hz (Notes 3,6) 1.0 2.3 - 1.0 2.3 - 1.0 — [>A / 1 Hz Current Density fo 1000Hz (Notes 3,6) 0.4 0.6 0.4 0.6 0.4 0.6 Input Resistance — Rin Differential Mode (Note 4) 1.5 6 1.2 5 - 0.8 4 MS Input Resistance — p |N Common Mode (Note 4) 1.5 6 1.2 5 - 0.8 4 MS Input Voltage Range IVR ± 11.0 ±12.3 ±11.0 ±12.3 - + 11. 0 + 12.3 V Common Mode CMRR Rejection Ratio Vcm ±11V 114 126 106 123 - 100 120 dB Power Supply PSRR Rejection Ratio Vs = + 4V to ± 18V 1 10 1 10 - 2 20 yV/V Large Signal Avo Ri£2kQ, Vo - + 10V 1000 1800 1000 1800 - 700 1500 V/mV Voltage Gain Rt>600Q. Vo - + 10V 800 1500 800 1500 600 1500 Output Voltage Vo Ri£2kQ + 12.0 + 13.8 - ±12.0 ±13.8 - ±11.5 ±13.5 V Swing R1S6OOS ± 10.0 ±11.5 ±10.0 ±11,5 — ± 10.0 + 11.5 ~ Slew Rate SR Ri£2kQ (Note 4) 1.7 2.8 1.7 2.8 1.7 2.8 V/ps Gain Bandwidth Prod. GBVV (Note 4) 5.0 8.0 5.0 ao _ 5.0 8.0 MHz Open Loop Output Ro Resistance Vo = 0, lo = 0 - 70 - 70 - - 70 Q Power Consumption Pd Vo _ 90 140 90 140 - 100 170 mW Offset Adjustment Range Rp = 10kQ - ±4.0 - ±4.0 - ±4.0 mV 1. Input offset voltage measurements are performed 0.5 seconds after application of power. A/E grades guaranteed fully warmed up. 2. Long term input offset voltage stability refers to the average trend line of Vos vs. Time over extended periods after the first 30 days of operation. Excluding the initial hour of operation, changes in Vos during the first 30 days are typically 2.5yV - refer to typical performance curve. 3. Sample tested. 4-. Guaranteed by design. 5. See test circuit and frequency response curve for 0.1Hz to 10Hz tester. 6. See test circuit for current noise measurement. parallel-connected l°/o resistors: this is, strictly speaking, not necessary, but is done to enable constructors making up the exact values with other combinations of resistors. Capacitors C« and Cu limit the DC amplification of the opamp to unity. Automatic offset correction in this stage was decided against because of the requirement to suppress very- low-frequency (below 5 Hz) compo- nents. Although the nominal gain of IC 2 is only 14 dB, the frequency- selective networks cause an ad- ditional gain of 20 dB for signals below 50 Hz. The coupling capacitors in the out- put circuit of ICz are not strictly necessary, because the automatic offset correction at the input stages works so well that there is no dis- cernible DC at the output of IC 2 . The supply lines to the different stages are decoupled separately The relevant network consists in each case of two 1000 yF electrolytic capacitors, each shunted by a 220 n ceramic capacitor for better high- frequency operation. Each electro- lytic capacitor is connected in series with a low-value resistor to further improve the decoupling. Table 2 Mam electrical characteristics of the OP-27 oper- ational amplifier Line amplifier The quality of the line amplifier is particularly important for the faithful reproduction of compact discs, when a good dynamic range, broad bandwidth, and minimal distortion are essential. elektor india January 1967 1-47 000S61S8 t rfSiZVdO ®HU Fig. 10. The two important semi- conductor de- vices used in the preamplifier dual transistor MA T-02 and op- erational ampli- fier OP-27 The dynamic range is determined by the maximum supply voltage to the ICs, which here has been made as high as possible at + 18.5 V. This value makes possible an undistorted output voltage of about 12 V, which is ten times as high as the nominal out- put level of 1.2 V (to give about 20 dB headroom). Since the noise produced oy opamps is very low. and the gain of the devices is only about 14 dB, the signal-to-noise ratio is of the order of 100 dB. With the headroom of about 20 dB, this gives a total dynamic range of around 120 dB! As stated in Part 1, the voltage dividers at the inputs merely serve to reduce crosstalk and hardly at- tenuate the wanted signal. Only the CD input is provided with an at- tenuator to lower the signal level by about a half. The reason for this is that the majority of CD players pro- vide a fairly high ouput signal— of the order of 1 V. The closer the CD player ouput is to the nominal sensi- tivity of the preamplifier, the smaller the likelyhood of overload during peak levels. The signal-to-noise ratio is not affected in the least by the at- tenuator (bear in mind that the output level control on the CD player per- Fig. 11 The cir- cuit diagram of the line ampli- fier. This ampli- fier is of particular import- ance in the re- production of sounds from a compact-disc player. The con- trols have been inserted between the two opamps contained in the amplifier to pre- vent them having any effect on the input or output impedances. i |220n [22 On lOOOp [25 V 1000 1 1000pj?!>V [220n RooomTIsv 1000p;25V IC4 OP 27 , 1 iot.0 IC4' OP 27 IN4148 SlCfCO/ mono 1-48 forms the same function). The circuit of the line amplifier— see Fig. 11— consists of two Types OP-27 opamps per channel. The two-stage arrangement has the benefit of a greater dynamic drive range, be- cause, since the volume control is normally nowhere near fully open, and. like the balance control, is fitted between the two amplifiers, the first opamp can deliver a greater un- distorted signal without overloading the second opamp. This set-up has the further advantage that both con- trols are isolated from the inputs and the output. The first stage. ICa (ICO. has a gain of 6 dB. Its output is connected to the second amplifier via a stereo/mono switch (and. as already stated, -the volume and balance controls). The switch is actually a relay contact to obviate long signal paths to a con- ventional switch. The IK resistor, Rso (R50'), ensures that the opamps do not short-circuit each other's output in the mono condition. Each channel has its own individual (mono) balance control, Pi (Pi'), but the volume control, P2 , is of the customary stereo type. The in- dividual balance controls enable set- ting the output signal to maximum level. Moreover, good-quality stereo balance controls are virtually unob- tainable! The second stage, IC5 (ICs’), has a gain of about 10 dB, resulting in the line amplifier delivering an output signal of 1.2 V for an input of 200 mV. The output is provided with DC blocking capacitors: again, these are not strictly necessary, since the opamps have no offset problems. But it could just happen that one of the signal sources delivers a DC compo- nent, and this would be amplified together with the signal. The output terminals are connected to the opamps via relay contacts: the relay action is delayed at switch-on, but is immediate on switch-off. The output terminals are also discon- nected briefly when the inputs are switched to obviate annoying clicks. As in the phono amplifier, the supply lines are thoroughly decoupled. Each opamp is supplied via a separ- ate 10R resistor, and individually decoupled by two 1000 mF electro- lytic capacitors, each of which is shunted by a 220 n ceramic capaci- tor for improved high-frequency op- eration. As will be seen next month in the constructional details, the earth tracks of the two channels are kept separate on the printed-circuit board, and combined only at the main earth rail. This arrangement im- proves the already excellent channel separation figures. elektor india January 1987 ATLAS, MINERVA, CARMINAT, CARIN AND PROMETHEUS Not Greek gods but Renault's electronic cars of the future From the closely-guarded research laboratories of Renault, first details have now been released on some of the French com- pany's spectacular ad- vances into the cars of tomorrow’s world, where computers and microchip electronics will take over the "thinking" aspects of motoring — from actual navigation and route- finding to the timing of departure and arrival, selecting alternative routes to avoid traffic jams, and even pin- pointing the car’s location at any given time. All this has evolved into a language of its own, em- bracing words like ATLAS, CARMINAT, CARIN and PROMETHEUS - acronyms tot the various research projects now in hand. The following feature pro- vides a fascinating insight into the current and future stages of "robotic" cars and motoring being de- veloped by Renault and its European associates. Project ATLAS In today's world, communi- cation and information are growing in import- ance day by day. This tendency is reflected in the development of the automobile by increased integration of electronics In the passenger compart- ment — an already ap- parent and indisputable evolution. The motorist now regards his vehicle less as "wheels" and more as an integral part of his environment. In- formation for road users is becoming increasingly organized with the crea- tion of radio-guides, organized planning of peak holiday departures, and the setting-up of infor- mation centres. As a result, the motorist wants more information — and to be able to com- municate, not just with his vehicle but with the out- side world. It is against this back- ground that in 1981 Renault launched a research programme whose objective was to obtain: — a device integrated into the car enabling selected supplementary information to be given to the driver, and — an evaluation "tool” to define new automobile equipment, associated with the following:— * The development of new electronic tech- nology (sensors, capacities for handling information, miniaturisation, etc. * The services offered by organizations outside the car. * Improvements in re- liability, through a re- duction in the number of components and controls used by the driver. Project ATLAS (Acquisition through Telediffusion of Automobile Logistics for Services) is the result of this research, undertaken with Telediffusion of France (TDF) since 1982. ATLAS makes it possible to treat in real time and dis- play on an interactive, touch-sensitive screen, in- formation for the driver which can be classified under three categories:— Information related to the vehicle itself, said to be endogenous, and gener- ated by sensors (warnings, maintenance, diagnostic, and general mechanical condition). Importantly, only information made compulsory by regulations features on the dashboard (speed, fuel level, mileage, etc.)— all other information being available on the screen. This redistribution of the siting of information is aimed to increase the safety of the "transport" function and, at the same time, increase the amount of information available. Pre-recorded information, described as "loaded”, and available on a com- pact disc, or memory card (for example, the Renault dealer network list, a practical guide to Renault equipment, extracts from the car handbook, perusal of microprocessor card, etc.). Information outside the ve- hicle, categorised as "ex- ogenous" which will be transmitted by a telediffu- sion network (road infor- mation. traffic, alternative routes, weather forecasts, etc.). As the amount of in- formation proposed could be very large, it is up- dated and transmitted in real time. Project ATLAS makes cur- rent evolution concrete fact, through: — appearance of new banks of facts; — development of the automobile product; — new expectations of motorists in matters of comfort and functional dependability, and — changes in the behav- iour of users, allied to the scope of communi- cations and the evolution of social relations. Development of the ATLAS system The first stage of research work made it possible to present Renault’s "DIALOG" (voice response) model at the Paris Motor Show in October, 1984. A road- going system on a Renault Espace 2000 was also presented by TDF at the Montreux Symposium in June, 1985. Analysis of the first elements obtained led Renault to centre its aloktor uvdia January 1987 1-49 research work on the development and treat- ment ot "endogenous" in- formation and diagnostics (collection of information, treatment and design, ergonomics and inte- gration into the passenger compartment). These aspects are in fact more within the domain of the car maker. All matters relating to the "exogenous” part of Pro- ject ATLAS were entrusted to the Societe SAGEM (Societe d'Applications Generates d’Electricite et de Mechanique) because of its competence in on- board electronics, syn- thetic images and ar- tificial intelligence, and j navigation. , TDF will continue its work on the transmission of in- fo motion because of its specific competence in this field. Contact was also made with Philips in connection with a numeri- cal information receptor. "Finally"', says Renault, ”it should be remembered that systems of the ATLAS type have European voca- tion, bote at the level of service (road information, and more generally the whole of the information given), and at the techni- cal level (European mini- mum standards). "Also, among the tech- nologies developed within the framework of the ATLAS system, most seem to con- form with the declaration of principle adopted by the European Ministers af the second ministerial J conference on the EUREKA project at Hanover on November 516, 1985: — transport technology; — information and com- munication; — protection of the en- vironment. "Thus, the ATLAS system will only find its full dimension on a European scale. In the same way, it favours normalisation of transport and exchange within the European Community."' As a result of these developments, Renault put in hand a dossier within the framework of the EUREKA project, christened MINERVE (Media Intelligent 1-50 elektor india January 1987 I pour I'Environnement Routier du Vehicule Euro- peen), at the same time continuing its own work Control of the MINERVE project was entrusted to j Societe SAGEM Project CARMtNAT More recently, Philips has been working in parallel with ATLAS on the CARIN project (Car Information and Navigation). This pro- ject consists of fitting vehicles with an electronic co-driver, able to: — determine the itinerary; — guide the driver to his destination; — give the position of the vehicle, and indicate it at any time, — and to supply infor- mation on the environ- ment or the destination. In the first instance, par- ticular effort was devoted to navigation and the use of a compact disc in the vehicle. The CARIN system was first demonstrated in 1985 Philips, contacted by SAGEM in relation to the MINERVE dossier, wished like Renault to resolve this problem on a European scale. The companies decided to pool their efforts and experience in a common | project — CARMINAT. This 1 combines the knowledge acquired through CARIN, MINERVE and ATLAS, and was presented within the framework of the EUREKA project. It should lead, in 1989/90, to a range of products which can be used on European vehicles. Project PROMETHEUS \ On the initiative of Daimler-Benz, and with the active support of Renault in view of its experience with the ATLAS project, European automobile con- structors have developed an extensive research pro- gramme whose objective is to create concepts and solutions for fluid traffic movements, with reduced impact on the environ- ment and increased econ- omy, combined with maximum safety. This vast programme broadens and extends the actions already de- scribed. It has been bap- tised "PROMETHEUS"', acronym for Programme for a European Traffic with Highest Efficiency and Un- precedented Safety, and falls perfectly within the framework of the dynamics | of the European pro- j gramme EUREKA. ! Project PROMETHEUS also brings in the fields of fun- damental research essen- tial to attain the objectives set (micro-electronics, ex- pert systems and artificial intelligence, and com- munication diffusion tech- \ nology). Many European experts ( are associated in the pro- ject. This is how the follow- ing French institutes are associated with PRO- METHEUS as experts: — CNRS, principally im- plicated in the scientific knowledge of artificial in- telligence problems and advanced electronics; — INRIA, specialists in advanced techniques of artificial vision and identification of forms and movements, together with the treatment of speech; — INRETS, for traffic ques- tions and dynamic infor- mation; — CCETT of Rennes (Centre Commun d’Etudes de telediffusion et de Tele- communications), special- ists in these areas. Automobile equipment suppliers and industrialists in electronics will be as- sociated with the project after the one-year prelimi- nary phase to define the technological specifica- tions resulting from the fol- lowing three axes of re- search:— PRO-CAR: development of a computer "co-driver", to improve vehicle safety; PRO-NET: development of communications networks from vehicle to vehicle; PRO-ROAD: development of communication be- tween the road environ- ment and the computer co-driver. Vehicles will thus receive information making it possible to organize maxi- mum fluidity of traffic. The specifications contain- ed in ATLAS, MINERVA and finally CARMINAT signifi- cantly cover the concepts ! of PRO-CAR and PRO- ROAD contained in the PROMETHEUS project, and use the same basic re- 1 search in micro-elec- tronics, expert systems and diffusion techniques. The major stages of pro- ject ATLAS 1981 - Preparation of the ATLAS project brief. 1982 - TDF-RENAULT agreement. Renault: study of the needs ol clients. TDF: study ot the trans- mission of facts to those on the move. 1983 : Static model. Renault verilication of func- tional ergonomics. TDF: signal reception tests on the road — Working model Construction of a working model fitted with the ATLAS system (Renault 20) 1984 — First reception on board a moving ve- hicle ot a radio-dif- fused programme (Renault 20) — Presentation of the DIALOG model at Paris Motor Show (October. 1984) 1985-Presentation of the DIALOG model at the Geneva Motor Show (March, 1985). — Presentation ot the ATLAS system in work- ing form on a Renault Espace 2000 at the Montreux Symposium (June. 1985) 1986 — Presentation ot the ATLAS system In work- ing form on three vehicles (2 Renault 21 . TXEs, 1 Renault Espace 2000 ). Renault UK Limited Western Avenue London W3 ORZ TEMPERATURE PROBE FOR DMM This article deals with a plug-in temperature-to-voltage converter for use with a digital multimeter (DMM). The design includes a battery test facility and a home-made probe for ease of measurement. The Type LM35 frgm National Semi- conductor is stated to have the fol- lowing features:* H Calibrated direct in degrees Cel- cius (Centigrade) (°C). a Linear + 10.0 mV/°C scale factor, at O.S °C accuracy at +25 °C (LM3SC). B Rated for full —55 to + 150 °C range. ■ Suitable for remote applications. £ Operates from 4 to 30 volts. H Less than 60 mA current drain. M Low self-heating, 0.8 °C in still air. ■ Non-linearity only ±0.25 °C typical. ■ Low-impedance output, 0.1 Q for 1 mA load. Circuit description Fig. 1 shows the circuit diagram of the proposed temperature probe. Diodes D 3 and D 4 have been in- | eluded to obtain a circuit ground potential which is some 1.2 V lower than that of the temperature sensor. Resistor Rs ensures that the sensor output voltage can be negative with respect to the DMM ground in the case of measuring temperatures below 0 °C. Resistor R* decouples the probe output from the high- impedance DMM input (Zin = 1 MQ, usually). The remainder of the circuit serves as the sensor supply and the battery test facility. Actuation of push-button Si causes the voltage at junction R2-R3-C1 to be nearly equal to Vbatt, as Ci is not charged at the onset. Transistor Ti conducts and Di lights if the terminated battery voltage is higher than 7 V. After a predeter- mined period, Ci is fully charged, and Ti turns off the LED. The battery test thus immediately indicates a flat battery if the LED remains off after ! actuation of Si. Construction A suggested method of constructing the temperature probe is shown in j the photograph at the head of this article and in the drawing of Fig. 3. The component overlay and track pattern of miniature PCB Type 86022 I is given in Fig. 2. I | The temperature sensor proper is I 1 conveniently fitted onto the tip of a I salvaged, temperature-controlled, j soldering iron, whose heating el- ement has been removed from the metal tube. The LM35 is preferably secured onto the tip with two-component glue, while a 3-wire cable is run through the tube to make the connection to the plug-in unit; the length of the probe cable should be a maximum J one metre or so. As shown on the in- ! elektor * Data taken from manufacturer's data sheet. India January 198? 1-51 Fig. 1. In essence, the temperature-to- voltage con- verter is com- posed of a precision tem- perature sensor, IC>, and a bat- tery condition tester. LM35C Fig. 2. Track layout and com- ponent mounting plan for the plug- in converter. The small size of the board allows the circuit plus bat- tery to be fitted in a compact enclosure. R2 2x 1N4148 Resistors <’ sWI: Ri-330 Q Rj;Rj - 100 k R4 = 1 k Rs = 18 k Capacitor: Semiconductors: Di = LED (may be mounted in Digitast keytop) D 2 = 4V7 zenerdiode 0.4 W Dj;D4 = 1N4148 Tt BC547B ICi = LM35C Miscellaneous: Si - ITT Digitast Type S switch (illumination is optional)* 2 off wander plugs * PP3 battery plus clip Probe tube * PCB type 86022 (see Readers Services) troductory photograph, the probe tip may be insulated with a short length of heat shrink sleeving. If this is done, however, the sensor enclosure should remain uninsulated. Finally, the tube is carefully sealed to enable measuring the temperature of liquids. As shown in Fig. 3, the completed board and PP3 battefy are housed in a transparent plastic case. Although a Euro-type, moulded mains plug makes for a very simple connection to the DMM input sockets by virtue of the correct pitch, two correctly spaced wander type plugs will also do quite nicely. As Si is to be actuated when plug- ging the unit onto the DMM, a small pin must be fitted onto the Digitast keytop. This pin is made to protrude from the converter enclosure and tested for reliable action. The PCB should be well insulated from the battery to prevent short- circuits and damage caused by the corrosive battery contents. Every constructor is left free to make his own, approximately 5 cm high, converter enclosure, which should have a hole for the probe cable to enter. Applications As the LM35 provides a linear output of + 10 mV/°C, the DMM display reading is simply the measured tem- perature, provided you have grown accustomed after a while to imagin- ing the decimal point shifted two digits to the right. For example, a reading of 0.256 V represents a probe temperature of 256 mV/10= 25.6 °C. Similarly, —0.307 V re~ peresents —30.7 °C. Fig. 3. Artist's impression of a suggested direct plug-on enclosure: Si is fitted with a pro- truding pin to achieve instan- taneous battery test and con- verter operation as the unit is plugged onto the DMM DC input sockets. 1-52 eleklor mdta January 1987 M \\ rm*n(T a straightforward 'straight-through' receiver Why should there be a need to construct your own medium waveband receiver? Surely it is far cheaper to buy one at the local supermarket? This may well indeed be true, but it is far more fun to actually build one yourself. After all, many of our readers belong to the younger generation and there is nothing quite like building your first radio — and getting it to work! — as many of our more experienced readers will testify. Amateur constructors often feel like magicians. It is quite amazing what can be accomplished with very few com- ponents. Take the design for this receiver for instance; an RF amplifier and a couple of transistors to bring music to your ears! In any case, many readers felt that it was high time that a simple receiver circuit found its way into the EPS list once more. The object of the exercise is to end up with a neat, economical portable radio. One that fits comfortably inside a coat pocket and can keep you up to date with the latest news and pop music, as you travel around town. Another important factor, of course, is that a single 9 V battery should last as long as possible (a few months at | least). When designing such a project, the first choice has to be between AM and FM. Nowadays, FM is favourite, but the problem here is that is not so easy for the novice to build, especially if the finished unit is to be really small. Elektor does have printed circuit-boards available for something a little larger than that described here, but by no means one that requires so few com- ponents, it can be virtually put together with your eyes closed. Which is our main objective, remember. We therefore came to the conclusion that there is nothing wrong with the medium waveband. It certainly has not run out of stations yet and what is more, the set will be much simpler (and cheaper) to build than an FM radio. It can be far smaller in size and last, but by no means least, it needs no finnicky aerial. In other words, it really is a pocket radio. Superhet or superreg? Now that we have decided upon medium wave and the main requirements are that it be small, simple to build and conservative on batteries, we need to i work out a few more design parameters. The majority of manufactured radio receivers operate on the superhetero- dyne principle. However, most single waveband receivers utilise the super- -egenerative principle. This is, in fact, the recipe for a reliable receiver if it is I to have a fairly high performance and feature reasonable sensitivity in spite | of its compact size. Nevertheless, if such considerations as simplicity of I construction and ease of calibration are involved, the 'super’ part is best I omitted. This is further illustrated in figure 1. All the most common AM receiver principles are shown there. First the 'straight-through' receiver a This is comprised of an adjustable LC tuned circuit, a high frequency ! amplifier, a detector, an audio amplifier, 1 a detector, an audio amplifier and a oudspeaker. The RF stage could even be left out, so that the set would then be a 'sophisticated' crystal receiver. If • s to be sufficiently sensitive, how- ever rather a lot of RF amplification will be necessary. This is why the RF amplifier usually incorporates an ad- justable feedback network (see dotted line) which enables the set to be ad- justed to the point of oscillation (maxi- mum sensitivity) for every station. The reflex receiver in figure 1b also offers a reasonable degree of sensitivity. Here the RF amplifier stage is not only used in the conventional manner, but it also amplifies the audio signal. This type of receiver used to be very popular in the days when transistors were rather expensive and difficult to obtain. Figure 1c shows that even the 'simple' superhet can be quite complicated. The aerial signal is now 'added' to that of an oscillator in the mixing stage. The oscillator produces a somewhat higher (or lower) frequency than the input signal and is varied simultaneously with the tuning capacitor. This generates a constant 'sum' or 'difference' frequency regardless of the actual frequency of the input signal. This 'intermediate' (IF) frequency is filtered at the output of the mixer and is further amplified. If necessary, the signal can be filtered and amplified several times to improve the selectivity. This is because the constant frequency of the IF signal makes the tuning of the LC circuits for each station superfluous. Obviously, the receiver will be rather complicated to set up. Straight-through Seeing that practically all the receivers that have been published in Elektor over the past few years were either superheterodyne or superregenerative, our design staff thought that it was time that a simple version was produced. In any event, an 1C exists which will fit the bill perfectly, but more about this later. Thus, after due consideration, the recipe illustrated in figure la was chosen for the miniature MW receiver, albeit without the feedback stage. The latter, even in the version shown in figure 1b, will make any receiver a lot less portable. Also, construction be- comes a critical task, the set is likely to 'whistle' and more often than not the receiver will have to be operated with both hands as the amount of feedback has to be adjusted for each individual station. If an ordinary 'straight-through' receiver can be built to incorporate enough RF amplification for feedback to become superfluous, without causing it to oscillate, it will have many practi- cal advantages The miniature integrated circuit that we have in mind does just this and furthermore features other useful characteristics, as will be seen later. Compared to more usual sets, a simple single tuned circuit receiver (such as this one) will be much less selective and therefore not so sensitive. Since MW receivers, especially pocket-sized ones, are more often than not used for ; reception of a limited number of local radio stations, this disadvantage will not be so noticeable. It is amply com- j pensated by the following advantages over other types: • it is much easier to build • it does not require any alignment • it does not include an oscillator, thereby avoiding stability problems • no mixing is involved, reducing 'whistle' considerably eleMor i.wiia January 1987 1 -53 Figure 1. The three most common types of AM receiver: a straight-through receiver (al.a reflex receiver (hi and a superheterodyne receiver (c). • its sound is of superior quality to that of the average superhet The ZN 414 By far the easiest method of con- structing a straight-through medium, waveband receiver is to use the ZN 414 integrated circuit from Ferranti which was designed specifically for this purpose. Having only three pins, it looks more like a transistor than a 'proper' 1C. Although it has been around for quite some time, it continues to provide the best solution for a receiver where a minimum number of components is required This is clearly illustrated in the diagram in figure 2. It shows the complete MW receiver constructed around the ZN 414. All that is required is a single transistor amplifier stage to provide a first class matchbox receiver. Certain items immediately catch the eye. First, the low supply voltage The ZN 414 is designed to be powered from a single battery. Its supply voltage range is between 1.2 and 1.6 V and the current consumption is in order of 0.3 mA. This device could hardly be more economical. Also remarkable is the fact that the coil (LI ) consists of a single winding, instead of the usual double-wound or tapped inductor, and that the detector diode which one would usually expect is missing. The double wound coil is superfluous as the 1C features an extremely high input impedance (4 Mil) which is only a very slight load for the parallel tuned circuit. Not only does this make the coil that much easier to wind, but also it helps to prevent interference from short wave transmitters. As far as the detector diode is concerned, this Is already inte- grated in the 1C in the form of a transis- 2 1.5 V 01111 2 Figure 2. What could be simpler? The straight-through receiver using the ZN 414 1C. tor detector which uses capacitor C3 as the only external component. The block diagram of the medium waveband receiver, see figure 3, shows just what goes on inside the case of the ZN 414 (see inside the dotted areal. It is comprised of a high im- pedance input stage (drawn here as an emitter follower), a (three stage) RF ! amplifier with a frequency range of j 1 50 kHz . . . 3 MHz and a gain of j 72 dB, an AM detector and, finally, an ! automatic gain control (AGC). Too much should not be expected from the latter, as its range is about 20 dB, : just enough to smooth out any slight I differences in amplitude between the 1 various radio stations. As soon as the I unit is in close proximity to a powerful j transmitter, however, the automatic gain control will be unable to adjust to the particular station required. Nevertheless, it is far better to have 20 dB than none at all, as is the case in some elementary receivers. Circuit diagram From the block diagram in figure 3 | it can be seen how straightforward the complete pocket sized medium wave receiver is. Apart from the parallel tuned circuit, the ZN 414 and the audio amplifier, all it needs is a suitable circuit to derive the 1.3 V required by the ZN 414 from the power supply for the audio amplifier. A simple bleed 81111 3 Figure 3. The block diagram of the miniature MW receiver. The entire section inside the dotted area is incorporated inside a single 1C no bigger than a BC 107. 1-54 elokto? mdia January 1987 Figure 4. The circuit diagram of the complete MW receiver featuring reasonable sensitivity, good selectivity and good quality sound. resistor and zener diode would have been more than adequate, but a far better method has been employed here. The complete circuit diagram of the MW receiver is shown in figure 4. The actual receiver section is constituted by IC1 and the surrounding components and is, of course, identical to the diagram shown in figure 2. The only difference between the two is that the values of R2 and C3 have been slightly modified. This is because they are based on the ideal supply voltage for the ZN414, which is between 1.3 and 1.4 V. When calculating the value of R2 three parameters have to be taken into account. First, the ratio R1/R2 will affect the automatic gain control. Since the value of R1 must be 100 k£2, only the value of R2 can be altered. There- fore, the value of the latter will also affect the gain of the ZN 414 and, as the voltage supply to the 1C must be at a constant level, the gain will be reduced if a relatively high value is chosen for R2. Moreover, it is important that the values of R2 and C3 constitute a low pass filter with a turnover frequency of around 4 kHz, which is necessary for the detector included in the 1C. The solution, therefore, is to select the best compromise value for R2 and to find an effective method of regulating the supply voltage for theZN 414. This is why the voltage source constructed around transistor T1 has been added to the circuit. The voltage on the emitter of T1 can be adjusted between approxi- mately 1.2 and 1.45 V by means of the preset potentiometer P2. This may not seem to be very much, but it affects the gain of the 1C somewhat considerably. This is an advantage as the sensitivity of the receiver can now be adapted to specific circumstances by presetting the gain of the amplifier as required Ob- viously, this will be at a maximum in isolated areas and lower in the vicinity of powerful local transmitters so that the set is not overdriven, which could cause distortion and poor selectivity. Batteries spend a very brief period of their lifespan at their rated nominal voltage and for this reason, together with the fact that the supply voltage for IC1 is critical, the voltage source T1 is not fed directly from the battery Instead, the voltage is first regulated by a zener diode (D1) to iron out any fluctuations in the battery voltage Since the receiver also has to be econ- omical, the current supply to the zener diode is limited by means of a fairly large series resistor (R6). As the current consumption of the ZN 414 is very low the zener diode will operate very well, even at a low'i voltage than that which it is rated at (about 3.9 V in this case). So much for the receiver section. Now for the audio amplifier. Initially, it was proposed that one of the well-known amplifier ICs should be used. These, however, turned out to rapidly exhaust the small 9 V battery's current supply. Instead, it was decided to combine two pnp transistors and two npn transistors to form a discrete amplifier. Very little can be said about this, as it is con- structed entirely according to the 'four transistor recipe'. It requires very little current and there is virtually no quiesc- ent current for the output transistors T4 and T5. Thus, when there is no input signal the entire amplifier will only consume around 2.5 mA. Since the current requirement for the ZN414 is also fairly modest, the receiver will only consume a total of 4 mA. A reasonable battery will there- fore last a considerable time, provided the volume is not turned up to an ear-splitting level, that is. The maximum output power of the audio amplifier is in the region of 250 mW. In theory it will produce more from a 9 V battery (about 1 W maximum into 8S2), but the voltage gain of the audio stage is limited so that no more than 4 Vpp is available across the loudspeaker output even when the output signal from the ZN 414 is at a maximum (approximately 30 mV e ff). This maintains the current consumption at a level acceptable to the 9 V battery and also eliminates the need for heat- sinks on the two output transistors. Construction The printed circuit board and com- ponent overlay for the medium wave band receiver are shown in figure 5. The only components which are not actually mounted on the board are the variable capacitor Cl, potentiometer PI and the rrltrkUir india January 1987 1 -55 loudspeaker. The leads connecting the capacitor to the board should, ob- viously, be as short as possible. As you probably already know, the performance of a parallel tuned circuit is largely dependent on the Q of the tuning inductor. For this reason, the aerial coil, LI, will have to be wound with the utmost care and attention. It is best to use the parameters specified, that is, 48 turns of 0.3 mm diameter enamelled copper wire on a ferrite rod with a diameter of 10 mm and a length of 10 cm. The ferrite rod can be mounted onto the board by means of two short pieces of string. Holes have already been drilled in the printed circuit board for this very purpose. It is a good idea to wind LI around a paper or cardboard tube so that it can be moved up and down on the ferrite rod later; the permeability of ferrite and ferroxcube material tends to vary, so therefore it may be necessary to 'trim' the receiver if the stations are not at the correct places on the waveband. Further remarks. Firstly, something that probably does not need mentioning. As the ferrite rod coil is in fact an aerial, it would be unwise to mount the com- pleted receiver in a metal easel Secondly, the zener diode D1 must be either a 250 mW or a 400 mW type, as stated, as otherwise the input level for the voltage source T1 (3.9 VI will not be correct. This is because the current flowing through D1 is far lower than normal in order to keep the current consumption of the circuit to a mini- mum. Thirdly, as the output transis- tors do not require any quiescent current, the value of resistors R13 and R14 are fairly critical. If the stated values are not adhered to the chances are that the output transistors will start to draw current after all and, as there is no temperature compensation net- work, this could well have a detrimental effect on them. Using the values given in figure 4, transistors T4 and T5 will not have to be cooled. They can be ordinary types without any need for heatsinks. Results In practice, the miniature medium waveband receiver was found to per- form very satisfactorily. Being a single coil type, it may require constant re- tuning due to the set 'drifting' off frequency, especially where distant stations are concerned. Even so, it is eminently suitable as a 'stand-by' receiver for news bulletins etc. which is quite often all that is required any- way. It is only when the owner wishes to listen to a weak station in the neigh- bourhood of a powerful one that the MW receiver is going to have problems. This can often be remedied by turning the receiver towards the weaker station thereby eliminating the stronger one. Local stations can be received very well. In unfavourable circumstances, an ex- ternal aerial may be experimented with. This should be connected to the top of the tuning coil via a small value capacitor (4p7). This, however, should hardly ever be necessary. If the input signal is clean enough, the sound quality of the receiver will be suprisingly good. In this respect it really stands out amongst similar commercial radios. Finally, the receiver is remarkably inexpensive. If, like countless other constructors, you have a 'junk' box full of ferrite rods, tuning capacitors and transistors, it will only cost a few pence. M 1-56 elector india January 1987 (an important factor) Noise in UHF/VHF receivers can be determined by using extensive and expensive test equipment. However, tests with a noise generator can give usable results at a much lower cost. Such a noise generator can, of course, be constructed by the amateur. What is noise? Noise is caused by highly complicated physical and thermodynamic processes. Briefly, it is the random movement of electrical charge carriers. Noise increases with rise in temperature: at absolute zero (-273°C = 0 K) noise is zero, for at this temperature all movement is frozen. This is why during certain critical processes, cryogenic techniques are used to attenuate the noise factor 1 Figure 1. Circuit diagram of the simple high frequency noise generator. with very low temperatures. However, it is not always practical to go to these extremes. The signal -to-noise ratio is the best known method for determining to what extent noise (N) affects the signal (S). This can be done by expressing the signal-to-noise ratio in dB: S/N = 10 logS/N dB Taking a certain point in the receiver (after the demodulator for instance), it can be determined how many micro- volts arc required at the input in order to obtain a certain signal-to-noise ratio at the output. How to determine the noise factor The noise factor in receivers can be calculated in two different ways, either from a sensitivity or from a noise measurement. In order to test sensitivity a signal generator is required; however, good quality HF signal generators tend to be very expensive . . . Instead of measuring the sensitivity with only one frequency, we can apply many frequencies at once: use a noise signal, in other words. This is how it works. First the basic noise N of the receiver is measured when the noise generator is switched off. Then the noise generator is switched on and the noise level is set (by means of an attenuator) in such a way that twice the input level can be measured at the output. This corre- sponds to a S/N ratio of 3 dB. The nice thing about using noise methods is that the S/N ratio is not dependent on temperature or bandwidth. Circuit A small generator can be built with inexpensive and readily available com- ponents as shown in figure 1. A high frequency transistor (T2) is connected Figure 2. Part of the frequency spectrum of the circuit of figure 1. On the upper trace the frequency is shown horizontally (100 MHz per cm) and the amplitude vertically (2 dB per cm). The lower trace represents the noise produced by the spectrum analyser 1—97 dBm: 0 dBm is 1 mW with an impedance of 50 it). as a zener diode. It is fed by a DC voltage source (T1). The noise voltage and therefore output level is determined by the setting of potentiometer PI which controls the amount of current that flows through the zener diode. The output impedance of the circuit is approximately 50 J2. The photograph in figure 2 shows part of the generator’s noise spectrum. Obviously, the circuit cannot be ex- pected to perform miracles. The stability (temperature coefficient of the voltage source T1) achieved in the long run is not ideal, but for comparative (short term) noise tests it is quite adequate. K elektor mdia January 1987 1-57 Dimmers i selex 19 Have you noticed the advertisements (or dimmers in the newspapers? There are so many of them now a days!" "Yes. with these dimmers, we can adjust the light to be brighter or darker " "Is there a transformer inside such dimmers to increase or decrease the voltage output? "No, there is no transformer inside the dimmer It works electronically" "You mean there are electronic transformers?" "It is rather an electronic switch called TRIAC and it works on the principle of Phase Control " "Phase? I have heard something about the Phase. It has something to do with the alternating voltage!" "Correct, The waveform of the alternating voltage is a sinewave. This is how it looks" "I know this, the voltage alternately becomes positive and negative But what does a dimmer do to this sinewave?" "The TRIAC inside the dimmer acts as a switch and allows only a part of every half wave to pass through to the light bulb. The waveform then looks somewhat like this!" 1 How does this happen?" "This happens due to the properties of the TRIAC. It is a switch which can only be switched ON, and it does not switch OFF unless the current flowing through it drops | to zero” and the alternating voltage automatically becomes zero after every half cycle, so the current flow also must become zero every half cycle. "Exactly, that is what happens inside the dimmer. We can switch ON the TRIAC at any place over the half wave, and it automatically switches OFF when the waveform crosses the zero level. The process repeats on every half cycle " "But then how does the light become darker or brigher?" "For this we just have to adjust the point at which the TRIAC is switched on or triggered The more the half wave passes through, the brighter is the light " Now I understand, to make the light dimmer, we must allow only a small part of the half wave to pass through j But why is it called Phase Control ?” Because the point of time of a wave is related to the Phase angle and the brightness of the light depends on the Phase angle of the wave at which we switch on or trigger the TRIAC "And that is why we call it Phase Control" "Yes, If we trigger the TRIAC at the beginning of a half wave, we get the brightest light. If we trigger the TRIAC at the end of a half wave we get a very dim light." "Wait a minute It is really useless to trigger the TRIAC before tha peak valve The maximum value will then j always pass through!" "True, the peak value will always pass through, but it is not the peak value that decides the brightness. It is the effective value that decides the brightness." "Oh yes, I remember, the effective voltage is less than the peak value”. "The effective voltage depends upon the area of the wave that passes through" "Then the Phase Control is nothing else but simply : Effective Voltage Control, I always wonder why the electronics experts make things so complicated?" 1-58 doklor india January 1987 Field Meter The purpose of the field strength meter described here is not the measurement of any interference field: This instrument is used for determination of the field strength of some useful signals, like those of a remote control transmitter. Near the transmitter antenna, the field is very strong and then it expands in free space The farther we go from the transmitting antenna, the broader is the scatter and weaker is the field strength. The energy available from the transmitted signal goes on reducing as we go away from the transmitter antenna. A remote controlled model must move within the area where the field strength is enough for the model to react with Our field strength meter can be used to decide upto what distance the field is strong enough The field strength is normally stated in mV/m, however the device described here indicates just the ratio value, from which a conclusion about the actual field strength can be easily drawn A field strength meter is a useful instrument for all those involved in HAM activities and those involved in remote controlled model airplanes etc For them it is interesting as well as useful to know, how much energy is being transmitted by the radiating antenna Also, with the field strength meter, one can search for the most suitable antenna for a transmitter, and do the calibration. Itcanalsobe used for determining the transmitting characteristics of an antenna. Everyone of us owns a field strength meter in the house: the amplifier system Though it does not measure any transmitted field strength, it certainly detects and amplifies the 50 Hz hum When you touch an input terminal with a finger, you can hear a loud hum coming from the amplifier In this case, our body serves as the receiving antenna and the 50Hz disturbance is picked up and amplified. If you take the amplifier outside the house and away from it, the hum vanishes Inside the house, there is a strong field set up by the current carrying mains wiring Outside the house, this field dies down. Another field strength meter we come across is the car radio When we are passing below a high voltage line on the road, it picks up the 50Hz interference and amplifies it Once we cross that part of the road the field set up by the high voltage overhead transmission line dies down and the hum from the radio diminishes 1 0 turns of insulated copper wire Dia 0 8 to 1 .2 mm SOOp 83778X 2 83778X - 3 The Circuit Figure 2 shows the circuit diagram of the field strength meter It consists of just four passive and one active component, one receiving antenna and one 0-50 fiA meter movement It does not need a supply voltage, as it draws the energy directly from the field which it is measuring. The antenna picks up the HF signal transmitted by the transmitter. The parallel (MHz) Figure 1 The signals emitted by a transmitter scatter in free space The farther away we go from the transmitter, the lower is their strength Figure 2 The most important part of the circuit is the parallel resonant circuit formed by LI & Cl The resonant frequency of this circuit decides the signal frequency to which the field strength meter reacts. Figure 3 The resonant frequency of LI Cl combination must be as that of the signal being measured Only then the signal amplitude is highest and canbe processed by the further part of the circuit and indicated by the meter. All other frequencies are filtered out Both the curves show the behaviour at the tuned frequencies of 13MHz and 27 MH z selex Measuring Range Extension A question most frequently faced by a beginner is "I have a 100pA measuring instrument and I would like to measure 1A with it. how do I do it?” The solution is quite simple Use a parallel resistance! In technical jargon this is called a 'SHUNT'. [ Simple! isn't it? Not quite so, there is a small proolem with the shunt The required parallel resistance can be calculated only if we know the internal resistance of the measuring instrument, and even if we I are able to calculate it, it is most likely that the calculated value will not be a standard value. A simple and practical way of making a shunt is shown in figure 2 Ordinary solder wire is used as a shunt resistance. The required length can be determined by trial and error The equipment required for this is one variable voltage source, one multimeter, a resistance of 1CMI/5W and some solder wire. A diode (1 N 4001 ) can be used to I protect the measuring instrument. Now, using the multimeter, it is possible to set the current in the circuit at 1A by adjusting the supply voltage. The length of solder wire in parallel with the instrument is adjusted in such a way that the needle deflects to full scale at 1A current through the circuit It is also possible to set the shunt in such a way that the full scale deflection stands for 2A or even 3A Be careful and remember to disconnect the power supply when even the solder wire is being removed for adjustments Results of an experiment carried out with a set up as shown in figure 2 are given below for reference which can serve as a guideline The actual values will differ depending on the diameter of solder wire and its composition. The typical results are as follows ; Instrument lOO^A F.S D movement. Solder Modified Wire Range length 1 A 34 cm 2A 1 6 cm 3A 10 cm Solder wire of 0.8 mm dia was used The shunt was found to work effectively even at 3A current with full I scale deflection 1 -60 elekiw »ndu» January 1987 1 selex 4 Component List Cl 500 pF. Variable C2 1 rjF Ceramic PI 25 K 1 2. Potentiometer LI 1 0 turns of insulated copper wire (dia 0 8 to 1 2 mm) D1 AA 119 (Germanium) Ml Moving Coil meter 0 50 nA. Other parts 1 SELEX PCB 1 Antenna 1 Suitable enclosure 3^ Banana plugs and sockets if necessary Figure 4 The component layout on a standard SELEX PCB Figure 5 The photograph shows internal construction of the field strength meter with the back cover removed resonant circuit, made up of coil LI and the capacitor Cl is used for tuning to the frequency of the signal Capacitor Cl is a variable type, with a continuous adjustment possible between zero and maximum value With the given values of LI and Cl it is possible to tune to any signal from 13 MHz to 40 MHz. This range covers both the radio amatures as well as the remote control enthusiasts. Along with the antenna, the parallel resonant circuit picks up the signal to which it is tuned and passes it on to the indicating part of the circuit consisting of the diode D1, capacitor C2, potentiometer PI, and the meter Ml. The amplitude of the signal being picked up is maximum at the tuned resonant frequency fr. Figure 3 shows this graphically for 13 MHz and 27 MHz If Cl is moved away from the tuned position, the amplitude suddenly drops down The tuning of the parallel LC circuit depends on the resistive component of the impedance of L and C. With increasing frequency the resistive component of Coil impedance increases, whereas that of the capacitor impedance decreases. The circuit resonates at the frequency at which the resistive components of both the coil and capacitor impedance become equal to each other As in our circuit the coil LI is fixed and Cl is variable, the change in resonant frequency is entirely dependant on the value of Cl The signal is rectified by the diode D1 and a DC voltage is generated across C2. Potentiometer PI converts it into suitable current for the meter Ml to indicate the value. Setting of PI decides the sensitivity of the field strength meter. The sensitivity should be adjusted depending on the field strength being measured. The indicator deflection depends on four factors: the transmitter output capacity, the antenna, the distance between transmitter and the instrument and the sensitivity setting of PI The Construction The construction is very simple as we have only a few components to assemble The component layout is shown in figure 4 The diode D1 must be of Germanium, which has a threshold voltage of only 0.3 V. As our signal amplitude is very low. a Silicon diode with a threshold of 0.7 V will not be suitable The variable capacitor can either be mounted directly on PCB if possible, or it canbe fitted on an aluminium angle and then the angle can be fixed on to the PCB The Coil LI is made by giving 10 turns of insulated copper wire around a pencil The wire diameter can be 0.8 to 1 .2 mm The pencil can be taken out after winding the coil without disturbing the turns. The turns should be as close to each other as possible C2 should be of ceramic type. The advantage of ceramic capacitors in that they have high stability, low losses and good tolerance. All these affect the measuring range of the field strength meter A moving coil meter with a full scale deflection of 50nA is used as an indicator. The simplest component is the antenna A wire of about 20 to 30 cm length can be used as an antenna, or even a bicycle spoke can be used as an antenna, if a telescopic antenna is not available. Lastly, the entire instrument must be enclosed in a metalic enclosure to shield it from any interference fields and to pick up only the signal to which it is tuned. eiektor india January 1987 1-61 With the last pin soldered, the soldering iron kept aside, we are finally ready with our PCB with all components assembled! We connect the power supply and switch it on nothing happens !! Unfortunately, after so much of effort we dont get the result At this point what we badly need is a continuity teser Because, if the circuit does not function after we have asembled it correctly, most probably these is something wrong with the connections Either a soldered connection is not good enough or the solder has unintentionally spread to unwanted areas - creating a short circuit where no connection was desired Or. may be we have missed a connection totally and left it unsoldered. All these possibilities can be checked with a simple continuity tester described in this article Connections between components can be quickly checked with this continuity tester An audible beep indicates that the connection is proper Absence of beep shows an open connection, or a high contact resistance If the tester beeps when connected to two points which are not intended to be connected to each other, it means there is an unwanted short circuit The tester circuit is so designed, that a contact resistance of more them 1 II shows as an open circuit j There is no risk of damaging ! the sensitive components by the tester because the test signal is very small The Circuit The main component of the tester circuit is the Operational Amplifier (Op Amp) IC1 The Op Amp is connected as a differential amplifier, which means that the amplifier reacts only to the difference between the voltages on the inverting (Pin 2) and the non inverting (Pin 3) inputs. The difference signal is strongly amplified and carried to the output (Pm 6). Normally the points A and B are at equal voltage level, namely at approximately half the operating voltage This is so because R1 and R3 have equal values The introduction of R2 in the circuit makes the voltage at A more positive by about 2 mV compared to point B Thus the input pin 2 lies at somewhat higher voltage than pin 3 As the Op Amp has a very high gain.it switches the output to zero volts. Now if the test tips are connected to each other, R2 gets short circuited The potentiometer PI is so adjusted that when R2 is short circuited, the voltage at pin 3 is slightly more positve than that at pin 2 This gives a positive voltage at the output of the Op Amp 1-62 eleklor rndia January 1987 I selex The Op Amp behaves in the following manner: In case of short circuited measuring tips, the output goes high, approximately to the supply voltage If the test tips are connected across a resistance of more than 1 !!, then the Op Amp output becomes zero To convert the output voltage into an audible output signal, oscillator is constructed with Nl, R7, P2 and Cl The oscillator output drives the piezo- buzzer. Bz The oscillator is an astable multivibrator and produces a 4 6 KHz signal The current taken by the oscillator is about 3 mA. to drive the buzzer The frequency can be adjusted with P2, and the frequency adjustment also affects the volume because the buzzer works most efficiently at its resonant frequency The oscillator is turned on or off by the Op Amp output signal When the output is 0". there is no audio output When it becomes T the oscillator starts driving the buzzer and produces sound output The oscillations take place as the capacitor Cl is alternately charged and discharged This produces a square wave, which drives the Piezo Buzzer Construction & Adjustment Because of the few components used, the construction is quite simple A component layout on SELEX PCB is shown in figure 2 Correct polarity must be observed for C2. and Pin numbers of ICs must be properly connected A 9V miniature battery is used as the power supply and connected through the switch SI The assembled circuit must be tested before fitting into the enclosure For tins purpose, PI and P2 both should be kept in their center position On shorting points A and B. the buzzer should give an output If buzzer does not make any sound, adjust PI till it |tist starts making a sound Then adjust P2 to set the volume For correct adjustment, a 1 !> resistance is connected across A and B and PI is set at a point where the buzzer just starts giving an audible output In this way the tester will not indicate a short circuit even for small values of resistors If nothing works as outlined above, check the PCB assembly carefully Are all the components correctly placed? Are they all of correct values? Also check the voltage at A and B, it should be approximately about 4 5V on both points The output of IC1 must be low when terminals A and B are not shorted It should be almost equal to the supply voltage when A and B are shorted If all this is in order and still the tester does not work, check the wiring Once the circuit starts functioning, it can be fitted into a small handy plastic cabinet Such an assembly is shown in figure 3 Figure 1 The continuity tester indicates short and open circuits in an assembled electronic circuit board For resistances less than 111 it indicates a short circuit by giving an audible beep sound Figure 2: The entire circuit of the continuity tester can be mounted on a SELEX PCB Only the sockets, switch and battery are fitted externally The installation in a plastic enclosure is quite easy. All one has to do is just drill a few holes and fit everything inside «l«rk 1 o» mdia January >987 1-63 ELECTRONIC WEIGHING SCALE AFCO have developed an Electronic Precision Weighing Scale, which works on the strain guage Loadcell. Having a capacity of 1999 gms it gives a reading on a LCD screen with + 1 gm resolution The scale features a detachable deep square pan and a rotary switch to correct the reading when the deep pan is not in use Compact in size, it is suitable for use in office, Kitchen, laboratory, postal department etc. For further details, please contact. M/S AFCO MARKETING PVT LTD 104 Creative Ind. Estate 72. N. M. Joshi Marg Sitaram Mills Compound Bombay-400 Oil. Phone 39 89 34/89 64 72 WINDING TEMP INDICATOR PECON has developed a solid state winding temperature indicator for power transformers Available from 2 to 4 contacts with repeater and 4 20 mA output for DAS operations, it can withstand all types of voltage and current surges prevalent in power plants. This indicator comes for various voltages upto 250V in both AC & DC For further information, contact POWER ELECTRONICS & CONTROL. 612. Yashkamal. Tilak Road. Vadodara -390 005 HUMIDITY SWITCH IRA has developed a humidity switch, the Humiswitch - 861 for control of humidity in instrumentation, LT & HT control panels etc This switch, based on LSI technology is reliable, accurate, compact and useful for controlling humidity to tolerable limits to avoid the risk of flashover and mal operations. Humiswitch 861 has an electronic transmitter and an electronic control switch connected by a 5 core cable The electronic transmitter is equipped with sensors & signal conditioners for both RH and dry bulb temperature and can be used for controlling only | humidity or both humidity and dry bulbs temperatures Where temperature control is required, a circuit for giving alarm/switching on blowers or coolers can be provided for keeping the temperature within reasonable limits For further details, contact M/S INSTRUMENT RESEARCH ASSOCIATES PVT LTD P B No. 2304/1-2 Magadi Road Bangalore-560 023 DIGITAL MEGGER SCR Electroniks have developed a digital megger. Digi Meg Available in two basic versions viz LED model (suitable for 230V AC or 1 2V DC) and LCD model (working on 9V battery) the models feature • range of upto 2000 meg ohms, resolution of 0.01 meg ohms and 0.1 meg ohms respectively, accuracy of ♦. 1%. test voltage of 500V DC and 3Vi digit 0 8" display (LED or LCD) For further details, please contact. SCR ELECTRONIKS Opp Fatima High School Kirol Hoad. Vidyavihar BOMBA Y 400 086 AMPLITUDE CONTROL Static Power Systems have developed solid state amplitude control panel for electromagnetic vibrating feeders, screens and other equipment This control features a smooth start from zero to the full capacity, plug in-type modular cards, voltage variation, isolation transformer for control & trigger circuits etc. These controllers are available upto 500 V DC and 70 amps For further information, please write to: M/S STATIC POWER SYSTEMS PVT LTD D 148 Bonaza Ind Estat Ashok Chakravarty Road Kandivli (W) Bombay 400 101 PHONE 691173 D C CALIBRATOR PRECISION'S Universal D C Calibrator is a microprocessor based instrument which can measure the output of any standard thermocouple type B.E.J.K.R.S.T It features automatic cold junction compensation, temperature display with a resolution of 0.1 °C. measurement as well as simulation of millivolt and milliampere signals etc. The unit comes in a portable cabinet with simple panel controls. “1 For further information contact M/S PRECISION ELECTRONICS 38 -D GIDC Bhaktinagar RAJKOT 360 002 ( Gujarat ) VOLTAGE STABILIZERS Digitech have developed the Powerline' servo controled a.c voltage stabilizers which stabilize the voltage to 230V 10.5% in 1 -0 and 400V i 0.5% in the 3-0 version. A number of models rated from 0.5 KVA to 100 KVA are available The control circuit is I.C based and 3 LEDs on the panel indicate the input line status and the correction being carried out The correction rate is 30V/Second Other features iclude No waveform distortion, no rf interference, output voltage adjustability, auto/manual mode of operation and voltmeter for voltage monitoring For further details, please contact DIGITECH ELECTRONICS D1/GF-9 Viral Bhavan Dr Mukher/ee Nagar Commercial Complex DELHI 110 009 SMPS Omnitronix have introduced switch Mode Power suppl y with built in automatic voltage stabilizers for TVs Mains isolated, it features line and load regulation. EMI/RFI filtering, line transient supression circuit and a modular construction. For further details, contact: M/S OMNITRONIX C-5, Amijyot. Ambawadi. Ahmedabad 380 006 1-64 elektor mdu» January 1987 one solution. Features like never before: • High grade imported raw material • Sintered in controlled nitrogen atmosphere • Low loss factor • Wide range of permeabilities • Choice of specific AL Values. • niter Uhokes ti bMKb • CTV's • Computers & Terminals • Transducers- and the areas of application are endless. Our engineers’ application assis- tance helps enhance your products’ performance. MURUGAPPA ELECTRONICS LTD. World Standards in India Manufactured by : HB HILVERSUM ELECTRONICS Prop. Bundy Tubing of India Ltd. Madras. Marketed by : MURUGAPPA ELECTRONICS LIMITED. PARRY HOUSE 3rd Floor. 43 Moore Street. Madras 600 001 INDIA Tel NO&26505/ 29251 Ext 261 Telex 41 -301 TIMS IN/41 -7429 AMEX IN Branches e Bangalore - Tel Nos60127B/603742 • Bombay- Tel No.31BD00 Telex 11-2237 PARY IN e Calcutta - Tel Nos.449932/33 Telex 21 7B6B AJAX IN • New Delhi - Tel No.6434274 • Secunderabad Tel No 701 51 Telex 1556-205 PARY IN • Allahabad - Tel No.55134 LINTAS M MEL PPG 72719 elektor India January 1987 1-65 display indicates a zero and an internal relay energises to changeover the contacts A push button switch is provided for resetting the time weight efficient, full wave single phase rectifier bridge. Available in two types, PCB mounted or chassis/heatsink mounting types, they are rated for currents of 1 to 8 Amps for a voltage range of 6Vrms to 700Vrms when connected to a 12V. 88Ah rechargeable lead acid battery The Nitepower has a maximum switching time of 5 seconds and is suitable for operating lights, fans, telex machines, telephone exchanges, intercoms, TVs and computers For further details contact ELSONIC SANTO CORPN .. 8/1 , Palamgrove Road. Bangalore-560 04 7 Digital Multimeter Ledtron have introduced Digicone 1210 autoranging Digital multimeter. Measuring upto 1000V AC/DC; 20 Mohms; 10 A AC/DC the multimeter can test diodes and has a buzzer for audible continuity testing. It has a rugged design, is portable and compact. The contact is rated at 230V/6A and the timers are available in Delayed ON or Delayed OFF models. The models come in 2to 4 digit display and blind versions For further information contact M/s.ALFA PRODUCTS COMPANY. FF-11 Bajan House. 97 Nehru Place. Post Box 4324 New Delhi- 1 10 019 The internal construction has a low thermal resistance and low forward voltage drop. The rectifiers can be used in electronic instrumentation, controllers, consumer electronics, business machines, power supplies etc. LCR meters Murugappa Electronics Ltd are marketing AG-4301 B and AG-4303 digital LCR meters made by Ando Electric of Japan Designed for measuring components quickly a. id accurately, the meters use a new measurement technique and displays L. C, R, D and Q at 2 different frequencies of IKHz and 100 Hz. In addition it also has a residual charge protection upto 50V. facility for superimposing upto 30V DC. If used in conjunction with Ando's comparator AG4902, fast GO NO-GO determination of components can be made against preset upper and lower limits of component parameters For further details, write to SOLID STATE ELECTRONICS CO PVT. LTD. Plot No. 9/123. Marol Co-op. Ind. Estate. P O. Box. 7432. J.B Nagar Post. Bombay -400 059 Liquid Level Controller Accents Liquid level controller (LLC) monitors the level of a liquid in a tank It ensures that this level either does not rise above or fall below some preset thresholds, thereby protecting the pump from over/ under load The LLC has a compact lOcms x lOcms control unit with probes attached Depending on the liquid level, as measured by this probe, the control unit automatically switches on/ off either a pump or some other device whose operation is to be controlled Electronic Pain Killer Johan have introduced an electronic pain killer based on Transcutaneous Nerve Stimulation therapy It removes the pain from the nervous system and muscles by sending external electrical energy to the affected parts The instrument work on a 9V battery, weighs only 75 gms and comes in a range of pleasing colours. The device is useful in*backache. migraine, arthritis, muscular pain, sprains and fatigues. For details contact . M/s. LEDTRON ELECTRONICS. 1 70 Lohar Chawl. Bombay-400 002 UPS Elsonic have developed Nitepower 2C0 SN solid state uninterruptible power supply system. Sometimes referred to as a storage type mini generator, the system is compact and generates quare waves at 50Hz which are fed to the output triacs which turn on only when the mains fail. The unit gives 160W of power during a power failure for 3 hours For details contact MURUGAPPA ELECTRONICS LTD Agency Division. TIAM house 28 Rajaji Road. Madras-600 001 For further details, contact M/S ACCENT CONTROL (P) LTD. Kataria Mansion. Dr Annie Besant Road. Worli. Bomba y- 400 018 Digital Timers Alfa have developed a range of Timers with quartz crystals Having a high timing accuracy of 0.01% the timers have a wide range of operation The time setting is done through thumb wheel switches and the set is displayed on the switches. When the timer is switched ON, the LCDs display the count down and as the time lapses the For further information contact M/s. JOHARI ELECTRO-TECH CO Vandana. 28. neharu park. Jodhpur-342 003. Bridge Rectifiers Solid State Electronics have developed a series of light 1-66 elektor india January 1987 MOTOROLA C Jy THE VMEbus COMPUTER SYSTEM * HARDWARE DESIGN STATION p-— * SOFTWARE DESIGN STATION S | ‘ OEM USER STATION * SINGLE BOARD COMPUTER * ‘ PERIPHERAL CONTROLLER MT "" * A/D D/A INTERFACE BOARD ^ * CARD CAGE, BACKPLANE * CHASSIS AND POWER SUPPLY Semiconductor Products INTEGRATED CIRCUIT, RECTIFIER, ZENER, SCR, PRESSURE SENSOR ELEMENT, UJT, FET, PHOTOELECTRONIC PRODUCT, DISCRETE MICROMINIATURE PRODUCT. Artwork Drafting Aids & CAD For PC8 Bishop Graphics. Inc INsfiBHWr Reer^Ralay microelectronic & Arrestor PROOUCTS mec Unimec Keycap System & Modular Switch COMPONENTS CAPACITORS. RESISTOR NETWORKS MONOCHROME /COLOR MONITOR PRINTER. PLOTTER FOR COMPUTER PffOFf SSIOMAL FUJI DYNAMICS CO.. LTD. CENTRAL CONTROL SIGNAL GENERATOR SYSTEM R AOIOINOUSTRI6 CATV/MATV Equipment JALCO •A QC Clutch fft RF Switch. Connector Video • RF Modulator UNAOHM CATV fveid strength meter Sped rum fad strength meter & Sweep mwter generator OVL JIT'C' DELAY LINES. XMJ ELECTRONIC la>^V WIRE, RIBBON/FLAT/FIBRE OPTIC CABLE Authorised Distributor ProfessKW^ade UUV/MATV ft Communtcaoon Coaxial Cable H*gn Power Cordless Telephone Tone Voice Radio Paging System i i m ■— i ii i i— ri Ml' l\.JI ivtlw lyroir ruirn^i EEIC GENERAL ELECTRONICS & INSTRUMENTATION CORPORATION (PTE) LTD 101 Kitchener Road #02-17. Jalan Besar Plaza Singapore 0820 Systems Division: Block 6. Syed Alwi Road Telephone 298 7633 Telex: GEIC RS 24416 Fax: 2910905 #02-351. Singapore 0820 Telephone: 2965398 elector india January 1987 1-67 Zero Speed Switch I EC's zero speed switch is designed for speed control of conveyors, crushers, rolling mills etc. Solid state in nature, the unit is enclosed in a dust & vermin proof housing and has 3 ranges of operation from 5-50 rpm, 50-500 rpm and 500-5000 rpm. It also features i a variable 0-15 seconds initial bypass delay. The unit takes an input of 230V AC, 50Hz supply and the output is a relay rated at 6A, 230V, 50Hz ELECTRONIC VltP WIICII For further information contact M/S. INDIAN ENGINEERING , COMPANY \ Post Box 1 6551 . Worli Naka Bombay-400 018. Daisy Wheel Printer Saras Electronics is offering a Daisy Wheel Printer, CPD-22 from Japan. The CPD-22 is 22 cps printer compatible with DIABLO and QUME 96 characters print wheels and ribbons. Also compatible with all the popular computers the CPD-22 uses any paper, fanfold, sheet, envelopes, labels etc., has a form width of maximum 13 inches and has a copy capacity of original *3 copies The CPD-22 has many other features and takes advantage of word processing software Microsoft Word; Lotus 1 -2-3. Wordstar and incorporates shadow printing, double strike. | For more details, please contact M/S. SARAS ELECTRONICS. Suite 301. Purhoit House. 144. Mint Street. Madras-600 079 Wirewound Resistors RKE have introduced Silicon coated wirewound resistors type PWR for direct mounting on PCBs. Available in 3,5, and 10 Watts, these resistors have a completely welded structure and have excellent stability & reliability. Ideal for automated PCB assemblies, these resistors are suitable for T V . commercial, industrial, power and telecommunication equipment. — Mj ensuring constant torque operation in the overall range Its important feature is that during reversal or deceleration •n either direction, it prevents wastage of mechanical energy This is done by feeding the energy back into the mams supply Modular in construction, the system comprises power components, control switchgear and PCB rack fitted in standard cubicles It incorporates safe guards like electronic overcurrent trip, under voltage, trip, overvoltage trip. etc. It is designed to suit 3 phase. 415V. 50Hz, AC supply line. For more details, quote ref No P3/2 84 and write to Advani-Oerlikon Limited Post Box No 1546 Bombay 400 001 For more details, please write to ARADHANA ELECTRONICS (P) LTD.. 10. Sr math complex. S D Road. Secunderabad 500 003. AC DRIVE SYSTEM Advani Oerlikon have developed a solid-state AC drive system named ADOR AMPVERT' for variable speed control of AC squirrel cage induction motors The system enables bidirectional speed control with regenerative braking using the principle of current source inverter. It maintains a constant voltage frequency ratio ROTARY SWITCH WITH ADJUSTABLE STOP TRS 12 'Comtech' TRS- 12 is a Rotary switch which is offered in 3 models, FirstL 1 pole 12 positions. Second 2 pole 6 positions and Third 4 pole 3 positions A stop ring is provided with each switch to enable the user to adjust the switch-stop - position to meet his requirements. Each model is available with printed circuit and solder terminals having tin- glow plating to impart quick solderability. The body is made up of glass- filled Nylon and the contacts are made from brass and phospher bronze The switch at present is offered with nonshorting contacts (Break before make), having a rating of 350 mA at 110 V Ac/Dc, and with contact resistance of 20 milliohms max ; The switch is having a minimum mechanical life of 20,000 detent operations. The shaft accepts any knob suitable j for 1/4" diameter. For futher details contact COMPONENT TECHNIQUE 8. Orion Appartment 29 A Lallubhai Park Road Andheri (West) Bombay-400 058 DIGITAL DC MICRO VOLT METER VMV15 A clever indirect measurement with VMV15 eliminates costly & complicated ELECTROMETER: for conductivity measurement upto few thousand Meg Ohms. In addition VMV15 possesses all advantages of digital meter over analog VMV15 has a resolution of 1 micro-volt. With optional H V probe the range covered is upto 2000 Volts. Provision of optional adaptor converts the meter to DC PICO-AMMETER with 1 PA resolution. Battery operation makes it more versatile tor floating measurements, like that of measuring MICRO-OHMS with constant current source For details contact VASA VI ELECTRONICS (Marketing Division ) 63 Q A Ik a rim Trade Centre Hamganj SECUNDERABAD 500 003 PHONE 70995 1-70 elektor mdia January 1987 Attention! TV makers. The promised one has arrived. ‘S’ correction aluminium electrolytic Capacitors. -an import substitute from ELCOT. RANGE MFD 2.2 4.7 6.8 10 12 Volt 25 25 25 25 25 Max Ripple current 5App 7.0App 8.0App 1 0.OApp lO.OApp For a clear, well resolved image in a TV. good components are essential. S' correction aluminium electrolytic capacitors trom ELCOT are indis- pensable tor that With a long working life.the range has excellent high frequ- ency. high ripple current and stable temperature characteristics. For a quality TV. it has to be your'choice A proof of ELCOTs dynamic achieve- ment pattern This special range of Capacitors came into the international TV component scene lust during the early eighties. ELCOT, moving last in the track, is now in a position to offer you the range, off the ELCOT shell. The know-how and do-how are wholly indigenous. Yes' Many can promise, but only a lew deliver The ELCOT bias for quality ELCOTs quality control action programme is really unbeatable It begins at the raw material procure- ment stage and continues. Until the laultless finished product matches ELCOTs failproof performance para- meters. That's why they perform so well under extreme conditions. Yes! When you want to make a quality TV. go m lor ELCOT components. For dependability, reliability, and on-the-dot delivery Electronics Corporation of Tamil Nadu Ltd. (A Govt, of Tamil Nadu Enterprise) LLA Buildings, 735, Anna Salai, Madras 600 002. Phone : 89642 Telex 041 -61 13 LCOT IN c ' T PI T C >_ u i Quality Components from ELCOT Any other component wilt be a compromise Branch Offices 2/20 A Janpura A. Hospital Hoad NEW DELHI 14 let 694076 fPP). Room No 3. 22. Sunil Shopping Centre. Opp Navrang Theatre. J P Hoad Andhen West. BOMBAY. TCL 622042; 149/A. Motilal Nehru Road CALCUTTA 29 4 3 738. Ramkote, Hyderabad I. Tel 552980; Triveni. 35 518, Warnam Road Cochin 1 6 Authorised Dealers NEW 0ELHI: Oeep/yothi Enterprises I Tel 6412072) Rahyte Micro Devices I, Tel 734663 6436990). Orym Electronics (Tel 5727407. 5721559. 5728072) BOMBAY Mehtromcs ITel 387353) Saha/anand hopes Pyt ltd ITel 41363271. PUNE Esteem /- Irastructure /Tel. 64037 63681). AHME0ABAD Shree/i Electronics fTel [Tel 397171. 399435). CALCUTTA M A Shah ITel: 279699 2661861 8AR00A Mavveet Services Cor/m Tel 43643 1 BANGALORE Linear Systems Inc ITel 351575). Maudgal Marketing Company ( Tel 227411). HYDERABAD Marvel Electronics ITel 62262). Teliraina Enterprises Tel 551379/ SECUNDERABAD. Cosmos Electronics ITel. 822419 825577) TRIVANDRUM Bhuvanesh Sales Corporation ITel 61719). Electronic Equipment 8, Components ITel 77748). NAGPUR Rematroms. 191/1. Rachna Apartments. Cement Road, Shiva/i Nagar, NAGPUR 10 “lektcx india January 1987 1-71 YEAR INDEX- 1986 Audio video and sound generator Audio-controlled mams switch 8/9.100 Digital volume control 8/9 96 Disco sound limiter 8/9 93 Four-tone siren 8/9.42 Headphone amplifier 10.40 High dynamic range mixer 8 9 24 High-power AF amplifier (1 ) 7 18 High-power AF amplifier (2) 1146 Line bar generator 8 9 46 Lourspeaker protection 8/9 1 1 3 Metal percussion generator 8 9 60 Microprocessor signal processor 8/9.102 Mini stereo amplifier 8 9 24 Mobile audio power amplifier '9 80 Noise gate 8 9 80 Portable mixer (1) 6 18 Portable mixer (2) 7 39 Portable mixer (3> 10 46 Quartz-controlled tuning fork 8 9.55 RGB to monochrome converter 8 9 84 Satellite loudspeakers 5 46 SCART switch. 8 9 62 Speech processor with background suppression 8/9.91 Subwoofer 5 18 Subwoofer filter 8 9 66 Synchronization separator 8 9 59 Telephone bell simulator 8/9.38 Top-of-the-range preamplifier (1) 12 19 True-class B amplifier 8/9.50 Tuning AF power stages 8 9 86 Two-tone chime 8/9.84 VIP bleeper 8 9 81 Channel multiplier for flat TV panel 1.45 Designing a closed loudspeaker 3.46 Versatile stereo amplifier 6 49 TV interference suppression 7 36 VHF/UHF TV modulator 7 48 Guitar fuzz unit Quartz controlled tuning fork Sound sampling & digital synthesis . Power supplies and batteries Battery guard Current indicator ... DC-operated battery charger Direct current monitor Electronic fuse Low-drop voltage regulator . Nicd battery chargers One-chip DC convertor Simple Nicd charger 8/9.57 8/9.72 3 22 8/9.56 .8/9.87 8/9 74 8/9.100 8/9.33 8/9.83 Supply protection 8/9^85 Switch-mode power supply 8/9.90 Visible power-on delay 8 9 102 Voltage inverter ’ ’ 8/9 1 01 Lithium Batteries 1 34 Dissipation limiter 160 Mobile audio power amplifier 2.38 DC operated battery charger 3.22 Supply failure indicator 7 37 723 as a constant current source 10.44 Generators and Oscillators Calibration generator 8/9.114 DC operated 50 Hz timebase 8/9.112 Fast voltage controlled pulse generator 8/9 63 HCMOSVCO 8 9 74 Line bar generator 8/9.46 Programmable odour generator 8/9.90 Symmetrical cascode oscillator 8 9 26 Up down clock generator 8 9 71 Voltage comparision on a scope 1 1 25 Computers and microprocessors 8 -bit ADC 8 bit DAC 40-track adaptor 2708 alternatives Computerscope (1 ) CPU gear box Filtered connector Flashing colours High resolution graphics card (5) 8/9.68 8/9.88 8/9.110 8/9.46 11.18 8/9.111 8/9.58 6 26 2 32 High resolution graphics card ( 6 ) 3 39 High resolution graphics card (7) 4.45 Improved sound for the BBC micro 8 9 82 Joystick adaptor 8 9 89 Listen-m key for datarecorders . ... 8/9.110 Mandelbrot graphics 8/9.78 MSX extensions (1) : I/O bus. digitizer. 8 bit I/O port 2 46 MSX extensions ( 2 ) cartridge board 3 30 MSX Extensions (3) : add-on bus board 4 33 PIA for electron 8 9 45 Real-time clock 5 36 Sidewav RAM for BBC and Electron Plus One 8/9.94 Universal peripheral equipment (1) 8 way relay board 7 33 Microprocessor navigation 1 46 Protective computers from fraud 1 47 8 bit/I/O bus 126 High resolution graphics card (4) 1 49 Junior Computer .5.42 Measuring and test equipment Heart beat monitor Loudspeaker impedance meter Pocket frequency meter RMS-to-DC converter Single-trace CRT converter Jumbo clock Magetiser Sensitive light meter 8/9.54 10.34 8/9.103 8/9.34 7.25 1.18 4 50 . 12.41 Domestic Call counter 8 961 Deceptive lock .................. g g qq Dessicator ... 8951 Electronic bell-pull 8 9 92 Industrial clock controller 8 9 37 Infra-red light switch 2 23 Jumbo dimmer 8 9 108 Light sensitive switch 8/9.50 Long interval timer 8/9.50 Mams-based remote controller 8/9 65 Remote control for light switches 8/9.30 Random lights controller 8/9.58 Rodents deterrent 8/9.35 Solid state dark room light 8/9.77 Staircase light controller 8 9 109 Super dimmer 8/9 75 Thermostat-controlled soil heating 8/9.36 Toilet ventilator control 8/9 48 Versatile timer 8/9.68 Watchdog 8/9.39 Deep freeze alarm 1 25 Telephone exchange 154 Intercom 4 48 Active aerial with SMDs 3 28 IDU for satellite TV reception (1 ) 1 1 .26 IDU for satellite TV reception (2) 12.28 Low noise aerial booster 8/9.27 Narrow band IF filter 8/9.72 RF circuit design ( 1 ) test oscillator 3 48 RF circuit design (2) VHF filters 4 28 RF circuit design (3) VHF amplifier 5.32 RF circuit design (4) : superrengenerative SW receiver 11 38 RF circuit design (5) VHF/UHF noise generator 12 50 S meter 8/9.43 Tunable active aerial for SW 8/9 106 Tunable FM booster 8/9 32 1-80 elOktor india January 1987 Hobby and car Car burglar alarm Car fuse monitor Car lights monitor Car radio alarm Car radio alarm Courtesy light delay Dark-room exposure meter Halogen lamp protector LED revolution counter Motor-cycle gear indicator Solid state ignition Talk funny Simple auto slide changer Siren Headphone amplifier Colour wheel Electronic toss up Musical greeting cards Miscellaneous and design ideas Alternating flasher Analogue & digital Colour wheel Current drive for stepper motors Electronic rotary switch Electronic toss-up L.C. displays Mains zero-crossing detector Musical greeting cards Servo motor tester Servo robot driver SMD die Stepper motor control Two-gate bistable Up/down counter control Voltage controlled attenuator Voltage-to-current convertor Zero modem connector Phase-corrected cross-over filter Real load resistors Alternating flasher Stepper motor control Smart LED Selector Corrections Active subwoofer (May 86 P 18 Battery guard (Aug Sept. 86 p 57) Car burglar alarm (Aug/Sept 86 P 67) Car theft alarms (general) 1986 High-power AF amplifier (1) (July 86 P 18) Infra-red light switch (Feb 86 P 23) MSX extensions (2) (March 86 P 30) MSX extensions (3) (April 86 P 33) PIA for Electron (Aug Sept 86 P 45) RF.circuit design (2) (April 86 P 28) Telephone Exchange (Jan 86 P 54) VHF premaplifier (Mav 86 P 32) 8/9.67 8/9.56 8 9 42 ft/Q 8/9.79 8/9.97 1 1 44 8 9 82 8 9 98 8/9.36 2 18 5 26 6 35 . 6 40 10 40 8/9 49 8/9 86 8/9 112 8/9 73 8 9 69 8/9.49 8/9 104 8/9 70 8/9.86 6 46 8/9 114 8 9 112 8/9.29 .8/9.25 8/9 44 8/9 107 8/9 64 .8/9 28 2 16 .8/9.31 1 24 1.30 1045 8/9.73 8 9 107 8/9.47 5.74 10.74 11 74 1 1 74 7 74 10.74 6 74 5 74 10.74 5.74 7.74 1 1 74 Informative articles and electronics technology 8mm video 4.18 The accordion image sensor 3 37 Actuation systems for flight control 1 2 26 Air defence systems for countries and continents 11 23 The battle for supertelevision 12 44 CAD in practice at Renault 2 44 Car Electronics 2 26 CCD video memory systems 7 28 A compact radar for helicopters 7.51 Computers and health care 6.31 Computers of tomorrow 10 51 Early detection of electronic failures 6.42 Educational software for the handicapped 2 42 Electric propulsion for satellites 10 30 Electronically controlled cameras 3.17 Electronics and temperature control 6.33 The future for artificial intelligence 3.35 How much longer will silicon be used? 1 1.40 Inductors in practice Jockeying for supremacy in Europe's own space race Light work for submarine cables Loudspeaker efficiency Loudspeaker impedance correction Magnetic field sensors Micro electronics and pharmaceuticals A million frames hold the new Domesday Monitoring highways electronically Optical fibre network for offices Photonics Pioneering nuclear power for peaceful purpose Protecting data from prying eyes Research and the future Satellite TV receiving equipment Software for the BBC computer the META assembler Tell-tale magnetism of heart throbs Surface Mount Technology The accordio image sensor 4.39 . 1 1.36 4 42 7 44 6.28 6 38 8/9 52 6 43 7 52 8/9.40 4.24 . 6 44 2 41 10.38 3.25 1042 1247 ... 1 38 3 37 SELEX Selex-8 Digi-Course II (Chapter-2) Semiconductors Transistors Resistance bridges Resistance decade box Selex-9 Digi-course II (Chapter 3) Wet-finger-test Experiments with transistor Transistor tester Selex- 10 Digi-course II (Chapter 4) Variable power supply Attachment for multimeter Selex-1 1 Digi-course II (Chapter 5) Capacitors Different types of capacitors Capacitors in series/parallel connections The filter capacitor Darlington pair Selex - 12 Digi-course II (Chapter 6) Mini amplifier Z-diode tester Selex- 13 Digi-course II (Chapter 7) The oscilloscope TV antenna signal distributor Tips for Selex PCB Selex-14 Digi-course II (Chapter 8) Threshold voltage and the LED Capacitance decade box High current and Magnetic field Selex-1 5 Measuring techniques (Chapter 1) Loudspeakers * Magnetic flux phatogram How does a transformer work? Selex- 1 6 Measuring techniques (Chapter 2) The heavy weight of electronics Unknown transformer data Transformer Coils in Series & Parallel ... Selex - 17 Measuring Techniques (Chapter 3) Measuring power with a multimeter Power calculations Selex- 1 8 Relays Wire movement in a magnetic field Bicycle dynamo .1.61 1 63 1.64 .1 65 1 66 2 53 2 55 2 56 2 58 3.51 3 53 3.56 . 4 52 4.54 4 55 4 57 4 57 4 59 5.51 5 52 5 55 6 54 6 56 6.60 6 61 7.54 . 7.56 . 7 58 . 7 61 Ill VI ... VIII 10.52 10 54 10 56 10 58 11.55 11.57 11.60 12.52 12.54 12.54 elekto* mdia January 198*7 1 81 advertisers index ADVANCE INDUSTRIES 1.74 ADVANI OERLIKON 1.19 AIR INDIA 1.15 ANANT ENTERPRISES 1.78 APEX ELECTRONICS 1.73 B M P. MARKETING 1.82 CHAMPION 1.11 COMPUTER CENTRE 1.77 COMTECH 1.06 COSMIC 1.84 CYCLO 1.06 DEVICE 1.16 DYNALOG MICRO SYSTEM .120 ECONOMY ENGINEERING ... 108 ELCOT 1 71 ELECTRONICA 1 14 ELTEK BOOSK IN KITS 1.77 ENGINEERING SYSTEM 1.04 GENERAL ELECTRONICS . ... 1.67 IEAP 1-12 INDIAN ENGINEERING 1.12 ION ELECTRICALS 1 .04 KEJRIWAL 1.10 KLAS 110 LEADER 1.08 LOGIC 1.74 MECO INSTRUMENTS 1.73 MICRONICS 1.78 MOTWANE 1.13 MURUGAPPA 1.65 NCS ELECTRONICS 1.74 PNS ELECTRONICS 1.78 PANTAKI 1.77 PIONEER 1.08 PHILIPS 1.07 PRECIOUS ELECTRONICS 1.79 PROFESSIONAL ELECTRONICS 1.14 ROCHER ELECTRONICS 1.72 SAINI ELECTRONICS . 1.09 SMJ ELECTRONICS 1.72 SONODYNE 1.02 SUPERB PRODUCTS 1.061.73 SWASTIK 1.69 TEJUTRON ELECTRONICS .. 1.74 TESTICA 1.10 TEXONIC INSTRUMENTS 1.12 TRIMURTI ELECTRONICS 1.72 UNLIMITED ELECTRONICS ... 1.14 VASAVI ELECTRONICS 1.05 VISHA ELECTRONICS 1.83 WESTON 1.04 ‘One good turn leads to another' AUTOMATIC AND MANUAL AUTOMATIC COIL WINDING MACHINE ARMATURE WINDING MACHINE \ HEAVYDUTY COIL IfHAND W WINDING ■ MACHINE Manufactured by: 1 — B.M.P. ft EQUIPMENT CO Marketed by: I Comarketing pvt. ltd. A RECD OFFICE : LAI BANGLOW. JYOTI STUDIOS. KENNEDY BRIDGE BOMBAY • 400 007. TELEPHONE : 386°<}4 . 512 1253 classified ads KITS - MW Transmitter 500 meters Rs 150.00. Remote control relay 500 meters Rs 1 25 00 Send 50% advance by MO, Ask for kits list to SUPER ELECTRONICS, Shivaji Nagar. Barsi-41 3 41 1 For Printed Circuit Boards & name plates, also facility for Art work, layout designing contact SHIV ENTERPRISES P Bhagat Marg. Tukaram Nagar, Ayre Road, Dombivali (East) 421 201 CORRECTIONS Low noise aerial booster Top of the range Preamplifier (Part 1) ( Aug Sept 1986-p. 21) (Dec 1986 p. 12 24) On the component overlay, the col- lector of Ti is erroneously shown to be connected to the PCB ground plane, while it should go to junction L 2 -C 4 -R 4 -L 3 (turn the transistor 90° cw). The infocard mentioned in the note on page 12-24 (see note printed in Italic) will be published in the February 1987 issue. 1-82 elektor india January 1987 R N No 3988 1 /83 ^YW 228 I 1C No 9 1 Black magic ■ Nakamichi AX-1000 Featuring SMPS, a unique advance in audio technology, coming to India for the first time. Vibrating with 250 watts of peak energy, breaking all sound barriers, touching rare heights,' here comes, at last, an Ampli Deck marvel Backed by the audio expertise which will fill your senses as never °f Cosmic this latest generation never before. model, has a dynamic one touch recording system, a super hard pemi This classic black model — alloy head, soft touch controls, L. £. D. rtakamichi AX 1 000 with its unique peak level indicators, double gap Switch Mode Power Supply 5. M. P S. I erase head plus much much more for has music surging through its over all excellent performance. This sophisticated < ircuitry. with such powerful Ampli-Cassettc Deck has sonic purity and clarity, that one hears arrived, to cast a spell, even on the not the reproduction of music but the perfectionist, actual recreation of it. So get ready for some hypnotism. Cosmic Nakamichi AX-1000 It's pure black magic Price Rs 4,500/- all inclusive ;only for Bombay city) cosmic We are sound Printer Publisher — C.R. Chandarana fnniril ai la ■ . : ... . . 2. Koumari. 14th A Road. Khar. Bombay 400 052. k , u .. . .. u . .w w i 1 .... . . 1> ..-.i rt uiu oi . I mploment. CTV 1 0