Rs. 7.50 elekt©P elekte? In a beautiful bound Volume at no extra cost Our Back Issues are increasingly in demand HENCE BOOK ONE 1) Send full amount by DD/ MO ' PO To: Elektor Electronics Pvt. Ltd., 3, Chunam Lane, D. Bhadkamkar Marg, Bombay-400.007. 2) Despatch will be made by Registered Post Parcel Only 3) NO. CHEQUES-NO VPP Also Distributed by: INDIA BOOK HOUSE SHARP WELL DEFINED CHARACTERS SPEED: 3 LINES/SEC ON 58 MM PAPER 3/2 COLUMNS OF SPECIAL CHARACTERS 15/16 COLUMNS OF NUMBERS - 0 to 9 ULTRA LOW POWER CMOS INTERFACE SERIAL OR PARALLEL BCD INPUT OPTIONS PRINT IN RED & BLACK TO DISTINGUISH ALARM AND NORMAL CONDITIONS TWO PRINT MODES - AUTO AND MANUAL PLUG-IN MODULAR INTERFACE CARDS FOR 6. 12 OR 18 COLUMNS TABLE TOP OR PANEL MOUNT MODELS DOOR WITH MAGNETIC CATCH OPTIONS 1) Real/elapsed lime clock with print inte 2) Automatic decimal point or character circuits for special applications sui 3) Portable battery powered printers. 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I '. 1 '-• M \ *%% > Sfe , « » • I FAST SEMICONDUCTORS •INTEGRATED CIRCUITS • MICROPROCESSOR & MEMORY CHIPS •DISPLAYS OPTO ELECTRONIC DEVICES •CRYSTALS & OSCILLATORS • TRIMPOTS • TRANSISTORS DIODES • TANTALUM CAPACITORS SWITCHES • CONNECTORS • SCR’s etc. Manufacturer's Include Advanced Micro Devices. Analog Devices, Apex Microtechnology. C TS. Fairchild Semiconductor, Fujisoku, Fujitsu. General Instrument. Grayhill. Harris. Hitachi, Intel. Intersil. Matsushita, Mitomo, Mitsubishi. Motorola, Mostek, National Semiconductor. NEC. PM I, RvA . Raytheon. Rockwell, Statek Corpn., S G S, Signetics, Silicon General, Siliconix. Synertek, Texas Instruments, Toshiba. Unitrode, Western Digital, Zilog. ELMATRONIC DEVICES Head office: 14, Hanuman Terrace. Lamington Road, Bombay 400007, Tel. : 362421 Gram: ELMADEVICE Telex: 11-5614 15, Hotel Kamadhenu Annexe. Trinity Circle, M.G. Road. Bangalore - 560 008. 7-08 etektor India July 1984 17-A/2,Karve Road, 30, Prasad Chambers, Pune 411 004. Tel.: 35983 Gram: ELMADEVICE Telex: 0145-505 ELMA Trivandrum: Resident Representative: Mr. Koshy Eapen. “Roshni", University Road, P.O. Palayam, Trivandrum - 695034. Tel.: 64029. Formerly Manufactured For EXPORT Only Now Sales Permitted In INDIA MFR FOR Mil Specs Performance These resistors are being exported to quality conscious users in EUROPE MFR FOR Prompt Supply adequate inventory in E24 Series for ex-stock delivery MFR FOR Most competitive prices. 1% 100 ppm costs you only Rs. 50-00 per 100 We have Special Rates for bulk orders Metal Film Resistors in 5% and 0.1% tolerance are also available. Manufactured by : MFR Electronics Components Pvt. Ltd. 40. SDF II, SEEPZ Andheri (East) BOMBAY 400 096. Marketed by: precious® Electronics Corporation • 3,Chunam Lane Dr BhadkamkarMarg Bombay-400-007. Phone : 367459/369478 • 9, Athipattan Street Mount Road Madras 600-002 Phone : 842718 <<>* n r.e" c, r<'® 8,i * \ *?£z2S€k v^^oc*- 5 ’■' \ irtS* c\*®° ftCy 0 a O '* 8 V 8 ^ 'g^t-s^ „A»d* " IVISKAl 17, Kalpana Building 349, Lamington Road, BOMBAY-400 007. Tele: 362650 WE OFFER FROM STOCK J COMTECH l.c.'s : TTL. CMOS, MOS, LSI, Microproccessor. Micro computer etc. Zener Diodes : 400 mw & 1 Watt s •’ Red, Green, Yellow in 5mm and 3mm dia 1C Sockets ; SMK & Molex make Trimpots : Multiturn Bourn's, VRN & Beckman make Single Turn cermets : EC as well as imported Floppy Discs : 8" as well as mini floppy of memorex, & dyson make ZQOSR'C ELECTRONICS CORPORATION 2/12, Hirji Bharmal Trust Bldg. M.G. Road, Ghatkopar (E) Bombay 400 077. Phone No. : 51 3722 5 NEW DOE SECRETARY The government of India has made important changes in the department of electronics (DOE) with the appointment of Mr. S.R. Vijaykar as secretary in the place of Dr. P.P. Gupta Mr. Vijaykar has been the chairman and managing director of the Electronics Corporation of India Limited. Dr. Gupta, who became secretary in May. 1 98 1 , will now go back to the Computer Maintenance Corporation as its chairman and managing director. The department will also have two additional secretaries, Mr. Ashok Parthasarthi and Dr. N. Seshagiri. MTB PLAN A new package plan called "Material, Technology and Brand name" has been announced for the benefit of small-scale TV manufacturers in the country by the Electronics Trade and Technology Development Corporation. The corporation will float tenders tor procuring 500,000 colour picture tubes and 300,000 black and white picture tubes, as a part of its effort to supply components to small manufacturers at a cheaper rate. The philosophy behind this scheme is to make bulk imports, along with technoilogy transfer, to derive cost advantage. To overcome the competition faced by small manufactures from the established units, the MTB plan allows the use of the trade name "ET andT" of the corporation by small units. Initially, the package would cover TV units but later it would be extended to video tapercorders. entertainment appliance, calculators, computers for schools, electronic telephone instruments and plain paper copiers. The MTB's another objective is to achieve standardisation of technology and components by creating a large demand and a corresponding strong base, resulting in competitive prices for the consumer items, according to the Mr. P.S. Deodhar. chairman of corporation. In the next two or three years, the colour TV sets would be fully indigenised, he hopes. At least 70 per cent of the TV units are expected to become members of the MTB and even established units are eligible to take advantage of the scheme. TELECONFERENCE The prophetic dictum, "Communicate, do not commute". (Sir Arthur C. Clarke) has become a fact of life. 1 t is such a fact that the Overseas Communication Service of the government of India will shortly offer facilities for teleconferencing among participants in four locations from different parts of the world, on a regular, commercial basis. When this facility is available, experts could save crores of rupees spent on travelling abroad, accommodation in expensive hotels and conserve precious time, just by making a visit to the conference room of the OCS. Bombay, from where one could simultaneously have a dialogue with counterparts in four other locations, thanks to the satellite communication system for video conferencing and computer networking for business and industry. The OCS was a witness to the first global teleconference on medicine, sponsored by the American Telephone and Telegraph Communications, on May 1 5. 1 984. The participants were in 24 locations in 1 8 countries across 1 1 time zones and India. Bombay and Delhi were the venues. Bombay was connected to the USA by INTELSAT satellite and submarine cable. Reception at the OCS was trouble-free. Prof. M. Samii delivered a talk on the management of tumours in acoustic nerves from Hanover in West Germany. Representatives of World Health Organisation and International Telecommunication Union gave their remarks from Geneva. Perhaps, link with 24 locations was too ambitiousi A lesser number would have been a greater success, felt the participants. PEICO PROJECTS Peico electronics and electricals limited will invest approximately Rs. 1 6 crores in a number of new projects. The company has received letters of intent for oscilloscopes, frequency counters and timers, portable diagnostic ultra-sound instruments. X-ray diagnostic systems, micro motors, tape deck mechanisms and magnetic heads, in addition to industrial licences for the manufacture of dumet wires and othe critical components. The chairman and managing director of the firm, Mr. C.J. Seelan. has been quoted as saying that the price of colour TV could not be lowered unless the components were manufactured indigenously. Fteico had already applied to the government for setting up a unit to manufacture components forcoloutTVsets. SATELLITE ANTENNA Pioneer Electronics Limited. Bangalore, have obtained licence for the prod uction ot systems for receiving TV programmes directly from statellite. This system. TVRO, will enable viewers to see programmes from 1 0 different channels and a number of TV sets can also be connected to it. The system requires a , flat area measuring 20" x 20" for installation. Each TVRO. costing about Rs. 99,000 (taxes extra) weight 600 kg, and programmes from the Middle East. USSR. France. UK. and East European countries can be received by the TVRO. it is claimed. OPTICAL FIBRES Telecommunications network in the country will soon utilise optical fibres. Two lines using optical fibres would be first installed in Madras city and over a 100 km of optical fibre would be bought from European countries and used in the southern zone, according to the Union deputy minister for communications, Mr. V.N. Patil. Experimental use of optical fibres for a telephone network at Pune had been successful and in nine months, not more than six faults were ■ reported from this segment. VCR POLICY The government will shortly announce its policy on the manufacture of video cassette record ers and video cassette players. A high-level inter-ministerial committee has submitted its report in this regard. The general expectation is that the ceiling on manufacture of 500 VCR sets may be scrapped. There shall be no upper limit or else the limit will be enhanced. There are about 50 licensed VCR manufacturers in the country. The government would not allow bulk import of VCRs under any circumstances, official sources maintain. >7-15 f the Figure 4b. . . . ZX Spectrum. of the Figure 5. This simple mains power supply, pro- viding 5 V at 1 A. suffices to power all extensions. rjuly 1984 7-25 7-26 e ZX81 and ZX Spectrum makes eight freely pro- grammable output ports and eight input ports e from figure 9 that cursor control is Table 5 10 LETZ = 86 20 LET X = 127 30 IF IN KEY $ = 5 AND X > 0 LET X = 40 IF IN KEY $ = 6 AND Z >0 LET Z = Z - 1 50 IF IN KEY $ = 7 AND S < 174 LET Z = Z +1 60 IF IN KEY $ = 8 AND X < 254 LET X = connect two joy-sticks to the Spectrum without using interface II. All you need to know is the plug pinout of the joy-stick. Figure 10 shows the standard pinout, in this case of the Atari joy-stick as used with the Sinclair interface II. If you use other types, check the pinout with an ohm- meter. Otherwise, the connections may be made as shown in figure 11 with, for in- stance, fiat ribbon cable. The program of table 5 may still be used by changing the key numbers accordingly. Video output Normally, the ZX computer is connected 7-28 to the aerial input of a TV receiver. The computer contains a UHF modulator which converts the video signal into a UHF signal similar to the one received from the TV transmitter. The UHF signal is demodulated in the TV receiver into a video signal. For normal TV broadcasts this is perfectly all right, but with a com- puter so close to the TV receiver this is, from a technical point of view, a bad solut- ion, if only for the simple reason that because of the double conversion there is bound to be loss of quality. Nowadays, single-colour data monitors (green or amber) are available at attractive prices, although normal colour versions remain pricey. Many modem colour TV receivers are provided with a SCART socket or DIN A/V socket for connecting a video recorder (the problem of some loss of quality also arises with the video recorder). However, these sockets make it possible to connect the video signal from the computer directly to the video input of a monitor or TV receiver. With both computers this is readily done by means of a small interface. The result is far better definition and, in the case of the Spec- trum, better colour reproduction. In the Spectrum the video signal is already available at the edge connector (terminal IS at the underside of the board, see also figure 4b). If there is no signal present, there is a wire bridge missing on the board. This is located close to TCI and TC2 and has been drawn in the com- ponent layout of the board. If necessary, this wire bridge should be soldered in. The signal amplitude is 1 Vpp with a d.c. offset of +2 V. The signal must be buf- fered if a colour monitor or TV receiver is used. This may be done, for instance, with the video amplifier described in our January 1984 issue. This amplifier is ad- justed so mat its output signal into 7b Q (video input impedance of the TV receiver) is also 1 V pp . Equally good results may be obtained from a simple emitter follower (see figure 12), in which the d.c. offset comes to good use! This circuit, as well as that of the video amplifier, may be used with both the Spectrum and the ZX81. As the ZX81 provides a stronger video signal than the Spectrum (about 2 V pp ), it is advisable to connect a 68 ohm resistor in series with the output signal to give better matching with the 75 Q input. The video signal of the ZX81 may be taken from pin 16 of IC1, or from a point directly connected to this and which is more ac- cessible (for instance, D9 may be un- soldered and its anode connection used). With a bit of luck it may be possible to fit the interface in the computer case. In the Spectrum you can then take the video signal directly from the input of the ASTEC modulator at the edge of the com- puter board. The connecting point is situated in the centre of one of the shorter sides of the modulator and is in easy Although the video signal is always buf- elektor indW 1984 7-29 a choice of rasta, funky, or disco beats . . . or would you really prefer the monotonous 'boom-boom' of other drum synthesizers? Contemporary music is quickly reaching the stage where it is the rule rather than the exception to use computers, or at least synthesizers, as 'instruments'. Many people see this as unnecessary but would like a small degree of electronicization in their music. Guitarists have long been familiar with phasers, flangers, echos, and so on but another essential member of any group, the drummer, seems quite happy with strictly mechanical drum sticks. Now, to throw the cat in among the pigeons, we have designed an to play with. disco Nobody could say that we neglect elec- tronic music at Elektor. Admittedly, it has been dormant for quite a while now but we felt this was necessary to give readers who are so inclined the time to come to grips with our last major work, the preset unit for the polyphonic synthesizer. The project proposed here is a more modest design; sort of a drum 'synthesizer 1 . The drum sound is relatively easy to ob- tain as it is simply a matter of generating a sinusoidal audio signal and modulating this with an envelope having a very steep attack and an exponential decay. This gives the effect of an apparent amplitude modulation due to the fact that lower fre- quencies have a greater 'impact' on the ear than higher frequencies of the same amplitude. The 2206 again . . . The circuit diagram of figure 1 shows a design with two inputs and at least three merits: it works well, it is easy to make, and it doesn't costs a lot. The two inputs could also be considered as a further merit as they expand the range of- poss- ible applications. 1 electronic drum for the drummer drum The heart of this circuit is the XR 2206 function generator (IC3) which provides the sinusoidal signal. The frequency of the signal output at pin 2 is proportional to the current flowing between pin 7 and ground. This current is controlled by tran- sistor T1 as a function of the voltage ap- plied to its base. We will see later how this control voltage is derived. A 15 V positive pulse applied to the CLK input charges Cl almost instantaneously via Dl. The discharging time across D2, which begins immediately after the falling edge of the pulse, is determined by the position of the wiper of PI. Impedance matcher IC2 is needed to pre- vent the amplitude of the envelope curve, derived from the charging and discharg- ing of Cl, from being proportional to the repetition frequency of the input pulses. The envelope signal is fed to the voltage to current converter, Tl, (via R3, P2, and R5) for the frequency modulation and to pin 1 of IC3 for the amplitude modulation. We were not satisfied with just the illusion of amplitude modulation so even with no trigger input the frequency of oscillator IC3 is within the audible range. If this were not the case envelopes with a small 7-30 2 amplitude would not even be able to trig- ger the oscillator, or, strictly speaking, to make it rise above the sub-audio range. The lowest frequency is set by biasing the base of T1 with P3, the minimum ampli- tude is decided by tuning preset P4 so that no output signal is seen from IC3 after the envelope has decayed com- pletely. The two inputs So far we have avoided mentioning the source of the trigger pulses that are ap- plied to the input. This could be a se- quencer, a rhythm box, a synthesizer keyboard, ... or any one of a long list of equipment capable of providing the (0 ... IS V) positive pulse required by the circuit. The pulse provided by the ‘O' or ‘S' outputs of the metronome published in the December 1983 issue of Elektor is another suitable possibility. If this is used the values of C2 and C3 in the metronome must be increased to about 470 n to en- sure that the pulses are long enough to charge Cl (in the disco drum) completely. A drum would not be a drum without hav- ing something to hit. With this in mind our demon drum designer came up with the piezo-percussion instrument shown in figure 2. This consists of a disc of plywood about 20 cm in diameter, a thick sheet of rubber to cushion the blows, and a piezo electric buzzer which in this case acts as a pressure sensor. The buzzer sup- plies pulses to IC1 with an amplitude pro- portional to the intensity of the blow. This signal should only be used when a fre- quency modulation proportional to the in- tensity of the blow is desired, as indicated by the different envelopes in figure 3. A 3130 was chosen for IC1 because, at rest, the output of the amplifier must return to zero to enable Cl to discharge. In the same vein the leakage current of Cl is quite important; the smaller it is the better. For this reason a pair of 2 pF non- electrolytic capacitors in parallel are to be favoured over a single 4.7 pF electrolytic. When we finished our electronic drum we decided that the best way to test it was to ask some famous drummer to try it out. No expense was spared (!) and we eventu- ally managed to get hold of the resident group at the Muppet Theater, Doctor Teeth and his Electric Mayhem Orchestra. The drummer, Animal, sat in front of the drum and then it seemed as if all Hell broke loose. A couple of hours later Doc- tor Teeth came to talk to us. ‘Hey, man, I'm sorry about your drum but Animal says it not only sounds good, it tastes good as well!’. M Figure 3. Just as the calibrated pulses supplied example, provide envelopes with a constant amplitude, the pulses given by the drum pad in figure 2 result in envelopes whose amplitudes are pro- portional to the intensity of the blows. an inexpensive high quality computer printer Sooner or later every serious computer user feels the need for a printer. A look at the price and a quick check of the bank balance generally causes a state of gloom to set in with a lot of programming time being spent humming verses of Blaise Pascal’s not-so-well- known ode Oh, for a little printer'. Now, however, there is a cure for this condition. Most electronic typewriters have a keyboard laid out as a matrix which is controlled by means of software. All that is needed, then, is to tap into the output of the matrix and feed in the codes for the characters to be printed and the machine will recognize them just as if the same key has been pressed. The best part of all is that this does not even require any drastic modifications to the existing circuit. daisywheel typewriter printer interface Table 1. An example of how the eight lowest ad- dress lines of EPROM IC1 Certain electronic typewriters that have appeared recently are equipped with an interface for a computer (such as an RS232C, Centronics, IEC, and so on). These are of no interest to us as they do not need any adapting, provided the inter- face chosen is the right one. There are others which, although electronic, are not intended to be controlled by a micro com- puter. Many of these, however, have a suf- ficiently good quality to price ratio to make them a sound proposition for modification to a high-quality printer for a computer system, even if it already has a dot-matrix printer. First, of course, there is the little matter of an interface, but that need no longer be a worry. We have designed a Centronics interface for a cer- tain type of electronic typewriter and it is versatile enough so that it could relatively easily be modified for other types of machines. The machine we chose is the Smith Corona EC1100 portable electronic type- writer, mainly because it is a simple, robust, machine with a good quality to price ratio and it is quite freely available. It is a daisywheel machine and, as we have already made clear, it serves as a reference here rather than being the only Table 1 Y7 Y6 Y5 Y4 Y3 Y2 Y1 "'' 0 0 0 0 J I 10ft 0 0 0 0 0 0 0 ' A6 A5 A4 A3 A2 At A0 Simulating the matrix decoding As figure 1 shows, the keys are arranged in a matrix of 8 x 9 lines which the pro- cessor in the typewriter (an 8039) will decode by sweeping it with a 2 ms positive pulse. When a key is pressed the pulse applied to one of the input lines of the matrix (columns Y0 . . . Y8) reappears at one of the output lines (rows AO . . , A7) and the cross-reference thus obtained tells the processor which key was pressed. Our modification must therefore place the code corresponding to the character to be printed on output lines A. To do this the ASCII code for the character must be combined with the input code to the matrix (Y0 . . . Y8) generated by the pro- cessor to form an EPROM address con- taining the exact same data that would be present on lines AO ... A7 if the key for the same character were pressed. This means that the keyboard does not have to be modified at all and can be used nor- mally. An example of this procedure (for the ASCII character ‘P’) is given in table 2 and we will return to this later. Moving on to the circuit diagram of figure 2, we see that only a few ICs are needed. The most essential one is, of course, IC1, a 2716 EPROM, whose data outputs are con- nected to the A7 . . . AO lines of the matrix. The diodes, D1 . . . D8, are included to en- sure that the existing keyboard can still be used when the interface is connected. Ad- dress lines A10 . . . A4 receive the seven- bit ASCII code for the character that is to be printed from the computer via its Cen- tronics output (D6 . . . DO). The four re- maining address lines, A3 . . . AO, receive the code generated by IC8 (a 10 to 4 line BCD encoder). This is the BCD equivalent of the input code to the matrix (Y7 . . . Y0) Table 2 EPROM IC1: addresses 18 A7 A 6 A5 A4 A3 A2 A 1 B 0 fl fl i IB 1 that is inverted by NS . . . N12 so that the 40147 will accept it. This conversion is in- dicated in table 1, the left side of which contains the configuration of the matrix lines showing the positive pulse (the 'l 1 ) sweeping the lines. The right side of the table is the resultant codes output from IC8, which are, of course, in negative logic (so T is 0 V and ‘0’ is +5 V). A specific example, outputting the code cor- responding to the character 'P', is given in table 2. The key for this character is number 29 and when pressed it links Y5 to A4. The BCD code corresponding to the matrix configuration when the pro- cessor is scanning line YS is AheX Thus the EPROM address containing the data corresponding to the ASCII character ‘P’ is constituted by codes 50 hex (ASCII 'P') and AheX- The data must be programmed such that line A4 in the matrix is activated; i.e. with 10HEX- The second EPROM, IC2, is needed for a few specific functions: shift, keyboard II (KBII), and carriage return (CR). The SHIFT A line is activated every time an ASCII code output by the micro computer cor- responds to a character in the upper j EPROM IC 1 : data D7 D 6 D5 D4 D3 02 D1 DC | fl B B 1 B 0 0 fl Table 2. An example of how the EPROM is ad- dressed for a given ASCII code Ifor the character P I. The address is 50 HEX and the data is 10 HEX . register of the typewriter keyboard. Line KBII can only be activated by the pro- cessor when line Y8 is active because of the presence of N3. This signal gives ac- cess to several special characters, further details of which can be found in the Smith Corona user's manual. Timing the signals For the CR signal we must move on to the timing of the signals. We also have to start by taking a step backwards to the moment when the data appeared at the Centronics output of the micro computer. When the data is valid the processor outputs a negative strobe pulse. This pulse triggers monostable MMV1 whose output pulse (set with PI) is about 100 ms. The BUSY line is then activated, via N2, preventing the micro computer from sending any new data to the Centronics port. This results in a printing speed of about nine characters per second. Simultaneously MMV2 produces a pulse of about 50 ms which delays the enabling (OE) of IC1 so that the codes for SHIFT, KBII, and CR given by IC2 always appear a fraction of a board of the Smith Corona EC 1100 by means CONE 2 where we find the pulse that sweeps the keyboard to detect any key that Is pressed, and CONE 1 to which we irfeH .7-33 Figure 2. The Centronics interfece is brenched parallel to the existing keyboard and simulates a key being pressed by ap- plying the pulse that ap- pears at one of the input lines IY0 . . . Y8I of the matrix to one of the out- put lines IA0 . . . A7). Potentiometer PI should be adjusted to give the maximum possible print- ing speed without the typewriter failing to print any of the characters properly. The interference threshold can be greatly improved by connecting lines DO. D6 in the Centronics socket to earth via 10 k resistors. The interface is then 'off when there are no signals second before those output by IC1. The CR pulse poses a particular problem as no character may be either received or printed while the carriage is on the return journey — unlike a printer the typewriter is not bidirectional. This is why the CR signal resulting from the GDhEX code ap- plied to IC1 and IC2 controls a third monostable to activate the BUSY line for the duration of the carriage return. Capacitor C4 in the time base of IC7 charges to a certain extent depending on the time between two CR pulses so that the duration of the carriage return is pro- portional to the number of characters in the line ended by the 0 DheX code. The typewriter automatically performs a line feed (BArEX) after a carriage return. Computers generally follow a BDreX ( cr ) with a UArEX (LE) which gives two line feeds instead of one unless the 0 ArEX code is suppressed in EPROM IC1, as we have done. This saves the trouble of having to suppress it in the computer. As we did not want to lose the line feed func- tion completely it is assigned the code 0F H EX (CTL-O). The RC network made up of R7 and CIO is used to conver t the BUSY signal (active logic high) to an ACK signal (active on the falling edge) which some Centronics inter- faces require. Construction and fitting Building this project is greatly simplified by using the printed circuit board design shown in figure 3. As usual, it is a good idea to fit the wire links first to ensure that they will not be forgotten. The EPROMs should be mounted in good quality sockets, especially if the typewriter used is not the EC 1100 as these ICs will then probably have to be removed several times until the coding is fully correct. As the layout of the printed circuit board in- dicates, the mounting point have been provided to be compatible with the case of the typewriter. To connect the interface to the typewriter a pair of 10 and 12 pin male and female connectors will be needed, as shown in figure 4. These are not strictly essential, however, as the cable could simply be soldered at the ap- propriate points on the Smith Corona’s printed circuit board, marked CONE 1 and CONE 2. The type of connection used for the Centronics input is left to your own initiative as it must be modified to what is needed. The supply voltage for the interface is tapped from the typewriter itself (pin 2 of CONE 1 = +5 V). A ground connection must be made between point ‘0’ near C7 on the printed circuit board of figure 3 2 7-34 elektof India julv and the GND point near CONE 6 (the supply connector). The current consump- tion of the interface is about 150 mA, which the existing supply can provide without any problem. When you pick up the EC 1100 to start to modify it one of the first things you will note is the lack of any type of screw holding the two halves of the case together. As with most such problems, separating the halves of the case to get at the innards is easy once you know how. The top part of the case is fitted with several plastic clips which mate with grooves in the bottom half so to separate the two the sides of the top must be pressed and lifted to release the clips. Programming the EPROMs We have purposely left the programming of the EPROMs until last. This part of the etektof India julv 1 984 7-35 daisywheel typewriter printer interface Table 4. The contents of EPROM IC1. Table 5. This is the data stored in EPROM IC2. All addresses not mentioned contain 01 HEX Table 6. D000 : 01 D 100 s 0 D010: 01 0110: 0 0020 : 01 0120: 0 0030 : 01 0130: 0 0040: 01 0140: 0 0050: 01 0150: 0 0060: 01 0160: 0 D070 : 0 1 0170: 0 0080: 01 D 180 : 0 0090: 01 D 190 : 0 D0A0: 01 D1A0: 0 0080: 01 O1B0: 0 D0C0 : 0 1 D1C0: 0 0000: 05 0100: 0 D0E0: 01 D1E0: 0 D0F0: 01 D1F0: 0 0200: 01 0210: 00 0220: 00 0230: 02 0240: 00 0250 : 00 0260: 00 0270: 00 0280: 00 0290: 00 D2A0 : 00 0280: 00 D2C0 : 01 D2D0 : 01 O2E0 : 01 D2F0 : 00 0300: 01 0310: 01 0320: 01 0330: 01 0340: 01 0350: 01 D360: 01 D370 : 01 0380: 01 0390 : 0 1 D3A0 : 00 0380 : 0 1 D3C0 : 02 0300 : 0 1 D3E0: 02 O3F0: 00 0400: 00 0410: 00 0420: 00 0430: 00 0440: 00 0450: 00 0460: 00 D470 : 00 0480: 00 0490: 00 O4A0 : 00 0480: 00 D4C0 : 00 D4D0 : 00 D4E0 : 00 O4F0 : 00 0500: 00 0600: 01 0510: 00 D610: 01 0520: 00 0620: 01 0530: 00 0630: 01 0540: 00 0640: 01 0550: 00 0650: 01 0560: 00 0660: 0! 0570: 00 0670: 0: 0580: 00 0680: 0: 0590: 00 D690 : 0: D5A0 : 00 D6A0 : 0: 0580 : 0 1 O6B0 : 0 D5C0: 01 D6C0 : 0 0500: 01 0600: 0 D5E0 : 00 D6E0: 0 D5F0 : 01 D6F0 : 0 0700: 01 D710: 01 D720 : 01 D730 : 0 1 0740: 01 0750 : 0 I 0760 : 0 I 0770 : 0 1 0780 : 0 1 0790: 01 D7A0 : 0 1 D7B0: 00 O7C0 : 02 0700: 01 D7E0 : 00 D7F0 : 01 = 0 ? -Oi 'O'? □ □ □ □ □ project may seem somewhat illogical due to the layout of the keys and their pos- itions in the matrix (as figure 5 shows). In EPROM IC2 only one sixteenth of the memory space is filled as the first four ad- dress lines are not used. The table cor- responding to the contents of EPROM IC1 is arranged according to the ASCII codes (which are not indicated). These EPROMs can be programmed by the user himself or may be purchased pre-programmed from Technomatic Ltd. Finally, a quick recap of the commands recognised and executed by the machine: CTL-K (0B H EX) = VT, CTL-H (08 H EX) = BS, DEL (7Fhex) = erase, and CTL-O (0 Fhex) = BF instead of the usual CTL-J. 7-36 The anemometer featured in our November 1983 issue contains a memory which stores the minimum and maximum windspeeds measured in the form of positive analogue voltages. A simple addition can make this memory store negative values also. The resulting maximum and minimum memory is suitable for a number of applications. As an example of these we describe an electronic version of Six's famous thermometer; other possibilities are left to your own ingenuity and imagination. maximum and minimum memory The amateur meteorologists among you where no doubt delighted with the anem- ometer and wind direction indicator published in our November 1983 and February 1984 issues respectively. Ypur weather station can now be augmented with an electronic maximum and minimum thermometer. Such a thermometer, using alcohol instead of electronics, was in- vented by the British physicist Six. It enables the recording of both the highest and the lowest temperatures reached since the thermometer was set. The circuit Only a synopsis of the circuit is given here as a detailed description appeared in our November 1983 issue. The memory ot uie anemometer stores two voltages between 0 V and 1 V, of which one represents the highest recorded windspeed, and the other the lowest. As these values are continuously compared with the current windspeed, they are always up to date. The attraction and usefulness of such circuits is their facility for retaining analogue values for a long time. The actual storing takes place in digital form in a binary counter. Before the content of the store can be compared with the current value, it is changed into an analogue voltage by a digital to analog converter. Whether the memory is up- dated or not depends on the result of the comparison. analogue voltages remembered . . . . . digitally! The memory must, however, be expanded to make it usable with negative input voltages. The temperature sensing unit can be calibrated to give an output voltage of 0 V at an ambient temperature of 0 °C. Temperatures above 0 °C result in positive voltages, those below in negative voltages. In the circuit described, the in- put voltage range can be set between -IV and +1 V. The circuit of the augmented memory is given in figure 1, which shows that the ad- ditional stage consists of an operational amplifier, A6, and associated components. The opamp, which functions as a voltage follower with unity gain, is powered by the existing symmetrical + 5 V supply. The values of R18, P3, and R19 are necessary to enable the output voltage of A6 to be preset somewhere between 0 V and —1 V. The actual value preset by P3 is somewhat more negative than that representing the lowest expected temperature. The func- tion of A6 is to shift the earth potential of the D/A converter IC9, current /voltage converter A5, and the measuring instru- ment to the preset value. The other addition is, of course, the tem- perature sensor, the circuit of which is shown in figure 2. The sensing unit, IC2, is a type LM335 which converts changes in temperature into voltage variations. Its temperature/voltage slope is 10 mV/K in the range -40 °C . . . + 100 °C. The output of IC2 is fed to opamp IC1 which arranges for the output voltage to be 0 V at an am- bient temperature of 0 °C. Output voltage Ut is then related to the ambient temperature at 10 mV/°C provided that the output of A6 can really go down to —1 V. This is guaranteed as long as R4, R5 and R6 are high-stability (1%) metal-film resistors, and P3 has been adjusted correctly. Construction and calibration The printed circuit used is identical to that of the anemometer (EPS 83103-1), which is constructed as described in the anemo- meter article, with the exception of the wire bridge alongside C9 and R16. Instead of this, break the earth connections of pin 2 of IC9 and pin 3 of IC4 and wire these pins, together with junction C9/RS, to the output (pin 6) of IC12. The circuit around this opamp, and, for that matter, the one of the temperature sensor, is so small that it is best built on a small piece of wiring (Vero) board. Start the calibration by adjusting P3 so that the output of A6 lies between —1 V and 0 V as required; normally, this will be —400 mV, corresponding to an ambient temperature of — 40 °C. Then adjust P2 to give +1 V (+100 °C), measured with a digital multimeter, at the junction R16/R4/C9. It may be necessary to enlarge R16 slightly to achieve this result. The setting of PI and the value of R17 are both dependent on the measuring instru- ment and its scale. They have to be set/computed on the assumption that the voltage at T is 10 mV/°C It is interesting to connect a digital multi- meter between T and earth, because that instrument can read negative voltages. A temperature below 0 °C will therefore be indicated as such. The same can, of course, be achieved with a centre-zero meter which has been calibrated from -40 °C to +40 °C Finally, adjust PI in the sensing circuit to give a voltage of 0 V at pin 6 of IC1 at an ambient temperature of 0 °G If you want to avoid working with ice cubes, you may adjust PI to give a voltage of 2.730 V at its wiper, measured with a digital voltmeter. lead-acid battery charger The lead-acid battery has improved so much in recent years that it can often be a good and less expensive substitute for the popular NiCad battery. A special charger is required, however, as the lead- acid battery must be charged at a constant voltage rather than constant current. The charger described in this article uses one of two charging voltages automatically selected depending on the current flowing through the battery. In this way we get an optimal compromise between short charging time and long battery life. \ / What springs to most people's minds when the lead-acid battery is mentioned is the automotive version. That is a heavy box full of acid providing the energy to start the car and needing occasional maintenance to keep it healthy. Lead-acid batteries are also used for a multitude of other applications, such as large torches, small cordless household appliances, models, and, of course, as an emergency supply for important equipment in case of mains failure. The modem lead-acid battery is available in all shapes and sizes. There are even gas-tight versions enabling the lead-acid battery to be used in many applications as a replacement for the commonly used NiCad battery. The lead-acid battery has a few important advantages over its NiCad counterpart, especially if the current requirement is fairly high. Its energy capacity is much greater than the NiCad's, and the same can be said of its output. The lead-acid battery’s greatest strength is the large number of charging and discharging cycles possible relative to the low pur- chase price (compared to the NiCad). The lead-acid battery must be charged in a completely different way than the NiCad equivalent. The latter requires a constant charging current whereas the former needs a constant voltage. The battery then controls the charging current itself so that the minimum of gases are generated. The difference between these two methods of charging is shown in figure 1. The charging voltage of a lead-acid bat- tery is largely responsible for its lifespan. It should be noted, in passing, that the life of a completely discharged lead-acid bat- tery is only a few weeks, so it is a very bad idea to simply leave a battery discharged. Using a high charging voltage gives a short charging time but also a short lifespan, while a low charging voltage results in a long charge time and long lifespan, lb give you an idea of the values we are talking about here, a General Electric gas-tight lead-acid bat- tery has a lifespan of three years with a ‘high’ charging voltage of 2.45 V per cell. It is then charged to 95% of nominal capacity in eight hours. A ‘low’ voltage charge at 2.30 V per cell increases the lifespan to eight years (provided the bat- tery is continuously connected to the charger) but the time needed to charge is then fifteen hours (see figure 2). The im- portance of the charging voltage is ap- a two-stage design to enable fast charging without reducing the battery's lifespan .7-39 ly shows the effect of charging voltage on the battery's lifespan. ■ — - ? f 1 £ A parent by the fact that the difference bet- ween the two voltages is only 0.15 V. The lead-acid battery charger must make some sort of compromise between charg- ing time and lifespan. The voltage at the last part of the charging cycle is es- pecially important for the battery's lifespan. If the current is too large it will cause a deterioration in the lead grid to which the active part of the battery is fixed. A lower charging voltage will make the current correspondingly smaller so there will be less deterioration. This is particularly important if the battery is nearly always connected to the charger. The solution for this is a charger that adapts the voltage to the current flowing through the battery. The lead-acid battery charger described here uses a two-stage system in which the charger itself switches from high to low voltage when the charging current falls below a previously set value. The circuit is not only suitable for normal charging but can also be used for applications where the battery is generally on stand-by. The charger Even though the operation may sound somewhat complicated the circuit is quite simple and, as figure 3 shows, only con- tains 16 components. It is based on an LM 317 voltage regulator (IC1) which en- sures that the voltage at the output is con- stant. This voltage is initially defined by voltage divider R5/R6 + P2. The low voltage that decides the current in the second part of the charging cycle is set with preset P2. A thyristor and a resistor (and a normally closed push button) are connected parallel to R6 and P2. When the thyristor conducts R4 is switched in parallel with R6 + P2 so that the output voltage drops somewhat (this is the second part of the charging cycle). The moment that Thl trig- gers depends on the output current. This is the reason why resistor R7 is connected in the zero voltage line. The gate of the thyristor is connected to the output voltage of IC1 via R2, Rl, and PI. If the charging current is fairly large the voltage drop across R7 keeps the potential dif- ference between gate and cathode too low to trigger the thyristor (the voltage across R7 is negative with respect to that across Rl + PI so the gate-cathode voltage >s Uri + pi - UR7). After a certain length of time the battery is charged so far that the current has fallen to the value set with PI. The thyristor is then triggered, R4 is con- nected in parallel with R6 + P2, and the output drops to the low voltage. As we have already seen, the difference between high and low voltage is quite small at about 0.15 V per cell. When the output voltage is the low value LED D3 will light. In order to prevent the thyristor from be- ing triggered as soon as the circuit is powered up, but with the battery not yet connected, a push button, SI, is included. After connecting the mains supply and the battery, SI is pressed causing the high voltage to appear at the output and a 'large' current to flow through R7. The push button is then released and Thl re- mains off as long as the current through R7 stays high enough. The charging current can be measured by connecting a meter in parallel with R7. This is indicated with dotted lines in figure 3. Calibration and use This circuit is easily constructed on a piece of Veroboard. Some of the com- ponents in the diagram have two values, one of which (marked with an asterisk) should be used for the 12 V version and the other for a 6 V version of the circuit. The IC must be mounted on a heatsink as it tends to get rather warm. The value of resistor R7 depends on the capacity of the batteries that are to be charged, as we will see shortly. The circuit must be supplied with a rec- tified and smoothed voltage of at least 3 V more than the output voltage from the regulator. The supply used must be able to provide at least 1/10 of the current capacity of the battery but this should not be more than about 1.5 A as this is the value at which the LM 317’s internal cur- rent limiting comes into action. This cur- 7-40 eleklof india jutv 1984 rent limiting does depend on the exact type of regulator used; for the LM 317K or LM 317T it is 1.5 A but for LM 317H or LM 317M the current is limited at 0.5 A. The value of resistor R7 is calculated from the formula; R7 = 0.3 V/Iswitching- The switching current (or, the current at which the circuit switches from high to low voltage charging — which seemed a bit long to put in a formula) can be set to any value. A good compromise would be a current that is 1/10 or 1/20 of the nominal battery capacity (see figure 4). The circuit must now be calibrated with the power switched on but without any battery connected. If everything is work- ing the thyristor will conduct and D3 light. Connect an accurate, preferably digital, meter onto the output and set P2 until the meter reads exactly the number of cells multiplied by 2.3 volts. Three cells need 6.90 V and six cells give a value of 13.8 V. Press SI and keep it pressed. Now measure the output voltage, which must be the number of cells times 2.45 volts (7.35 V for 3 cells and 14.7 V for 6 cells). If the voltage is not close to this value the resistance of R4 may have to be changed and P2 then readjusted. The final adjust- ment is to set the switching point with preset PI. The most obvious method of doing this is to connect a partly dis- charged battery to the charger. Rotate the wiper of PI completely towards R1 and then press SI to start high-voltage charg- ing. Measure the current through the bat- tery (by connecting a voltmeter across R7; I = U/R7) and check from time to time, every half hour or so, whether the current has dropped to the desired value. When this point is reached PI must be trimmed until the LED just lights. The charger is then ready for use. Using the circuit is very straightforward: — Connect the supply to the charger and switch on. The LED should light. — Connect the battery to the output of the charger. — If fast charging is desired press SI. The LED is then not lit. — After a certain length of time D3 lights to indicate that the switching point has been passed and that the charger is charging at normal speed. Finally, a note about the characteristics shown in this article. In principle these only apply for General Electric lead-acid 4 7-41 PCBs PSUs on PCBs building power supplies the easy way The printed circuit board has been completed and tested. It is working fine and now ready to fit into the case. But what about the power supply? Is it still that ‘Christmas tree - tacked onto the transformer terminals? It happens to most of us (or so it would seem) judging from the comments in our reader’s letters. All too often the power supply is forgotten until the last moment, especially if the test equip- ment includes a variable power supply. The ideal situation is, of course, to have a printed circuit board for the power supply as well as for the project and this is possible via the Elektor Print Service. In many Elektor circuits the power supply has been included on the main printed circuit board. However, there are a number of others that are entirely separate and the purpose of this article is to group these together as a handy reference. We have included the most useful cir- cuit diagrams and it will be apparent that many can be modified to suit specific requirements. The 78** regu- lators are interchangeable provided the transformer can supply 3 volts above the regulated voltage (e.g. the 7815 requires 1 8 V from the transformer). Remember also that the working volt- ages of the capacitors must be adequate (otherwise they could become momen- tary action switches - once!). +5 V 500 mA Issue E26, June 1977, page 6-25. This circuit with component changes will suit many applications. Board number EPS 9448-1 . 1 1 IC1 1 if „ A 7801 ■i 7-42 elektor india july 1984 olOpdOo +15 V 250 mA and -15 V 250 mA Issue E42, October 1978, page 10-38. Originally designed for the Elektor TV scope but very .useful where op-amps are used. Board number EPS 9968-5a. Miscellaneous (not on p.c proper, see figure I Trl - mains transformer. 2 x 18 V/250 mA SI * double-pole mains si FI - fuse, 100mA +15 VIA Issue E31 , November 1977, page 1 1-37. Board number EPS 92 1 8b, limited stocks still available, price £ 1.0S. m ^ cHK» o-ih^> 0 PPINTTAB' 0 PPINTTAB' 0 PPINTTAB' MERGE UTILITY- PRINT iPRINTlPRINTTAB' 101 "wr i * ten b 2050 PRINT iPRINTTABt 10 ' " f eb . 19. 1984 2060 PRINT jPRINT iPRINT 2070 PRINT'Be sure that both files to b 2090 PRINT “wi th the RSEO utility to ren PRINT! INPUT- In which drive are the 0*=LEFT* :D=ASC :IF D-Y- THEN2140 REM RESET MEMORY INPUT POINTER POKE9098 . 0 : POKE9099 , 128 I DISK 2270 FOR X-1T0 LEN' 2280 POKEA.ASCtMIDI 2298 NEXT 2300 P0KE8993, 16 7-48 elekta BASIC HEXDUMP ! begin. As soon as it knows the unit where the files can be found (D$) and their names (F$ and S$ are two arbitrary names that must be in the directory of the unit designated by D$ — lines 2000 . . . 2160) the processor initializes the pointer in- dicating the start address where the file transferred to memory can be found. It then loads a machine code program and a look-up table at $E400 (from sector 7 of track 12; this is part of the space after the directory!). The machine language pro- gram is started by the GO instruction at line 2180. This loads the series of instruc- tions found in the right side of table 2 in direct mode (ie. without line numbers) in- to the area from $8000 on. From line 2190 to line 2290 the BASIC program places the names of the files that are to be merged (F$ and S$) in direct mode after the two LO instructions that have just been loaded. The instruction at line 2300 pro- grams the distributor to make the memory the input divice. The BASIC editor then receives the sequence of instructions starting at $8000 as if they were input one- by-one via the keyboard and it then ex- ecutes them one after the other. What this means is that it loads file F$, transfers it to $8000 (LIST S), and then loads file S$ and transfers it, in turn, to the space after F$. It then executes the DISK! "GO E452” in- struction which is the last it receives in direct mode from the memory as an input device. The machine-code program at $E452 places a POKE 8993,1 instruction in direct mode after the two files loaded at address $8000 and as this instruction has no line number it will be executed as soon as the interpreter meets it. The purpose of this last command is to reestablish the input distributor in its original form where the keyboard is the input device. Now the BASIC editor loads files F$ and S$ into its workspace to form a single new file which it compacts and lists as it goes along. When it arrives at the last numbered line in the second file it finds the POKE 8993,1 instruction which it executes in direct mode thus making the keyboard again the active input device. If a LIST instruction is now given the display on the screen will show that the workspace does, in fact, contain files F$ and S$. RSEQ In order to be able to effectively merge existing files it is essential to be able to easily manipulate the numbering of the lines in both files and then later of the single file resulting from the merger. On disk 2 of the 5 supplied with the Ohio Scientific DOS is a utility program called RSEQ that could be used to perform this task. Until now none of the myriad articles on the various aspects of the Junior Com- puter have dealt with adapting disk 2 for the Junior. The hexdump given in table 3 does just that, enabling JC users to easily change the line numbering of BASIC files, especially those that are to be merged. The adaptation procedure is quite simple. First copy the master diskette (this is always advisable as a safeguard) and then load track 0 of disk 2 by means of the TRACK 0 R/W UTILITY (RA200) at address $A200 (or elsewhere). The contents of this track must then be changed according to the hexdump in table 3 and the modified first page of track 0 is then reloaded to the diskette (WA200/2200.8). And that’s all folks! U Table 3. Diskette 2 from the set of 5 supplied with the Ohio Scientific DOS contains a utility. RSEQ. renumber lines in a file. The hexdump given here lists the modifications needed to adapt this for ijuly 1984 7-49 echo sounder Running a yacht aground does not necessarily mean its destruction, or even that there is any damage, but no skipper is happy with it. At best, it means a lot of effort to get the craft afloat again; at worst, well that does not bear thinking about ... It can safely be said that many such mishaps could have been prevented by the judicious use of some sort of sounding apparatus! sonar for yachts MMV = monostable FF = flip-flop (bistable one 1C. Furthermore, a 'shallow depth' alarm has been provided. In the past, sounding, that is, measuring the depth of the sea bed, was carried out by a weighted line, the sounding-line. Nowadays, these are found almost ex- clusively on board yachts only. They con- sist of a ball of lead (the weight) and a line that has been marked suitably at regular intervals, so that when the lead touches the sea bed the depth can be read off the line. The big disadvantage of such a sounding-line is that it can only be used at low speeds and at shallow depths. The echo sounder does not suffer from these disadvantages and, moreover, its in- dicator may be mounted in the wheel- house near the other navigational aids. An echo sounder is a sonar system that measures the time interval between the transmission of a burst of ultrasonic energy and reception of the consequent reflected waves. In this, a specially designed electro-acoustic transducer is used of which the transmitter is called an underwater sound projector, while the return echo is detected with a hydrophone. The usual configuration of an echo sounder is shown in figure 1. The sound projector transmits a pulse in the frequen- cy range ISO . . . 200 kHz. This pulse is reflected by the sea bed and detected by the hydrophone. The hydrophone converts the echo into an electrical signal which is used to fire a small neon tube which is motor-driven at uniform speed along a concentric, calibrated disc. The neon lamp thus fires at a scale division cor- responding to the depth sounded. As the pulse is transmitted at exactly the moment the neon lamp passes through zero, the depth can be read off directly. Experi- enced skippers are also able to deduce the type of sea bed. For instance, sandy ground causes a narrow flash of light, stony ground a wider one with a frayed top, and soft ground an even wider one with a frayed bottom. The present design has a digital read-out 7-50 common. During transmission, this circuit 1 7-51 he circuit of ally of the r ICO), clock IC3/IC4, pulse IC5. counter/ der IC1, and splay. The is connected to the modulator and during reception to the amplifier. This has, of course, the advantage that the transmit and receive frequencies are identical and, moreover, the absolute frequency is not terribly important. The 200 kHz pulse from the modulator is amplified in the output stage and applied to the sound projector via driver T8 and inductor L2. This inductor, together with the self-capacitance of the sound projec- tor and C22, forms a circuit which is tuned to 200 kHz. In the interval between transmit pulses, the echo is detected and evaluated. It is applied to the 1st h.f. amplifier and then, via P4, to the 2nd h.f. amplifier which is now connected to Iil/C14. The poten- tiometer enables setting the sensitivity of the echo sounder. The output of the selective amplifier is applied to a threshold detector which only reacts to signals which lie above a certain level. Noise pulses on the signal are suppressed by a combination of pulse recurrence detector and integrator. If the pulse train is interrupted, the pulse recurrence detec- tor evaluates the received echo as spurious and causes integrator capacitor C15 to discharge. If the received pulses are too short (as, for instance, noise pulses), C15 does not charge fully and the pulses are rejected as spurious. If the detector is fed with a true echo, the display driver is switched on. A protection circuit briefly switches the receiver off if the display driver has been on too long. This is effected by the charging of capacitor C19 from the signal at the driver stage; when C19 is charged, an on-chip transistor is switched on. Capacitor C9 ensures that the gain of the 2nd h.f. amplifier is low immediately after a pulse has been transmitted to prevent any ringing of the transducer being evaluated as an echo. This causes the minimum depth that can be sounded to be around 2 m. If this is not acceptable, the value of C9 may be reduced. Note that the sensitivity in that case must also be Construction and assembly The most important aspect is, of course, the fitting of the transducer: some possibilities are shown in figure 5. It is essential that it is fitted perpendicular to a line drawn through the length and to one drawn through the width of the vessel. It may be necessary to mount the transducer onto a suitably shaped adapter as shown in figure Sc. If the hull is of fibre-glass, the whole assembly may be fitted in-board. The cable from the transducer to the elec- tronic part of the echo sounder must not be tied together with other cables, as this might give rise to noise pulses which would upset the proper operation. An im- portant point here is NOT to shorten the cable provided with the transducer! If you already have an echo sounder, there’s no need to buy another transducer, as the one you are using already is almost certainly suitable for the present circuit. The VDO Echo Sounder Modis 120 (operating on 200 kHz), or Spaceage, Euromarine, or Seafarer (all operating on 150 kHz) have transducers which can hardly be told apart. All these transducers are available at most ship's chandlers or marine electrical suppliers. Construction of the electronic part of the echo sounder on the printed-circuit board shown in figure 6 is child's play compared with the fitting of the transducer. Inductor L2 must be hand-wound, but LI may be bought ready made. The three-digit display is constructed on the printed-circuit board shown in figure 7. The voltage regulator and its heat sink should be fitted at the track side of the board onto suitable (insulated) spacers or, properly insulated, at one of the side- walls of the case. The two pc boards should be screened from one another by an earthed metal plate. Same-name ter- minals on the two boards should be con- nected to one another. Warning! The earth connection of CL (figure 7) is not at the same side of the board as CL. Terminal DS on the same board should be connected to earth with a wire bridge, and DP should be wired, to +5 V. The case should be plastic or metal and — important — splash-proof. Spindles of potentiometers and switches, LEDs, and sockets, must be sealed during fitting. The red perspex display window must be fixed to the case with water-proof glue. Do not forget the connections to the 12 V ± 2 V supply. Before fitting the boards into the case, the circuits have to be calibrated. 1th P4. while P3 enables ippression. Tuned circuit I/C14 is common to the 7-53 Calibration First, adjust P4 for maximum sensitivity of the receiver. Next, place the transducer at right angles, and at a distance of 0.5 m, to a reflecting surface. If the transducer has already been installed, place a reflecting surface similarly in front of it. Then adjust the core of inductor LI so that the display indicates 2.3 (metres). This figure results from the fact that in identical time inter- vals sound in air travels only 0.217 as far as it would in water. Since the simulated water depth is 0.5 m, the circuit behaves as if the depth were 0.5/0.217 = 2.3 metres. Then vary the distance be- tween the transducer and the reflecting surface: in air this lies approximately be- tween 0.5 and 1 ... 1.5 m, corresponding to a displayed depth of 2.3 to 4.6 .. . 6.8 m. The change in distance must be clearly indicated by the display; if it does not, the core of LI must be adjusted until the real maximum sensitivity has been found. If you have an oscilloscope available, calibration is somewhat easier. But BE CAREFUL with connecting a probe to IC9 because if any two pins of this IC are short-circuited, it gives up the ghost. Let our (unfortunate) experience be a warning to you! Connect the probe of the oscilloscope to pin 1 of IC9 and trigger the oscilloscope with the signal at pin 3 of IC5. Then adjust the core of LI for maximum amplitude of the echo which is visible a few milli- seconds after the transmit pulse (see photograph). The current consumption of the echo sounder with the display on is about 200 mA or an average of 40 mA at 12 V. Some final points Inductor L2 must be home-made on a suitable pot core of about 18 mm diameter and 11 mm height. The inductance of the secondary winding, L2b, should be such that the resonant frequency of the circuit formed by it, the transducer self-capaci- tance, and C22 is exactly the same as that of the transducer. It may be calculated f = l/2n^LC where f is the resonant frequency in Hz, L is the inductance in H and C is the total capacity in F. 7-54 ^ Au< H°3oH > o o o o o o Z H > Splash-proof cas 12 V supply cat Piezo buzzer PB PC board 84062 By transposition, L = l/4n*PC which with f = 200 kHz, C = 3n2 gives a value for L2b = 198 The corresponding number of turns, N, is calculated from N = V L2b/Ls, where Ls is the specific inductance of the pot core. If, for instance, Ls = 250 nH, the number of turns works out at 28. If the turns ratio, n, is chosen at 1:9, L2a must be 3 turns. When a pot core with different specific in- ductance is used, the above calculation for N must, of course, be redone; the turns ratio may be kept at 1:9. Equally, when a different transducer is used, the inductance of L2 must be recalculated. Furthermore, if the frequency is not 200 kHz, capacitor C14 should be recalculated from C14 = l/4n l PLl, where f is the new frequency and LI = 630 mH. The depth at which the ‘shallow depth' alarm is actuated may be set with the aid of the following formula depth (m) = 9xlO^(Pl+R16+R17) where PI, R16, and R17 are in ohms. Where the transducer is not fitted at the deepest part of the vessel, measure the distance, Dk, between the underside of the transducer and the lowest part of the keel. Replace the 4098 in the 1C6 position by a 4538, change C9 to 12 n, and connect a resistor Rk in series with R13. The value of Rk is calculated from: Dk = gxlO^OUc+lO 4 ), where Dk is in metres and Rk in ohms. Therefore, Rk = 10 6 Dk/9 - 10' If, for instance, Dk = 1.5 m, the value of Rk = 157 k. The display will then, of course, indicate the depth between the deepest point of the keel and the sea bed, not that between the transducer and the sea bed. Warning! When setting and calibrating PI, Dk must, of course, be borne in mind. M 7-56 The display of this versatile audio peak meter is formed by a row of LEDs and features a 'peak hold' facility that can be used while the normal signal levels are monitored. The meter includes an input buffer stage that can be switched to enable the monitoring of signals at loud- speaker level or at line output level. An optional variable-frequency band- pass filter is also included. audio peak meter. . . 1-40 dB/decade) Display driving circuit ■ LED switching thresholds (dBI -40. -20, -10, -6. -3.0, *2. +4, +6. +8. +10 ■ typical corresponding peak power levels (W) 10 J . 10-' , 1 . 2, 5. 10, 15. 25, 40, 60, 100 ■ input voltage for +10 dB switching threshold: 10 V (d.c.) . . . with peak hold facility Figure 1. This diagram shows typical constituei stages in an audio peak As the input sensitivity can be matched to either line level or power amplifier output level, the audio peak meter may be used with virtually any sound system. Line level inputs may lie between 1 50 mV and 5 V while the power handling capability ex- tends up to 250 W. Other characteristics are shown in the box at the beginning of this article. The display characteristics may be tailored to provide a peak response or a simulated VU response. Like many circuits of this nature, the present one can be broken down into various stages as shown by the block diagram of figure 1 . The first stage is the input buffer which includes gain adjustment for the input level matching. The variable band-pass filter is an optional stage that may be useful in particular applications. The next stage consists of a full-wave rectifier and provides overall gain adjustment for the following peak and buffer stage. Finally there is the display decode section. The display is formed by a row of LEDs with either ‘dot’ or ‘bar’ mode of operation. The circuit diagram The input shaping circuit The various inputs to be monitored are selec- ted by switch Sla in the input buffer stage of the circuit diagram shown in figure 2a. Position 1 of Sla connects the input to earth and this is therefore the ‘off position. Position 2 selects a calibration signal input, of which more later. The loudspeaker power level input is selected by position 3 while various line outputs are selected by positions 4, 5, and 6. This method allows the meter to be used readily for monitoring in widely differing situations. The gain of the input amplifier is adjusted automatically by switch Sib. The addition of suitable resistors to positions 4, 5, and 6 enables the peak meter to cater for a wide range of input levels. The next stage consists of a variable-fre- quency band-pass filter which enables selective metering of the signals as in a real-time analyser. The stage has unity gain and may be omitted as required by simply connecting the output of input amplifier A1 1 7-57 Figure 2a. The input signal shaping circuit complete directly to the non-inverting input of op- (via R32 and R33 respectively) are about with the optional band- amp A4 with switch S2 in position 2. The equal and produce a simulated VU response. pass filter based on A2. other portions of S2 select the required The final stage of the input shaping circuit filter response. consists of an output buffer, opamp A7, Position 1 provides a high-pass response which adjusts the gain in the 'peak' and 'VU' and constitutes a rumble filter. Position 3 positions, connects the non-inverting input of A4 to earth, which switches off the opamp. The The display drive unit remaining positions, 4 ... 8, select various The display (see figure 2c) consists of a row frequency bands that are provided by a of LEDs: the switching threshold for each Wien bridge band -pass filter constructed LED is determined by resistors R38 . . . R61. orauud opamp A3. The reference voltages, Ur, fixed by these The output of the variable band-pass filter resistors are applied to one of the inputs is passed to a precision full-wave rectifier of comparators A8 . . . A18, while the input consisting of A4 and A5. Preset P2 in the signal from A7 is fed to the other inputs, feedback loop of opamp A4 provides gain Note that the polarity of the comparator adjustment applicable to all input levels: it inputs depends on the input signal and on is adjusted at the appropriate calibration Ur. When the level of the input signal input level. Operation of the rectifier is as exceeds that of one of the thresholds, the follows: opamp A4 increases the magnitude relevant comparator switches off and its of both positive and negative signals by the output is pulled up to +9 V. forward voltage drop across diodes D1 and Switch S4 selects a moving dot or bar D2. The resultant signal is rectified by A5 display. In the bar mode, the outputs of and the consequent drop across D3 and D4 gates N1 . . . N10 are held high. When any cancels that introduced by D1 and D2. comparator switches off, the corresponding The rectifier is followed by a peak charging AND gate, Nil... N20, receives a second stage, opamp A6. The peak sampling re- high input and thus provides a high output, sponse is selected by switch S3: it is effected This results in the LED in that particular by the discharge of capacitor Cl 5 via switch- channel being switched on. selected resistors R28 . . . R30 in series with In the dot mode, the outputs of gates R31 and/or R32. N1 . . . N10 are dependent on the state of In position 4 the discharge resistor has been the output of the next higher comparator, omitted: this results in a very slow dis- When a given comparator output is high charge rate which is only due to the input while the next higher output is low, both in- currents of opamps A4 or A5 and the puts of the relevant AND gate, Nil . . . N20, reverse (leakage) current of diode D6. are high so that the appropriate LED lights. In position 5, the charge and discharge rates However, when a given comparator output is 7-58 elektc 2b TT “S” ~S T T IC1 IC6 IC13 © _£ jL Figure 2b. The full-wave and peak charging stages. high while the one above is also high, both the NAND and AND gate outputs will be low, and the LED will remain off. In the dot mode, therefore, only the topmost compa- rator with a high output causes an LED to be switched on. A further facility of the display is that of ‘peak sampling’, which means that the highest LED that lights will remain on until the 'peak display' function is disabled. The four R-S latches of IC9 are controlled by switches S5 and S6 and provide the peak sampling. The latches are enabled when both switches are closed and reset by the brief opening of S6. Each latch reset is also con- nected to the outputs of all higher latches via diodes D7 . . . D12. The latches are set whenever their LED is switched on by the display logic. However, the diodes effec- tively provide an OR reset to the latches with the result that only the uppermost latch to be set will hold an LED on. The operation of the normal dot or bar mode is independent of the peak display and a latched peak LED will therefore not hold lower LEDs off. This means that a peak level may be held while the normal dot or bar mode continues to function. Calibration It will be patently obvious that any level indicating mechanism is only as good as its calibration, a fact any pilot who survived a duff altimeter will tell you! Initially, the calibration input level should be set to suit the power levels to be moni- tored: the one used here is 950 mV (d.c.) which corresponds to 10 W (peak) into an 8-ohm load. All preset potentiometers should be set to the middle of their travel, and switches SI ... S3 set to the following positions: 51 - position 2 (calibration input) 52 - position 2 (filter bypass) 53 - position 2 (peak response) Adjust P2 to the correct output from opamp A7. It may be necessary to adjust P3 if the reading cannot be achieved with P2 alone. The output may be monitored on a DVM (digital voltmeter) or an LED display. Next, move S3 to position 5 (VU mode) and adjust P4 for the appropriate reading. The loudspeaker input can now be calibrated by setting SI to position 3 and adjusting P2. Calibration of the line inputs is more sub- jective. If a line input is to be used with a tape recorder, the recorder metering may be used for comparison, particularly if it responds to peaks. In that case, a steady audio tone from a test record or oscillator is required, but inter-station hiss replayed from tape is an alternative. It should be noted that the line output should be used when the recording level of a tape recorder is monitored. Where tape recorder metering is not used, the line level may be calibrated to a direct voltage derived from equipment specifi- cations or by calculation. It may then be necessary to multiply r.m.s. values by 1.414 (\/2) to get peak values. A line voltage often used for 0 dB (the Dolby level) is 500 mV peak. Whatever method is used, PI should be adjusted to obtain the appropriate level at the output of opamp A7. Switch SI must be set to one of the line inputs (4 ... 6) while switches S2 and S3 should remain in position 2 (filter bypass and peak response respectively). M The ‘normal’ level used in audio engineering is 1 mW into 600 n (= 775 mV across 600 «) and is conventionally designated 1 7-59 marcs tubelights of 2" in series. This el unit gives normal tubelight illumir AUDIO CASSETTES La Safari Industries are manufacturing "Safari” cosmic memory audio cassettes in three ranges-CM60. CM90 and HCIO. Further information can be obtained from : For more information, contact : Instrument Control Devices. 14. Advance Industries. Tinwata Building. Manorama Niwas. Datar Colony. Tribhuvan Road. Bombay-400 004. Bombay-400 078 DIAL TESTER Sbaj electronics offer digital insulation tester-cum-dial tester, designed with 1C and seven segment read-out display, which can measure insulation of cable in 4 M Ohms and 1 0 M Ohms range. It also measures telephone dial speed, impulse count and weight break ratio. FREQUENCY COUNTER Vasavi Electronics have developed one of the smallest digital frequency counters. VDC 1 8. which operates on battery and mains as well With seven digit. o,5” LED display its frequency range is 30MHz sensitivity. 1 0 m.v. Another, model VDC 1 9 has a frequency range upto 500MHz. For more information contact : La Safari Industries. 7 7. Tribhuvan Road. BOMBAY-400004. ^ More details can be had from : ™ Sbaj Electronics. 19. Mother Gift Building, Grant Road. Bombay 400017. For details contact : Vasavi Electronics. 162. Vasavi Nagar. DIN TRANSFORMER Secunderabad-500 003. „ . Dm type current transformers, confor- ming to DIN 42600. housed in ABS plastic casing, lot metering applications are available with Meco instruments. The transformers are made in a standard range from 50/5A with a burden of 1 .5 A upto 600/5A with a burden of 1 5 KVA. POWER SUPPLY Spectron offers "Uninterruptible power systems” in the range of single phase output upto bKVA and 3-phase outputs upto 10 KVA. Systems with single phase or 3-phase inputs are avai- lable. Automatic, solid state static switches ensure instanteneous switch- ing over. P-CLIPS Novoflex have introduced non-corrosive and non-conductive P-clips for fixing cables, pipes and components in domestic and industrial appliances. The adjustable type AP clips over cable or cable loom ranging from 1 4 mm to 30 mm. Type BP are adjustable through four fixing holes. The P series non-adjustable clips are available in cable loom diameter range upto 1 2 mm. ponents redundant, soldered circuit appi For more details, write to Selectronics (Gujarat) priv. Ruxmani Park. Kankaria. Ahmedabad-380 022. 'limited, 5. COMPONENT BIN To support 10 tP" tape sf. speed of 100 IPS. will also . by Sujata. i details can be obtained from Further details are available with Anika Instruments Private Ltd.. 12/4, l/lilestrone. Mathura Road. Faridabad 12 1 003. TEMPERATURE INDICATOR A portable digital temperature indicator. ESD-100, has been developed by Elec- tronics systems and devices, manufac- turers’ of electronic process control instruments. Housed in a small, plastic moulded cabinet with LCD. ESD-100 is designed to measure in the range 0 to 1200 degree C. The source of power supply is a 9V battery. Mechanical vibrations and holding position do not affect the accuracy of the reading. The company has also developed a digital temperature indicator/controller, called ESD-90/ESD-92. For further information contact Industrial Research Associates. 302. Acharya Commercial Centre. Near Basant Talkies. Chembur. Bombay 400 074. LCD-DPM Lascar Electronics of Wiltshire have intro- duced a low power LCD DPM with digital hold of displayed reading. Consuming just 1 mA from a 7 to 15V supply, the DPM 10 features auto-polority auto-zero, 200mV f.s.d.. low battery indication. 1 2. 5 mm digit height and programmeable decimal points. Time engineers have devised Component bin IS-2 1 for storing and easy handling of electronic and light engineering compo- nents on the assembly table. A 300 de- gree swing of the trays facilitates two operators to work simultaneously. Electronics Systems and Devices. 38-39/7. Hadapsar Industrial Estate. I Pune41 1 013. For more details, write to . Time Engineers. P.Box. 308, M.I.D.C. Railway Station. Satara Village Road. Aurangabad-431 005. PERTEC'S PRODUCTS Pertec peripherals corporation, USA, markets its products on computer peri- pherals in India through Sujata sales and electronic limited. This firm will also be re- sponsible for maintenance of all Pertec equipment sold in India. Pertec's popular product range includes vacuum column tape drives, tension arm tape drives, the streaming tape drives and Winchester cartridge disk drives. In addition. "Sujata” markets printers, disk drives, floppy disk drives and termipals. are widely used in the Indian computer industry. Pertec's "Vindicator" series t/2" streamer tape Contact: For more information contact : Al-Ameen commercial and industrial Sujata Sales & Electronics Ltd. 11 2. Bajaj company limited, 23/1. Second floor. Bhavan. Nariman Point. Crescent Road. Bangalore-560 OO I. Bombay-400 02 1 . Trade enquiries maybe addressed to Electronics India Co, 3749. Hill Road. Ambala Cantonment 133001. EPOXY-COATED RESISTORS High voltage, high values, epoxy-coated resistors are made available by the Bangalore-based Al Ameen commercial and industrial company to withstand pulse voltages of upto 1 500 volts. The resistors with close tolerances find appli- cation in black and white and colour tele- 1C1I KCta SOLAR CELL TESTER An instrument to test solar cells and solar panels. Solarest-900 1 . produced bv Anika can be used for testing photovol- taic solar cells and solar panels at con- stant voltage or constant current in forward and reverse basis. It can plot IV and P V curves and compute open circuit voltage and short circuit current. GAUSS METER For measuring DC magnetic flux density. Industrial Research Associates have developed a G ' uss This gauss meter is cased on the hall effect. For measunng flux in small gaps thin probes are supplied. The instrument may be usd for routine checking of permanent used ma- gnets, alectro-magnets, solenoids, relays, radar and microwave equipment. DC machines, loudspeakers and magnetic crack detection. ECHO REVERB UNIT Selectronics (Gujarat) private limited have introduced a solid state device. Echo Reverb Unit" to produce echo, rever- bration and a host of other interesting effects. The unit can be easily added tq any existing audio or music system and it can also be used for recording echo 7-62 Multimeter incorporates frequency meter The model 1504 from Thurlby interface. PSU. integrating software and all 8 mm in 33 m rolls associated cabling. Astec's research and Copperfoil Enterpr development division is already working 141 Lyndhursx Dri capacities of 256 K/bytes per 50 feet of Essex RU11 1JP. tape. Eventually it is anticipated that Telephone: 040 24 capacities in excess of 1 megabyte will i housed in a newly designed high BS case which incorporates a tion tilt-stand/handle. A carrying ailable for portable applications. Telephone: 507M Thurlby . 16 and 20 uit boards, is ributor Nietrc Copperfoil tape t 24 V. 'intellige _^TOn\ \ READERS] [epS printservice Many of our circuits are accompanied by printed circuit designs. Some of these designs, but not all. are also available as ready-etched and pre-drilled boards, which can be ordered from our office. A complete list of the available boards is published under the heading 'EPS print service' in every issue. Delivery time is approximately three weeks. It should be noted however that only boards which have at some time been published in the EPS list are available; the fact that a design for a board is published in a particular article does not necessarily Technical queries Please enclose a stamped, self-addressed envelope; Letters should be addressed to the department concerned - TQE (Technical Queries). Although we feel that this is an essential service to readers, we regret that certain restrictions are necessary: 1. Questions that are not related to articles published in Elektor india cannot be answered. •2. Questions concerning the connec- tion of our designs to other units (e.g. existing equipment) can- not normally be answered. An answer can only be based on a com- parison of our design specifications with those of the other equipment. 3. Questions about suppliers for com- ponents are usually answered on the basis of advertisements, and readers can usually- check these themselves. 4. As far as possible, answers will be on standard reply forms. We trust that our readers will understand the reasons for these restrictions. On the one hand we feel that all technical queries should be answered as quickly and completely as possible, on the other hand this must not lead to overloading of our technical staff as this could lead to blown fuses and L reduced quality in future issues. INTIMATE FRIENDS OF AN ELECTRONIC ENGINEER Diumuiul ^D H ES ;E DESOLDERING ThreSeal I VASAVI’s VLCR7 SAVES YOU FROM AGOIMY OF BRIDGES. « capadtanct • MODULAR Constr M/s. VASAVI ELECTRONICS 1 62, Vaaavi Nagar, SECUNDERABAD-500 003. Ph. 70995 Grama: VELSCOPE mm n ■» l. ............ . MMMBIW"^-****** IV**« i PPP*P*PM9BB3ltt| ssskik- :;■ ■ • «aaRH«S!d hmk: rn<; n i*'>tt mj . :s l t ir *■'”«, t* pi i||||d ■■■■fe^Maki.aa.^a^ii.MMUM'.iu.L^iWjr'"'"'" Improved designs with maximum performance at minimum cost Aplab is the largest Indian manufacturer and exporter of worlddass Oscilloscopes. NOW AVAILABLE EX-STOCK Aplab 3030 15 MHz compact single trace oscilloscope * DC-15 MHz bandwidth * 5mV/div. sensitivity ’ Built-in component tester * One x 10 probe free * Aplab 3131 * 15 MHz dual trace triggered oscilloscope * DC-15 MHz bandwidth ' 5mV/div. sensitivity on both channels * Built-in component tester ‘ Two x 10 probes free Other models available at short deliveries 3033-15MHz, Battery operated • 3034-15MHz, Dual, Battery operated • 3035-10MHz, Wide screen • 3337-30MHz, Dual • 3339-30MHz, Dual, VDU scope • 3536-50MHz, Delayed sweep. Dual • 3537-50MHz, Dual • 3538-50MHz, Dual Storage scope. Applied Electronics Limited Aplab House, A-5 Wagle Industrial Estate. Thane 400 604. Phone: 591861 (3 lines) Telex: 011-71979 APEL IN. 8/A Candhi Nagar. Secunderabad 500 003. Phone: 73351. 22C, Manohar Pukur Road, Calcutta 700 029. Nos. 44 & 45 Residency Road, Bangalore 560 025. Phone: 578977 Telex: 0845-8125 APLB IN. MF-3 Stutee Building, Bank Street, Karol Bagh. New Delhi 110 005. Phone: 578842 Telex: 031-5133 APLB IN Hplab —Leadership through technology Philips PP 9006 E/X Digital Multimeter Incredible performance at a believable price! Full 4 digit display for extreme accuracy and precision. Philips PP 9006 E/X with very wide voltage and current ranges offers full 4 digit resolution and accuracy. True rms measurements enables AC signals to be measured independently of wave form and distortion. An optional probe can be added on, to measure temperatures. PP 9006 E/X. a no-compromise 4 digit multimeter with the proven convenience of autoranging Small and sturdy and, built to international standards. Another advanced Philips Multimeter: PM 2502 — General Purpose Multimeter For further details contact: Philips India Plot 80. Bhosari Industrial Estate Pune 41 1 026 PHILIPS Philips — the trusted Indian household n, classified ads. advertisers index CONDITIONS OF ACCEPTANCE OF CLASSIFIED ADVERTISEMENTS 1) Advertisements are accepted subject to the conditions appearing on our current rate card and on the express understanding that the Advertiser warrants that the advertisement does not contravene any trade act inforce in the country. 2) The Publishers reserve the right to refuse or withdraw any advertisement. 3) Although every care is taken, the Publishers shall not be liable for clerical or printer's errors or their consequences. 4) The Advertiser's full name and address must accompany each advertisement submitted. The prepaid rate for classified advertisement is Rs. 2.00 per word (minimum 24 words). Semi Display panels of 3 cms by 1 column. Rs. 150.00 per panel. All cheques, money orders, etc. to be made payable to Elektor Electronics Pvt. Ltd. Advertisements, together with remittance, should be sent to The Classified Advertisement Manager. For outstation cheques please add Rs. 2 50 Electronics Tools like Soldering Irons, Pliers,, Cutters, Screw Drivers, Tweezers at Competitive Prices. Con- tact Aradhna Electronics (P) Ltd., 10, Srinath Complex, Saro|inidevi Road, Secunderabad 500 003. Telephony Intel Continental requires distributors/dealers for: Telephone S T D Locks. Digital Wall/Table/Car Clocks. Insect Killer. Bank Token Indicators, LE Ds. Chairing 39. Sangram Colony. Mahavir Marg. APLAB ARUN ELECTRONICS CALOMIX COMPONENT TECHNIQUE ... COSMIC DOMINION RADIOS ELECTRICAL INSTRUMENT CO ELCOT ELMATRONICS GENERAL SALES AGENCY . . . 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Cosmic pro power amplifiers are available in a range from 30 watts total output to 600 watts total output. Select from the widest range of amplifiers in India, matched with appropriate speakers, and play your kind of music on turntables and tapedecks - all by Cosmic, the. pioneers in stereo systems in India, with over a quarter century of experience in manufacturing and § marketing quality sound equipment. International quality created for India by COSHHC Printer & Publisher - C. R Chandarana. 2. Koumeri. 1 4th A Road, Khar, Bombay -400 052. & Printed at Truoti Offset. 1 03. Vasan Udyog Bhavan, Off Tulsi Pipe Road. Lower Parel. Bombay-400 01 3. COOTC taaxo- EU * tFSl — fj t_?OoO' O Q[ 'O 'O^ o © — n ■ n -- - - : _ t! "0 1/ L ^ ® f 7 ' p^rrrp—