ISSN 0970-3993 Volume-7, Number-8 August 1989 Address : ELEKTOR ELECTRONICS PVT. LTD. 52, C Proctor Road, Bombay-400 007 INDIA Telex: (011)76661 ELEK IN CONTENTS Editorial A testing Special Features The invisible invader, ELCOM stems it Lin CMOS circuits Practical filter design (7) Computers Floppy disk monitor Universal MIDI Keyboard interface General Interest DC-AC power converter The digital model Science & Technology The versatile cable that tells a tale Test pattern generator Tracking Information Telecom News Industry News Electronic News Appointments Classified ads Index of advertisers Printed at : Trupti Offset Bon Copyright ® 1989 Elektuur B.V. A TESTING TIME Our society has become highly dependent on technology. We have nearly become slaves of the technology. Or so it seems, when we visualise a scenario where no satellite is in the sky for the benefit of the Indian people. The latest mishap to the Indian National Satellite, INSAT-1D has put us in such a crisis situation. Both the indigenous rockets and the foreign-made satellites have been dogged with problems successively, though not by design but by mere accident. While the launching of the intermediate range missile, Agni, may appear as a bright spot on the dark space screen, the crippled INSAT-1C and the stillborn INSAT-1D, coupled with INSAT-1B, nearing the end of its life, put our television, communication and weather services in vulnerable position. Even if INSAT-1D had been launched as per schedule it would not have given any additional sendee but would have substituted INSAT-1B. Though INSAT-1C is giving partial services, to make up for INSAT- 1B, the Indian Space Research Organisation has sought the services of foreign satellites and hopefully, the crisis can be overcome with this. Now, ISRO is banking on INSAT-2 series, which will be indigenous unlike the INSAT-1 series. The decision to invest on the indigenous satellite programme, was delayed a bit. Had it been taken much earlier, the time lag could have been avoided. As ISRO reassures us, by mistakes, Indian space scientists have learnt a lot and the damage to satellites does not mean financial loss as they have been insured. Having realised that there is no substitute for self-reliance, India is keen on building its own rocket for launching satellites in the geosynchronous, orbit. If the cyrogenic teclmologies for this project are not available abroad, India will do it by herself, though it may take couple of years more. As ProfU.R. Rao, chief of ISRO says: Indian space programme is on a steady orbit The only tiling that can stop us is our lack of determination. 1 8.05 TEST PATTERN GENERATOR A. Rigby A programmable digital pattern generator for all of you who do not have access to specialized equipment for faultfinding in digital circuits. The operation of many digital circuits is, in principle, not simpler or more complex than that of analogue circuits, but the de- pendency of certain signals on others gives digital faultfinding a labyrinth ef- fect. Furthermore, it is often impossible to isolate a particular section of the circuit for a stand-alone test. The omission of a single control signal, whose function may not be known at all initially, may cause the whole circuit to 'stall', making it im- possible to track the cause of the malfunc- In synchronously operating digital cir- cuits, state changes take place only as a result of clock signal transitions. This makes the operation of this type of circuit relatively simple to follow, especially if the clock signal or signals can be gener- ated by external means. By contrast, a level change at a particular point in an asynchronous digital circuit is taken over by the rest of the circuit. This means that a spurious pulse at any point in the circuit can easily disrupt the normal operation of the entire digital equipment. A test pattern generator as described here enables programmed data to appear in a predefined order at the input of the circuit under test. An oscilloscope is used to check whether the circuit gives the cor- rect response to the applied test patterns. Patferns for testing The generator is capable of supplying up to 255 8-bit test words, or a sequence thereof. The number of test words can be set by the user. A short sequence therefore takes hardly time to program, and need only be programmed once. A sequence of, say, five test words simply corresponds to five bytes loaded into the memory of the test generator. The remaining 250 mem- ory positions are not used and need not be loaded. The block diagram in Fig. 1 shows that the heart of the circuit is formed by a RAM memory. Two 8-way DIL switch blocks serve to program the test words and the length of the test word sequence. The memory locations are addressed by a counter, which counts from 0 to 255. The generated address (A) is compared to the preset length of the sequence (B). When A and B are equal, output a=B of the word comparator is actuated. Depending on the position of the mode selection switch, the test pattern is either stopped or repeated. When the switch is set to CONTINUOUS, the output signal of the comparator causes the address counter to be reset and to start counting from 0 again. When the mode switch is set to single, the oscillator is inhibited, so that the last counter state is There are three more switches in the circuit. One of these serves to select either the 'single step' or the 'run' mode. In single-step mode, the clock pulse for the circuit is generated by a push-button, while in run mode it is generated by means of a clock generator. Switch OC en- ables the outputs to be switched to high- impedance (three-state). The last switch, marked run/prog causes the WE (write enable) input of the memory to be con- nected to the clock signal (program), or to the positive supply voltage (run). In the run mode, the memory is made 'read- Circuit description The circuit diagram of Fig. 2 shows how the previously discussed functions are given their practical form. The test gener- ator is composed of only six integrated circuits. Since only 256 of the 2,048 memory locations in RAM IC3 are used, address lines A8, A9 and A10 are connected to ground. The Type 6116 2Kx8 CMOS static RAM is used here because it is currently cheaper and more readily available than any 256-byte type. The counter that drives the eight re- maining address lines of the RAM is formed by IC2, a Type 74HCT393. This 8-bit bistable counts continuously from 0 to the value set with switch block Ss. IC< compares the current counter state at in- puts Qn with the preset word at inputs Pn. When the words are equal, output P=Q goes low. Depending on the position of S-i, either the outputs of N3 and N< are blocked, or the counter is reset. After being reset, the counter starts at state 0 The memory databus is connected to an input buffer with three-state outputs, ICi, and an output buffer, ICs. When the memory is read out, RAM input WE is logic high, and ICi is switched to high-im- pedance mode. The output buffer is trans- parent, and latches the data from the databus on the negative edge of the clock signal. The buffer passes all data applied to its D inputs as long as input C is logic high. When c is made logic low, the nega- tive clock pulse transition causes the data at the D inputs to be latched in the buffer's internal registers. The data remains there and on the outputs, until input c is made high again. The C5C input allows the out- put drivers in the buffer to be switched to high-impedance, so that the test generator is effectively disconnected from the circuit under test without the need of leads to be unplugged or wires to be removed. Manual or automatically? As already discussed, the circuit can be controlled either by a clock generator or with the aid of the single step switch. Si. R-C network Ri-Ci suppresses bounce pulses generated when the single step button is actuated. Schmitt-trigger gate N3 gives the switch signal a digital shape and Gate N4, capacitor C2 and resistors Pi and R3 form an adjustable clock generator. One input of N3 and N4 is connected to switch S4, which enables the gates to be blocked. When S4 is set to continuous, one input of both gates is taken high via R2, so that the clock oscillator is enabled. The span of potentiometer Pi is fairly large at 1:100, allowing the user to set the optimum test frequency for many types of digital circuit. External push-button St, with associ- ated debouncing network R9-C3, makes it possible to reset the counter. The enable inputs of ICi and the WE input of IC3 are logic high as long as S3 is open. The input buffer is in high-impedance mode, and IC3 behaves as a read-only memory. The cir- cuit is thus set to the 'run' mode. When S3 is closed, input WE is pulled low during the active part of the clock pulse, and the input buffer is enabled. The circuit is in 'program' mode because the dataword set on S7 is stored into the mem- ory during the rising edge of the clock pulse. The clock signal at the pole of S2 is applied to the clock input of bistable FFi Fig. 1. Block diagram of the test pattern generator for digital circuits. Fig. 2. Circuit diagram of the tester. i8.19 Parts list Resistors (±5%): Ri = 100k R2;R3;R4;R6-Ri7 = 10k Rs;Ri8 = SIL resistor array 8x10k Pi = potentiometer 100k linear Capacitors: CitCs-Cs- lOOn C2= InO Semiconductors: ICi = 74HCT541 IC2 » 74HCT393 IC3 = 6116 or 8416 IC4 - 74HCT688 IC5 - 74HCT563 ICs = 74HCT132 Miscellaneous: Si;Ss = SPST push-to-make button. S2;S3;S4 > miniature SPDT switch. Ss = miniature SPST switch. S7;Ss = 8-way DIP switch or hex thumb- wheel-switch. Ki = 20-way pin header. PCB Type 890020 Fig. 3. Track layout and component mounting plan. via inverter Ni. Output Q4 of FFi in turn clocks a second bistable, FF2. The bistables (there are actually four in each device) are thus cascaded to form an 8-bit counter. Suggestions The clock frequency has been chosen rather arbitrarily but will be suitable for most applications. If required, the value of C2 should be adapted to give a different frequency. A larger value of C2 results in a lower clock frequency, and a smaller one in a higher clock frequency. It is also possible to- create a larger frequency range by selecting different capacitors by means of a rotary switch. Toggle switch S2 may be replaced by a three-position type. In that case, the third position is used for selecting an external clock source, e.g., one available in the cir- cuit under test. Construction The compact printed-circuit board de- signed for the tester makes construction a matter of routine. The track layout and component overlay are given in Fig. 3. Start the construction with the fitting of the ten wire links on the board. Next, fit the 18 solder terminals and connector K2. The HCT ICs are all low-cost types, so that sockets are not strictly required. Although the board allows the fitting of two 8-way DIL switch blocks, it is better, in many cases, to use switches that can be mounted on to the enclosure. Hexadecimal thumb- wheel switches are convenient in the prac-. tical use of the test generator and are, therefore, suggested as an more ergon- omical and simple-to-connect alternative to DIP switch blocks. The power supply is purposely not ac- commodated on the board because a regu- lated 5 V source will nearly always be available as part of the circuit under test. The digital test generator draws about 30 mA. I DATABYTE PROGRAMMED ON S7 Fig. 4. Prototype of the test generator housed in a compact enclosure with the word configuration and word number switches mounted on to the front panel. Fig. 5. Bit pattern displayed on a logic ana- Programming The memory has to be loaded with the desired bit-patterns (test words) before the circuit can be used to test a digital system. Fortunately, programming is straightforward: • Set the number of test words as a hexade- cimal value on Ss (OOh-FFh). • Set S3 to program, S2 to step and Si to SINGLE. Set the desired bit pattern on S7. • Press STEP to store the bit pattern in mem- • Set the next bit pattern. When S4 is set to single, the circuit will not accept further data when the number set with Ss is reached. After loading all bit patterns, S3 is set to RUN to sequentially feed the data to the circuit under test. De- pending on the position of S2, this feeding out takes place automatically or ma- Timing and level measurements may start after the digital outputs of the tester have been connected to relevant points in the circuit under test. The tester does not provide a strobe pulse, but this is fairly simple to implement by programming, say, bit 8 accordingly. In that case, the test word is 7-bits wide, and the sequential data stream has a maximum length of 128 samples because the strobe bit must toggle in between samples. Finally, one interesting application of the test generator should not be left un- mentioned here. It is fairly simple to use the instrument for driving a D-A ( digital - lo-analogue ) converter. This combination creates a simple programmable waveform generator. LINCMOS CIRCUITS LinCMOS™ is a process that gives to linear devices a superior performance over metal-gate CMOS by the use of polysilicon gates and an optimized ‘N well’ structure. Equivalents of many popular operational amplifiers, comparators and timers have already been available for some time. The major benefits of these devices are lower power consumption, faster switching and the ability to operate from very low supply voltages. While giving good ± supply rail perfor- mance. with a total voltage not exceeding 16 V. the input and output are optimized for single'supply operation. This is achieved with an input common mode range that included gnd (~V DD with ± supplies) and an output range that pulls down to within a few millivolts of gnd (with a load connected to gnd). The TLC27x range are specified to work with supply voltage down to 3 V and will thus operate with the supplies that are commo- ny available for ttl and hcmos. For maxi- mum dynamic range, single rail operation with 16 V supplies should be used. For low power and battery operation, the TLC25x range are specified to operate with 1 V total supply voltage. High bias mode gives a wider band- width (2.3 MHz) and faster slew rate (4.5 V/ps) than standard bipolar opamps (especially single-supply devices) for the same order of supply current. The enhanced bandwidth gives an increase in the open-loop to closed-loop gain ratio at a particular frequency improving accuracy of, for example, filter circuits, or allowing higher frequency operation. Slew rate enhancement gives a wider large-signal bandwidth and generally allows the imple- mentation of faster circuits. Medium bias mode gives standard bipolar opamp performance at roughly a tenth of the supply current. The main advantage of the low bias mode is the low power consumption with sufficient bandwidth and slew rate for basic sensor interface and audio applica- Low bias and offset currents allow cir- cuit simplification through the elimination of bias current balancing resistors, higher impedance circuits for greater accuracy (for instance, smaller, higher tolerance capacitors) and circuit current defined only by feedback components. Another advantage is insignificant noise due to bias current (shot noise): noise is dominated by noise voltage and resistor noise — see Fig 3. Fig. 1. Circuit diagram of a typical LinCMOS operational amplifier. LinCMOS is a trade mark of Texas Instruments. Table. 1. Comparison between bipolar, BIFET and LinCMOS operational amplifiers. Fig. 2. The voltage at the bias-select pin ol a LinCMOS operational amplifier influences the characteristics of the device. Operational amplifiers The operational amplifier is the most popular of all LinCMOS circuits. In fact, the first devices available in the new technolo- gy were the now well-known opamps Type TLC25 1/271 (single), TLC252/272 (dual), and TLC254/274 (quad). These are intended as replacements for the standard Types 741/3140, MCI 458/C A3240, and LM324. A close examination of the TLC271 reveals that the opamp, apart from the usual inputs, output and supply connec- tions, has a so-called bias-select pin. The voltage at this pin determines the current drawn by the device — see Fig. 2. In the low-bias mode (bias-select pin connected to the +ve supply voltage), the current is only (typically) 10 pA. The price to be paid for this low current is a poor slew rate of only 0.04 V/ps and a unity-gain band- width of a mere 1 00 kHz. The speed is determined largely by the device's internal capacitances. When the supply current is small, the charge and dis- charge currents through these capacitances will assume a larger importance, whence the lack of speed. However, there are a number of applications in which the low slew rate is of no importance In the medium-bias mode, the current is about 15 times higher, but the slew rate and unity-gain bandwidth are correspond- ingly better: 0.6 V/ps and 0.7 MHz res- pectively). These values are comparable to those of, for instance, a standard 741. Note however that the latter draws a current of 1.7 mA. In the high-bias mode, the current rises to 1 mA, but for that you get a very fast opamp with a slew rate of 4.5 V/ps and a Fig. 3. Equivalent input noise voltage vs frequency for high (H), medium (M) Fig. 4. Maximum output voltage V 0M vs output current l 0 at various supply and low (L) bias modes. voltages. unity-gain bandwidth of 2.3 MHz. The dual versions TLC252/272 and the quad Type TLC254/274 are not provided with bias-select pins (for which they have no space in any case). In these versions, the bias mode is permanently set internal- ly. The type number indicates which bias mode the device provides. For instance, a TLC27L2 is a low-bias type; a TLC272 is a high-bias version; and the TLC272M2 is a medium-bias type. Power supply and load As mentioned briefly already, to obtain maximum dynamic range, LincMOS op- amps are optimized for single-rail opera- tion from supplies not exceeding 16 V. The output voltage vs output current characteristic for loads connected to earth is given in Fig. 4. An open-circuit output, or one with the load connected to earth, can be pulled to within a few millivolts of 0 V. The output can only be pulled to the +ve supply level if the load is connected to the +ve rail or an external pull-up resistor is added. Such a resistor has, however, the disadvantage of resulting in a relatively large power consumption at low output voltages. Also, the open-loop amplifica- tion drops sharply when the output voltage gets close to the -i-ve supply voltage. This is caused by N5 — see Fig. 1 — switching off. When relatively heavy loads are used, it should be noted that the sinking rate may exceed the sourcing rate; in other words, that the output current is greater than can be provided. If, therefore, large output currents are required without addi- tional components, it is recommended that the load is connected to the +ve supply rail as shown in Fig. 5b. Frequency compensation will be determined largely by the resis- tances in the feedback loop and by the load. The value of these resistance will, therefore, be normally quite high. As far as DC signals are concerned, that presents no problems. When AC signals are involved, however, more account must be taken of input and other stray capacitances (C s tray in Fig. 6) than in conventional opamp circuits. To obtain a sufficiently wide bandwidth, it may in some cases be necessary to use a compensating capacitor as shown in Fig. 6 to reduce the feedback at high frequencies. Comparators A number of comparators available in LincMOS technology are shown in Table 2. The TLC372 and TLC393 are pin-compat- ible replacement of, for instance, double comparator Type LM393. Quad compara- tor Type LM339 may be replaced by the TLC339 or TLC374. As with opamps. the current consump- tion of LincMOS comparators is substan- tially lower than that of bipolar equiva- lents. while the input current is very low (typically 5 pA). There is not much differ- ence in the input offsett voltages. The outputs of most comparators are of the open-drain type, enabling logic func- tions to be produced by interlinking them. Normally, a pull-up resistor will also be required, but not with the TLC3702 and TLC3704, since these have totem pole outputs. Unlike some opamps, comparators do not offer a choice of three bias modes. The bias mode is inherent in the type. For instance, the TLC393 draws 22 pA (typi- cal) compared with the 0.8 mA drawn by an LM393. but it is slightly slower (2.5 ps agains 1.3 ps). A TLC372 has a higher power consumption, but is much faster (650 ps) Fig. 5. Circuit adaptations for obtaining a larger output current in a load connected (a) to earth, (b) to the +ve supply rail, and (c) symmetrically. Fig. 6. Input and other stray capacitances may be countered by a compensating capacitor. In low-power applications, the current COMPARATORS Table 2 Table 2. Some LinCMOS comparators and their main parameters. Fig. 7. Pinouts of the various LinCMOS circuits discussed in this article. TIMERS Table 3 Table 3. A variety of LinCMOS timers and their main parameters. It should be noted that Texas- Instru- ments is not consistent in their recommen- dations on maximum supply voltage volt- age. In some data sheets they mention 16 V and in others. 18 V. It is. perhaps, wise to be on the safe side and stick to 16 V. Timers As might be expected, there are equiv- alent LinCMOS ics for the renowned 555 series of timers. In fact, there are four: the TLC555 (single) and TLC556 (dual) to replace the standard (LM/NE)555 and 556 for supply voltages from 2 V to 18 V and the TLC55I and TLC552 for operation from low voltages (down to 1 V). Apart from the much reduced power consumption, the great benefit LinCMOS timers offer is the greatly extended fre- quency range. The maximum frequency is about ten times higher than that of a stan- dard 555 (2.1 MHz against 200 kHz), because the saturation normal transistors have to cope with has no or negligible effect in the new technology. Even at rela- tively low frequencies (from 20 kHz to some hundreds of kHz), the TLC555 has a major advantage in that the frequency can be defined much more precisely by exter- nal components. Note that the frequency range is extended also at its lower end. Since the input impedance and input leakage current are much smaller than in a bipolar 555. the rc networks that are con- nected to these timers can have a much higher value. This makes realization of very long time delays (up to hours)possi- ble. ELECTRONICS NEWS MODI XEROX POINT India’s first retail outlet chain for computers, Computer Point, is to be acquired by Modi Xerox Ltd. Set up in 1984 by a group of technoc- rats, Computer Point initiated a new trend as several computer re- tail outlets sprang up in different parts of the country following its success. Computer Point opened four out- lets in Bombay, Delhi, Madras and Bangalore where small buyers could visit the shop, see the pro- ducts and purchase their choice. Initially, Computer Point sold im- ported home computers of Spec- trum and computer stationery and then it became a public limited company. Computer Point was ap- pointed sole distributor for Lotus products and it also diversified into selling products of other Indian manufacturers. The company em- barked on an ambitious target of opening 40 outlets in die country by 1990 but this could not be achieved following serious cash flow problems. Subsequendy, manpower problems also com- pounded the crisis. Lotus joined hands with Tata Consultancy Ser- vices, and Computer Point lost a major chunk of its business. The promoters of die company, Mr B.M. Ghia and Indian Organic Chemicals Ltd. chose to sell their shares in Computer Point. For Modi Xerox, Computer Point’s oudets would provide die much needed infrastructure for selling its own office automation equipment, in addition to computers. 1 8.25 FLOPPY DISK MONITOR M. Noteris It often happens that PC users are left completely unaware of what is actually happening to the floppy disk inserted in the machine. Is the machine reading, attempting to read, or writing, and if so, to which track? This simple monitor circuit for IBM PCs provides the answers by making the control signals of the disk drives visible. The drive select LED on a floppy disk drive does just what it is supposed to do: indicate drive activity. Many PC users have, therefore, no idea whether the floppy disk they have just inserted is read from or written to. Clearly, this is an un- acceptable situation in this day and age of data security and a few bits on a disk determining access to files that represent many hours of work. While the present circuit can not restore data on a corrupted floppy disk, it helps to prevent the most serious of mishaps because you witness how they come about! The principle The floppy disk monitor works on the simple principle of visually indicating the status of the various control signals used for the floppy disk drives in a PC. Practi- cally all user manuals supplied with PCs give a disk-drive wiring diagram that in- dicates the signals Drive Select (DSO to DS2, and, in some cases, DS3), Read Data, Write Enable, Step, Direction and. Track 0. The movement of the head in the disk drive is fairly simple to monitor by clock- ing a counter with the Step pulses, driving the up/down input of the same counter with the Direction signal, and driving its reset input with the Track 0 signal. The visual indication function is assumed by a Type 4543 IC that decodes BCD data sup- plied by a counter Type 4510. The 4543 is capable of supplying the required 20 mA segment current for a Type 7760 LED dis- play, of which two show the current track Since the maximum number of tracks supported by the floppy disk monitor is 80 (0-79), two counter/display circuits are cascaded by driving the carry in input of the decade driver with the CARRY out signal of the unit driver. Signals Read Data and Write Enable are visualized with the aid of the decimal points on the LED displays. These indica- tions are referred to as DPR ( decimal point read), and dpw ( decimal point write) in this The circuit The circuit diagram shown in Fig. 1 may cause some readers to wonder why two • monitors all floppy disk drives available for PC/XT, PC/AT and compatible PCs: j S'A-inch, 3VS-inch, single/double sided, double or quadruple density • static display of head position (current track number) • read and/or write indication for selected • read indicator shows data flow resulting from pulses induced in the head by the magnetic carrier • monitors two floppy disk drives simulta- | neously 8.26 Type 74HCT240 bus buffers are used. The six signals used for controlling all disk drives in a PC are carried in parallel be- tween the disk controller board and the disk drives, so that the signals for the ac- tuated drive must be selected before they can be directed to the associated indicator circuit. This directing of control signals is accomplished with the aid of the drive select lines, DSO, DS1 and DS2, which en- able the bus buffers depending on the po- sition of switches Si and S2. Since all control signals involved" are active low, they are inverted by the 74HCT240s to enable driving the display units. A number of bus buffer inputs are connected to outputs to make sure they are properly terminated. With Si in the position indicated in the circuit diagram, signal Drive Select 2 en- ables bus buffer IC2 with a low level at inputs TG and 2C. Pull-up and pull-down resistors are fitted on the output lines of the bus buffers since these are switched to high-impedance when the device is dis- abled via the TC and ZG inputs. Output lines R (reset) and u/D (up/down) are pulled low, and CLK (clock) is pulled high. The Track 0 signal guarantees that the displays are always correctly reset to zero, which is useful when, for one reason or another, the counter loses track of the step pulses. Monostable multivibrator MMVi shapes the Track 0 signal supplied by a slotted optocoupler in the disk drive. The arm on which the head is mounted inter- rupts a light beam when it is in the ex- treme outer position with the head(s) over track 0 of the disk. The monostable leng- thens the track 0 signal to about 1.5 ms to make sure that the display counter is properly reset even with drives that use the fastest step rate, 3 ms. Edge-triggering is used to cope with tolerance on the track 0 detection circuit and associated mechanical parts. In certain disk drives, the signal is still active even when the head is half way between tracks 0 and 1 . R-C network R12-C2 resets the counter circuits to zero at power-on by supplying a brief 'high' pulse via line X. More about drive selection Although the cable from the disk control- ler board has four drive select wires, DSO- DS3, the practical number of floppy disk elektor india august 1989 b.27 drives supported in IBM PCs and com- patible machines is usually limited to two. This is because each floppy disk drive re- quires two signals, one to control the motor, and one to control the actual selec- tion of the drive. Thus, the motor in drive A is energized under the control of a low level on line DSO, while the drive proper is enabled under the control of a low level on line DS2. It should be noted that the above func- tions of DSO and DS2 are the other way around on some PC compatibles of Far Eastern make. The floppy disk monitor solves a potential problem arising from this oddity by virtue of rotary switches Si and S 2 . Another noteworthy point is that sig- nal Write Enable is fed to the display unit. The use of Write Data would appear more logical at first. The background to the use of Write Enable is that some disk control- ler boards, for instance, those of Western Digital, generate clock pulses on the Write Data line except when actually writing to the disk drive. This clock pulse stream can not be used by the display circuits, and would cause these to light the write indi- cation (DRW) continuously. Counter and display module The counter/display circuit is based on an earlier design published in Ref. 1. Fig- ure 2 gives the circuit diagram. The mo- dule is composed of four identical combinations of a synchronous BCD counter Type CD4510, a latching BCD-to- 7 segment display driver Type CD4543, and a common-cathode LED display Type 7760. Cascading is achieved by connecting Parts list DRIVER BOARD Resistors (±5%): Ri;R2» 330S2 I Ru-Rn = 15k [ Ri2 = 10k Capacitors: Ci;C3= lOOn I C2=1p0; 16 V; radial C4= lOOg; 16 V Semiconductors: Di-De = LED; red; 3 mm j ICi = 74HCT123 | IC2;IC3 = 74HCT240 Miscellaneous: I Si ;S2 = two-pole, three-way rotary switch. [ Ki = 34-way pin header. PCB Type 890078 i8.29 the CARRY OUT (CO) output of each of the two units counters to the carry in (Cl) input of the associated decade counter. The functions of the U/D (up/down), and R (reset), Ph, Bl, PE and LD are covered in Ref. 1. Construction The driver circuit of the floppy disk moni- tor is built on the printed-circuit board shown in Fig. 3, and the counter/ display module on that shown in Fig. 4. Neither board should present any difficulty in populating. Start the construction of the driver board by fitting the 12 insulated wire links. Continue with the resistors, of which most are fitted upright, the capaci- tors, the soldering terminals, IC sockets, and, finally, the 34- way pin header, in that Each display board accommodates two displays and two driver circuits. The ready-made printed-circuit board must, therefore, be cut into three along the two dotted lines printed at the component The fitting of the parts is carried out as usual. The interconnection between the two control boards to the display circuit requires further detailing, however. Tak- ing one pair of displays as an example, the construction is started by populating the display board, and then the associated control circuit. Resistors Ri through Rs are mounted between the control board and the display board, and give the complete assembly the required rigidity. Proceed with connecting paired points Ph/COM, R, o, U/D, PE, Clk, + and LD. The co output of the units display driver is con- nected to the ci input of the decade dis- play driver, as shown in the circuit diagram of Fig. 2 (note the mirrored posi- tion of the displays in this drawing). The completed counter/display units are connected to the driver circuit via the 6 signal lines and the 2 supply lines. In the standard version of the floppy disk moni- tor, there are two counter/ display units and one driver unit. The remaining connections are those for the LEDs and the rotary switches. In- stall the wiring as shown in the circuit diagram. Power supply The circuit is conveniently powered from the 5 V rail provided by the computer’s power supply. The prototype of the floppy disk monitor is a stand-alone unit that is powered via a small socket as used on portable cassette recorders. The PC is fitted with a similar socket, and the two units are interconnected by a 30 cm long 2-wire supply cable. If the circuit is installed permanently in the PC, the ground and +5 V connections may be made at appropriate points on the motherboard. Another, more practical, solution is shown in Fig. 7. A cable should be made to enable the supply voltage to be taken from one of the disk drives. Cables The floppy disk monitor is connected to the disk controller board via a home-made flat ribbon cable. This cable is crucial to the operation of the circuit and is, there- fore, drawn in Fig. 5. The job is almost done if the right parts are to hand: 50 cm or so of flat-ribbon cable, two 34-way IDC (insulation displace- ment) sockets, and one 34-way IDC header. The sockets and the header may be types with or without a strain relief clip. The two sockets are mounted at the cable ends, and the IDC header at about 15 cm from one of the sockets. Do not twist the cable in between the header and the sockets: use the coloured wire in the cable to mark pin 1 of the connectors. The existing cable between the floppy disk drives and the controller board must be disconnected at the side of the control- ler board. Figure 6 illustrates how the soc- kets at the ends of the previously described cable are connected to the disk controller board and the floppy disk monitor. The free end of the cable to the floppy disk drive is connected to the header on the home-made flat cable. The connection as detailed is not af- f ec ted by the number of floppy disk drives monitored with the present circuit. All ac- tivity on one, two or even three floppy disk drives may be watched closely from circuit can be modified as required by using rotary switches with the corre- sponding number of positions. The floppy disk monitor is not suitable for use with hard disks because these have a much higher number of tracks and In practice, the floppy disk monitor is a simple, yet effective aid for the PC user. It obviates, for instance, the use of a soft- ware utility to find out on which track a program or file is started, or how it is arranged on the disk. Reference: 1. Versatile counter circuit. Elektor India , April 1985. Modifications As already noted, the basic version of the circuit is intended for monitoring the con- trol signals of two floppy disk drives. It is, however, possible to realize a version for a single drive. In that case, only one universal counter module is used, while one of the two bus buffers on the driver board may be omitted. A three-drive version of the monitor simply requires a third universal counter module, and, in addition, the shaded part of the circuit in Fig. 1. It is possible to mount the additional 74HCT240 on top of IC2 or ICa, soldering pins 2, 4, 6, 8, 10, 17 and 20 to the IC below, and bending the remaining pins away from the IC body for wiring as indicated in Fig. 1. Unfortunately, IBM PCs and compati- bles do not normally allow the use of more than two floppy disk drives. There are ways to overcome this limitation, but these fall outside the scope of this article. In an IBM environment, therefore, the floppy disk monitor can not keep an eye on more than two drives. For computers that do support more than two floppy disk drives, the monitor PRACTICAL FILTER DESIGN - PART 7 by H. Baggott After last month's discussion on Butterworth filters, we turn our attention in this seventh part of the series to a network that does not have such steep skirts, but makes up for that by its excellent pulse behaviour and very smooth transition characteristic: the Bessel filter. The major advantage of Bessel sections is their phase behaviour, which is more linear than that of any other type of filter - see Fig. 38. If the Bessel amplitude char- acteristic is projected on a linear scale, it is a straight descending line. It is only be- cause of its usual projection on a logarith- mic scale that the characteristic looks like a typical filter skirt. The transfer charac- teristic of a Bessel filter is. therefore, mod- erate. A roll-off of 6n dB per octave is not attainable: the curve is particularly poor around the cut-off frequency and this is not dependent on n (n is the order of the filter). Bessel tables The tables giving the data for the com- putation of Bessel filters are compiled si- milarly to those for Butterworth sections, described in detail last month, and they should therefore not present any problems. Again, the component values are given for a cut-off frequency of I Hz. Table 6 gives the pole locations of Bessel filters from the 2nd to the 10th order, while Tables 7, 8 and 9 give the component val- ues for a passive section under different operating conditions. Bessel characteristics The characteristics in Fig. 37-39 show the plus and minus points of a Bessel fil- ter. For instance, the roll-off is noticeably less steep than that of a Butterworth filter. Also, the knee is virtually the same for all orders of the filter. One of the positive qualities of the Bessel filter is seen in Fig. 38. The delay vs frequency characteristics Table 9. Normalized component values for active filters with a single feed- back path. are highly linear up to the cut-off frequency (from about the 3rd order onwards). With higher orders, the delay remains linear for some time beyond the cut-off frequency. This linear behaviour is also found in the step response in Fig. 39: there is virtually no overshoot or sign of ringing. Some examples Example 1. Third-order low- and high-pass Bessel filters are required for a loudspeaker system with a nominal impedance of 8H. The cut- off frequency is required to be 2500 Hz. Solution. It is assumed that the source impedance is negligibly small and that the required filter is a passive one. The computation of the low-pass section is simplicity itself. We take a standard passive low-pass filter and insert the component values for a 3rd-order section from Table 8 — see Fig. 40a. Subsequently, those values are transferred to the real load impedance (8£2) and the actual cut-off frequency (2500 Hz): C = CI(fR) L' = LRf The resulting section is shown in Fig. 40b. Next, the high-pass filter. All capacitors in the low-pass fil- ter are replaced by inductors and all inductors by capacitors. In Part 3 we have seen that normalized filter values of a high-pass section are found by 'inverting' the normalized values of a low- pass filter. For the present example, this has been done in Fig. 40c with the addition of a factor 4n\ which is necessary because the formulas 1 1C and ML apply to normalized values for to = 1 rad/s, whereas in the tables in these articles the stan- dard values are given for/= 1 Hz, whence the correction factor. The formulas thus become: C h =l/(4jfZ.|) Fig. 37. Gain vs frequency characteristics of a Bessel filter. Fig. 38. Delay time vs frequency characteristics of a Bessel filter. Fig. 39. Step response of a Bessel filter. 1 8.33 Fig. 40. Dimensioning a passive low- and high-pass filter: Fig. 41. An active Bessel filter of the sixth order; cut-off frequency is 20 KHz. load impedance Is 8ti and cut-off frequency is 2500 Hz. L h = l/(4n ! Cl) Since a calculator is required anyway, it is quite simple to include the factor (4id = 39.48). The computation of the resulting high- pass filter terminated into 812 and having a cut-off frequency of 2500 Hz is then car- ried out in the usual way — see Fig. 40d. Example 2. A low-pass Bessel filter is required with a cut-off frequency of 20 kHz. The time delay must remain constant up to not less than 30 kHz. The attenuation at 100 kHz must be at least 50 dB. Solution. First, the delay and attenuation frequen- cies must be converted to 1 Hz and this gives values of 30/20=1.5 and 100/20=5. Next, we ascertain which order of filter meets the requirements. In Fig. 38 we see that a filter of about the sixth order is required to keep the delay constant up to around one-and-a- half times the cut-off frequency. It is then seen in Fig. 37 that a sixth order filter is required to give an attenuation of at least 50 dB at 5xf c . A sixth-order filter is an even-order one, so it must be constructed from 2nd- order sections — see Table 9. The capaci- tor values for the three sections may be taken direct from Table 9. Next, choose a suitable value for the resistors. The actual capacitor values and the wanted cut-off frequency are then computed with the aid of the formulas used in the first exam- ple — see Fig. 41b. Two calculations for the first section: C\ = 0.1708/(20,000x2200) = = 3.88x10-’ = 3.88 nF. C 2 = 0.04076/(20,000x2200) = =926xl0 l2 = 926 pF. Next month: Chebishev filters. ELECTRONICS NEWS BUYING SOFTWARE FIRMS Indian companies can acquire software companies abroad by pay- ing for such acquisitions out of 30 per cent of excess export earnings made over and above their export obligations, according to the latest policy decision of the government A condition imposed under this policy is an additional export obli- gation of 15 per cent of the foreign exchange released. Under the pre- vious policy, the software expor- ters were allowed to import compu - ter systems, software and hardware subsystems, office equipment spare parts and so on. This facility is now modified to in- clude the purchase of a company abroad. Though the potential is enormous. Software exports in 1988-89 were worth only about Rs 80 crores and the target fixed for 1989-90 is Rs 300 crores. The world demand for software is currently estimated at 100 billion dollars and it is pro- jected to touch 300 billion by the turn of the century. The decision of the government to allow purchase of software companies abroad is to be seen in this context Marketing problems were among the major constraints which af- fected the export of Indian software. Only a few large com- panies have their branches abroad. Others find it difficult to market their products as it involves con- tinuous monitoring and substan- tial expenditure. Hie industry' suggested acquisition of foreign companies as one of the ways of solving this problem. But, the condition that the com- panies should pay from the excess 30 per of the earning for such ac- quisitions may not help many as few companies are anywhere near exceeding their export earnings by 30 per cent of the obligation. To evoke an enthusiastic response from die industry and to accelerate the growdi of the software industry this condition may have to be di- luted, it is felt UNIVERSAL MIDI KEYBOARD INTERFACE Final Part D. Doepfer Table 3 shows a practical example of how the EPROM contents can be adapted to the available keyboard, in this case a 72-key type with a range from F to E. As dis- cussed last month, programming the EPROM is simply a matter of entering the actual key numbers in ascending order, starting with the lowest key. Note that the most-significant nibble of each pro- grammed byte is 0, 2, 4, 6 or 8. The practi- cal connection of this keyboard is shown in Fig. 6b in last month's instalment. Since there are 72 keys, 5 decoder boards are required to cover the 6 octaves. Programming one's own EPROM is, fortunately, not required in most cases, since the EPROM supplied through the Readers Services (ESS575) provides the data required for a 96-key C-to-B key- board (8 octaves). Most keyboards are smaller and will not require a repro- grammed EPROM if their contacts go to the correct inputs on the decoder boards. Construction The construction of a MIDI keyboard en- tails mechanical as well as electronic work. It is important to note that the larger part of the descriptions that follow are based on the construction of a 72-key key- board with wooden keys and spiral spring contacts. This is but an example, however, and many other configurations and con- structions are possible. Keyboards with and without keys may be obtained from music stores. Main controller board Figure 7 shows the main controller board. Start the construction by fitting the six wire links on it (excluding Ji and J2) be- cause a number of these are covered later by IC sockets. Use insulated wire to pre- vent short-circuits with the socket pins. Voltage regulator ICs must be fitted on a small heat-sink if the input voltage ap- plied to socket K2 is higher than about 10 V (Cs is omitted in that case). Wire links Ji and J2 connect address lines A9 and A10 to ground if the used part of the EPROM is located in the lower addressable range (this is so in most cases). Diodes D3 and D< are mounted upright (note the orienta- tion). Resistors Ru-Ru are contained in a single-in-line (SIL) array of which the 4 other internal devices are not used. The resistor array may be replaced by 4 verti- cally mounted resistors whose top con- nections are commoned by a horizontal wire which goes to the hole next to pin 1 of the EPROM. Transposition switch Si must be not be installed direct on to the board because its pinning does not correspond to that of the solder terminals (the centre contact must be wired to point c). The MIDI connector is a 5-way DIN type for mounting at the edge of the printed circuit board. Decoder boards The number of decoder boards required depends on the keyboard type. One decoder board, of which the design is shown in Fig. 8, scans up to 16 keys, and is configured to address a particular group of keys with the aid of a jumper, J i, which goes to point A, B, C, D, E, or F as shown in Fig. 6. Each of the cascaded decoder boards has a different jumper in- stalled. Jumper A is always used for the decoder board connected to the lowest key group. If the total number of keys on the keyboard is not a multiple of 16, as, for instance, in the case of a 72-key type, only the extreme right-hand decoder board may be cut in two. The track design of the decoder board allows this to be done fairly easily to the right of contact Ss. cable must be fitted with an IDC-type 16- pin DIP header. As shown in Figs. 6a and 6b, the cable connects socket Ki on the controller board to socket Kj on the near- est decoder board. The decoder boards are interconnected in ascending order with cables between sockets (or pin headers) K2 and Ki. These are shown in dotted lines on the component overlay, and must, there- fore, be installed at the track side of the board. Wire-wrap sockets or pin headers should be used to make sure that the pins can be soldered properly to the tracks. Wire-wrap sockets mate with 16-way I DC CONTROLLER BOARD Connections The controller board is connected to one of the decoder boards with the aid of a 16-way flat-ribbon cable. Both ends of this -R14 = 1 KO (8-way SIL array) Capacitors: Ci;C2 = 22p C3= loop C4= 10n Cs = IpO; 16 V; tantalum Cs=10p;16V C7-C11 = 2p2; 16 V; tantalum C9 is not fitted when ICs is mounted 1 Semiconductors: Di ;D4 = LED D2;D3 = 1N4148 Ds = 1 N4001 ICi = E510* IC2 - EPROM 2764 (ESS575; Services page) IC3 = 74HC00 or 74HC132 IC4 = 74HC138 ICs = 7805 ICs = 74HC688 IC7 = 74HC273 ICs = 74HC04 or 74HC14 Note: HCT equivalents may be HC and HCT types must not b this circuit. Miscellaneous: Xi - quartz crystal 4 MHz. St - miniature toggle switch with centre-off S2 » push-to-make button. Ki = 1 6-way DIL socket or 2 8-way pin headers. «2 = PCB mount socket for 3.5 mm supply plug. K3 - PCB mount 5-way DIN socket. Heat-sink for ICs. PCB Type 890105-2 Fig. 7. Track layout and component overlay of the main controller board. The supply voltage is applied via K2. DECODER BOARD Capacitors: Ci = 1p0; 16 V; tantalum Semiconductors: Dt-Dt6 = 1N4148 ICi = 74HC154 or 74HCT154 Miscellaneous: Kt;K2;(K3) = 16-way pin header or wire-wrap 1 6-way flat-ribbon cable with IDC or DIP connectors. Solder terminals as required. PCB Type 890105-1 DIP headers, and pin headers with IDC sockets. It is also possible to do without flat-cable connectors altogether and use individual wires. With 3, 4 or 5 decoder boards, and 16 wires per connection, how- ever, this solution is rather time-consum- ing. When a keyboard with fewer than 96 keys is used, and it is not desired to change the contents of the default EPROM (ESS575), study the configuration diag- ram of Figs. 6a, and find the decoder board and point S1-S16 to which the lowest key contact on your keyboard is con- nected. Figure 6a shows examples of how keyboards with 72 keys and 54 keys are 'fitted' into the available range of 8 oc- taves. Again, note that the standard EPROM is used (ESS575), so that pro- gramming is not required. Non-connected contacts may be left open or tied to the BE bus to simulate a closed rest contact. Mechanical work Since there are many types of new, used and otherwise ready-made keyboards around, the mechanical construction is not standard as is the electronic construc- The choice of the keyboard and the contact type is fairly difficult, and the best way to avoid problems is, of course, to purchase a keyboard with integral switch- over keys. Unfortunately, such a device is probably hard to obtain, so that the key- board and the contacts may have to be purchased separately. Gold-plated wire contacts are simply glued on to the decoder boards prior to soldering their contacts. Keyboards with wooden keys and spring-type contacts are probably the best you can get, but they require great care and precision in assembling success- fully with the decoder boards. Although the decoder boards (Fig. 8) have been designed to fit in line with the contacts and the keys themselves, they are also suitable for use with wooden keys i8.37 and separately installed contacts, as shown in the accompanying photographs. The bs and be lines are constructed as bus bars that run along the full length of the cascaded decoder boards. The spiral springs touch the upper bar when the keys are pressed. The bars are made from sil- ver-plated wire fitted on to solder termi- Each decoder board has holes to enable it to be secured on to the keyboard with screws and PCB spacers. The BE and BS bus bars or the contacts must not be used for keeping the boards in place. At least 3 of the 5 screw holes must be used: the two at the edges and the one in the centre of the board. The cross-sectional drawing of Fig. 9 gives a suggested construction of a keyboard with wooden keys and spiral spring contacts. Horizontal bus bars To begin with, do not install the solder terminals for the BE and bs bus bars, or the contacts. Use an unpopulated decoder board to mark its position on to the rear of the keyboard. Wood screws may be used in some cases, and metal screws with PCB spacers in others, depending on the con- struction, size and ma terial of the rear side and the base plate or frame of the key- The decoder boards allow 5 positions for the solder terminals that hold the bus bars. As will be recalled from Part 1 of this article, the keyboard processor measures the player's strike force as the time that lapses when the pole of the actuated key travels from the rest contact to the work contact. The key release time is estab- lished in a similar manner by measuring the work-to-rest time. Since all rest con- tacts are connected to bus bar be, and all work contacts to bus bar BS, it will be evident that the 5 positions of the bars allow the constructor to gear the velocity characteristic very accurately to the player's preference (are you the construc- tor and the player? Good!). While fitting the solder terminals and the bus bars, it is important to observe the distance between them, and the distance between the key contact (the spiral spring) and the bs bus bar. These distances must be uniform over the full length of the bars. A vernier slide gauge or a micrometer must be used to check this. In practice, it was found that a bar distance of 3 mm gave optimum results with the prototype keyboard shown in the photographs. Po- sition errors of less than 0.5 mm were clearly noted by experienced players. To find the optimum position of the bars on your particular keyboard, fit only 2 solder terminals on a single decoder board, that is provisionally secured on to the keyboard. Experiment with the bus distance until you are satisfied with the velocity response of the keyboard, then install the bars permanently and check for uniform spacing. The use of silvered wire is a must to prevent corrosion of the con- tacts. Silver-plated wire is usually sold in diameters from 1 to 2 mm. The key pole should not reach the work contact, i.e, the bs line, until the key is fully down. This requires accurate positioning of the decoder boards, and is best achieved by making the screw holes slightly oval at the top with the aid of a small round file. Do not make the holes in the keyboard itself any larger. The position of the bs bus bar with respect to the pole is fairly critical. If the pole reaches the work contact too early, adjacent keys will be actuated along with the wanted ones while playing rapidly. Also take into account the relatively large inertia of wooden keys, which take quite some time to return to the rest position. In general, if the work contact is not located at the very end of the pole travel, notes will blend (no NOTE OFF message) dur- ing rapid, but still staccato, playing. The problem in this case is common to all mechanical keyboards: the limit of the repetition rate is reached. In conclusion, the work contact as well as the rest contact must be actuated neatly and reliably at the end of the pole travel, and at all times. The drawing of Fig. 9 shows a sug- gested construction on the basis of wooden keys and spiral spring contacts. It is recommended first to glue the spring in a hole in the key, and then solder the other end to the decoder board. After the glue has hardened, the spring is pulled gently just before soldering it at the track side of the relevant decoder board. This is done to make sure that the spiral remains straight when the associated key is struck. Spring movement, however small, is un- acceptable in the rest position. When movement is noted, heat the solder joint and carefully pull the spring a little to get more tension. Try out the feel of the keys by playing a few notes within the octave. Do not fit or adjust the remainder of the keys until the results of this test are satis- SCIENCE & TECHNOLOGY The versatile cable that tells a tale by Dennis Moralee A new pressure-sensitive cable with important security possibilities, developed as part of a British naval research project, is about to open up a whole range of mili- tary, industrial and domestic applications. Vibetek, the new sensing cable, incor- porates a rugged piezoelectric polymer that allows it to respond directly to applied pressures, impacts, stress and strain, vibra- tion and even sound. Compared to tradi- tional piezoelectric sensing devices, using single crystals or microchip thin films that are limited to sensing at a single point location, Vibetek provides continuous sensing along cable runs of over several hundred meters. It also offers a much more sensitive response, is robust and competitively priced. The new cable may be used simply to replace exist- ing pressure-sensitive lines in, for example, traffic moni- toring applications, where it can be buried just below a road surface in order to count the number of vehicles pass- ing over it. Its high sensitivity makes it possible for the cable to be put about 30 cm or more below the road surface, pro- tecting it from physical dam- age while still providing accurate and reliable detec- tion of passing vehicles. Its rugged construction will ensure that it survives for two years or more where conven- tional cables would last only a small part of this time. Highest vibration frequencies Moreover, it can detect not only the large applied pressures of road vehicles but the lighter loads as well. And because its response is highly linear and its electrical output precisely proportional to the applied pressure, different forms of road traffic can be distinguished and accurately weighed, proving the facilities of a dynamic weighbridge. It is also sensitive over a wide range of frequencies, which in traffic-sensing appli- cations can stretch from the near-static loads of slow-moving vehicles to the high- est vibration frequencies transmitted through the road surface. Linked to an electronic signal processing instrument, the cable can provide information about a passing vehicle's weight, speed, load- dis- tribution, acoustic noise level, and even its engine condition. In suitable circum- stances, it can also monitor the conversa- tion of passing pedestrians. The capabilities of the Vibetek cables are even more important in military and civilian security applications. For exam- ple, in one military situation, an army patrol, camping overnight in rough terrain, used the new cable as a trip wire along a lengthy security perimeter that included not only roads, farm tracks and fields, but also sections of running streams. Through monitoring, the patrol could detect and track the movements of every type of intruder sent against it — ranging from a single infantryman to a whole pla- toon and wheeled and tracked vehicles. Security functions In everyday life, the security provided by Vibetek's capabilities is noteworthy. A length of cable attached to a perimeter fence around an industrial site, for instance, can pinpoint all attempts to tam- per with it. Buried in a floor or wall or even simply run under a carpet, it will detect all move- ments in a protected building, and may even pick up intruders' conversations, pro- viding the perfect antidote to nimble-fin- gered thieves of artworks and security safes. Raychem Ltd* 1 ' of Swindon, the origi- nal developer of Vibetek, has set up a sub- sidiary company to develop the market both for the cable and complete electronic systems incorporating its use. Called FOCAS' 2 *, the new firm is staffed mainly by former Raychem personnel. Raychem is a minority shareholder with the majority owned by security specialists, Cookson Group plc' 3 *. FOCAS has already built up consider- able interest in Vibetek among many British companies, particularly in the security field, and new com- mercial uses for the cable are expected to reach the market It is currently being supplied in two forms: an extremely sensitive premium grade called Vibetek 20, and a more rugged, cheaper version, Vibetek 5. Both use a piezo- electric layer of polyvinyli- dene fluoride (pvdf), formed coaxially between inner and outer electrodes. In the case of Vibetek 20, these are made from a special alloy and silver respectively as part of a unique co-extru- sion process. In Vibetek 5, however, the pvdf layers are conventional copper compo- nents surrounded by an extra rugged pro- tective jacket. Both forms of cable allow easy connection through conventional cabling techniques, yet have very impres- sive technical characteristics. References: 1 . Raychem Ltd • Faraday Road • Dorcan • SWINDON SN3 5HH • Telephone (0793) 28171. 2. FOCAS • Faraday Road • Dorcan • SWINDON SN3 5HH • Telephone (0793) 28171. 3. Cookson Group PLC • Clements House • 1 4 Gresham Street • LONDON EC2V Telephone 01-606 4400. TRACKING TESTER This high-grade piece of test equipment, designed by ELV GmbH, can be used for tape speed calibration, wow, flutter and drift measurements on reel-to-reel tape recorders, cassette recorders and video recorders. A close study of the tape tracking charac- teristics, together with signai-to-noise and frequency response measurements, is of undisputed importance for aligning audio and video tape recording equipment, and for quality assessment. Tracking errors are caused by irregular tape transport, and are manifest as frequency deviations in the played back signal. At least two standards are available for tape tracking measurements. One is the DIN standard ( Deutsche Industrie Norm), which is based on a test frequency of 3150 Hz. The other standard has been defined by the CCIR ( Comite Consultatif Internationale de Radio), and is based on a test frequency of 3000 Hz. The tracking tester described here supports both stand- ards by providing either test frequency at the flick of a switch. Tests and procedures A basic distinction is made between two test procedures: Speed deviations and drift This measurement requires a test cassette with a prerecorded reference signal of 3150 Hz (DIN) or 3000 Hz (CCIR). The ac- curacy of the frequency of this reference tone is adequate for all practical purposes, and enables measuring absolute tape speed deviations as well as drift. The lat- ter is particularly noticable at the begin- ning and the end of the tape, when the reel motor(s) have to compensate relatively rapid changes in the load and torque. The operation of the tracking tester for this type of measurement is detailed below. Wow and flutter These tracking errors consist of slow fre- quency variations in the range from 0.3 to 6 Hz (wow), and as faster modulation ef- fects up to 100 Hz, which results in a flut- tering sound. The tracking tester has three ranges for wow and flutter measure- Depending on the selected mode and range, the tracking tester measures the relative deviation of the instantaneous tape speed (wow and flutter), or the relative deviation of the average tape speed (drift). The relative deviations are expressed as a percentage of the relevant standard values. As already mentioned, drift measurements require a test cassette. Operation The tracking tester is powered by a 9 VDC/200 mA mains adaptor connected to a socket on the rear panel of the enclo- The power on/off switch is found at the right on the front panel. A light-emit- ting diode (LED) above the switch indi- cates whether the instrument is in operation. The required test standard, CCIR (3000 Hz) or DIN (3150 Hz), is selected with the aid of a single switch at the centre of the front panel, near the top cover of the enclosure. The signals to and from the tape recorder are connected to the track- ing tester either separately via phono soc- kets or combined via a 5-way DIN socket. Wow and flutter measurement Measurements without a test cassette first require recording the test frequency on to a tape inserted in the apparatus under test. The tracking tester supplies a stable reference frequency of 3000 Hz or 3150 Hz for this purpose. This frequency is obtained from a quartz crystal oscillator and a fairly complex filter that together guarantee a stable sine-wave signal with a distortion smaller than 1%. After recording the test signal, the tape is rewound and played back. The wow and flutter measurement can then be car- ried out either with the reference tape or the previously recorded tape. Playing back the home-made recording will, in general, result in readings that are about 40% higher than those obtained with a proprietary reference tape. This dif- ference is caused mainly by the fact that tracking fluctuations are also taken into account during the recording. Toggle switch test/measure is set to the measure position, and the range switch to '1%'. The calibrate control has no effect at this stage. The wow and flutter percentage is read from the 1%-scale on the large moving- coil meter. High-quality and top-of-the- range recorders with very low wow and flutter may require the tracking tester to be set to the lower ranges of 0.3% or 0.1% full-scale deflection. Speed deviation and drift These measurements invariably require a proprietary test tape to provide a suffi- ciently accurate reference tone of 3000 Hz or 3150 Hz. • For absolute speed measurement, the test/measure switch is set to test. • Set the range switch is to position 'Drift 5%'. • Turn the calibrate control until the meter indicates 0% at the centre of the With the TEST/MEASURE switch set to measure, the meter indicates the absolute tape speed deviation in a range of 5%. The service documentation with the Wow and flutter Fig. 1. Block diagram of the tracking tester. tape recorder may be consulted to find out how the tape speed can be adjusted to obtain the lowest possible deviation (less than 0.5% is acceptable in most cases). Following the absolute tape speed measurement, drift should be checked against the data supplied by the manufac- turer. Rewind the test tape, and select the MEASURE mode. Calibrate the instrument for a reading of 0%. Play the test tape back to see how the long-term behaviour of the mechanical assembly affects average tape speed. Tape pull, determined by the va- rying effective diameter of the pulling reel is also a major cause of drift. Careful mechanical adjustments as outlined in the maintenance manual may give the re- quired improvements. Principle of operation The principle of measurement used in the tracking tester is illustrated in the block diagram of Fig. 1 . The quartz crystal oscil- lator and a number of dividers supply a rectangular signal at 3000 or 3150 Hz. A low-pass filter converts this signal into a sinusoidal shape with a distortion smaller than 1 %. This is adequate for the measure- ments in question, because accuracy and stability are the prime aims. When set to test, the mode selection switch supplies the generated reference signal to a monostable multivibrator which functions as a frequency-to-voltage (f-V) converter in conjunction with the fil- ters that follow it. The pulse ratio is such that the centre of the meter range can be set with the calibration control during drift measure- When the mode switch is set to the MEASURE position, the f-V converter is driven with the output signal of the re- corder under test. When the absolute tape speed is higher than the standard speed, the input frequency of the converter is higher than the reference frequency (3000 Hz or 3150 Hz). This means that the MMV receives more trigger pulses within a unit of time, so that the low -pass filter at the output supplies a higher voltage. The needle of the moving-coil meter deflects to the right, and the relative deviation can be read from the scale as a percentage. Like- wise, the needle deflects to the left of the centre when the tape speed is too low. Wow and flutter measurements work on a similar basis. The only difference with drift measurement is the use of an additional rectifier that records short- term frequency changes which are the re- sult of relatively fast tracking errors in the tape mechanism as discussed earlier. Since this measurement need not dis- criminate between positive and negative deviations, the full scale, starting at 0, is available for the read-out (a centre indica- tion is not required). A differential ampli- fier is used for this purpose. The circuit in detail The circuit diagram is given in Fig. 2. The quartz crystal oscillator set up around gate Ni supplies a 3.2768 MHz signal to divider IC2, a Type CD4040. The divisor is either 1040 or 1092 as decoded by gates Ns, N6 and N7, and selected by switch Si (ccir/DIN). In the first case, the output frequency at pin 14 of IC2 is 3150 Hz, in the second case, 3000 Hz. A first-order passive low-pass filter is formed by R4, Rs, Ri, and O, and a third- order active low-pass filter by R-, Rn, R9, Cr, Cs, Cb and opamp OPi . The active filter is dimensioned for a roll-off frequency of about 3.5 kHz to achieve sufficient sup- pression of harmonics. A clean 3000 Hz or 3150 Hz sine-wave is available at pin 7 of OPi. A further opamp, OP2, raises this signal to a level of 0 dBm, or 775 mVrms (2.2 Vpp) into 600 SI. This level may be set by adjusting preset R11. * The sinusoidal test signal is used for recording purposes by feeding it to the output terminals (pins 1 and 4 on the DIN socket, and the phono-type recording socket) as well as for use as an internal reference during drift measurements. Toggle switch S2a selects either the tape signal or the internal reference signal. Either of these is applied to the input of amplifier OP3 via C9 and R13. Comparator OP4 converts the output signal of OP3 into a rectangular waveform. The monostable multivibrator around N3, N4 and IC6 is triggered at each rising pulse edge applied via C12 and R25. Counter/oscillator IC6 forms part of the MMV to ensure that the drift of the instru- ment itself can not affect the meter read- ings in the most sensitive range. Each positive pulse transition at pin 12 of gate N3 causes the output, pin 11, to change from high to low. This state is latched because of the bistable configura- tion of the two gates, and counter ICs is enabled via pin 12. The oscillator in the CD4060 starts to operate at a frequency determined by R28, R29 and Ci6. Ripple counter output pin 7 goes high after 8 clock cycles, which resetsbistable N.1-N1 via pin 2. The output of N3 disables 1C<> and resets the MMV to its initial state. Pin 3 of gate N4 is high for the duration of the oscillator activity. This pulse is used for further processing, and is marked by high stability in respect of the pulse width. That the instrument is capable of measuring tape tracking errors down to 0.1 % is mainly by virtue of the third-order active filter around R27, R41, R42, C20, C21, C22 and OP6, in combination with first- order low-pass section R43-C23. Opamps OP7 and OPs are configured to provide further amplification, while S3b forms the range selector. A peak rectifier is set up around OP9 and D11-C29. The reference level of the rec- tified signal is shifted from half the supply potential to ground by OPto, so that track- ing measurements can use the full meter scale starting at 0%. The centre-zero indication for absolute tape speed measurements is obtained with the aid of integrating network R26- C15 and an amplifier based on OPs. In the TEST mode, the meter is set to the centre indication with R39 (coarse) and R40 (fine). The measuring range is ±5%. Setting up The tracking tester can be adjusted with a frequency meter and an oscilloscope. To begin with, preset Ru is set for an output level of 775 mV™, at pin 1 of OP2. Other reference levels may be set where these are required. The calibrate control is set to the centre of its travel. Switch S2 is set to test, and preset R39 is adjusted until the meter indicates 0% at the centre of the scale. Range switch S3 is set to 'Drift 5%' for this adjustment. When the centre indication can not be achieved by turning preset R39, the devia- tion of the oscillator frequency generated by IC6 is too large. This frequency should be 49.2 kHz nominally with a maximum tolerance of ±10%. It can be measured at pin 9 of IC6, while pin 12 of gate N3 is provisionally made logic high with the aid of a short wire to the +8 V supply rail. Make small changes to R29 and/or R28 to pull the frequency within the acceptable range. Two series-connected resistors are used here for this setting instead of the more usual trimmer capacitor, which would magnify the effect of stray capacit- ance. The minimum equivalent resistance of R28-R29 must not be made lower than 6.8 k£2, and not higher than 22 kfl. The wire connection at pin 13 of N3 is removed after the necessary corrections have been When a frequency meter is not avail- able, R28 and R29 may be changed in 1 kU increments until the centre-zero indica- tion is achieved within the range of R39. The above corrections are not likely to be necessary in most cases, since the cir- cuit is dimensioned such that R39 covers the required control range. The frequency correction with the oscillator components around ICs is described for the sake of No other adjustments are required. Construction The circuit is built on two printed circuit boards, the main board and the oscillator board. The component overlays in Fig. 3 and the Parts List are given as an aid for populating the boards, which should be started with the low-profile components. All soldering is done at the track sides. The main board has some components that are mounted at the track side: voltage regulator ICs, electrolytic capacitors C15, C24, C25 and all solder terminals. After a thorough check of the com- pleted boards, the oscillator board may be mounted upright on to the main board in a manner where the copper surfaces at the side of Dio line up with the associated surfaces on the main board. The copper surfaces are then joined with plenty of solder to secure the oscillator board at right angles on to the track side of the main board. The oscillator board is rela- tively small and light, so that additional mechanical support is not required. The two phono sockets and the DIN socket are secured on to the front panel, which also serves to hold the main board by means of the nuts on the threaded shafts of the switches. One nut is first turned on to each of the shafts, followed by a locking washer, after which the spindles are inserted into the holes pro- vided in the front panel. Finally, the PCB assembly is secured to the front panel by one additional nut for each protruding switch shaft. The spindles of the potentiometer and the range switch are then cut to length and fitted with the associated knobs. Finally, the wiring is installed in ac- cordance with the circuit diagram. This includes the connection of the moving- coil meter and the supply voltage. The latter is applied to the circuit via a 3.5 mm jack socket on the rear panel of the enclo- sure. The recommended input voltage is 9 VDC. The meter is secured to the inside of the front panel. This requires removing a part of the rims at the inside of the top and bottom halves of the enclosure to ensure that the face of the meter is flush with the front panel. The meter is carefully secured with a some two-component adhesive or super-glue applied at the corners. Parts list Resistors: Ri ;R2;R2i-R24=390R R10-IKO R29-IK8 R45;R59=4K7 R28=6K8 , R4;R5;R6;Ri2;Ri3;Ri7;Ri8;R2S=10K R48=22K R43;R5i;R54=33K R31 ;R32=39K | R7;Rb;R9;R27;R34;R36;R4i ;R42-47K Ri4;Ri5;Ri6;Ri9;R25;R46;R47;Rso;R52; Rs3;R55;R56;Rs7.100K R44=120K Rsb=150K R3o;R3B=180K R49=330K R37-390K R33;R35=560K R20=1MO R3=20M Ri 1 ;R39=1 OK preset H R40=1 OK linear potentiometer; spindle Capacitors: i Ci=4p7 j C2=10p I Cs=82p j Ci2=100p j Ci6=1n0 i Cs=2n2; 5% C22=6n8: 5% I C4=10n;5% j C3=22n; 5% j Ci7;C2o;C23=47n; 5% | C2i=120n; 5% C7-Cn;Ci3;Ci4;Ci8;Ci9;C26-C29=10p; 16 V C25=22p ; 1 6 V Cis;C24=100p; 16 V Semiconductors: IC4=TL084 ICe=LM324 IC7-LM358 j ICi=CD4001 IC3=CD4023 IC2=CD4040 ] ICs=CD4060 ICs-7808 I Dio;Dn«1N4148 j D1-D9- LED; 3 mm; red Miscellaneous: Qi - 4 MHz quartz crystal. 53 = 3-pole, 4-way rotary switch for PCB mounting. Si;S2 - miniature DPDT switch. 54 = miniature SPDT switch. 1 0 solder terminals. 30 cm screened wire, single core. 20 cm screened wire, 2-core 0.4 mm 2 . i8.43 US 0 1 13 < -o I^JKsJM 1 n ( 1 '!°a°££r 0 O O O P 0,0 o mm heU^h MULTI-LAYER PCBS by A.J. Kool (ULTimate Technology, Norcross, USA) The introduction of multi-layer printed-circuit boards challenged designers in their creativity to use these additional layers efficiently. One of the ways to increase the area left for actual wiring is the use of buried vias. Buried vias connect copper layers in layer pairs. They are not drilled through the entire board, leaving more space for routeing on the other layers. Since the advent of surface mount technology - smt - these buried vias have become more popular with designers. The increased use of these vias, however, presents the designers with a new set of problems that only few cad systems are able of coping with. What are buried and blind vias? The idea of creating buried and blind vias comes from the manufacturing of the printed-circuit board. A multi-layer board is built from a set of (thin) double-sided boards. The copper layers of these thin boards form the copper layers of a multi- layer board. They are all etched and then stacked together, separated by insulation layers. This is the lamination process il- lustrated in Fig. 1 . Fig. 1. The layers are laminated together as thin boards. Buried vias are created by drilling and metallization of the thin boards before the lamination process. By doing this, the lay- ers of the thin boards are connected with vias. At this point, the whole set of thin boards is laminated, the vias in the middle layers are buried (not visibile from the outside) and the vias in outer layers are blind (visible from one side only) - see Fig. 2. For the designers, there is no differ- ence between buried and blind vias. When the idea of drilling and metal- lization is taken one step further, we may laminate boards I and II. drill and metal- lize the resulting board and complete the rest of the lamination process - see Fig. 3. Fig. 3. Layers I and II are drilled and metallized before laminating the other layers. Vias created like this are called 2nd order buried vias. By using 2nd, 3rd or higher order vias, we obtain a complicated lami- nation and metallization sequence that increases the routeability of printed-circuit boards, but also their cost. Using a cad system Until recently, CAD tools would only handle the buried vias between layer pairs. No provisions were available to have vias through more than two layers. Now smt is used more extensively, more designers are looking for cad tools that handle buried and blind vias in a highly automated way. To have a cad system automatically han- dle these vias, it must first know how the designer is planning to laminate the pcb. Arc 2nd. 3rd and higher order buried vias allowed? These are the things a cad sys- tem must know before vias can be used. When this is known by the system, a via placed between the top layer and Inner 3 can be computed to be 'through the board' or a 2nd order (if this was possible in the lamination sequence). Another aspect the cad system must deal with is the size of the drill hole. A multi-layer board with 10 layers is not (much) thicker than a 2-layer board. A sin- gle layer-pair of the 10-layer composite board is very thin. The via drill diameter may be smaller for these thin boards than for the through-the-board vias. The cad system must compute the number of layers the drilling hole will cross and select the drill diameter accordingly. If the designer wants to extend 1st order buried vias to a higher order, the drill diameter may need to be changed.To be able to manufacture the board, the pcb manufacturer needs to have a drill file for each layer-pair and each half-product that has buried vias. Finally, a drill file for the complete board is needed for the through- the-board vias and component pins. The 10-layer board of Fig. 4 needs 8 drill files: 5 for the layer-pairs, 2 for the half-prod- ucts and 1 for the complete board. Fig. 4. Example of a lamination sequence speci- fication for a 10-layer board in the ULTIboard pcb system: [(l+ll)+lll+(IV+V)]. This specification means: first handle (drill and metallize) the layer pairs I through V individually, then laminate I and II together and IV and V and handle these half-products. Then laminate III to.the half-prod- ucts and process the through-the-board vias. You might consider this sequence for a dense smt board with components mounted on both sides. The layers of layer-pair III (inner 4 and 5) would be the power and ground planes. The others (top, Inner 1, 2, 3, 6, 7, 8 and bottom) will be signal layers. Conclusion Currently available cad systems are sufficient for handling boards with 4 sig- nal layers. In a few years' time, when the need arises for a board with 6 or more lay- ers, all cad systems will almost certainly have to be able to support the higher order buried vias to some extent. 1 8.45 DC-AC POWER CONVERTER J. Ruffell Holidaymakers, do not forget this low-cost power converter when you are packing for this year’s camping tour. The converter works from the car battery, is simple-to-build from standard components, and provides you with up to sixty watts to power mains-operated loads such as a shaver, a small fluorescent tube, and (dare we suggest it?) a soldering iron. There is nothing to beat the good old camp fire, candles-, or pale moonlight to light holidaymakers gathered for the evening barbecue on the camping site. An electric light source, on the other hand, is the thing you want when tentpegs are to be driven in the ground in the middle of the night, somewhere, in the dark, on an un- familiar site. An AC converter is also handy for the daily shave, for the portable TV set, a small fluorescent tube, a radio, oscilloscope or computer. Circuif descripfion The circuit diagram of Fig. 1 shows that the DC-AC power converter is built from commonly available and inexpensive parts. Circuit ICi, a CMOS Type CD4047, is used as an astable multivibrator whose outputs, Q and Q, supply a square wave signal that has a frequency of about 50 Hz. To prevent excessive loading of the chip outputs, the complementary signals are fed to the gates of Type BS170 low-power MOSFETs. These transistors are capable of switching at high speed, they guarantee low turn-on and turn-off times, and pro- vide sufficient drive for the bipolar power stage composed of drivers T3-T4 and power devices T5-T6. Like the MOSFETs, the transistors used in the power stage are selected for their switching speed, with an aim to keep dissipation in Ts and Ts as low as possible. Zener diodes D2 and Dj pro- tect the power transistors against voltage peaks generated by the transformer, which forms an inductive load. The power transformer is a standard type, i.e., not a toroid, and is used 'the other way around' to step up the low volt- age to the mains voltage. The low-voltage winding with its centre tap forms the pri- mary. The centre tap is not connected to ground as usual in most power supplies, but to +12 V. The power transistors, Ts and Tg, alternately take the outer connec- tions of the primary to ground, passing considerable current. This, in turn, in- duces a voltage in the secondary, which is the mains winding in this case. A fuse completes the AC-DC converter. 50 Hz quartz-controlled Most radio alarm clocks use the frequency of the mains voltage as the timing refer- ence. A small extension circuit enables the DC-AC converter to supply the mains voltage at a constant and accurately defined frequency of 50 Hz. The printed- circuit board of the converter is provided with a connection for accepting the 50 Hz Figure 2 shows that the 50 Hz refer- ence signal is derived from a 3.2768 MHz quartz crystal. The circuit uses only two CMOS ICs, and operates from 12 V. The quartz crystal is an inexpensive type com- monly used in clock timebase circuits. The frequency of oscillation is trimmed with C2. A fixed, ceramic, 12 pF capacitor may be preferred over the trimmer in some cases, and results in a frequency deviation that is perfectly acceptable for the appli- cation in question. When the trimmer is used, it is adjusted for a frequency of 204.8 kHz at test point TP. The 50 Hz sig- nal available at point 3 of the timebase is connected to point 2 of the DC-AC conver- ter. In this configuration, a wire link is installed between points 5 and 6. When Fig. 2. This quartz-crystal controlled timebase is an optional extension of the power converter. the external timebase is not used, the wire link is installed between points 4 and 5, while point 2 is grounded via a link to Construction and practical use There is little to say about the construction of the power converter because the popu- lation of the printed circuit board (Fig. 3) is entirely straightforward. By virtue of the high overall efficiency, the power transistors can do with a relatively small heat-sink. When the unit is mounted in a Parts list Resistors: Ri = 560k R2 = 1k2 R3;R4 = 2k2 Re;R7 * 560; 5 W Capacitors: Ci - 8n2 C2 - 47g; 6V3 C3- lOg; 16 V Semiconductors: Di ■ zener diode 5V6; 400 mW D2;D3 = zener diode 47 V; 1 W Ti;T2- BS170 (Cricklewood Electronics) T3;T4 = B0139 Ts;Te = BD249 ICi = 4047 Miscellaneous: Ft = luse 1 00 mA; slow. Tri = mains transformer 2x10 V; 2.2 A. Heat-sink for Ts and T6; max. 4°C/W. Insulating washers and bolts for Ts and T6. PCB Type 890056 metal enclosure, the transistors are con- veniently bolted on to a side panel. Do not forget to use insulating washers and a touch of heat-conducting compound. The introductory photograph shows the prototype in a sturdy metal enclosure with a shaver-type output socket and heavy-duty wander sockets for connect- ing the battery cable. The low-voltage winding of the trans- former is switched to achieve high effi- ciency. As a result, the generated high voltage is a fairly clean square wave, which remains largely rectangular with 1 8.47 Paris list 8.51 Fig. 37. Internal data structure of the control program. Two separate modules handle the data pro- cessing: the data managing unit and the RS232 command handler. is performed by the data managing unit. This part of the program carries out the loading and processing of the controller and keyboard data and ensures that these are transmitted via the rails in good time. The second module, the RS232 com- mand handler, interrupts the data manag- ing unit as soon as RS232 instructions appear on the line. It interprets the received commands and ensures that the system undertakes correct action for each instruction. All incoming data are collected, pro- cessed if necessary and put into sequence before they are retransmitted via the rails. In this respect, the system resembles a post office. In the ram a number of buffers have been reserved for sorting data. Other buffers merely collect incoming data and yet others hold data ready for transmis- The internal data structure is shown in Fig. 37, which also shews the position of the two modules and to which buffers they have access. As already mentioned, the data manag- ing unit performs the routine tasks. It loads the controller and keyboard data in the locomotive output buffer and key com- mand buffer respectively. It also carries out any required data conversions and, for instance, adaptation of Elektor Electronics or Marklin locomotive data formats. More- over, it.retransmits data via the rails, including any stored in the RS232 com- mand buffer. The RS232 command handler takes care of the communication with an external host computer. On the one hand it contains module routines with which the RS232 interface is realized (the system does not use a special RS232 chip) and on the other hand it contains a decoding routine to decipher incoming commands. Incoming locomotive control instruc- tions are placed direct into the locomotive output buffer. This means, in effect, that the data managing unit loses control of the associated locomotive address until this is released again by the RS232 interface. Switching instructions are loaded into a separate buffer. Yet other buffers are used by the RS232 command handler for moni- toring or ascertaining the position of sig- nals or turnouts (points). The RS232 command handler has access also to the locomotive input buffer for monitoring and ascertaining the posi- tion of controllers and set locomotive addresses. The monitoring (feedback) buffer is accessible only via the RS232 interface. If it is necessary that a given monitoring signal requires a certain action, this has to be pro- grammed via the host computer. This means that if you do not intend to connect the system to a computer, there is no sense in using monitoring units. Cost aspects Before you start work on a complete and far-reaching digitization of your model railway, you would, no doubt, appreciate what sort of outlay you may expect. A first glance at the main pcb may make you hesitate even to begin thinking about starting, but, although it looks complex (and therefore expensive?), we believe that the proposed system is very inexpensive for what it offers. The main expenditure will almost cer- tainly be the main pcb (for price, see Readers' Services section), which is dou- ble-sided and through-plated (not easy to make yourself or even to have made). But almost all the components used on this board are fairly, or very, cheap. Also bear in mind that the locomotive addresses may be set with the aid of cheap diodes. More sophisticated means (dil switches, for instance) are entirely your Another point worth remembering is that connecting the locomotive controllers via din connectors is, strictly speaking, an unnecessary luxury. The main expense in the booster lies in the mains transformer and the heat sink, but even for a non-digital track you need at least one transformer. Here, it is worth bearing in mind that it is invariably much cheaper to buy an appropriate transformer from an electronics retailer than to insist on a proprietary "model train trans- The keyboard circuits, as well as those for the monitoring units, have been kept as simple and inexpensive as feasible, partic- ularly since we realize that most users will want (or need) a number of these units. 8.52 NEW PRODUCTS Photoelectric Switch Electro Arts have a developed a Photo electric with a range of 10 m for diverse industrial applications. The unit works on a modulated infrared beam and is not affected by vibrations, ambient light and weather condition. Working on 220 V AC, the unit is available in light sensings or Dark sensing modes. M/s. Electro Arts • 4, Vaishali • Gan- gapur Road • Nashik-422 005. PCB Inspection Projector A PCB Inspection Projector (Model 175) for inspection of PCB artworks, negative, films etc is being marketed by Dynascan Inspection Systems Company. The projector has a screen size of 175 x 175 mm, with a magnification of 10 x and can accomodate a PCB of maximum size 450 x 375 mm. Lighting is provided by means of three halogen bulbs. A stereo microscope is available for Inclined/ straight viewing for through holes in- spection. A Digital Readout Systems can also be provided for measuring track widths, lengths, pad diameters, hole diameters etc. M/s. Dynascan Inspection Systems Com- pany • Plot No. 1 • Benningana Halli • Old Madras Road • Bangalore-560 016. Programming Module (PGM-8540) Professional Electronic Products is of- fering a PAL Programming Module (PGM-8540) for programming Prog- rammable Array Logic (PAL) devices of MMI. National Semoconductors and Texas Instruments. This device is an at- tachment to PEP’s Univer PROM Prog- rammer PP-85, and is supplier alongwith the necessary software. This software runs on a PC/XT checking of trace waveforms and simulations can be done on the PC itself. A large number of PAL devices can be programmed through this. M/s. Professional Electronic Products • Opp- Old Octroi Post • Delhi Road • P.B. No. 316 • MEERUT-250 002. • Tel: 20159, 20460. Automatic Light Switch Electronics Hobby Centre has brought out a solid state Automatic Light Switch which does not use a transformer and re- lays. This switch puts the light ‘ON’ at dusk and ‘OFF’ at dawn. Working on 220 V AC, it is available in. ratings of 300 and 600 W. The circuit is encased in plastic ABS cabinet and is available in both wall mountings or plugging type models. M/s. Electronics Hobby Centre • F-32, Nand Dham Industrial Estate • Marol • Bombay-400 059 • Ph: 636 6123. PCB Racks Circuit Aids. Inc., has developed FRP moulded PCB Racks designed to hold PCBs of any thickness vertically. The maximum card length that can be ac- comodate is 18” and each rack can hold 25 cards. The racks can be mounted on a trolley for easy transportation. * 0 ^ M/s. Circuit Aids Inc. • Nom 451, II Floor, 64th Cross • V Block, Rajaji Nagar • Bangalore-560 010. • Tel:- 359694. 8.54 NLW PRODUCTS Plug-In-Timer Pla has introduced Series PT Plug-in- Electronic Timer suitable for 8 pin base. Compact and light these timers have a range from 0.1 seconds to 60 minutes with ON/OFF delay action. Contact rated at 6 A at 24 V DC/240 V AC. M/s. SAI Electronics • (A Divn. of Starch & Allied Industries) • Thakor Estate • Kurla Kiron Road • Vidyavihar (W) • Bombay-400 086 • Ph: 5113094/5113094/ 5136601. Ribbon Stuffing Machine Track Engineers have developed a rib- bon stuffing/refilling machine for com- puter printer ribbons. The machine is useful for filling the new ribbon from rib- bon rolls into the cassette. The machine consists of a variable speed drive at 250 rpm with a precise speec controller and an electronic counter. As the ribbon is filled into the cassette, the counter pro- vides the length in meters. The speed controller facilitates the use of same machines with all the cassettes. The op- eration is very fast with one cassette re- quire about 2-3 minutes to fill. Different sized ribbons can also be filled by the machines. These machines are suitable for new ribbon manufacturers as well as dealer providing refilling services. M/s. Track Engineers • 209, Devendra Industrial Estate • I.okmanya Nagar • Pada No. 2 • Thane (W)-400 606 o Tel: 509446. Data Well Outlet PRIM A INDUSTRIES has introduced a Data Wall Outlet for terminating Rs 232 and BNC connectors for LAN installa- tions. This is manufactured from high grade ABS plastic and comprises of three parts viz, the wall mounted enclo- sure, the connector mounting plate and the dust cover. Useful for computer in- stallations and other electronic based systems. The Wall outlet provides for neat installations by eliminating untidy cabling and connectors lying on the M/s. Prima Industries • 16, Sargent House • Allana Road • Bombay-400 039 • Tel No. 242086. Power Supply Analyser ATE Ltd is offering Chroma 600 Switch- ing Power Supply Analyzer, manufac- tured by Chroma ATE Taiwan. The analyser can simulate a wide variety of static, dynamic, transient load condition in order to determine the stability and re- sponse of the power systems. Suitable for testing power supply variable in R&D, production and QC application. Available in 4 models. M/s. A.T.E. Limited • Electronic Divison • 36, SDF 2, SEEPZ • Andheri (E) • Bombay-400 096. Grommet Ring Grommet Ring used for protecting wires. Cable cords against damage from sharp panel edges, have been developed by Novoflex. These rings are highly flex- ible and have good resistance to fluids, mineral oils, alkalies etc. They are self extinguishing with good insulating prop- erties. Available for Panel hole diameter 5 mm to 30 mm. These rings are used in a wide number of industries. M/s. Novoflex Cable Care Systems • Post Box No. 9159 • Calcutta-700 016 • Tel: 299-4382, 29-5939, 299-3991. 8.56 NEW PRODUCTS Emergency Light Prolite is offering a wide range of Emergency Fluorescent tube lights. The range includes mini tube light (of 8W / 9W/22W) and standard tube lights. ( 1 0W/20W/40W) . Powered by Sealed Dry Maintenance Free Rechargeable Batteries, each unit consists of - a battery charger - High frequency inverter. - solid state switching circuit - Auto cut-off circuit Useful in a number of places like banks, hospitals, factories, offices, homes etc., the units are available in both desk top/ wall mounting versions. M/s. Professional Lighting Industries • 25, Singh Industrial Estate No. 3 • Ram Mandir Road • Goregaon (W) • Bom- bay-400 104 •Tel: 672 35 21. Ceramic Capacitor Kit A.T.E. Ltd. is marketing a Multilayer Ceramic Chip Capacitor kit manufac- tured by Vitramon Ltd. of U.K. It com- prises of a box containing 54 individual containers of chip capacitors totalling over 5000 pieces in 0805, 1206, 1210 and 1812 sizes with Nickel Barrier Termina- tions. A wide range of capacitive values ranging from 0-47 pF upto 220 nF is in- cluded. The chip kit is useful for pro- totyping and design engineering applica- tions. M/s. A.T.E. Limited • (Electronics Divi- sion) • 36, SDF 2, SEEPZ. Andheri (E) • Bombay-400 096. Digital Frequency Counter Vasavi Electronics is marketing a com- pact digital frequency counter VDC 18. Features include Mains/Battery opera- tions, 7 digit LED display, 500 MHz fre- quency range, light weight, resolution selection etc. M/s. Vasavi Electronics • M-8, Chenoy Trade Centre • Parklane • Secun- derabad-500 003 • Ph: 70995. Soldering Iron Bits Soldering Iron Bits 30 W-24 V are being offered by Khanchandani Industries. Manufactured from high conductivity Copper Rods of 99.99% purity, these are Nickle plated for enhancing their life and easier solder flow. M/s. Khanchandani Industries • 36, Shanti Indl. Estate • Sarojini Naidu Road • Mulund (West) • Bombay-400 080. Key Switch Integral Systems have introduced Key Switches 1 K 9 in various sizes. Made of ABS or acetal, the contacts are rated at 0.1 A, 30 V.D.C. The Switch has an operating life of 2 million times with the contact mechanism comprising of a gold plated rotating ball which offers a fresh surface as contact, each time the plunger is depressed. This ensures a longer life compared to conventional switches where the sheet metal contacts suffer from problems of distortion, fatigue etc. Integral Systems and Components Pvt. Ltd. • 45/7 A, Gubbanna Indl. Estate • 6th Block • Rajajinagar • Bangalore-560 010 • 35 42 47. NEW PRODUCTS ANTISTATIC ELECTRO STATIC DISCHARGE BAGS. Marvel Products have introduced reusa- ble economical P.V.C material E.S.D semi transparent bags for storing P .C.B & Electrostatic sensitive components these bags arc available in various sizes (As per specifications) with printed cau- tion warning sign. For further information contact:- • Marvel Products • 208, Allied Industrial Estate, • Mahim • Bombay-400 016. PRINTED CIRCUIT CARD FIXTURE The PCF-10 is a handy PCB fixture unit for every electronic assembly and main- tainance workshop. A pair of adjustable card guides allow the user for holding PCB’s of various sizes at any convenient position, either horizontal or vertical. It incorporates a unique arrangement to hold PCB's in a vertically locked position for providing easy access to both sides of printed circuits and especially for remov- ing IC’s without damaging the printed circuit board. The PCF-10 is light in weight and can be used as a table top fix- ture. It has working dimensions of 240mm x 300mm to cover most require- ments of every electronic workshop. Also available with additional card hol- ders for use in factory production line wherever a system incorporates inter- laced PCB wiring. Contact: • M/s. Electro-Links • Plot No. 49, • Shop No. 9, • New Link Road, • Behram Baug • Jogeshwari (West) • Bombay-400 102. UPS Prolite has recently introduced a solid state Uninterruptible Power Supply Sys- tems for various industrial and consumer applications. Rated at 400 VA, it incor- porates Rechargeable Maintenance free Batteries of 24V. 18AH. The system also has a pulsed boost-cum-trickle charger to monitor and control the battery charg- ing. This unit is also available in the OFF LINE Mode. M/s. Professional Lighting Industries • 25, Singh Industrial Estate No. 3 • Ram Mandir Road, Goregaon (West) • Bom- bay-400 104 • Ph: 672 35 21. Spectrum Analyser THE spectrum analyser FSB by Rohde & Schwarz is claimed to be the first spec- trum analyser in the 100 Hz to 5 GHz (5.2 GHz) range with intrinsic noise below- 145 dBm (6 Hz); on a colour sc- reen with a usable display range of 105 dB in a measuring range > 170 dB. Thanks to its measuring characteristics, user-oriented expert functions, and au- tomatic test routines it is suitable for complex testing to CEPT regulations as well as for microwave link applications. The low phase noise of<-110dBc(l Hz) 1 KHz from the carrier and the wide in- termodulation free range > 100 dB make high dynamic range measurements pos- sible. The large resolution band width range of 6 Hz to 3 MHz (typ., quasianalog setting) and the span from 10 Hz to 5.2 GHz make the FSB indis- pensible for all selective level measure- ments. M/s. Rohde & Schwarz • Liaison Office India • B-Block, Ground floor • 9, Prithviraj Road • New Delhi-110 011. R. N. No. 39881/83 Allowed to post without prepayment. LIC No. 91 MH BY WEST-228 DO IT YOURSELF UCN 5 bookshops. LEARIM-BUILD- PROGRAM The Junior Computer book is for anyone wishing to become familiar with microcomputers, this book gives the opportunity to build and program a personal computer at a very reasonable cost. The Indian reprint comes to you from ■ elekte? Send full payment by M.O./I.P.O./D.D. No Cheque Please. ! Packing & Postage free to: eIeIoor eIectromcs pvT frd. 52-C, Proctor Road, Grant Road (E|. Bombay-400 007.