ISSN 0970-3993 SPECIAL FEATURES: * Computers in Banking * Computer Mouse * Personal Computer Decisions * Speeding-up the Cpmputer PROJECTS: * 3 Vi - Digit SMD Voltmeter * Intruder Alarm * DC-DC Power Converter * Active Loudspeaker Crossover Filters * Automatic Outdoor Light. Volume-7, Number-12 December 1989 Publisher : C.R. Chandarana Editor: Surendra Iyer Circulation : Advertising : J. Ohas Production: C.N. Mithagari Address: ElEKTOR ELECTRONICS PVT. LTD. 52, C Proctor Road, Bombay -400 007 INDIA Telex: (011)76661 ELEK IN OVERSEAS EDITIONS Elektor Electronics (Publishing) Down House, Broomhill Road, LONDON SW18 4JQ Editor: len Seymour Elektor sari Route Nationals; Le Seau; B.P. 53 59270 Bailleul - France Editors: D R S Meyer; G C P Raedersdorf Elektor Verlag GmbH Siisterfeld-StraBe 25 5100 Aachen - West Germany Editor: E J A Krempelsauer Elektor EPE Karaiskaki 14 16673 Voula - Athens - Greece Editor: E Xanthoulis Elekluur B.V. P"- Peter Treckpoelstraat 2-4 \ 6191 VK Beek - the Netherlands Editor: PEL Kersemakers Electro-shop 35 Naseem Plaza Lasbella Chawk Karachi 5 - Pakistan Manager: Zain Ahmed Ferreira & Bento Lda. R.D. Estefania, 31-1° 1000 Lisboa-Portugal Editor: Jeremias Sequeira ^ Ingelek S.A. Plaza Republics Ecuador 2-28016 Madrid - Spain Editor: A M Ferrer Electronic Press AB Box 5505 14105 Huddinge - Sweden Editor: Bill Cedrum The Circuits are domestic use only. The submission ot designs or articles implies permission to the publisher to alter and translate the text and design and to use the contents in other Elektor Publications and activities The publishers cannot guarantee to return any material submitted to them. Material must be sent to the Holland address (given above). All drawings, photographs, printed circuit boards and articles published in elektoi publications are copyright and may not be reproduced or imitated in whole or part without prior written permission of the publishers. Patent protection may exist in respect of circuit devices, components etc. described in this magazine. The publishers do not accept responsibility for failing to identify such patent or other protection. ■ty*. Printed at : Trupti Offset Bombay - 400 01? Copyright ® 1989 Elektuur B.V. CONTENTS Special Features Super sun-storm management 12.10 Robots for satellite repairs 12.10 Video phones & HDTV 12.11 Remote diagnosis 12.11 Banking Computers 12.15 Audio & Hi-fi PROJECT: Active loudspeaker crossover filter (2) 12.15 Components Practical filter-design Part 10 (Final) 12.30 Computers Computer mouse 12.18 Personal computer decisions 12.46 Speeding up the computer 12.48 Design Ideas Protecting asynchronous motors 12.36 General Interest PROJECT: The digital model train Part-8 12.20 PROJECT: Automatic outdoor light 12.32 PROJECT: Intruder alarm 12.33 PROJECT: DC-DC power converter 12.42 a Radio & Television Travelling wave tubes 12.60 Science & Technology Intelligence intentionally & self awareness 12.38 Test & Measurement PROJECT: 3'A digit SMD voltmeter 12.25 elektor india dccember 1989 12.03 COMPUTER MOUSE J. Ruffell Raptly looking at the screen and cheerfully moving the mouse around on our desks to make our way through menus, few of us appear to be aware of the operation of the most popular pointing device for computer applications. A computer mouse is also called a pointing device because it allows the cursor (usually an arrow or crosshairs) to be moved across the computer screen. You use your hand to control the direction and speed of the cursor. Many mouse-oriented programs allow you to select an option from a menu on the screen simply by pointing at it and clicking a button on the mouse. The mouse has become so popular because it obviates keyboard commands that distract the at- tention from the screen and are relatively slow and susceptible to errors. Another major application of the computer, draw- ing, would be unthinkable without a mouse. Principle of operation One aspect common to all computer mice is that movement is converted into signals that can be handled by a computer. This is achieved basically as shown in Fig. 1. An auxiliary spindle presses a small ball lightly against two spindles that are mounted at right angles to each other. Its own weight, and in some cases the auxil- iary spindle also, keeps the ball in contact with the desk surface or mouse pad. The movement of the ball is hardly obstructed because the areas where the spindles touch the ball are small. The friction is, however, sufficient to cause the spindles to rotate if the ball is moved horizontally ( x component) or vertically (y component) in a two-dimensional plane. In this man- ner, the spindles extract the horizontal and vertical components from the mouse movement. These two components are converted into four electrical signals. This is done by mounting a slotted disk on to each spindle. The slots are arranged such that the light beam of one optocoupler is fully passed when the other optocoupler is about half way open. As the spindle rotates, the optocouplers produce two rec- tangular signals with a phase difference of 90°. The direction of travel of the spindle (in one plane) can be deduced from the phase relation of the two signals. Tire number of periods of the rectangular sig- nal indicates the relative distance covered by the ball, and its speed. Figure 3 shows how the two rectangu- lar signals are used to deduce the direc- tion of travel of the mouse. One optocoupler signal is called reference, the other direction. The reference signal deter- mines the instant the minimum step size (distance travelled) is reached in the direc- tion indicated by the direction signal. This instant is marked by one of the level tran- sitions (pulse edges) of the reference sig- nal. Since most computer interrupts are called by negative pulse edges, it is con- venient to look at the l-to-0 transition of the reference signal. As shown in Fig. 3a, the direction signal is logic high at the negative edge of the reference signal. For the opposite direction, however (Fig. 3b), the direction signal is low at the negative edge of reference signal. In terms of pro- gramming, this means that the number representing the cursor position on the screen must be changed on the falling edge of the reference signal. In this soft- ware routine, the direction signal must be read to determine whether the cursor po- sition must be incremented or de- cremented at a particular step size, e.g., one screen position. If, after first connect- ing a mouse and installing the software 12.18 elektor India december 1989 Fig. 2. Slotted discs and optocouplers are used to digitise ball movement. driver, the cursor movement is opposite to that of the mouse, the reference and direc- tion signals probably need to be swapped. The above description of the basic operation of a mouse applies, at least in principle, to most other pointing devices that allow the user to control the cursor position on the screen direct by moving the mouse accordingly. There are, how- ever, also applications that 1 quire a dif- ferent approach. Take, for instance, a program that enables a drawing on paper to be copied into the computer by means of a mouse. In this case it is the drawing, not the computer screen, that determines the cursor position. This type of mouse is known as a digitiser, and is usually sup- plied with a special pad. The paper is in- serted between the digitiser and the pad. The window in the digitiser 'sees' the pad surface through the paper. Because the pad 'communicates' with the digitiser, an output signal is available that enables the computer to determine the absolute posi- tion above the pad, and, of course, above the paper, which is secured on it. Lifting the digitiser and putting it down again a little further is therefore perfectly accept- able, since the new position is detected immediately. This is in contrast with a ball-type mouse, which can not supply positional information if it is lifted from the desk. Another system to convey positional information to the computer is a combina- tion of a graticule pad and a mouse with built-in reflection sensors. The internal operation is functionally similar to that of the discs and spindles in the ball-type mouse. The optocouplers are replaced by sensors that detect the light reflected by the pad. The function of the discs is taken over by the pad with its pattern of light and dark areas. Like the ball-type mouse, the optical mouse produces a reference and a direction signal. Its clear advantage is, of course, the absence of moving parts. However, the optical mouse also has its disadvantages: these are mainly that the pad has to be kept clean, and that the pattern on it is critical. To the computer The simplest way to convey the rectangu- lar output signals supplied by the mouse is, of course, by means of a cable. The computer has either a built-in mouse adapter ('bus mouse', e.g. the Amstrad PC1512/1640 series), or a standard RS232 serial port to which a mouse with built-in 'intelligence' can be connected (e.g., most standard IBM PCs and compatibles). The latter mice are often microcontroller- driven, and supplied with a special soft- ware program, called the mouse driver, that enables the PC to translate data re- ceived at high speed via the RS232 port to be translated into cursor movement. The current required for powering the circuit in the RS232 mouse is obtained from the computer's serial port. This is possible only by virtue of the low current drain of the serial mouse. The latest in pointing device technol- ogy is the wireless mouse, which com- municates with the computer via an infra-red link. Position output and the way the data is processing in the driver are, however, not different from those of the conventional 'mouse with tail'. Signal processing As already stated, the mouse signals are usually processed by means of a driver program installed on the computer. Most computer users will content themselves with being able to automatically install the mouse with the correct parameters as partof the system configuration programs called at power-on. For advanced applica- tions, however, mouse manufacturers like Genius supply a programming guide and auxiliary programs (e.g.. Genius Menu Fig. 4. Serial mouse with on-board CMOS microcontroller to guarantee a low current drain from the RS-232 port on the computer. Fig. 3. The phase relation between the ref- erence and direction signals is used to de- duce the direction of travel. Maker) that give the user the opportunity to implement his own pull-down menus and mouse control in a particular pro- gram. Among the many functions of the driver or the microcontroller in the serial mouse is adaptive resolution control, or con- trol of the step size as a function of mouse speed. If the mouse speed exceeds a cer- tain predefined value, the cursor step size is automatically increased. The advantage of this system is that a relatively small mouse movement enables large distances to be covered rapidly on the screen. elektor india december 1989 1 2.19 THE DIGITAL MODEL TRAIN - PART 8 by T. Wigmore Construction & testing IC sockets may be used, but it should be noted that this is no longer accepted prac- tice, at least as far as standard logics cir- cuits are concerned. Some sockets are more expensive than the IC itself and, more importantly, the reliability of a circuit is inversely proportional to the number of connexion s. None the less, for the more expensive ICs, such as the A-D converter (1C25) and the EPROM (IC13), a good- quality socket is recommended. Bear in mind also that the printed-circuit board is through-plated: any desoldering of ICs is, therefore, a tricky operation. So, check and double-check whether the 1C is the correct one before soldering it on to the board. The parts list shows ICs of the HC- and HCT-type. The HC-types may be replaced by HCT-types, but FICT-types should NOT be replaced by HC-types. Power supply. Start by fitting D38-D41, D36, C24, C25 and C27. Next, fit IC29 on to the relevant heat sink and mount the re- sulting assembly on to the board. There are tracks underneath the heat sink that are protected by a thin layer of lacquer only: it is therefore necessary to give these extra insulation (by, for instance, a suitably-sized piece of thin cardboard or old PCB or insu- lating tape). The IC should be fixed to the heat sink with an M-3 bolt, nut and wash- er, and a generous amount of heat con- ducting paste. Connect the mains transformer to the ~ terminals on the PCB. If you intend to use more than It) keyboards in addition to the main board, a transformer of higher rating than indicated in the parts list must be used, or the keyboards (dealt with in Part 9) must have a separate power supply. Assuming that the keyboards will be fed by the present supply, wire link A must be fitted. It is possible to use a suitable mains adapter provided this delivers 9 V at not less than 800 mA. If the adapter delivers a direct voltage, D39 and D40 may be replaced by wire links and D38 and D41 must be omitted. Switch on the mains and check that the output voltage of IC29 is 5 V ±5%. If it is not, disconnect the mains, discharge C25 via a 100 U resistor, and check all the com- ponents and the preceding work thorough- ly. If the output is all right, switch off the mains and discharge C25 via a 100 Cl resis- tor. Oscillator. Fit 1C8, IC21, R2, R3, C22, C37, C40 and the crystals on to the board. Switch on the mains and verify that a sym- metrical signal of 2.458 MHz exists on pin 12, and a signal of 614 kHz on pin 8 of IC8. Microprocessor. Fit 1C4, R8, R12, R18, R19, R24, C34, D34 (observe polarity!), Tl, IC24, R13 and C23. These components constitute the power-up reset for microprocessor IC4. The operation of IC4 is tested by placing an instruction on the data bus by means of hardware. In the first instance, this is the STOP instruction (76jq: 011 1 011 0g). For Parts list Resistors: Ri = 100Q R2;R3 - 4k7 R4;Rs;Rii;Ri2;Ri7-R2o;R22;R23;R24= 10k R6;Rio = SIL resistor array 10k R7;R8;Ri5 = 3300 R9;Ri4;Ri6 = 47k Ri3 = 15k R 21 = 6k8 Capacitors: C 1 -C 16 = lOn (pitch 5 mm) Ci7 = 47p Cib;Ci 9= lOOp; 25V C 2 o;C 2 i = 220n C 22 = 33p C23 = 4p7; 6V3; tantalum C24;C27 = 470n C 28 -C 42 = lOOn (pitch 7.5 mm) C 25 = 2200p; 16V; axial C 26 = lOg; 6V3; tantalum Semiconductors: □i-D32;D37 = 1N4148 D 33 = green LED D 34 = red LED D 35 = yellow LED D36 = 1 N4001 D38-D41 = 1 N5401 Ti;Ta = BC557 T 2 = BC547 ICt = 74HC(T)245 IC 2 = 74HC(T)74 IC3 = Z80PIO (Z8420 or Z84C20) IC4 = Z80CPU (Z8400 or Z84C00) IC5;IC6 = 74HCT238 IC7 = 74HCT139 ICs = 74HCT93 IC 9 = MCI 489 or SN75189 IC 10 = MCI 488 or SN75188 ICi 1 ;IC26 = 74HCT32 IC 12 = Z80CTC (Z8430 or Z84C30) I C 1 3 = 2764 (ESS572) IC 14 = 6264 IC 15 = 78L12 IC 16 = 79L12 ICi7;ICi9 = 74HCT174 ICis = 4066 IC 20 = 74HCT244 IC 21 = 74HCT04 I C 22 ; IC 23 = 74HCT374 IC24 = 74HCT74 IC 25 = ADC0816 IC27 = MCI 45026 IC 28 = 74HCT1 38 IC 29 = 7805 Note: ICs from the HC-series may be re- placed by HCT-equivalents. Do not use a HC type if a HCT type is stated. LS-types are not suitable because of their higher cur- rent consumption. Miscellaneous: Ki-Kis = 5-way 180” DIN socket for PCB mounting . 36 off M2x5 screws for securing Ki-Kia. K 19 = 20-way SIL female header; angled: 0.1 -in. pitch (e.g., Assmann AWRF A20Z). K 20 = 9-way feamle sub-D connector; angled; for PCB mounting. 2 off M3x8 screws for securing K 20 . K 21 = optional 40-way for future extensions. REi = OIL reed-relay; 5 V coil voltage; e.g., Siemens V231 00-V40O5-AO00. Xi = quartz crystal 4.9152 MHz. 51 ;S3 = push-to-make button. 5 2 = push-to-break button. Heat-sink for IC 29 : size 30x37.5 mm (e.g., SK09 from Dau Components/Fischer). Mains transformer 8 V or 9 V @ 1 A min. sec. PCB Type 87291-5 Additionally required for each loco controller (max. 16 allowed): Loco controller: Potentiometer 100k linear (rotary or slide type) with knob. 5-way DIN-plug; 180”. One (EEDTS) or two (Marklin-system) SPST switches. Loco address settings (4 options): 1) fixed address setting: diodes 1N4148, max. 6 2) variable address setting: 8 diodes 1N4148 and 1 8-way DIP switch block. 3) variable addresss setting: 8 diodes 1N4148 1 6-way header with 2x8 contacts in 0.1 -in. raster, max. 6 jumpers 4) extra-flexible address setting: as option 3 but instead of jumpers: 16-way flatcable connector 2 BCD-encoded thumbwheel switches ' number of sockets depends on number of connected loco controllers. Socket K18 is preferably a 6-way type for PCB mounting. 12.20 elektor india december 1989 N XXXXZXXX Fig. 49. Operation of the microprocessor is test- ed by instructions on the data bus formed by resistors. The STOP instruction (01110110b) ' s formed as shown at the top, and the NOP instruction (00000000) as shown in the lower illustration. this, eight 4k7 resistors are connected as shown in Fig. 49a to where later (possibly) K21 will be connected. When the mains is switched on, D34 should light. Switch off the mains and place the NOP instruction (00000000) on to the data bus as shown in Fig. 49b. Switch on the mains and check the data bus for any short-circuits. Pin AO should have a symmetrical square wave of 307 kHz; A1 one of 307/2 kHz; A2 one of 307/4 kHz; and so on up to A15, which should have one of 9.375 kHz. Fig. 50. Component layout of the double-sided, through-plated main printed circuit board. The board is illustrated here on a scale of 95:100. 00900000000 0000000 00' ,00000000000000000000 I xzxzzxzz > 2 1W»5 SSO&ODBSOSDSBOO&ObOl aaaaaai .aaaaaaa. 9 ICll « Si? icis ‘oeoooog 6 aaaaaai im • mil aaaaaaaa, IC28 4 | IC27 J qgpoooc r «ror elektor india december 1989 1 2.21 Memory. The next step is the mounting of the EPROM (IC13) that con tains the con- trol program, the RAM (104) and the memory address decoder (IC28). At the same time, fit decoupling capacitors C33, C35 and C36. Next, fit IC3, 102, Rll, R16, R17, R9 (immediately adjacent to C25), R22, R15, D35, T3, IC7, IC26, C32, C41, C42, SI and S2. Switch on the mains and press SI, when the program should go into the ser- vice routine, indicated by the flashing in a 1 Hz rhythm of D35. If this happens, 1C3, 102, IC4 and the memories work satisfac- torily. If, however, D33 lights, the control program has gone into the internal RAM test routine: this is almost certainly caused by 103 and associated components. Serial output. Fit IC11, 107, 108, IC23, IC27, C30, R7, R14, D33 and T2. Switch on the mains and press SI: a low-frequency square wave should then be present at pins QO to Q7 of IC23. The frequency of that signal at QO should be 1 Hz and that at successive output pins should be one half of that at the preceding pin. Pin QO becomes alternatively high and low every half second; Q1 every second; Q2 every two seconds; and so on. These frequencies were chosen this low to enable them to be checked with an ordinary mul- timeter. A similar check must be carried out at the outputs of IC17. Again, the first output becomes alternatively high and low every half second and the last one, Q6, every 16 seconds. Note that D35 flashes in unison with output QO of IC23, and D33 in unison with Q6 of IC17. ±12 V supply. The +12 V supply is used not only for the RS232 interface, but also for the booster. It is, therefore, required even if the RS232 interface is not used. Fit C18-C21, IC15 and IC16. The input voltage for the supply (±20 V) is taken from the booster board (see Part 6 - September 1989) and connected via K17. This connector is shown in the parts list as a 5-way DIN socket, but a (hard-to-obtain) 6-pin type is preferred, because this pre- vents the connecting cable from being plugged into one of the other DIN connec- tors by accident. Because of the presence of the ±20 V potentials that would almost cer- tainly have disastrous consequences. The wires in the cable between the main board and the booster board must be connected to identically-numbered pins on K1 and K17. If a 6-way type (which has different pin numbers) is used for K17, stick to the numbers given on the boards. Switch on the mains to the booster unit (NOT to the main board). The potential at pin 1 of K18 (with respect to pin 2) should be -20 V and that at pin 3 (again with respect to pin 2) should be +18 V. The out- put voltage of IC15 should be +12 V and that of IC16, -12 V. A-D converter and locomotive address decoder. Fit Rl, R4, R5, C26, C31, C38, IC1, IC2, IC25 and resistor-array R6. Instead of an array, eight 10 kfi resistors may be fit- ted vertically as shown in Fig. 51. Note that the common earth connexion must be at the underside. eight 10 kU resistors may be fitted vertically. To enable writing the loco addresses associated with the loco controllers, IC6 and (if more than eight loco controls will be used) IC5 are needed. Loco controls may then be connected to K9-K16. The controller with the highest connector num- ber has the highest priority if the addresses are coded identically. In other words, if in positions 10 and 14 the controllers have the address 00, that in position 14 will have priority over that in 10. Construction of a loco controller. The A-D converter can not be tested until a loco controller is available. From a circuit point of view, these controllers are fairly simple: three possible designs are shown in Fig. 52. For each of these designs a 5-way DIN plug (180°), a 100 kQ potentiometer and one or two switches are required. Note that the housing of the DIN plug is used as the sixth (earth) pin. It is possible to connect the loco con- trollers direct to the main board, i.e., with- out plugs and sockets. This is a particular- ly logical (and less expensive) method for controllers that are to be built in perma- nently. Each loco controller is associated with one or two switches for the switching on and off of the controller, the setting of the type of data format and, possibly, the addi- tional decoder switching function. If a mixture of Elektor Electronics and Marklin loco decoders is used, the con- troller design shown in Fig. 52a should be used. The design in Fig. 52b is intended for Elektor Electronics controllers and that in Fig. 52c for Marklin or the modified Elek- tor Electronics controller (see Part 3 - April 1989). A controller is considered to be out of action if both pin 4 and pin 5 of the DIN connector are open and therefore also if the relevant DIN connector on the main board is not connected up. Switch SI in Fig. 7b and 7c may be replaced by a wire link at the relevant DIN connector. A controller can then be taken out of action only by removing the plug from the DIN socket. If the connexions between the main board and the controllers are fairly long, it is recommended to use screened cable. Each loco controller needs a filter capa- citor and two diodes, all of which may be fitted on the main board. Diodes D1-D32 must be fitted vertical- ’I f 1 87291 -VII -17 H I 87291 -VII -18 Fig. 52. Three possible designs of a locomotive controller. Choice of the design depends on the type of locomotive decoder used. 12.22 elektor india december 1989 Setting the loco addresses. In general, loco addresses must be presented in BCD for- mat as shown in Fig. 54. Valid addresses are in the range 00—80 (note that Marklin does not count 00 as a valid address). Invalid addresses are simply ignored. A number of possibilities of setting the ad- dresses is shown in Fig. 56. The method of Fig. 56a is by far the least expensive, but has the disadvantage that addresses can be changed only with the aid of a soldering iron. The method in Fig. 56b is the one used in the present design. The DIL switches permit setting and altering the addresses at any given moment, even during opera- tion of the system. It is also possible to program the loco addresses via the RS232 port: this method will be discussed in a later instalment. 87291 -VII -19 Fig. 53. Possible design of a front panel for the loco controllers. □ □ □ PF □ □ □ x 80 40 20 10 / 8 4 2 1 y \ 7 Y example of locomotive address = = 59 (40+10+8 + 1) 4 «: connexion v open Fig. 54. Loco addresses (00-80) must be presented in BCD format. J 16-way header shorten _ flatcable digit 2 tens digil 1 units □ □ □ □ □ □ > digit 2 _ — digits 1 & 2 common Fig. 55. Thumb-wheel switches may be connected via flatcable. Unused wires should not be connected to prevent unnecessary capacitive loads. ly. Since the DIN sockets are subject to fairly large mechanical strains dur- ing the insertion and withdrawal of plugs, they should be fixed to the board with M2x5 nuts and bolts or with small self-tapping screws before the solder connexions are made. Loco controllers and the A-D con- verter may be tested by connecting them to K16, which is the most impor- tant loco controller socket. The setting of the loco addresses will come later: for the time being, they will be written as 00. Switch on the mains to the main board, but do NOT press SI. The nor- mal control program will then be active. After a moment or two press SI when D33 should light. Also, the sig- nals resulting from the A-D conver- sion are present at outputs D3-D7 of IC25, while at pins 6 and 9 of IC2 the switch position may be verified: if the output is 0, the switch is closed and if it is 1, the swatch is closed. Output relay. Fit Rel, D37, IC10, R20, R21 and C29. When the mains is switched on, pin 3 of IC10 should have a d.c. potential of -10 V to -12 V. When SI ('go') is pressed, the output relay will be energized in unison with the lighting of D33. Also, the same potential as at pin 3 of IC10 should be present at pin 4 of K17. When in this condition a loco controller is connected, the potential should vary slightly when the poten- tiometer is adjusted. The degree of the variation depends on the loco address. This voltage is no longer a true d.c. poten- tial as may be verified with an oscillo- scope, which will show the repeatedly sent loco control instructions whose rear por- tion varies according to the position of the potentiometers and function switches, while their front portion varies according to the relevant loco address. Fig. 56. Four possibilities of setting loco addresses: (a) with diodes (address = 48); (b) with diodes and DIL switches (address = 21); (c) with diodes and shorting plugs (address = 42); (d) with diodes Keyboard interface. This section of the and thumb-wheel switches (address = 71). board need ' of course ' onl y be P°P ulated > f clektor india december 1989 12.23 it is intended to connect keyboards (which will be dealt with in next month's instal- ment) to the main board. Fit resistor-array RIO (but see Fig. 51), R23, C28, IC19, IC20, IC21 and K19. The choice of a single-in-line type for K19 was deliberate, because if the keyboards are installed permanently, they may be con- nected by means of wire links instead of by relatively expensive plugs. RS232 interface. To populate the last sec- tion of the main board, fit IC9, Cl 7, K20 and K18. The installation of the main board is left to your own requirements, but bear in mind that keyboards must be connected to the left-hand side of the (flat) case Some operational tips Loco controllers are scanned from left to right. If several controllers are set to the same address, the one at the extreme right will have priority over the others. As in the Miirklin system, it is possible to set the speed of one locomotive with a given controller and then use that con- troller for a different loco address, without affecting the operation of the first loco. If the mains is not connected to the sys- tem and SI is pressed, the green LED (D33) will light, but go out as soon as SI is released. The system can not and will not send data until the booster is switched on and the go key (SI) has been pressed. If the connexion with the booster is broken, the system will automatically come to a halt. The system ignores brief (< 0.5 s) short- circuits. Again, if the system switches itself off, it may be reactuated by pressing SI. In emergencies, the system may be stopped by pressing S2: this not only inca- pacitates the control program, but it also removes the power from the rails. If desired, a number of these stop switches may be installed in series along the track. Switch S3 is the system reset control, which normally will not be used. Only if the system does not appear to react to any other control or if D34 unexpectedly lights, should this switch be used. NEW PRODUCTS TV Picture Cleaner Say goodbye to disturbances in your TV Picture caused by tubelights, grinders, belnders, autorickshaws, scooters and low-flying aircraft. The TV Picture Cleaner, when connected to antenna cable, removes them electronically. The product can be easily connected to the antenna cable. Used throughout the world, this device has been designed and manufactured in India by Magnum Elec- tric. Magnum Electric Company Pvt. Limited • 2, Ramavaram Road • Manapakkam • Madras- 600 089. Phone: 434547. Microprocessor Controlled Charge Amplifier voltage signal. Main characteristics are continuous range setting from ± 10. . .999,000 pc and LCD parameter set- tings. The parameters remai set if mains failure occurs. Frequency range from 0- 200 kHz, automatic zero offset correc- tion, in built low pass filter with 8 select- able cut off frequencies, 3 selectable time constants. An IEEE-488 Interface enables the Charge Amplifier to operate via a Computer. Available against Ac- tual Users import Licence or Open Gen- eral Licence as applicable. M/s. Integrated Process Systems • 9, M.P. Avenue • Santhome • Madras- 600 004. features an In Circuit Low Voltage Tes- ter. Other attributes include a Con- tinuity Tester, Data hold facility, Diode Tester and add-Ons to measure high vol- tage upto 30 KV DC/20 KV AC. (HV Probe), Currents upto 20 A (Current Shunt), Frequencies upto 20 KHz (A.F. Probe) and 10 MHz. Pla Electro Appliances Pvt. Ltd. • Thakor Estate • Kurla Kiri Road • Vid- yavihar (West) • Bombay- 400 086. The mains operated, microprocessor controlled single channel; charge Amplifier Type 5011 from our Principals M/s. KISTLER INSTRUMENTS AG, SWITZERLAND, is a new concept in converting the charge yielded by Piezo Electric Transducers into a proportional Digital Multimeter Pla has introduced a 4V4 digit LCD digi- tal multimeter. This accurately measures AC/DC voltage, current and a broad range of resistance. The instrument also 12.24 elektor india december 1989 31/2-DIGIT smd voltmeter T. Wigmore This little circuit is simple to build, offers good accuracy and can be used in all applications requiring a small voltmeter with a clear LED read-out. Much of today's electronic equipment re- quires a digital read-out to show system status or process variables. Such read- outs are usually compact voltmeter mo- dules with an LC (liquid crystal) display. The present read-out is also a voltmeter, but uses displays with light- emitting diode (LED) segments. A LED indication was chosen for this application because it remains visible in the dark (this require- ment would also have been met by an LCD with back-lighting). Also, the use of 7-segment LED displays in combination with a drive circuit built with SMA (sur- face-mount assembly) components allows a really compact voltmeter to be realized — see Fig. 1. This is particularly import- ant if the meter is to be built into existing equipment. One integrated circuit The circuit (Fig. 2) is formed by a single integrated circuit Type ICL7107 from In- tersil. This voltmeter IC is the LED version of the perhaps even more familiar ICL7106 for LCDs. The ICL7107 contains everything required for the analogue-to- digital conversion of the input signal, and the driving of a 3VS-digit read-out. The chip is used in a more or less standard application circuit with some extra com- ponents to afford flexibility as regards the power supply. Analogue-to-digital conversion Analogue-to-digital (A-D) conversion can be accomplished in a number of ways. Fast converters almost invariably use Fig. 1. The compact voltmeter module seen at different viewing angles. elektor india december 1989 12.25 314>-DIGIT SMD VOLTMETER • Read-out: 3Vfe-digit LED display • Sensitivy: +200 mV; differential input with symmetrical supply • Decimal point: 2 positions; indication 188.8 or 18.88 • Reference: internal or external • Supply voltage: single 5 V (limited common-mode); 5 V with negative bias; symmetrical (±5 V) • Current consumption: max. 200 mA from positive (+5 V) supply; 300 pA from negative supply • Size: 55x37x11 mm flash ADC chips that are characterized by a large number of internal comparators. The other principle, successive approxi- mation, is based on a resistor ladder net- work whose R-2R junctions are connected to counter outputs. The result of the D-A conversion is compared to the input sig- nal. If a difference is detected, the clock oscillator with the counter is controlled accordingly until the output voltage of the internal D-A converter equals the exter- nally applied voltage. In practice, the ac- curacy of this type of converter is that of the R-2R network, and the off-set voltage of the voltage comparator. The ICI-71 07 and other ICs in its family work on yet another principle, w’hich is entirely analogue and based on an inte- grator. Internal off-set voltages are com- pensated prior to any measurement cycle, so that a high accuracy is achieved even with small input voltages. Since the meas- urement principle is based on the com- parison of an input voltage, U i, with a reference voltage, Uref, the display value is in fact Ui/Umi. Interestingly, the refer- ence voltage may be applied externally. Three phases The measurement cycle of the 1CL7107 consists of 3 phases. Figure 3 shows the signal path in the analogue input circuit for each of these. During the auto-zero phase (Fig. 3a), inputs IN LO and IN HI are disconnected. Internally, a closed loop is formed consist- ing of input buffer amplifier A i , integrator A 2 and comparator Ar (Gnt is discharged as yet). The internal ground is formed by the analogue common potential. The auto- zero capacitor will charge to a voltage that compensates the off-set voltages of Ai, A’ and A 3 . Also, Cref is charged to the refer- ence potential. The auto-zero phase is followed by the integration phase. The input voltage be- tween IN LO and IN HI is applied to an integrator formed by Az-Rmt-Cint. The in- tegration interval is defined as 1,000 clock cycles. During this interval, the output voltage of the integrator rises to a value directly proportional to the input voltage. The last phase is the de-integration phase. The input voltage to the integrator is disconnected again and replaced by the voltage on Crd. An internal circuit allows the reference voltage to be connected with the opposite polarity of the previously ap- plied input voltage. This causes the inte- gration process to be reversed, and the interval to be timed by the internal clock. The number of clock pulses is directly pro- portional to the ratio of the reference volt- age to the input voltage. This principle is best understood by assuming the refer- ence voltage to be equal to the input volt- age, which results in a de-integration phase that is just as long as the integration phase. The length is 1,000 clock cycles, which is shown on the display. If the input voltage is only half the reference voltage, the de-integration process takes half the time of the integration process, and the display will read 500 to indicate that Uin = O.SOOUref. The length of the de-integration phase depends on the input voltage. With rela- tively long de-integration phases, the auto-zero phase is automatically short- ened so that the total measurement time — and with it the number of read-outs per second — remains constant. The integra- tion phase always lasts 1,000 clock cycles, the de-integration phase 0 to 2,000 clock cycles, and the auto-zero phase 1,000 to 3,000 clock cycles. One complete measure- ment cycle takes 4,000 clock cycles, bear- ing in mind that the clock frequency is divided internally by 4. A clock frequency of 48 kHz gives an internal clock fre- Fig. 2. Circuit diagram of the voltmeter. quency of 12 kHz to allow 3 measure- ments per second. Common mode The dual slope measuring principle used by the ICI-71 07 has been discussed in some detail to show' up the limitations of the common-mode arrangement. Clearly, satisfactory measurements can be made only if the reference and input voltages lie within common mode range, V-(+l V) to V+C-0.5 V), of the in- ternal amplifiers. Another requirement is for the integrator output voltage to re- main well below' the positive supply volt- age. During the integration phase, the LD1-.LD3= HD1105 LD4 = HD1108 All components (except displays) SMD 12.26 elektor india december 1989 integration phase 890117- 13 (1000 cycles) (0 - 2000 cycles) Fig. 3. Signal paths illustrating the basic three-phase operation of the analogue input stages of the ICL7107 voltmeter chip ( courtesy GE-Intersil ). voltages at in lo and in hi are connected to the inputs of the internal buffer ampli- fier and the integrator, and must, there- fore, fall within the common-mode range. The reference voltage is never applied di- rect, but via the previously charged capa- citor Gel. This means that the common-mode voltage range (CMVR) of the reference voltage is the supply volt- age, i.e., V+ to V— . During the integration phase, the inte- grator uses the potential at in lo as the reference. De-integration, however, is ef- fected with respect to the 'common' potential. Consequently, any difference between the in lo potential and the com- mon potential causes a voltage jump at the integrator output during the switch-over from integration to de-integration (see Fig. 3b). Displays In the circuit diagram in Fig. 2, the oscil- lator frequency is set to 48 kHz by compo- nents Ci-Ri. This frequency results in 3 read-outs per second, and may be adapted to individual requirements by changing Ri-Ci as appropriate, bearing in mind that the integrator time-constant, R 2 -C 4 , must be changed at the same time. Input filter Ra-Cs ensures a stable read- out. The segment current capability of 5 to 8 mA of the ICL7107 obviates additional driver transistors and current limiting re- sistors. The read-out is composed of 3 common-anode 7-segment LED dis- plays Type HD1105, and 1 common-ca- thode display Type HD1108. The latter is used because l^-digit, 12.7 mm-high, LED displays are difficult to obtain in com- mon-anode versions. Fortunately, the ca- thode of the minus sign on the HD1108 is not connected to the A and B segment. Both the HD1105 and HD1108 are manu- factured by Siemens. Internal and external reference The internal reference source of the 1CL7106 and the ICL7107 may be used with a sufficiently high supply voltage (more than 6.5 V between V- and V+). The temperature characteristics of this refer- ence may, however, cause problems with the SMA 1CL7107 because this is a rela- tively small chip, and drives LEDs direct. For this reason an external reference, e.g., the ICL8069, may be used. Other reference devices may be used provided R.i is modi- fied accordingly to ensure optimum bias current (note that the voltage difference between ref LO and V+ is typically 2.8 V). Resistor R- has a value that allows multi- turn preset Pi to be adjusted to give a reference voltage of 100 mV between REF LO and REF hi. Construction The printed-circuit board (Fig. 5) accom- modates the voltmeter circuit and the dis- plays. The board is cut in two to enable the display section to be jn minted either ver- tically or horizontally on to the voltmeter board. All components, except the optional reference, IC 2 , multiturn preset Pi and the 4 displays, are surface mount assembly (SMA) types. The values of R 3 and R- depend on whether or not IC 2 is used, while compo- nents Rj, C 7 and Di may be required only with certain power supplies as discussed below. The two jumpers on the board allow the decimal point to be positioned either between the first and second digit (e.g., 100.0) or between the second and third digit (e.g., 10.00). The third option, 1.000, is not possible because the fourth digit is a common-cathode type. Power supply In most cases, the voltmeter will be incor- porated into an existing piece of equip- elektor india december 1989 1 2.27 Fig. 4. Signal waveforms with terminals lo an common connected (top drawing) and with a potential difference between lo and common (lower drawing) ( courtesy GE-Intersil). Parts list C5;C6;C7 = 47n All parts surface-mount assembly except Semiconductors: when marked ♦. Di = zener diode 4V7; 400 mW LDi ;LD2;LD3 = HD1 1 05R (Siemens) * Resistors: LD4 = HD1 108R (Siemens)* Ri = 100k ICi = ICL7107 (GE-Intersil) R 2 = 47k R 3 = 4k7 IC 2 = ICL8069 (GE-Intersil) * R4 = 470n Miscellaneous: Rs = 680fi PCB Type 8901 17 Re = 1 M0 3 II o> £ Pi = 1 k0 multiturn preset * Capacitors: Cl = loop C2=100n C3 = 470n C4 = 220n r o o Ol <00000000000 00000 000000000 ( 1)0 am UJ 00 LD4 LD3 LOS LDI 1 ! | — 1 I “| • / / l / / / / Cl , 0.1 Cl. , ; JP3 ; JP2 , boooooooooo 00000 oooooooooj Fig. 5. Track layout and component mounting plan of the printed-circuit board. 1 2.28 elektor india december 1389 o 890117-18 o Fig. 6. Power supply configurations. ment with an internal power supply. Without displays, the voltmeter draws 1.5 mA at 6 V max. between V+ and ground, and -300 pA at 9 V max. between V-and ground. With displays, the current drawn from the positive supply lies be- tween 70 mA and 200 mA, depending on the number of actuated display segments. The negative supply need not source more than 300 pA, and is not even required in some applications. The positive supply voltage is limited to prevent the maximum dissipation of the ICL7107 being exceeded. Figure 6 shows the various supply op- tions. The first drawing. Fig. 6a, shows the most universal solution based on a sym- metrical power supply. A 0 fl or other low-value resistor is fitted in position R-t (0 Q resistors are quite common in sur- face-mount technology), and Di is not fitted. The circuit of Fig. 6b may be used if a sufficiently high, regulated, supply volt- age is available in the equipment. It should be noted that the input voltage is not measured with respect to ground. Another possibility is shown in Fig. 6c. A single-rail power supply with an output voltage of 12 V or more may be used if the negative supply to ICi is limited by fitting Di and Ra. In many cases, a single 5 V supply may be used as shown in Fig. 5d. This applica- tion requires the use of the external refer- ence and the fitting of JPi. Input voltage and sensitivity In deciding the range of the input voltage, due account should be taken of the com- mon-mode voltage. Fit jumper JPi if the input voltage floats with respect to the display unit. Non-floating input voltages must lie in the range V-(+l V) to V+(-0.5 V). When the input voltage is close to V-, the read- out, on going negative, may change sud- denly to a large value, e.g., -005 instead of 000, -001 etc. This effect may be prevented by shifting the common-mode input volt- age towards the middle of the supply volt- age. Set the sensitivity to 200 mV full-scale indication by adjusting Pi for 100 mV be- tween ref LO and REF HI (the reference voltage is half the full-scale indication). The preset allows small adjustments to be made as required for other sensitivities. If the meter is to be made less sensitive, either an external voltage divider must be fitted, or Pi must be made larger. The lat- ter solution, however, requires the inte- grator resistor to be increased accordingly to prevent clipping of the integrator. elektor india deccmber 1989 1 2.29 PRACTICAL FILTER DESIGN - PART 10 by H. Baggott This final part of the series discusses all-pass filters. Strictly speaking, these networks are not filters since (ideally) they have zero attenuation at all frequencies. However, they introduce a specific phase shift or time delay that is very useful in many applications. Although all-pass networks have zero attenuation at all frequencies, they intro- duce a certain phase shift and act, there- fore, as a sort of delay line. They may be used, for instance, to delay a signal in time or to modify the phase behaviour of an other filter. A look at the complex field of these fil- ters shows that their zeros of network function are mirror images of their poles. Since the poles are always located to the left of the v-axis (because of the required stability of the filter), the zeros must always be to the right of the ordinate. Thus, a first-order network is always a real pole-zero combination. It is interesting to note that owing to the unique character of an all-pass net- work the introduced phase shift is always twice the value of that of a conventional filter. The maximum phase shift in a tradi- tional first-order filter is 90°, while that in a first-order all-pass network is 180°. First-order network The transfer function of a first-order all- pass network is T(jw) = j co - a j( 0 + a where a indicates the location of the pole. The absolute value is I T (j n>)l= ■yj co' + a 2 a/ of + a It is seen that for every frequency the nominator and denominator have the same value. The associated phase shift is i p= - 2 arctan ( col a) The time delay. /, is also important in all-pass filters; it is calculated from dy _ 2 a d w ru 3 + or The time delay in a first-order network is always maximal at very low frequencies and decreases gradually with increasing frequencies. The gradient of the increase depends on the value of a. When a is small, the time delay is large at 0 Hz, but decreases very rapidly with rising frequen- cies. When a is large, the time delay is rel- atively small at 0 Hz, but remains fairly constant over a wide range of frequencies. Second-order network A second-order filter affords rather more freedom in design, so that the time delay curve can be matched more accurately to the requirement. The transfer function of this type of network is 2 (O r 2 (j 1; and (c) an unbalanced network with a Q< 1 impedances, so that they may be cascaded without any problems. The compuation of such a filter is quite easy: L = R/a C= MaR where R is the desired output impedance. The construction of the ladder network should not present any difficulties, but in building an asymmetric type it should be borne in mind that the inductor is centre- tapped: the magnetic coupling factor between the two halves must be 1. The phase shift and time delay curves given in Fig. 53 are given for a-values of 0. 1. 1.0 and 10. Note that the value of a may be chosen freely, dependent,; of course, on the desired time delay curve. Second-order networks are a little more complicated and may be designed for Q- values smaller and greater titan 1. Several designs are shown in Fig. 54: in (a) a lad- der network; in (b) an unbalanced filter for (2-values greater than 1 and in (c) an unbalanced filter for (2-values smaller than 1 . The designs in (a) and (b) use standard components throughout, whereas that in Fig. 55. Designs of active first-order networks: 55a shows a lagging network and 55b a leading one. Fig. 56. An active second-order network; this design is suitable for (7-values from 0 to 20. (c) requires a centre-tapped inductor. The values of the various components are cal- culated as follows. The components in these circuits are calculated as follows. a 2 + p C = — 5 — i 2 aR V = 2 *> C , L =-*- 2 2 a R (a 2 + ft") i _ 2L S ~ a + ~ ; : or + p R(p~-3cf) Active networks There are even better possibilities of de- signing active all-pass networks than pas- sive ones, but for clarity's sake they will be restricted to first- and second-order net- works. Good designs of a first-order filter are shown in Fig. 55: (a) is an inductive type and (b) a capacitive type. Furthermore, both circuits invert the input signal (which has nothing to do with the phase shift). Note that not a few people mix up the two circuits under the impression that the one in (b) is a lagging type. (coR jCj) +1 (p= -2arctan( coR p The design of an active second-order network is shown in Fig. 56. It consists of a band-pass filter and a summing amplifi- er. The computation of the components is rather more complicated than with the first-order filter. First we assign a value to C and then: R^R } /2 IQ' -1 *3 aC Next, R5 is given a suitable value, say, 22 k£2. For unity gain, R(> = Rs, but if amplification is required, Rt> should be given a larger value. For 2-values greater than 0.7, Rl is not required, while R , = R } /4Q~ elektor india december 1989 12.31 and With the aid of second-order all-pass networks, it is possible to design delay lines that have a constant time delay over a given range of frequencies. The pole positions may be obtained from the tables given earlier in the series. The calcula- tions are fairly complicated and will not be gone into here. Although it is possible to design delay lines in this manner, the normally specific requirements of these devices make it dif- ficult to to give general examples. The formulas given in this final part must, therefore, suffice. automatic outdoor light shine a light on your door j Bodewes The purpose of this circuit is to automatically switch on an outside light to illuminate your front door, when a visitor arrives. The circuit uses a light detecting resistor (LDR) as the sensor. For the circuit to work an external light source such as a lamp post is required. Needless to say this source needs to be close by. Please remember that the removal or repositioning of lamp posts needs the authority of the local coun- cil, so we do not recommend this circuit to anyone who has to extensively remodel the landscape. The LDR is mounted into a tube, behind a lens, and aimed at the light source. This structure is positioned, so that the person approaching the front door, causes a shadow to fall onto the lens. Do not forget to ensure that the tube containing the LDR is water tight. Immediately the LDR is in shadow, its resistance will increase. This results in T1 applying a negative pulse to T2 via Cl and R6. T2 con- •v* V tinues to conduct until this negative pulse arrives. As soon as T2 cuts-off, C2 starts to charge. When the voltage across C2 rises above 2 V, the schmitt-trigger formed by T3, T4, T5 (and their surrounding components), switches on transistor T6. T6 conducts and triggers the relay, which switches on the outside light. The rate at which C2 discharges is adjusted by PI . When the voltage across C2 falls below 1 .5 V the schmitt-trigger returns to a quiescent state. T6 will cut-off switching off the relay and therefore the light. The light will remain on for a maxi- mum of one minute. Longer periods are possible, but then C2 will have to be substituted with a larger capacitor. Switch SI and R3 are connectecfin parallel to R2. SI can be a make/break contact mounted on the front door. When the door is opened the light will switch on, going out immediately it is shut. In order for the circuit to work effec- tively, the tube containing the LDR (and lens), must be positioned, relative to the light source, so .that the voltage measured at the junction of R1 , R2, is not less than 3 V, and not more than 20 V. 12.32 elektorindia decamber 1989 INTRUDER ALARM In today’s society, it makes good sense to provide some form of intruder alarm system in the home, if for no other reason than the family’s peace of mind. Effective, reliable and simple to control, the intruder alarm system described in this month’s article uses readily available low-cost components only. E. Chicken, MBE, BSc, MSc, CEng, FIEE Apart from its low current demand from a battery during non-alarm conditions, the alarm is also noteworthy for its sys- tem-test bleep on switching on and on leaving the house, its pulse drive of the external sounder to economize on battery power, and automatic time-out of the in- ternal and external sounder to minimize social disturbance. The block diagram given in Fig. 1 shows the various stages of the circuit, their interconnections and related signal routes. The way in which the stages inter- act in detail is explained below. Circuit description Power supply As shown in the circuit diagram of Fig. 2, the alarm is powered by a small 12 V re- chargeable battery that is trickle-charged by a mains adapter with d.c. output. In the quiescent condition, the current drain from the battery is less than 1 mA. Current consumption in the actuated condition is virtually that of the external sounders alone. Charging current for the rechar- geable battery is limited to about 15 mA by R 7 in series with LED D4, which, mounted on to the front-panel of the en- closure, serves as a charging indicator. The output voltage of the mains adapter must be measured and the value of R7 chosen such that the maximum LED cur- rent of about 20 mA is not exceeded. On/off control Control of the alarm system is effected by a single-pole ON/OFF switch, Si. Actually, the circuit is never switched off complete- ly as long as the battery is connected, but the current drawn with the switch in the OFF position is negligible. Closing Si to switch the system off con- nects R: to the negative supply rail, caus- ing Ti to conduct. Diode Di is forward-biased, and the resultant voltage drop of about 0.6 V maintains conduction of T i in the event of a reduction of the supply voltage. That conduction in turn maintains the off condition of the system, and so minimizes the possibility of false alarms. When Ti is switched on, Dj ceases to conduct so thatCi is charged to the supply voltage via Rs and Ri.. For convenience, low voltages from 0 to, say, +2 V will be referred to as logic 0, and the higher +12 V supply rail voltage as logic 1 . This voltage on Ci forms a logic 1 that is inverted by NAND gate Ni to present a 0 to one of the two control inputs of the bistable formed by N 2 and N.i. So long as pin 6 of N 2 remains at 0, the output of the bistable, pin 4 of N 2 , is held at 1 to prevent the alarm sounders being actuated. Switching the system off simulta- neously takes the RESET pins of timers IC2 and IC3 low, which prevents the timers being inadvertently triggered into a false alarm sequence. As long as the system is switched off, D 2 is forward-biased via Ti and R14. When the system is switched on, switch Si is in fact opened, so that Ti ceases to conduct. This causes the collec- tor voltage to drop to practically 0 V via R4, so that D 3 is forward-biased via Rs and Ri. As a result, Cs discharges slowly via Rt, D 3 and R4. The lowest voltage on C3 is reached in about 15 seconds, determined by time constant CifRi+Rb). The final voltage on Ci as determined Fig. 1 . Block schematic diagram showing the general structure of the intruder alarm. elektor india december 1989 1 2.33 by potential divider Rs-Rr is about one tenth of the supply voltage, plus the for- ward drop of D 4 . In total, this makes about +1.8 V, which represents a logic 0. The resultant logic 1 at the output of NAND gate Ni causes bistable N 2 -N 3 to toggle 15 seconds after switching the system on. The logic state at output pin 4 of the bi- stable becomes 1, and can be changed to 0 according to the logic level applied to the control input terminal, pin 1 of N 3 . Alarm sensing When all doors and windows protected by the detector loop are closed, and assum- ing that the detector switches are of the normally-closed type, R 13 is connected to the negative supply rail, causing T 2 to con- duct via R 12 -D 7 -R 13 . The function of D; is similar to that of Di as discussed earlier. With all detector switches closed and the loop unbroken, Ds conducts via T 2 and Rh. Diode Ds does not conduct because its cathode is connected to the positive sup- ply rail via T 2 , as is its anode via Rs. Capacitor O supplies a logic 1 to the second input of bistable N 2 -N 3 after it has been charged via Rs and R 9 . The two logic 1 s at the bistable inputs maintain a 1 at the output, pin 4 of N 2 . As stated earlier, this 1 inhibits the sounding of an alarm. Breaking the detector loop disconnects R 13 from the negative supply rail, causing T 2 to stop conducting. Its collector poten- tial drops to nearly 0 V, so that Ds is for- ward-biased via Rs and Rio. As a result, Ca discharges in about 0.5 s via Rs, Ds and Rio, its terminal voltage dropping to about +1.8 V, which represents a 0. The 0.5 s delay produced by Cs- (Rs+Rni) assists in the prevention of false alarms by interference spikes and other transients in the loop circuit such as by doors shaking in the wind. Control terminal pin 1 of the bistable accordingly changes from 1 to 0, so that the level at the output terminal changes from I to 0, where it will remain latched in the absence of an alarm condition until the other control terminal, pin 6 of N 2 , changes state, i.e., until the system is switched off. The condition necessary for the generation of alarm signals is a Oat the output of the bistable. Sounder timing The alarm system has provision for two sounders, one low-power internal alarm such as an active piezo-electric buzzer, and one high-volume external alarm such as a 12 V bell. The circuit automatically switches off each of the alarm sounders after a reason- able period of time: 4 minutes for the ex- ternal sounder, and 8 minutes for the internal sounder. The individual timing circuits may be altered, however, to suit personal preference. Low-power CMOS timers Type 555 (IC 2 ) and 556 (IC 3 ) are used in the interest of battery economy. When the circuit is switched on, the timers are simultaneous- ly released from the reset condition be- cause their pins 4 are taken logic high. Internal sounder While the system is on, any break in the detector loop, such as by a protected door or window opening for longer than 0.5 s, initiates operation of the internal sounder. When the loop is broken, Cb passes the l-to-0 transition at the output of the bi- stable to pin 2 of IC 2 , which is triggered into monostable operation for a period of about 8 minutes. Network C 6 -R 16 forms a differentiator to sharpen the trigger pulse. On entering the premises, residents have about 15 s to switch off the system before the monostable switches on the in- ternal sounder. Prior to the arrival of the trigger pulse at pin 2 of MMV IC 2 , its out- put, pin 3, is normally at 0. This level keeps Tr off via base resistor Ri+ Immedi- ately upon the arrival of the negative- going trigger pulse at pin 2 of IC 2 , its out- put rises from 0 to 1. This level is main- tained for about 8 minutes as determined by C 8 -R 17 . Transistor T 4 is switched on, and actuates the internal sounder in its collector circuit. When the 8-minute peri- od has lapsed, the low level at pin 3 of IC 2 causes the internal sounder to be turned off by T 4 . For convenience of testing during the construction and installation stages, LED D« provides a visual indication of circuit operation without the internal sounder being connected. If actuated, the internal sounder is switched off simultaneously with the system. External sounder The operation of the external sounder cir- cuit is slightly different from that of the Fig. 2. Circuit diagram of the intruder alarm. Note that the timers, IC2 and IC3, must be low-power versions to ensure minimum current drain from the battery. 12.34 elektor india decombor 1989 internal sounder. Assuming that the sys- tem is switched on and the detector loop not yet broken, the output of bistable N 2 - Nj is at 1 . Capacitor Cs charges rapidly via Ds, until its terminal voltage is also at 1. Subsequently, Ts is turned off by the 0 supplied by inverter Nr. Timer IC 3 is not yet triggered into action, so its output ter- minal, pin 9, is at 0. Hence, darlington transistor T 6 -T 7 is kept off in the absence of an alarm signal — external sounder Bz 2 is not actuated. Circuit ICs, a CMOS Type 556, contains two timers Type 555. Pin 4 of the first 555 in the chip is held logic high via R 2 -D 1 -R 1 , so the timer is ready to be triggered. The instant the detector loop is broken, the l-to-0 pulse transition at the output of bistable N2-N3 causes Ds to block, enab- ling Cs to discharge through Ris. The time constant formed by these two components introduces a delay of about 15 s in the transition from 1 to 0 at the input to inver- ter Nr. After this delay, the resultant tran- sition from 0 to 1 at the base of Ts causes the transistor to conduct. The collector voltage of Ts drops from 1 to 0, and the negative-going pulse edge is differen- tiated by Cio-R24to be passed as a sharp- ened trigger pulse to pin 6 of dual timer IC 3 . The first timer in IC 3 is configured as a monostable with a 4-minute time period, the output of which is used to control the second timer circuit, which is configured as an astable multivibrator (AMV). This circuit can produce its 1-s on/off pulse rate only during the 4-minute period of operation set by C 11 -R 25 for the preceding monostable in the IC. The time period, f, in seconds can be calculated from t = 1.1( Ci 1R25 ) Output pin 5 of the first timer is normally at 0 until the arrival of an input trigger pulse, whereupon the output state changes abruptly from 0 to 1. Pin 5 is wired to the reset input, pin 10, of the second timer in the 1C package. When taken high, this pin enables the AMV to oscillate at a rate of 1 Hz during the 4- minute period defined by the first timer. The period (in seconds) of the oscillator signal is calculated from / = 0.7Cm( R 26 + 2i?27 ) The square-wave oscillator signal drives darlington transistor pair T<.-T7, so that the external sounder, Bz2, is switched on and off at a rate of about 1 s until the 4-minute monostable period has lapsed. As with the internal sounder, a visual indication of external alarm activity is provided. Diode D12 protects T? from transient voltage spikes generated as the current through the inductance formed by Bzz is inter- rupted. Capacitors C12 and Cis are for de- coupling and do not form part of the timing circuits. System assurance bleep Provision has been made for a system as- surance bleep to indicate that the system is functional, prior to the resident's depar- ture from the premises. Two assurance bleeps are generated: one before the end of the 15-s switch-on delay at the instant of switch-on, and one as the exit door is opened for departure. While the system is switched off, C-i has no voltage on it because Ti conducts. Following switch-on, the 1 5-s delay before the system becomes 'live' allows time for the injection of a short control signal di- rect to the internal sounder control tran- sistor, T-t, bypassing timer IC 2 . When the circuit is switched on, T 2 and D 2 become non-conductive so that C 4 is allowed to charge via Ris and R14 in about 0.25 s, which in effect momentarily causes the base of T 3 to be taken low via R14. The upshot is that both T 3 and Tt conduct just long enough to enable the internal sounder to produce a short bleep. The same process occurs with T 2 and Dh which, like D 2 , is connected to the junc- tion of Cj and R14, except that in this case the charging of C4 is initiated by the break- ing of the detector loop w r hen a protected door or window is opened. Construction A convenient and low-cost method of con- struction is to use readily available copper SRBP shipboard with 0.1 -inch hole spac- ing. The use of sockets for the ICs is rec- ommended, but the layout of components is not at all critical. Inter-component wiring is by thin in- sulated wire. If stranded wire is used, care must be taken to avoid unintended con- tacts by loose unsoldered strands. The external wires are connected to ter- minal posts on the board. The two alarm- test LEDs are purposely located on the board for visual access during testing. A separate box may be required to ac- commodate the battery, and possibly the mains adapter. The on/off switch is either a key-oper- ated type, or a cheaper standard on/ off miniature toggle switch. A reasonable compromise as regards safety might be to use a standard SP5T toggle switch, and to conceal it from view either complete with the electronic assembly, or in a small sep- arate enclosure. Further practical considerations The door and window switches are mag- netically operated types that have the ad- vantage of not drawing current from the battery. Constructors wishing to include a motion detector of some sort in the loop must bear in mind that such a device may well draw 20 mA or more whether actu- ated or not, which would have to be taken into consideration when choosing the bat- tery and the associated charger. Also, the motion detector requires a separate cable to carry its supply voltage. One approach might be to replace the single-pole on/ off switch with a double-pole (DPDT) type, the other pole of which is used to connect the +12 V to the motion detector only while the system is switched on, assuming that the battery is being recharged during the off condition. The cable-test loop shown in the circuit diagram provides an indication in the event of the loop having been tampered with, for instance, cut by a prospective intruder who plans a return visit while the house is unoccupied. It would need to be a separate pair but within a two-pair cable; if both pairs are cut simultaneously, the system would be switched on, and the detector loop to be broken, so that the alarm is set off immediately. If such a situation is thought unlikely, the cable- test loop may be omitted, and a substitute wire link installed on the board. The de- tector loop would then need to be twin PVC insulated cable of, say, 7x0.2 mm running from the board to each detector in turn, and back to the board via the unbroken wire of the pair. The choice of the external sounder is entirely up to the constructor, but care should be taken not to overload the tran- sistor driver or the battery. The author used a weatherproofed sounder giving a choice of continuous or warbling tone at a sound level of 107 dBA for only 20 niA of current drain from the 12 V battery. It is standard practice to enclose the external sounder in a weatherproof enclosure, in- stalled high up on the wall out of easy reach, and with its supply cable hidden behind the box as an anti-tamper precau- tion. elektor indie december 1989 12.35 PROTECTING ASYNCHRONOUS MOTORS by Mehrdad Rostami, University of Tehran, Iran The circuii described here was designed for protecting heavy-duty asynchronous motors during the start-up period. As is well-known, without protection such motors may easily get damaged by poor starting. The circuit may also be used lor other applications where a trip circuit needs to be triggered, such as, for instance, in the monitoring of liquid levels. Every motor has a time-speed character- istic that shows how, or otherwise, it starts and reaches its normal speed. A number of such curves are illustrated in Fig. I. If the characteristic of a particular motor is similar to the lower (bold) one. any attempt at start- ing the motor should be stopped immediate- ly and the motor in-spected thoroughly. The dashed curve in-dicates the lower limits of acceptable motor performance, while the upper curve shows normal values of a prop- erly functioning motor. Circuit description The circuit diagram in Fig. 4 consists of five identifiable blocks: (1) oscillator and time base — IC4, IC5 and IC6; (2) address unit and memory — IC7. ICS and IC9: (3) shaft pulse receiver and counter — ICI4 and IC15; (4)comparator — IC12 and IC13: and (5) automatic stop unit — FF1 and FF2. The input to the circuii consists of pulses generated by a rotary encoder comprising an opto-coupler and perforated man-made fibre disk fitted securely on to the shaft of the motor as shown in Fig. 2. The pulses gener- ated by the opto-coupler are applied to receiver/counter ICI4 and then to counter 1CI5. The 555 oscillator.. IC4. generates 50 Hz pulses that are divided by 5 in IC5. The out- put of this 1C is taken to switch S 1 and also applied to a second :5 divider. IC6. The output of either divider may be selected by SI and from there applied to cas- caded circuits IC9 and IC 10. The output of 1C 10 is used to reset the shaft pulse counters, IC 1 4 and IC 15. at the end of each period of 0.5 s or 0. 1 s depending on the setting of S 1 , and also to clock the address unit, IC7 and IC8. The eprom must be loaded with the data of the appropriate motor curve. If, for instyance, the rotary encoder is supposed to send eight pulses in the first 0.5 s period (SI set to 2 Hz) — which, of course, depends not only on the rotary speed of the shaft of the motor, but also on the number of perfora- tions in the disk — the first memory cell of IC 1 1 must be loaded with 00001000. The number of pulses is determined from the timing diagram of the relevant motor: a typi- cal ttime vs rotary speed characteristic is shown in Fig. 3. Similarly, if the pulse generator is sup- posed to send 12 pulses in the second 0.5 s period (SI set to 2Hz). the second memory cell of the eprom must be loaded with 00001 100. This process must be repeated for each subsequent 0.5 s period (up to a total of 20 seconds, when a properly working motor will have started). The outputs of the eprom and the shaft pulse counters are applied to two Type 7485 comparators, 1C 1 2 and IC 1 3. At the end of each 0.5 s period. IC9 gen- erates a pulse that is used to drive one of the inputs of and gate N2 high. When the level at pin 7 of comparator IC 1 3 is also high, the second input of N2 goes high. also. This results in the output of this gate becoming a logic 1 . which is applied tots of and gate N3. The second input of N3 is supplied by autostop unit FFI, a D-type bistable. This bistable is reset by and gate N I when address 00010100 is applied to the eprom. Its Q output then goes high, which causes the second input, and thus the output, of gate N3 to go high. This causes a second D-type bistable, FF2, to be set. When that happens, the coil of a trip device in the starting circuit of the motor is energized so that the starting circuit is broken. Circuits IC 1 2 and IC 1 3 compare the data input from the eprom with that from coun- ters 1C 1 4 and IC15. If these data streams arc identical, pin 7 of IC 1 3 re-mains low', pre- venting the operation of the automatic stop unit. Schmitt triggers N4. N5 and N6 form an auto reset circuit for setting/resetting the bistables and returning the counters to their original state. Fig. 1. Time-speed characteristics of a an asyn- chronous motor. The lower (bold) curve indi- cates a defect motor; the dashed curve indi- cates the lower limit of acceptable performance; and the upper curve is typical for a properly functioning motor. Fig. 2. The rotary encoder consists of an opto- coupler and a perforated man-made fibre disk fitted on to the shaft of the motor Fig. 3. Typical time vs rotary speed diagram of an asynchronous motor. A properly working motor should start within 20 seconds. 12.36 Glektor india december Fig. 4. Circuit diagram of the protection unit. \l \\ PRODUCTS Digital V-A-F Meter Jivan has introduced Digital V-A-F meter. This measure voltage. Ampere & Line Frequency. It has a compact size of 96 (H) x 96 (W) x 170 (D) mm. It directly measures measures voltage upto 600 V, with P.T., it can measure any desired voltage. The current range is upto 10 A, but with C.T. , it can measure any desired current. The frequency range is from 20.000 to 99.99 Hz. Jivan Electro Instruments • 394, GIDC Estate • Makarpura • Baroda-390 010 • POWER CONNECTORS G.H. INDUSTRIES introduces Power Connectors Pitch 3.96 mm, 5.08 mm, 5.0-7. 5 mm, 5.0 mm Range : 2 Way to 22 Way. Male Square Pin Headers are also availa- ble with or without Friction Lock, Straight or Right Angle. Current - Rat- ing 7.0 Amps. Voltage 250 Volts. ISP-3960 G. H. INDUSTRIES • 84-B Government Industrial Estate • Kandivli • Bombay- 400 067 • elektor india december 1989 1 2.37 SCIENCE & TECHNOLOGY Intelligence, Intentionally and Self Awareness by Dr T. Farrimond, University of Waikato, New Zealand This paper deals with some of the problems in ascribing intelligence to computers. It is suggested that machines which only process the symbols of language are not intelligent even though they may produce an output similar to that from an intelligent human. It is maintained that self awareness in humans, coupled with the ability to interact directly with the environment by means of the senses, is central to intelligent functioning, which includes the development of a social/ecological conscience. In his article “Artificial Intelligence”, M. Seymour 1 provides an interesting and infor- mative account of some of the problems met by computer designers in attempting to pro- duce machines that exhibit artificial intelli- gence. The article discusses arguments for and against what constitutes artificial intelli- gence including the existence or otherwise of intentionality (Searle, 1 984)-. The present paper examines some of the concepts from the point of view of a psychologist, who was a student at Manchester when Alan Turing was working on the theoretical aspects of information processing. The power of elec- tronic devices has increased enormously since that time, but perhaps there has not been a similar growth in defining the termi- nology used to describe computer activities and brain activities. At the simplest level there has been revival of anthropomorphism, a condemnatory appellation feared by biologists accused of reading human characteristics into the behaviour pattern of lower animals. Howev- er, equally imprecise use of language is exemplified by phrases such as ‘computers talking to each other’. This is largely a mat- ter of economy in the use of words, since it is easier to use concepts already in existence than to invent new ones, but there are dan- gers in over-extending the concepts to include things that are not justifiable. The problem is that with terms such as intention- ality it is difficult to provide a definition that does not also include or imply the term intention, which then also has to be defined. In describing a spiral staircase, it is easier to make a visual representation by drawing one (or to wave one's arm to illustrate the con- cept) than it is to describe it verbally. If this is true for a concrete example such as this, then for abstract concepts the difficulties involved in using words to define them are enormous. Is the term intentionality sufficient to cover those things the brain does that are different from a computer? How does one recognize intentionality? Can intentionality be proven and is it important to do so? The concept of intentionality is essential in dealing with human affairs, particularly when legal dis- putes arise and require resolution. We resort to a court of law where proof of intention may well determine the outcome of a case. Did the accused know what she was doing when she set fire to her husband's bed? Evi- dence may be produced to prove diminished responsibility; a person may be described as intellectually sub-normal and so not account- able for his/her actions. The implications in this case may be that the accused did not properly understand that the outcome of the action might be injury or death. Similar inca- pacity may also be ascribed to a person under the influence of drugs or suffering from some mental disorder. The question of responsibility is the key to determining whether the sentence should be 10 years or alternatively some form of medical treat- ment. In each case what is examined are the following. (a) Could the individual predict the out- come of the act that caused the accident (is there an ability to follow a logical sequence of events on a probabilistic basis to a conclusion or variety of possi- ble conclusions)? (b) Did the person intend to set in train the causal events that resulted in harm? If a person accidentally backs into a lever that releases a winch carrying a load of iron, causing it to fall and kill someone it is not the ability to understand the causal relationships that determines guilt - but whether there was intention to do harm. In this example there was not. (c) Was there an awareness on the part of the accused that he or she was carrying out the action? Point (c) is releva., t, for example, in the case of hypnosis. A woman under hypnosis may be persuaded to rote-play the part of some- one in authority and perform an act not nor- mally acceptable to her simply because she regarded herself as another person during the period of hypnosis. In this case a causal sequence of events has occurred in which there is intention on the part of the subject to carry out an act, but because self aware- ness is absent, the individual would not be regarded as culpable in law. Even though her behaviour incorporates the two elements usually considered necessary for intelligent behaviour, i.e., it exhibits appreciation of causality and also intentionality, she is not seen as responsible for her behaviour. It may be argued that intelligent human behaviour involves these elements - causality, intention and self awareness and for a computer to be regarded as intelligent it also should exhibit the same properties. It is this point of self awareness which I con- tend is different from intentionality and is possibly the central issue in determining whether behaviour is intelligent or not. It is assumed that the use of the term intelligence is a reference to human mental and behavioural processes since these are the only points of reference we have for what we mean by intelligent behaviour. External behaviour Would a machine designed to look and move exactly like a human being so that it would 12.38 eleklor india december 1989 be accepted at a barbecue (or even a social function!) really be intelligent? One could forgive the hostess for assuming that it is, since from the outside the machine does all the things normally expected of a human: it speaks, moves about, listens attentively and even laughs in the appropriate places. It is tempting to argue that it is only the behaviour of the machine that is important, i.e.. outside appearances and behaviour are all that matter. If these are indistinguishable from human behaviour, the machine should be regarded as human, and therefore intelli- gent. Indeed, this may be the effect on the hostess until it is demonstrated to her that a group of electronics enthusiasts have con- structed the machine and are operating it remotely: one controlling locomotion, anoth- er speech, and so on. Thereafter, the hostess would no longer accept as fact that because someone (thing) exhibits intelligent human behaviour it is genuinely intelligent. This emphasizes the problem that without further knowledge about the controlling mecha- nisms it is difficult to prove that a behaviour pattern is intelligent or not. But is is obvi- ously not safe to infer intelligence on behaviour alone. In the example given, the intelligence is elsewhere and is external to the machine. A distinction should be made between the analogous behaviour and identical behav- iour. Herein lies the distinction between machines at present and humans. The behaviour of a machine may be analogous to that of a human without necessarily being identical. Although it may be the expressed aim of engineers to produce intelligent machines, it is doubtful whether they would want them to be intelligent in the human sense, since they may no longer wish to co-operate with the inventor - and may prefer to go on strike. Certainly, any organism (biological or mechanical) with self awareness would also be aware of its rights as a thinking being and its utility as a tool (that is, slave) would be reduced. An interesting prospect also opens up in the area of culpability for mistakes. If a machine is regarded as culpable and it trans- gresses, what should its punishment be? Absence of need for programming It has been envisaged that one day it may be possible to build a machine that can think, that is, need not be programmed to perform its functions. This statement as it stands per- haps needs elaboration before its implica- tions can be considered. If the term ‘thinks’ refers to performing certain analytical func- tions, the similarity to human thinking is restricted to one level of activity. It would be necessary to define the term in other ways if it were to include intentionality and self awareness. The presence of one level of functioning does not automatically mean that the other levels are present. Terms such as intelligence, cognition, perception, etc., have evolved from attempts to categorize (by using symbols) certain aspects of human behaviour. The words are not specific but incorporate implied connections with all other aspects of human mental activity. Gregory in his book The Intelligent Eye emphasizes the relationships that exist be- tween the eye and the brain. The eye is an extension of the brain in a psychological as well as in an anatomical sense. The unitary nature of perception, cognition, intelligence, etc., makes it difficult to talk about simply one aspect of human behaviour without automatically including all the others. It would make little sense to examine human cognition without at the same time consider- ing intelligence, memory store, and percep- tual abilities, for cognition depends upon them all. Also, an individual's cognitive state is constantly changing, not only from new experiences, but by re-analysis of stored information from within, where models exist of the world (imagery) available to the indi- vidual for the process of thinking, research- ing and creating. The capacity of the brain In an attempt to duplicate the equivalent of a neural net system as found in the brain, experimenters have constructed electronic networks with a large number of intercon- nections. However, the human brain is not simply a neural network. The complex of 10 billion (10’) interconnected brain cells con- fers only one part of the brain's processing power, for along with nerve cells there are over five times as many smaller glia cells. All these cells have numerous fine branches extending from them to form interconnec- tions with other nerve cells: some individual cells may have several hundred connections, others several thousand and in the cerebel- lum certain cells may have one hundred thousand connections. The number of inter- connections has been estimated to be of the order of 50 trillion (50 x 10”). Nor is this the whole story. Memory storage in the brain seems to involve changes in the protein molecules associated with the nerve cells. Additionally, certain glia cells are not fixed relative to adjacent brain cells but may move into active areas of the brain, thus modifying the brain's structure in response to incoming stimuli. Glia cells, unlike larger brain cells, have the ability to subdivide as well as move, so that their number and distribution may change depending upon the activities of the brain. What makes the human brain so interesting is that the owner is, to some extent, able to observe his/her mental states and decide upon a course of action thereby. This course of action is not unchangeable but open to modification. Even though humans have characteristic patterns of behaviour by which they may be recognized as individuals, it is still possible for a person to examine past behaviours and bring about a change for no other reason than that a change is regarded as desirable. This capacity makes human behaviour notoriously unpredictable even when we know a person very well. This is not the same as Turing's 3 suggested incorpo- ration into a machine of a ‘random element’ consisting of a random number series which produces changes in the behaviour of the machine. In human terms, such a random element would be more character- istic of psychotic human behaviour, where there may be an absence of awareness of the behaviour on the part of the psychotic and little appreciation of its effect upon others. Self awareness is the ability that gives humans the capacity for controlled variability and includes intentionality and appreciation of causality. The origin of self awareness Although it is difficult to be specific on this point since we no longer remember what we experienced in the few months preceding our birth, it is possible to con- jecture that our sense of ‘self’ begins to develop quite some time before birth. Acoustic images of developing foetuses show them yawning, moving, sucking their thumbs, etc., indicating the presence of kinaesthetic and tactile awareness. There seems little doubt that, like Tristram Shandy, we are responding to, and becom- ing aware of, our own bodies in relation to the environment surrounding us. In other w'ords, we are developing self awareness. Self awareness includes the development of body image, that is, the knowledge that our bodies are unique, yielding sensations that are related to each other. Visual and tactile investigation by a young baby of its body yields a complex integrated pattern of sensations that, in conjunction with kinaesthetic feedback from muscles and joints, gives the child a sense of personal identity that is different from all other objects in the environment: other objects are regarded as external to the self. To achieve this development of body image, the child must move relative to the envi- ronment. so that it experiences variations in the size of objects as distance changes and variations in shape as viewing angles change. Both the distance information gathering senses of vision and hearing are co-ordinated with the body senses of touch, pressure, pain, temperature and kinaesthetic feedback, to produce an orga- nized pattern of information resulting in elektor india december 1989 1 2.39 self awareness. The experiment by Held and Hein (1963) 4 with kittens indicates that visual ability requires integration of changing visual patterns (brought about by moving in the environment) with simultaneous stimula- tion of body senses and locomotor activity on the part of the animal. In this experi- ment, two kittens were kept in the dark until their eyes opened. Then they were placed at opposite ends of a bar pivoted at its centre so that it could rotate. Only one kitten, 'a', had its feet on the floor and so could walk around in a circle. It could also turn around on the spot because of the design of the apparatus. The other kitten, 'B\ stood in a basket that prevented foot contact with the floor but, because of an interlinking system of gears and chains, it was moved whenever kitten a moved: it could not initiate movement itself. Both kittens therefore received similar visual stimulation. When the kittens were released after 30 hours, kitten a could make normal visual responses, such as avoiding a cliff, blinking to avoid an object approaching the eye and avoid obstacles. Kitten b was unable to do any of these tasks and only learned to see when allowed to walk. It has been stated that “artifical intelli- gence is the study of computer programs" (Boden) 5 . In humans, it would perhaps be more accurate to say that intelligence is a function of the body and equates with sen- sitvity to external and internal stimuli. The new born baby has no program derived from outside sources, although it shows responses: exhibiting sensitivity to (and reflex movements away from) painful stimuli. Light and sound convey little meaning at this stage; learning is initially related to the body senses. For example, if the baby makes random movements of the hands, it may strike the side of the cot and receive a sensation in that hand. If the baby strikes its own face, it receives a sen- sation in the face as well as in the hand. This is a unique experience different from all other contacts with the world outside the individual's body. The baby soon asso- ciates these sensory inputs with the inter- nally derived sensations from the muscles that are involved in making the move- ments, so from the beginning sensory information establishes a complex body image. This is later extended to include visual and auditory patterns and rapid learning occurs. It is worth noting that lan- guage need not be involved. A deaf child exhibits intelligent behaviour solely by observation of the environment: recogni- tion of a person's facial expressions or ges- tures is an early form of communication. In humans, simple signals and signs later become more complex to include written and verbal symbolization so developing into language as used in the conventional sense. It is at this level of symbolization that it becomes possible to manipulate words or numbers as models of the envi- ronment. The usefulness of the scientific method has depended upon establishing an accurate correspondence between symbols and reality. When the symbols no longer do the job of predicting or explaining, one returns to the experiment as exemplified by Faraday 6 . There is a danger that the symbols may be regarded as the repository of intelligence, when in fact the symbols only exist because of Ihe intelligence used to con- struct them initially. Mechanical manipula- tion of symbols according to the rules of language may bring benefits in solving problems, but the program responsible for the manipulation (itself a language) lacks the attributes of self awareness and sensi- tivity to the environment that characterize human intelligence. Brain and machine translations A machine may reproduce functions that may be similar to human ones, for in- stance, translating English into French. The process of translation is established by comparison of the two sets of visual sym- bols, since the languages follow very simi- lar patterns. Languages describe the vari- ables in our environment and these are, in most physical aspects, common to all societies. The same things are given differ- ent symbols (either auditory in the case of speech or visual in the case of written lan- guage). The dynamics of events in the environment are also constant: 'a girl runs', 'an object falls', 'a goat jumps', and so on. Therefore, translation involves matching two symbolic patterns, but to produce language, a perceptive organism must first observe the environment and establish a linguistic model of the ‘real world', which may be used for interchange of ideas. In the case of a second language, some important similarities are estab- lished, for instance, finding what symbols in French stand for man, woman, girl, goat, etc., after which translation is rela- tively easy because of the communality of experience of the environment embodied in human languages. The translation of Egyptian hieroglyphics was not possible until the discovery of the Rosetta stone where the same message had been record- ed in hieroglyphics, Greek and Coptic. The recognition of the name of Ptolemy, which occurred in all these versions, made it possible for Champollion to equate the unknown hieroglyphics with a known lan- guage and so produce a translation. Lan- guages have contained within them a causal pattern echoing the environment from which the language was derived. The interesting aspect of languages is that once they have been established, they may be processed in a variety of different ways because of the built-in degree of corre- spondence to our world, which makes them useful tools. However, language can not express unambiguously all aspects of the real world since linguistic concepts of language (including mathematics) relate to generalities and not specifics. Linguistic devices may be used to define a particular dog as spaniel, but specificity requires more descriptive information. We soon reach a point where language is no longer capable of conveying the information that a few seconds' direct contact with the dog would provide. State of health, condition of coat, friendly or not, does it like you, how old is it, how heavy, etc. Language is a substitute for reality, and this limitation extends to all descriptive applications. The problem of ascribing intelligence to a device that solely processes language is revealed if a nonsense-language is used. The machine may produce 'solutions’ to nonsense problems fed into it (following a set of rules), but these would be meaning- less. The machine is no less capable than machines using real language, nor is its program less complex. The only difference between a nonsense machine and a lan- guage processing machine is the degree of correspondence of the symbols used to our environment and this is something that an external observer perceives. This is intelli- gence by implication, that is, Ihe recogni- tion that certain activities resemble (or dif- fer from) human intelligence: in the case of language processing, intelligence is a function of neither the machine nor the program. If a black box processes problems, it is tempting to regard the machine (or pro- gram) as intelligent since its behaviour resembles that of intelligent humans. If the black box is enlarged to make a room capable of housing hundreds of thousands of people, these may be arranged to pro- cess information in the same way as a machine. Chains of individuals handle the input, make available stored information and present an output as a machine does. In this case, where does the intelligence lie? The grouping of individuals is analo- gous to the circuitry of a machine, but no 'group intelligence’ is generated simply by the use of a number of individuals. The instructions to the subjects are carried out by the occupants of the room, but each person is simply carrying out part-func- tions, the implications of which are not recognizable since their relation to other functions is not apparent. The program 12.40 elektor india december 1989 represents the instructions that the workers are carrying out. Intelligent performance is recognizable only by observing thg perfor- mance of the whole group. Intelligence then is not in the program itself, but in the way the program was designed. This sug- gests that it is possible to design a machine that performs according to its program- ming in an apparently intelligent way without it necessarily being intelligent. The machine would need to organize its behaviour by itself, monitor the environ- ment and be responsive to it and be aware that it was doing so if its behaviour were to be equated with human intelligence. Intelligence A definition used by Alfred Binet in- volves at least four factors: 1 . Direction - the ability to set up a goal and work toward it: 2. Adaptability - the ability to adapt onself to the problem and use appropriate means to solve it; 3. Comprehension - the ability to understand the problem; 4. Self evaluation - the ability to evaluate one's performance and to determine the correctness of approach. Examples of intelligence in humans cover an enormous number of activities ranging from simple identification of objects to solving complex problems involving the practical manipulation of equipment and the development of theoretical models (based on the result of experimentation). This involves both language and mathe- matics. In Binet's factor of self-evaluation, the concept of self awareness is implicit since to evaluate one's own performance requires that one must be aware of what the performance was, who the performer was and that the evaluator of the perfor- mance was the original performer. This type of self-analysis with its recognition of individual identity is a fundamental fea- ture of human intelligent behaviour. Occa- sionally one finds in the literature refer- ence to ‘idiots savants'. Really, the term is self-contradictory since idiocy and sagaci- ty are mutually incompatible. The term is used to describe those individuals who, while showing limited general intelli- gence, are somehow able to perform bril- liantly in a specific area, for example, adding up large columns of figures, or working out the day on which a particular dale falls in the calendar fifty years hence, etc. In human terms, they would not be regarded as intelligent but rather as having a processing facility for certain data. Wechsler 7 described intelligence as the purposeful and rational ability to deal with the environment. Human intelligence requires that an individual be able to inter- act with the environment, perceive rela- tionships, predict events and be aware of the effect of his/her actions on others. This is an example of primary intelligence. Symbolic representations in the form of language and mathematics are evolved later as convenient tools for processing information derived from primary intelli- gence. As stated earlier, when symbolic systems have been constructed, these lend themselves to processing in a variety of different ways, but they are the outcome of intelligence rather than intelligence per se. Terms such as cognitive science or artifi- cal intelligence as applied to the process- ing of symbols refer to aspects of human abilities and there is a danger in attributing too much to processing functions solely on the grounds that they reflect some aspects of human intelligence. In the introduction to his book on inten- tionality, Searle has argued for the inclu- sion of mental activities when concepts such as intentionality are considered; he rejects "any form of behaviourism or func- tionalism, including Turing machine fun- actionalism, that ends up by denying the specifically mental properties of mental phenomena”. My own thoughts from a psychological viewpoint also stress cau- tion in reading too much into machine per- formance, since there is a danger of estab- lishing a form of anthropomorphism that may militate against exploration of human brain functions by model making. Systems of linguistic analysis and response are closed systems (at present). Once the rules are provided, behaviour is determined by the logic of the system, even though changes in patterns may be affected by the introduction of new data. Self awareness would represent a constant monitoring by the system of its perfor- mance in relation to the world outside and to itself. Some aspects of social self awareness are outlined by Duval and Wicklund (1972), Argyle (1969) and Fcnigstein, Scheierand Buss (1975) 8 . Elements introduced by human self aware- ness are not necessarily logical or related to a predetermined goal of efficiency or accuracy. Departures from a logical path may be brought about by the recognition of similarity between the 'individual' and other individuals (which is the beginning of social intelligence and moral responsi- bility). Emotions such as pity, compassion, love, etc., may produce departures from a logical behaviour pattern since self aware- ness links all forms of behaviours with oneself. Ethical considerations involving feelings of empathy for others arise, involving both animals and humans. ‘If I were a gorilla, would I like my habitat destroyed?’, and so on. Introspection brings a new level of internal control of behaviours that may seem unintelligent (when in love, for instance), yet each behaviour is intelligent within the frame- work of the individual's perception of his/her feelings. The list of human attributes that may influence intelligent behaviour is enormous and includes, along with love, altruism, self-sacrifice, admira- tion, aesthetic appreciation, and so on. Without such sensitivity to environmental factors, it would be difficult to argue that intelligence was at work. The current con- flict between developers and conservation- ists is an outcome of a wider intelligence coming into conflict' with commercial intelligence. It would seem prudent from the outset that exploration into the areas of cognitive science and artificial intelligence should not be restricted to a narrow spec- trum, but should attempt to deal with the wider issues involved in intelligent behaviour. References 1. “Artificial Intelligence”, M. Seymour, Elektor Electronics India, June 1988. 2. Intentionality: an Essay in the Philoso- phy of Mind, John R. Searle, CUP 1983. 3. Alan M. Turing, p. 133, Sara Turing, W. Hel ler & Sons. 1959. 4. “Movement produced stimulation in the development of visually guided behaviour" R. Held and A. Hein. Journal of Comparative and Physiological Psy- chology, 56. 872—876. 1963. 5. Artifical Intelligence and Natural Man. p. 3, Margaret Boden, The Harvester Press, Hassocks. 6. Michael Faraday: a Biography, L. Pearce Williams. Chapman and Hall. 1965. 7. The Measurement and Appraisal of Adult Intelligence, D. Wechsler. Williams and Wilkins (1958), Baltimore Md. “Intelligence defined and undefined: a rel- ativistic appraisal”, D. Wechsler, Ameri- can Psychol., 30, 135-139 (1975). 8. “Public and Private Self Conscious- ness: Assessment and Theory'', A. Fenig- stein, M.F. Scheier and A.H. Buss, Jour- nal of Consulting and Clinical Psychology, 43, 4, 522-527 (1975).. Social Interaction, M. Argyle, Atherton Press (1969), New York. A Theory of Objective Self Awareness, S. Duval and R.A. Wicklund, Academic Press (lt>72) New YHork. elektor india december 1989 12.41 DC-DC POWER CONVERTER T. Wigmore This high-efficiency step-up converter supplies up to 30 V at 75 W when powereo from a 12 V car battery. The converter is ideal for many mobile and other out-of-doors applications: it functions as a power source for your DC-operated soldering iron, RF power amplifier, or NiCd battery charger for portable equipment such as a flasher or a video camera. DC-DC converters for stepping up the car, battery voltage are generally based on a switched-mode power supply (SMPSU) or a power multivibrator driving a trans- former. The power converter described here is based on the first principle, and uses the Type TL497A integrated circuit from Texas Instruments. This device en- ables good voltage regulation with low output noise to be achieved fairly easily, and in addition guarantees a relatively high conversion efficiency. Design background The converter described is of the flyback type. The flyback principle is the only practical way of generating a direct out- put voltage from a lower direct input volt- age. The central switching element in the converter is power S1PMOS transistor Ti (see Fig. 1 ). When it conducts, the current through Li rises linearly with time. Dur- ing the on-time, magnetic energy is stored • Flyback-type step-up converter • no special inductor required • input voltage: 12 VDC • output voltage adjustable between 20 and 30 V • maximum output power: 75 W • efficiency: 70%, independent of load cur- rent • voltage reduction at load variation from zero to maximum: <200,mV • ripple voltage: <500 mVpp. in the inductor. The moment the transistor is turned off, the inductor functions as a source of magnetic energy, which is sup- plied as an electric current to the load via Di. In this process, it is important that the transistor remains off during the time taken by the magnetic field to decay to zero. When this condition is not met, the current through the inductor rises to the saturation level. An avalanche effect then causes the current to increase very rapid- ly. The relative on-time, or duty factor, of the transistor control signal must, there- fore, not be allowed to reach the value of one. The highest permissible duty factor is dependent, among other factors, on the output voltage, because this determines the rate of decay of the magnetic field strength. The maximum output power that can be supplied by the converter is governed by the maximum permissible peak current through the inductor, and the frequency of the switching signal. The limiting factors here are mainly the satu- ration instant and the maximum tolerable ratings for the copper losses in the induc- tor, and the peak current through the switching transistor (remember that a'burst' of a particular energy content is supplied to tire output at each switching period). TL497A The operation of this integrated circuit is rather unconventional, so that a brief de- scription is given below. In contrast to widely used fixed fre- quency, variable duty-factor SMPSU con- troller ICs, the TL497A is qualified as a fixed on-time, variable frequency device. This means that the duty factor is control- led by means of frequency variation to maintain a constant output voltage. This method results in a fairly simple circuit, but has the disadvantage of the switching frequency reaching down into the audible range when the load current is low. In actual fact, the switching frequency becomes lower than 1 Hz when the con- verter is not loaded. The slow ticks heard as a result are the charge pulses applied to the output capacitors to maintain a con- stant output voltage. In the absence of a load, the output capacitors are, of course, slowly discharged by the voltage sensing resistors. The on-time of the oscillator on board the TL497A is fixed, and determined by Ct. The oscillator may be disabled in three ways: first, if the voltage at pin 1 exceeds the reference voltage (1 .2 V); second, if the current through the inductor exceeds a certain maximum; and third, via the in- Fig. 1. Circuit diagram of the step-up converter. hibit input (this is not used here). During normal operation, the oscilla- tor causes Ti to conduct so that the induc- tor current rises linearly. When Ti is switched off, the magnetic energy stored in the inductor is used to charge the out- put capacitors. The output voltage, and with it the voltage at pin 1 of the TL497A, rises a little, so that the oscillator is dis- abled until the output voltage has dropped to a sufficiently low level. This process is repeated cyclically, at least, in theory. In a configuration with real compo- nents, however, the voltage rise caused by the charging of the capacitors within one oscillator period is so small that the oscil- lator remains enabled until the inductor current reaches the maximum value defined with R 2 and IU (the voltage drop across R 2 and R 3 is 0.7 V at this stage). The current rises in steps as shown in Fig. 2b because the duty factor of the oscillator signal is greater than 0.5. When the maximum current is reached, the oscillator is disabled, and the inductor is allowed to pass its energy to the capacitors. In this condition, the out- put voltage rises to a level high enough to keep the oscillator disabled via pin 1. The output voltage drops, and a new charge cycle commences. Unfortunately, the switching oper- ations outlined above are coupled to rela- tively high losses. In a practical application, this problem is resolved by making the on-time (i.e., Ci) large enough to ensure that the inductor current does reach the maximum within a single oscil- lator period (see Fig. 3). The solution in this case is the use of an air-cored induc- tor, which has a relatively low self-induct- ance. Some waveforms The timing diagrams in Fig. 3 show the signal waveforms at the main points in the circuit. The central oscillator in the TL497A operates at a low frequency (lower than 1 Hz if the converter is not loaded). The switch-on instant, shown as the rectangular pulse in Fig. 3a, is deter- mined by capacitor Ci. The switch-off time is determined by the load current. During the on-time, Ti conducts so that the inductor current rises (Fig. 3b). In the non-conductive period after the current pulse, the inductor functions as a current source. The TL497A compares the attenu- ated output voltage at pin I with its inter- nal reference voltage of 1.2 V. If the measured voltage is smaller than the ref- erence voltage, Ti is driven hard again to enable the inductor to store energy . The above charge and discharge cycles cause some ripple voltage on the output capacitors (Fig. 3c). The feedback arrange- ment enables the oscillator frequency to be adjusted for optimum compensation of voltage losses caused by the load current. The timing diagram in Fig. 3d shows considerable swing of the drain voltage owing to the relatively high Q (quality) factor of the inductor. Although the para- sitic oscillations do not affect the normal operation of the power converter, they may be damped with the aid of a 1 k(2 resistor in parallel with the inductor. From theory to practice Naturally, a switch-mode power supply is designed for maximum rather than quies- cent output current. High efficiency and a stable output voltage with little ripple are also prime design goals. In general, the load regulation charac- teristics of a flyback type switch-mode power supply give little cause for concern. During every cycle, the on/ off ratio is ad- justed in accordance with the load cur- rent, so that the output voltage remains fairly stable in spite of large load current variations. The situation looks a little different as far as the overall efficiency is concerned. A step-up converter of the flyback type typically generates relatively large cur- rent surges, which cause considerable power losses (remember that power rises exponentially with current). In practice, however, the proposed converter has a total efficiency higher than 70% at maxi- mum output current, which is remarkable given the simplicity of the design. Fig. 2. Showing how the inductor energy is built up under the control of the oscillator signal. elektor india december 1989 1 2.43 a ut tin I 'out oscillator n * 1 1 b 1 flyback period 890030 • 12 Fig. 3. Timing diagrams of the main signals in the circuit. The current reaches its maxi- mum value within one period of the oscillator signal. The switching frequency at maximum load is made as high as possible to allow the use of a relatively small self-induct- ance. The practical circuit is based on an air-cored inductor. Significant losses caused by a ferrite core are thus avoided. A fast power-FET of the S1PMOS type is used to switch the inductor current. The Type BUZ10 or BUZ10A was chosen be- cause of its short recovery time. To achieve acceptable efficiency, the transis- tor must be used as a switching element. Parts list Resistors (±5%); Ri = IkO R2;R3 - 0£11 ; 4 W R« = 18K11 Rs = 1 K2 Pi = 10U2 preset H Capacitors: C: = 680p C2IC3 = 470g; 35 V; radial C4 = 1000g; 16 V; radial Inductor: Li = 30 pH (home-made, see text) Semiconductors: Di = BYV79 Ti= BUZIOor BUZ10A ICi = TL497A Miscellaneous: Heat-sink for Ti. PCB Type 890030 12.44 elektor india december 1989 This, in turn, requires it to be driven into saturation, resulting in a relatively long turn-off time. Obviously, the longer it takes for the transistor to interrupt the inductor current, the lower the overall ef- ficiency of the converter. Unconvention- ally, the BUZ10 is driven by the oscillator test-output of the TL497A (pin 11) rather than the internal output transistor. Diode Di is another essential part in the circuit. The requirements for this de- vice are an ability to withstand high cur- rent surges, and a low forward drop. The Type BYV79 meets these conditions, and must not be replaced with a general-pur- pose type. Returning to the circuit diagram of Fig. 1, it should be borne in mind that current peaks of 15-20 A are not uncom- mon in the circuit. To prevent problems arising with batteries having a relatively high internal resistance, capacitor Cr forms a buffer at the input of the conver- ter. Since the converter charges the output capacitors with short, surge-like current pulses, two capacitors are connected in parallel to ensure that stray capacitance remains as low' as possible. The power converter is not short-cir- cuit resistant. Short-circuiting the output terminals is the same as short-circuiting the battery via Di and Li. The self-induct- ance of Li is not so high as to limit the current for the time required by a fuse to blow. A home-made inductor Inductor Li is wound from 33V5 turns of enamelled copper wire. Figure 5 shows the dimensions. Most manufacturers sup- ply enamelled copper wire on an ABS reel. r Fig. 5. Suggested construction of the in- ductor on an ABS reel. which is suitable as the former for making the inductor. Drill two 2 mm holes in the lower rim to pass the inductor wires: one hole beside the cylinder and the other at the outside of the rim. There is little point in using thick w'ire to wind the inductor, because the skin-ef- fect, i.e., the displacement of charge car- riers towards the outside of the w'ire, must be taken into account given the frequen- cies used in the converter. To ensure a low resistance at the required inductance, it is recommended to use tw'o wires of 1 mm diameter, or even three or four wires of 0.8 mm diameter in parallel. Three NEW PRODUCTS 9” Monochrome Monitors 9" Monochrome Monitors with compo- site video nad for ITL input are now av- ailable with reverse polarity protection for 12V DC input. The Monitor has Green Phospher Tube and has resolu- tion of 800 x 35 video Amp. Bandwidth of 22 MHz. M/s. Anitex Marketing & Engineering Co. Pvt. Ltd. • 234, Jaygopal Industrial Estate • 510, Bhavani Shankar X Road • Dadar • Bombav-400 028. Hardware Locks Real Time Systems have developed Hardware Lock which preents unau- thorized copies of software. This has in- stallation software. Once installed, the installed files can be freely copied but will not run without the device in the parallel part. The software contains its own loader which does the loading and hicrarchial decision making structure to give maximum protection to software. Further .no two units of installation software are same for added security. There is no limit to the number of files that can be installed with one device. In addition to this there is a data file protec- tion unit DFP-1 which protects the prog- ram source code, letters, reports and 0.8 mm wires result in a total diameter that is roughly the same as that of two 1 mm wires, but has the advantage of re- sulting in a 20% larger effective surface. The inductor is close-wound and may be encapsulated in a suitable resin or pot- ting compound to limit the sound level (remember that the frequency of oper- ation is within the audible range). Construction and alignment The printed-circuit board designed for the DC-DC converter is shown in Fig. 4. A number of constructional points require attention. Resistors R 2 and Rn run fairly hot and must, therefore, be mounted at a few mil- limeters above the board surface. The peak current through these resistors can be as high as 15 A. The power-FET also runs hot, and requires a medium-size heat-sink and the usual insulating materi- al. The diode can do without cooling, al- though it is conveniently bolted on to the same heat-sink as the power-FET (do not forget to insulate it electrically). During normal operation, the inductor heats up. Heavy-duty terminals and wires must be used at the input and output of the converter. The battery is protected by a 16 A delayed action fuse inserted in the input supply line. Remember that the fuse does not protect the converter! The circuit is simple to align: adjust Pi for the desired output voltage between 20 and 30 V. The output voltage may be made lower, but not lower than the input voltage, by using a smaller resistor in po- sition R4. The maximum output current is about 3 A. other data bases. Bothe thse units oper- ate with IBM PC-DOS. Real Time Systems • Plot No. 8, 4th Main Road Avenue • Dhandeeswarar Nagar • Velachery • Madras-600 042. elektor india december 1989 1 2.45 PERSONAL COMPUTER DECISIONS by Linda Bishop* In choosing a pc system, the key question is not so much which processor platform is the best’, but rather which is the most appropriate platform for you. It is not simply a choice of speed either. Memory access and multitasking capability must also be considered in a platform decision. And then, of course, there's software. What type of applications will you run? What operating system do you need? In software, as in the platform decision, several criteria should be explored: price, performance, applications and the future. OS / 2 addresses all these issues. OS / 2 allows multi-tasking, multi-user operation, breaks the 640 K barrier of Dos and supports the graphical user interface of presentation manager. This will make network communication easier, provide bigger databases, more complete and sim- ple applications, and allow computers to do several things at the same time. What makes OS/2 unique is that it is the first full-fledged multi-tasking system for the 80286 microprocessor that can switch back and forth between protected mode and real mode to run the new pro- grams designed for OS / 2 as well as most existing DOS programs.This will give dos users a smooth upgrade path to OS / 2. The built-in network support of OS / 2 allows multi-user operation: this facility of having several programs running at the same time is, of course, a most useful one. Moreover, OS/2 permits distributed ap- plications, that is, it allows the program in your pc to work (communicate) with pro- grams in other pcs. OS/2 was written for the 80286 pro- cessor, taking advantage of the special protected mode feature. This feature is also provided by the 80386. OS/2 was not written to take advantage of any of the new features of the 80386 and no perfor- mance advantages are obtained by running OS/2 applications on an 80386. The 80386 is no faster than an 80286 when running 16-bit software at the same clock speed. The primary reason for this is that the 80286 executes more 16-bit in- structions in fewer clock cycles than the 80386 or 80386SX. Out of 190 existing * Linda Bishop is a product marketing engineer for Advanced Micro Devices’ Per- sonal Computer Products Division, Austin, Texas. She received her BSEE from the University of Michigan (Dearborn). Prior to joining AMO, she worked for Motorola. 16-bit instructions, the 80286 is faster on 74, the 80386 is faster on 50 and the two devices are the same on 66 instructions. In fact, the only way the 80386 is able to run OS / 2 at all is by emulating the 80286. The applications that are available today as well as those currently being developed will not take advantage of the 80386 until an OS / 386 specific version of the operating system is available some lime next year: OS / 386 general applica- tions are planned to become available sometime in 1991-92. Once an 32-bit operating system is available for the 80386, the device will have an advantage over the 80286. But there is no guarantee that 80386, and espe- cially 80386SX, personal computers avail- able now have the configuration to run new 80386 32-bit software four years from now. After all, the first 80286-based pc sold several years ago at 6 MHz with 640 K of memory is hardly suitable for running 16-bit OS/2 now. The same situ- ation is likely to exist in four years' time for today's 80386 pc as far as running 32- bit 80386SX software is concerned. What is important for the OS / 2 oper- ating system then is not whether it is run on an 80286 or an 80386, but rather the speed of the processor. The bulk of the processor's work is multi-tasking, that is, the accomplishing of several things at the same time by dividing the computer's time into ‘time slices’ that last only a fraction of a second. These time slices are handled so fast that it appears as if programs are run simultaneously. Since the processor is actually carrying out ali the tasks at sepa- rate intervals (time slices), the faster the processor, the quicker the multiple tasks will be completed. An adequately equip- ped 80286 system running at least 12-16 MHz with vga (Video Graphics Array) graphics forms a very cost effective OS/2 foundation . High-speed system pricing 80286 vs 80386 286-20 386-20 Dificrcnce Dell $2,999 $4,099 37% Zeos $2,095 $2,995 43% Northgate $2,599 $3,699 42% PC Brand $2,379 $2,995 26% Dataworld $1,555 $1,995 28% CompuAdd $1,695 $2,295 35% Paradox OS/2 Benchmark 0 286 - 16 (U 386SX -16 386 • 16 890189-12 Figure 2 Display Write 4.0 OS/2 Benchmark 890189-13 Figure 3 1 2.46 elektor irtdia december 1989 The 80286 system offers everything for the needs of today's and tomorrow's user. Fast 80286 (16, 20 and 25 MHz) sys- tems available now have the 16 Mbyte memory access capability and the protect mode for multiple applications required of OS/2. The 80286 is one of the best-selling processors on the market today and it is widely available. Moreover, its price is at an economical level for the system designer. Owing to its die size, packaging and complex processing, the 80386 is more expensive. Moreover, systems built around this device require 32-bit peripher- als: the design cost is, therefore, higher as well. This leads to significant price differ- ences between identically configured 80286-based and 80386-based personal computers. As shown in the table, an 80386-based system costs on average 35% more than an 80286-based system. The 80286 and 80386SX pcs used in the tests to arrive at the comparison bar graphs in Fig. 1, 2 and 3 are Everex stf.p models, while the 80386 is an IBM System 80. The 80386 pc uses page mode memo- ry access for 0.8 average wait states with 80 ns drams. Both the 80286 and the 80386SX run zero wait state with 60 ns drams. The performance of these pcs is indicative of that of other pcs. The benchmark in Fig. 1 is based on the R:Basc database program. The source database used is PC Magazine's Index for Volume 4.0. First, a Grouping Select Query (SQL) was performed, followed by a category tally to count the number of PICTURE-IN-PICTURE MINIBOARD FROM SIEMENS The SDA 9088 Picture Insertion Processor from Siemens allows the picture-in-picturc facility to be installed not only in digital tv sets, but also in analogue ones. The need for only two chips reduces time and material requirements and increases relia- bility. The SDA 9088, which is designed in Siemens 1 Mb it dram technology, also provides a much better picture quality than previous designs. The SDA 9088 permits the insertion of a reduced-size picture into the main pic- ture by using picture signals that may be based on completely different standards and synchronization principles. The com- bination of frame memory, control, digital signal processor and digital-to-analogue converters on a single chip enables equip- ment manufacturers to realize the picture- in-picture function in tv sets and video recorders on a high-performance and par- ticularly cost-effective basis. occurrences in a category. Next, a calcula- tion loop was performed on the first 100 records. The results are shown in seconds. The bar graphs show that the 80286 pc outperformed the 80386 pc by 4%, while the 80386SX was 24% slower. The bar graphs in Fig. 2 are obtained from running the Paradox database pro- gram on the three computers. The source database is again PC Magazine’s Index Volume 4.0. First, a Grouping Select Query was performed. Next, a report was run with the output sent to a file on ram disk. The query results were then sorted and a conditional delete of the records in the query results was performed. The results are shown in seconds. As is seen, the 80286 pc was 18% faster than the 80386SX. The comparative tests illustrated in Fig. 3 were based on the ibm word proces- sor program Display Write 4.2. The benchmark started with a 100 K, 40-pagc document. A global search and replace was performed, changing one frequently used word for another. Next, the margins were narrowed, forcing a complete text rewrap. Lastly, the document was repagi- nated. The results arc shown in seconds. Again, the 80286 pc was faster than the 80386 pc by 4%, while the 80386SX was 8% slower than the 80286 pc. Comparative tests are influenced both by the processor and by the memory inter- face. In the pc systems used, the memory interfaces were relatively equal (0.8 wait states on the 80386 and 0 wait state on the 80286 and 80386SX machines). Thus, the performance difference measured between the 80286 and 80386SX was caused ELECTRONICS SCENE Although the picture-in-picture func- tion has been in existence for some years, it has failed to become widely established in domestic video equipment owing to its high cost, incurred mainly by the expen- sive but indispensable frame memory and the peripherals required for the analogue- to-digital converters. Through the use of the most up-to-date semiconductor tech- solely by the different processors with the former performing faster than the latter. The performance difference between the 80286 and 80386 must take into account the different memory interface techniques. A 0.8 wait state system (as on the 80386 pc) has about a 9% perfor- mance degradation compared to a true zero wait state system (as on the 80286 pc). Taking this into account, the 80286 and 80386 systems performed essentially the same. As OS/2 software becomes more pre- valent, pc performance will become more important. Performance is primarily a function of processor clock speed and memory interface in the pc. Clock speeds of 16 MHz and beyond will be needed to run multiple applications effectively. It should be borne in mind that there is little difference in performance between the 80286 and 80386 running at the same clock speed on OS / 2. In addition to performance, price will also remain a major factor in personal computer decisions and it was seen that 80286-based pcs remain substantially cheaper titan 80386-based systems. The 80286 has, moreover, a lot of life left for dos, as well as OS / 2, systems and will continue the trend toward higher clock speeds. According to Dataquest, the 80286 will increase its current market share of IBM and compatible pcs from 30% to 33% by 1992 and become the entry-level pc, replacing 8086/8088 based machines. Following a stable path to OS / 2, the 80286 is the best platform for cost vs per- formance. nology, it has now been possible to inte- grate all essential functions into a single circuit. The primary function of the pip is to reduce the picture produced by the sec- ond picture signal and synchronize it with the main picture. Two formats are available for the inserted picture: 1/9 and 1/16 the size of the main picture. The insert may be dis- played in any of the four corners. A posi- tioner for each corner permits adjustment to the particular set's geometry. In contrast to previous designs, picture reduction is effected not by omitting the pixels that are not needed but by digital filtering of the horizontal and vertical sig- nals to ensure that all the information is utilized. The SDA 9088 handles all worldwide tv standards: a detector performs automat- ic transfer to the standard being received. It is also able to supply standard-converted picture signals at a line frequency of 32 kHz. elektor India december 1989 1 2.47 SPEEDING UP THE COMPUTER by Pete Chown The architecture of the computer If you look at a modern micro, say, an 80386-based IBM compatible, you will dis- cover that nearly all the memory band- width is used up. If faster memory were installed, it might be possible to increase the speed of the processor by several times, but that would be the limit for that particular architecture. In an earlier article 1 I mentioned one way out of this dilemma: parallel process- ing. There are, however, many other ways of speeding up appar- ently sequential processors so that they can reach speeds of up to 600 MFlops (million floating point operations per second). At present, the Cray-3 represents the limit of that approach as far as commercial machines go. The Cray-2 is the fastest one that has been commer- cially released. Cacheing Cacheing is one of the simplest techniques that can be used to speed up a computer. Earlier, I mentioned that faster memory could allow the speed of most ma- chines to be increased substantial- ly. Unfortunately, fast memory costs a disproportionate amount more, and so manufacturers decid- ed to use the fast memory only for instructions that are currently being executed. This means that the cache is loaded with the pages of main memory that are being used (normally in the opposite phase of the processor clock to that on which the processor reads the memory), and it is then avail- able for use. Using a cache has one other advantage. Memory protection - so that one process can not alter another's memo- ry - is very hard to implement fast enough for the processor's request to access a par- ticular word to be checked in time. On a large machine, only of the order of 100 ns would be available. If a cache is used, however, the system can verify that the process is allowed to use a particular page before it is ever loaded into the cache. A major cause of the inefficient use of caches is that each time the machine switches context (that is, changes the pro- cess it is executing) at least part of the cache has to be reloaded. Multiple processors Because large machines are generally used for time-sharing, it is quite acceptable for them to incorporate several processors. Generally, however, these share the same bus, so that problems are not encountered with lack of memory on one processor, or problems with an t/o device controlled by another processor. Caches are used to avoid continual conflicts for memory. This tends to be a not very efficient technique, because in practice a large number of conflicts for memory do occur. The best-known machine to use this sys- tem is the vax 8900. It has four processors sharing a bus (each of which is the same as the single processor used in the 8700). Adding a fourth processor does, however, add only about 15% of the performance that the processor would generate on its own. The reason for this is that conflicts for memory mean that the processors are standing idle for much of the time. The reason that dec decided to use this technique is probably that it allowed them to keep the same architecture: a radical redesign would have meant changing the instruction set, and the major selling point of the vax range is that programs for any vax can be run on any other. The other advantage of this system is right at the top end of the computer market: the US Navy have produced a supercomputer using 1 6 largely independent processors, giving them the edge over single-processor equi- valents. Pipelining and vector processing Pipelining and vector processing are other major ways in which manufacturers speed up their com- puters. They are, however, much more complex to implement than the other systems. The techniques are similar: some computers imple- ment pipelines but not vector pro- cessors, but generally speaking the reverse is not true. In pipelining, the processor, in- stead of starting on one instruction and executing it to completion, reads instructions continually. Once it has completed reading an instruction, the processor begins fetching the instruction's operands. At the same time, the next instruc- tion will be read, the previous instruction will be executed, and the result of the instruction before that will be written to memory or registers. In practice, things are not this simple. A pipeline tends to be longer than just indicated, because the aim is to keep the processor- memory interface busy for as much of the time as possible. Since not all instructions need their operands fetched, there would be a tendency for the interface to run out of information to fetch or store. Problems with pipelines tend to be encountered with jumps. When the proces- sor jumps, everything in the pipeline is useless because it no longer wants to exe- cute those instructions. It is not possible to make the pipeline start taking instructions from the destination of the jump, because the jump might be conditional and the condition would not have been evaluated. Another problem is when store loca- tions change after the pipeline has been loaded. If one instruction uses the result of B90161 • 11 Construction of the Cray machines 1 2.48 eloktor india december 1989 the previous one, the old value that was present at that location in store would already have been loaded. There is no solution to this except the long one - with each and every instruction it must be checked that the operand being loaded is not going to be stored by an instruction already in the pipeline. This is particularly difficult with indirection, because care must be taken that the information about where the operand is coming from is avail- able in time. If it is not, the processor must stop until it is, which leads to inefficiency. As with caches, pipelines suffer when a processor switches context. Whereas with the cache some of it might be able to be preserved, the entire pipeline must be dis- carded since there is nowhere for it to be put until the processor returns to that pro- cess. Vector processors take the idea of pipe- lining a stage further. With large machines providing a large variety of complex mathematical operations, the execution of an instruction is by far the longest step in the pipeline. Consequently, the informa- tion about where to find the operands is passed out to a lot of arithmetic proces- sors. This saves the main processor from having to find out what the operands are, or to execute the instruction. The problems with this are obvious. The difficulties with making sure that the operands of an instruction have not been modified since the instruction was loaded become much worse. Because some instructions complete faster than others, there is a danger of instructions being exe- cuted in the wrong order: tens of short instructions could have been executed in the time it takes for a complex floating point function to be evaluated and one of these short instructions might have wanted to use the result of the long one. Another problem is memory bandwidth - the multiple processor problems are obviously much worse. This has, however, been almost completely solved. Memory, instead of being addressed over a single bus, is addressed on a chip-by-chip basis, so that as long as all the processors wish to access different chips, they can do so at the same time. This solution does, howev- er, lead to another snag: the large amount of wire needed to connect each individual chip! It is interesting to note that this archi- tecture is based on parallel processing, even though the machines appear sequen- tial to the user. The parallelism is on a very small scale, and so it has been described as ‘fine’ parallelism, whereas true parallel processing machines have been described as having ‘coarse’ paral- lelism. As these computers get faster, the exact length of wire used to connect two points becomes significant in determining timing. Consequently, Cray Research decided to cut each piece of wire in their machines the same length! Unfortunately, these lengths have to be also as short as possible for the same reason and this led to the cir- cular construction of the Cray machines as illustrated. It also led to the situation where the wires are almost impossible to get at, forming a three-dimensional web of cables that are tight enough for it to be dif- ficult to reach a wire near the middle. RISC processors Rise processors are not really viable as a technique for building large machines. The reason is that you are faced with a choice of ways of improving performance - make each instruction do more or exe- cute faster. Small machines had been tend- ing to follow the former route despite the fact that there was not really enough pro- cessing power on a single chip to do it. A large increase in speed was therefore ob- tained when micros began to follow the latter route. Large machines have pipelines, caches and so on, and also aim to do a lot per instruction. Consequently, the Sun, Apollo and Hewlett Packard machines tend to set the limit for this type of technology. There is now a move to provide a mainframe style processor on a chip, since this is becoming viable with greater relia- bility and packing density. This will effec- tively make the Rise processor obsolete in a few years’ time, at least as far as the very fastest workstations are concerned. This trend towards micros that are more like mainframe is actually another way of speeding up computers. We are ap- proaching the limit as far as supercomput- ers go. but if workstations that only sever- al people use get nearly that fast, they will effectively have a much more powerful machine because there are far fewer pro- cesses for it to run. There will always be a place for the supercomputer, however, in performing single processes that are too complex for a workstation to do. It will, however, be- come increasingly wasteful to use a super- computer for a lot of fairly small jobs. One area of potential for Rise that has not received much attentional is that of arithmetic processing. It would be possible to build a Rise machine with, say, 256 bytes of ram and several registers that would carry out operations between regis- ters only and not ram. It would thus be very simple and could, therefore, run at high speeds. It could then be programmed with short, repetitive calculations that could be done over and over again. Managing a pipeline I have already discussed some of the prob- lems that arise from pipelining and vector processing. One of the easiest ways to understand the problems and how they are solved is, however, to look at how a vector processor would execute a certain sequence of instructions. Since this is only for illustration, the instructions will be given in words - not in any form of mnemonic that would make it harder to follow. The instructions are to calculate the coordinates needed to draw a circle by trigonometry. Square brackets indicate indiscretion The label ‘pointer’ points to a location containing the address where the forty pairs of coordinates are to be placed. 1. Load register A with 0. 2. Load register B with 0. 3. Label: 4. Calculate cos(A), pul in register C. 5. Calculate sin(A), put in register D. 6. Multiply C by [radius). 7. Multiply D by [radius]. 8. Store register C at [pointer] + B. 9. Store register D at [pointer] + B + 1 . 10. Add 2 to B. 1 1 . Add pi/20 to A. 12. Jump to label if A < 2 * pi. Let us now' consider how a vector pro- cessor would execute this section of code. It would start by filling its pipeline from the beginning. No evaluation of operands would be necessary for instructions 1 and 2. When these got to be executed, they will be run at the same time because the processor would recognize that (hey did not refer to the same part of store. Instructions 4 and 5 could not be exe- cuted until instructions 1 and 2 had been completed, because the values of the same registers are used. Once 1 and 2 had been completed, however, they would be exe- cuted together. The same would be (rue of instructions 6 and 7, but here one of the advantages of a fast processor shows up. The processor has been instructed to look at a particular memory location in order to find the radius of the circle. There is no reason why this should wait to be evaluated until the rest of the instruction can be. Different processors would tackle it in different ways: those with just a pipeline and no vector processor would attempt to find time to evaluate it while the instruction is in the pipeline, while those with a vector processor would simply hand the pointer to one of the arithmetic units and instruct it to look at that place in store. The two additions would take place concurrently, since they do not refer to each other in any way. The jump would then be encountered. The pipeline would have been unable to follow the jump to its conclusion to get subsequent instructions, because it is a conditional one. It is, there- elektor India decamber 1989 1 2.49 assume that the jump will not be taken, and it will have to abandon all the infor- mation it has built up about the instruc- tions following the loop, except when the loop finally ends. Nothing has been lost compared to a conventional processor, however, because the bus would merely have been sitting idle. Once back at the start of the loop it might have kept the instructions because such an eventuality was likely or it might have to start build- ing up its pipeline from scratch again. Conclusions Because we are reaching the limits of semiconductor-based computers, the large computer of today is a far more complex thing than its predecessors. The normal rules of structured design have been aban- doned in a search for the last megaflop, leading to such peculiarities as computers with all the wires the same length (nor- mally, of course, no one would think of building a large system other than in stan- dard 19 in. rack-mounted cases on a care- fully constructed backplane). The tech- niques do, however, work and we have probably got computers an order of mag- nitude faster from them. It is, however, a tribute to the people who design them that they work at all. ■HMMMj NfclW PRODUCTS Hand Cleanser Advance Labs have introduced Actoplus Hand Cleanser. This remove grease, oil, smal particles of metal, dust, grime and dirt instantly when applied. A small quantity is applied in paste form and either washed away wth water or simply wiped clean with cotton waste or cloth. There are no side effects as it is abso- lutely safe. Advance Lab • 11, Below Shantidoot Hotel • Dr. Ambedkar Road • Dadar • Bombay- 400 014. Sequential Timers (Cyclic) Vectrol Engineers introduces a solid state cyclic timers. These are available with two change over contacts. Timer switches a given device/load sequentially “ON-OFF” on giving signal/application of control supply and stops it when a soap signal/command is given. Timers can be supplied with ‘ON’ time count or ‘OFF’ time count start first on applica- tion of start command/signal/control supply to timer. Timer provides precise ‘ON-OFF’ sequence ratio with excellent repeat accuracy. Cyclic timers are used in chemical/phar- maceutical and other allied industries, where device/load is required to repeat the operation automatically in succes- sion, until the stop signal is given. Vectrol Engineers • 4 A/32, Versova View 1 Co-op. Hsg. Society • Four- Bunglow road • Andheri (W) • Bombay- 400 058. Grasslin Time Switch The MIL 2008 Q series is fitted with a Quartz Electronic Drive Control and a step motor. The Quartz frequency is 14.9 million Hertz and the Quartz stabiliza- tion guarantees the exact running of the driving mechanism. These time switches are designed for the accurate and effort- less control of oil heating installations, electric heaters, air conditioning plants, water processing plants, street lights, traffic signals, etc., etc. Human nature being what it is, howev- er. these techniques will probably be with us even when optical computers appear, and we will simply take our thousand times speed increase, and do exactly the same with optical fibres. MIL 2008 Q is available with contact rat- ing of 16Amps. 250V AC and available with daily programme and weekly prog- ramme dial. Operates on mains supply and continue to run for 150 hrs. after power failure on a battery back-up. M/s. Sai Electronics • (In association with Cupwud Arts) • Thakore Estate • Kurla Kirol Road • Vidyavihar (West) • Bombay-400 086. Ph: 5136601/5113094/ 5113095. 12.50 elektor india december 1989 ( 2 ) The first part of this article dealt with the design considerations concerning loudspeaker crossover filters in general, and active crossover filters in particular. This month a practical circuit is given, with details on how to modify it according to personal taste. As explained last month, several de- cisions must be made before starting with the actual design of any loud- speaker crossover filter system. In chronological order: — What type of filters: active only, hybrid or passive? This article only deals with filters that are active, at least in part. — What type of system, three-way or two way? This decision will be based on such factors as desired cabinet size, available financial resources, desired frequency range — and personal taste. - Which speakers? This depends in part on the answer to the previous question. - What crossover frequencies, and how steep the filters? These decisions are both based on the answer to the previous question. - Which amplifiers? This is a source of endless discussion, but the answer obviously depends in part on the type of system and the speakers used. The points of interest in this article are the design decisions for the filter proper: two-way or three-way, what crossover frequency or frequencies, and how steep? These points are illustrated in figure If. If a two-way system is required, the crossover frequency is assumed to be f 1 — f2 can be ignored. For a three-way system, fl is the lower crossover frequency and f2 is the higher. The filter slopes ■ can be 6-, 1 2- or 18 dB / octave, and the 12- and 18 dB/octave slopes are numbered in figure If. As an example, a three-way system with crossover frequencies of 400 Hz and 4 kHz and filter slopes of 12 dB/octave at the lower crossover point and 18 dB / octave at the higher fre- quency can now be defined briefly as ‘fl = 400 Hz, f2 = 4 kHz, filter slopes 1, 4, 6 and 7’. This shorthand notation will be used extensively in the tables given in this article. The most complex circuit diagram is given in figure 5: a three-way system with all slopes 18 dB/octave. This corresponds to the figure 6 layouts for printed circuit board and parts. When any less-complex set up is to be assembled it will only be necessary to complete the ‘through paths’ with wire links on the printed circuit board. This will be illustrated in detail further on. For added convenience, all the circuits and parts-layouts have been duplicated several times — each time showing the simplified schemes and jumper wires needed for the less complex filters. The schemes we have chosen to illustrate are: — Three-way system with 1 2 dB/octave slopes (figures 7 & 8). — Two-way system with 18 dB/octave slopes (figures 9 & 10). — Two-way system with 12 dB/octave slopes (figures 1 1 & 1 2). — Two-way system with 6 dB/octave slopes (figures 13 & 14). The frequency responses of the figure 5 filter set are plotted in figure 15. Figure 16 gives the plots for the figure 7 circuit. In both cases the frequencies chosen for illustration are 500 Hz (fl) and 5 kHz (f2). Design procedure The suggested procedure for finding the required design is as follows. First of all decide, using figure 1 f or table 1 , which set of filter characteristics is to be realised - and which crossover fre- quences ( values of fl and f2) are to be taken. Table 2 may now be used as a kind of ‘railway timetable’ to determine which PC board positions are to be left ■open, which positions must be bridged by a jumper wire and which of the tables 3 ... 8 is to be referred to for the component values. The examples given will illustrate this. Loudspeaker connections In just the same way as with passive filters it is important to connect the individual loudspeakers in the correct relative phases. The rules are as follows: When the filter provides a three- way symmetrical crossover with 12 dB/octave slopes, the midrange unit should be connected in opposite sense to the woofer and tweeter. Both systems of a stereo pair should of course be identically wired. ® © © L M H © © © Figure If. A few frequency-response plots, with slopes of 12 and 18 dB/octave and one or two crossovers, as an aid to interpretation of table 1. If elektor india december 1989 12.51 - When the filter provides a symmetri- cal two-way crossover with 12 dB/octave slopes, the tweeter should be connected in opposite sense to the woofer-midrange unit. © 0 L H 0 © — The problem is different with 18 dB/octave and 6 dB/octave slopes, where the phase shift in the filters at crossover totals 270° or 90°. It is convenient to connect all speakers in the same sense in these cases. The loudspeaker-coupling electrolytic capacitors in the midrange and treble channels can in principle be given a smaller value than that in the woofer channel, thus saving space and cost. However, one must bear in mind that a smaller value component will have a lower alternating current (‘ripple’) rating. The smallest value that still has a current rating at least equal to the loudspeaker maximum RMS current will usually have a large enough capacitance too. In case of doubt ensure that the RC cutoff point of the 12.52 elektor india december 1989 capacitor with the loudspeaker’s nominal impedance is 3 ... 5 times lower than the high-pass crossover frequency in the channel concerned. The factor 3 ... 5 should also be observed with the woofer! This results in the well-known rule of thumb: where f c is the lower crossover fre- quency. Nothing useful is gained (and there is a risk of too much phase shift or amplitude rolloff being caused) by also reducing the values of the input coupling capacitors of the midrange and treble amplifiers. Cl 6 and C21 in the filter are ‘unnecessarily large’ for the same reason. One final remark concerns the function of the presets PI , P2 and P3. These are not intended as tone control adjust- ments! They should be used only to compensate for possibly unequal sensi- tivities of the individual amplifier- speaker channels. Deliberate maladjust- ments of not more than 3 dB (tone controls after all!) may however occasionally be permissible. Component list for figures 5 and 6. Resistors: R1 f R2 = 220 k R3.R8.R14. R19 l ,R24‘ = 5k6 R4.R9.R15, R20 1 ,R25 ! = 2k2 R5 2 see table 3 R6 3 see table 3 or 5 R7 see table 3, 5 or 7 RIO 4 see table 4 R1 1 5 see table 4 or 6 R12 R13 see table 4, 6 or 8 R16 5,6 see table 3 R17 3,6 ,R18' see table 3 or 5 R21 1,4 see table 4 R22 1 ,R23 1 ,R26 I see table 4 or 6 P1.P2.P3' 10 k preset Capacitors: Cl = 470 n C2.C6.C1 1 . C15 1 .C20 1 = 4n7 C3 4 see table 3 C4 5 see table 3 or 5 C5 see table 3, 5 or 7 C7.C16.C21 1 = 10 p/25 V C8 1 see table 4 C9 3 see table 4 or 6 CIO see table 4, 6 or 8 C12 1 ' 4 see table 3 C13 6 .C14' see table 3 or 5 Cl 7° see table 4 C18 1 .C19 1 see table 4 or 6 C22 = 100 p/40 V C23.C24.C25, C26\C27' = 100 n Semiconductors: T1.T3.T5.T7 1 , BC107 B, BC547 B T9 1 or equivalent T2.T4.T6.T8 1 , BC177 B, BC557 B T10 1 or equivalent Footnotes means: omit part for two-way filter set means: replace by wire link for 12 dB/oct and 6 dB/oct. 3 means: replace by wire link for 6 dB/oct. 4 means: omit this part for 12 dB/oct or 6 dB/oct. 5 means: omit this part for 6 dB/oct. 6 means: replace by wire link for two-way filter set. NB. The 6 dB/octave slopes are only useful in a very limited number of two-way system designs— the tables therefore do not give values for three- way design. Figure 15. Frequency response of the figure 5 circuit, as measured with fl set at 500 Hz and 12 at 5 kHz. Figure 16. Frequency response of the figure 7 circuit with the same crossover points as figure 15. Figure 5. Complete circuit diagram of an active filter set for two symmetrical 18 dB/octave crossovers (three-way). Figure 6. Component layout and p.c. board copper-side plan for the figure 5 circuit. (EPS 9786) eloktor india december 1989 1 2.53 Table 3. Table 1. The 18 dB/octave low-pass filter, having the response given in figure 2a , with the nominal crossover frequencies obtainable The different possible combinations of symmetrical or asym- using El 2 series component values. metrical crossovers and 12 or 18 dB/octave slopes. f (Hz) R (k£i) c a (nF) C b (nF) C c (nF) filters slopes at filters slopes at fi R5 R6 R7 C3 C4 C5 fi to be be combine from refer to f2 R16 R17 R18 Cl 2 C13 C14 V* figure If figures 97 10 10 10 220 560 33 18 12 18 18 2, 4, 6 & 7 119 10 10 10 180 470 27 18 12 12 12 2,4.5 8< 8 146 10 10 10 150 390 22 18 12 18 12 2, 4, 6 8i8 179 10 10 10 120 330 18 18 12 12 18 2,4, 5& 7 214 10 10 10 100 270 15 12 18 18 18 1,3, 6& 7 268 10 10 10 82 220 12 12 18 12 12 1,3, 5 8i8 322 10 10 10 68 180 10 12 18 18 12 1,3, 6& 8 392 10 10 10 56 150 8.2 12 18 12 18 1 , 3, 5 8t 7 472 10 10 10 47 120 6.8 18 18 18 18 2, 3, 6 8i 7 5 & 6 574 10 10 10 39 100 5.6 18 18 12 12 2, 3, 5 Si 8 684 10 10 10 33 82 4.7 18 18 18 12 2.3, 6& 8 824 10 10 10 27 68 3.9 18 18 12 18 2, 3, 5 & 7 974 10 10 10 22 56 3.3 12 12 18 18 1 , 4, 6 & 7 1191 10 10 10 18 47 2.7 12 12 12 12 1,4, 5& 8 7& 8 1461 10 10 10 15 39 2.2 12 12 18 12 1,4,6 & 8 1786 10 10 10 12 33 1.8 12 12 12 18 1,4, 5 & 7 2143 10 10 10 10 27 1.5 18 18 — 2&3 9& 10 2679 10 10 10 8.2 22 1.2 12 12 — 1 & 4 11 & 12 3215 10 10 10 6.8 18 1 12 18 — 1 8i 3 3921 8.2 8.2 8.2 6.8 18 1 18 12 - 2 & 4 4728 6.8 6.8 6.8 6.8 18 1 5742 5.6 5.6 5.6 6.8 18 1 6841 4.7 4.7 4.7 6.8 18 1 8244 3.9 3.9 3.9 6.8 18 1 9743 3.3 3.3 3.3 6.8 18 1 response (see figure If) 1 2 3 4 5 6 7 8 9 10 component -V R5 t3 wl wl R6 t3 t5 wl R7 t3 t5 t7 C3 t3 — — C4 t3 t5 — C5 t3 t5 t7 C8 wl t4 wl C9 t6 t4 wl CIO t6 t4 t8 R10 — t4 — R11 t6 t4 — R12 t6 t4 t8 R13 t6 t4 t8 R16 t3 wl R17 t3 t5 R18 t3 t5 C12 t3 — C13 t3 t5 C14 t3 t5 Cl 7 wl t4 C18 t6 t4 Cl 9 t6 t4 R21 — t4 R22 t6 t4 R23 t6 t4 R26 t6 t4 see figure 3b 2b 2a 3a 3b 2b 2a 3a 4a 4b Cross-reference table of frequency-determining components, starting from the 'available response curves' of figure If. The components are numbered as in the complete circuit and layout diagrams (figures 5 & 6); t3 t8 are the value-table references, 'wl' means 'wire link' and ’ means ’omit'. The 18 dB/octave high-pass filter, having the response given in figure 2b, with the nominal crossover frequencies obtainable using El 2 series component values. C {nF} C8 = C9 = CIO C17 = C18 = C19 100 82 68 56 47 39 33 27 22 18 15 12 10 8.2 6.8 5.6 4.7 3.9 3.3 2.7 2.2 1.8 1.5 1.2 1 f (Hz) R a (kn) Rb (kn) R c (kn) fi R10 R11 R1 2 = R13 f2 R21 R22 R23 = R26 114 10 3.9 150 139 10 3.9 150 168 10 3.9 150 204 10 3.9 150 243 10 3.9 150 293 10 3.9 150 346 10 3.9 150 423 10 3.9 150 519 10 3.9 150 635 10 3.9 150 762 10 3.9 150 952 10 3.9 150 1140 10 3.9 150 1390 10 3.9 150 1680 10 3.9 150 2040 10 3.9 150 2430 10 3.9 150 2930 10 3.9 150 3460 10 3.9 150 4230 10 3.9 150 5190 10 3.9 150 6350 10 3.9 150 7620 10 3.9 150 9520 10 3.9 150 11400 10 3.9 150 12.54 elBktor India december 1989 How to use the tables. • Decide on the type of filter required, and refer to figure If and/or table 1 for the ‘shorthand notation’. Note that responses 9 and 10 are 6 dB/oct low- pass and high-pass, respectively; these are not shown in figure 1 f. • Proceed to table 2. Under each of the (two or four) chosen response curves, further information is given regarding a group of frequency-determining components. This can be either *wl’ (wire link), ' (omit) or reference to one of the tables 3 ... 8 (e.g. ‘t3’ means ‘refer to table 3’). • Proceed to the tables referred to. As an example, assume that slope 3 is required at a lower crossover frequency f 1 = 400 Hz. Under response 3, table 2 refers to table 3 for R5 . . . R7 and C3 . . . C5. Proceeding to table 3, the nearest frequency to the desired 400 Hz is 392 Hz. For this frequency, the values of R5 . . . R7 are shown as 10 k«, C3 = 56 n, C4 = 150 n and C5 = 8n2. Bibliography Electronics, August 18th 1969, p82 etc (filter circuits) J.R. Ashley & L.M. Henne: Operational Amplifier Implementation of Ideal Electronic Crossover Networks; JAES, January 1971. S. Linkwitz: Active Crossover Networks for Noncoincident Drivers; JAES, February 1976. J.R. Ashley & A.L. Kaminsky: Active and Passive Filters as Loud- speaker Crossover Networks; JAES, June 1971. R.H. Small: Constant-Voltage Crossover Network Design; JAES, January 1971. B.B. Bauer; Audibility of phase distortion; Wireless World, March 1974. H.D. Harwood: Audibility of phase effects in loudspeakers; Wireless World, January 1976. Table 5. The 12 dB/octave low-pass filter, having the response given in figure 3a, with the nominal crossover frequencies obtainable using El 2 series component values. f (Hz) R (kn) C b (nF) C c (nF) fl R6 = R7 C4 C5 f2 R1 7 = R1 8 C13 C14 102 22 100 47 125 18 100 47 150 15 100 47 188 12 100 47 225 10 100 47 274 10 82 39 331 10 68 33 402 10 56 27 479 10 47 22 577 39 10 4.7 682 33 10 4.7 834 27 10 4.7 1020 22 10 4.7 1250 18 10 4.7 1500 15 10 4.7 1880 12 10 4.7 2250 10 10 4.7 2740 10 8.2 3.9 3310 10 6.8 3.3 4020 10 5.6 2.7 4790 10 4.7 2.2 5840 8.2 4.7 2.2 7040 6.8 4.7 2.2 8550 5.6 4.7 2.2 10190 4.7 4.7 2.2 Table 7. The 6 dB/octave low-pass filter, having the response given in figure 4a, with the nominal crossover frequencies obtainable using E 1 2 series component values. f (Hz) R (kfl) C c (nF) fl R7 C5 106 10 150 133 10 120 159 10 100 194 10 82 234 10 68 284 10 56 339 10 47 408 10 39 482 10 33 589 10 27 723 10 22 884 10 18 1060 10 15 1330 10 12 1590 10 10 1940 10 8.2 2340 10 6.8 2840 10 5.6 3390 10 4.7 4080 10 3.9 4820 10 3.3 5890 10 2.7 7230 10 2.2 8840 10 1.8 10600 10 1.5 Table 6. The 12 dB/octave high-pass filter, having the response given in figure 3b with the nominal crossover frequencies obtainable using El 2 series component values. f (Hz) C (nF) Rb (kn) R c (k£2) fl C9 = CIO R 1 1 R1 2 = R13 f2 C18 = C19 R22 R23 = R26 113 100 10 39 137 82 10 39 165 68 10 39 201 56 10 39 239 47 10 39 289 39 10 39 341 33 10 39 417 27 10 39 511 22 10 39 625 18 10 39 750 15 10 39 938 12 10 39 1130 10 10 39 1370 8.2 10 39 1650 6.8 10 39 2010 5.6 10 39 2390 4.7 10 39 2890 3.9 10 39 3410 3.3 10 39 4170 2.7 10 39 5110 2.2 10 39 6250 1.8 10 39 7500 1.5 10 39 9380 1.2 10 39 11300 1 10 39 Table 8. The 6 dB/octave high-pass filter, having the response given in figure 4b, with the nominal crossover frequencies obtainable using El 2 series component values. f (Hz) R c oG T I o^o f o 5 2o-^o6geHH»f| i -i °£”3j° i r^-x < H rib i *o < H^g3^ 6 V < ^^19 h o o 1we.a| 0 <£V °HH>S -Qh.-P $ ©‘Sfc 0 s-i o oHho o- — {] | — o -*• • •.. cs6 t ©15 ...30V T1,T3,T5,T7,T9 = BC547B, BC107B T2.T4.T6.T8.T10 = BC557B. BC177B 3 - way, 12 dB/oct. As an example, assume that a three-way 12 dB/oct. filter system is required (slopes 1, 4, 5 and 8 in figure If) with crossover frequencies fl = 400 Hz and f2 = 3 kHz. Referring to table 2: for slope 1, C8 = wire link; R1 0 = omitted ; C9, Cl 0, R 1 1 ... R 1 3 are to be found from table 6. In the latter table, the nearest frequency to the desired fl is 417 Hz. The corresponding component values are given as C9 = CIO = 27 n; kll = 10 k; R12 = R13 = 39 k. Back to table 2: for slope 4, R5 = wire link; C3 = omitted; R6, R7, C4 and C5 are to be found from table 5. Proceeding to this table, the component values corresponding to f 1 = 402 Hz are shown as R6 = R7 = 10 k; C4 = 56 n and C5 = 27 n. Back to table 2 : for slope 5 , C 1 7 = wire link; R21 = omitted; C18, C19, R22, R23 and R26 are to be found from table 6. For f2 = 2890 Hz (the closest to the desired 3 kHz), this table gives the component values: C18 = C19 = 3n9; R22 = 10 k; R23 = R26 = 39 k. Now table 2 again: for slope 8, R16 = wire link; C12 = omitted; R17, R18, C13 and C14 are to be found from table 5. For f2 = 2740 Hz, this results in R17 = R18 = 10k; C13 = 8n2; Figure 7. Circuit diagram of an active three- way filter with symmetrical 12 dB/octave crossovers. Figure 8. Parts layout modified for the figure 7 circuit. C14 = 3n9. Finally, referring to the parts list for figure 6 gives all other component values. Note that the footnotes 2 and 4 are valid in this case (12 dB/oct); however, we had already found these wire links and omitted parts from table 2. 12.56 elektor india december 1989 oH |-o o^fTSj ^ h , ■« £ .. • ra8 joHH>8 } = 5.93 x10 V* The approximate power gain, G, in deci- bels, of a TWT may be calculated from G = A + BCN where A is the initial mode establishing loss on the helix. Typical values are -6 dB to -9 dB; B is a gain coefficient representing circuit attenuation and space charge: C is a gain parameter determined by the impedances of the circuit and the elec- tron stream; N - the number of active wavelengths in the tube. Factor C is accounted for by C and N by 'a , 2 P x ( ) (co/v) 2 8 Vo N = ( l/X o ) (c/v ) where to = beam current Vo = beam voltage / = axial length of the helix Xo = free-space wavelength v = phase velocity of wave along tube c = speed of light. Voltages and currents To obtain maximum efficiency from a TWT, its operating voltages are all-im- FREQUENCY «CHll Fig. 3. Typical TWT small-signal gain characteristics. portant. There are 3 main voltages to con- sider: the collector voltages, the helix volt- age, and the heater voltage. Table 2 list the voltage and current specifications of a number of TWTs. Collector voltages are usually of the order of 2 kV, although the current trend is towards voltages below' 1 kV. Collector current is typically between 20 mA and 1 A. Voltage regulation to within 10% is required for reasons outlined above. Multiple collectors can help to increase efficiency. Helix voltages are typically between 2 kV and 10 kV, and currents between 10 mA and 500 mA. The heater voltage, finally, is between 3.5 V and 6.3 V at a current demand of 0.5 A to 2.5 A. The filament heats up the cathode to a temperature of about 650 °C to enable electron emission to take place. Type » Voltage (kV) Current (mA) Collector 1 Collector 2 Helix Heater (V) Cathode Collector Helix Heater (A) Efficiency (%> Gain (dB) 500CW 4.2 . 2.2 6.3 650 65 3.4 QKW5004 1.45 2.5 6.3 135 55 TL4010 1.55 37 40 N1078 2 2 25 37 N10025 2.1 49 34 28 QKW5005 1.8 3.8 6.3 135 12 0.5 40 N1024 2.5 2.5 22 TL12019 4.2 44 37 Ku200W 8.6 6.3 215 3 1.4 TL30011 5 38 29 Table 2. Electrical characteristics of a selection of TWTs. elektor India decomber 1989 1 2.61 Special applications and developments Pulsed TWTs have been developed to pro- duce a short coherent burst of RF energy, for radar applications. The frequency, bandwidth and peak-power specifica- tions of these special TWTs have been op- timized to meet the demands of radar users. Modem metallurgical processes have enabled TWTs to be produced with a low mass and special alloy focusing magnets that give accurate beam control. Low' mass of the TWT and, of course, its associated multi-voltage power supply, are prime considerations to keep the payload w'eight of launch vehicles to a minimum. What to look forward to Recent history has seen industry commit- ment for delivery of amplifiers that cover the frequency range of 10,7 GHz to 12.7 GHz, mainly as a result of the increas- ing use of satellite-TV in the communica- tions and direct-broadcasting segments of the X and Ku radio bands. Tube designs that can address this whole bandwidth are in the inventory of a number of major TWT manufacturers including Telefun- ken, Varian Associates, T-CSF and Hughes EDD. It is important, however, to recognize that new circuit technologies M W PRODUCTS Electrostatic Film Cleanser Circuit Aids Inc introduces Electrostatic Film Cleanser indigenously manufac- tured meeting to International Stan- dards. This instrument, solves the film cleaning problem eliminates static charges and dust and other impurities permanently. It features single pass operation with no contamination with total static control. Widely used in photographic films, laminators, PBC manufacturers, etc. based on 2-stage collectors are showing promise of efficiencies previously associ- ated only w'ith 4-stage collector designs. In addition, these 2-stage collector de- signs are expected to yield substantially improved phase linearity over 'classic' de- signs and could, to a large extent, help to remove, or at least relax the requirements of, linearization devices from future TWT systems. Research has shown that a typical Ku- band satellite-TV TWT with a bandwidth of 2 GHz and a 2-stage collector may be expected to exhibit greater than 50% effi- ciency w'ith a 4-stage depressed collector. The previously mentioned developments in TWT technology, however, allow de- vices to be produced that provide efficien- cies up to 54% with 2-stage collectors. In these new TWTs, the 2-stage collector has not been modified. The circuit improve- ment, which primarily involves optimiza- tion of velocity taper techniques, produces beam efficiencies of the order of 27-30%, which is significant at X and Ku- band frequencies. In addition, these new circuits further reduce phase distortion with typical AM-PM conversion at 2 to 4 dB. Also, third-order intermodulation (IM) products are significantly reduced. At saturation, the two-carrier third-order IM product is not less than 14 dB down from single-carrier saturation. In conclusion, it is interesting to project M/s. Circuit Aids Inc. • No. 451, II floor, 64th Cross • V Block • Rajajinagar • Bangalore- 560 010. Tel: 359694. Voltage Spike and Noise Suppression Outlet Strip Magnum have developed a voltage spike and noise suppression outlet strip called SPIKEBUSTER for computers, compu- ter peripherals, audio equipment, TVs, CTVs, VCRs, VCPs, copiers, medical equipments, laboratory instrumenta- tion, communications systems, photo- composing machines, programmable logic controllers and other devices con- taining sensitive integrated circuits and electronic tubes. Consisting of an EMI/RFI filter and a voltage spike protector circuit built into a power strip with three 5 amp sockets/ one 15 amp socket. An OEM version providing the output on a 15A 3-crore cable in lieu of the sockets is also availa- ble. It prevents sensitive electronic equip- ment from malfunctioning severely or being badly damaged on account of specific disturbances on the electricity mains. nnouticr Fig. 4. Typical TWT saturated power out- put as a function of RF input frequency. the' performance, and in particular the ef- ficiency, of TWTs that utilize these new techniques w'ith 3 or 4-stage collectors. Conservative estimates would place mini- mum TWT efficiency at 58 to 60% for the next generation of low-mass devices. Magnum Electric Company Pvt. Limited • 2, Ramavaram Road • Manapakkam • Madras- 600 089. Know-How for the Manufacture of Electronic Chokes Craftsman Electric is offering know-how for the manaufacture of Energy Saving Electronic Chokes used in Tube-Lights of 40 Watts capacity (4 feet). Electronic Chokes have the advantage. Low Power Consumption, Longer Tube Life, Low voltage operation. Produces less heat generation No starter bulb or capacitor required. Improved Power Factor, and Better illumination. Craftsman Electric • 149, West Samban- dam Road • Coimbator-641 002. Tamil Nadu. 12.62 efektor indis december 1989 NEW PRODUCTS COMPONENT SOCKET ADAPTORS & COVERS These are suitable for mounting discrete components such as resistors, capacitors, diodes and other electronic components, forming into a circuit of re- quired design, and are designed to plug directly into IC sockets as modular parts. These carriers conserve space on PC board by enabling maximum density of packaging. Contact rows are spaced at 0.300” & 0.600” centres. The contacts are spaced at 0.100” & 0.200” centers. These are available in various sizes from 2 to 40 pins. Top covers which can be eas- ily glued to the adapters are available for 8,14,16 & 24, 40 pins. These covers pro- tect the circuit. These devices are used for assembling modular & subminiature circuits and also in microprocessors as programmable shorting plugs. Instrument Control Devices • B-4, Abubaker Compound • Behind Garib Nawaz Hotel • Raghvendra Mandir Road • Oshiwara • Bombay -400 102. TRUCK INDUCTIVE PROXIMITY SWITCHES HANS TRUCK GmbH & Co. KG, West Germany, manufacture Inductive Proximity Switches with sensing distance of 60 mm, based on the principle that the current in an oscillator circuit is altered when metal enters or leaves its oscil- latiang field. The oscillator coil is built into a ferrite core and an H.F. magnetic oscillating field is produced at the active face of the switch. Metal entering the field damps the oscillator and reduces the current drawn by the oscillator cir- cuit. The current change is used to pro- vide switching signal. Oscillation nearly ceases when the active face is fully co- vered by metal. These products can be imported under OGL. M/s. Arun Electronics Pvt. Ltd. • B/125- 126, Ansa Industrial Estate • Sakivihar Road • Sakinaka • Bombay-400 072. • Tel: 583354/587101. FOUR PORT SERIAL CARD FOR XENIX/UNIX Mega’s MTS 8903 Four Post Serial Card iis an interface to connect upto 4 termi- nals to any IBM compatible PC/AT286/ AT386 running under Unix operating systems. Compatible with the AST 4 post card , the MTS 8903 has four RS 232- C asynch-ronous serial ports. The card II O address and the interrupts are selecta- ble. Further two of the ports can be con- figured as standard PC serial ports. The MTS 8903 Four Port Serial Card can also be used under MS-DOS with the support of a device drive to perform file transfer and device sharing between 4 PC/XT/AT and a host computer which may also be a PC/XT/ AT. M/s. Mega Tromech Systems Pvt. Ltd. • 24, 12th Main • 1st Block • Rajajinagar • Bangalore- 560 010. DIGITAL IC TESTER Features: Function table of any Digital IC can be checked within seconds without any ex- ternal wire and soldering. Total sixteen thumb-wheels are pro- vided for easy programming. An imported zip IC socket is provided for easy fixing and removal of ICs. A rectangular current meter to measure the current drain by the IC. Built-in regulated Power Supply. An independent IC7447-cum-BCD tes- ter. Five logic level indicators are provided for monitoring the out-put. Leptron Electronics Products • 8, Vid- hyanagar • JALNA-431 203. elekJor india december 1989 12.63 NEW PRODUCTS MODULAR PCB MOUNTING MULTIWAY TERMINALS These are specially designed for Elec- tronic Printed circuit boards. These con- nectors are available in 2 way & 3 way lengths and can be interlocked into each other to form required number of ways with 5 mm pitch distance conforming to international standards. The connection is by soldering of pins on the printed cir- cuit boards, and screw clamping the wire termination. The housing is moulded in special industrial grade plastics. The maximum wire size is 2.5 mm square and rated for 10A current. Instrument Control Devices • B-4, Abubaker Compound • Behind Garib Nawaz Hotel • Raghvendra Mandir Road • Oshiwara • Bombay-400 102. SINGLE PHASE DC POWERPACKS Static Power Systems offers Megacorp Single Phase Powerpacks, manufactured with technology using Thyristor Control , these power packs are primarily used for speed control of DC Motors provided in Plastic extruders, Printing, Rubber and Type Machineries, Welding equip- ments, Packaging machines etc. Single phase powerpacks are available up to 5 H.P. (3.7 KW) Ratings and can also be used as basic convertor in manufacturing battery chargers, Electroplating re- ctifiers, Power Control units for ovens. Regulated DC power supplies etc. Megacorp Power Packs are also availa- ble in three phase versions up to 200 KW Ratings and are made of Expoxy coated chasis which can be readily mounted by various OEM’s in the main panels of their machines. M/s. Static Power Systems Pvt. Ltd. • D- 148, Bonanza Indl. Estate • Ashok Chak- ravarty Road • Kandivali (East) • Bom- bay-400 101. Bulk Requirements of ICs of Vari- ous Types Cycl-O Computers is an importer and stockist of RAM, dynamic RAM, bipo- lar PROMs; op-amps, voltage com- parators, voltage regulators, line receiv- ers, peripherals drivers, memory driv- ers, display drivers; TTLs-LS, S, H, ALS, AS, HC. PALs, remote servo con- trollers, remote controls, transmitters and receivers; photo detectors, LED dis- plays, fiber optic components, source and detector, assembly, opto couplers isolators, 8-bit/16-bit microprocessors, A/D and D/A converters, analogue switches, amplifiers, counter circuits, clock circuits, discretes/FETs, display drivers, data communication, linear de- vices, multiplexers, ROMs/EPROMs, microprocessors and pheripherals; and power transistors TO220, T03, fast switching transistors, fast swiching dar- lington, diodes, zeners, thyristors and triacs/diacs. For more details write to: Cycl-O Computers • 308 Diamond Plaza • Above Swastik Cinema * Lamington Road • Bombay- 400 004. SOLID STATE RELAYS Satronix have introduced PCB/Chassis Mount solid state relays of 2A, and Amps output current relays. AC input models can accept AC signals ranging from 90 to 280 Volts AC. The DC input signals can be operated from 3 to 32 Volts making them easy to interface to the microprocessors and other logic level devices. Output voltage can be selected from 40 to 280 Volts AC. All relays in the series benefit from zero-voltage turn on as well as the zero current turn-off. Solid-State design without mechanical contacts and associated arcing virtually eliminates electro magnetic interference and transients. Satronix • Module • 1 Electronic Sadan 1, • Bhosari MIDC • Pune-411 028. 12.64 elektor india december 1989 R. N. No. 39881/83 Allowed to post without prepayment LIC No. 91 MH BY WEST-228 LIC No. 91 PRECISION WE MAKE PERFORMANCE OP-AMPS AFFORDABLE The AD 707 features the best d.c. accuracy specification available in a non-chopper stabilized design, it features a maximum Input offset voltage of 1 5 pV (C Grade) & input offset voltage drift of 0.1 pV/°C (C Grade) The AD 548/648 features ultra low input bias current-down to 10 p A. The AD 707/548/648 are available in the plastic MiNl- dip, cerdip & TO-99 metal can. The AD 707 Is also available in an 8 pin plastic small outline (SO) package. AD707JN AD548JN AD 648 JN (Single) (Dual) input Was current 2-SnA 20DA 20pA input offset voltage 90 pV 2mV 2mV input offset voltage drtft 1.V/°C 20 nV/°C 20t*V/°C input voltage Noise p-p 0.6 nV 2eV 2*V Price (100'S) $ 1.37 $ 0.82 $ 1.37 SPEED The AD 744 is fast settling BiFET op-amp. it can settle to 0.01% (for 10V step) in 500 nsec.(K grade) and to 0.0025% (for 10V step) in 1.5 psec (K grade). It also has a slew rate of 75 v/psec. The AD 711/712 combines good speed and bias current specifications. The AD 744/711/712 are available in the plastic MINI- OIP, CERDIP, and TO-99 metal can. AD744JN AD 711 JN AD712JN (Single) (Dual) input Dias current 100 PA 50 pA 75 pA input offset voltage imV 2 mV 5 mV Setting Time to 0 . 01 % 0.9*5 1*5 1*5 Typical slew rate 75 V/*S 20V/*S 20 V/^S Price MOO'S) $ 2.47 $ 0.88 $ 1.37 Whether It is Precision or speed you can count on the leader - Analog Devices inc For more details contact your nearest Analog Devices representative in India (kO ^' 648 ANALOG SALES (INDIA) PVT. LTD. Pune (REGO OFF) : 149.1 -A Plot No 5 Krishna. Aundh. Pune 411 007. Ph : 53880 TLX 145-470 N Delhi (BR. OFF) : C-197 Sarvodaya Enclave. New Delhi 1 10017. Ph 6862480 TLX 031-73228 Bangalore (BR. OFF) : 992 13th Main Rd. Indiranaflar. Bangalore 580038. Ph : 560506 TLX 845-8994 ANALOG DEVICES SJAS 8848