Electronics for You Projects 2001

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(1)EFY. 2000. &. PROJECTS. 01 VOLUME. More than 90 fully tested and ready-to-use electronics circuits. IDEAS. 2001. Electronics For You issues.

(2) Contents JANUARY 2001 CIRCUIT IDEAS. 2001. 1). ELECTRONIC STARTER FOR SINGLE-PHASE MOTORS ------------------------------------------------------------- 7. 2). MODEM 'ON'/'OFF' INDICATOR ------------------------------------------------------------------------------------- 8. 3). TOUCH-SELECT AUDIO SOURCE ----------------------------------------------------------------------------------- 9. 4). PRECISION ATTENUATOR WITH DIGITAL CONTROL -------------------------------------------------------------- 10. 5). PRECISION AMPLIFIER WITH DIGITAL CONTROL ---------------------------------------------------------------- 11. 6). RANDOM NUMBER GENERATOR BASED GAME ------------------------------------------------------------------- 12. CONSTRUCTION PROJECTS 1). BUILD YOUR OWN PENTIUM III PC (PART-I) ------------------------------------------------------------------- 14. 2). AUTOMATIC ROOM LIGHT CONTROLLER -------------------------------------------------------------------------- 21. FEBRUARY 2001 CIRCUIT IDEAS 1). 9-LINE TELEPHONE SHARER ------------------------------------------------------------------------------------- 27. 2). ELECTRONIC CARD LOCK SYSTEM -------------------------------------------------------------------------------- 28. 3). PULSED OPERATION OF A CW LASER DIODE -------------------------------------------------------------------- 29. 4). GENERATION OF 1-SEC. PULSES SPACED 5-SEC. APART -------------------------------------------------------- 31. 5). HIGH-/LOW-VOLTAGE CUTOUT WITH TIMER --------------------------------------------------------------------- 32. CONSTRUCTION PROJECTS 1). BUILD YOUR OWN PENTIUM III PC (PART-II) ------------------------------------------------------------------ 34. 2). INTELLIGENT WATER LEVEL CONTROLLER ----------------------------------------------------------------------- 40. 3). A UNIQUE LIQUID LEVEL INDICATOR ---------------------------------------------------------------------------- 43. MARCH 2001 CIRCUIT IDEAS 1). AUTOMATIC HEAT DETECTOR ------------------------------------------------------------------------------------- 48. 2). MUSICAL 'TOUCH' BELL ------------------------------------------------------------------------------------------- 49. 3). NON-CONTACT LIQUID-LEVEL CONTROLLER --------------------------------------------------------------------- 50. 4). AC MAINS PHASE-SEQUENCE INDICATOR ------------------------------------------------------------------------ 52. 5). HIGH-POWER BICYCLE HORN ------------------------------------------------------------------------------------ 54. 6). LUXURIOUS TOILET/BATHROOM FACILITY ---------------------------------------------------------------------- 55. CONSTRUCTION PROJECTS 1). INTERFACE YOUR PRINTER WITH 8085 MICROPROCESSOR ---------------------------------------------------- 58. 2). MORSE PROCESSOR ----------------------------------------------------------------------------------------------- 63. APRIL 2001 CIRCUIT IDEAS 1). EEPROM W27C512 (WINBOND) ERASER ------------------------------------------------------------------------- 74. 2). INTELLIGENT ELECTRONIC LOCK --------------------------------------------------------------------------------- 75. 3). STABLE 455KHZ BFO FOR SSB RECEPTION ---------------------------------------------------------------------- 78. 4). AUTO SHUT-OFF FOR CASSETTE PLAYERS AND AMPLIFIERS ---------------------------------------------------- 81. 5). HOUSE SECURITY SYSTEM ---------------------------------------------------------------------------------------- 84. 6). SIMPLE WATER-LEVEL INDICATOR-CUM-ALARM ----------------------------------------------------------------- 87. CONSTRUCTION PROJECTS 1). ACCESS-CONTROL SYSTEM ---------------------------------------------------------------------------------------- 90. 2). TELEPHONE LINE-INTERFACED GENERIC SWITCHING SYSTEM (PART-I) --------------------------------------- 87.

(3) Contents MAY 2001 CIRCUIT IDEAS. 2001. 1). PRECISION INDUCTANCE AND CAPACITANCE METER ------------------------------------------------------------ 93. 2). UNDER-/OVER-VOLTAGE BEEP FOR MANUAL STABILISER ------------------------------------------------------ 95. 3). ULTRA-SENSITIVE SOLIDSTATE CLAP SWITCH ------------------------------------------------------------------- 97. 4). 15-STEP DIGITAL POWER SUPPLY -------------------------------------------------------------------------------- 98. 5). MICROPHONE FOR COMPUTER ----------------------------------------------------------------------------------- 100. CONSTRUCTION PROJECTS 1). PROGRAMMABLE MELODY GENERATOR (PART-I) --------------------------------------------------------------- 102. 2). TELEPHONE LINE-INTERFACED GENERIC SWITCHED SYSTEM (PART-II) -------------------------------------- 110. JUNE 2001 CIRCUIT IDEAS 1). VERSATILE ZENER DIODE TESTER ------------------------------------------------------------------------------- 117. 2). DTMF PROXIMITY DETECTOR ------------------------------------------------------------------------------------- 119. 3). STEPPER MOTOR CONTROL --------------------------------------------------------------------------------------- 120. 4). LOW-COST INTERCOM -------------------------------------------------------------------------------------------- 121. 5). HIGH-POWER CAR BATTERY ELIMINATOR ---------------------------------------------------------------------- 122. 6). AUTOMATIC PLANT IRRIGATOR ---------------------------------------------------------------------------------- 123. CONSTRUCTION PROJECTS 1). PROGRAMMABLE MELODY GENERATOR (PART-II) -------------------------------------------------------------- 125. 2). AUTO CONTROL FOR 3-PHASE MOTORS ------------------------------------------------------------------------- 129. JULY 2001 CIRCUIT IDEAS 1). PC-BASED DIAL CLOCK-CUM-ELECTRONIC ROULETTE ---------------------------------------------------------- 136. 2). SIMPLE TELEPHONE RING TONE GENERATOR ------------------------------------------------------------------- 138. 3). DUAL-INPUT HIGH-FIDELITY AUDIO MIXER ------------------------------------------------------------------- 139. 4). ANTI-THEFT SECURITY FOR CAR AUDIOS ----------------------------------------------------------------------- 140. 5). UNIPOLAR/BIPOLAR TRIANGULAR AND BIPOLAR SQUARE WAVE GENERATOR ------------------------------ 141. CONSTRUCTION PROJECTS 1). TELEPHONE REMOTE CONTROL ---------------------------------------------------------------------------------- 143. 2). MICROCONTROLLER-BASED SCHOOL TIMER -------------------------------------------------------------------- 146. AUGUST 2001 CIRCUIT IDEAS 1). LONG-RANGE CORDLESS BURGLAR ALARM --------------------------------------------------------------------- 153. 2). WATER-LEVEL CONTROLLER -------------------------------------------------------------------------------------- 154. 3). INVISIBLE BROKEN WIRE DETECTOR --------------------------------------------------------------------------- 156. 4). PC-BASED MULTI-MODE LIGHT CHASER ------------------------------------------------------------------------ 157. 5). FUSE STATUS INDICATORS FOR POWER-SUPPLIES ------------------------------------------------------------- 159. CONSTRUCTION PROJECTS 1). DIGITAL CAPACITANCE-CUM-FREQUENCY METER --------------------------------------------------------------- 162. 2). FLUID-LEVEL CONTROLLER WITH INDICATOR ------------------------------------------------------------------ 166. SEPTEMBER 2001 CIRCUIT IDEAS 1). A HIERARCHICAL PRIORITY ENCODER -------------------------------------------------------------------------- 171.

(4) Contents. 2001. 2). DIGITAL MAINS VOLTAGE INDICATOR --------------------------------------------------------------------------- 173. 3). ELECTRONIC DICE ------------------------------------------------------------------------------------------------ 175. 4). LIGHT-OPERATED ORGAN ---------------------------------------------------------------------------------------- 177. CONSTRUCTION PROJECTS 1). MGMA-A MIGHTY GADGET WITH MULTIPLE APPLICATIONS --------------------------------------------------- 179. 2). TRAFFIC AND STREET LIGHT CONTROLLER --------------------------------------------------------------------- 183. OCTOBER 2001 CIRCUIT IDEAS 1). DIGITAL FAN REGULATOR ---------------------------------------------------------------------------------------- 192. 2). STEREO TAPE HEAD PREAMPLIFIER FOR PC SOUND CARD ---------------------------------------------------- 194. 3). RUNNING LIGHTS AND RUNNING HOLES ----------------------------------------------------------------------- 195. 4). HEART BEAT MONITOR ------------------------------------------------------------------------------------------- 197. 5). 12V, 3A POWER SUPPLY ----------------------------------------------------------------------------------------- 198. 6). A SIMPLE TRANSISTOR TESTER --------------------------------------------------------------------------------- 199. CONSTRUCTION PROJECTS 1). LEAD-ACID BATTERY CHARGER WITH ACTIVE POWER CONTROL ---------------------------------------------- 201. 2). MICROCONTROLLER-BASED DIGITAL CLOCK -------------------------------------------------------------------- 204. NOVEMBER 2001 CIRCUIT IDEAS 1). SPELLER EFFECT SIGN DISPLAY --------------------------------------------------------------------------------- 210. 2). DARKROOM TIMER ----------------------------------------------------------------------------------------------- 211. 3). LONG-RANGE TARGET SHOOTER --------------------------------------------------------------------------------- 212. 4). ACTIVE SHORTWAVE ANTENNA ---------------------------------------------------------------------------------- 214. 5). POWER SUPPLY FOR WALKIE-TALKIE --------------------------------------------------------------------------- 215. 6). HIGH-PERFORMANCE INTERRUPTION DETECTOR --------------------------------------------------------------- 216. CONSTRUCTION PROJECTS 1). AMPLITUDE MEASUREMET OF SUB-MICROSECOND PULSES --------------------------------------------------- 218. 2). AUTOMATIC SUBMERSIBLE PUMP CONTROLLER ---------------------------------------------------------------- 221. DECEMBER 2001 CIRCUIT IDEAS 1). DIGITAL RELAY TESTER FOR RAX AND MAX -------------------------------------------------------------------- 226. 2). DECORATIVE SIGNBOARD ---------------------------------------------------------------------------------------- 228. 3). OVERLOAD PROTECTOR WITH RESET BUTTON ------------------------------------------------------------------ 230. 4). FASTEST FINGER FIRST INDICATOR ----------------------------------------------------------------------------- 231. 5). CONDENSER MIC AUDIO AMPLIFIER ---------------------------------------------------------------------------- 232. 6). SMOKE ALARM --------------------------------------------------------------------------------------------------- 233. CONSTRUCTION PROJECTS 1). TRANSISTOR CURVE TRACER ------------------------------------------------------------------------------------ 235. 2). TRIPPING-SEQUENCE RECORDER-CUM-INDICATOR ------------------------------------------------------------- 241.

(5) January. 2001.

(6) Circuit Ideas. 2001.

(7) C I R C U I T. I D E A S. ELECTRONIC STARTER FOR SINGLE-PHASE MOTORS SARAT CHANDRA DAS. A. novel single-phase electronic starter circuit meant for 0.5HP and 1HP motors is presented here. It incorporates both overload and short-circuit protections. A special current-sensing device has been added in this starter to sense the current being drawn by the motor. If the motor jams due to bearing failure or defect in the pump or any other reason, it would draw much higher current than its normal rated current. This will be sensed by the current-sensing device, which will trip the circuit and protect the motor. Some other reasons for the motor drawing higher current are as follows: (a) Windings damaged or short-circuit between them. (b) Shorting of motor terminals by mistake. (c) Under voltage or single phasing occuring in the mains supply source (normally, a 440V AC, 3-phase with neutral four-wire system). The main components used in the circuit comprise a specially wound sensing transformer X1, another locally available step-down transformer X2, single-changeover relay RL1, two double-changeover relays (RL2 and RL3), and other discrete components shown in the figure. The mains supply to the motor is routed in series with the primary of transformer X1 via normally-open contacts of relay RL3. The primary of transformer X1 is connected in the neutral line. To switch on the supply to the motor, switch S1 is to be pressed momentarily, which causes the supply path to the primary of transformer X2 to be completed via N/C contacts of relay RL1. Relay RL2 gets energised due to the DC voltage developed across capacitor C2 via the bridge rectifier. Once the relay energises, its N/O contacts RL2(a) provide a short across switch S1 and supply to the primary of transformer X2 becomes continuous, and hence re-. EDI DWIV S.C.. lay RL2 latches even if switch S1 is subsequently opened. The other N/O contacts RL2(b) of relay RL2, on energisation, connect the voltage developed across capacitor C2 to relay RL3, which thus energises and completes the supply to the motor, as long as current passing through primary of transformer X1 is within limits (for a 1HP motor). When the current drawn by motor exceeds the limit (approx. 5A), the voltage developed across the secondary of transformer X2 is sufficient to energise relay RL1 and trip the supply to relays RL2 and RL3, which was passing via the N/C contact of relay RL1. As a result, the supply to the motor also trips. The contact rating for relays RL1 and RL2 should be 5 amperes, while. ELECTRONICS FOR YOU ❚ JANUARY 2001. contact ratings of relay RL3 should be 10 to 15 amperes. Transformer X1 can be wound using any suitable size CRGO core. (One can use a burntout transformer core as well.) The primary comprises 30 to 31 turns for use with 1HP motor and additional eight turns, if you are using a 0.5HP motor. Fuses F1 and F2 are kitkat type. The ‘on’ pushbutton is normally-‘off’ type, while ‘off’ pushbutton S2 is of normally-‘on’ type. Capacitors C1 and C2, apart from smoothing the rectified output, provide necessary delay during energisation and deenergisation of relays. Diodes across relays are used for protection as freewheeling diodes. Starters for 0.5HP and 1HP motors are not easily available in the market. Users are therefore compelled to use 10-amp rated circuit breaker for such motors. A mechanical starter or auto starter would turn out to be costlier than the circuit given here, which works very reliably. Parts used in this circuit are easily available in most of the local markets..

(8) C I R C U I T. I D E A S. MODEM ON/OFF INDICATOR T.K. HAREENDRAN. H. ere is an interesting, low component-count, and easy-to-build electronic circuit for the Internet surfers. This circuit, using two LEDs, indicates the modem status, i.e. whether it is in use or not. The incoming telephone line terminating on a master phone is shunted by a metal oxide varistor. The circuit is configured around the popular timer chip NE555N, which is wired as an astable multivibrator. When power is applied to the circuit, the astable starts working as usual. However, LEDs D2 and D3 connected to its output pin 3 would not glow as transistor T1 is in off condition and hence resistor R4’s bottom end is hanging in high impedance state. However, when the modem is working, voltage drop across preset VR1 illuminates the LED inside the optocoupler (IC2). As a result, transistor T1 gets sufficient base-bias through ac-. EDI DWIV S.C.. tivated transistor inside opto-coupler via resistor R3. Consequently, LEDs D1 and D2 start blinking at the bistable IC1’s frequency determined by the val-. ues of resistors R1 and R2 and capacitor C1. A 9V, 0.5A AC adapter can be used to power the circuit. Finally, one minor adjustment is required for successful op-. ELECTRONICS FOR YOU ❚ JANUARY 2001. eration of the gadget. For this, first switch on the supply to the gadget and then switch ‘on’ the modem. Now adjust the wiper of preset VR1 very slowly until the LEDs start blinking. Memorise the wiper position and fix it in this position using a good-quality glue/compound. After construction, fix the complete circuit in a suitable and attractive cabinet with one LED in its front panel. Keep. the whole unit near the modem and fit another LED near the master telephone with the label ‘Modem in Use’..

(9) C I R C U I T. I D E A S. TOUCH-SELECT AUDIO SOURCE SARAVANAN J.. O. ften you need to connect output from more than one source (preamplifier) such as tape recorder/player and CD (compact disc) player to audio power amplifier. This needs disconnecting/connecting wires when you want to change the source, which is quite cumbersome and irritating. Here is a circuit that helps you choose between two stereo sources by simple touch of your hand. This circuit is so compact that it can be fixed within the audio power amplifier cabinet and can use the same power supply source. The circuit uses just two CMOS ICs and a few other componenets. The ICs used are MC14551/CD4551 (quad 2channel analogue multiplexer) and CD4011 (quad 2-input NAND gate). When touch-plate S1 is touched (its two plates are to be bridged using a fingertip), gate. EDI DWIV S.C.. N1 output (IC1, pin 3) goes high while the output of gate N2 at pin 4 goes low. This causes selection of CD outputs being connected to the power amplifier input, which is indicated by lighting of LED1.. When touch-plate S2 is touched, the outputs of gates N1 and N2 toggle. That is, IC2 pin 3 is pulled ‘low’ while its pin 4 goes ‘high’. This results in selection of tape recorder outputs being connected to the. ELECTRONICS FOR YOU ❚ JANUARY 2001. input of power amplifier. This is indicated by lighting of LED2. Pin 9 is the control pin of IC2. In the circuit, the state of multiplexer switches is shown with pin 9 ‘high’ (CD source selected). When pin 9 is pulled ‘low’, all the switches within the multiplexer change over to the alternate position to select tape player as source. EFY Lab note. Although one can connect pin 7 (VEE) of IC2 to ground, but for. operation with preamplifier signals going above and below ground level, one must connect it to a negative voltage (say, –1V to –1.5V) to avoid distortion..

(10) C I R C U I T. PRECISION ATTENUATOR WITH DIGITAL CONTROL. I D E A S. EDI DWIV S.C.. ANANTHA NARAYAN. W. hen instruments are designed, an analogue front-end is essential. Further, as most equipment have digital or microcont-roller interface, the analogue circuit needs to have digital control/access. The circuit of a programmable attenuator with digital control is described here, where digital control can be a remote dip switch, or CMOS logic outputs of a decade counter (having binary equivalent weight of 1, 2, 4, and 8, respectively), or I/O port of a microcontroller like 80C31. The heart of this circuit is the popular OP07 op-amp with ultra-low offset in the inverting configuration. A dual, 4channel CMOS analogue multiplexer switch CD4052 enables the change in gain. An innovative feature of the circuit is that the ‘on’ resistance (around 100 ohms) of CD4052 switch is bypassed so that no error is introduced by its use. Resistors R1 to R6 used in the circuit should be of 0.1 per cent tolerance, 50 ppm (parts per million) if you use 3½-. gain selection resistors for proper calibration to required accuracy. However, for testing or trials, use 1 per cent 100ppm MFR resistors. The expected errors will be around 1 per cent. To keep parts count (hence cost) to a minimum, the common or ground is used as the positive input terminal and one end of resistor R1 as the negative. This is so because the op-amp inverts the polarity as it is used in inverting configuration. This does not matter as the equipment will be isolated by the power supply transformer and all polarities are relative. In case you want the common to be the negative, you will have to add some stages (IC4 and IC5 circuitry shown in precision amplifier circuit described later). The OP07 pinout is based on standard single op-amp 741. Any other op-amp like CA3140, TLO71, or LF351 can be used but with offset errors in excess of 1 per cent, which is not tolerable in precision instrumentation. The OP07 has equivalent ICs like. The following design considerations should be kept in mind: (a) Input: 500V max Since ¼W resistors can withstand up to 250V, resistors R1 and R2 in series are used for 1 meg-ohm with 500V (max) input limit. These resistors additionally limit the input current as well. Diodes D1 and D2 clamp the voltage across input of op-amp to ±0.5V, thereby protecting the op-amp. (b) Output The output can be connected to a 7107/7135-based DPM or any other analogue-to-digital converter or op-amp stage. Use a buffer at the output if the output has to be loaded by a load less than 1 meg-ohm. Use an inverting buffer if input leads have to have polarity where ground is the inverting terminal. (For details, see next circuit.) (c) CD4052 CMOS switch The on-resistance (100-ohm approx.) comes in series with the op-amp output source resistance, which produces no error at output. Caution. The circuit does not isolate, it only attenuates. When high voltage is present at its input, do not touch any part of the circuit. (d) Digital control options (i) A and B can be controlled by I/O port of a microcontroller like 80C31 so that the controller can control gain. (ii) A and B can be given to counters like 4029/4518 to scroll gain digitally. (iii) A and B can be connected to DIP switch. (iv) A and B can be connected to a thumbwheel switch. Notes. 1. Digital input logic 0 is 0V and logic 1 is 5V. Truth Table (Control input VS attenuation) X,Y (ON-switch (2) (1) Gain Pair) B A (Attenuation) X0,Y0 0 0 1/1000 X1,Y1 0 1 1/100 X2,Y2 1 0 1/10 X3,Y3 1 1 1. digit DPM, i.e. ±1999 counts (approx. 11 bits). But for 4½-digit DPM (approx. 14 bits), you may need to have trimpots (e.g. replace 1k-ohm resistor R6 by a fixed 900ohm resistor in series with a 200-ohm trimpot) to replace R3, R4, R5, and R6. µA714 and LM607 having ultra-low offset voltage (<100µV), low input bias current (<10nA), and high input impedance (>100M), which are the key requirements for a good instrumentation op-amp for use with DC inputs. ELECTRONICS FOR YOU ❚ JANUARY 2001. 2. All resistors are metal film resistors (MFR) with 1% tolerance, unless specified otherwise. 3. C2 and C3 are ceramic disk capacitors of 0.1µF = 100n value..

(11) C I R C U I T. PRECISION AMPLIFIER WITH DIGITAL CONTROL. I D E A S. EDI DWIV S.C.. ANANTHA NARAYAN. T. his circuit is similar to the preceding circuit of the attenuator. Gain of up to 100 can be achieved in this configuration, which is useful for signal conditioning of low output of transducers in millivolt range. The gain selection resistors R3 to R6 can be selected by the user and can be anywhere from 1 kilo-ohm to 1 meg-ohm. Trimpots can be used for obtaining any value of gain required by the user. The resistor values shown in the circuit are for decade gains suitable for an autoranging DPM. Resistor R1 and capacitor C1 reduce ripple in the input and also snub transients. Zeners Z1 and Z2 limit the input to ±4.7V, while the input current is limited by resistor R1. Capacitors C2 and C3 are the power supply decoupling capacitors. Op-amp IC1 is used to increase the input impedance so that very low in-. puts are not loaded on measurement. The user can terminate the inputs with resistance of his choice (such as 10 megohm or 1 meg-ohm) to avoid floating of the inputs when no measurement is being made. IC5 is used as an inverting buffer to restore polarity of the input while IC4 is used as buffer at the output of CD4052, because loading it by resistance of value less than 1 meg-ohm will cause an error. An alternative is to make R7=R8=1 meg-ohm and do away with IC4, though this may not be an ideal method. Truth Table (Control Input vs Gain) X,Y (On-switch (2) (1) Gain Pair) B A (Av.) X0,Y0 0 0 1/10 X1,Y1 0 1 1 X2,Y2 1 0 10 X3,Y3 1 1 100. ELECTRONICS FOR YOU ❚ JANUARY 2001. Gains greater than 100 may not be practical because even at gain value of 100 itself, a 100µV offset will work out to be around 10 mV at the output (100µV x 100). This can be trimmed using the offset null option in the OP07, connecting a trimpot between pins 1 and 8, and connecting wiper to +5V supply rails. For better performance, use ICL7650 (not pin-compatible) in place of OP07 and use ±7.5V instead of ±5V supply. Eight steps for gain or attenuation can be added by using two CD4051 and pin 6 inhibit on CD4051/52. More steps can be added by cascading many CD4051, or CD4052, or CD4053 ICs, as pin 6 works like a chip select. Some extended applications of this circuit are given below. 1. Error correction in transducer amplifiers by correcting gain. 2. Autoranging in DMM. 3. Sensor selection or input type selection in process control. 4. Digitally preset power supplies or electronic loads. 5. Programmable precision mV or mA sources. 6. PC or microcontroller or microprocessor based instruments. 7. Data loggers and scanners..

(12) C I R C U I T. RANDOM NUMBER GENERATOR BASED GAME. I D E A S. NA ANJA RUP. K. UDHAYA KUMARAN. T. his electronic game is simulation of one-arm bandit game. Electronics hobbyists will find it very interesting. When toggle switch S1 is in ‘run’ position, all segments of 7-segment displays (DIS1 through DIS3) will light up. On turning toggle switch S1 from ‘run’ to ‘stop’ position, displayed digits will continue advancing and the final display is unpredictable. Thus the final number displayed in DIS1 through DIS3 is of random nature. The speed with which the number in 7-segment display keeps changing on flipping switch S1 from ‘run’ to ‘stop’ condition slowly decays before stopping with a random number display. To play this game, one has to obtain three identical numbers in displays DIS1 through DIS3. The contestant would score 1 (one) point if he manages to get a final display of ‘000’, 2 points for getting ‘111’ display, 3 points for ‘222’,… and so on—up to ten points for ‘999’. He should try to score maximum possible points in fixed numbers of attempts (say, 20 to 25 attempts). Apart from using this circuit as a game for entertainment, one can use it as random number generator for any other application as well. The decay time with the given component values is around 15 seconds before the display could stop at a final random number. The circuit comprises clock oscillator built around NE555 timer IC4, three-stage clock pulse counter built using three CD4033 ICs (IC1 to IC3), and three 7-segment LED displays (DIS1 to DIS3). In clock oscillator circuit, NE555 timer IC4 is used in a similar way as a free-running astable multivibrator, the only difference being the additional capacitor C1 introduced between pin No. 7 of IC4 and junction of resistors R22 and R24. When toggle switch S1 is in ‘run’ position, both terminals of capaci-. tor C1 are shorted by switch S1 and timer IC4 works as a free-running astable multivibrator. The operating frequency is in the vicinity of 35 kHz, determined by the value of timing components. When toggle switch S1 is flipped from ‘run’ to ‘stop’ position, capacitor C1 is introduced in the discharge path of pin No. 7 of IC4 and junction of resistors R22 and R24. At the same time, capacitor C4 comes in parallel with timing capacitor C3 to change the operating frequency of the astable from around 35 kHz to around 65 Hz. Now capacitor C1 slowly starts charging as it is connected in the discharge path of the timing capacitors C3 and C4. The clock frequency of IC4 gradually reduces and after 15 seconds, when capacitor C1 is sufficiently charged, the oscillat-. ing frequency gradually drops and finally it stops oscillating. Thus, pin 3 of IC4 becomes low. Second part of the circuit comprises three cascaded ICs, IC1 through IC3 ELECTRONICS FOR YOU ❚ JANUARY 2001. (CD4033 decade upcounter cum 7-segment decoder). In conjunction with three 7-segment displays (DIS1 to DIS3), these form a 3-digit clock counter. The clock counting speed is dependant upon the clock pulse frequency of IC4. It is connected to clock input pin 1 of IC1 while chip enable pin 2 of IC1 to IC3 are held low. Thus all clock counter ICs advance by 1 for every positive clock transition. Reset pin 15 of all counter ICs is held low through resistor R25. Thus reset facility is not used in this circuit. Due to persistence of vision, one cannot distinguish 0-9 counting in DIS1 to DIS3 when the clock frequency is high. All 7-segment displays appear to show digit 8, while the red LED1 remains lit continuously, indicating clock counter is in running condition. On sliding toggle switch S1 from ‘run’ to ‘stop’ position, the counting speed of individual digits falls immediately due to the clock frequency changing to around 65 Hz. Now, the counting speed will be 65 Hz for DIS3, 6.5 Hz for DIS2, and 0.6 Hz for DIS1. This speed of individual digit counting slowly. decays, until the counter stops and LED1 stops blinking, and the final count (random numbers) are displayed in DIS1, DIS2, and DIS3..

(13) Construction. 2001.

(14) C O N S T R U C T I O N. BUILD YOUR OWN PENTIUM III PC PART-I. RA UND N. K. K.C. BHASIN AND NEERAJ KUNDRA. T. he procedure presented here would enable you to assemble your own multimedia personal computer. It is assumed that you have a fundamental knowledge of how a PC functions and some basics of electronics. By way of tools you only need Philips-head and flat-blade screwdrivers. A simple multimeter is the only test equipment that you would ever require during assembly, for AC and DC voltage measurement. All the parts needed to assemble this multimedia PC with processor speed of 700 MHz are listed under Parts List. The cost of parts may vary from dealer to dealer and also with time. The total cost of the listed parts at current price level ranges from Rs 33,000 to Rs 37,000. It is suggested to source these items from authorised dealers who would meet their warranty obligations. We have also mentioned the brand names of the parts that we used during assembly of the basic unit. It is, however, not necessary to use identical makes, except, of course, the main processor and the motherboard, based on identical chipset mentioned later in this article.. length of the cable provided for interconnections to the motherboard or addon cards has to be taken into account, as there must be some slack after these are installed and connected.) This will improve the cooling and reduce the chances of electromagnetic interference between them. • The motherboard contains sensitive components, which can be easily damaged by static electricity. Therefore the motherboard should remain in its original antistatic envelope un-. til it is required for installation. When it is taken out from the envelope, it should be immediately placed on a suitable grounded conductive surface. The motherboard itself should be held from edges and the person taking it out should wear an antistatic wrist strap that is properly grounded. In the absence of a proper wrist strap, you may make one on your own using a peeled off multi-strand copper cable and ground it properly. Similar handling precautions are also required for DIMMS and cards. • If you are using a motherboard different from the one mentioned in the. Precautions Before starting the actual assembly of the PC system, the following precautions would help you to avoid any mishap during the assembly process: • While the motherboard has to be fitted at a fixed place inside the PC cabinet, the locations of add-on cards (as and when used) and the drives (hard disk drive, floppy disk drive, and CD-ROM drive) within the drives’ bay of the cabinet can be changed within certain limits. But it is better to place them far away from each other. (Of course, the The authors represent a combined team from EFY and IT Solutions (India) Pvt Ltd, New Delhi. Fig. 1: Block diagram of motherboard employing 810E chipset ELECTRONICS FOR YOU ❚ JANUARY 2001.

(15) C O N S T R U C T I O N. Key Features of Motherboard Using Intel 810/810E Chipset Processor • Full support for the Intel Pentium III and Celeron processors using PGA370 socket. • Supports 66MHz and 100MHz bus speed including all PGA370. • Supports 133MHz bus speed (810E chipset version only). VRM 8.2 (Voltage Regulator Modules) On-board • Flexible motherboard design with on-board VRM 8.2, easy to upgrade with future processors. System Memory • A total of two 168-pin DIMM sockets (3.3V SDRAM types). • Memory size up to 512MB. • Supports SDRAM at 66/100 (PC100) MHz. • Supports symmetrical and asymmetrical DRAM addressing. • Banks of different DRAM types and depths can be mixed. System BIOS • 4-Mbit Intel Firmware hub (with security feature). • PnP, APM, ATAPI, and Windows 95/98. • Full support of ACPI & DMI. • Auto-detects and supports LBA hard disks with capacities over 8.4 GB. • Easily upgradable by end-user. On-board I/O • Supports two PCI-enhanced IDEs PIO mode 3, mode 4, and ultra DMA 33/66 channels (optional ultra DMA 66 cable). Twin headers for four IDE devices including IDE HDDs and CDROMs. • One ECP/EPP parallel port (via a header). • Two 16550A UART parallel port (via a header). • One floppy port. Supports two FDDs of 360KB, 720KB, 1.2MB, 1.44MB, or 2.88MB (via a header). • Four USB ports (via a header, optional). • PS/2 mouse port (via a header, optional). • AT keyboard port (factory option for PS/2 type). • Infrared (IrDA) support. Plug-and-play • Supports plug-and-play specification 1.1. • Plug-and-play for DOS, Windows 3.X, Windows 95, as well as Windows 98. • Fully steerable PCI interrupts. On-board VGA • Hardware motion compensation for S/W MPEG2 decode (DVD). • 3-D hyper pipelined architecture. • Full 2-D hardware acceleration. • 3-D graphics visual enhancements. • Dynamic display memory (DDM) or optional 4MB display cache (810DC100 or 810E chipset version only). • Resolution up to 1,600x1,200. • Win 95 vxd, Win 98/NT5 mini-port drivers support. • VGA port (via a header). On-board AC97 Sound • Integrated AC97 controller with standard AC97 CODEC. • Direct Sound and Sound Blaster compatible. • Full-duplex 16-bit record and playback. • PnP and APM 1.2 support. • Win 95, 98, and NT drivers ready. • Line-in, line-out, mic-in and MIDI/game port. Power Management • Supports SMM, APM and ACPI. • Break switch for instant suspend/resume on system operations. • Energy star ‘Green PC’-compliant. • WAKE-ON-LAN (WOL) header support. • External modem ring-in wake-up support. Expansion Slots • One audio modem riser (AMR). • Four PCI bus master slots (ver 2.1 compliant).. parts list, modify the guidelines mentioned here as per the directions given in the user’s manual (which is supplied with the motherboard you may be using), since there would be some differences between any two makes of the motherboard.. • Start the assembly only after going through this article at least once. Only when you feel at ease, start the assembly of your machine as per the guidelines included in this article and the applicable user’s manuals. ELECTRONICS FOR YOU ❚ JANUARY 2001. • Never try to insert a card in PC slots or try to plug/unplug a connector with power supply to the PC ‘on’. • Ensure that the mains 3-pin socket or the socket on your stabiliser/UPS that you would be using for connection to the SMPS of the computer and/or the monitor is correctly wired with ‘live’ line on your right hand side. To find out which line is live (phase) and which one is neutral, use your multimeter in 250V AC or higher range. The live line will show full voltage w.r.t. neutral pin and nearly the same voltage w.r.t. the ground pin, while the neutral pin (w.r.t. ground pin) would/should show very little voltage (less than 10V AC). Else, the mains wiring has a problem that needs to be set right. • Don’t drop any screw or other conducting material on your PC’s motherboard as that might cause shorting of pins/tracks and consequent damage when you switch it ‘on’. • Make sure that you have a large, flat surface area to work on. That will reduce the chances of small screws etc falling and getting lost. • While screwing components on to the chassis, do not use excessive force as that may damage the screws or their grooves/holes.. Pentium III technology Some points to be noted about the Pentium III processor being used here are: • Intel’s Pentium III processors support various clock speeds from 450MHz to 933 MHz. The one meant for desktop version goes up to 1.13 GHz. (We are using here a 700MHz version.) • Integrates P6 dynamic execution architecture and a dual independent bus (DIB) architecture. • Has a multi transaction system bus. • Incorporates Intel’s MMX media enhancement technology. • Supports Internet streaming single-instruction multiple data (SIMD) extensions. • Compared to Pentium II, it has 70 new instructions, enabling advanced 3-D imaging, streaming audio and video, and speech recognition. • Has a 32k (16k for instructions and another 16k for data) as primary (level 1) non-blocking cache for rapid access to most heavily used data. In addition, it.

(16) C O N S T R U C T I O N. has 512k unified, non-blocking (level 2) cache or 256k advanced transfer cache integrated on die, which runs at the core frequency of the processor with very low memory access time.. The motherboard. Fig. 2: PC Partner motherboard layout diagram. TABLE I JP1, JP2—System Bus Frequency. JP1 1. Open. JP2 1. Open. CPU Clock Speed 133MHz (100MHz CPU run at 133MHz Front Side Bus). 1. Open. 1. 1-2. 100MHz (66MHz CPU run at 100MHz Front Side Bus). 1. Close*. 1. 1-2*. Auto*. JP15 - BIOS (Firm Ware Hub) Boot Block Protect. JP4 - CMOS Clear. JP15 Close* 1. Function Unlocked*. JP4 1. 1-2*. Function Normal. 1. Locked. 1. 2-3. CMOS Clear. Open. JP34 - On Board Crystal PCI Sound (Optional). JP29 - Keyboard Power On Select. JP34. JP29 1. 1-2*. 1. 2-3. Function. 1. 1-2*. PCI Sound Enable*. 1. 2-3. PCI Sound Disable. Function Powered by +5V* Powered by +5V Standby (Allows Keyboard Power On) * Default settings. JP35, JP36 - On Board AC97 Codec Sound. JP35 1 1. 1-2*. JP36 1. 2-3* (S)#. Function AC97 Sound Enable*. 2-3. 1. 1-2 (P)#. AC97 Sound Disable. # P = Primary AMR, S = Secondary AMR. ELECTRONICS FOR YOU ❚ JANUARY 2001. While the processor is the most important part of the motherboard, the motherboard itself is the most important part of the computer system. Together with the chipset, it forms the brain of your computer. The modern motherboards do away with the large number of controller chips and cards that were used in the older XT and AT versions, such as clock generator, bus controller, timer/counter, monitor/printer adopter, FDD and HDD controllers, multi-I/O or super IDE controller card, and DMA controller. All the functions performed by these controllers/ cards (and others) are now performed by just two or three chips and that too at much higher speed. The motherboard based on Intel’s 810/810E chipset (being used in the present system) combines the advantage of a multimedia (full-screen, full-motion video with realistic graphics) and enhanced Internet performance at a budget price. With this motherboard, one does not need separate sound, video, or graphics enhancement cards. A block diagram of a motherboard employing 810E chipset is shown in Fig. 1. Key features. The main features of the PC Partner motherboard used in this project are shown in the accompanying box. A layout diagram showing the relative position of the jumpers, connectors, major components, PCI slots, and DIMM and CPU sockets is shown in Fig. 2. Jumper settings. Positions of various jumpers within the motherboard are shown in Fig. 3. The jumper settings for enabling various functions are shown in Table I. Default settings are shown with an asterisk mark. (Note. Leave all these jumpers in their default setting positions for the present project. The processor speed setting is to be done through CMOS setup as indicated later.). Hardware installation and checkout Verifying components. First, carry out a physical check of all the items as per the parts list to ensure that there are no ap-.

(17) C O N S T R U C T I O N. Fig. 3: Jumper positions within motherboard. measures approx.180mm (width) x 330mm (height) x 360mm (depth). The drive bays comprise two 133.35mm (5.25-inch) exposed, one 89mm (3.5-inch) exposed, and two 89mm (3.5-inch) internal bays. It has 200W SMPS of VESTA make pre-installed (+5V @16A, +12V @6A, 5V @0.5A, and – 12V @0.5A). LEDs with 2-pin SIP connectors are provided for power ‘on’ (green and white twisted. wires), HDD (orange and white twisted wires) activity indication, and to reset push switch (blue and white twisted wires), which are required to be connected to the appropriate pin pairs (Berg type) on the motherboard. (Please refer Fig. 2 to spot the corresponding connectors near JP34/JP4, but for the time being, leave them alone.) An 8ohm, 0.5W speaker (with black and red twisted wires and 4-pin connector), to go into corresponding 4-pin speaker connector on motherboard, also forms part of the cabinet.. Fig. 4: Power on/off switch wiring. parent deficiencies and no signs of any physical damage, and the parts are correct as indicated by the labels on the items/ packages. For example, the Pentium processor pack should comprise Pentium III processor labeled 700MHz/100MHz system bus, fan/heat-sink assembly, and installation manual with 3-year limited warranty. Similarly, ensure that the 64MB SDRAM DIMM bears the label (such as PC100) to indicate that it is compatible with 100MHz system bus speed. Checking cabinet and its accessories. The AT mini tower PC cabinet. Fig. 6: DIMM installation. A. (a). (b). A. (c). (d). Fig. 5: Installation of Pentium III processor in PGA 370 socket ELECTRONICS FOR YOU ❚ JANUARY 2001. Checking SMPS. The control console on the cabinet also has a DPDT pushbutton switch to switch on the mains (230V AC) to SMPS of the computer and a parallel-wired 3-pin AC socket on SMPS for connecting AC power to the monitor used with the PC. At this stage, slide the shielded connectors of the four power supply wires of the SMPS into the corresponding connectors on the DPDT switch as per the diagram provided on the SMPS case (top side). The same is reproduced in Fig. 4. The white and black wires have a return path via blue and brown wires, respectively, when the power supply switch is flipped ‘on’. Connect the 3-pin power cord provided with the cabinet to the socket at the back of SMPS and plug 3-pin plug into the socket of the mains supply or the UPS, as appropriate. Switch on the SMPS. The fan blower inside the SMPS should start running,.

(18) C O N S T R U C T I O N. other, this forms a 12-pin Item Description Make AT power supAT cabinet with SMPS, power cord, ply connector power switch, reset switch, speaker, with orange LEDs, complete with connectors and installation hardware packet. IMIL, Chennai wire (carrying Motherboard with Intel’s 810 power good chipset PC Partner, USA along with signal) emauser’s manual, CD (containing nating from drivers for onboard devices) and pin 1. headers for motherboard connectors. The volt* (refer check-list) PC Partner Pentium PIII-700 Processor Intel ages on vari64MB (PC 100)SDRAM (168-pin DIMM) Alpha ous pins of HDD (hard disk drive) Seagate this joint 12FDD (floppy disk drive) 3.5” Sony pin connector CD-ROM drive 52X with audio cable Samsung Keyboard Logitech with their Mouse(3-button) Logitech colour codes Colour Monitor 14” LG are shown in USB connector bracket with 2 headers Table II. *list of connectors/brackets forming part of motherboard. Check the corHeader (connectors with cables) for HDD (40-pin twin) - one rectness of Header for FDD (34-pin twin) - one these voltages Header for PS/2 mouse - one within the Port bracket set with headers for: (a) VGA (15-pin ‘D’ connector ending into 16-pin FRC and range as given parallel port (25-pin ‘D’ ending into 26-pin FRC) - one in Table II. (b) Com1 and Com2 (two 9-pin ‘D’ ending into 10-pin FRC) - two Then switch (c) Onboard AC97 sound codec (line-in, line-out, mic-in and off the power MIDI/game port ending into 26-pin FRC) - one supply and take out the 3indicating availability of +12V supply pin plug from the mains socket. If the to the fan. Now verify all DC outputs of AT power connector voltages are correct, you can safely assume that voltthe SMPS as follows. There are two distinct 6-pin Molex ages in all other power connectors [4female power connectors with projection pin Molex, carrying +12V (yellow wire) in the middle. If these are held such followed by two black wires (ground) and that all black wires are adjacent to each +5V (red wire)] meant for various drives. TABLE IV. PARTS LIST. TABLE II At Power Connector Pin Voltages Pin Voltage Range Wire Pin Voltage Colour 1 *P. G. 4.5V (min) Orange 7 Ground 2 +5V +5%/-4% Red 8 Ground 3 +12V +5%/-4% Yellow 9 -5V 4 -12V +10%/-9% Blue 10 +5V 5 Ground Black 11 +5V 6 Ground Black 12 +5V *P. G. = Power good signal which is +5V (delayed, 100ms – 500ms).. Range +10%/-8% +5%/-4% +5%/-4% +5%/-4%. Wire Colour Black Black White Red Red Red. TABLE III VGA– VGA Out Connector CN34* Pin Signal Name Pin Signal Name 1 Red signal 9 NC 2 Green signal 10 GND 3 Blue signal 11 NC 4 NC 12 Display data channel data 5 GND 13 Horizontal sync 6 GND 14 Vertical sync 7 GND 15 Display data channel clock 8 GND *This connector is for the VGA display port. Connect a VGA or higher resolution display monitor to it. ELECTRONICS FOR YOU ❚ JANUARY 2001. Parallel-Port Connector CN6 Pin. Signal Name. Pin. Signal Name. 1 2 3 4 5 6 7 8 9 10 11 12 13. StrobeData bit 0 Data bit 1 Data bit 2 Data bit 3 Data bit 4 Data bit 5 Data bit 6 Data bit 7 ACK Busy PE SLCT. 14 15 16 17 18 19 20 21 22 23 24 25 26. AFD Error INIT SLCTIN GND GND GND GND GND GND GND GND GND. are also correct. Motherboard fitment. The chassis on which motherboard is to be mounted can be easily removed from the PC cabinet. Unscrew it and gently slide it out from the main casing. Lay it flatly on the antistatic workbench (properly grounded conductive surface). Mark the side facing the keyboard connecter cutout on the chassis. All motherboards have standard mounting holes. The hardware supplied comprises plastic and metallic motherboard retaining fasteners/screwholders. Metal-type screw-holders are better as these have better strength and also these ground the motherboard to the chassis. You may use four metallic screw-holders for the four corner holes in the motherboard, while the plastic fasteners may be used for the middle holes of the motherboard. Before attempting fitment of the motherboard, align it on the chassis such that the keyboard connector on the motherboard is towards the side marked earlier for this purpose. Now fit all the screw-holders/fasteners, as discussed above, on the chassis, opposite the holes on the motherboard, using Philips screws provided in the hardware packet. Align the motherboard above the fasteners and push it down, so that the self-retaining heads of plastic fasteners pop out from the respective holes. For the metallic screw-holders, use Philips screws to secure the motherboard to the.

(19) C O N S T R U C T I O N. TABLE V COM1/COM2– Serial Connectors CN4*, CN5* Pin Signal Name Pin Signal Name 1 DCD 6 DSR 2 SIN 7 RTS 3 SOUT 8 CTS 4 DTR 9 RI 5 GND 10 NC *These connectors are for the serial port bracket. Both connectors have the same pinouts.. considerable force to engage it into the projection. You may use the flat screwdriver tip to do this, but be careful that screwdriver does not slip and damage the tracks on the motherboard [refer Fig. 5(d)]. 6. Connect the 3-pin fan connector to the corresponding connector CN17 marked ‘CPU Fan’ on the motherboard. DIMM installation (Fig. 6). There are two 168-pin SDRAM DIMM sockets. TABLE VI Audio & Game Port Pin Header CN341* Pin. Signal Name. Pin. Signal Name. Pin. Signal Name. Pin. Signal Name. 1 2 3 4 5 6 7. VCC VCC SWC SWA XTC XTA MSOUT. 8 9 10 11 12 13 14. GND XTD GND SWB XTB MSIN SWD. 15 16 17 18 19 20 21. NC VCC Line-out Line-out GND GND MIC-in. 22 23 24 25 26. MIC-in NC GND Line-in Line-in. *This header is for the audio port bracket. It connects audio ports-stereo line-out, stereo line-in and microphone—and a game port (for a joystick or MIDI device) to your system.. chassis firmly without using excessive force. Pentium processor mounting (refer Fig. 5). The processor is to be fitted into the PGA370 (pin grid array with 370-pin recesses) socket, which is a ZIF (zero insertion force) socket. Take out the processor and its heat sink fitted with cooling fan and heat sink retainer clip ‘D’. Now proceed as follows: 1. Lift handle ‘A’ to its vertical position [refer Fig. 5(a)]. 2. Align the processor pins with the socket holes and insert the processor into its socket [refer Fig. 5(b)]. 3. With the processor in its socket, lower handle ‘A’ and bring it to its closed (horizontal) position [refer Fig. 5(c)]. 4. Orient the heat sink (with fan on top) such that the depression on one side of the heat sink matches the corresponding projection on PGA370 socket, and place it (along with fan) over the processor [refer Fig. 5(c)]. 5. On the PGA370 socket, there are two small projecTABLE VII tions on opposite CN7: USB Port sides, in which the Pin Assignment heat sink clip has to 1 VCC be inserted. While 2 GND it is fairly easy to 3 USBP1insert one side, it is 4 USBP0+ rather tricky to in5 USBP1+ sert the left-out 6 USBP07 GND side as it needs to 8 VCC be pulled down with. on the motherboard with socket 1 marked ‘1’ and socket 2 left unmarked. The two sockets can together accept 512MB SDRAM (i.e. up to 256 MB each). We propose to install a single 64MB DIMM, which is quite adequate for current type of applications. It can be inserted into any of the two sockets and the same will be automatically suitably configured during setup. Remove the DIMM from its anti-static envelope, holding it by its edges. Proceed as follows: 1. Using fingertips, push the retainer clips on either side of the DIMM socket slightly away from the socket. 2. Position the DIMM to be installed above the socket, aligning the two small notches at the bottom edge of ELECTRONICS FOR YOU ❚ JANUARY 2001. TABLE VIII IDE Connector Pin Definitions (J18, J19) Pin Function Pin Function 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39. Reset IDE Host data 7 Host data 6 Host data 5 Host data 4 Host data 3 Host data 2 Host data 1 Host data 0 GND DRQ3 I/O WriteI/O ReadIOCHRDY DACK3IRQ14 Addr 1 Addr 0 Chip select 0 Activity. 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40. GND Host data 8 Host data 9 Host data 10 Host data 11 Host data 12 Host data 13 Host data 14 Host data 15 Key GND GND GND BALE GND IOCS16GND Addr 2 Chip select 1GND. DIMM with the corresponding keys in the socket. 3. Push the DIMM vertically down, inserting its bottom edge into the socket. 4. Once seated properly, push DIMM down from the top edge until the re-.

(20) C O N S T R U C T I O N. TABLE IX Floppy Connector Pin Definitions (JP26) Pin Function Pin Function 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33. GND GND Key GND GND GND GND GND GND GND GND GND GND GND GND GND GND. 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34. FDHDIN Reserved FDEDIN IndexMorot enable Drive select BDrive select AMotor enable DIRSTEPWrite dataWrite gateTrack 00Write protectRead dataSide 1 selectDiskette. tainer clips snap into place and the DIMM is firmly held into its position. Cable set installation. While the motherboard chassis is still not replaced into the case, you could install one of the ends of all the cables originating from the motherboard. The installation of cables, which originated from SMPS and the control panel of the case (LEDs,. TABLE X PS/2 Mouse Connector* Pin. Description. Pin. Description. 1 Mouse data 2 NC 3 Ground 4 +5V 5 Mouse clock 6 NC *This connector is for the optional PS/2 mouse port bracket.. reset switch, and the speaker), would be completed after the motherboard chassis is screwed back into the PC case. The cables to be connected to the FRC-type male connectors/headers on the motherboard are listed below, and the pin assignments are shown in the referred tables. On the motherboard, normally, only start pin 1 is indicated. In an FRC connector, all odd number pins are in one row while even number pins are in the opposite row; pin 2 is opposite pin 1, pin 4 is opposite pin 3, and so on. Pin 1 on the mating FRC female connector can be identified by an arrow mark over it. Ribbon cable wire going into pin 1 is of red (sometimes blue) colour. Some of the FRC connector pairs. ELECTRONICS FOR YOU ❚ JANUARY 2001. have a notch and the corresponding projection, which serves as a key so that they can go only the correct way. The cables used for the drives have an additional connector in the middle (for slave in case of HDD and drive B in case of FDD, which will be explained later). Using the tips given here, you can install the motherboard end of the following cables: • 16-pin VGA connector CN34 (refer Table III). • 26-pin parallel-port connector CN6 (refer Table IV). • 10-pin serial/com ports 1 and 2, CN4 and CN5 (refer Table V). • 26-pin sound cable connector CN31 (refer Table VI). • 8-pin USB connector CN7 (refer Table VII). • 40-pin IDE-1 connector for HDD/ CD-ROM drive CN1 (refer Table VIII). • 34-pin FDD connector CN3 (refer Table IX). • 6-pin PS/2 mouse connector CN8 (refer Table X). Stay tuned for the concluding part in next issue.

(21) CONSTRUCTION. AUTOMATIC ROOM LIGHT CONTROLLER. NA ANJA RUP & I ED DWIV S.C.. REJO G. PAREKKATTU. U. sually, when we enter our room triggered first and then activates an up/ in darkness, we find it difficult down counter accordingly. The BCD outto locate the wall-mounted put of the counter, at any time, represwitchboard to switch ‘on’ the light. For a sents the number of persons inside the stranger, it is tougher still as he has no room. The output of the up/down counter knowledge of the correct switch to be is decoded by 7-segment decoder/driver turned on. Here is a reliable circuit that and displayed on 7-sement display. Sitakes over the task of switching ‘on’ and multaneously, the output of counter is switching ‘off’ of the light(s) automatically compared by 4-bit magnitude comparawhen somebody enters or leaves the room tor. during darkness. This circuit has the folThe output of comparator remains lowing salient features: high as long as BCD output of counter is • It turns on the room light when- greater than zero. A logic gate is used to ever a person enters the room, provided initiate energisation of a relay to switch that the room light is insufficient. If more ‘on’ the light when comparator output is than one person enters the room, say, one high and it is dark outside. after the other, the light remains ‘on’. • The light turns ‘off’ only when the The circuit room is vacant, or, in other words, when all the persons who entered the room have The detailed section-wise description of left. the circuit shown in Fig. 2 is as follows: IR transmitter. The IR transmitter • A 7-segment display shows the numcircuit consists of an astable multivibrator ber of persons currently inside the room. • The circuit is resistant to noise and built around NE555 timer IC1. The outerrors since the detection is based on input of IC1 at pin 3 is a rectangular waveform of around 36kHz frequency. This outfrared light beams. • The circuit uses commonly avail- put is used to drive two IR LEDs, which able components and is easy to build and transmit modulated IR light at 36kHz frequency. Modulating frequency of 36 kHz test. The functional block diagram of the is used because the IR receiver modules circuit is shown in Fig.1. It comprises used in this circuit respond to IR signals 36kHz IR transmitter, two IR detector modulated at 36kHz frequency. The modules, two monostable multivibrators, multivibrator frequency can be correctly up/down-counter, 4-bit magnitude com- adjusted with the help of preset VR1 (10 kilo-ohm). Resistor R3 is a current limitparator, 7-segment decoder display, light sensor, and relay driver. Two pairs of IR transceivers are employed in order to detect whether the person is entering or leaving the room. When a person enters the room, IR detector 1 gets triggered, followed by triggering of IR detector 2. Conversely, when a person leaves the room, IR detector 2 gets triggered, followed by triggering of IR detector 1. A priority detector circuit determines which of the two detectors is Fig. 1: Block diagram of automatic room light ELECTRONICS FOR YOU ❚ JANUARY 2001. ing resistor that keeps the IR LEDs, current within the required range. IR detector modules. The IR detector modules used in the circuit are commonly available in the market. These PARTS LIST Semiconductors: IC1, IC2, IC3 - NE555, timer IC4 - 74LS192, up/down decade counter IC5 - 74LS85, 4-bit magnitude comparator) IC6 - 7447, BCD to 7-segment decoder/driver IC7 - MCT2E, opto-coupler IC8 - 7805, +5V regulator IC9(N1-N4) - 74LS00, quad 2-input NAND gate IC10(N5-N10) - 74LS14, hex schmitt inverter gate T1, T2 - BC548, npn transistor T3 - SL100, npn transistor D1-D3 - IN4001, rectifier diode IRLED1, IRLED2 - Infrared LED Resistors (all ¼-watt, ±5% carbon, unless stated otherwise): R1 - 3.3-kilo-ohm R2 - 10-kilo-ohm R3 - 100-ohm R4, R5, R21 - 1.2-kilo-ohm R6, R7, R12 - 33-kilo-ohm R8, R9 - 180-kilo-ohm R10, R11 - 1-kilo-ohm R13-R19 - 470-ohm R20 - 100-kilo-ohm VR1 - 10-kilo-ohm preset Capacitors: C1 - 0.001µF, ceramic disk C2, C3, C4 - 0.01µF, ceramic disk C5, C6 - 4.7µF, 16V electrolytic C7, C8 - 10µF, 16V electrolytic C9 - 1µF, 16V electrolytic Miscellaneous: M1, M2 - IR sensor modules DS1 - LT542 (common anode display) RL1 - 12V, 200 ohm, 2 C/O. LDR1 - LDR (Dark resistance > 120 kilo-ohm) L1 - 230V, 100W electric bulb - 12V power supply - Printed circuit board - IC sockets.

(22) CONSTRUCTION. Fig. 2: Schematic diagram of automatic room light controller. Fig. 3: Timing waveforms. have three terminals for Vcc (+5V, here), ground, and the output signal, respectively. In the normal state, the output pin (pin 3) of this detector remains at high state, and when an IR light of correct modulating frequency is detected, its output pin goes low. The pin configuration of the IR modules may vary from one manufacturer to the other. (Pin configuration of module TSOP 1136 for 36 kHz used by EFY is shown in Fig. 2.) (Articles based on the IR sensor module have been published in Nov. 2000 and some other previous issues of EFY. Readers may refer the same for more information about the module.) Since the IR transmitter in this circuit is continuously ‘on’, emitting IR light, in the normal condition, the output pins of both IR modules will be at low state. Therefore transistors T1 and T2 will remain cutoff. When a person en-. ELECTRONICS FOR YOU ❚ JANUARY 2001. ters or leaves the room, the infrared light beams are interrupted one-by-one and the output of each IR sensor module, in turn, goes high, which results in conduction of associated transistors T1 and T2. Which transistor will turn ‘on’ first depends on whether the person is entering or leaving the room. In the circuit, two NE555 timer ICs (IC2 and IC3) wired as monostable multivibrators are used. The pulse width of the output waveform (on time) for these multivibrators is fixed at about 0.9 seconds by suitably selecting the values for the timing capacitors C5 and C6 in conjunction with their associated resistors R8 and R9. These monostable multivibrators get triggered when their trigger input pins (pin 2) go low. Thus the multivibrators are triggered only when the IR light beams are interrupted. Although the output pulse width of both the multivibrators is approximately the same, there is, however, a phase difference corresponding to the elapsed time between the successive interruptions of the IR beams. Refer to the waveforms shown in timing diagram of Fig. 3. Priority-detector logic circuit. The priority detector circuit uses three NAND gates, five inverter gates, and two differentiators. The timing diagram given in Fig. 3 helps in understanding as to how the priority-detector circuit detects a person going out of the room. At first the outputs from the monostable multivibrators are NANDed by gate N1 and its polarity is inverted.

(23) CONSTRUCTION. Fig. 4: Actual-size, single-sided PCB layout for the circuit. again by gate N7. At the same time, the outputs of monostable IC3 and IC2 get differentiated by the capacitor-resistor combinations of C7-R10 and C8-R11, respectively. Each differentiated output is passed via Schmitt inverter pairs of N5N6 and N10-N9 to convert the differentiated pulses into rectangular pulses. The rectangular pulses obtained at the output of gates N6 and N9 are again. NANDed with the output of gate N7 in NAND gates N2 and N3, respectively. The rectangular pulse at pin 4 of NAND gate N2 ends before the output of gate N7 goes high and hence the output of NAND gate N2 stays high, while both inputs to NAND gate N3 are simultaneously high for the duration of rectangular output of gate N9. As a result, the output of gate N3 applied to countdown. Fig. 5: Component layout for PCB ELECTRONICS FOR YOU ❚ JANUARY 2001. clock pin 4 of IC4 causes the counter to count down on its trailing edge (low-tohigh transition) and the output count goes down by one count. Similarly, when a person enters the room, pin 4 of counter IC4 remains high, while its pin 5 (count up) gets a lowgoing pulse resulting into counter output advancing by one count. Values of capacitors C7 and C8 and resistors R10 and R11 can be varied for optimum performance. (Lab note. The component values have already been optimised and logic circuit is suitably modified for highly reliable performance of this part of the circuit, after considerable effort.) Up/down counter. Up/down decade counter 74LS192 (IC4) is used as the counter. When the power is turned ‘on’, its outputs Q0 through Q3 are in the low state. Whenever a person enters the room, a low-going pulse is applied at its count-up pin 5, while its count-down pin 4 is held at logic 1 and its output count advances by one. Similarly, when the person leaves the room, a similar pulse is applied at its countdown input (pin 4) while its countup pin 5 is held at logic 1 and its output decreases by one. Thus the 4-bit output always represents the number of persons still inside the room. The output of the decade counter is connected to 7-segment decoder/driver IC6 (7447) that displays the number on common-anode 7-segment LED display (LT542). Magnitude comparator. The output of the up/down counter is also applied to 4-bit magnitude comparator that acts as zero detector, i.e. it detects whether the number of persons inside the room is greater than zero or not. The 4-bit output of the decade counter is always compared with a reference 4-bit number (0000), and if a match occurs, the output at pin 5 (P>Q) of the comparator goes low to represent an ‘empty room’ condition. In all other cases (when the number of persons in the room is greater than zero), P>Q output will be at high state. This output is given as one of the inputs to NAND gate N4 (followed by inverter gate N8). Thus, as long as the room is not empty, one of the inputs to N4 gate will be high. The second condition for the light to get switched ‘on’ is yet to be satisfied. Whether there is sufficient light in the room or not is checked by the light sensor circuit..

(24) CONSTRUCTION. Light sensor. The light sensor is wired around the opto-coupler MCT2E. The resistance of the LDR depends upon the amount of light in the room. An LDR with resistance below 5 kilo-ohm in normal light and more than 120k resistance in darkness is required. When there is sufficient ambient light, the transistor inside the opto-coupler is turned ‘on’ and the input of NAND gate (pin 3) is driven to low state. Thus the output of NAND gate remains at high state and that of inverter gate N8 at low. However, when the light is insufficient, the resistance of the LDR increases, turning off the transistor inside the opto-coupler. The sensitivity can be controlled by adding a highvalued variable resistance (about 680k) across the LDR. When both conditions are satisfied (that is one or more persons are inside the room and the ambient light is insufficient), the output of NAND gate goes ‘low’ and that of inverter gate N8 goes ‘high’ to turn on transistor T3, thereby energising relay RL1. A 230V, 100W electric bulb is connected via the relay to the. AC mains. Once the relay gets energised, the LDR is effectively removed from the circuit (since the LDR is connected to the N/C contact of the two pole relay) to prevent the flickering of the lamp with changing resistance of the LDR.. Assembly and testing The full circuit, with the exception of the IR transmitter, can be assembled on a single general-purpose PCB. However, an actual-size, single-sided PCB for the circuit in Fig. 2 is shown in Fig. 4. The component layout for the PCB is shown in Fig. 5. The receiver-transmitter pairs are placed about a metre apart as shown in Fig. 6. The distance between the two sensors (receiver modules) is about 40 cm. A steel pipe of 5mm diameter and 3cm length can be placed in front of the IR module in order to improve its directivity. After assembling the circuit, adjust preset VR1 (10k) until pin 3 of both the IR sensor modules go high (5V). If the circuit still does not function properly, ad-. ELECTRONICS FOR YOU ❚ JANUARY 2001. Fig. 6: Proposed layout of IR transmitter and receiver pairs. just the distance between the sensors. The metal cabinets of the IR modules must be connected to ground. Note that the circuit works with a regulated +5V supply, except the power supply to the relay coil. The circuit has no off-time memory, and so its working is interrupted during power failure. Another disadvantage is that the circuit can count only up to 9. But it is quite unusual to have more than nine people in a normal living room. Take care about the IR sensor module pin connections. It may be damaged if connected wrongly. ❏.

(25) February. 2001.

(26) Circuit Ideas. 2001.

(27) CIRCUIT. IDEAS. 9-LINE TELEPHONE SHARER. EDI DWIV S.C.. DHURJATI SINHA. T. his circuit is able to handle nine independent telephones (using a single telephone line pair) located at nine different locations, say, up to a distance of 100m from each other, for receiving and making outgoing calls, while maintaining conversation secrecy. This circuit is useful when a single telephone line is to be shared by more members residing in different rooms/apartments. Normally, if one connects nine phones in parallel, ring signals are. heard in all the nine telephones (it is also possible that the phones will not work due to higher load), and out of nine persons eight will find that the call is not for them. Further, one can overhear others’ conversation, which is not desirable. To overcome these problems, the circuit given here proves beneficial, as the ring is heard only in the desired extension, say, extension number ‘1’. For making use of this facility, the calling subscriber is required to initially dial the normal phone number of the. ELECTRONICS FOR YOU ❚ FEBRUARY 2001. called subscriber. When the call is established, no ring-back tone is heard by the calling party. The calling subscriber has then to press the asterik (*) button on the telephone to activate the tone mode (if the phone normally works in dial mode) and dial extension number, say, ‘1’, within 10 seconds. (In case the calling subscriber fails to dial the required extension number within 10 seconds, the line will be disconnected automatically.) Also, if the dialed extension phone is not lifted within 10 seconds, the ring-back tone will cease. The ring signal on the main phone line is detected by opto-coupler MCT2E (IC1), which in turn activates the 10-second ‘on timer’, formed by IC2 (555), and energises relay RL10 (6V, 100ohm, 2 C/O). One of the ‘N/O’ contacts of the relay has been used to connect +6V rail to the processing circuitry and the other has been used to provide 220-ohm loop resistance to deenergise the ringer relay in telephone exchange, to cut off the ring. When the caller dials the extension number (say, ‘1’) in tone mode, tone receiver CM8870 (IC3) outputs code ‘0001’, which is fed to the 4bit BCD-to-10 line decimal decoder IC4 (CD4028). The output of IC4 at its output pin 14 (Q1) goes high and switches on the SCR (TH-1) and associated relay RL1. Relay RL1, in turn, connects, via its N/O contacts, the 50Hz extension ring signal, derived from the 230V AC mains, to the line of telephone ‘1’. This ring signal is available to telephone ‘1’ only, because half of the signal is blocked by diode D1 and DIAC1 (which do not conduct below 35 volts). As soon as phone ‘1’ is lifted, the ring current increases and voltage drop across R28 (220-ohm, 1/2W resistor) increases and operates opto-coupler IC5 (MCT-2E). This in turn resets timer IC2 causing: (a) interruption of the power supply for processing circuitry as well as the ring.

(28) CIRCUIT. ELECTRONIC CARD LOCK SYSTEM. IDEAS. RUP. ANJA. NA. PRIYANK MUDGAL. T. his circuit of electronic card lock system is much simpler and cheaper than other similar circuits that have appeared in earlier issues of EFY. The circuit is configured around an addressable 1 of 16 demultiplexer CD4514B (IC1). Any number in binary form, when available at input pins 2, 3, 21, and 22 (address pins A0 through A3), makes corresponding output go logic high, thus turning on the appliance through relay contacts. Up to 15 appliances can be switched on/off (one at a time). Output Q0 (pin 11) can be used for visual indication, to show that circuit is active.. A 40W bulb illuminates LDR1 to LDR5 constantly. This pulls down bases of transistors T1 through T5 to ground. LDR1 ensures that card is properly inserted into the card slot. When the card is correctly inserted, it covers the hole/opening for LDR1 and thus blocks the light from falling on LDR1. As a result, transistor T1 conducts and extends positive supply to the collectors of transistors T2 through T5. Then, depending upon the holes blocked/punched in the inserted card, any combination of emitters of transistors T2 through T5 turns logic ‘high’ (transistors’ output corresponding to blocked LDRs only goes. ‘high’). These outputs connected to address input pins A0 through A3 of IC1. ELECTRONICS FOR YOU ❚ FEBRUARY 2001. TABLE I Appliance LDR2 LDR3 LDR4 LDR5 no. 1 * * * 2 * * * 3 * * 4 * * * 5 * * 6 * * 7 * 8 * * * 9 * * 10 * * 11 * 12 * * 13 * 14 * 15 - Blocked hole corresponding to selected binary address. * Punched holes corresponding to LDR position on card. switch on the corresponding appliance (one out of 15). The card used should be of opaque plastic. It should be able to withstand some heat from the bulb, even though the appliance remains ‘on’ only for the period for which the card is in the slot. The card has a triangular notch that shows correct orientation/direction of insertion of card and prevents false operation. LDRs can be placed in a line, or randomly, to increase security. The order in which holes should be punched for each appliance is given in Table I. Two illustrations, one each for card-2 and card-5, are shown in the accompanying figures. An elevation and plan/top view of the gadget is also shown in the figures..

(29) CIRCUIT. PULSED OPERATION OF A CW LASER DIODE. IDEAS. EDI DWIV . C . S. DR. ALIKA KHARE. H. ere a simple low-cost technique for converting a CW laser diode at 670 nm wavelength to pulsed laser up to a frequency of 500 kHz. A low-power pulsed radiation source is very important for any laboratory involved in optical pulsed systems—laser, pulsed discharges, optical communication, fibre-optic sensors, image processing, etc—where one is required to check the frequency response of the detection system or optical simulation of an optical source or local networking using optical fibre cable. Fast-speed LED offers the so-. lution for such requirements, but because of very low power and large divergence, its use remains limited. On the other hand, a pulsed diode laser offers a very good solution for this problem. Commercial systems are usually expensive. However, a CW diode laser operating at 670 nm can easily be pulsed up to a frequency of 500kHz with low-cost technique, using a function generator and. an inexpensive push-pull amplifier interface circuit. The block diagram of the system is shown in Fig. 1. A 3mW CW diode laser at 670 nm with voltage and current rating of 3V at 100mA, respectively, is used. The source (a function generator) is capable of delivering square pulses of 3V amplitude, which are amplified by a complementary symmetry pushpull circuit shown in Fig. 2. The output of the amplifier is connected to the diode laser for pulsed operation. The laser is focused onto a photodiode terminated with 50ohm resistor (Fig. 1). The output of photodiode is displayed on digital storage oscilloscope and it is also connected to the PC for getting a hard copy. Up to a frequency of around 20 kHz, the threshold voltage for laser oscillations is around 2.4V. For frequencies greater than 20 kHz, the threshold for laser oscillations depends on the operating frequency and is higher than 2.4V. The behaviour of laser pulses up to 10 kHz is nearly similar. Laser output at a typical frequency of 2 kHz is shown in Fig. 3, at various voltages (2.6V, 3.4V, and 4V). The input waveform ‘A’ is shown at the bottom of the figure. For a driving pulse of about 3V (which is the normal operating voltage for CW operation), the laser pulse becomes flat after a delay of approximately 40 µs (time taken to build up the laser oscillations to ELECTRONICS FOR YOU ❚ FEBRUARY 2001. its maximum amplitude). Above 3V, probably population inversion is developed much above threshold, before the laser oscillations build up into the cavity, and so we observe the sharp peak in laser output (for more details, refer Laser Fundamentals book by W. T. Silfvast, published by Cambridge University Press), exponentially decaying to a steadystate value with a time constant depending on the initial peak intensity and the carrier life time in the excited state. After the input pulse is over, the oscillations die down within 5 µs. Therefore above 3V, up to a frequency. of 10 kHz, the laser is operated in quasi CW mode. In the frequency range of 10 kHz to 50 kHz, the laser output keeps on increasing, even during the flat portion of the input current pulse, and falls down to zero during the off period of the driving pulse. Fig. 4 shows the laser waveforms at 50 kHz, 100 kHz, 200 kHz, 300 kHz, and 500 kHz, respectively. All these pulses were recorded at around 4V. In this range of frequencies,.

(30) CIRCUIT. the duration for which voltage is on/off is of the order of less than 5 µs, and so the driving pulses switch off before the termination of laser oscillations. Therefore the laser output shows a modulation with. IDEAS. the DC component in it. Beyond 500 kHz, it is difficult to observe laser oscillations even at voltages higher than 4V. Lab note. Tests conducted at EFY using laser diode of laser torch (rated. ELECTRONICS FOR YOU ❚ FEBRUARY 2001. for <5mW) with identical inputs at 2 kHz did not show any marked departure of output waveform (square wave) from the input square wave..

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