EFY 2000 & PROJECTS 00 VOLUME More than 90 fully tested and ready-to-use electronics circuits IDEAS 2000 Electronics For You issues
C o n t e n t s JANUARY 2000 2000 CONSTRUCTION PROJECTS 1) MICROPROCESSOR-CONTROLLED TRANSISTOR LEAD IDENTIFIER --------------------------------------------- 1 2) CONVERSION OF AUDIO CD PLAYER TO VIDEO CD PLAYER I ----------------------------------------------- 9 CIRCUIT IDEAS 1) MULTIPURPOSE CIRCUIT FOR TELEPHONES ------------------------------------------------------------------------- 13 2) SIMPLE CODE LOCK ----------------------------------------------------------------------------------------------
C o n t e n t s MAY 2000 2000 CONSTRUCTION PROJECTS 1) DIGITAL NUMBER SHOOTING GAME --------------------------------------------------------------------------------- 63 2) PC INTERFACED AUDIO PLAYBACK DEVICE: M-PLAYER ---------------------------------------------------------- 66 CIRCUIT IDEAS 1) STEPPER MOTOR DRIVER ------------------------------------------------------------------------------------------------- 73 2) ELECTRONIC DIGITAL TACHOMETER ----------------------------------------------------------
C o n t e n t s SEPTEMBER 2000 2000 CONSTRUCTION PROJECTS 1) DISPLAY SCHEMES FOR INDIAN LANGUAGESPART II (Hardware and Software) -------------------- 123 2) DIGITAL CODE LOCK ----------------------------------------------------------------------------------------------------- 133 CIRCUIT IDEAS 1) BINARY TO DOTMATRIX DISPLAY DECODER/DRIVER ----------------------------------------------------------- 137 2) AUTOMATIC SPEED-CONTROLLER FOR FANS AND COOLERS ------------------------------------------------ 139
January 2000
CONSTRUCTION MICROPROCESSOR-CONTROLLED TRANSISTOR LEAD IDENTIFIER ARUP KUMAR SEN T ransistor lead identification is crucial in designing and servicing. A circuit designer or a serviceman must be fully conversant with the types of transistors used in a circuit. Erroneous lead identification may lead to malfunctions, and, in extreme cases, even destruction of the circuit being designed or serviced.
Fig. 1: Schematic circuit diagram of the transistor lead identifier CONSTRUCTION tions. As a result, the LEDs connected to the collector and emitter leads start flickering alternately with different brightness. By inserting a resistor in series with the base, the LED glowing with lower brightness can be extinguished. In the case of an NPN device (under normal biasing condition), conventional current flows from source to the collector layer.
CONSTRUCTION nected to inputs of IC 3 (7486, quad 2input EX - OR gate). Gates of IC3 are so wired that they function as controlled EX - OR gates. The outputs o f IC 3 are controlled by the logic level at pin 12. Thus, we obFig. 2: Effective biasing of PNP transistors using set 1 binary numbers tain two sets of outputs (marked Q 0, Q 1 , and Q 2 ) from IC 3 as given in Tables III (for pin 12 at logic 1) and IV (for pin 12 at logic 0) respectively.
CONSTRUCTION (logic 1)à SW2à R14àinternal leadàBC junction àcollector leadàslot-3à D1à SW3à Q2 (logic 0) 2. Q1 (logic 1)à SW2à R14àinternal LED (IC6)àslot-2àbase leadàBE junction à emitter leadà slot 1à D5à SW1à Q0 (logic 0) Thus, only the internal LED of IC6 would start flickering, and the data that would be formed at the emitters of the transistors is also 010. Accordingly, the base-Id that would be developed in this case is 0000 0010=2(H).
CONSTRUCTION Fig. 5 (iv) DISPLAY ROUTINE USING ALTERNATIVE CIRCUIT OF FIG. 4 TABLE V PC7 0 PC6 0 PC5 0 PC4 0 PC7 0 PC6 0 PC5 0 PC4 0 PC3 0 PC2 1 PC1 0 PC0 1 PC2 1 PC1 0 PC0 1 TABLE VI PC3 1 vice uses the set-2 binary numbers for identification of the collector (hence the emitter), the same number (base-Id) obtained during base identification cannot be sent through port C, if the device under test is of npn type. The base-Id found must be EX-ORed first with OF (H).
CONSTRUCTION PARTS LIST Semiconductors: IC1 - NE555, timer IC3 - CD4017, decade counter-decoder IC3 - 7486, quad EX-OR gates IC4,IC6,IC7 - MCT2E, optocoupler IC5 - CD4066, quad bilateral switch IC8 - LM7805, 3-terminal +5V regulator T1,T2,T3 - BC147, npn transistor D1,D3,D5 - 1N34, point contact diode D2,D4,D6 - LED, 5mm D7,D8 - 1N4002, rectifier diode Resistors (All ¼ watt +/- 5% metal/carbon film unless stated otherwise) R1,R9,R10,R14, R15,R19,R20 - 1 kilo-ohm R2 - 33 kilo-ohm R5 - 47 kilo-ohm R4,R11,R16
CONSTRUCTION Memory Map And Software listing in 8085 Assembly Language RAM Locations used for program :2000H - 21BBH Stack pointer initialised :2FFFH Monitor Program :0000H - 0FFFH Display Data Table :2160H - 219AH Control/Status Register of 8155 :80H Port A (Input) of 8155 :81H Port B (Output) of 8155 :82H Port C (Output) of 8155 :83H Address Op Code Label Mnemonic ;Initialisation, base and type identification 2000 31FF2F MAIN: LXI SP,2FFFH 2003 3E0E MVI A,0EH 2005 D380 OUT 80H 2007 3E07 MVI A,07H 2009 D38
CONSTRUCTION Address Op Code 210B D383 210D 7E Label Mnemonic OUT 83H MOV A,M 210E 2110 D382 78 OUT 82H MOV A,B 2111 2113 D383 1F OUT 83H RAR 2114 FE00 CPI 00H 2116 CA2121 JZ 2121H 2119 47 MOV B,A 211A 211D 211E CD3320 23 C30921 CALL DELAY INX H JMP 2109H 2121 C9 RET ;Error Sub-routine 21A0 219121 21A3 CDFC20 21A6 21A9 21AC CD3320 CD3320 219621 21AF 21B2 21B5 21B6 CDFC20 C30020 00 218D21 21B9 C3AF21 Data table: Addr.
CONSTRUCTION CONVERSION OF AUDIO CD PLAYER TO VIDEO CD PLAYER I G.S. SAGOO PUNERJOT SINGH MANGAT T he analogue technology is giving way to the digital technology as the latter offers numerous advantages. Digital signals are not only free from distortion while being routed from one point to another (over various media), but error-correction is also possible. Digital signals can also be compressed which makes it possible to store huge amounts of data in a small space.
CONSTRUCTION card to the audio/video input of TV via jacks J7 and J11 respectively. Use only shielded wires for these connections. ● Check to ensure that the step-down transformer provides 12-0-12 volts at 1 ampere of load, before connecting it to the MPEG card. Connect it to the MPEG card via jack J1. ● Switch on the TV to audio/video mode of operation. Adjust the 100-ohm preset connected at the video output of MPEG card to mid position.
CONSTRUCTION DSP IC EFM DSP IC /RF Pin KS 5950 KS 5990, 5991 KS 9210 B KS 9211 B E, 9212 KS 9282 KS 9283 KS 9284 CXD 1125 QX CXD 1130 QZ CXD 1135 CXD 1163 Q CXD 1167 R CXD 1167 Q/QE CXD 20109 CXD 2500 AQ/BQ CXD 2505 AQ 5 5 5 5 5, 66 66 66 5 5 5 5 36 5 9, 20 24 24 CXD 2507 AQ 14 CXD 2508 AQ CXD 2508 AR CXD 2509 AQ CXD 2515 Q CXD 2518 Q LC 7850 K LC 7860 N/K/E LC 7861 N LC 7862 LC 78620 LC 78620 E LC 7863 LC 7865 36 36 34 36, 38 36 7 7, 8 8 30 11 11 8 8 LC 7866 E LC 7867 E LC 7868 E LC 7868 K LC 7868
CONSTRUCTION adding the following information which we have been able to gather during the practical testing of the project at EFY. 1. There may be more than one PCB used in an audio CD player (i.e additional for FM radio and tape recorder functions) and even the DSP chips referred in Table1, may not figure on it. For example, we could not find the subject IC used in AIWA audio CD player. The PCB, which is located closest under the laser system, is related to CD player part.
CIRCUIT IDEAS CIRCUIT IDEAS MULTIPURPOSE CIRCUIT FOR TELEPHONES G.S. SAGOO RANJITH G. PODUVAL T his add-on device for telephones can be connected in parallel to the telephone instrument. The circuit provides audio-visual indication of on-hook, off-hook, and ringing modes. It can also be used to connect the telephone to a CID (caller identification device) through a relay and also to indicate tapping or misuse of telephone lines by sounding a buzzer.
CIRCUIT IDEAS transistor T1. The reset keys are wired to set pins 6 and 8 of each IC. (Power-on-reset capacitor C1 has been added at EFY during testing as the state of Q output is indeterminate during switching on operation.) This circuit can be usefully employed in cars so that the car can start only when the correct code sequence is keyed in via the key pad. The circuit can also be used in various other applications. AUTOMATIC BATHROOM LIGHT JAYAN A.R.
CIRCUIT switches to a high level when the door is opened. (See waveform B in Fig. 2.) Thus, a lowto-high going voltage transition is available at point B for every opening of the door, from the closed position. Capacitor C2 is connected at the output to filter out unwanted transitions in the output voltage generated at the time of closing or opening of the door. IC 7474, a rising-edge-sensitive dual-D flip-flop, is used in the circuit to memorise the occupancy status of the bathroom.
CIRCUIT sumption is extremely low. This makes it possible to power the circuit from a battery. The input sensing current through the fluid (with all the four probes im- IDEAS mersed in water) is of the order of 70 µA, which results in low rate of probe deterioration due to oxidation as also low levels of electrolysis in the fluid. Note: This circuit should not be used with inflammable or highly reactive fluids.
CIRCUIT few seconds. The program (software) and data used for the purpose are given below in mnemonic and machine code forms. The program is self-explanatory. The program and data have been entered at specific memory locations. However, the readers are at liberty to use any other memory area in their kits, depending on their convenience.
CIRCUIT IDEAS Address OP CODE LABEL Mnemonic Comments Address OPCODE 21 CD Repeat for next period DATA 20 50 20 51 20 52 20 53 20 54 20 55 00 00 00 00 00 00 DELAY 25 00 25 01 25 02 25 03 25 06 C3 09 21 JMP AA SUBROUTINE 1B NEXT 7A B3 C2 00 25 C9 DCX D MOV A, D ORA E JNZ NEXT RET LABEL Mnemonic DESIGNING AN RF PROBE RUPANJANA N.S. HARISANKAR, VU3NSH R adio frequency probe is used to directly measure the level of RF RMS voltage present across two points.
February 2000
CONSTRUCTION PC BASED SPEED MONITORING SYSTEM G.S. SAGOO SANTHOSH JAYARAJAN T As interface circuit can easily be wired on any general-purpose PCB, no PCB layout is included for it. The two wires to be extended to 25-pin parallel port may be connected using a 25-pin male ‘D’ connector. Lab Note: Magnetic proximity switches, from various manufacturers, are available in the market. The important specifications include operating DC voltage range, operating current and its sensitivity, i.e.
CONSTRUCTION PARTS LIST Semiconductors: IC1 - 7805 regulator 5V IC2 - MCT2E opto-coupler Resistors (all ¼ watt, ± 5% metal/carbon film, unless stated otherwise) R1 - 300-ohm R2 - 150-ohm Capacitors: C1 - 1000µF, 16V electrolytic C2 - 0.22µF polyster Miscellaneous: X1 - 230V AC primary to 0-9, 250mA sec. transformer BR-1A - Bridge rectifier, 1-amp. S1 - Proximity switch (refer text) Fig. 4: Structural block diagram of software HELPS.
CONSTRUCTION with extension. (b) Enter the x-axis scale factor to enable the graph to be ‘stretched’ on the xaxis to observe cramped points properly. After entering the x-axis scale, the graph appears along with all relevant data, like scale factors for x and y axis, file name, and units, etc. (c) While still in the graph mode, you may view a new graph after pressing F1. For returning to the main menu, press F2. 3. Help. This module provides one page of help and reads from a file called #include
CONSTRUCTION s=inp(0x379);t=s;while(s==t)s=inp(0x379);break; default:textcolor(YELLOW+BLINK);cprintf (“Trigger mode: Manual ..Press any key to Start”); getch();break; } startgraphics(); for(int pointno=1;pointno<481;++pointno) { char in; display(unit); speedf=roundoff(speed); infile<
CONSTRUCTION cleardevice(); setbkcolor(LIGHTGREEN); setcolor(RED); moveto(150,200); outtext(“Exiting to DOS..”); delay(2000); closegraph(); exit(1); } //Display the helpfile if resident or else indicate error// void displayhelp(char helpfilename[10]) { fstream infile; textbackground(BLACK); window(1,1,80,25); textcolor(LIGHTRED); const int max=80; char buffer[max]; clrscr(); infile.open(helpfilename,ios::in); if(infile.fail()) { window(10,8,70,9); textcolor(YELLOW+BLINK); clrscr; cprintf(“.....
CONSTRUCTION STEREO CASSETTE PLAYER G.S. SAGOO REJO G. PAREKKATTU A n electronics hobbyist always finds pleasure in listening to a song from a cassette player assembled with his own hands. Here are the details of a stereo cassette player with the following features, which many electronics enthusiasts would love to assemble and enjoy: 1. Digital 4-function selector (radio, tape, line input, and transmit). 2. Four sound modes (normal, low boost, hi-fi, and x-bas). 3. Bass and treble controls. 4.
CONSTRUCTION and 13) of CD4066 , as shown in Fig. 3, is made high, it can switch AC and/or DC signals between its corresponding output pins (3-4, 89, 10-11, and 1-2 respectively) in both direc- tions. In other words, it acts like an analogue switch which can be turned on or off by making its input control pin high or low. A single IC contains four such switches/sections (A, B, C, and D). The control inputs of the two ICS (CD4066) are derived from the decade counter IC (HEF4017).
CONSTRUCTION VR3 and VR4. But the midrange frequency components get attenuated due to capacitor C41 (0.047µF). In the hi-fi mode (Q1 output of IC7 high), pole-P of the switch is in contact with terminal 1. In this position, normal gain is achieved for entire audio frequency range (since capacitor C41 is disconnected from the feedback path).
CONSTRUCTION Fig. 7. Actual-size, single-sided PCB for stereo cassette player Fig. 8.
CONSTRUCTION tact with terminal 3 (Q3 output of IC7 high), normal gain is provided for the high-frequency components (treble) and higher gain is available for a wide range of low frequencies (including some midrange frequencies). This is termed as the X-BAS mode. The gain of the amplifier for different frequencies, in each of the above-mentioned modes, is also dependent on VR3 and VR4 potmeter settings. In the actual circuit diagram, the bipolar analogue switcher (CD4066) replaces switch SW.
EAS C I RC ICR CUUII TT I ID D EAS BASS AND TREBLE FOR STEREO SYSTEM control. When the slider of potentiometer VR1 is at the lower end, minimum treble signal develops across the load. The lowest point is referred to as treble cut. As the slider is moved upward, more and more treble signal is picked up. The highest point is referred to as treble boost. Bass would be cut if capacitive reac- Hence, bass has nil attenuation, and it is called bass boost.
CIRCUIT IDEAS power supply, the supply to the transformer is not available and the relay deenergises. Thus, once the supply is interrupted even for a brief period, the relay is de-energised and you have to press switch S1 momentarily (when the supply resumes) to make it available to the load. Very-short-duration (say, 1 to 5 milliseconds) interruptions or fluctuations will not affect the circuit because of presence of large-value capacitor which has to discharge via the relay coil.
CIRCUIT Fig. 2 Fig. 3 so the displays (DIS.1 and DIS.2) remain off. However, at the end of positive pulse at pin 1 of IC1 (and base of transistor T1), the frequency counter is latched. During the following 4-second low level period, transistor T1 conducts and displays DIS.1 and DIS.2 show the current count.
CIRCUIT current converter. The design procedure is as follows: Calculate RI according to the application from one of the following equations: (a) DC voltmeter: RIA = full-scale EDC/IFS (b) RMS AC voltmeter (sine wave only): RIB = 0.9 full-scale ERMS/ IFS (c) Peak reading voltmeter (sine wave only): RIC = 0.636 full-scale EPK/IFS IDEAS (d) Peak-to-peak AC voltmeter (sine wave only): RID = 0.
CIRCUIT MT2, i.e. connect MT1 to the negative and MT2 to the positive side. For a good working triac, S2 would not initiate conduction in the triac and the LED would remain off. On the other hand, momentary depression of S5 would initiate conduction of the triac and LED1 would glow. The indication of a leaky triac is similar to that of an SCR. If, during both the above-mentioned tests, the LED lights up, only then the triac is good.
March 2000
CONSTRUCTION RESONANCE TYPE L-C METER RUPANJANA ARUP KUMAR SEN T he voltage developed across a capacitor or an inductor in a seriesresonant LCR circuit reaches its maximum value at resonance. This fact can be used to find the value of an unknown inductance or a capacitance. The present circuit is based on this very principle and it may be used to measure an inductance of even less than 1 µH, or a capacitance of the order of a few pico Farads.
CONSTRUCTION The frequency of the RF source may be varied from 1.8 MHz to 14.3 MHz by connecting different crystals of known resonant frequencies. (Refer parts list.) Transistor T1, along with capacitors C3 and C4, and crystal Xtal, forms the Colpitts oscillator. The crystal operates Fig. 3: Single-layer coil near its parallel resonant frequency.
CONSTRUCTION sponding to a particular frequency, and is given by the relation: TABLE II Construction Details of the Coils Coil Radius(r) (inch) L1 10.4/16 10.4/16 L2 L3 0.25 0.25 L4 L5 10.4/16 Length(l) (inch) 5/16 3/16 1.25 13/16 2/16 Turns(N) L* (µH) 20 7 10 2.2 77 25 50 15 4 0.4 metres, where f is the frequency in MHz.
CONSTRUCTION of LED D5, or peak on the meter. The intensity of LED D5, or the deflection of the meter pointer, would be the maximum at resonance. If no peak is found, it might be due to low signal input to the peak detector. Gradually decrease the incircuit resistance value of potmeter VR1. If still no peak is found, it would mean that crystal frequency is not appropriate. Try with another crystal. 5. Note down the capacitance values from the dials of CT and CF.
CONSTRUCTION ELECTROLYSIS-PROOF COMPLETE WATER-LEVEL SOLUTION RUPANJANA LOKESH KUMATH O Description Fig. 1: Circuit diagram of complete water level solution (contd. refer Fig. 2) ne major problem in using water as a conducting medium arises due to the process of electrolysis, since the sensor probes used for level detection are in contact with water and they get deteriorated over a period of time.
CONSTRUCTION Note: Identically marked points in Figs 1 and 2 are interconnected Fig. 2: Part circuit of complete water level solution (contd. from Fig. 1) used as protection diodes. The under- and over-voltage cutoff section (Fig. 1). It comprises a dual comparator, two pnp transistors, and a few other discrete components. This part of the circuit is meant to stop the motor in case of a low mains voltage (typically 180V to 190V) or a voltage higher than a specified level (say 260V to 270V).
CONSTRUCTION Fig. 3: Actual-size, single-sided PCB layout for the circuit shown in Figs 1 and 2 Fig. 4: Component layout for the PCB high and resets IC4(a) to make Q high again. This starts the motor again. But if water still does not flow into the OHT this time, Q of IC4(a) becomes low again to switch off the motor. Simultaneously, IC5 gets another clock pulse and IC4(a) is reset once again after 10 seconds to restart the motor.
CONSTRUCTION Fig. 5: Proposed front-panel layout after taking appropriate remedial action such as filling the foot-valve of the motor with water or by removing the air-lock inside the pipe. Reservoir/sump tank level detection (Fig. 2). To start the motor when the water level in the reservoir is sufficient (level B), and to stop the motor when the level falls below a particular level (level A), are the two functions performed by this section.
T I D E A S C I RC ICR CUUII T IDEAS The BCD outputs of IC2 are connected to IC3 (CD4028), which is a 1-of10 decoder. As per sequential BCD in- through Triac10) via corresponding transistors (T1 through T10) to light up the bulbs connected to them. Initially, when output O0 of IC3 goes high, the output of flip-flop formed by NOR gates N3 and N4 goes high, thus keeping pin 10 of IC2 at logic 1, and the counter counts up.
C I R C U I T I D E A S Fig. 1 Fig. 2 pin connected to the inverting terminal of a comparator inside the IC) is not grounded via a capacitor, but the potential at this pin is made to change in accordance with the audio level. This causes the internal flip-flop of timer NE555 to set and reset according to the audio level, and hence the output frequency varies correspondingly.
C I R C U I T I D E A S CLEVER RAIN-ALARM NA ANJA RUP M.K. CHANDRA MOULEESWARAN U sually rain-alarms employ a single sensor. A serious drawback of this type of sensor is that even if a single drop of water falls on the sensor, the alarm would sound. There is a probability that the alarm may be false. To overcome this drawback, here we make use of four sensors, each placed well away from the other at suitable spots on the roof. The rain alarm would sound only if all the four sensors get wet.
C I R C U I T I D E A S LASER CONTROLLED ON/OFF SWITCH EDI DWIV S.C. Dr K.P. RAO his circuit is built around a 555 timer using very few components. Since the circuit is very simple, even a novice can easily build it and use it as a controlling device. A laser T isfactorily, though it can be controlled from still longer distances. Aiming (aligning) the laser beam exactly on to the LDR is a practical problem. The circuit is very useful in switch- only in dark or dull-lit environments.
C I R C U I T causes transistor T2 to cut off and relay RL1 is not energised. When the telephone handset is lifted, the voltage across points X and Y falls below 12 volts and so zenor diode D5 does not conduct. As a result, base of transistor T1 is pulled to ground potential via resistor R4 and thus is cut off. Thus, base of transistor T2 gets forward biased via resistor R5, which results in the energisation of relay RL1. The tape recorder is switched ‘on’ and recording begins.
C I R C U I T warded by the author, the transformers X1, X2, and X3 primaries as well as switch S1 were connected after the contacts of contactor. As a result energisation of contactor was not feasible. Even when switch S1 was shifted to a ‘live’ phase, relay RL1 (as well as contactor C) was energising/de-energising in quick succession during single-phasing and causing sparking—for obvious reasons. Hence the circuit was suitably modified at EFY (as presented). 2.
April 2000
CONSTRUCTION SMART CLAP SWITCH RUPANJANA LOKESH KUMATH C ircuit of a smart clap switch, incorporating certain unique features, is presented here. It overcomes the shortcomings observed in normal clap switches. The following two special features, which you would not have observed in other clap switches, are included in its design: (a) It comprises a 4x4 clap switch, i.e. it operates only when you clap four times to switch ‘on’ a device.
CONSTRUCTION Fig. 1: Schematic diagram of smart clap switch goes from ‘low’ to ‘high’, it acts as a clock (CLK1) for first section of IC3. As a result Q1 of the IC3 goes ‘low’ to trigger IC4, which produces a pulse of about 3.5-second duration at its output pin 3. The output of IC4 is inverted by transistor T1, which toggles the second JK flip-flop inside IC3. As a consequence, its Q2 output goes ‘low’ and the count present at the parallel load inputs are loaded.
CONSTRUCTION Fig. 2: Actual-size, single-sided PCB layout for the circuit Fig. 3: Component layout for the PCB cause QC output (connected to C input) would still be ‘low’ when load input becomes active low, at the end of 3.5-second. period. Thus 0000 is loaded into IC5, thereby keeping the relay or the device connected to the switch in its previous state. This happens up to a total of three claps occuring within the allotted time duration of 3.5-seconds.
CONSTRUCTION ELECTRONIC VOTING MACHINE JUNOMON ABRAHAM N ow-a-days electronic voting machines are being used effectively. The confidence of the voter in its flawless working is gradually building up and these machines are thus becoming quite popular throughout the country. (Please note that the design being presented here is not intended to resemble that of electronic voting machines used by the Election Commission. If any resemblance is noticed between the two, it is totally unintended.
CONSTRUCTION Fig. 1: Schematic diagram of the electronic voting machine.
CONSTRUCTION her vote.) 7. Now, the voter can cast his/her vote by pressing the appropriate keyboard switch allocated to the candidate of his/her choice. The acceptance of the vote by the system is acknowledged by a beep sound as well as the display of the ‘ ’ symbol in the display and ‘off’ condition of LED D4. 8. Steps 6 and 7 have to be repeated for casting a fresh vote. 9.
CONSTRUCTION Fig. 3: Actual-size, single-sided PCB layout for the circuit Fig.
CONSTRUCTION accepting any further vote. Thus, the maximum number of votes that can be registered against any one candidate should not exceed 9999. This is the limitation in the present design. Keyboard. This module is used for checking key closure and generating the binary value corresponding to the closed switch. Password security This voting machine has a password option. The length of the password is limited to a maximum of seven digits.
CONSTRUCTION Address Opcode Mnemonics Comments Address Opcode 00F0 76 Count subroutine 00B6 31 FF 80 LXI SP, 80FF 00B9 3A D0 80 LDA 80D0 Load contents of mem loc 80D0 00BC FE 80 CPI 80 If overflow occurs, generate 00BE C2 C4 00 JNZ 00C4 continuous beep 00C1 D3 C0 JNZ 00C4 00C3 76 HLT 00C4 3E 1A MVI A, 1A If there is no overflow, 00C6 26 40 MIV H, 40 load data byte for displaying count 00C8 CD 70 00 CALL count mode indicator ‘[’ and KEYBOARD glowing LED D4 00CB 0E 04 MIV C, 04 Increment the count of the
EAS C I RC ICR CUUII TT I ID D EAS WATER-TANK LEVEL METER S.C. DWIVEDI M.K. CHANDRA MOULEESWARAN T he water-tank level meter described here is very simple and useful for monitoring the water level in an overhead tank (OHT). The water level at 30cm intervals is monitored and continuously indicated by LEDs arranged in a meter-format. When all the LEDs are ‘off’, it indicates that the OHT is empty. When the water level reaches the top limit, the whole LED-meter begins to flash.
CIRCUIT board, in a single line, so that they may be pushed through the cutouts in the front panel of the enclosure from inside. The water level at 30cm intervals is monitored by corresponding sensors, causing the input to the concerned inverters (normally pulled ‘high’ via resistors R1 through R10) to go ‘low’, as soon as water reaches the respective sensors. On initial switching ‘on’ of the power supply, when the tank is empty, all the electrodes are open.
CIRCUIT IDEAS minal A and B are combined using a bridge, comprising diodes D1 to D4, to obtain 1Hz clock pulses. These clock pulses are applied to the base of transistor T1. The collector and emitter of transistor T1 are connected across calculator’s ‘=’ terminals. will be further incremented according to pulse rate. So one call should always be included before counting the calls.
CIRCUIT rent local call meter reading will blink once every second. In prototype circuit, the author used TAKSUN calculator that costs around Rs 80. The display height was 1 cm. In this calculator, he substituted the two buttontype batteries with two externally connected 1.5V R6 type batteries to run the calculator for more than an year. The power ‘off’ button terminals were made dummy by affixing cellotape on contacts to avoid erasing of memory, should someone accidentally press the power ‘off’ button.
CIRCUIT IDEAS LATCH-UP ALARM USING OPTO-COUPLER S.C. DWIVEDI PRADEEP G. T he latch-up alarm described here is based on single IC NE555, configured as an astable multivibrator. The timing components are selected such that the oscillation frequency of the multivibrator lies within the audio range. Instead of a flip-flop stage, an opto-coupler (MCT2E) is used for latching of the alarm. Under normal condition, pin 4 of IC1 is pulled to ground via resistor R2, and its output at pin 3 is held ‘low’.
CIRCUIT S2 (PLAYL). Pressing (grounding) this pin ends the power-down mode and initiates the play cycle. The stored/recorded message is played until finished or this pin is taken ‘high’. S3(PLAYE). Pressing (grounding) this pin momentarily ends the power-down mode and enters the play mode. Subsequent taking of this pin ‘high’ has no effect. However, pressing this pin once more finishes the play mode and the chip enters the power-down mode. The action is analogous to the falling-edge trigger mode.
May 2000
CONSTRUCTION DIGITAL NUMBER SHOOTING GAME RUPANJANA A. JEYABAL M any electronic video games are available in the market. But for those who may prefer to assemble the game themselves, a digital number shooting game circuit is described here. A train of single-digit random numbers appears on a 7-segment display, and the player has to shoot a number by pressing a switch corresponding to that number before it vanishes. If he shoots the number, he scores ten points which are displayed on the scoreboard.
CONSTRUCTION Fig. 2: Circuit diagram of the digital number shooting game frequency (of the order of 1 Hz to 4 Hz). Its frequency can be varied with the help of potentiometer VR1. For proper functioning of CD4033 and CD4017, their clock-enable (CE) pins 2 and 13 respectively must be held ‘low’. These pins are connected to the output of gate N3 (pin 10).
CONSTRUCTION Fig. 3: Actual-size, single-sided PCB layout Fig. 4: Component layout for the PCB 1. The spurious pulses must be ignored. 2. The counter must advance only on the first pressing of the switch for a number and further pressing must be ignored. 3. The pressing of the switch should be effected only after the corresponding number is displayed. To fulfil all these conditions, the dual JK flip-flop IC CD4027 (IC4) is employed and only one of the two flipflops is used.
CONSTRUCTION EDI DWIV S.C. PC INTERFACED AUDIO PLAYBACK DEVICE: M-PLAYER N.V. VENKATARAYALU AND M. SOMASUNDARAM S ounds of various kinds have always fascinated human beings. Many devices have been invented for recording and playing back the sounds— from magnetic tapes to DVD (digital versatile disc), from Adlib cards to high-performance sound cards with ‘surround sound’ capability. For personal computers (PCs), there is a wide variety of such devices.
CONSTRUCTION At frequnecies higher than f2 (f>f2, high end of audio range), capacitors C2 and C3 overcome the effect of potentiometer VR1. As C2 and C3 behave as short, potentiometer VR1 has no effect on the output response. Now, the gain is controlled by treble potentiometer VR2.
CONSTRUCTION The software can be used to play with the following From byte Number Information effects: of bytes • Play normally RIFF chunk: • Play with a 0 4 Contains the characters ‘RIFF’ different playback 4 4 Size of the RIFF chunk rate, i.e.
CONSTRUCTION strcpy(&(Menu[MNU_FILE].Tip[1][0]),“Save as a *.wav file”); strcpy(&(Menu[MNU_FILE].Tip[2][0]),” “); strcpy(&(Menu[MNU_FILE].Tip[3][0]),”Quit the program”); Menu[MNU_FILE].AtX=2;Menu[MNU_FILE].AtY=2; // The EFFECT menu option Menu[MNU_EFFECT].nextMenu=MNU_OPERATION; Menu[MNU_EFFECT].prevMenu=MNU_FILE; Menu[MNU_EFFECT].Child=FALSE; Menu[MNU_EFFECT].num_items=5; for(i=0;i<5;i++) { Menu[MNU_EFFECT].Enabled[i]=FALSE; Menu[MNU_EFFECT].subMenu[i]=NONE; Menu[MNU_EFFECT].
CONSTRUCTION RemoveMenu(MenuID); return(0); } else { if(prevMenu!=NONE) { RemoveMenu(MenuID); return(ShowMenu(prevMenu)); } } break; case RIGHT_ARROW: if(subMenu[CurSelect]!=NONE) { RetVal=ShowMenu(subMenu[CurSelect]); if(RetVal!=0) { RemoveMenu(MenuID); return(RetVal); } } else { if(nextMenu!=NONE) { RemoveMenu(MenuID); return(ShowMenu(nextMenu)); } } break; case DOWN_ARROW: textbackground(LIGHTGRAY); if(Enabled[CurSelect]) textcolor(BLACK); else textcolor(BROWN); gotoxy(StartX+1,StartY+CurSelect+1); cpri
CONSTRUCTION void SetEnvVariables(){} void SaveFile(){} void main() { int ch; textbackground(BLACK);textcolor(LIGHTGRAY); clrscr(); _setcursortype(_NOCURSOR); DrawScreen(); MenuInitialise(); sFileName[0]=0; strcpy(sPlayBackRate,”22400"); for(;;) { DisplayTip(“Ready”); ch=getch(); if(ch==0) ch=getch(); ch+=300; switch(ch) { case AltF:ch=ShowMenu(MNU_FILE);break; case AltE:ch=ShowMenu(MNU_EFFECT);break; case AltO:ch=ShowMenu(MNU_OPERATION); break; } switch(ch) { case FILE_EXIT: ch=AltX; break; case FILE_OPEN
CONSTRUCTION OUTPUT;dlen=NoSamples; BOOL bits16=FALSE; if(wave.fmt.
EAS C I RC ICR CUUII TT I ID D EAS STEPPER MOTOR DRIVER S.C. DWIVEDI PIYUSH P. TAILOR S tepper motors are widely used where precision and accuracy are the primary considerations during rotation or positioning. Microprocessors or microcontrollers are often employed for controlling their operation. But it may not always be convenient or necessary to use microcontrollers, as it would make the gadget unnecessarily costlier.
CIRCUIT ELECTRONIC DIGITAL TACHOMETER IDEAS S.C. DWIVEDI ADITYA U. RANE achometer is nothing but a simple electronic digital transducer. It finds many applications in our T stripe is pasted on the rotating part of the machinery. The reflected light from the contrasting stripe falls on the junc- day-to-day life. Normally, a tachometer is used for measuring the speed of a rotating shaft, gear, or a pulley.
CIRCUIT used for the entire circuit. The circuit shown in Fig. 2 employs 7805 regulator. This 4-digit counter can be readily interfaced to many circuits such as clock-frequency meter, digital voltmeter, tachom- eter (as explained here), stop watch, etc. A reset switch is connected between pin 13 and VCC. IDEAS The chip 74C926 pulls its carry output (pin 4) ‘high’ when the counter reaches 6,000.
CIRCUIT IDEAS PRECISION DIGITAL AC POWER CONTROLLER S.C. DWIVEDI PRATAP CHANDRA SAHU S CRs and Triacs are extensively used in modern electronic power controllers—in which power is controlled by means of phase angle variation of the conduction period. Controlling the phase angle can be made simple and easy if we set different firing times corresponding to different firing angles.
CIRCUIT IDEAS quartz clocks and is readily available in the market. But use of a 1kHz crystal using a quadNAND IC CD4093 as clock generator, as shown in Fig. 2, is better as it provides the exact time interval required. In that case, CD4060 oscillator/divider is not required. The CD4017B counter-cumdecoder IC then divides this 1kHz signal into ten equal intervals, which are programmed via the single-pole, 10-way rotary switch.
June 2000
C O N S T R U C T I O N PORTABLE OZONE GENERATOR K PADMANABHAN, S ANANTHI AND KIRIT PATEL S.C. DWIVEDI T his article is dedicated to the good health of EFY readers in the year 2000 and beyond. It describes an ozone generator for portable (and portable1) use. Ozone gas is now-a-days used for treatment of drinking water, disinfection, and air-purification.
C O N S T R U C T I O N Fig. 3: Actual-size, single-sided PCB layout Fig.
C O N S T R U C T I O N was also noticed. The circuit Metering circuit is more efficient and silent in its discharge. One can easily assemble this portable ozone generator in a plastic breadbox (used for storing one full bread), which is all insulated(with no exposed metal parts) The cost of making a simple unit is much less than Rs 1,000. The air pump used in this project is an aquarium pump which costs less than Rs 100.
C O N S T R U C T I O N circuit has a high-voltage winding for the EHT of the picture tube. This EHT is connected to the electrode (aluminium foil) of the ozone discharge tube. The LOT used should be two-limb type, i.e, the low-voltage windings should be on the left limb of the ferrite core, and the EHT winding (primary and secondary), which is generally epoxy potted, on the right limb. The LOT should have an external EHT diode and not an internally wired EHT diode, as is common in colour television LOTs.
C O N S T R U C T I O N of the LOT winding, in place of the mains rectified 200V DC, as shown in Fig. 2. For testing, one is not required to use 230V directly at all. The same in Fig. 2. For testing, one is not required to use 230V directly at all. The same 12V, or the unregulated 12V prior to the 7812 regulator, can be connected. In Fig. 2, the BA159 anode is shown connected to the mains rectified supply at the positive terminal of the 100uF, 400V electrolytic capacitor.
C O N S T R U C T I O N But now this connection is removed and only the pump is made to work. The end of the aquarium air-pump, which produces air under pressure, is connected by a s short length of tube to the corked glass tube of the discharge tube assembly. The other end of the tube is fixed to another similar polythene tube of adequate length (say, one metre).
C O N S T R U C T I O N CONFERENCE TIMER S.C. DWIVEDI K. UDHAYA KUMARAN VU3GTH D uring a conference where speakers are allotted different time slots for completing their speech, it is essential to use a suitable conference timer which could be programmed for the given time slot. It should not only provide indication as to when the allotted time slot. It should not only provide indication as to when the allotted time is over, but also about the leftover time at any given instant.
C O N S T R U C T I O N Fig. 2: Appliance ‘on/off’ switching application for timer (CD4510B). They convert the BCD code to 7-segment positive logic output code to display the equivalent decimal digits. While displaying decimal digits 9 and 6, their tails are not displayed. The store function available in these ICs is not used in this circuit and hence the store pin 5 of IC1 and IC2 is made permanently low. Fig. 3: Actual-size, single-sided PCB layout Fig.
C O N S T R U C T I O N may be. Due to conduction of diode D7, transistor T2 will be ‘on’ state and thus binary counter (IC5) is in runing condingion. At the same time, ‘auto reset’ transistor T4 will also be in ‘on’ state, with its collector pulled low. Thus, IC5 will continue to operate normally. When slide switch S1 is slided from ‘set’ position to ‘start’ position, the red LED1 immediately glows. Transistor T4 goes to 'cut-off' and its collector transits from 'low' to 'high' state.
T I D E A S C I RC ICR CUUII T IDEAS ADD-ON STEREO CHANNEL SELECTOR RUPANJANA PRABHASH K.P. T he add-on circuit presented here is useful for stereo systems. This circuit has provision for connecting stereo outputs from four different sources/channels as inputs and only one of them is selected/ connected to the output at any one time. When power supply is turned ‘on’, channel A (A2 and A1) is selected.
C I R C U I T ing through the channels continues until it receives an audio signal exceeding the preset threshold value. The skip I D E A S switch S1 is used to skip a channel even if audio is present in the selected channel. The number of channels can be eas- WATER TEMPERATURE CONTROLLER RUPANJANA VIJAY D. SATHE T he circuit presented here controls the temperature of water as well as indicates it on an LED bargraph. When the temperature of water is 0o C, none of the bargraph display LEDs glows.
C I R C U I T when surrounding temperature is 0dig C. (To cater to resistance tolerances and calibration, resistor R6 (22-ohm) and 1kilo-ohm preset VR1 were added at EFY lab. During testing.) Ideally, at 0oC, the bridge has to be in balanced condition and, for other temperatures, the bridge will be unbalanced.
C I R C U I T vides DC path for charging of the battery. But, in the absence of AC mains I D E A S supply, diode D4 is reverse biased and acts as an ‘off’ switch, inhibiting the conduction of diode D3, which allows normal functioning of transistor PARALLEL TELEPHONES WITH SECRECY T2. The inverter can be switched ‘off’, when not required, by using ‘on/off’ switch S1. Low battery voltage indicator circuit comprises transistor T3, senser diode D6, LED 2, variable resistor VR1, and resistors R4 through R6.
C I R C U I T I D E A S S.C. DWIVEDI C.K. SUNITH T he circuit described her is different form conventional door bell circuits in the sense that it can produce two different tones-one of a lower frequency and the other of a much higher frequency. The circuit uses a timer IC 555, which has been wired in free-running mode. When switch S1 is depressed, the circuit oscillates at around 1.5 kHz, resulting in a higher frequency note.
July 2000
CONSTRUCTION BUILD YOUR OWN C-BAND SATELLITE TV RECEIVER S.C. DWIVEDI S. DAS GUPTA atellite TV reception has gained much popularity in India over the last three decades, specially after the live telecasting of the Gulf war by CNN. Both the S-band and C-band satellite signals are available to India. C-band signals are beamed from various satellites like Asiasat, Aralisat, and Insat 2B. In India, the C-band reception is much more popular compared to the S-band.
CONSTRUCTION Fig. 3(a): Block diagram of C-band satellite receiver (b) Polarator: Inside the feed horn, there is a p r o b e , which is req u i r e d to move according to the polarisation of the satellite signals. Fig. 3(b): Pin out of DBS timer with FM demodulator F o r receives the signals from the satellite and large dish assemblies, a motorised focuses them to the focal point where the polarator is prefered. The motor used in feed horn is positioned.
Fig: 4: Circuit diagram of C-band satellite receiver CONSTRUCTION 105 Another important parameter of the LNB is its noise temperature. The noise equivalent temperature of most of the good-quality LNBs ranges from 26 oK to 40 o K (K stands for kelvin). The picture on a 26oK LNB will show less noise compared to that of a 40oK LNB, especially when the received signal is weak.
CONSTRUCTION Fig. 5: Power supply unit band from channel 2 to channel 12) to operate the domestic receiver directly. The block diagram of a satellite receiver is shown in Fig. 3(a). The coaxial cable from LNB is connected to the tuner (which contains RF and IF modules) through ‘F’ socket. To simplify the design for an average constructor, the Mitsumi TSU2-EOIP tuner is used in the circuit. Pinout of the tuner are shown in Fig. 3(b) while its specifications are given in Table II.
CONSTRUCTION Fig. 6: PCB layout for the circuits in Figs 4 and 5 (track-side) with the help of potmeter VR1 (audio B/W control) by changing the voltage at pin 2 (phase comparator section) of IC. Potmeter VR1 generally changes the phase of the audio signal. After processing of the audio IF signal, including its amplification and rectification, an AF output is available at pin 14.
50 ELECTRONICS FOR YOU ❚ JULY 2000 97 Fig. 7: Component layout for the PCB of Fig.
CONSTRUCTION Pin no: Voltage (V): Pin no: Voltage (V): IC2 (NE592) Pin Volt Pin Volt Transistors T1 T2 T3 T4 T5 T6 Fig. 8 TABLE III IC1 (NE 564) 4 5 6.5 6.5 12 13 2 2 1 7.5 9 1 2 1.5 10 4.5 3 1 11 1 1 9V 11 8.5V 2 0V 12 8.5V 3 9V 13 0V Base 3.2V 7V 8.2V 7V 7V 2V Emitter 3.2V 7V 8.2V 7V 7V 0V Collector 7V 12V 12V 12V 12V 2V 4 8.5V 14 9V 5 0V Testing 6 3 14 4 7 1 15 1.5 8 0 16 0.5 6 0V 7 9V 8 9V 8 0V 10 12V with component side serving as a ground plane.
CONSTRUCTION EPROM-BASED PROGRAMMABLE NUMBER LOCK RUPANJANA JUNOMON ABRAHAM M ost of the code lock/number lock Please note that its reset pin 4 is concircuits presented in EFY so far nected to output A = B (OA=B) pin 3 of have been based on discrete comparator IC4 (CD4585). Thus, as long TTL and/or CMOS ICs. This circuit is based on a familiar EPROM 27C32, wherein the required code is stored. It is a number lock, which can be programmed to any coded number. The length of the number can also vary.
CONSTRUCTION Fig. 2: Acutal-size, single-sided PCB layout Fig. 3: Component layout for the PCB grounded in this circuit. With each clock pulse from IC1, the counter IC2 output increments by one and so also the address of EPROM. Since the clock pulses from IC1 are also being applied to clock pin 6 of 4-bit shift register IC5 (CD4035), let us examine how the data at its input pins 3, 4 (K, J) and output pin 1 (O0) changes.
CONSTRUCTION ally via IC5 with the help of switches S1 (marked zero) and S2 (marked one). A ‘zero’ is entered by momentarily depressing switch S1 alone, and a ‘one’ is entered by depressing switch S1 momentarily, after holding switch S2 in the pressed condition. The ‘D0’ bit of EPROM and ‘O0’ bit of shift register (CD4035) are compared by magnitude comparator (CD4585).
EAS C I RC ICR CUUII TT I ID D EAS POWER-SUPPLY FAILURE ALARM S.C. DWIVEDI M.K. CHANDRA MOULEESWARAN M ost of the power-supply failure indicator circuits need a separate power-supply for themselves. But the alarm circuit presented here needs no additional supply source. It employs an electrolytic capacitor to store adequate charge, to feed power to the alarm circuit which sounds an alarm for a reasonable duration when the mains supply fails.
CIRCUIT lector and emitter of the in-built transistor) is connected to the two terminals of the ‘=’ (of Casio FX-82LB used during actual testing at EFY) button’s keypad tracks, with collector connected to the more positive terminal than the emitter. Thus, once every second the ‘=’ button is activated.
CIRCUIT in 1-volt steps. Dial II has ten resistors of 1,100-ohm value each. This dial is marked from 0 to 0.9 volt in 0.1 volt steps. Dial III has eleven resistors, having a value of 1,210-ohm each, with dial marking from 0 to 0.09 volt in 0.01 volt steps. The values of the resistors in a given ring are 1.1 times the values of the resistors in the preceding ring. The bridge shown in the illustration would read the value of unknown voltage as 6.
CIRCUIT IDEAS gins to count in a particular sequence, as shown in Table I. Whenever the output of a flip-flop goes high, the associated transistor connected at its output saturates. It drives current through the array of LEDs connected as collector load, thereby causing them to turn ‘on’. Upon arrival of first clock pulse, the LSB will be set. The counter will now count 0001. This means that the array of LEDs at the centre of the display panel will be lit.
CIRCUIT Fig. 2 successive overloads. Under this condition, the system has to be manually reset. (Successive overload condition indicates that the inverter output is short-circuited or a heavy current is being drawn by the connected load.) The circuit uses an ammeter (0-30A) as a transducer to detect overload condition. Such an ammeter is generally present in almost all inverters. This ammeter is connected between the negative supply of the battery and the inverter, as shown in Fig. 2.
CIRCUIT tive half cycles and off-period of ring signal. Once the handset is picked up, the relays will still remain energised because of low-impedance DC path available (via cradle switch and handset) for the in-built diode of IC1. After completion of call when handset is placed back on its cradle, the low-impedance path through handset is IDEAS no more available and thus relays RL1 through RL3 are deactivated.
August 2000
CONSTRUCTION DISPLAY SCHEMES FOR INDIAN LANGUAGESPART I (HARDWARE AND SOFTWARE) K. PADMANABHAN, S. ANANTHI, K. CHANDRASEKHARAN, AND P. SWAMINATHAN F or displaying text of Hindi, English, or any other Indian language on a TV-like screen, as may be required for public announcements or for educative programs etc, presently there are two possible ways: 1.
CONSTRUCTION Fig. 1(a): Schematic diagram of 8085 microprocessor based multilingual display system (memories and decoder portion) our other Indian languages, we cannot manage to use even a simple font within this 8 x 8 matrix (which needs one byte per line or 8 bytes per character). The smallest size in Indian language requires a 12 x 12 matrix, and hence we need 1.5byte space horizontally and a total of 12 x 1.5 = 18 bytes space for each letter.
CONSTRUCTION Fig. 1(b): 6845 character and video generator portion of multilingual display system The character generator is just a list of dots for the characters in an order. It does not necessarily require any hardware. Though such a list of dots, if stored in this order in an EPROM, can be a hardware component. In the PC based design, this is just a file containing the dot patterns, while in the design using a dedicated CRT controller with a microprocessor, this is actually a hardware component, i.e.
CONSTRUCTION Fig. 2: Keyboard for English, Hindi, and Tamil languages just as in ‘d’, with 64 being the code. The table low-address is also 10 64 and the high address equals 10 64 Fig. 3: Character code + 80, and so generation in 12x12 format on.
CONSTRUCTION TABLE I: ASCII Key Codes for English, Hindi, and Tamil languages 124
CONSTRUCTION Program in BASIC for Computer Based Display for English, Hindi, Tamil, etc Languages dim C(3,2048),ad(3,257),d(12),q(8) open “chtamil2” for random as #1 len=1 field #1, 1 as A$ cls total%= LOf(1) for lan%=1 to 3 for i%= 0 to 255 ‘total% get #1 ‘get one byte rem pick and store the address for all 256 codes a= asc(a$) ‘ print a; ad(lan%,i%) = a rem low address in 00-7F and high add.
CONSTRUCTION This involves a simple 8085 microprocessor and an additional CRT controller. The dedicated CRT controller chip 6845 has been popular ever since it was first used by the IBM in its display controller cards. The circuit of this board is shown in Figs 1(a) and 1(b). It comprises: 1. Video generation circuitry including dot and character clocks. 2. Pixel or video RAM. 3. Character dot pattern EPROM for four languages 4. 8085 firmware on EPROM for four languages 5. 6845 CRT controller IC. Fig.
CONSTRUCTION 8085 µP-KIT BASED SIMPLE IC TESTER pin ZIF socket and two hex buffer 7407 ICs. The +5V supply needed for the interface circuit (and ground) is obtained from the kit’s power supply itself. The total cost of the interface circuit would be less than Rs 300. RUPANJANA Both the 8255s have been configured for mode ‘0’ operation (which is a basic S.
CONSTRUCTION IC Tester Program Environment MEMORY MAP (MAY VARY FROM KIT TO KIT): RAM LOCATIONS USED FOR PROGRAM STACK POINTER INITIALISED PORTA (OUTPUT) OF A8255/B8255 PORTB (OUTPUT) OF A8255/B8255 PORTC (INPUT) OF A8255/B8255 CONTROL WORD REGISTER OF A8255/B8255 : 9200H - 9450H : 9FFFH : 08/10 : 09/11 : 0A/12 : 0B/13 PROGRAM LISTING Label Mnemonics Comments LXI SP,9FFFH LXI H,93A0H MVI A,00H MVI B,00H CALL OUTPT ;(UTILITY SUBROUTINE IN THE KIT ; TO DISPLAY ACC CONTENT) 920D CD640A* CALL RDKBD ;(UTILITY
INR C ; NEXT INPUT COMBINATION MOV A,C CPI 02H ; CHECK IF ALL INPUT COMBINATIONS ARE OVER JNZ LP2 JMP GOOD ; OR JMP GOOD1 MVI C,00H ; SET GATE INPUTS MOV A,C RLC ORI 01H ; SET GATE OUTPUT 1 MOV B,A CALL PROCESS INR C ; NEXT INPUT COMBINATION MOV A,C CPI 04H ; CHECK IF ALL INPUT COMBINATION ARE OVER JNZ LP3 JMP GOOD ; OR JMP GOOD1 MVI A,89H ; (8255 CONTROL WORD FOR CONFIGURING REG. ; A & B AS O/P AND REG.
CONSTRUCTION 9380 9383 9386 9388 938A 31FF9F 211094 3E00 0600 CD160B GOOD1: LXI SP,9FFFH LXI H,9410H MVI A,00H MVI B,00H CALL OUTPT 938D 76 ;DATA TABLE ;NAND ;AND 9300 24 9310 00 9301 09 9311 00 9302 2D 9312 09 9303 2D 9313 24 9304 36 9314 12 9305 1B 9315 12 9306 1B 9316 3F 9307 36 9317 3F ; (UTILITY SUBROUTINE IN THE KIT TO ; DISPLAY ACC CONTENT) HLT ;OR 9320 00 9321 00 9322 2D 9323 2D 9324 36 9325 1B 9326 3F 9327 3F ;EXOR 9330 00 9331 00 9332 2D 9333 2D 9334 36 9335 1B 9336 1B 9337 36 ;NOT 9340 2A
CUIT IDEAS C I RC ICR U IT IDEAS LOW-COST PCO BILLING METER S.C. DWIVEDI DHURJATI SINHA T he circuit presented here can be used in PCOs for displaying the actual bill. The overall cost of this circuit is less than Rs 200 while a commercial equipment serving similar pur- pose may cost more than Rs 10,000 in the market. The comparative disadvantages of the presented circuit are as follows: 1. The calculator used along with this circuit is required to be switched ‘on’ manually before making a call. 2.
CIRCUIT IDEAS AUTOMATIC MUTING CIRCUIT FOR AUDIO SYSTEMS S.C. DWIVEDI SUNISH P. F ig. 1 shows a muting circuit, which makes use of IC LB1403. Signal from any preamplifier, such as HA1032, LA3161, or LA3160, is connected to the base of amplifier transistor T1. Variable resistor VR1 is used to control the gain of input signal.
CIRCUIT change line to telephone 2, the person at telephone 1 may inform the person at telephone 2 (in the intercom mode) that he is going to changeover the line for use by him (the person at telephone 2). As soon as changeover switch S3 is flipped to the other position, 12V supply is cut off and telephones 1 and 3 do not get any voltage or ring via the ring-tone-sensing unit.
CIRCUIT transistor T2. The transistor T2 will be enabled only when the charging capacitor raises its base potential to overcome the reverse bias voltage at its emitter. Thus, capacitor C6 and resistor R6 determine the duration of the on-delay, which is approximately three minutes for the given values. As soon as relay RL1 energises due to the switching action of transistor T2, the boosted voltage appears at the output. The adjustment of trimpot VR2 controls the IDEAS bucking point.
September 2000
CONSTRUCTION DISPLAY SCHEMES FOR INDIAN LANGUAGESPART II (HARDWARE AND SOFTWARE) K. PADMANABHAN, S. ANANTHI, K. CHANDRASEKHARAN, AND P. SWAMINATHAN T he 6845 is a programmable CRT controller, which can be programmed so as to generate a raster with the desired number of horizontal and vertical raster lines [refer Fig. 1(b)]. For detailed explanation of its programming method for an application using 6845 CRTC, you can refer chapter 16 of the book ‘Learn to Use Microprocessors’ published by EFY.
CONSTRUCTION Fig. 5: Actual-size, component-side track layout for the schematic diagram of Fig. 1 each) and then coupling it to the base of transistor BC148B to invert the sync signals at its collector. The video signal is the dot pattern obtained from the shift register IC 74LS165. This register is loaded at each character-clock beginning. The shifting is accomplished by the dot clock. Pin 7 of IC 137 74LS165 outputs the dot pattern.
CONSTRUCTION a new key is typed. The data bus lines are likewise connected by a 74LS245 bidirectional buffer. The pixel data for the typed-in character must be written into the video RAM, after reading the table of dots stored in the character code EPROM and writing the same into the video RAM. The table of data (dots) for each language occupies a 2k memory area, and hence four languages can be selected by address lines A11 and A12 of the character generator EPROM.
Fig. 7: Component layout for PCB EPROM. 2. Since 12 horizontal dots per character are insufficient for an Indian language, a 12 x 12 matrix is chosen, though English appears as an expanded font. The hook characters in Hindi like ‘Hu’ and ‘hoo’ need one more dot—the 13th dot— vertically. The hook characters are non139 a portal dedicated to electronics enthusiasts www.electronicsforu.
CONSTRUCTION space-moving characters in the standard typewriters of the Indian languages. Particularly in Hindi, there are multiple hooks, such as in ‘hoom’. In the typewriter, the hook characters do not advance (move space) after they are typed. The program checks the code, and if it is a hook code, it does not write immediately the dots corresponding to that hook into the video memory, but waits for the succeeding keyboard stroke(s) for a non-hook character to follow before shifting the cursor.
CONSTRUCTION Errata for Part I of the article 1. Refer Fig. 1(a). Please renumber data pins 9 through 11 and 13 through 17 of (Appendix I) Addr.
CONSTRUCTION 0168 0169 016A 016C 016D 47 1A E6 0F B0 12 MOV B,A LDAX D ANI 0FH ORA B STAX D ;Save in B ;Read video RAM ;store in video RAM (only alter left nibble) 016E 23 INX H 016F 1B DCX D 0170 C3 2B 01 JMP NXTLIN ;JUMP TO NEXT LINE 0173 46 LOAD_RT: MOV B,M ;NIBBLE IN B 0174 1A LDAX D ;Get from video ram 0175 E6 F0 ANI F0H ;save left nibble 0177 B0 ORA B 0178 12 STAX D 0179 23 INX H 017A 7E MOV A,M ;get next nibble 017B 17 RAL 017C 17 RAL 017D 17 RAL 017E 17 RAL 017F 47 MOV B,A ;save in B, left part
CONSTRUCTION 0294 DA A5 02 JC RIG_NIB ;LEFT NIBBLE ROUTINE 0297 3E FF LEFT_NIB: MVI A,FFH 0299 13 INX D 029A 1A LDAX D 029B E6 0F ANI 0FH 029D 06 F0 MVI B,F0H 029F B0 ORA B 02A0 12 STAX D 02A1 1B DCX D 02A2 C3 6F 02 JMP NXTL ;RIGHT NIBBLE 02A5 1A RIG_NIB: LDAX D 02A6 E6 F0 ANI F0H 02A8 06 0F MVI B,0FH 02AA B0 ORA B 02AB 12 STAX D 02AC 13 INX D 02AD 3E FF MVI A,FFH 02AF 12 STAX D 02B0 1B DCX D 02B1 C3 6F 02 JMP NXTL ;COMPARE HOOK CHARACTER (TAMIL) 02B4 FE 50 CHOOKT: CPI 50H 02B6 CA D0 02 JZ NM 02B9 FE 70
CONSTRUCTION 03CA 3A 29 11 THIRL: 03CD CD 29 11 03D0 5F 03D1 16 14 03D3 3A 28 11 03D6 17 03D7 17 03D8 17 03D9 17 03DA E6 F0 03DC 47 03DD 3E 0C 03DF B0 03E0 32 00 18 03E3 3A 25 11 03E6 1F 03E7 DA F1 03 03EA 7E 03EB 12 03EC 23 03ED 7E 03EE 13 03EF 12 03F0 C9 03F1 7E R: 03F2 0F 03F3 0F 03F4 0F 03F5 0F 03F6 E6 0F 03F8 47 03F9 1A 03FA E6 F0 03FC B0 03FD 12 03FE 13 03FF 7E 0400 07 0401 07 0402 07 0403 07 0404 E6 F0 0406 47 0407 23 0408 7E 0409 0F 040A 0F 040B 0F 040C 0F 040D E6 0F 040F B0 0410 12 0411 C9 ;KEYBOAR
CONSTRUCTION 04F1 04F2 04F3 04F4 04F5 04F7 04FA 04FB 77 04 13 78 FE 10 C2 EB 04 C9 55 40 46 09 TABL EINIT: 04FF 12 08 10 11 0503 00 10 00 0B 0507 00 00 00 00 ;CLEAR SCREEN ROUTINE 050B C5 CLEAR: 050C E5 050D 0E 00 050F 0D A1: 0510 CA 28 05 0513 26 14 0515 2E 00 0517 79 0518 32 00 18 051B 3E FF A3: 051D 77 051E 2C 051F 7D 0520 FE 80 0522 C2 1B 05 0525 C3 0F 05 0528 E1 A2: 0529 C1 052A C9 0700 0700 TABLE1: 0700 FF FF FF FF 0704 FF FF FF FF 0708 FF FF FF FF 070C FF FF FF FF 0710 FF FF FF FF 0714 0718 071C 07
CONSTRUCTION DIGITAL CODE LOCK RUPANJANA BISWAJIT GUPTA A versatile digital code lock circuit is presented here, which can have up to 32-digit long secret code. The length of the secret code can be easily varied by changing the position of jumpers. The available options are to make the code 2-, 4-, 8-, 16-, or 32-digit long. When the keyed-in code matches with the stored secret code, a relay gets energised.
CONSTRUCTION quad 2-input ORgate chip, of which only one gate is used here. This gate is wired as a reset circuit (both for auto and manual reset operation) for IC8 and IC6. One can reset both the counters (IC6 and IC8) manually, by pressing reset switch S3. Auto-reset function will take place whenever preset number of digits of secret code has been entered, either for verification/operation or for registration. In verification mode, the secret code would either be right or wrong.
of data into the RAM, while 8-bit comparator IC3 is disabled. Thus, the keyboard data (corresponding to a pressed key) at the output of IC1, buffered by IC2, is present at D4 through D7 pins of RAM (IC5). This data gets stored at an address corresponding to the selected page, via 4way DIP switch S2, and its location is determined by outputs Q1 through Q5 of 12-bit counter IC8.
CONSTRUCTION can be assembled on a 12x10 cm single-sided, general-purpose PCB, using a few wire jumpers. However, an actual-size, single-sided PCB for the complete circuit shown in Fig. 1, and that of power supply in Fig. 2, is shown in Fig. 3. The component layout for the PCB is shown in Fig. 4. The total cost of construction of this circuit will not exceed Rs 800. The use of IC bases for ICs will be a good practice.
EAS C I RC ICR CUUII TT I ID D EAS BINARY TO DOTMATRIX DISPLAY DECODER/DRIVER RUPANJANA JUNOMON ABRAHAM D otmatrix display is suitable for displaying alphanumeric characters and symbols. Dedicated dotmatrix display driver ICs are available, but these are costly and not easily available commercially. It would therefore be wise to make your own dotmatrix display, using easily available common ICs.
CIRCUIT counter IC CD4060, repetitively outputting the required bit pattern, corresponding to bit pattern for ‘Z’ in this case. Fig.
CIRCUIT ters only to numerics, capital English letters, and some symbols. You are at liberty to store bit patterns for any other data, in any other style, in the EPROM. The input ‘BI’ indicating blanking input (actually this is the OE signal of EPROM) can be used for blanking the IDEAS display. You can also use this line for converting it into a blinking display by connecting it to a suitable output pin of counter CD4060.
CIRCUIT IDEAS fan run at the three speeds for an equal amount of time by connecting three decimal decoded outputs of IC3 to each of the transistors T1 to T3. One can also get more than three speeds by using an additional relay, transistor, and associated components, and connecting one or more outputs of IC3 to it. In the motors used in certain coolers BLOWN FUSE INDICATOR S.C. DWIVEDI ASHUTOSH KUMAR SINHA G enerally, when an equipment indicates no power, the cause may be just a blown fuse.
CIRCUIT tion, using presets VR3 and VR4. For electronic loads such as TV and VCR, the ontime delay may be set for 10 seconds to 20 seconds. For refrigerators, the delay should be preset for about 2 minutes duration, to protect the compressor motor from frequently turning ‘on’ and ‘off’. In this circuit, the on-time and offtime delays depend on charging and discharging time of capacitor C1. Here the discharge time of capacitor C1 is quite less to suit our requirement.
CIRCUIT IDEAS ONE BUTTON FOR STEP, RUN, AND HALT COMMANDS S.C. DWIVEDI (BASED ON MOTOROLA APPLICATION NOTE) T he logic signals to step, run, and halt a computer or other appropriate digital devices or system may be generated by this circuit, which is operated by just a single pushbutton. The only active devices used are a dual tarily. The run command occurs if the button is held down for a time exceeding about 300 ms.
October 2000
CONSTRUCTION MOSFET-BASED 50Hz SINEWAVE UPS-CUM-EPS S.C. DWIVEDI PARTS LIST R.V. DHEKALE AND S.D. PHADKE M ost of the UPS (uninterrupted power supplies) available in the market internally use a frequency ranging from 100 Hz to 50 kHz. The regulation of output voltage is done using the pulse width modulation technique, which produces a quasi-square waveform output from the inverter transformer.
Fig. 2: Schematic diagram of MOSFET-based sinewave inverter optional circuit of no-load/over-load protector (within dotted lines) CONSTRUCTION 158 7473, which produces the two 50Hz squarewave outputs at its pins 8 and 9 with a phase difference of 180 degrees between the two. One of the outputs is coupled to the base of transistor T1 through diode D1 and series current-limiting resistor R3, while the second output is given to the base of transistor T2 through diode D2 and series resistor R4.
CONSTRUCTION Fig. 3: Battery current vs load (squarewave O/P) Fig. 4: Battery current vs load (sinewave O/P) shown in the circuit. Drains of MOSEFTs of one bank are connected to one extreme taping of 9-volt primary of the inverter transformer X1, and that of the MOSEFTs of the second bank are connected to the other extreme 9-volt taping of the same transformer. Centre tap of the primary is directly connected to the positive terminal of 12V, 7Ah battery.
CONSTRUCTION Fig. 6: Actual-size solder-side track layout for the PCB. and capacitor C2 on the secondary side act as filter/resonant circuit (at 50 Hz) to produce a waveform approaching a sinewave. LED1, when ‘on’, indicates that the system is on back up. Charger circuit. This circuit comprises step-down transformer X2, followed by rectifier, regulator, and doublechangeover 12V relay RLY. Mains supply of 230V AC is applied across the primary of the transformer through triac BT136.
225V AC. This enables the user to take timely action such as saving data (in case load comprises a computer). Battery deep-discharge cut-out. If the UPS system keeps operating in the inverter mode, the battery voltage will drop eventually to prohibitively low level (say, 5 volts). If such condition occurs frequently, the life of the battery will be considerably reduced. To remove this drawback, it is necessary to use battery deepdischarge cut-out circuit. If battery voltage goes below 9.
CONSTRUCTION Fig. 7: Component layout for the PCB while the comparator circuit is identical to over-voltage comparator. And hence, no separate explanation is required to be included. The output of the circuit is connected to the gate of SCR1 in Fig 2. Spike suppression. Since triac TR is connected in series with the primary of charging transformer X2 and gate voltage is obtained from the under-/over-voltage cut-out, a spike is treated on par with the over-voltage (>270V) condition.
CONSTRUCTION Fig. 8: Wiring diagram of chasis/panel mounted components to the PCB transformer of 32-amp primary rating, the power of the UPS-cum-EPS can be increased to 500 watts or 625 VA. The transformer ratings as mentioned above are applicable for squarewave output. The transformer primary rating will be 25 per cent higher in case of sinewave output. Also the number of MOSFETs per bank should also be correspondingly higher.
CONSTRUCTION R-2R D/A CONVERTER-BASED FUNCTION GENERATOR USING PIC16C84 MICROCONTROLLER PRASANNA WAICHAL D igital to analogue conversion is a process wherein the analogue output voltage or current is a function of the digital input word (binary S.C. DWIVEDI code). D to A converters (DACs) find extensive application in analogue input-output (I/O) systems, waveform generators, signal processors, motorspeed-controllers, voice synthesisers, attenuators, etc.
CONSTRUCTION PARTS LIST Semiconductor: IC1 - PIC16C84, microcontroller D1-D5 - 1N4148 switching diode LED1-LED5 - 0.3-inch dia red LED Resistors (all ¼-watt, ±5% carbon, unless stated otherwise): R1, R15-R23 - 10-kilo-ohm R2-R6 - 560-ohm R7-R14 - 20-kilo-ohm Capacitors: C1, C2 - 27pF ceramic disk Miscellaneous: XTAL - 3.575545MHz crystal S1 - Push-to-on switch its variants are used in most of the integrating type DACs.
CONSTRUCTION Application Fig. 8: Software flowcharts for generation of various waveforms The low-cost R-2R ladder-type DAC (Fig. 2) requires no power supply at all, nor any active components such as buffers, op-amps, and storage registers. Its linearity is very good. Just give the digital input and take the analogue output.
The 8-bit port-B of this device has been used as an output port, which is directly connected to the DAC. The 5-bit port-A has been used both to input keypress data and to output display data to the LEDs. Actually, the I/O pins on this port are time-shared/multiplexed between the keys and the LEDs. This means the same lines are used at one time for reading the keys and at another time for outputting data to drive the LEDs directly.
CONSTRUCTION APPENDIX ‘A’ Assembly language program for implementation of function generator using PIC16C84 ERRORLEVEL –302 INCLUEDE
T I D E A S C I RC ICR CUUII T IDEAS SIMPLE SWITCH MODE POWER SUPPLY age rating of capacitors C7 and C8 should be at least twice the secondary output of each secondary section. BY396 rectifier diodes shown on the secondary side can be used for a maximum load current of 3 secondary (output). Ensure that each winding is separated by an insulation layer. Two separate heat sinks are to be provided for the two transistors (BU208D). The filter capacitor for mains should be of at least 47µF, 350V rating.
‘bUSY’. The last two displays are not used in the word ‘bUSY’. Rails ‘A’ and ‘B’ are active low for the common-anode displays used here. Segments that are to be always ‘off’ are left disconnected and are shown as hollow lines. Those segments which are either lit during ‘toiLEt’ display (pulled ‘low’ via bus ‘A’) or during ‘bUSY’ display (pulled ‘low‘ via bus ‘B’) are shown shaded in the figure. Connect a +5V supply rail to the common anode pin of all the displays.
C I R C U I T ‘low’ or v i c e versa). The outputs of flip-flops drive the c o r r e sponding relays, in conjunc- I D E A S tion with the four relay driver transistors SL100. The wires earlier removed are connected to this circuit. On the switch panel board, the micro-switches are connected, and under the board the connections are wired as suggested above. Relays RL1 though RL4 are 9V, SPSTtype micro-relays of proper contact ratings.
counter upon every depression of switch S1. Upon the arrival of first clock edge, the counter advances to 001. The outputs of the counter go to IC4 (IC 74138), which is a 3-line to 8-line decoder. When IC4 receives the input address 001, its output Q1 goes low, while other outputs Q0 and Q2 through Q7 stay high. The output Q1, after inversion, drives transistor T1, which actuates relay RL1. Now power is delivered to the fan through the N/O contact RL1/1 of relay RL1 and the tapped resistor RT.
C I R C U I T TELEPHONE RINGER USING TIMER ICs I D E A S RUPANJANA PRABHASH K.P. U sing modulated rectangular waves of different time periods, the circuit presented here produces ringing tones similar to those produced by a telephone. The circuit requires four astable multivibrators for its working. Therefore two 556 ICs are used here. The IC 556 contains two timers (similar to 555 ICs) in a single package. One can also assemble this circuit using four separate 555 ICs.
November 2000
CONSTRUCTION PC-TO-PC COMMUNICATION USING INFRARED/LASER BEAM RUPANJANA K.S. SANKAR S erial communication between two PCs has been covered earlier too in EFY. However, two separate ICs (1488 and 1489) were used in those projects (for TTL to RS-232C and viceversa level conversion), using wireless radio wave technology. This level conversion required use of three different voltages, i.e. +12V, -12V and +5V.
CONSTRUCTION and both PCs ‘think’ that there is a null modem cable connected between them. Table II shows the correspondence between the various pins of a 9pin (or 25-pin) ‘D’ connector of serial port of PC. In some PCs, the serial port is terminated into a 9-pin ‘D’ connector and in some others into a 25pin ‘D’ connector. Testing Assemble two transceiver modules and connect each of them, using 3-core cables, to Com-1 ports of the two PCs.
CONSTRUCTION with the torch on the photodiode. LED1 should flicker at the burst frequency rate of the transmitter. This proves that the IR signals are being detected by photodiodes and converted into RS232-compatible levels by the MAX232 and output at pin 7 of MAX232 ICs is available for the PC to read the pulses.
CONSTRUCTION Program Listing for PC-to-PC Communication in C /* PROGRAM FOR LASER / IR COMMUNICATION BETWEEN TWO PCs */ /* by K.S.Sankar for EFY Nov/Dec’2000 */ #include /* Header Files */ #include #include #include #include
CONSTRUCTION cprintf(“ Press any key to quit .”); getch(); main(); } goto loop; } else if(!kbhit()) { st[flag] = inp(COM);/*Get character from Com1 port */ flag++; bytecount++; ot = clock()/18.
CONSTRUCTION TABLE X Line Status Register Bits ing corruption of the data. Finally, we succeeded, after modification of the circuit as shown in Fig. 3. We were able to flawlessly transfer files, from about 5metre distance, between two 386-based PCs. We included a 38kHz modulator in the transmitter section and used IR receiver module, which includes a bandpass filter and demodulator for 38kHz carrier.
CONSTRUCTION MULTI-EFFECT CHASER LIGHTS USING 8051 MICROCONTROLLER ADITYA U. RANE S.C. DWIVEDI T he 8051 microcontroller, first de- follows: — 8-bit CPU with register A (accuveloped by Intel, finds many applications in small development mulator) and register B. — 16-bit program counter (PC). systems such as speed control of DC — 16-bit data pointer (DPTR). motors, timers, process-control applications, and temperature controllers.
CONSTRUCTION Pins P3.0 (RXD) P3.1 (TXD) P3.2 (INT0) P3.3 (INT1) P3.4 (T0) P3.5 (T1) P3.6 (WR) P3.7 (RD) cussed relates to its input-output (I/O) ports. The 8051 has a total of four 8-bit ports, namely, P0, P1, P2, and P3. P0. The P0 port may be used as input, output, or as combined low-order address and a bidirectional data bus for external memory, which is an alternate function. P1. Port P1 does not have any alternate function.
PARTS LIST Semiconductors: IC1 - 8051 microcontroller IC2 - 74373 octal ‘D’ type latches IC3 - 2764 EPROM 8-kbytes IC4 - 7805 regulator +5V T1-T8 - BC547 npn transistors TR1-TR8 - BT 136, triac LED1-LED8 - Red LED Resistors (all ¼-watt, ±5% carbon, unless stated otherwise): R1-R16 - 560-ohm R17 - 47-ohm R18 - 10-kilo-ohm Capacitors: C1, C2 - 30pF ceramic disk C3 - 100µF, 16V electrolytic C4, C5 - 10µF, 25V electrolytic Miscellaneous: XTAL - 12MHz quartz crystal L1-L8 - L1 through L8 could each be a series o
CONSTRUCTION Program Listing For Multi-effect Chaser Lights Add.
T I D E A S C I RC ICR CUUII T IDEAS AUTOMATIC BATTERY CHARGER S.C. DWIVEDI YASH DEEP N ormally, chargers available in the market do not have any sort of control except for a rotary switch that can select different tappings on a rheostat, to vary the charging current. This type of control is not adequate because of the irregular fluctuations in the mains supply, rendering the control ineffective. A simple circuit intended for automatic charging of lead-acid batteries is presented here.
C I R C U I T The reference terminal of regulator (IC3) is kept at 3.9V using LED2, LED3, and diode D6 in the common lead of IC3 to obtain the required regulated output (15.9V), in excess of its rated output, which is needed for proper operation of the circuit. This output voltage is fed to the base of transistor T3 (BC548), which along with transistor T4 (2N3055) forms a Darlington pair. You get 14.
C I R C U I T ‘zero cal’. Now increase mV input to 21.85 (corresponding to 400oC). Then vary VR2 till +out terminal is at 430mV (temp. +RT). This is ‘gain cal’. Now, as VR1 and VR2 are interdependent, you may have to repeat ‘zero cal’ and ‘gain cal’ a few times till you get the above values. Properties of J thermocouple and design aspects of gain block used in the temperature measurement instrument are summarised below: J Thermocouple (ANSI Symbol ‘J’) 1.
C I R C U I T hence the melody generator UM66 (IC1) does not get any power supply and is thus off. When bell switch S1 is pushed (closed), the audio output from module 1 is shorted to ground and at the same time transistor T1 base is pulled to ground via resistor R3. As a result, transistor T1 is cut off, to pull I D E A S its collector high. The voltage at collector of transistor T1, after limiting by zener ZD1 to 3V, serves as power supply for melody generator UM66.
C I R C U I T I D E A S sary drive given to triac5. Similarly, when outputs Q6 through Q9 become high, triac-4 through triac1 go off one by one and the earlier lit up bulbs go off last. The second part of the sequence is also over and then the PROXIMITY DETECTOR RUPANJANA K.S. SANKAR T his proximity detector is constructed using an infrared diode detector.
December 2000
CONSTRUCTION ELECTRONIC BELL SYSTEM Dr D.K. KAUSHIK I n this innovative project, a simple electronic bell system using commonly available ICs is presented for use in educational institutes. This simple and easy-to-fabricate project has the following features: • It sounds the bell automatically after every period of 40 minutes. • It displays in digital form the current time and period number of the class going on. • The system automatically switches off after the last period (11th period).
Fig. 2: Schematic diagram of electronic bell system for institutes CONSTRUCTION 192 mon-cathode 7-segment displays, and a few passive components. For more details of the digital clock, the readers may consult ‘Car Clock Module’ project in September 1986 issue or Electronics Projects (Vol. 7) published by EFY. Push-to-on switches S1 and S2 (slow and fast time set) may be used to set the time of the digital clock. (Note.
CONSTRUCTION tinue to work as usual and hence the accuracy of the periods is Fig. 3: Pin configuration of MM5369 not affected by the ‘on’ and ‘off’ times of transistor T4. To count and display the current period, a two-digit counter is designed using two CMOS decade counter cum 7segment decoder/driver CD4026 ICs (IC5 and IC6) and two 7-segment common-cathode displays (LT543). The pulse obtained every 40 minutes from pin 3 of IC10 is also connected to the input of this two-digit counter.
CONSTRUCTION Fig. 6: Component layout the period display from 00 to 01 (indicating that the first period has started). Hereafter, the circuit works automatically, sounding the bell for a few secondsafterevery40minutes.Intheevening,after theeleventhperiodisoverandtheinstituteistobe closed, the power supply to parts II and III of the circuit gets automatically switched off. Though the ringing of bell and display of periods discontinue, the digital clock continues to work as usual.
CONSTRUCTION SIMPLE TELEPHONE RECORDING/ ANSWERING MACHINE S.C. DWIVEDI B.B. MANOHAR T his project is intended to provide you with a simple recording and answering machine, which in the absence of the subscriber/owner of the telephone instrument, responds to the incoming calls and also records them automatically. Description handset) carry 50V DC. However, during ringing, the lines carry 133Hz, 80V AC (modulated pulses), as shown in Fig 5.
CONSTRUCTION transistor T1 is pulled ‘low’. This lowgoing pulse is coupled to trigger pin 2 of timer NE555 (IC1) configured as monostable (retriggerable). The output pulse width of IC1 is given by the relationship Pulse width = 1.1 R4 x C3 … seconds Fig. 3: Line diagram of telephone recording/answering machine showing interconnection amongst accessories used in the system tance of transistor T1) acts as voltage/ current limiting network for transistor T1.
CONSTRUCTION microprocessor interface; otherwise both chips are identical.) Fig. 5: Ringing tone timing waveform Important points IC4 via relays. If we use C90 cassette tapes for the incoming calls, and assuming that pulse width of timer IC4 is set for 3 minutes, we can record/ answer 15 incoming calls, since we can use only one side of the tape in this set-up and hence we can play/record the messages for 45 minutes only.
CONSTRUCTION PARTS LIST (Fig. 2) Semiconductors: IC1, IC4 - NE555 timer IC2 - CD4017 decade counter IC3 - CD40106 inverter IC5 - 7812 regulator (+12V) T1 - BC547 npn transistor D1-D7 - 1N4007 rectifier diode LED1, LED2 - Red LED Resistors (all ¼-watt, ±5% carbon, unless stated otherwise): R1 - 100-kilo-ohm R2, R7 - 4.7-kilo-ohm R3, R4, R8 - 10-kilo-ohm R5 - 33-kilo-ohm R6 - 2.2-ohms R9, R10 - 1-kilo-ohm VR1 - 1-mega-ohm preset Capacitors: C1, C2, C4, C5 - 0.
C I R C U I T MULTICHANNEL CONTROL USING SOFT SWITCHES I D E A S S.C. DWIVEDI P. SABARINATHAN T his circuit uses only one octal Dtype latch, IC 74LS373, and some associated circuitry to control eight different gadgets. To control more devices, identical circuits, in multiples, can be used. The circuit incorporates the following features: (a) Individual ‘on/off’ control for all channels. (b) Emergency ‘off’ control for all channels. (c) Immediate ‘on’ control for all channels.
C I R C U I T of the feedback from Q0 to D0, point ‘A’ remains high even after releasing the ‘off’ switch. As a result, relay RL1 is deactivated and LED1 also goes off. In case of emergency, press the I D E A S emergency off switch S17 to disable all the outputs of IC1. In this state, the outputs of IC1 are in high impedance state, and as all transistor bases are almost ‘open’, all the relays get deactivated. AN EXCLUSIVE SINEWAVE GENERATOR RUPANJANA J.
C I R C U I T I D E A S TTL THREE-STATE LOGIC PROBE S.C. DWIVEDI T. SURESH A TTL logic probe is an indispensable tool for digital circuit troubleshooting. Various methods can be used to design a logic probe. The most common designs employ opamps, logic (OR, NOT, XOR) gates, and transistors. The circuit presented here uses NAND logic gates of Hitachi HD series IC HD74LS00, which is a quad-NAND IC. Special technique has been employed to obtain three-state operation using just a single IC.
C I R C U I T contain some residual carrier. This is known as carrier leakage. By adjusting the 100-ohm preset (VR2) and trimmer (C7) you can anull the scarier leakage. To receive DSB signals you need a beat frequency oscillator to reinsert the missing carrier. If you don’t have a beat frequency oscillator, or want to transmit only AM signal, adjust preset VR2 to leak some carrier so that you can receive the signals on any ordinary radio receiver.
C I R C U I T accuracy, which is quite reasonable and adequate for some practical applications. The bulb (which is 230V, 100W, filament type) shown in the figure is mounted on a wooden box with a bulb holder. Connection to the mains supply is obtained using long wires, which are terminated into a 3-pin power plug that ensures non-reversibility of live and neutral leads. The bulb drops the voltage to a safer level at the terminating probe. Resistor R1 limits the current.
C I R C U I T I D E A S The functions of the various pins are given in Table I. Pins 2 through 9 are data pins. Here, we will use data pins 2 to 5, corresponding to data bits D0 through D3 of port 378(hex) for LPT1 or 278(hex) for LPT2. Also, pin 25 is used as the ground pin. The PC’s parallel port cannot sink much current. At the most, it can handle a few milliamperes. So, if the parallel port is connected directly to an electrical device, it will damage the parallel port.
The End
