Automatic Telephone Answering Unit Remote Controlled Switch Board. Multiple Control Remote Switch. A Digital Speech Security System. Telephone Controlled Remote Switch Digitally Controlled Function Generator Programmable Digital TimerCum Clock Running Lights Effect FourinOne Burglar Alarm Telephone Call Counter ReadytoUse Object Counter Automatic Temperature Controller Simple Logic Probe Automatic Switch for Audio Power Amplifier Darkness Controlled Light Switch Quality FM Transmitter Yearly compilations to Yearly compilations of interesting and useful construction projects and circuit ideas published in Electronics For You.
U a am to Use Microprocessors with floppy: Ananthi fourth enlarged edition. An EFY publication with floppy disk. Extremely useful for the study of K-bil processors at minimum expense. Authored by Rajesh Verma. VU2RVM, it deals exhaustively with the subject — giving a lot of practical information, besides theory. This publication describes the ins and outs of almost all types of batteries used in electronic appliances.
Includes Directory of Indian manufacturing and distributing units. Buyers' Guide and Index of Brand Names, plus lots of other useful information. Technical Education Institutes Directory: In regular publication since EFY is the natural choice for the entire electronics fraternity, be it the businessmen, industry professionals or hobbyists. Asia's first magazine on Linux. Completely dedicated to the Open Source community.
Regular columns by Open Source evangelists. With columns focused for newbies, power users and developers. A monthly magazine for 'Techies' and those who want to be. Its readers have two things in common — a background related to IT and the thirst to know more. Topics covered boast technical depth.
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No part of this book may be reproduced in any form without the written permission of the publishers. In keeping with the past trend, all relevant modifications, corrections and additions sent by the readers and authors have been incorporated in the articles.
It is a sincere endeavour on our part to make each project as error-free and comprehensive as possible. However, EFY cannot resume any responsibility if readers are unable to make a circuit successfully, for whatever reason. This collection of a large number of tested circuit ideas and construction projects in a handy volume would provide all classes of electronics enthusiasts — be they students, teachers, hobbyists or professionals — with a valuable source of electronic circuits, which can be fabricated using readily-available and reasonably-priced components.
These circuits could either be used independently or in combination with other circuits, described in this and other volumes. We are sure that this volume, like its predecessors, will generate tre- mendous interest among its readers. Dynamic Display 1 1 2. An Intercom with Handset 14 3. Multirange Adjustable Timer 29 5. Automatic Brightness Controller for TVs 32 6. A High Impedance Adapter for a Multimeter 36 7. Neo Digital Clock-Part 1 39 8. Boolean Function Emulator 52 Refrigeration Temperature Controller 6 1 Heavy Duty Voltage Stabiliser 64 1 3.
Composite Electronic Organ 76 1 5. Digital Clock With on-off Timer 85 1 6. Day Date Computer 90 Electronic Ignition System for Automobiles 94 1 8. Resetting Protector for Computers Add-on Telephone Devices Master-Slave Clock Add-on Devices for Double Cassette Recorder 1 19 Dynamic Psychedelic Lights Digital Channel Selector Section B: Electronic Switch for 3-Band Transistor 1 33 2. Electronic Number Lock 3. Three-in-one Circuit 4. Match Box Size Radio 5. Static Audio Wattmeter 6.
Variable Switching Power Supply 7. Tubelight Without Choke and Starter 1 39 8. Automatic Star-to-delta Converter 9. Cassette Copier A Precise Timer 1 1.
Mains Supply Interruption Indicator 1 2. Electronic Car Horn Indicator Bell Multi-tone Generator AM Transmitter Indoor Advertising Board 1 9. Simple Touch Dimmer Using Triacs 1 5 1 Charging Reminder for Emergency Lights 1 5 1 I to 1 0 Pulses from 40 1 7 Counter 1 52 Smoke Alarm Pulse Generator Automatic Voltage Stabiliser 1 55 Automatic 2-mode Running Light Simple Electronic Sand-glass FM Communication System Mains Wiring Fault Detector Programmable Organ 16 1 Digital Stop Watch Frequency Measurement on Multimeter A Simple Intercom Mini Chaser Mains Voltage Indicator Compact Audio Cassette Duplicator Super Simple Interruption Counter Harmonic Distortion Meter Condenser Lamp Dimmer Simple Counter Using Calculator Multioutput Regulated Power Supply Improved Melody Doorbell Voltage-window Comparator Follows Reference Voltage 1 77 Seconds Display for Digital Clock ; Auto Cut for Manual Stabilisers 1 8 1 Delay Starter - Door Alarm The LED Scanner Melody from IC Timer Disco Light Project 1 87 IC Voltage Regulator 1 87 Audio Frequency Oscillator Linear High Current Regulator Ignition Indicator Signal Injector cum Tracer Inverter-based 3-in- 1 Timer All-in-one Circuit for Fridge Ni-Cd Cell Charger Digital Volume Controller 1 96 Phase Sequence Change Indicator 1 97 7 1.
LML Vespa Flasher Dual Trace Generator Complementary Lighting Control 20 1 Short-proof Power Supply Universal Cell Evaluator Overdrain Protector for Lead-acid Accumulators Clap Switch Section A: Viswanathan S everal circuits for displays using different integrated circuits have been published earlier in EFY. This ad- vertising display mainly for name board uses the popular IC The display has only one mode, i. Each letter is lit up by ordinary V AC bulbs controlled by triacs. LEDs can also be used with proper driving circuits.
One can increase or decrease the number of ICs accord- ing to the number of letters to be dis- played. All ICs are connected in cascade. Understanding the first two stages and how they initiate the op- eration of the next stage helps in understanding the operation of com- plete circuit. The output at pin 3 goes to high state, thus triggering the triac connected to it for lighting up the first letter. Apart from providing the drive to the triac gate, the output of IC1 is also connected to the control voltage termi- nal pin 5 of IC2 through a delay circuit consisting of a resistor and a capacitor.
When the capacitor gets charged and exceeds the voltage by twice the voltage set by the variable resistor connected to pin 2 of IC2, its output goes to high state and thus the second letter is also lit up through the second triac. This process continues in se- quence from second to third letter and so on, lighting up all the letters. The output of the last IC is also con- nected to the threshold term inal pin 6 of IC1 through a delay circuit consisting of a resistor and a capacitor. At the same time, control voltage of IC2 is also pulled to negative, discharging the capacitor.
When it goes below the threshold voltage level set by the variable resistor connected to pin 6, its output also goes to low state switching off the second bulb. This process continues in sequence and all the bulbs go off one by one. This makes a continuous loop and the timer operates endlessly.
R1-R7 — ohm R8-R15 — 4. Components layout for the PCB shown in Fig. Switch on the power. Only the first bulb gets lit up. Adjust the preset connected to the trigger terminal of IC2 to reduce the trigger voltage level. At a critical voltage, IC2 gets triggered for lighting the second bulb. In this way all the presets connected to the second termi- nal can be adjusted and all the bulbs switched on one by one.
Switch off the power for a few seconds and switch on again for rcchecking the sequence. Most of the presets have to be read- justed because even touching the preset may trigger the IC. When the output of the last IC goes to high state, IC1 goes to low state. So the first bulb is switched off. Adjust the preset connected to the threshold ter- minal pin 6 of IC2 for increasing the threshold voltage level.
At a critical voltage, the second bulb also goes off. Thus all the presets connected to pin 6 can be ad- justed and all the bulbs go off one by one. This cycle is repeated endlessly. A final setting is re- quired for making the delay time equal in the sequence. All precautions mist be taken against electrical shock as the circuit works on AC mains. Power supply taken from 12V, mA step-down transformer, full- wave rectifier and a lOOOpF filter capacitor is enough for the given circuit.
When more letters are to be displayed, current rat- ing of transformer may also be increased. I Stencil-cut letters fixed on box having separate compart- ments for each letter are easy to make. Bulbs fitted on holders in each compartment light up the letters. It has advantages like low voltage op- eration, ring and ring-back functions, free from feedback howling and talk- listen changeover. The sound quality is superb. It covers wide frequency range. The transmitter The transmitter comprises a con- denser mic.
It is a low power, 8-pin audio amplifier IC, intended for use in portable radio receivers. It works on very low voltage, viz, 2. The sensitivity of the transmitter is enhanced by the use of the condenser mic. If the system is intended for use in a noisy location, the sensitivity of the mic. The amplifier circuit is shown in Fig. The receiver An earphone of a stereo head- phone set is used here as the receiver.
Ringer circuit Two alternate circuits are given for the ringer. One can select either of the two, subject to the availability and economy of the components. The nega- tive-going pulses available at the col- lecter of T2 are used to drive a piezoelectric buzzer placed inside the other handset. The charging and discharg- ing of C9 make interruptions in the audio frequency. Bird sound ringer circuit.
IC — BE1 T1. Rl, R8, R9, R Earphone — 1 no. This produces an attrac- tive bird sound. The ring pulse will come back to the receiver of the calling person so that he can know if someone has at- tended the other station. This provi- sion is made simply by connecting the incoming line with the outgoing line through a diode. This diode should have extremely low leakage current Otherwise it will cause problems like oscillations, motor-boating etc. The whole circuit works on 3V DC. If the distance between two sta- tions is more than 30 metres, the volt- age should be raised to 4.
Dry battery is recommended. If pen- light cells are used, they can be housed inside the handset. If separate power supply units are used for each station, the connection wires between two sta- tions can be limited to three. However, a central power supply system can also be used as shown in Fig.
Connection diagram of a separate power supply. Connection diagram of central power supply. Now no power is applied to any circuit and the incoming line is connected to the buzzer or loud- speaker in both stations. This provides power to the ringer circuit and its output is connected to the outgoing line. This produces ring- ing at the other station. Now both persons can talk to each other.
At the end of the conversa- tion, both sets have to be set to 'off position. The connection diagram for the intercom is given in Fig. Construction of handset An average hobbyist may find it difficult to obtain handsets for inter- com projects. These are available in various shapes and attractive colours. It should have minimum size of 20cm x 3cm x 6cm.
Some holes have to be drilled on the box for clear sound reproduction. The earphone should be placed in such a way as to get close coupling to the car. Figs 6 and 7 show the PCB and compo- nents layout for the intercom. The PCB, loudspeaker, buzzer, switches and battery holder must be fixed in the handset by using rubber based adhesive Fig. Avoid nuts, bolts or screws. A 3-core shielded wire should be used to connect the handset with the main lines.
Since all parts of the intercom can be housed inside the handset, the need for a tablesct or speaker box is elimi- nated. The handset can either be hung on the wall or kept on a table. Actual size PCB layout for the intercom. An in- about 10 minutes. Then switch off the digcnous method is explained here, mains and let it cool down. A wet rag Clean the surface of the cylinderical may be used for cooling. When thor- heating portion of a 10W soldering oughly cooled, loosen the egrd from iron and apply a thin coat of grease the iron.
A sample test with a piece of over it. Coil the cord closely over it. If the power supply is in- iron, its temperature can be kept within creased above 6V, feedback howling reasonable limits. Keep it heating for may occur. This can be reduced by Fig. All joints of connecting wires must be soldered to reduce line resistance and transmission losses. The project is very interesting.
If I want to use a dynamic mic. You have shown both earphone and loudspeaker in handset layout diagram.
Please tell me why two sound producing components are used? Is it possible to use either loudspeaker or earphone? You have given details for only 2-station intercom; can I increase the number of sta- tions? It needs no extra components for generating music. Then si ze of the PCB can be reduced to half m shown here. IC BEL has become very popu- lar. If it is not available, an amplifier circuit usingTBA8 10 can be used with a power supply of 4.
If a dynamic mic. A loudspeaker cannot be used in place of an earphone. If done so the sound waves from the loudspeaker will reach the mic. At the same time a loudspeaker is nec- essary for producing loud ringing. In both stations there should be one speaker each. Three or four wires are necessary for connect- ing one station with another. Bulky wiring and complicated switching will be required for increasingthe number of stations.
But remember, the melody pro- duced by UM6 6 has now become very popular as it is widely used in door- bells, quartz clocks etc. Imagine the confusion created by the melody of an intercom placed in a room where a clock or doorbell having the similar tune already exists! R4 should be read as VR1 wher- ever mentioned in the text not in the Fig. Finally, for improvement of the project, only earphone and mic.
Other parts, viz, switches, battery, loud- speaker and PCB etc can be housed in a separate box which also acts as a rest for the handset. A larger speaker may be used in this case. Shankar everal circuits on cassette players and a few circuits on record- ers have been published in EFY, but none of them provide recording qual- ity equal to that of professional record- ers. This is because of their simplicity and low-cost orientation. With a little more expense you can make yourself a high quality recorder with double cas- sette deck facility.
Three factors make this circuit su- perior to the other circuits: While recording, the circuit provides AC bias instead of DC bias to the recording head. Further, it leaves the tape in demagnetised condition when there is no signal. This reduces tape hiss to a large extent. The circuit uses AC bias to the erase head also. In conventional circuits, a resistor in series with the erase head is used for erasing.
In this process the tape is saturated magneti- cally instead of demagnetising. But saturated tape produces too much hiss which is simply not bearable in! On the other hand, AC bias completely demagnet- iscs the tape which is a superior method of erasing. The circuit uses variable moni- I toring system with peak level indica- tor so that the record level can be ad- justed manually to an exact value the tape is meant for. Too much recording level increases distortion and too low recording level increases noise. So an optimum level has to be chosen which is achieved through the peak level indicator.
R27 — ohm C28, C30, R8. C45, RR39 — ohm C VR4 — kilohm pot. VR8 — kilohm, trimpota VR5. VR6 — kilohm preset Miscellaneous: OlpF ceramic disc — Tape deck mechanism C4. C18, — Heatsinks C22 — 2. ICs LA are used as tape pre- amplifiers for both decks. The outputs of the preamplifiers are given to a 2-polc, 3-way switch. This switch se- lects the input to the power amplifiers as well as display amplifiers. In one position the output of tape 1 is selected, in the mid position output of tape 2 is selected and in the third po- sition aux or line-in terminals arc se- lected.
One may use 2-pole, 4-way switch if mic. The selected input is fed simul- taneously to the display amplifiers and power amplifiers. The selected input goes to volume control pots at power amplifier side and record level presets at display amplifier side. The inputs of display are connected to k presets during playback and to k pots during recording.
These pots act as record level control during re- cording. The presetting of the pots is explained later. Note that the record level indicator or peak level indicator is a must and should not be dispensed with to make the circuit simpler or low-cost. The detailed circuit diagram is shown in Fig. Recording During recording, the outputs of display amplifiers are connected to the recording heads through a frequency pre-emphasis network and bias oscilla- tor circuit. As stated earlier, the circuit uses AC bias for recording as well as eras- ing. Hence an oscillator is required to bias the recording and erasing heads.
This is a hartley oscillator wired around transistor BCB. The tuned secon- dary causes the transistor to oscillate at frequencies higher than 80 kHz. The transformer may be any IFT used in radio receivers. The output of bias oscillator is mixed with the audio sig- nal from display amplifier and pre- emphasis network through a 27k resis- tor and pF capacitors.
These boost the high frequency components of the audio so as to meet the requirement of oxide tape. Do not alter the values of these components. Adjustments of VR6 and VR7 are ex- plained later. Display amplifiers may be wired on ready-made PCBs available in the market, so as to minimise ground loops and hum. The same amplifiers are used for recording also and: One may cascade the transistor stages to obtain better resolution by using more LEDs. It is necessary to calibrate the dis- play properly before it is used for re- cording.
Here is a method for calibration. Record a tone of 1 kl Iz on a pre-calibrated cassette deck at OdB level. The cali- bration for playback is over. Calibration for recording is a bit tedious. But once ad- justed, the presets need not be touched again. Record a tone of 1kHz and adjust the record level control pots so that the indicator shows OdB.
Now play back the recorded tone. By means of this method of trial and error, one can calibrate it in four or five trials. It is a single-in-line IC with 12 pins on one side. Circuit for microphone recording. Actual-size PCB layout for the cassette recorder.
Use a 2 V transformer with 5-amp continuous rating. Two diodes are connected in parallel to increase the current ca- pacity of the rectifier. A filter capacitor of lO. OOOpF should be used for better hum rejection. Construction Most of the circuit modules can be assembled on general-purpose PCBs. Both preamplifiers should be wired on a single PCB and care must be taken to avoid ground loops. The record-play switch, pre- emphasis circuit and bias oscillator should be as- sembled on a single board. This removes ground loops in the circuit and prevents the circuit from oscillating.
This is not shown in the circuit heatsink of about gms. The output 30W power into' a 4-ohm load. Avoid using too long wires, is double ended without any output Ground the chassis of both the decks capacitor. Such configuration is com- Power supply as well as the volume control, record- mon in most power ICs. It delivers Since amplifiers are of high watt- level control, and transformer bodies. Components layout for the PCB in Fig. The com- ponents layout is shown in Fig. A separate PCB is used for display module.
The assembling should be done as explained here. The power amplifiers should be assembled first. After assembling all the components power amp , apply around 6V to the Voc track and ground. Connect the speakers and keep the volume control at minimum. The output should be absolutely si- lent. The volume control wiring should be done with 2-core shielded wire at exactly the same points as shown in Fig. Other- wise ground loops will be formed causing hum and distortion. Now raise the volume and apply signal to the power amplifiers. Test for the output.
The IC should get slightly warm. After testing the power amplifiers, solder the pre- amplifier section. The LA ICs arc delicate and hence should be sol- dered in shortest time pos- sible. After assembling, connect temporary con- nections the output of preamp and the input of power amp through the volume control Connect If you want to use microphones for quate power rating in place of LI.
For 6V Construction and testing wires. Do not use the shield as motor, use a suitable resistor of ade- A suitable PCB for the circuit is common ground for both channels. The wiring diagram for the circuit. If it is not proper, refer the by connecting speakers at their out- troubleshooting section given later.
The puts instead of ohm, 1 W resistors motor should be the given supply. If and applying input. If distortion is the working is satisfactory, the display noticed as rarely it does , increase the amplifiers are to be soldered next. For value of R7 and R27 to ohms. Hence it is required to i distortion-free.
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