electronic projects

Battery charger circuit using SCR  Description. A simple battery charger based on SCR is shown here.Here the SCR rectifies the AC mains voltage to charge the battery.When the battery connected to the charger gets discharged the battery voltage gets dropped.This inhibits the forward biasing voltage from reaching the base of the transistor Q1 through R4 and D2.This switches off the transistor.When the transistor is turned OFF,the gate of SCR (H1) gets the triggering voltage via R1 & D3.This makes the SCR to conduct and it starts to rectify the AC input voltage.The rectified voltage is given to the battery through the resistor R6(5W).This starts charging of the  battery. When the battery is completely charged the base of Q1 gets the forward bias signal through the voltage divider circuit made of R3,R4,R5 and D2.This turns the transistor ON.When the Q1 is turned ON the trigger voltage at the gate of SCR is cut off and the SCR is turned OFF.In this condition a very smal...

Air flow detector circuit Description. This circuit can give a visual indication of the rate of air flow.It can be also used to check whether there is air flow in a given space. The filament of a incandescent bulb is the sensing part of the circuit.When there is no air flow the resistance of the filament will be low.When there is air flow the resistance drops , because the moving air will remove some of the heat generated in the filament.This variations in the resistance will produce variation of voltage across the filament.These variations will be picked up by the opamp (LM339) and the brightness of the LED at its output will be varied proportionally to the airflow. Circuit diagram with Parts list. Notes. The filament L1 can be made by removing  the glass of a 40W incandescent bulb. The circuit can be powered from a 12 V DC power supply.

Water level alarm circuit Description. Here is a simple water level alarm circuit using 555 timer that will produce an audible alarm when the water level reaches  a preset level.The circuit can be powered of a  3V battery and is very handy to use. The circuit is based on an astable multivibrator wired around IC1 (NE 555).The operating frequency of the astable multivibrator here will depend on capacitor C1, resistances R1,R2 and the resistance across the probes A&B.When there is no water up to the probes,they will be open and so the multivibrator will not produce oscillations and the buzzer will not beep.When there is water up to the level of probes,some current will pass through the water,the circuit will be closed to some extend,and the IC will start producing oscillations in a frequency  proportional to the value of C1,R1,R2 and the resistance of water across the probes.The buzzer will beep to indicate the presence of water up to the level of the sensing pr...

Low cost fire alarm circuit. Description. W hen there is a fire breakout in the room the temperature increases. This ultra compact and low cost fire alarm senses fire breakout based on this fact. Transistor BC177 (Q1) is used as the fire sensor here. When the temperature increases the leakage current of this transistor also increases. The circuit is designed so that when there is an increase in the leakage current of Q1, transistor Q2 will get biased. As a result when there is a fire breakout the transistor Q2 will be on. The emitter of Q2 (BC 108) is connected to the base of Q3(AC 128). So when Q2 is ON Q3 will be also ON. The transistor Q3 drives the relay which is used to drive the load ie,light,bell,horn etc as an indication of the fire. The diode D1 is used as a free wheeling diode to protect it from back EMF generated when relay is switched. Do you need to get a better understanding on the basics of electronics? We have listed 4 of the best books to learn the basics of...

Single Chip FM Radio circuit Description. Here is a compact low cost  FM radio circuit  using IC TDA 7000. This circuit is designed as per the data sheet and the result is excellent.Ideal for all category of electronic enthusiasts. The TDA7000 is a monolithic integrated circuit for mono  FM portable radios,  where a minimum on peripheral components is crucial. The IC TDA 7000 has a Frequency-Locked-Loop system with an intermediate frequency of 70 kHz. The intermediate frequency selectivity is achieved by active RC filters. The only function which needs alignment is the resonant circuit for the oscillator, thus selecting the reception frequency. Spurious reception is avoided by means of a mute circuit, which also eliminates too noisy input signals. Special steps are taken to meet the radiation requirements. FM Radio Circuit Diagram with Parts List.  Notes For L1 and L2 wind 5 turns of 0.6 mm enameled Copper wire on a 4 mm dia plastic former. For a...

Automatic Washroom Light Switch We turn On the lights in our washroom when we enter it and turn them off when we leave. We sometimes forget to turn Off the lights after leaving the washroom. This may lead to power wastage and also the lifetime of the lights may decrease. To avoid these problems, we are going to make a circuit which automatically turns On the lights when a person enters the washroom and it automatically turns it Off when he leaves it. By automating this, there are many advantages like, the person need not care to turn On the light always when he is using the washroom. The circuit which we are doing does it automatically for that person. Also, the person need not turn it off after using the washroom. There is no fear that he forgets to turn it Off. The circuit is also designed to consume lesser power so that the circuit can be used in any household or public washrooms without worrying about the power bills. Automatic Washroom Light Switch Circuit Diagram: The ...