Electronic Circuits and Diagram-Electronics Projects and Design

Car Head Lights Turn Off Circuit Description This circuit when setup in a car automatically turns off the head light after a preset time after the ignition switch is turned off.So you can walk out easily from the dark garage in the light of your car. When the ignition switched on first the voltage from battery is fed to the relay through diode D1.When the ignition switch is turned off it produces a negative going pulse at the pin 2 that triggers the timer. The output of the IC goes high for the time set by R1  .This makes the…

Automatic Wiper Control Description A continuously working wiper is a big problem when it is raining slightly.The wiper control given here makes the wiper to sweep at rates from 1S to 10 S. The circuit is build around an astable multivibrator using NE 555.Here the output at pin 3 remains high for a time period set by R2 ,and low for a time period set by R3.The low output pulse drives the transistor pair to drive the wiper motor to make one sweeping cycle and waits for next low pulse to arrive for next sweep.The high going pulse at pin…

Melody Generator Circuit Description Here is a simple melody generator circuit you can make using an IC.The  UM66 series are CMOS IC’s  designed for using in calling bell, phone and toys. It has a built in ROM programmed for playing music. The device has very low power consumption.Thanks for the CMOS technology.The melody will be available at pin3 of UM66 and here it is amplified by using Q1 to drive the speaker.Resistor R1 limits the base current of Q1 within the safe values.Capacitor C1 is meant for noise suppression. Notes Power supply  must be between 1.5V & 4.5V .Do not…

Water Level Indicator Description This is the circuit diagram of a simple corrosion free water level indicator for home and industries. In fact the the level of any conductive non corrosive liquids can be measured using this circuit. The circuit is based on 5 transistor switches. Each transistor is switched on to drive the corresponding LED , when its base is supplied with current through the water through the electrode probes. One electrode probe is (F) with 6V AC is placed at the bottom of tank. Next probes are placed step by step above the bottom probe. When water is…

A Lamp Dimmer/Fan Regulator Circuit We have modified this circuit: – Take a look – Modified Lamp Dimmer Description . This is the circuit diagram of the simplest lamp dimmer or fan regulator.The circuit is based on the principle of power control using a Triac.The circuit works by varying the firing angle of the Triac . Resistors R1 ,R2 and capacitor C2 are associated with this. The firing angle can be varied by varying the value of any of these components. Here R1 is selected as the variable element . By varying the value of R1 the firing angle of…

Fridge Door Alarm Circuit Description. This is a fridge door alarm circuit, which produces an audible alarm when fridge is left open for a preset time. This versatile alarm is based  on two 555 timer IC’s. Both ICs are wired as astable Multivibrators. An LDR is connected in parallel to the timing capacitor C1 of IC 1.When door is completely close there will be no light inside the fridge and LDR offers high resistance keeping R1 fully charged.When door is left open ,the lamp inside the fridge will keep glowing ,LDR will be illuminated, and its resistance falls. This makes…

High Power Siren Circuit Description. This article is all about a comparatively strong siren circuit useful for any purpose.A complementary transistor pair (BC 557 & 337) is arranged as an oscillator, directly drives the speaker.Transistor Q1(BC 557) is used to provide full charging of capacitor C2.When P1 is pressed, C2 discharges through R8 and the circuit starts oscillating at a low frequency that increases slowly until a high frequency steady tone is reached and it is kept.When P2 is released C2 starts discharging and and output frequency slowly decreases.When C2 is charged fully the circuit stops oscillations. Tips. Adjust the…

LED Emergency Light We have developed three circuits under Automatic LED Emergency Light. Two of them are designed by Mr. Seetharaman, a very valuable and important contributor of this website. We have listed the circuits here for your ease of  reading. If you have any doubts; please comment with circuit name or circuit number. 1. Simple Emergency Light using LED 2. Automatic Emergency Light using LM317 IC 3. Modified Version of Automatic LED Emergency Lamp using LM 317   1. Simple Emergency Light Circuit This is one of the most cost effective (cheap) and simple emergency light circuit developed for…

Tone Generator Circuit Description Here we present a simple and low cost tone generator circuit, a ding dong bell suitable for calling bell purposes.It is made around IC 8021. It is an 8 pin IC but only four pins are shown here. 8021 has an in-built circuitry to produce ding dong sound each time its pin 3 is pulled low. The sound is stored in a 4 bit ROM. A complementary-pair, two-transistor amplifier is used to amplify the sound to a fair level of audibility. A piezoelectric tweeter or an 8-ohm, 500mW speaker  can be used at the output. Each…

Make a Digital Stop Watch Description A digital stop watch built around timer IC LM555 and 4-digit counter IC MM74C926  with multiplexed 7-segment LED display. MM74C926 consists of a 4-digit counter, an internal output latch, npn output sourcing drivers for common cathode, 7-segment display and an internal multiplexing circuitry with four multiplexing outputs. The counter advances on negative edge of the clock. The clock is generated by timer IC LM555. The circuit works off a 5V power supply. It can be easily assembled on a general-purpose PCB. Enclose the circuit in a metal box with provisions for four 7-segment displays,…