laser door alarm circuit

Posted on Feb 6, 2014

This is a circuit for laser door alarm is based on the interruption of Laser beam. A low cost Laser pointer is used as the source of light beam. When somebody breaks the laser path, the alarm will be generated for few seconds. This is the figure of the circuit; The laser door alarm circuit has two sections. The laser transmitter is a laser pointer

laser door alarm circuit
Click here to download the full size of the above Circuit.

readily available. It should be powered with 3 volt DC supply and fixed on one side of the door frame. The receiver has a Phototransistor at the front end. L14F1 NPN Darlington phototransistor is used as the laser sensor. IC1 is used as a voltage comparator with its inverting input tied to a potential divider R2-R3. So that the inverting input is kept at half supply voltage. As a result, output of comparator remains low. LED and Buzzer remain off in this state. When a person crosses the door, laser beam breaks and T1 cease to conduct. Collector voltage of T1 rises and voltage at pin 3 of comparator increases and its output becomes high. This activates LED and buzzer. Capacitor C1 keeps the base of T2 high for few seconds even after the output of IC1 becomes low again. C2 gives current to the buzzer for few seconds even after T2 turns off.

Leave Comment

characters left:

Related Circuits

  • New Circuits



    Popular Circuits

    8 Watt Amplifier
    Simple LF converter
    A Balanced Output Board For The Stereo DAC
    Simple Code Lock
    fet amp circuit
    N1FN Key Collection
    Active Plug Classic
    Car Alarm Simulator
    A common car inverter circuit and principle