Photodiode Alarm

Posted on Feb 5, 2014

This Photodiode based Alarm can be used to give a warning alarm when someone passes through a protected area. The circuit is kept standby through a laser beam or IR beam focused on to the Photodiode. When the beam path breaks, alarm will be triggered. The circuit uses a PN Photodiode in the reverse bias mode to detect light intensity. In the prese

Photodiode Alarm
Click here to download the full size of the above Circuit.

nce of Laser / IR rays, the Photodiode conducts and provides base bias to T1. The NPN transistor T1 conducts and takes the reset pin 4 of IC1 to ground potential. IC1 is wired as an Astable oscillator using the components R3, VR1 and C3. The Astable operates only when its resent pin becomes high. When the Laser / IR beam breaks, current thorough the Photodiode ceases and T1 turns off. The collector voltage of T1 then goes high and enables IC1. The output pulses from IC1 drives the speaker and alarm tone will be generated. A simple IR transmitter circuit is given which uses Continuous IR rays. The transmitter can emit IR rays up to 5 meters if the IR LEDs are enclosed in black tubes.

Leave Comment

characters left:

Related Circuits

  • New Circuits



    Popular Circuits

    Touch Switches Collection
    Simple Audio-Frequency Vco
    Motor driver L298 Circuit Schematic Diagram
    Test wall socket with current limiting
    Doorbell Warning Switch
    upc1651 fm transmitter circuit
    PIC CW Temp Circuit
    car burglar alarm timer
    AVC Automatic Volume Control Circuit
    PC Controlled RC Car
    Parachute Recovery System
    Light Detector
    10 GHZ Transverter
    Simple and practical power SCR trigger circuit diagram
    555 Happy Birthday electronic circuit diagram candle