Light Fence Security Alarm Circuit Schematic

Posted on Feb 6, 2014

A simple light fence security beeper is presented here. This circuit can be used as a door alarm, gate alarm, pathway alarm, etc. Any 12 Volt dc power supply can power the whole circuit. Working of this circuit is straight forward. In standby mode photo transistor T1 receives light from the green LED (D1) and T1 conducts to disable the gated low-frequency astable built around IC1(4093). When this light path is

Light Fence Security Alarm Circuit Schematic
Click here to download the full size of the above Circuit.

interrupted by any object in the path, T1 stops conducting and IC1 is switched by the low level at its input point (pins 12&13). As a result the piezo-buzzer starts beeping at a slow rate determined by the in circuit values of R3, R4 & C1. Red LED (D2) is a visual warning indicator. With the help of suitable reflector and lens assembly, length of the light path can be increased. A minimum of 1 to 2 metres is possible with a high-bright green LED as D1. A laser pointer can also be used as the light source.

Leave Comment

characters left:

Related Circuits

  • New Circuits



    Popular Circuits

    12V to 3V Car adapter
    Astable oscillator
    Lc Sine-Wave Generator
    audio Can I use a PNP Transistor with an Electret Microphone to get an non-inverting output for my Arduino
    home-made light-operated camera trigger
    Reverse voltage and over-voltage surge protection circuit diagram XTR106