Proximity sensors are often important part in industrial automation, robotics etc. The circuit described here is based on infrared ray thus is a contact less proximity sensor. The circuit can also be implemented in security system.

This circuit provides a means of detecting the presence of anything by the reflection of infrared light and provides a direct digital output of object detection. By the use of modulation and high power bursts of infra-red at a very low duty cyde,a detection range of over a foot is achieved. Works on the principle of transmitting a beam of modulated infra-red light from the emitter diode LED2, and receiving reflections from objects passing in front of the beam with a photodiode detector Dl. The circuit consists of an infra-red transmitter, photodiode amplifier, and a variable threshold comparator.

If described components are unavailable on can also use general operational amplifiers with equivalent electrical characteristics.

   Schematic