AN INFRARED MOTION DETECTOR

This motion detector can be designed in various ways using different kinds of components. It is easy to build, designed with easily available and inexpensive compounds. It is therefore very cheap even in the market. They are perfect for theft detection. They can also be used to setup a trespasser alert system with alarm.

Do it yourself Infrared Motion Detector.

Below is the circuit drawing of a simple infrared motion detector which is able to sense commands.

Infrared rays which are reflected from still object will be placed in one phase, and the rays reflected from an object in motion will be in another phase. This is the motion the circuit uses to sense the motion. The ICI (NE 555) is usually wired as an astable multi-vibrator.

The IR diode which is connected at the IC’s output produces infrared rays of frequency 5 KHz. These rays are then picked by infrared sensor, photo-transistor Q1. At normal condition (when there is no intrusion), the IC2 output pin will be low.

In case of an intrusion, the reflected waveforms phase has a difference. The IC2 will therefore pick this phase difference. The IC2 pin output will go high to indicate the invasion. A buzzer or an LED can be linked at the output of this IC to point out the intrusion.

Points to note

  • The IR motion sensor circuit sometimes gets falsely triggered when there is a vehicle passing by or there is disturbance in the air.
  • Comparators IC2a and IC2b belong to the same IC2 (LM 1458). So the power supply shown is connected only once. Therefore, there is no problem with that.
  • If you are using a supplier greater than 12V, you can use like 7812 regulator to bring it down to 12 voltage.
  • You can modify this circuit idea to design other simple projects like anti-theft system, Intruder alarm and many others.

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