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Motion Detector

Introduction to Motion Detector:

The motion detector is used as intruder alarm, home automation system, energy efficiency system, etc. It will detect the motion of the people or objects and give the appropriate output according to the circuit. In general, it uses different types of sensors like Passive infrared sensor, microwave sensor , ultrasonic sensor etc.  There are some motion detectors which will use different technology and include number of sensors  to reduce the false triggering.


Here is a circuit which uses IR sensor and photo transistor for transmitting and receiving IR beam. This circuit is easy to construct and cost of circuit is very low when compared to normal motion detector.

Block Diagram of Motion Detector:

Motion Detector Block Diagram
Motion Detector Block Diagram

IR sensor will produce the high frequency beam which is projected on the photo transistor with the help of 555timer at the transmitter. When this high frequency beam has got any interruption, the photo transistor will trigger the 555 timer of receiver section and gives alert through the alarm.

Motion Detector Circuit Diagram:

Motion Detector Circuit Diagram
Motion Detector Circuit Diagram

Motion Detector Circuit Explanation:

  • Infrared sensor will make the high frequency beam of 5 kHz with the help of 555 timer which is set to stable multi-vibrator mode at the transmitter section.
  • The IR sensor will produce the high frequency beam which is received by the photo resistor at the receiver section. This frequency will be in one phase when there is no interruption between the IR sensor and photo transistor.  Total circuit will not give any output in this phase. 

Main Components in Motion Detector Circuit:

IR sensor: The main concept of IR sensor is to produce a beam of infrared light (whose wave wavelength is longer than visible rays and shorter than microwaves, in normal infrared wave length should be greater than 6µm). Infrared sensors are based on three different laws they are planks radiation law, Stephan Boltzmann law and Wien’s displacement law.

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