Introduction to Motion Detector Circuit Diagram with Working Principle

The first motion detector was invented in the early 1950s by Samuel Bango, and which was a burglar alarm. He applied the fundamentals of a radar to ultrasonic waves – a frequency to detect fire or thief and that which human beings cannot hear. Samuel motion detector is based on the principle of Doppler Effect. Nowadays, most of the motion detectors work on the principle of Samuel Bango’s detector. IR sensors and microwave sensors can detect motion by the alterations in the frequencies they emit.

Motion detectors are used as security systems in banks, offices and shopping malls, and also as intruder alarm in home. The prevailing motion detectors can stop serious accidents by sensing the persons who are in close proximity to the detector. We can observe motion detectors in shopping malls or stores with automatic doors. The main element in the motion detector circuit is the dual infrared reflective sensor or any other detecting sensor.

Motion detector
Motion detector

Types of Motion Detector Sensor

The motion detector is a device; it detects the motion of the people or moving objects and gives appropriate output to the main controller. In general, motion detectors use different sensors like IR sensors, ultrasonic sensors, microwave sensors and passive infrared sensor. These motion detection sensors are mentioned below.

1. Passive Infrared Sensor (PIR)

PIR sensor
PIR sensor

PIR sensors detect a person’s body heat when the person comes in close proximity. These sensors are small, low power, inexpensive and easy to use. Due to these reasons, PIR sensors are generally used in gadgets, home appliances, business enterprises, industries, etc. PIR gives digital output when it detects motion. It consists of pyro-electric sensor that detects the infrared radiation emitted from humans.

2. Ultrasonic Sensors

ultrasonic sensors
ultrasonic sensors

Generally ultrasonic sensors are also called as transducers, and these sensors are used to measure the reflection of a moving object. When a voltage is applied in the form of an electric pulse to the ultrasonic transducer, it vibrates with a certain spectrum of frequencies and produces sound waves. When any obstacle comes within the spectrum of the ultrasonic sensor, then the sound waves get reflect back (echoes) and the process generates electric pulse. Hence, the motion of the object is detected with these echo patterns.

3. IR Sensors

IR sensors
IR sensors

IR Sensor is an electronic device that emits or detects IR radiation to sense the aspects of its background. This consists of an IR LED source that emits the light with the specific IR wavelengths. This particular frequency of the IR beam is received by the detector circuit which also consists of an optical component to focus the infrared radiation and also to limit the spectral response.

Motion Detector Circuit

Motion detector circuit can be implemented by using different controllers like 555 timers, microcontrollers, etc., and by using different sensors like IR, PIR, and the Ultrasonic sensors discussed above.

Motion Sensor Detector Circuit with a Timer

Motion detector consists of two sections: transmitter and receiver. A 555 timer and IR sensors are used in the transmitter section, whereas photo transistor, another 555 timer and an alarm are used in the receiver section. In the transmitter section, the IR sensor generates a high-frequency beam, and this frequency depends on the RC constant of the timer. In the receiver section, a photo-transistor conduction enables the timer circuit to generate an alarm for a specific time that also depends on the RC constant.

block diagram of motion sensor
block diagram of motion detector
motion detector circuit
motion detector circuit

For sensing the motion of any object, the IR sensor and photo transistors are placed in such a way that the beam emitted by the IR LED towards the transistor gets obstructed. In the transmitter section, the IR sensor produces a high-frequency beam of 5 kHz with the help of the 555 timer, which is set to unstable the multi-vibrator; and, the frequency that is produced by the sensor in the transmitter is received by the photo transistor.

When there is no interruption in between the IR sensor and the photo transistor, then the frequency will be in one phase, and therefore, this circuit will not give any output in the receiver side. When there is a disturbance between the infrared sensor and the photo transistor, the frequency detected by the transistor will be in a different phase. This triggering makes the timer to give a buzzing sound. In this way, one can design the motion-detector alarm for several applications.

Motion Detection by Microcontroller

This circuit uses a microcontroller as a main controller similar to the timer in the above project. This system also uses ultrasonic sensor to detect the motion of any object. As we have discussed above, the ultrasonic sensor detects an object with the use of sound waves with specific spectral frequency. This object detection by the ultrasonic sensor is implemented in this project to operate door gun by properly programming the microcontroller.

motion detection by microcontroller
motion detection by microcontroller

When the object motion is sensed by the ultrasonic sensor that operates at a 40MHz sound frequency, it gives signals to the microcontroller as an interrupt signal. By receiving this signal, the microcontroller sends the command signals to the transistor circuitry to operate the door gun. With this ultrasonic motion detection, one can operate several loads like lamps, fans and other appliances in place of the door gun.

Applications of Motion Sensing Circuit

Motion detection can be used in:

Thus, this article concludes with the brief description, explanation and information about the motion detector circuit and its working principles. We hope that you have got a better concept and understanding of the motion detector.Furthermore any queries regarding this article or touch controlled projects, please share your views on this article in the comment section below.

Photo Credits

  1. Motion detector by thomasnet
  2. PIR sensor by sumeetinstruments
  3. Ultrasonic Sensors by imimg
  4. IR Sensors by wordpress
  5. motion detector block diagram by electronicshub
  6. motion detector circuit diagram by electronicshub


  1. Hi sir. I want to know what motion sensor can I use for posture alignment device that vibrates when the person is slouching. 🙂 thanks

    1. Tarun Agarwal says:

      Hi Nick
      The Biomechanics monitoring sensor is used for a person when he/her is slouching

  2. Deependra singh says:

    I glad to see this site

  3. norfairuz says:

    hello sir .can you help me what type of IR sensor that suitable to use to detect motion of human at night ? thank you

    1. Tarun Agarwal says:

      Hi norfairuz
      I sincerely appreciate your kind response regarding my article. As per your query, you can use an Infrared sensor for the purpose of motion detection.
      And once again please visit our domestic website
      For more details please contact to Mr. Sathish on +91 8885507011 or you can email us on

  4. Ghulam murtaza says:

    sir i need exact working operation of passive and active infarared sensors.please help me

    1. Ghulam murtaza says:

      sir i need a material or report on passive and active infared(working principle,advantages,disadvantages,applications)

      1. Tarun Agarwal says:

        Hi Ghulam Murtaza, Click the links below for help:
        Please check the user friendly website for complete details in the kit content section: and go through the FAQ: Further if you have any queries you can call us on the toll free no. 1800 108 7475 for clarifications/personal counseling. Raji (Mobile: +91 9959178000)

    2. Tarun Agarwal says:

      Hi Ghulam Murtaza, Click the links below for help:
      Please check the user friendly website for complete details in the kit content section: and go through the FAQ: Further if you have any queries you can call us on the toll free no. 1800 108 7475 for clarifications/personal counseling. Raji (Mobile: +91 9959178000)

  5. Himungshu Kashyapa says:

    Sir, can you please explain me the circuit? How all the things in the circuit work basically, in technical terms. I have selected this as my project. Thank you.

    1. Tarun Agarwal says:

      Hi Himungshu, Please follow the link: for help. You can download project abstract and seminar presentation also from the website. Please check the website for complete details in the kit content section: and go through the FAQ: for details. Further if you have any queries you can mail us at or please call on the toll free no. 1800 108 7475 for clarifications/personal counseling. Raji (Mobile: +91 9959178000)

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