PIR Sensor — Passive Infrared Sensor

A Passive Infrared (PIR) Sensor an electronic sensor that measures Infrared Ray (IR) light radiating from objects in its field of view. PIR sensors allow you to sense motion. They are small, inexpensive, low-power, easy to use and don’t wear out. They are most frequently utilized in PIR-based motion detectors. PIR (Passive Infrared) sensors are commonly utilized in security alarms and automatic lighting applications.

The PIR sensor consist of 3 pins, those are VCC(Input), GND(Ground), Output.

  1. Pin1 corresponds to the drain terminal of the device, which connected to the positive supply 5V DC.
  2. Pin2 corresponds to the source terminal of the device, which connects to the ground terminal via a 100K or 47K resistor. The Pin2 is the output pin of the sensor. The pin 2 of the sensor carries the detected IR signal to an amplifier from the
  3. Pin3 of the sensor connected to the ground.


Working Principle of PIR Sensor:-

Passive infrared (PIR) sensors use a pair of pyroelectric sensors to detect heat energy in the surrounding environment. These two sensors sit beside each other, and when the signal differential between the two sensors changes (if a person enters the room, for example), the sensor will engage A PIR sensor includes two main parts like pyroelectric sensor and fresnel lens.

In the following diagram, the sensor is a round metal including a rectangular crystal within the center. The passive infrared sensor does not radiate energy to space. It receives the  infrared radiation from the human body to make an alarm. Any object with temperature is constantly radiating infrared rays to the outside world. The surface temperature of the human body is between 36° C – 27 ° C and most of its radiant energy concentrated in the wavelength range of 8 um-12 um. A fresnel lens is a special lens that focuses the IR signals on the pyroelectric sensor. Here, the pyroelectric sensor is capable of detecting different infrared radiation levels.

Specifications and Features :

The features and specifications of the PIR sensor include the following.

  1. The recommended input voltage supply is +5V.
  2. The output voltage is 3.3V.
  3. It can differentiate between the movement of an object & human.
  4. Operating modes are repeatable & Non- Repeatable.
  5. The current drain is <60uA.
  6. The detection angle is <140°
  7. The detection distance is 3 to 7m.
  8. Blockade time by default is 2.5s.
  9. Working temperature ranges from -20-+80°C.
  10. Low power utilization – 65mA.

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