Lesson 1, Topic 1
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4.2 IR and PIR sensor


What is a IR sensor?

An infrared sensor is an electronic device that emits the IR rays and senses the same rays which are reflected by an obstacle.There are two types of infrared sensors: active and passive. Active infrared sensors both emit and detect infrared radiation. Passive infrared sensors are basically Infrared detectors. Passive infrared sensors do not use any infrared source and detector.

Pin Configuration of IR sensor:

What is PIR sensor?

PIR (passive infrared) sensors utilize the detection of infrared that is radiated from all objects that emit heat. This type of emission is not visible to the human eye, but sensors that operate using infrared wavelengths can detect such activity. They are sometimes referred to as ‘motion-based detectors’, as they sense the presence of people, animals and objects through the movement of their infrared wavelengths.They are referred to as “passive” due to the fact that no heat or energy is emitted by the sensor itself. 

Pin Configuration of PIR sensor:

Working of PIR sensor:

At a basic level, PIR sensors operate using positive differential change. Two IR-sensitive slots sit in front of the lens, with their field of “vision” determining the range of detection. While ‘idle’, the ambient level of infrared detected in the room (naturally emitted by all objects) is the same on both slots. The minute an object, person or animal moves through the detecting area, it is sensed by one of the slots before the other, causing a positive differential as it passes by, and a negative differential change as it leaves the area.These differentials are what the PIR sensor uses to detect movement