AN4368 Datasheet, PDF (1/18 Pages) STMicroelectronics – Signal conditioning for pyroelectric passive infrared

AN4368
Application note
Signal conditioning for pyroelectric passive infrared (PIR)
sensors
Sylvain Colliard-Piraud
Introduction
Pyroelectric passive infrared (PIR) sensors are widely used in daily life. They are a key component in
motion detection and can be used for security systems, automatic doors, or automatic light control. They
are commonly used to detect humans. For example, when someone is detected in a specified area an
alarm may be triggered or a specific room may be lit. Another common use is with regard to pets, for
example, cat flaps.
Everything on earth has infrared (IR) energy. The IR energy of an object depends on different
parameters such as its temperature, color, and texture. This energy is not visible with the human eye,
but PIR sensors can detect it.
Passive IR sensors are the opposite of active IR sensors that emit energy, such as ultrasound, light, or
microwaves. Active sensors are able to detect a change in the environment when the reflected emitted
signal is disturbed. Active sensors consume more energy than passive sensors.
A basic drawing of a PIR is shown below.
Figure 1: PIR sensor
November 2013
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