PIRs are basically made of a pyroelectric sensor (which you can see above as the round metal can with a rectangular crystal in the center), which can detect levels of infrared radiation. Everything emits some low level radiation, and the hotter something is, the more radiation is emitted. The sensor in a motion detector is actually split in two halves. The reason for that is that we are looking to detect motion (change) not average IR levels. The two halves are wired up so that they cancel each other out. If one half sees more or less IR radiation than the other, the output will swing high or low.
This chip takes the output of the sensor and does some minor processing on it to emit a digital output pulse from the analog sensor.
Main technical parameters:
- Power Supply: 3.3 – 5 V Input Voltage
- Sensitivity Range: up to 20 feet (6 meter)
- 110 x 70 degrees detection range