All objects emit infrared radiation which is not visible to the human eyes. A Pyroelectric/Passive InfraRed (PIR) sensor detects motion by sensing changes in infrared radiation. This includes movement of human or animals.
This module is very easy to use with only 3-pin connector. The pin-out is silkscreened on the board (you might need to remove the plastic lens to see it). Just connect VCC pin to 5V source, GND pin to ground and OUT pin is where you read the sensor. The OUT pin is normally LOW and gives you HIGH when motion is detected and goes back to LOW after a while when movement is no longer detected.
This module has 3.3V digital output, hence the usage of analog-to-digital converter is not necessary. It is also safe to use it with 3.3V system such as Raspberry Pi. The trigger delay and sensitivity are adjustable with two variable resistors. A removable plastic Fresnel lens is used to enhance its range and sensitivity.
This kind of sensor is commonly used in security system and energy saving lighting appliances. It is not always necessary to connect this sensor to a microcontroller. You can also connect it to a relay or an LED for a simple trigger.
Tips: A single trigger is normally a false alarm. Therefore you might want to wait for several triggers in a row in your coding.
