Arduino Interfacing with PIR Motion Sensor

Pir Sensor is most common to detect motion of Passive Infrared radiations that are emitted by Humans/Living things. These radiations are invisible to the human eye but are not to Fresnel lens which enhances the radiations onto PIR detector. The IR sensor itself is housed in a hermetically sealed metal can to improve noise/temperature/humidity immunity. There is a window made of an IR-transmissive material (typically coated silicon since that is very easy to come by) that protects the sensing element. Behind the window are the two balanced sensors. As shown below: PIR sensor itself creates a small millivolt when...