Moderately priced Passive Infrared
PIR Sensor modules are now widely available. By using these readymade and pre-configured PIR sensors, even an average electronics hobbyist can construct his/her own Motion Sensor Unit.
SB0061 is a pyroelectric sensor module,developed for human body detection. A PIR detector combined with a fresnel lens are mounted on a compact size PCB together with an analog IC (SB0061) and limited components to form the module. High level output (3.3V) of pre-settable variable width (5Secs -18 Minutes) is provided.
Working of the circuit is simple and straight forward. When any movement is detected within near 5-6 metres, around 3.3 Volt is appeared at the base of Transistor T1 and it conducts to fire the next relay driver transistor T2.
As a result, the 12V DPDT relay is energised to power the White LED through current limiting resistor R3. Spare relay contacts can be used as a switch to control any suitable external load. The white LED and the relay remains ON for a duration based on the mono time setting in SB0061, ie from 5 Secs to 18 Minutes.