Hi there,

Interfacing alright, but I am more interested in knowing about the motion detector itself.

Charles can you explain how motion detectors work in principle.

Are they all ultrasonic, RF or IR based. Do they compare the phase shifit in the reflected signal or monitor the gain due to reflected signal.

I got a motion detector. It has an LDR and (supposedly) a photo transistor (a small round shape thing with a square black photo cell like window on top of it). It works even in darkness.

Regards

Simon