A Question on Infrared Motion Detector

[Nicholas]

motion detector with tl084cn

Hi, all
I disassembled an Infrared Detector this afternoon. It is used on automatic sliding door.
I formerly thought that it is a presence detector rather than a motion detector. And I thought there must be a Pyroelectric Infrared Sensor inside.
But I found a couple of Infrared emitter and detector inside it. And I also found it is really a motion detector after I make a test.
Can you show me the hint on how does it really work on detecting human motion?
I mean I'm wondering its working principle.
I also found serval IC on the PCB. They are MC14066, MC14584, LM324 and TL084CN.
Thanks in advance.

 

[usernam]

h**p://www.seas.upenn.edu/courses/belab/LabProjects/1997/BE310S97M5R01.doc

this mite help. he has not used the IC's ur talking abt but u mite get an idea of the circuit.

 

[vfone]

This will help
http://www.glolab.com/pirparts/infrared.html