Hi Mark,

Interfacing a motion detector to an 8051 is not hard. Poptronic magazine had an article about how to do it about six months ago. On the hardware side they took and modified the motion detector output by eliminating the speaker and running its output into an optical coupler IC that is available from Radio Shack. Once you get your input feed into the 8051 you will need to write some software to control it. I have done this using an external modem. Whenever the motion detector goes off it calls a beeper using an external modem. The software example can be seen on http://members.aol.com/cpu8052/index.html. I am laying out a printed circuit board for the hardware; visit the web site for more details as they develop.

Regards,

Charles Bannister