You prolly couldn't do that with just a straight wire but if you make it a coil, or something with inductance then you could prolly measure the change in inductance when one of the objects move (thus streching or compressing the coil).. or you could take and put some kind of ferrious material in one object and a metal detector in the other :P then just use the pic to measure and act on the doppler freq. change. couple of analog ideas... -James, N9XLC -jrhall@globalsite.net -certified NERD -----Original Message----- From: adastra To: PICLIST@MITVMA.MIT.EDU Date: Wednesday, January 06, 1999 6:58 PM Subject: Ideas for Pic-based Motion detector? >Greetings, PICMASTERS: > >I need to devise a system which will detect a small movement between two >adjacent wires. The wires would be about 30 feet long and spaced >(non-uniformly) about 1 inch apart. They are normally stationary (fixed to >moveable objects), and I need to detect if they are suddenly moved either >closer together or farther apart, approximately plus-or-minus 1/4 inch, as a >result of an impact on one of the objects. (For various reasons, simple >contact switching will not work in this application.) > >I am thinking of a system where an RF signal(say,100 khz)is applied to one >wire and picked up by the other. The gain of the return signal could be >automatically set to establish an accurate baseline level, and an output >signal generated if the level changed suddenly. > >Perhaps the PIC could generate the RF signal, modulate it, and synchronously >detect the return. (Maybe the synchronous detection is overkill?) I also >need the PIC to generate some specific digital output data when the movement >is detected, but that is less of a mystery to me than the transmit-receive >scheme I am contemplating, as outlined above. > >Any comments or links pertaining to this (or any alternative)approach would >be much appreciated. > >(I guess this is essentially an analog problem, and I apologize if it is too >far off topic.) > >Thanks, Foster >