Just use a pair of PIR (passive infra red) motions sensors on the ends of the roof. The only way they'll see any 'motion' in the roof plane is if someone is trying to steal the cameras. As for capacitance sensing, just drive the roof with a high frequency (400kHz) AC signal though a high value (1k) resistor (and coax). Any loading by a human will cause the amplitude to drop. There will also be a phase shift so you could use the PIC PWM to generate the AC drive, and the CCP to measure the delay across the series resistor. Any load change will change the delay by enough uSec that you can detect it. And with long term averaging for the threshold, you can account for changes caused by rain, drying or temperature. Just be sure to put clamp diodes/MOV on the cable sufficient to handle a lightening strike . Robert Walter Banks wrote: > Theives have been known to take the replacements > in a week or so. > > w.. > > > Andre Abelian wrote: > > >>Hi to all, >> >>last night some one stole my 2 security cameras by going on the roof. >>Since there is an alley I put cameras just in case. now after 7 years >>of living there without seeing any problem this is our first problem >>seen. no thing got lost but this could be sign of some thing else. >>My plane is: >>any time some one goes on the roof turn alarm on >> >>My question is: >>around the roof there is 24 square feet metal that is isolated >>thinking to add capacitance sensitive circuit if any once wants to >>go on the roof it will trigger the alarm or any kind of sound. >>The reason for capacitance sensitive is if they wear gloves it still >>will sense it. >> >>I know cypress PsOC does this but I am not good at PsOC and my >>choice is PIC so far. Does any one have any capacitance sensitive schematic >>that I can add to pic? >> >>I can only see hand how he is removing the camera by bending the camera around >>but what purpose I do not know. >> >>thanks >> >>Andre >> >>-- >>http://www.piclist.com PIC/SX FAQ & list archive >>View/change your membership options at >>http://mailman.mit.edu/mailman/listinfo/piclist > > > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist