On Thu, 24 Feb 2005, Bob Ammerman wrote:

> For this 'long loop' design I would ensure that the switch path was low 
> impedance. This should greatly reduce its susceptibility to noise. Perhaps 
> one side tied hard to ground, and the other pulled up via a low resistance 
> resistor. The lower the better, within the current limitations of the wire, 
> switch, power supply, etc.

I think that the only reasonable way to make the line distance-proof is 
to match it in impedance and limit the bandwidth on it as much as 
possible. Limiting the bandwidth does not necessarily mean low pass 
filtering, it could be done with AC at a higher frequency to escape 
local noise sources. And adding bidirectional challenge/response 
communication with a microprocessor at the far end would be even better. 
What happens if that long wire triggers by mistake ?

Peter
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist