Icarus A 
Does someone have any circuit design on how to interface a tripwire, which I believe is a 'Normally Closed' switch (I think), and opens when "tripped". In my case my NC-switch is a momentary switch with sprint action, mounted on a pig-pen / kennel door / trap-door. As soon as a small animal passes thru, the circuit opens, and my processor should detect it. - Also, how far can I place this switch from the mini2440 ? - What kind of wiring can I run from the mini2440 to this switch ? - Also, I might have to have around 30-40 such switches/tripwires, so I guess I need to use IO-expanders. Wondering if the GPIO pins on the IO-expanders are functionally equivalent to the ones on the processor ? - Does anyone see a problem with this approach ?