I'm developing a timer system for dog agility matches. Using ATmega8 for the timing and display etc. and planning to use tiny15 for the start and stop ports.
My question is, will there be problems if I use external interrupts to start and stop the counting as I need to have atleast 25 meters (80 feet ?) of cable between the ports and mainboard. I haven't got all the parts yet so I'm asking in advance for any suggestions on how to avoid falsely starting or stopping the timing.
The ports only sends an 1 or 0, depending on if it has been toggled (ir beam broken).
For the cable I'm planning to simply use outdoor mains cable (three wires, vcc, gnd and signal).