I was wondering if anyone had any information on an RF or IR Lap timer?

I am looking to build a timer that would keep track of seperate times in a relay race (flyball for dogs actually). I found a software program that would interface via the parallel port so that would be my connection point.

I was originally thinking about a collar transmitter that would time the dog as soon as it broke the start line to when it came back..problem is i would need 4-5 different freq. One for each dog...and a very small narrow range. as it would have to activate it when they run past at the start and the end.

Does this make any sense?? I have found one setup with laser pointers and IR phototransistors that I might try..but the best way (i think) to go about this is RF. I figure i could probably buy the transmitter but I would need to make or at least modify the receiver.

Any ideas?

chunky