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By toddthuma
I am seeking advice on how to set up a system to time two CO2 dragsters racing simultaneously down a track. At the start end I wish to start separate timers on both cars as triggered by some mechanism. On the finish end, I would like to sense both cars crossing the finish line and report MPH (and or time) and 1st place finisher. I am hoping to connect the two ends with Sparkfun RJ45 breakouts and connectors. I intend to use an Arduino with a shield. The reporting I anticipate will be done with a large segment LED display. Ultimately, I will place everything in an enclosure, but I want everything working first.

I am not certain what to use as the "presence" sensor. The dragsters are held to the track with fishing line and eyelet screws. The CO2 dragsters move very quickly down the track. I assume the infrared, laser, or photocell trigger used on one end to start the timing can be used at the other end to stop the timing. The rest is math done by the program. The results are output to the segment displays.

I would like to purchase everything from Sparkfun. Any suggestions about which sensors to use to start the timing?