Okay, I know we've been questing for an all-mechanical DIY finish line, but my laziness got the best of me and after some easy convincing from some co-workers, I caved and bought a microcontroller with plans on building my own electronic finish line.
The controller itself was $30 or so, but the components - the LEDs, resistors, sensors - are all pretty cheap, so I think I can make a kit for less than $50. I'm still waiting on some more components to be shipped before I can do a full two-lane prototype, but so far a one-lane test with a photocell sensor looks promising. I am also going to try the IR sensor again to see which works better. Now that I have control over how the thing works I feel more confident in finding a good balance.
One problem I had with the IR sensor finish line in the past is ambient light. Well, I've accepted the fact that ambient light is a problem I just need to account for. My first attempt at a solution is building in a sensitivity dial that you change based on your environment, high for lots of light, low for darker room. To my surprise it actually worked.
So I'm diving into electronics head first and so far it's turning out pretty well. I'll see what happens when it gets time to solder and actually get all the parts into a nice package, but I'm hoping for the best.
If any of you guys are experienced at soldering or packaging together electronics, please reply or PM me. I might need to pick your brain soon.