Looking for a simple optical lap timing circuit design...

[Nullified]

Hi, I'm new here, but this place seems really cool and it looks like there's a lot of information on here. Anyways to the point, I'm on my University's (University of Missouri-Rolla) Formula SAE team and currently we use a standard stopwatch to time laps of our cars in practice, but I was hoping there might be a simple circuit that can be built to take times. There is only one car on the track at a time and it would be nice to have times accurate down to the thousanth (ex. 34.562 seconds). Does anybody know of where I can find a circuit that's designed to do this? Oh and to make things simple I would prefer it be an optical circuit.

Thanks in advance!

 

[philba]

What kind of display do you want? led or lcd? size? or do you want to hook it up to a computer? perhaps automatic recording of lap times would be be a good thing?

there are several components to this. counter, display, trigger and, optionally, communication to PC. I doubt you will find a circuit that is 100% what you want, but you should be able to find some pieces that can be put together.

the counter/timer part is straight forward. there are tons of circuits out there. however, most of them only do HH:MM:SS. getting to milliseconds won't be that hard but may take some design work. It's doable with out a microcontroller but a lot easier with one (steep learning curve, though). there are several counter chips that could do what you want.

The triggering mechanisms are going to be tricky. how wide is the track? distance is going to be your biggest headache. I would try using a laser pointer on one side and a photo transistor on the other. carefull alignment of the laser is needed. It also needs carefull shielding of the PT (to avoid ambient ligth effects). I would also modulate the laser pointer (not sure if that's even possible with a cheap laser pointer) and look for that on receive side to improve error rejection. Here's one that might be adaptable **broken link removed** note that you can use seperate power supplies for the laser and the rest of the circuit.

 

[Nullified]

Well the display doesn't matter too much, just whatever is simplest, and it might even be simpler to hook it straight up to a computer. I found this: https://www.willegal.net/light/light-main_body.htm which might be pretty much what I'm looking for but I would still need the laser most likely...

 

[philba]

It may well do what you want though I am always a little dubious of these kind of deals. no schematic and no source code for the microcontroller. If you have to make changes, you are kind of screwed. It looks like he will only provide the code in a pre-programmed chip. You will have to make your own PCB based on his design since there don't appear to be schematics available. It's up to you - it may work out fine though you should ask what happens if it doesn't work. will he help you get it working?

Phil