Digital stopwatch triggered by photoresistor/laser pointer gates

Thread Starter


Joined Jan 1, 2010
Hello all,

I am a new member of this community and would like to ask for your help in constructing a timing device which would time my son's hotwheels.

I am a total novice regarding electronics and circuits so apologies in advance for any stupid questions I may ask.

What I would like to construct is a timing device which has photoresistor/laser pointer start and finish gates which would trigger the stopwatch to start when the car passes through the start gate and would trigger the stopwatch to stop when the car passes through the finish gate.

I have seen examples of these timing devices discussed in various forums, but at a level of detail which I cannot follow. It would be greatly appreciated if anyone could offer some advice to a layman on how to construct the device.

So far I have purchased a cheap digital stopwatch and two laser pointers from Kmart, and some photoresitors from RadioShack.

Any help you can offer regarding the additional components I need, and how to assemble them into the timing device, would be greatly appreciated.

Thank you,