lap timer

I have had an arduino for about 7 months now and i haven't done anything really useful with it yet so i was thinking it would be cool if a could make a lap timer to record my lap times on my motocross track but i am not sure how to sense when the bike crosses the finish line.I was thinking of using a laser and photo diode for a break beam but i think there are better ways but i don't know what.Any suggestions?

make a wireless transmitter and press a button on your bike to send a signal to a receiver when you cross the line?

An important consideration here is:

do you only need to time one person/bike or more?

If serveral bikes are doing rounds, then the laser / photodiode setup would not work.

Starting a project Y with the idea of “making something useful with component X” is often a poor idea. A better approach is often “I want to achieve Y, which X do I require to execute?”.

@cross roads: so he would transmit a “button push” to an external timer? This would be a real overkill just for the sake of getting Arduino into the project. If a push button would be sufficient then a stop watch should be fine.

Udo

It would be nice if i could time multiple bikes at once.

"make a lap timer to record my lap times"

button push on a stopwatch may not be sufficient to record multiple lap times. Storing the times in EEPROM for readout later would be something arduino could do nicely.

"time multiple bikes at once" Ah ha! Scope growth! Happens every time. In that case, I suggest we find the stop watch timer I was helping Warren work on earlier this year. That could easily be adapted to have multiple buttons, one assigned to each rider, to capture the time a button is pushed and write it to EEPROM with a rider # for readback later, or in some manner yet to be defined, or in external memory if more data is needed. As far as a sensor or some other means of beam interruption, that is something to be investigated still.

Here we are

http://arduino.cc/forum/index.php/topic,8877.0.html

bunch of reading, you should be able to glean some good ideas to work from.