I've done something similar for my church youth group, who needed to=20
determine the winner of a 4-lane, 25' long race.  It was amazing how=20
close some of the cars were crossing the finish line!!  I used a 16F876,=20
since that is what I had on hand.  Program is in MPASM.

I started the timer when the cars were released at the start gate and=20
stopped the timer when the first car crossed the finish line (broke an=20
infrared light beam - one per lane).  I then displayed the winner via an=20
LED mounted above his lane and displayed the scale "speed" in approx.=20
MPH on a large, multiplexed, LED display.  The kids didn't like the=20
"slow" accurately-scaled MPH displayed, so I fudged it to make it seem=20
the cars were going somewhat faster than they really were!  It is easy=20
enough to change - just modify one constant and recompile and you're=20
good to go!  Should be noted that finish MPH was calculated based on=20
average speed *2 (SERIOUS approximation, assuming linear acceleration).

Anyway,the kids were happy, so that made it worthwhile!

If you're interested in my code, contact me offline & I'll send it to you.

Should be noted, there's hardware to build - at least a microswitch at=20
the start and sensors at the finish.

Good Luck!
Dennis

On 11/07/2011 04:43 AM, backup 725 wrote:
> Hello, I'm looking for some ideas on how I can start building (the
> software) a race timer. This timer has to count at least 20 seconds
> and be accurate enough to 100th of a second.
>
> An LCD would display the time to 3 decimal places and the circuit will
> have a "start", "stop" and "reset" buttons only. Hardware is not an
> issue.
>
> If you have any ideas or any other info then please put it here. Thanks.
>
> Oh BTW, I use 18F4520.
>
> T_ADD
--=20
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