[mdlug] Raspberry Pinewood Derby

[Aaron Kulkis]

Ingles, Raymond wrote:
> Used my Raspberry Pi at my sons' Cub Scout Pinewood Derby yesterday. It was a quick hack set up with about two hours of experimentation, but it worked.
>
> I hooked up a Playstation Eye (the PS3 version of the EyeToy) to the Pi and used it to record the finish line. The Eye is capable of 120fps at 320x240 resolution (125fps by some reports), but the best I could reliably get out of the Pi was 75fps. And to do that, I had to eliminate any and all recoding; I was just dumping the raw video directly to a file via ffmpeg. In my experiments, I never saw the Pi pull down more than 90fps at a burst.
>
> The Pi couldn't even play that 75fps video back at full speed; it pegged the CPU at around 30-40fps. (I imagine if I'd recoded it, it would have done better. It was YUV422 video, and had to be software-converted to RGB to play.)
>
> Anyway, I set it up to play at 15fps - which only hit maybe 50% of the CPU - then paused and went frame-by-frame when the cars appeared on the screen. They were a tad blurry, but there was only one race out of several dozen that was too close to call and had to be re-run. Next year I want to set up at least a sensor to trigger the start of recording. And I'll see if I can do enough vision processing to pick out the frame where the cars cross the finish line.
>
> All the scripts and such are home, but I'll see if I can extract and post them here. Not a bad hack for stuff I had just laying around.
>
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Would you like a schematic for a very SIMPLE digital-logic circuit which can determine
the winner as long as the cars arrival times differs by > 1E-7 seconds, using nothing
more than a 555 chip (to provide a clock), 3 latches, flip-flops (D, T, SR, or JK),
and bit of 7400 glue-logic ?

The chips should come to a grand total of < $5.00.

That way, you can use the camera footage only for "Ooooh! Aaaah!" Instant-reply, rather than having 
to rely on it for judging the race results.