Kub Kar Timer

Timer for Kub Kar (AKA Pinewood Derby) races

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My local cub leader reached out to me a few months back... he was building a new track, and wanted a timer for it. This is the result.

Since this is a one-off project, I didn't bother getting PCBs or anything fancy. It mostly used components that I already had on hand. If you had to buy all the components, you should be able to keep it under $25 or so if you get commodity stuff from eBay.

This track is a 3 lane version; however this design should work fine with minor modifications for up to 6 lanes (6 analog pins on the ATMega48).

Each track has a 4x 7 segment display, each of which is driven using a 74595 shift register (each one chained together and driven using hardware SPI). The core if the system is an ATMega48 AVR. The timer start button is a push switch rigged into the starting gate; the finish sensors are IR photo transistors above IR LEDs embedded into the track.

It is a fully enclosed system: no requirement for a computer, USB, or anything other than power. This was a conscious decision made to keep the required operator skill level as low as possible. If running an entire race with multiple heats, you can keep track of everything in a spreadsheet (a Libre Office spreadsheet is included in the git repo), or you can just run things for fun and see the times for each race.

The timer has a resolution down to 10ms, and can go up to 99 seconds (99.99).

There are only two buttons: the start button (hooked into the starting gate), and the stop / reset button (on top of the timer enclosure). The race starts when the starting button is released (when the starting gate falls). Each track timer stops when the car passes the sensor. Once each of the tracks is finished, pressing the reset button (on top of the timer enclosure) will reset everything to 00:00. To manually stop a race (if, say, a car did not finish the race), you can hit the reset button once to stop the race and again to reset.

The track, timer enclosure, etc (i.e. everything that is not the timer circuit) was made by the cub leader, and not included in the scope of this project.

  • Race Day

    The Big One04/29/2015 at 03:16 0 comments

    Today was race day, and things went off without too many bugs. The only real problem was the starting switch; it didn't get activated properly on the starting mechanism release. By holding the starting gate where the button is located, this problem was successfully worked around.

    The other change that I am going to make for next time is the timer resolution. This time I had 4 digits with 10ms resolution (99.99 seconds max). Next time I will have 1ms resolution, with a max time of 9.999 seconds.

    All in all, the race was fun and the kids (and their parents) enjoyed it.


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