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  • You are at /projects/pinewood_timer/

    The Pinewood Finish First

    This is a Pinewood Derby Race Judge that I designed and built for our local Cub Scout Pack 3 in Petaluma. Shown in action here at a Youth Festival in Petaluma where we demo'ed the pinewood derby outdoors in the blazing sun and the timer worked flawlessly!

    A few years ago I helped run a Pinewood Derby at our local Cub Scout Pack. We had an electronic finish line, built a few years before, that declared the winner of the race. It was a pretty nice timer in theory, it could judge 3 lanes and it printed the time results of each lane in big LED numbers above each lane. But the performance was terrible, the lights had to be dim and it was very touchy, if you looked at it funny it wouldn't register right. It also ran on batteries and you would have to change them a couple times for a half of days operation. Lastly it was complex, it used 3 Atmel processors and lots of wires, it wasn't very well mounted inside so it was also very fragile.

    So I decided to make a better unit. I had some big ideas on what a pinewood derby timer should do. It should operate in any condition, outside, inside, cold or hot. It should have a computer interface. It should tell you that it doesn't think the sensors are in alignment. It should be reliable. And finally it should be simple.

    I did some research and found that I should modulate the IR beams and use an off the shelf detector. Household remotes seemed to work in all kinds of nasty environments, so why could I not have the same reliability on my timer? So I turned to an off the shelf 38Khz receiver commonly used in Televisions and other consumer electronics. For the transmitter side I just created a PWM at 38Khz on an IO pin and wired that to the IR LED. This worked very well and it was almost 100% immune to ambient and direct light.

    In the industrial design section I wanted the pinewood timer to be foolproof in operation, I made all the connectors different, so you could not plug in the cables to the wrong place on the timer. The old timer used telephone jacks for everything, and you could plug in the wrong cables to the wrong place.

    I also made everything as solid as possible, I don't think you could break the electronics inside the timer by handling it. This was not the case in the old timer. The only fragile part on the new timer was the 3 light pipes glued on the bottom of the timer, these were just ABS fittings so at worse they would just have to be glued back on the timer if they broke off.

    It should be noted I didn't use the transistor switch on the output of 'IRo' but wired it directly to the IR out pins of J10.


  • Wood Finish Line being assembed.
  • Controller board and displays before being inserted in Finish Line Box.
  • Controller board being mounted on its mounting plate.
  • IR detector boards being mounted in the Finish Line Box.
  • Controller Board being fited in the Finish Line Box.
  • Controller Board installed in the Finish Line Box.
  • Pinewood Finish First In action - Worked Flawlessly on race day.
  • Old Timer Outside Very nice displays, the only bad thing about the new timer.
  • Old Timer Inside Notice 3 Atmel Processors!

    Design Files

  • Controller Schematic in pdf format.
  • Controller PCB board pdf of layout.
  • Complete Hardware and Software project file, AVR GCC source code and express PCB board files.

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    Last Update at 10-29-2018 2:47 pm
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