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
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!
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.