Raspberry Pi Pinewood Derby Replay System

As seen here, if you’re familiar with pinewood derby races, they are events were kids or adults build model cars to race down a ramp to see which goes the fastest. While it looks interesting, if these events were to be judged manually, there would certainly be arguments as to which car finished first. To mitigate this problem once and for all, Andre Miron came up with a novel device that not only senses each car at the finish line, but generates an instant replay on a nearby monitor.

An Arduino board takes care of sensing the cars passing the finish line, and displays which place each car came in on an attractive 7-segment display above. Along with this, a Raspberry Pi is setup to display live video, and when it receives a signal from the Arduino, it takes 1.5 seconds of video in its buffer, then plays it back twice in slow-motion. Since the video is taken at 90 FPS, this looks excellent slowed down, and would eliminate the next logical argument of “the sensor wasn’t working correctly.”

You can see it officiating a race in the first video below, and explained further in the second. Code is available in the second video’s description, and a hand-drawn wiring schematic is provided here.