Remote control cars have been popular toys for children and adults alike for decades now. And while there is plenty of fun to be had cruising around, a little bit of healthy competition can add another layer of enjoyment. To race or practice racing, you’ll want some way to time your laps. If you don’t have anyone to operate a stopwatch for you, then you should check out Tom Goff’s tutorial on how to create a non-contact lap timer.

Goff built this specifically for his son to time laps when racing his RC car. It is a simple, affordable, and portable device that is easy to take to any paved area and set up. It acts as both the start and finish line, so it triggers the timer the first time the RC car passes through and stops the timer the second time.

It recognizes the passing RC car using a DIY break beam sensor. Instead of using an off-the-shelf infrared module, Goff made his own sensor. One side has a very bright LED with the beam kept tight by PVC pipe and a convex lens. The other side has an Arduino Nano board that detects that beam using a light-dependent resistor (LDR). The Arduino utilizes the millis() function to count the elapsed time between beam breaks, then displays the results on an LCD screen. An 18650 lithium battery cell and charge controller in each unit provide power.