Tallying Trampoline Bounces with a Raspberry Pi

Eric Escobar’s daughter recently received a small trampoline for her birthday. Naturally she bounces on it constantly. While most dads would just be happy that this energy is being expended non-destructively, Escobar decided to actually measure the number of bounces.

The setup here is ingeniously simple, as he implemented an HC-SR04 distance sensor to measure how far the bottom of the trampoline’s diaphragm stretches towards it, identifying individual bounces. The build uses info from several sources, including this page for configuring the sensor itself.

Notably, the 5V output signal from this sensor must be modified to work with the Pi’s 3.3V. Also, while you’re getting an “analog” result from the sensor, the ping/responses generated are based on timing, not different voltage levels. Therefore, there's no ADC needed. The sensor can reportedly push out 100 samples/second, giving it an impressive resolution of ±.2CM.

Along with the inherent command line interface of the Pi, Escobar made a basic browser interface that shows the number of bounces with each page refresh. Of course kids aren’t the only ones getting indoor exercise these days. If you want to track your feline as it runs on a "hamster-style" wheel, check out this other Pi-based project.