PeterQuinn925 swims for exercise, and to train for the occasional triathlon, but when doing so he often zones out and forgets how many laps he has swam. To solve this problem without spending a lot of money on a commercial solution, he created his own counter using an Arduino Nano and an ultrasonic sensor.

The sensor detects when a swimmer approaches, and the system calculates distance based on this, assuming that a lap is roughly 50 yards or meters. This info is announced audibly via a speaker/amplifier using an Arduino speech library and is shown on a 7-segment display.

Still something of a prototype, the device is currently housed in a takeout food container, but it looks like an interesting and useful concept. Code is available on GitHub if you want to make one for yourself.