Surfsonar builds a depth sonar and e-ink readout into a surfboard

Foobarbecue, a surfer who rides at beach breaks like San Onofre Bluffs, kept wondering how deep the water was beneath him: waves break when they enter shallow water, and the best place to wait for a good wave is right over a sandbar that can move from day to day. Instead of guessing from wave behaviour, he decided to find out by building a depth-sensing sonar into his own surfboard, hoping to learn about the sand underneath, wave dynamics and maybe even surf better.

The build paired off-the-shelf parts: a Blue Robotics Ping2D sonar set into a hole in the bottom of a foamie board, a Raspberry Pi Zero W with a PiSugar battery, and a Waveshare e-paper display on the deck, chosen because it looks great outdoors in the sun. He cut a trench in the foam for the sensor cable, sealed the edges with silicone, and velcroed a Qi charging pad to the board rack so the electronics top up overnight; the code, mashed from the vendor examples, starts at boot and shows live depth readings.

On the first test surf the numbers were very reasonable once he was past the break: paddling out, he watched the depth tick up from about 2.4 to 3.2 metres at 100 percent confidence. Closer to shore the sonar returned nonsense readings, a failure that Hacker News commenters attributed to air bubbles in the surf zone acting as acoustic black holes rather than to the hardware.

The maker shared the full recipe, a waterlogging test of the cut foam (still 3 grams after two days soaked), and the code on GitHub, and posted it as a Show HN on 2021-10-18. The thread drew 332 points and 91 comments full of suggestions — acoustic matching compounds, passive listening to breaking waves, mapping depth with GPS — and the project carried on: a 2023-05-07 update added GPS and battery monitoring in a rebuilt version of the onboard computer.