Building a GPS Bike Speedometer the Easy Way
Want to measure your cycling speed without attaching some ridiculous contraption to your wheels? Mellow_Labs has the solution.
If you own a motorcycle and you want it to accelerate faster, the cheapest and easiest modification is a bigger rear sprocket. That gears down the drive train, improving acceleration at the expense of top speed and efficiency at high speeds — you now have shorter gears. But people who perform this modification usually end up with a problem: the speedometer is no longer accurate. That’s because the motorcycle’s computer calculates speed based on front sprocket rotations and those no longer match actual wheel speed. To avoid such problems and mechanical links altogether, Mellow_Labs designed this GPS-based bicycle speedometer.
Most conventional speedometers determine speed by measuring the rotations over time of something connected physically to the wheels. Even airplanes do something similar, just for wind speed. But GPS gives us a solid-state alternative. We can use GPS to learn the exact position of our vehicle and the time we checked that position. Perform two or more checks and calculating speed is simple. That’s exactly what Mellow_Labs did, using affordable maker-friendly components.
In reality, calculating speed with only two checks would be a mistake. Typical GPS readings aren’t very accurate and the only way to get a useful result would be to take readings at long intervals. But it is easy to mitigate GPS inaccuracies by taking frequent readings — ideally with several satellites.
Mellow_Labs achieved this using a DFRobot FireBeetle 2 ESP32-C6 development, a small microcontroller-friendly GPS module, and a 128×32 OLED screen. Power comes from a small lithium battery and that was easy to wire up thanks to the FireBeetle 2’s onboard charging circuitry. All of those components went into a simple 3D-printed enclosure that can attach to the bicycle’s handlebars — or really anything else. You could even throw it in a Ziplock back and see how fast you’re paddling while kayaking.
This may not be a new concept, but it is awesome to see this being done with affordable components that anyway can access.
