I wanted a cycling computer with turn indicators and I didn’t want to pay for one. So I built one.
The hardware
A small module that mounts under the saddle. Inside: a microcontroller, a GPS, a Bluetooth radio, and a reed switch that reads a wheel magnet as the wheel turns. The reed-switch + magnet combo gives you real-time wheel RPM with no latency — GPS alone is too smoothed to feel responsive on a bike. Rear-facing left and right indicator lights are controlled by app buttons. Powered by a cheap external power bank so the module itself doesn’t need charging discipline.
The app
Bluetooth pairing to a phone app that shows live speed, trip distance, the GPS breadcrumb, and session controls (start a ride, stop, export). The indicators are triggered from the same app. Nothing fancy — but everything reads instantly and nothing needs internet.
What I liked about the project
It’s the smallest self-contained hardware + software product I’ve built. Start a ride, mount the module, ride. The whole UX is about a dozen interactions. Every part of it is something I can fix. That feels different from software where “fixing it” usually means the feature shows up for everyone in production six weeks later.
A weekend project, still usable.