An open-source e-ink bike computer you can build yourself

Commercial bike computers are expensive and cloud-locked, but OpenTrailPaper turns a bare e-paper board into a readable, offline navigation tool.

OpenTrailPaper caught fire on Hacker News with 219 points. It is open-source firmware designed for the 4.7-inch LilyGO T5S3 E-Paper PRO development board. Once loaded, the head unit follows GPX routes on offline maps, records ride files to an SD card, and pairs with Bluetooth heart-rate and power sensors.

Why it matters: You get a crisp e-ink display that shines in direct sunlight without paying $400 or giving your ride data to a subscription service. It operates entirely without a phone once routes are synced.

Know this before building: It is a DIY project, not a sealed product. The basic setup lacks a barometric altimeter, compass, and waterproofing, so climbing data is estimated from map tiles, and you will need your own case. A 1,500 mAh battery lasts about 7.4 hours with the front light off.

If you hate screen glare and love open hardware, your next weekend project just landed.