Open-Source eInk Bike Computer Trades Sensors for Sunlight-Readable Simplicity

A new open-source cycling computer, OpenTrailPaper, pairs a 4.7-inch e-paper display with a single board carrying GPS, capacitive touch, a front light, USB-C, and Bluetooth 5 for heart-rate, power, and cadence sensors. The e-ink panel stays legible in direct sunlight, and an SD card slot holds offline maps, routes, and ride logs. Firmware flashes over USB straight from a desktop Chromium browser, lowering the barrier for tinkerers who want to build and modify the device themselves.

The design leans minimalist, and the tradeoffs reflect it. There is no barometric altimeter, so total climbing is estimated from elevation baked into map tiles rather than measured directly. The GPS is a basic single-band receiver that locks slower and struggles under tree cover, and the absence of a magnetometer means the map can only orient by direction of travel — it can’t point the right way when you’re stopped. Battery life measured around 7.4 usable hours on a 1,500 mAh build with the light off.

Usability rough edges remain: interaction depends mostly on the touch panel, which is awkward with winter gloves or in rain, and the bare board ships with no waterproofing or IP rating, requiring a case before wet-weather rides. As an open hardware project, its appeal is less about matching commercial units like Garmin or Wahoo and more about offering a hackable, transparent platform that riders can extend and repair on their own terms.