Open-Source eInk Bike Computer: OpenTrailPaper
Original: Show HN: Open-Source eInk Bike Computer
Why This Matters
Demonstrates growing DIY open-source hardware momentum in the cycling tech and wearables space.
OpenTrailPaper is open-source firmware for the LilyGO T5S3 4.7" E-Paper PRO board, turning it into a DIY bike computer with GPS tracking, offline maps, GPX navigation, FIT file recording, and Bluetooth sensor support. No subscription or account required.
OpenTrailPaper is an open-source firmware project that transforms the LilyGO T5S3 4.7" E-Paper PRO development board (ESP32-S3, 16 MB flash, 8 MB PSRAM, 960×540 e-paper display, BLE 5) into a fully functional bike computer. Core features include GPS speed and distance tracking, turn-by-turn GPX route navigation, structured workout playback from .erg/.mrc files, and ride recording to .fit files on an SD card — all without a phone or data connection once maps and routes are loaded. An optional iOS companion app (free, iOS 17+, Android in closed beta) handles route planning, offline map building, ride transfer, settings management, and over-the-air firmware updates via Bluetooth. The device runs approximately 7.4 usable hours on a 1,500 mAh battery with the front light off. Acknowledged limitations include no barometric altimeter (ascent is estimated from map tile elevation), basic single-band GPS, no magnetometer, no waterproofing, and weak hardware buttons. The project is explicitly described as a development project, not a finished retail product. Firmware can be flashed directly from a Chromium browser over USB. The maintainers are actively seeking contributions, including ports to boards with barometric altimeters, multi-band GPS, and weatherproof enclosures.