A DIY e-paper bike computer, Open Trail Paper, is firmware for the Lily GO T5S3 4.7" E-Paper PRO. It shows ride data and offline maps, follows GPX routes, records FIT files, and connects to Bluetooth sensors. You buy and protect the board yourself.

The device features a 4.7" e-paper panel readable in direct sunlight, an SD card slot, GPS, capacitive touch, a front light, battery, and USB-C. It pairs with heart-rate and power sensors over Bluetooth. An optional iOS app handles setup, route planning, map building, ride transfer, settings, and firmware updates over Bluetooth, but the head unit works without a phone during rides.

Tradeoffs include no barometric altimeter, basic GPS, no magnetometer, about 7.4 usable hours from a 1,500 mAh build, weak hardware buttons, and no waterproofing. The project welcomes suggestions and pull requests for better hardware.

Additionally, AI helped create an ANT implementation for ESP32 by messing with undocumented registers, available on GitHub. The project is a development effort, not a finished retail product.