OpenTrailPaper is an open-source e-paper bike computer project that transforms the LILYGO T5 E-Paper S3 Pro into a GPS navigation and cycling data platform with offline maps and sensor support.
OpenTrailPaper is an open-source DIY bike computer project built for the LILYGO T5 E-Paper S3 Pro development kit. The project combines ESP32-S3 firmware with Android and iOS companion applications to provide GPS tracking, offline maps, route navigation and cycling data on an e-paper display. It can follow GPX routes, record rides in FIT format and connect to Bluetooth heart-rate, power and cadence sensors.
The LILYGO T5 E-Paper S3 Pro provides the hardware foundation for the project. It features an ESP32-S3 processor, 8 MB of PSRAM, 16 MB of flash storage and a 4.7-inch e-paper touchscreen with a resolution of 960 × 540 pixels. The board also includes Wi-Fi, Bluetooth, a LoRa module and GNSS support, with the firmware able to automatically detect compatible GNSS modules.
OpenTrailPaper’s firmware is based on the ESP-IDF framework, while the project also provides companion applications for Android and iOS. These applications can be used to plan routes, transfer them to the bike computer, generate offline maps, change settings, retrieve recorded rides and install firmware updates through Bluetooth. Once maps and routes have been loaded, the bike computer can operate without requiring a phone or mobile data connection during a ride.
During a ride, the device provides GPS tracking, speed and distance information, live maps and turn-by-turn navigation prompts. It can also run structured workouts using ERG or MRC files and record ride data directly to a microSD card. The project includes tools for creating compatible offline maps using a smartphone companion app, a Python script or JavaScript running in a web browser.
The project is still a DIY platform and comes with some limitations. The T5 E-Paper S3 Pro is not waterproof, lacks a pressure sensor and magnetometer, and its GPS performance could be improved with multi-band GNSS hardware. The hardware buttons are also relatively small, while the touchscreen may be less practical when wearing gloves or riding in wet conditions. Nevertheless, by making the firmware, companion apps and supporting tools openly available, OpenTrailPaper provides makers with an alternative platform for building a custom e-paper bike computer.
