OpenTrailPaper
DIY hardware · open-source firmware

A DIY e‑paper bike computer

OpenTrailPaper is firmware for the LilyGO 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.

01 — Device controls

Device walkthrough

Each item shows the screen it describes. Use the orange touch target on the device to move between related screens.

Device screen

    02 — Optional iPhone app

    Use the app for setup and file transfer.

    The iOS companion can plan and transfer routes, build offline maps, copy recorded rides, change settings and install firmware updates over Bluetooth. The head unit does not need the phone during a ride.

    View in the App Store → Free · iPhone · iOS 17 or later Android is in closed beta — ask in the Discord to join.
    Route preview after searching a destination
    Plan a routeSearch for a destination, check the proposed route and send the GPX file to the device.
    Rides list in the app
    Copy recorded ridesTransfer rides from the device, then review the map, distance, power, heart rate and estimated ascent.
    Settings with a firmware update pending
    Settings and updatesSet FTP, timezone, units and backlight level, or install a firmware update over Bluetooth.

    03 — Device and phone

    What works without a phone

    After routes and maps are loaded, the head unit can record and navigate by itself. There is no account or subscription. The app is used when you want to prepare or transfer data.

    On the device — every ride
    • GPS tracking with speed, distance and a live map
    • Records each ride to a .fit file on the SD card
    • Turn-by-turn prompts along a loaded route
    • Runs structured workouts from .erg or .mrc files
    • Pairs with heart-rate & power sensors over Bluetooth
    • Works without a phone or data signal once maps and routes are loaded
    In the app — setup and transfer
    • Plan a route and send it to the device
    • Build offline maps for a new area
    • Create workouts and arrange the device screens
    • Pull rides off the device and review them
    • Change settings and update the firmware

    04 — Supported hardware

    Currently supported on one board

    OpenTrailPaper currently targets the LilyGO board below. It is a development project, not a finished or weatherproof retail product.

    LilyGO T5S3 4.7" E-Paper PRO

    ESP32-S3 · 16 MB flash · 8 MB PSRAM · 960×540 e-paper · BLE 5

    Supported

    Strengths

    • A 4.7" e-paper panel that is readable in direct sunlight
    • An SD card slot for offline maps, routes, ride files and logs
    • GPS, capacitive touch, a front light, battery and USB-C on one board
    • Bluetooth 5 for heart-rate, power and cadence sensors
    • Firmware can be installed from a desktop Chromium browser over USB

    Tradeoffs

    • No pressure sensor. There’s no barometric altimeter, so climbing is derived from elevation baked into the map tiles rather than measured — total ascent is an estimate.
    • Basic GPS. The receiver works, but a modern multi-band module would lock on faster and hold a fix better under tree cover or between buildings.
    • No magnetometer. Without a compass the map can only orient from your direction of travel, so it can’t point the right way while you’re stopped.
    • Measured baseline: about eight hours. A 1,500 mAh build ran for roughly 7.4 usable hours with the front light off. Power work is ongoing, so newer builds may differ.
    • Weak hardware buttons. Most interaction goes through the touch panel, which is fiddly with winter gloves or in the rain.
    • No waterproofing. The board ships bare with no seal or IP rating, so it needs a case or a bag of its own before you ride it in the wet.

    Got a better board in mind?

    Suggestions and pull requests welcome

    Help wanted

    A better target board would include a barometric altimeter, multi-band GPS, magnetometer, larger battery, usable hardware buttons and a weatherproof case. If you know of one, open an issue. Board ports are also welcome in the source repository.

    Have the hardware?

    Install the firmware and prepare an SD card.

    The setup page flashes the board over USB and can build basic offline maps. It requires a desktop Chromium browser; the iOS app produces maps with elevation data.

    Read setup instructions →

    05 — Sponsors

    Project sponsors

    Thank you to the organizations supporting OpenTrailPaper.