OpenTrailPaper Turns a $90 E-Paper Devkit Into Bike GPS

An Open-Source Bike Computer Built on an Off-the-Shelf Devkit

Cycling head units are one of those categories where the hardware is unremarkable and the software is the moat. OpenTrailPaper, covered by CNX Software on September 5, 2026, goes at that from the other direction: take a devkit you can buy for around $90, write open firmware for it, and end up with a 4.7-inch e-paper bike computer that records rides and navigates routes without a phone in the loop.

• Base hardware: LILYGO T5 E-Paper S3 Pro devkit, roughly $90 on Amazon or $103 on AliExpress
• Display: 4.7-inch e-paper at 960×540 with 16 grey levels and a GT911 capacitive touch layer
• Silicon: ESP32-S3N16R8 dual-core Xtensa LX7 at 240 MHz with 8MB PSRAM and 16MB flash
• Battery: 3.7V 1,500mAh, quoted at under eight hours per charge with the front light off

What the Hardware Gives You

The T5 E-Paper S3 Pro is a well-specified board for this job, which is presumably why it was chosen. Wireless covers Wi-Fi 4, Bluetooth 5.0 LE and an SX1262 LoRa radio. Positioning comes from either a u-blox MIA-M10Q or a Quectel L76K GNSS module, which the firmware autodetects. There is a PCF8563 real-time clock, a BQ25896 charger paired with a BQ27220 fuel gauge, a microSD slot and a 4-pin Qwiic connector for adding sensors. The whole thing measures 129 × 69 × 11 mm.

That LoRa radio is the part that separates this from a generic GPS logger. It is the same SX1262 that shows up across the maker mesh-networking ecosystem — the LILYGO T-Echo Card's solar LoRa mesh build uses it too — which means a bike computer built on this board sits one firmware feature away from off-grid messaging on group rides.

What the Firmware Actually Does

The feature list is closer to a commercial head unit than a weekend project. OpenTrailPaper displays a live map with GPS tracking, records rides as .FIT files so they import cleanly into the usual training platforms, follows GPX routes with turn-by-turn guidance, and pairs with Bluetooth heart-rate and power meters. It supports structured workouts from .erg and .mrc files, and it stores offline maps so none of this depends on a phone or a signal.

The firmware is written against ESP-IDF and the project publishes companion apps — iOS through the App Store, Android currently in closed beta via the project's Discord. Everything lives on GitHub under the RaemondBW/OpenTrailPaper repository, with a project site at opentrailpaper.com.

What Are the Limitations Before You Build One?

The project is refreshingly direct about them, which is a good sign. The device is not waterproof, which for a bike computer is the headline caveat — you will want an enclosure before it sees real weather. There is no barometric pressure sensor, so elevation comes from GPS rather than a baro, and GPS is single-band. There is no magnetometer either, so the map orients by direction of travel and will not rotate correctly when you are stopped. The buttons are small, and the touch layer is unreliable with gloves or in rain.

None of that is surprising for a devkit-based build, and most of it is addressable: the Qwiic connector is right there for adding a pressure sensor, and an enclosure is a printing job rather than a redesign. Sub-eight-hour battery life with the light off is the constraint that matters most for long days, though e-paper means the display itself costs almost nothing to hold an image.

Why E-Paper Is the Right Screen Here

Direct sunlight is where transflective and e-paper displays win outright, and a bike computer lives in direct sunlight. Sixteen grey levels at 960×540 is enough resolution for a legible map and a data field grid, and the panel draws power only when it refreshes. That is the same tradeoff that makes e-paper compelling across the maker-hardware space, from the PocketMage ESP32-S3 e-paper PDA to M5Stack's Paper Mono. More builds like this one are tracked in our mini computers and SBC coverage.

Sources: CNX Software — OpenTrailPaper transforms LILYGO T5 E-Paper S3 Pro devkit into a DIY e-paper bike computer — September 5, 2026; OpenTrailPaper project on GitHub — September 2026.