OpenTrailPaper bets open-source firmware can beat closed e-ink bike computers

OpenTrailPaper is open-source firmware for the LilyGO T5S3 4.7-inch E-Paper PRO development board that turns it into a bike computer: GPS tracking with a live offline map, GPX route following, FIT ride recording on an SD card, structured workouts, and Bluetooth pairing with heart-rate and power sensors. An optional free iOS app plans routes, builds offline maps and transfers files; once loaded, the head unit records and navigates with no phone, account or subscription.

That open firmware on a cheap e-paper dev board can serve riders who want offline maps, FIT files and ANT+ sensors without a closed, subscription-locked head unit.

The creator, who posts on Hacker News as stingrae and rides in the San Francisco Bay Area, launched the project on 2026-09-04 after using it himself, reporting more than 500 miles ridden on the unit. The Show HN text also pointed to a side result of the work: with AI help, an ESP32 ANT implementation had been built by probing undocumented registers, hosted at github.com/RaemondBW/esp32-ant, because ANT+ lacked official open-source ESP32 support.

The product page is candid that this is a development project, not weatherproof retail hardware: the board offers a 4.7-inch e-paper screen readable in direct sunlight, GPS, SD slot, touch, USB-C and Bluetooth 5, with about 7.4 usable hours from a 1,500 mAh battery, but has no barometer, magnetometer or waterproofing. E-Ink News Daily noted e-paper's low power and sunlight readability make it popular for bike computers, while ANT+ is widely used in cycling sensors without official open-source ESP32 support. The Hacker News thread on 2026-09-04 and 2026-09-05 debated e-ink contrast in sunlight, weather sealing and the future of ANT+ hardware, with commenters comparing the unit to Garmin Edge devices; the creator answered questions in-thread.

E-ink's low power draw and sunlight readability fit an outdoor bike display better than backlit screens, and the chosen board already bundles GPS, SD, Bluetooth and USB-C.

Attacking the ANT+ gap with an AI-assisted reverse-engineered ESP32 driver removed the biggest ecosystem blocker for open bike-computer firmware.

Publishing honest limits — no waterproofing, no barometer, 7.4-hour battery — built credibility with a skeptical DIY audience and fueled a constructive front-page thread.

No account, no subscription and phone-free operation directly answered the lock-in complaints riders make about commercial cycling computers.

The risk is scope: a bare, non-weatherproof dev board is a hobbyist product, so mainstream riders who want durability will still buy finished Garmin-style units.

An open-hardware bet earns trust by publishing the whole loop — code, protocol hacks, honest limits — so buyers accept DIY assembly because the source is theirs to fix.

As of 2026-09-05 OpenTrailPaper is a live open-source project rather than a company: the Show HN thread was still gaining comments, the free iOS app is listed on the App Store with Android in closed beta, and the project page invites board ports and suggestions for better hardware. The site calls it 'a development project, not a finished or weatherproof retail product.' No funding, revenue or legal entity has been disclosed, and the supporting ANT driver is published under an open-source license with a host-runnable test suite.