Show HN: Open-Source eInk Bike Computer
OpenTrailPaper introduces an open-source e-Ink bike computer, combining DIY hardware with custom firmware for ride data, navigation, and sensor integration. This project captures attention for its innovative use of e-paper technology and an impressive AI-assisted hack for ANT+ protocol implementation. It sparks a lively debate on the practicalities of e-Ink displays versus traditional bike computers or smartphones in the cycling world.
The Lowdown
OpenTrailPaper is a compelling open-source project that allows cycling enthusiasts to build their own e-paper bike computer using a LilyGO T5S3 4.7" E-Paper PRO board. The project's firmware provides comprehensive ride data, offline mapping capabilities, GPX route following, and FIT file recording, all while connecting to standard Bluetooth sensors.
- Core Functionality: The device displays essential ride metrics, navigates using pre-loaded offline maps and GPX routes, and supports structured workouts. All ride data is recorded to an SD card as FIT files.
- Sensor Integration: It pairs with various Bluetooth sensors for heart rate, power, and cadence, providing a complete data capture experience.
- Companion App: An optional iOS application simplifies route planning, offline map generation, ride data transfer, settings configuration, and firmware updates, though the device operates independently during a ride.
- Hardware and Design: The system leverages a 4.7-inch e-paper display known for its sunlight readability, an SD card slot for storage, integrated GPS, capacitive touch input, a front light, battery, and USB-C. Firmware installation is possible via a desktop Chromium browser over USB.
- Acknowledged Trade-offs: The current iteration lacks a barometric altimeter (relying on map elevation data), a multi-band GPS module (for faster, more accurate fixes), a magnetometer (limiting map orientation when stopped), and robust physical buttons or waterproofing. Battery life is approximately 8 hours.
- Technical Achievement: A standout feature is the AI-assisted implementation of the ANT wireless protocol for the ESP32, achieved by exploring undocumented hardware registers.
OpenTrailPaper presents a robust open-source alternative for cyclists seeking a customizable and self-owned device, showcasing significant DIY ingenuity despite its current hardware limitations.
The Gossip
The e-Ink Evaluation: Pros, Cons, and Comparisons on the Road
A central debate revolved around the practical suitability of e-Ink for a bike computer. Proponents praised its excellent readability in direct sunlight, low power consumption, and paper-like display quality, arguing these are paramount for outdoor cycling. The creator clarified that refresh rates can reach 20Hz and it has a backlight like a Kindle. Critics, however, raised concerns about refresh rates for navigation, visibility in low light or tunnels, lack of color for maps, and potential fragility or UV damage from prolonged sun exposure. Some suggested transflective LCDs or existing bike computer screens offer a better balance.
ANT+ Acquisition & AI Ingenuity: Decoding Undocumented Protocols
A significant point of fascination was the project's ability to implement ANT+ protocol support for the ESP32, reportedly aided by AI in deciphering undocumented registers. Commenters expressed surprise and admiration, noting the technical challenge of such a feat given ANT+ and Bluetooth Low Energy (BLE) are distinct protocols, albeit sharing the same physical layer. The discussion also touched upon the future of ANT+, with some pointing out its declining relevance due to EU regulations mandating data encryption, pushing new devices towards BLE.
The DIY vs. Device Dilemma: Phones, Commercial Units, and Open-Source Appeal
The discussion often compared OpenTrailPaper to existing commercial bike computers and the common practice of using smartphones for cycling. Enthusiasts for DIY and open-source solutions appreciated the project's customizability, ownership of data, and the simple joy of building. However, many weighed the current project's trade-offs (e.g., lack of waterproofing, basic GPS, short battery life compared to high-end units) against commercial offerings from Garmin or Coros, which boast long battery life and ruggedness. The use of phones as bike computers was also a popular topic, with participants noting convenience but also downsides like poor visibility, overheating, battery drain, and potential damage to phone cameras.