OpenTrailPaper: A DIY Open-Source eInk Cycling Computer

OpenTrailPaper is a community-driven firmware project designed specifically for the LilyGO T5S3 4.7 E-Paper PRO hardware. It transforms a development board into a fully functional bike computer capable of offline navigation and performance tracking.

---

🛠️ Technical Specifications

The device leverages a high-contrast e-paper display and the ESP32-S3 chipset to provide a sunlight-readable experience.

---

📱 Ecosystem & Workflow

The system operates through a synergy between the hardware head unit and a companion mobile application.

01. The Companion App

Currently available for iPhone (iOS 17+), with an Android version available via closed beta (request access in Discord).

App Capabilities:

• Route Planning: Search destinations and push GPX files to the device.
• Map Management: Generate and transfer offline map tiles.
• Data Recovery: Sync recorded rides to review distance, power, heart rate, and ascent.
• Configuration: Adjust timezone, units, FTP, and backlight brightness.
• Maintenance: Perform OTA firmware updates via Bluetooth.

02. Standalone Functionality

Once the initial maps and routes are synced, the device is dependent on a phone fully autonomous.

On-Device Features:

• Live Tracking: Real-time GPS speed, distance, and mapping.
• Data Logging: Automatic .fit file creation on the SD card.
• Navigation: Turn-by-turn guidance for loaded routes.
• Training: Execution of structured workouts using .erg or .mrc files.
• Sensor Integration: Pairs with BLE power and heart-rate monitors.

---

⚙️ Hardware Analysis

Supported Board: LilyGO T5S3 4.7 E-Paper PRO

It is important to note that this is a development project, not a retail product.

The Strengths:

1. Visibility: The 4.7" panel is perfectly readable in direct sun.
2. Storage: Integrated SD slot for logs and map tiles.
3. All-in-One: Includes GPS, capacitive touch, front light, and battery on one PCB.
4. Accessibility: Firmware can be flashed directly from a Chromium-based browser.

The Trade-offs:

• Altitude: Lacks a barometric pressure sensor. Total ascent is an estimate based on map data: $\text{Total Ascent} \approx \sum (\text{Elevation}_{\text{tile}_n} - \text{Elevation}_{\text{tile}_{n-1}})$
• GPS: Uses a standard receiver; lacks multi-band support, leading to slower locks in urban canyons or heavy forest.
• Orientation: No magnetometer (compass). The map only orients based on movement; it cannot point North while stationary.
• Battery: A 1,500 mAh battery lasts approximately $7.4$ hours (with the backlight off).
• Interface: The touch screen is difficult to use with rain or winter gloves.
• Durability: The board is bare; it has no IP rating and requires a custom case for weatherproofing.

---

🚀 Getting Started & Contribution

Installation

The setup process is streamlined via a web-based flasher.

• Desktop: Use a Chromium browser for USB flashing and basic map generation.
• Mobile: Use the iOS app for maps that include elevation data.

Help Wanted

The project is seeking improvements. A "perfect" target board would ideally feature:

{
  "desired_hardware": [
    "Barometric Altimeter",
    "Multi-band GPS",
    "Magnetometer",
    "Larger Battery Capacity",
    "Physical Hardware Buttons",
    "Weatherproof Enclosure"
  ]
}

---

🤝 Project Sponsors

Special thanks to the organizations making OpenTrailPaper possible:

• RideCall (ridecall.bike)
• Hummingbird Fuels (hummingbirdfuels.com)