Byonk

Bring Your Own Ink - Self-hosted content server for TRMNL e-ink devices

Features

• Lua Scripting - Fetch data from any API, scrape websites, process JSON - all with simple Lua scripts.
• SVG Templates - Design pixel-perfect screens using SVG with Tera templating (Jinja2-style syntax).
• Variable Fonts - Full support for variable font weights via CSS font-variation-settings.
• Smart Refresh - Scripts control when devices refresh - optimize for fresh data and battery life.
• 4-Level Grayscale - Blue-noise dithering optimized for e-paper’s 4 gray levels.
• Device Mapping - Assign different screens to different devices via simple YAML configuration.

Quick Start

# Run with Docker
docker run -d -p 3000:3000 ghcr.io/oetiker/byonk:latest

Or download a pre-built binary for your platform.

Point your TRMNL device to http://your-server:3000 and it will start displaying content.

How It Works

flowchart LR
    A[Lua Script] --> B[SVG Template] --> C[Dithering] --> D[TRMNL PNG]

1. Lua scripts fetch data from APIs or scrape websites
2. SVG templates render the data into beautiful layouts
3. Renderer converts SVG to dithered PNG optimized for e-ink
4. Device displays the content and sleeps until next refresh

Example: Transit Departures

Lua Script fetches real-time data:

local response = http_get("https://transport.opendata.ch/v1/stationboard?station=Olten")
local data = json_decode(response)

return {
  data = { departures = data.stationboard },
  refresh_rate = 60
}

SVG Template renders the display:

<svg viewBox="0 0 800 480">
  {% for dep in departures %}
  <text y="{{ 100 + loop.index0 * 40 }}">
    {{ dep.category }}{{ dep.number }} → {{ dep.to }}
  </text>
  {% endfor %}
</svg>

Result on e-ink display:

Next Steps

• Installation Guide - Set up Byonk on your server
• Architecture - Understand how Byonk works
• Create Your First Screen - Build a custom display
• API Reference - HTTP and Lua API documentation