E-Ink Hub

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TRMNL firmware not tested ​

Not tested on real hardware

This integration follows the published protocol and is covered by automated tests, but hasn't been tried on a real device yet. Reports are welcome in the issues.

TRMNL is an e-ink device whose open-source firmware can talk to your own server ("Bring Your Own Server", BYOS). The hub implements that server, so anything running TRMNL firmware works without writing any code:

How it works ​

  1. The device wakes, calls GET /api/display with its MAC (ID) and token (Access-Token), battery voltage, signal and screen size.
  2. The hub answers with image_url, a filename and refresh_rate (seconds to sleep).
  3. If the filename changed, the device downloads and draws the picture, then sleeps refresh_rate seconds.

refresh_rate is the time to the next scheduled change, capped by the frame's longest sleep (60 minutes by default). When nothing changed the hub returns the same filename, so the device doesn't redraw and the battery lasts.

Adding it ​

  1. In the hub: Add Canvas → Add manually → TRMNL with the device's MAC address (it's on the device's setup screen).
  2. On the device's Wi-Fi setup portal, choose a custom server and enter the hub's local URL, e.g. http://192.168.1.10:8080. The Connection tab shows it.
  3. The device calls /api/setup, gets its token and starts showing pictures.

Only devices added in the hub get a token: a TRMNL on your network can't register itself.

Pictures ​

By default the hub sends 1-bit BMPs at the device's resolution, dithered in the hub (what the stock firmware draws). For colour or greyscale panels pick another format under Connection, e.g. PNG dithered to Spectra 6 colours, if your firmware build supports it.