No, TRMNL generate the images themselves. The device requests the image every so often (with an interval configurable by the server). They've (understandably) built the firmware to be pretty specific to their service, though you can build your own server for it as well (it's just a JSON response with the image to fetch).

The API is:

You write HTML templates (that are stored on their servers) then can post data to them (or have them poll an endpoint to get the data) to "merge" into the template.

Think:

    <h1>Hi {{ username }}</h1>
    <div>You have {{ openPRCount }} open PRs</div>

And you need to provide (via push or pull):

    {"username": "joshstrange", "openPRCount": 10}

That might not be the exact syntax (I wrote my custom plugin a month or two ago and haven't touched it since).

They provide a "UI Library" (Design System) [0] to give you building blocks of UI to use if you want.

It made it really easy to get started. They limit to 1 screen update every 15min (that is the fastest you can have the screen update). But you can press the restart button on the back of the device to force it to update, you might need to force your plugin to re-generate the image before you do that.

If you want to flash your own firmware you can lower that (at the expense of battery life) value or even have it call out to your own server that can do whatever you want.

[0] https://usetrmnl.com/framework

Yeah, my BOM was $20 for the driver and $50 for the screen, plus $50 for the TRMNL license. About the same as the TRMNL I bought, in the end, though as you say the license is a big part of it.

My worry is about my lifetime license eventually turning into a subscription requirement.

The trick is that, if you're enjoying the process, the cost is negative! Trading in an iPhone doesn't sound very enjoyable, but to each their own.

stavros is one of my favourite posters on HN, and the writing on his site is full of beautiful turns of phrase like that.

> The Timeframe is a beautiful, battery-powered, high-resolution e-ink device that sits on my desk and reminds me of the inexorable grind that saps my creativity and drains me of the will to live.

From https://www.stavros.io/posts/making-the-timeframe/

edit: Ever since I read the Timeframe article I've been itching to do the same thing myself, but I suck at these things so worry that I'm just going to end up with more piles of electronic parts in my cupboard of broken dreams.

That option is for when you add it to your cart. You get API access with the device because you have one, but AFAIK you can't develop plugin without the dev option? I don't know, I'm confused :(