Of course the obvious solution for a display for a conference badge is e-paper or e-ink display. It has a number of advantages:

• keeps displaying with the device off, which means that you could even do without the battery, or — if you really want to have interactive elements there — have the microcontroller sleep most of the time,
• high contrast, readable from a distance,
• low resolution and color count — which means low RAM requirements,
• relatively new and very cool technology,
• physically robust (at least more so than glass displays) and safe when broken (no sharp edges),

It also has a couple of drawbacks:

• slow to update — even more so than the LCDs, partial updates help somewhat,
• expensive, at least until recently,
• requires additional components for the high-voltage driving — but any larger OLED has the same problem,
• no ready libraries — but I would write my own libraries for the display anyways,
• risky, requires research,
• no idea how easy to source it is in larger quantities.

But all in all, it is certainly an interesting option to explore. So I went to my favorite Chinese shopping website, and had a look around. Sure enough, most of those displays cost around 4x more than I would like the whole device to cost, but there are some interesting options. In particular, the GDEW0154T8 display can be bought for less than $5, even cheaper in larger quantities. But is there any documentation for it? Yes!

A bit of googling, and we can find this page, with links to the datasheet for the display and for the driving chip.

Looking at the datasheet, it doesn't look bad. Resolution 152×152, 1-bit color, 6s refresh time — sure, not too great, but for that price what can you expect. More importantly, there is a typical application circuit example there, and it only has 11 capacitors, 3 Schottky diodes, a resistor, a mosfet and an inductor. There is also a temperature sensor, but looking at the breakout boards, it seems to be optional.

I could live with that. More details when the breakouts and displays arrive.