Displaying the Weather on a Chroma 74 E Ink Shelf Label

E Ink displays, while incredibly power efficient, tend to be fairly pricey once you get beyond a couple inches in size. Hacker “YodaLogic,” who wanted to create several roomy ePaper panels to hang on the wall, noticed that a local hardware store had large two-color displays on every appliance. Given their wide use, it would seem they couldn’t be very expensive, so after snapping a picture of the label on the back, and doing a little research, it turned out that the store was using a Chroma 74 black and yellow electronic shelf label, which costs around $12 new.

The Chroma 74 here indicates a 7.4” screen size, which is almost identical to the Waveshare 7.5" display sold on Amazon for a price of around $65. This less expensive device also has the same 640x384 pixel resolution. This looked quite promising, and the idea was that an ESP32 could be easily hooked up to it via an ePaper HAT, displaying stats in glorious E Ink fashion. As often happens, things were much more challenging than they initially would have seemed, and a good portion of the project write-up is a deep dive into reverse engineering this inexpensive – in money, if not time – display.

The build also outlines how an ATtiny microcontroller was used to put the ESP32 to sleep, as well as wiring things up so the ePaper HAT (which cost more than the display) didn’t have to be used. The hack was ultimately successful, and the result looks great mounted to the wall with a custom wooden frame, while showing the weather in low-power wireless style!