Over the past two decades, e-paper has evolved from an exotic and expensive display technology to something cheap enough to be used for supermarket price tags. While such electronic shelf labels are now easy to find, actually re-using them is often tricky due to a lack of documentation. Luckily, [Aaron Christophel] has managed to reverse engineer many types of shelf labels, and he’s demonstrated the results by turning one into an ultra-low-power clock called Triink. It’s based on a 128×296 pixel e-ink display paired with an nRF52832 BlueTooth Low-Energy SoC and uses just 65 micro-amperes on average: low enough to keep it running for more than a year on a single battery charge.
The clock is housed in an enclosure that’s simple but effective: a 3D-printed triangular prism with a slot for the screen and space for the 18650 lithium battery. One side can be opened to access the internal components, although that’s really only needed to charge the battery. You can see how cleverly everything snaps together in the video embedded below.
The CPU spends most of its time in sleep mode, only waking up once a minute to update the display. In order to save power, [Aaron] wrote this routine in such a way that it only updates those pixels that have actually changed. Once an hour, it completely refreshes the screen in order to prevent burn-in. An integrated real-time clock keeps track of time and can be adjusted through BlueTooth by using a smartphone app.
If you’ve got a bunch of similar e-ink shelf labels gathering dust, you can find all the design files and software to build your own Triink on [Aaron]’s hackaday.io page. In fact, you might want to browse around some of his other projects too: he’s managed to reverse engineer three-color e-ink price tags for instance, and even combined 300 shelf labels into a giant e-ink display.
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- Source: https://hackaday.com/2023/02/24/low-power-challenge-e-paper-shelf-label-becomes-ultra-frugal-clock/
