Low Power Challenge: E-Paper Shelf Label Becomes Ultra-Frugal Clock

A clock with an e-paper display in a 3D-printed case

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.

A PCB for an e-ink clock
Power on the left, e-ink on the right: the custom PCB is clever and compact, too

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.

12 thoughts on “Low Power Challenge: E-Paper Shelf Label Becomes Ultra-Frugal Clock

  1. Is it sensible to use a rechargeable battery for an application like this?

    The cost of an item is a pretty good proxy for its environmental impact, so you need to use a lot of charge/discharge cycles of a lithium battery to justify using it over cheap low-impact consumables.

    Where’s breakeven? 10 years? Maybe some Dude will chime in with some numbers.

    (BTW, I have a digital clock that updates its display once per second and consumes less than 5 uA. It’s more than 20 years old. I used to wear it on my wrist, but the strap broke, and then those phone things came along, so it just sits on the shelf. But it still keeps time within 30 sec/year.)

    1. If electronics are not mass produced, basically all the cost of producing them goes into the development, so the point is moot. I bet the impact of the battery is a small fraction of the custom PCB labor, shipping, etc.
      Also, being able to re-use the display is quite a way to make up the damage.
      Lastly, by using a standard cell it is possible that a worn-out cell for high power applications can be repurposed for a task like this.

      1. It doesn’t matter how many are produced. The money you pay for goods or services goes *somewhere*, ultimately into food or fuel. Whether it’s to the delivery truck, or the engineers to buy groceries, or to their manager to pay for that vacation airplane flight, or to trickle down to a multitude of sweatshop laborers who still need to eat and breath. The end result is X dollars turns into Y environmental impact. Cheaper stuff makes less impact. That $100k Tesla has 3x the environmental footprint of a $33k Toyota.

        A LCD thermocouple oven thermometer I built almost 4 years ago is still running 24×7 on its original AA alkaline cells. It would be silly to put a rechargeable cell in that application.

        1. “That $100k Tesla has 3x the environmental footprint of a $33k Toyota.”

          Yes, and the Tesla goes carbon-negative compared to the ICE vehicle rapidly, because most of a vehicle’s emissions are during its use, not manufacture.

          “BuT WhaT aBOuT mANUfaCTUrING imPAct!!!!” has been a bleat from the anti-environmental crowd for several decades now about hybrids and now BEVs. The facts clearly show hybrids and BEVs are better for the environment when they reach just a fraction of their total typical lifespan.

  2. If you’ve got a bunch of these labels gathering dust, send them my way. I have no clue where people are sourcing these for cheap- eBay is full of people selling them like they’re made of gold.

  3. Rechargable lithium batteries weren’t the best choice here. Their self discharge will probably use more power than the device itself and if it doesn’t need charged very often then why go for a rechargable battery?

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