E-paper Price Tags Combined To Create A Large Wireless Display

E-paper price tags have become popular for retail stores over the past few years, which is great for hackers since we now have some more cheap commodity hardware to play with. [Aaron Christophel] went all on creating grid displays with E-paper price tags, up to a 20×15 grid.

E-paper price tags are great for these kinds of projects, since they are wireless, lightweight, and can last a long time with the onboard batteries. To mount the individual tags on the plywood backboard,[Aaron] simply glued Velcro to the backboard of the tags.┬áThe displays’ firmware is based on the reverse engineering work of [Dmitry Grinberg], flashed to a few hundred tags using a convenient 3D printed pogo pin programming jig. All the displays are controlled via a Zigbee USB dongle plugged into a PC running station software.

[Aaron] is also experimenting with the displays removed from their enclosure and popped into a 3D printed grid frame. The disadvantage is the loss of the battery holders and the antenna, which are both integrated into the enclosure. He plans to get around this by powering the displays from a single large battery, and connecting an ESP32 to the displays via ISP or UART.

This project comes hot on the heels of another E-ink grid display project that uses Bluetooth and a rather clever update scheme.

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A Deep Dive Into E-Ink Tag Hacking

Over the last decade or so, e-ink price tags have become more and more ubiquitous, and they’ve now reached the point where surplus devices can be found inexpensively on various websites. [Dmitry Grinberg] found a few of these at bargain-basement prices and decided to reverse engineer and hack them into monochrome digital picture frames.

Often, the most difficult thing about repurposing surplus hardware is the potential lack of documentation. In the two tags [Dmitry] hacked, not only are the labels not documented at all, one even has an almost-undocumented SoC controlling it. After some poking around and some guesswork, he was able to find connections for both a UART and an SWD debugging interface. Fortunately, the manufacturers left the firmware unprotected, so dumping it was trivial.

Even with the firmware dumped, code for controlling peripherals (especially wireless devices) is often inscrutable. [Dmitry] overcomes this with a technique he calls “Librarification” in which he turns the manufacturer’s firmware into libraries for his custom code. Once he was able to implement his custom firmware, [Dmitry] developed his own code to wirelessly download and display both gray-scale and two-color images.

Even if you’re not interested in hacking e-ink tags, this is an incredible walk-through of how to approach reverse-engineering an embedded or IoT device. By hacking two different tags with completely different designs, [Dmitry] shows how to get into these systems with intuition, guesswork, and some sheer persistence.

If you’d like to see some more of [Dmitry]’s excellent reverse-engineering work, take a look at his reverse-engineering and ROM dump of the PokeWalker. If you’re interested in seeing what else e-ink tags can be made to do, take a look at this weather station made from the same 7.4″ e-ink tag.

E-Ink Price Tags Fall Off Store Shelves Onto Your Workbench

There’s always a magic moment for our community in the lifecycle of any piece of technology: the point at which it first becomes available for pennies on the surplus market. Something which could previously be had only at a price is rendered down to mere pennies, and we are free to hack to our heart’s content.

Such a moment came for [Aaron Christophel] when he bought a quantity of used e-ink price tags (German, Google Translate link) that had formerly graced the shelves of a supermarket. A pile of readily hackable e-ink displays lay before him, so he set to work.

Cracking them open he found the display itself as well as a PCB with its own microcontroller, but he soon identified it as compatible with a WaveShare module for which he had data. Since its interface was thus identified as SPI he could desolder the unknown CPU and break out the pins for an Arduino or other board. The display itself turned out to be a custom model with a few quirks for price tags, it had a black border that could be enabled, and for some reason it appeared as a two-colour red-and-black model in which its black pixels responded as though they were the red channel. He has a quick overview video that we’ve placed below the break.

These displays have started appearing in our community, not least in electronic conference badges. This source of cheap components from the surplus market makes them ever more accessible, and we look forward to the projects that will come from them.

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