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7.4" E-Ink Shelf Label used as a Weather Station

Modified Chroma74 shelf label to be my weather station display. It is 7.4" 3-Color E-Ink units that cost $12 on eBay.

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The November Hack-a-day podcast encouraged me to share my e-paper journey. It seems I’m not the only one who is fascinated by its potential. I was interested in the technology for over two decades when I saw it during CES (Consumer Electronics Show). I remember e-Ink paper sheets that could be used repeatedly with an e-paper printer/scanner combo. Many trees were going to be saved by the promise of sheets of paper that keep images without power and can be reused 1000 times. Today, the e-paper is married to the controller; that is an improvement, but the price and sizes are far from desirable. Nevertheless, technology progresses, and new RGB displays are being developed. Is the technology ready for hackerspace?
I converted a 7.5” three-color E-Ink Electronic Shelf Lable to a weather station and a message board. Those units are used by my local hardware store and can be bought for $12 on eBay. The details section contains my long journey to make it happen.

    The e-paper technology looks perfect for periodic update information boards, such as door message sign or a custom weather display. And I want one with an atmospheric pressure graph, but not a little 2-inch display. I want a roomy display to hang on any wall regardless if there is no outlet near it. But a price for a decent size display such as 7.5” seemed still more than I was willing to pay, especially since I would like to put them in a few rooms. I already bought a few small displays, but I couldn’t find a good use for them. Meanwhile, every time I went to my local hardware store, I saw a big two-color E-paper display on every appliance. They looked like a full-blown solution for my use if I could get my hand on it. The device could not be costly, including the wireless interface, batteries, and a case, if they can have hundreds in every store just as labels. Thus, I took a picture of the back of the display and did some research.

      The store is using Chroma 74, Black and Yellow, Electronic Shelf Label. The yellow would be perfect for the sun on my weather display. The “74” stands the screen size, 7.4” and the size is almost identical to the Waveshare 7.5inch E-Ink sold on Amazon. It also has the same display resolution of 640x384. I probably was not the first who had that idea, but I could not find much on the web. The display is sold to retailers only and has a proprietary wireless interface. I was able to find the FCC certification with the internal pictures. The display cable and electronics matched a typical Waveshare E-Ink connector and circuit sold as a module on Amazon, plus a microcontroller and battery. Those displays do have good documentation and Arduino libraries. Encouraged by this find, I turned to eBay to see if I can get some. There were a few sellers with a surplus of brand new units for ~$12 (plus a few bucks for shipping). So I got a few. With decades of professional embedded design experience, how hard it’s going to be?

    Chroma74 units came quickly and looked perfect. I was hoping I will be able to get the display part number and download the datasheet. Then I will connect to an ESP32 through the E-Ink HAT, and I’ll be done. Unfortunately, too often, things are more challenging than they initially seem. I found the display part number (WFD0750BF19) on the display cable.  It was Wuxi Vision Peak Technology Co. 7.5 color display, but I could not find a published datasheet. The datasheets for other smaller modules were available, so I had something to try. The big surprise was that the display connector was epoxied to the controller board, unlike the FCC pictures. It’s not surprising that they glue the connector. It’s not only cheaper, but it is less prone to vibration.  Additionally, the cable had reversed pinout (or up-side-down connection).  The unit contained a single PCB with four sections and a set of six 2450 batteries in parallel. Per the unit brochure, they will power the display for five years – talking about efficiency.

     To see if there is an easy path, I decided to connect the display to the E-Ink HAT with a generic e-paper Arduino sketch for a 7.5” display. The connector was unglued with a lot of heat and patient. One wrong move and the cable would be damaged. The extra epoxy was cleaned with alcohol. The display’s flat cable was too tin, and I glued some thin plastic to match the regular connector thickness to ensure a good connection. The Waveshare E-Ink display HAT extension socket allows top or bottom connections; two steps forward, one step back. The glue connector has extra width to provide a glue surface on both sides. The sides needed to be trim to fit into the socket, but there is very little room for error. The connector has a 0.5mm pitch. With all the surgery behind, I connected to a generic e-paper HAT and the controller. No surprise, the display did work....

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Chroma74_EDP_test08.zip

Arduino ESP32 sketch that displays a test page and a color pattern. This sketch is using my guess LUT update black-and-white and color profiles.

x-zip-compressed - 23.63 kB - 11/28/2020 at 06:02

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  • New LUT and GxEPD library

    YodaLogic11/28/2020 at 17:10 1 comment

    Huge thanks to Aaron for joining the project. He was able to extract the stock LUT from the flash and get vibrant back and yellow colors. You can find a link to his Modded GxEPD library in the discussion section.  I already converted all of my displays to the ESP32, but Arron has many more to play with. He was able to program onboard CC1110 processor with a custom firmware and exercise RF module.  The RF module is bi-directional, so we can dedicate one unit to be a bridge with others. The battery-operated units then can register periodically and download the rendered image. I wish we all could get more of those displays.

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Yehat wrote 11/20/2020 at 18:52 point

Too bad that display is a deal only in US. 

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Dan Maloney wrote 11/20/2020 at 17:42 point

Wow -- those are pretty close to "our colors"! I may have to latch onto one of these Chroma74s and do something with it. Thanks!

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Mike Szczys wrote 11/23/2020 at 17:09 point

Was coming here to say it looks great with the Hackaday colors. Now we need a script that turns these into an article eReader.

Great job diving into this hardware @YodaLogic. I want one of these pretty badly!

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