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.

Similar projects worth following
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....

Read more »

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


  • 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.

View project log

Enjoy this project?



Aaron Christophel wrote 11/28/2020 at 16:40 point

Just added support for the CHROMA74 Yellow display to my Modded GxEPD2 library:

this uses now the stock LUT and make a very bright Yellow as intended 

The RED version is using a different LUT that still needs to be reversed.

  Are you sure? yes | no

Mike Szczys wrote 12/01/2020 at 00:57 point

This is awesome! I use your library for a silly project of mine[1] and picked up the Chroma 74 screen based on the work seen here. Very excited to have the library already sorted so I can upgrade to this! Thank you for making your library open source 😊

  Are you sure? yes | no

Aaron Christophel wrote 11/27/2020 at 15:35 point

@YodaLogic i am currently working on the same displays/pricetag and got 35pcs of it. I reversed the cc1110 firmware very far but was not able to drive the display but wrote a custom firmware for the CC1110 so i think it would be great to connect on that one to make a fully firmware for the stock PCB ?

  Are you sure? yes | no

kkrell2016 wrote 12/01/2020 at 11:23 point

Fascinating, great job.
I had a look at the GitHub repo. Unfortunately I could not find the CC1110 custom firmware. Only the backup of the original one. How far have you come with your project? Working on getting such a display.

  Are you sure? yes | no

Interzen wrote 12/01/2020 at 21:50 point

I am also interested in how far you have gotten on replacement firmware.  I used this as an excuse to learn Ghidra but could not open your project because it was not created as a 'shared project'.  I'm working through a tutorial now and then I will try to copy your project files into a new one that I can work with.

What are you using for a development environment and for accessing the two-wire debug interface?

  Are you sure? yes | no

Aaron Christophel wrote 12/03/2020 at 11:33 point

sorry wasnt notified.

The custom firmware is still in its beta and not shareable for now, as it was not refreshing the display until the LUTs where found, the spi communication is already working as expected.

I am using SDCC and just notepad++ as editor. 

This repo is a good starting point

Right now i am still trying to get the stock firmware running so the development of a new firmware is not needed as deep sleep is harder to archive

Bought a stock Access point today and wait till it arrives.

  Are you sure? yes | no

Tom Nardi wrote 12/02/2020 at 04:50 point

A complete custom firmware for this device, where we could simply send images over RF, would really be the dream. I could imagine having these devices all over the house, with each one getting room-appropriate displays over the air.

Very excited to see where this project goes.

  Are you sure? yes | no

Tom Nardi wrote 11/23/2020 at 04:22 point

I've seen these at the Home Depot and was wondering how long it would take for somebody to crack them open. Looks like bending it to our will isn't exactly plug-and-play yet, but good to see some first steps made.

Are you planning on releasing the profile you've created for the screen?

  Are you sure? yes | no

YodaLogic wrote 11/23/2020 at 14:33 point

The current profile is sufficient for me, but it's my best guess without a datasheet, and the initialization has to run twice. I want to provide a proper GxEPD device library, but I need the WFD0750BF19 datasheet. I hope someone from the Hackaday community can point me to it. Otherwise, I'll attach my current profile to this project. 

  Are you sure? yes | no

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

Too bad that display is a deal only in US. 

  Are you sure? yes | no

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!

  Are you sure? yes | no

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!

  Are you sure? yes | no

Similar Projects

Does this project spark your interest?

Become a member to follow this project and never miss any updates