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What's black, white, and red all over: Color E-Ink

A project log for NAVI

Chromebook : Internet :: NAVI : bash. A hackable E-Ink "mini-luggable" with batteries that last a year.

Milkey MouseMilkey Mouse 03/15/2018 at 02:293 Comments

I was looking for good docs on E-Ink displays and found articles like Essential Scrap's tutorial for repurposing old e-reader displaysSprite_TM's webpage-viewing low-power display, and the badgy project here on hackaday.io (coincidentally, the last two are both ESP8266-driven WiFi E-ink display projects). While I considered the ED060SC4 (preferably H2) mentioned in the Essential Scrap article, I wasn't looking forward to designing (or borrowing from an open-source hardware project) a driver with all of those weird voltages and the shift registers for setting pixels.

Upon further perusal I found a mention of Good Display in the comments of the badgy project. I looked on their website (or an affiliated reseller? It's a little confusing because half of it is in Chinese and the other half requires Javascript) and found a 7.5 inch BWR E-ink display (also on Aliexpress). As soon as I knew it was possible to have multiple colors I knew this was a feature the laptop needed. If editing code, for instance, the red could be used for minimal syntax highlighting. Looking at their demo video the display seems as responsive as the other ones I was considering, it has an SPI interface, and it only costs about $20 more than one of the old ED060SC4s. Some code can probably be shared with the badgy project as well. All things considered, the GDEW075Z09 seems like a better choice than an older recycled model.

Discussions

Lian Duan wrote 03/16/2018 at 09:04 point

GDEW075Z09 would be unrealistic for a terminal. It doesn't support partial refresh, a full refresh takes 15 seconds with multiple blinking. Stick with ED060SC4  or use a normal mono chrome TFT or OLED. E-ink is not particular energy efficient if continuous updates are needed.

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Milkey Mouse wrote 03/17/2018 at 06:04 point

Ah, it should have been obvious from the existence of an integrated controller - I just skimmed the datasheet as this is all bikeshedding anyway until I have other hardware working. To go even further into the weeds, someone has experimented with a fast partial refresh for a display controller in the same family as that on the GDEW075Z09 (https://www.youtube.com/watch?v=MsbiO8EAsGw). If I am stuck with the ED060SC4, though, at least I have the lower cost and direct access to the matrix for experimental LUTs.

I really do think an E-ink display is important because it should be possible to put the ESP32 in modem-sleep whenever I/O isn't happening (so e.g. reading a man page would only have the CPU on for scrolling) - the hardest part of that will be trying to graft it onto Linux's way of handling sleep. Looking into how smartphones do it might be useful since they have to keep network on to receive notifications but also try to be as aggressive with battery as possible.

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Lian Duan wrote 03/18/2018 at 12:21 point

I have tested out the experimental LUT from GxEPD project for GxGDEW042T2. Well, it does partial refresh, but ghosting is horrible. Anyway, there's no LUT for tri-color versions yet.

If power consumption at idle is your concern, Sharp's Memory LCD is also something you want to look into.

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