Frank BussFor a product later, the device shouldn't cost too much. So I searched for new ePapers, because the nice 4.2" Pervasive Display ePaper costs EUR 51. And I found the GDEW027C44 2.7" ePaper, also black/red/white, for about EUR 8. Still sufficient space for short messages, images or the coffee timer application.
And for the solar cell I found this panel for EUR 2.89:
Maybe not as efficient as the expensive ones you can get from Digikey, but the bigger size of 60x90mm should more than compensate it. It says 6 V / 0.6 W, but I guess only in bright sunlight at the equator, I will test it.
It has 2 solder contacts on the back:
There are many similar solar cell modules on eBay. If one module gets out of stock, I can just use one of the other modules. I think I can glue it to the case and use 2 holes to connect the cables, and it won't look too bad, because of the beveled edges.
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Time to refresh display - 16s. Wow, I didn't knew those panels are THAT slow. At least they use only 8mA during refresh, less than a single led.
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The refresh cycle can be tweaked a bit. The previous Pervasive Display needed about 8 s:
https://www.youtube.com/watch?v=3mhUmatstaY
And if you have e.g. just a black/white image, it is even faster. But it depends on the environment temperature as well, there are recommendations how fast you should cycle it for different temperatures. Slower when it is colder.
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Cool, thanks for video, looks like most of that time is used for clearing old picture.
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Yes, the clearing process is time consuming. It is interesting how it works: It uses a lookup table and the driver voltage is determined by the previous state and the next state. But with partial updates and custom lookup tables, you can update these displays with nearly 3 Hz:
https://hackaday.com/2017/10/31/ben-krasnow-hacks-e-paper-for-fastest-refresh-rate/
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