Error with Waveshare 3-color display

[tmmorin]

I have a waveshare 3-color 7.5" display.

I tried display=epd7in5bc_V2 which seems to be the 3-color variant.
But I get the following error:

22:23:30 Screen:initEPD:310:INFO - <waveshare_epd.epd7in5bc.EPD object at 0xb5453bb0> initialized
22:23:32 Screen:writeEPD:350:ERROR - failed to write to epd: display() missing 1 required positional argument: 'imagered'

I'm guessing that the code is possibly not ready for 3-color displays...?

The non-"bc" variant give a result that shows some stuff but seems buggy, wrong lines, flicker, etc.

(Thanks for pushing this great project on github, I hope I'll be successful in using it ! 👍 )

[txoof]

Indeed, the BC variant expects an additional parameter when writing to the display. I'll remove the bc versions from the documentation; you should be able to use the similar monochrome version in the configuration.

When you say you get buggy output, can you share photo of the screen? I had some terrible results with banding and partial refreshes when I plugged the hat into the GPIO headers. I switched to using the JST plug with dupont connectors directly to just the pins I needed and it completely resolved the quality issues. You can see some examples here.

EDIT: better link for banding issues: banding issue

I'll look into what needs to be done to update the drawing libraries to support the color screens. It looks like it's going to be a bit of a project though. txoof/epdlib#1

[txoof]

@tmmorin It actually looks a lot easier to fix than I thought. I'll need to do some hacking around on the epdlibrary side to make this work, but it should be a pretty easy fix.

I should be able to have a fix sometime this week.

Can you share some images of the "buggy" output?

[tmmorin]

Hi @txoof

I found a solution: txoof/epdlib#2 (perhaps close to what you had in mind ?)

The buggy output I had with the epd7in5_V2.py (without "bc") was that after displaying properly the picture, during the "e-Paper busy" waiting, the picture started to kind of fade step by step towards a finally fully white display. It seems that it's possibly because my display just would not support being driven by a driver that uses only the commands for a single display...

Now I have something that works nicely 😃
The display refresh time is a bit longer than I would have hoped (pushing the red image additionally take a bit more time), and the driver busy loop eats a lot of CPU (the while true without a sleep, in waveshare driver code, is quite violent...).

[txoof]

I'm so glad you have a working solution! Thanks for your work on this. You and I landed about the same place, but with slightly different approaches.

Those waveshare libraries are a piece of work with some really nasty "features".

I'll look into merging in your suggestion once I fix my build tool-chain. Some updates did a great job of breaking things. I should know better than to update stuff.

[txoof]

I'll test out the development version of epdlib against slimpi and finally build a new installable in the next day or so.

[txoof]

New epdlib version corrects this: txoof/epdlib@747fb57

[tmmorin]

Thanks!

[txoof]

@tmmorin my pleasure. I'd love to know if it's working for you and see a pic if you don't mind sharing.

[tmmorin]

Yes, sorry for being too implicit: it works and allows me to use slimpi with my waveshare 3-color screen.

I'll send a picture when I have something a bit nice to show.
I plan to have the ribbon cable at the top of my display. I'm working on small changes to rotate images by 180 degrees to compensate for that.

[txoof]

Ohh. That would be a great feature to add to the configuration; I'd love to collaborate with you on this.

[txoof]

@tmmorin I opened a new issue here #7 with some thoughts on what needs to be updated