Support more (Color) Displays? Includes a Howto

[jamesmunns]

I recently ordered a collection of the WaveShare displays, including:

• 4.2" Yellow/Black/White
• 4.2" Black/White
• 4.2" Red/Black/White
• 7.5" Black/White
• 5.83" Red/Black White

I'm happy to contribute or help test, as I plan to use these on a couple of embedded devices for my internet of streams project. I was wondering if you had any notes already on where I should be looking to help add support for the color displays.

[caemor]

Sorry for the late response.

• the 4.2" B/W is working already.
• the 7.5" B/W should also be pretty easy to add (I also got one at home but didn#t have the time to add it and test it)

AFAIK the colored ones just use two buffers instead of one so that also shouldn't be too complicated too add (where the biggest problem will be how to add/change color.rs and if 2 small buffers are better or one big buffer). I am really unsure about this problem.

Question to the naming convention: the call it 4in2(b) but wouldn't 4in2_red or something similar be better?

Steps that need to be done to add a display generally: (e.g for the 4in2 (b)/red one)

1. Get the Command table from the datasheet (e.g here: https://www.waveshare.com/wiki/4.2inch_e-Paper_Module_(B)#Datasheets ) and add it to a command enum like here (https://github.com/caemor/epd-waveshare/blob/master/src/epd4in2/command.rs) in a epd4in2b folder. This can also be found in waveshares new github repo (e.g.: https://github.com/waveshare/e-Paper/blob/master/4.2inch_e-paper_b%26c_code/wiringpi/obj/EPD_4in2b.h but be aware of quite a lot of copy&paste errors like the wrong ifndef epd2in7b at the top and better crosscheck it once more)

2. Optional: Add the LUT constants (like https://github.com/caemor/epd-waveshare/blob/master/src/epd4in2/constants.rs) if you can find any. But since the color ones only allow the default refresh they are most likely not included in the repos. This is also not too important/optional.

3. Add following constants from the next four lines to epd4in2b/mod.rs (https://github.com/caemor/epd-waveshare/blob/master/src/epd4in2/mod.rs#L61): width, height, default_background_color (twice for red/black displays?), is_busy_low

4. Implement WaveshareDisplay and InternalWiAdditions trait for your EPD4in2_Red struct.
   See https://github.com/caemor/epd-waveshare/blob/master/src/epd4in2/mod.rs#L76 and following for examples and crosscheck it with the waveshare repos for the differences between different devices

   The Traits that need to be implemented are explained here: https://github.com/caemor/epd-waveshare/blob/master/src/traits.rs

   Maybe some adoptions for either a twice as big sized buffer or double buffers need to be made.

   Communication is handled by the DisplayInterface and is working the same through all waveshare displays that I know besides that the busy_low pin is sometimes inverted.

   Now you can already draw to the display, but you might want to use the embedded_graphics ;-)

5. Implement the graphics traits (Drawing & Display) e.g. like here: https://github.com/caemor/epd-waveshare/blob/master/src/epd4in2/graphics.rs

   The graphics.rs file is handling most of the graphics stuff for you:
   https://github.com/caemor/epd-waveshare/blob/master/src/graphics.rs

   But most likely there also need to be done some changes for the multicolor display.

Further stuff:

• Most likely Red and Yellow Versions of the same size work completely the same and just show a different color (I still need to check that)

• Naming of function/traits: If you have better names for some of the traits/functions or think that some don't really match with what they do I am always happy with improvements.

Good references are:

• https://github.com/waveshare/e-Paper
• wikipages of the different displays e.g. 4.2inch_Module_B
• https://github.com/ZinggJM/GxEPD
• https://github.com/olikraus/u8g2

I am happy to help if you have more specific question but be aware that the colored displays are quite slow.

[marcelbuesing]

I just ordered a 4.2 B/W and a 7.5 Red/Black/White.

Has anyone started adding colored display support yet ? Otherwise I might also start looking into it once they arrive. @caemor thanks for those infos.

[caemor]

I haven't started working on it yet. I might have some time on Sunday at the Oxidize Conf.

[caemor]

I couldn't find any time on Sunday and gonna be travelling for the next 3 weeks, so you can just start if you want.

[DanSGiesbrecht]

I ordered a R/B/W display as well - I may have a go at this someday.

[caemor]

@jkristell added support for the 1in54 r/b/w display here: #35 and has an example on using it here: https://github.com/jkristell/nucleo-f401re/blob/add-eink-example/examples/eink.rs

[caemor]

Although multiple ones were added I am leaving this issue open since it also includes some documentation about how to add a display