Added LilyGo T5 4.7inch EPD PlatformIO example

[DavidM42]

This adds an example how to use this library with the LilyGo T5 4.7 inch EPD device with an Esp32 on board and some exra features like buttons on the side.
It includes

• A full PlatformIO config
• Some additional example code how to combine the epd-driver with the deepsleep functionalities of the Esp32
• An experimental (not ideal) calculation method to find out the battery percentage on this specific device

As discussed here over on the repo of the manufacturer driver fork I think this would be a good kickstart for buyers of that device.

If anyone can test it and maybe suggest improvements to stop random screen greying of the background or how to improve the battery percentage calculation that would be greatly appreciated.

Thanks again for this nice library

[vroland]

That looks interesting, thank you :) I'll try to review and test this this weekend!

[fdev31]

I wanted to do something a bit similar, but it went a bit too far I guess...
https://github.com/fdev31/LilygoT5-weather-photo-display

Also I'm not exactly certain about the best practices here... but It looks like you have more advanced battery handling code (mine was a simple example I borrowed somewhere). Is a lookup table really needed in theory ? (I thought some linear math as you did was good enough....)

[vroland]

For me, this produces rendering artifacts, because clear() is used without clearing the framebuffer.
I would clear the screen after power on, and then use the highlevel API:
`
void display_center_message(const char* text) {

epd_hl_set_all_white(&hl);

int cursor_x = EPD_WIDTH / 2;
int cursor_y = EPD_HEIGHT / 2;
if (orientation == EPD_ROT_PORTRAIT) {
    // height and width switched here because portrait mode
    cursor_x = EPD_HEIGHT / 2;
    cursor_y = EPD_WIDTH / 2;
}
EpdFontProperties font_props = epd_font_properties_default();
font_props.flags = EPD_DRAW_ALIGN_CENTER;
epd_write_string(&FiraSans_12, text, &cursor_x, &cursor_y, fb, &font_props);

epd_poweron();
err = epd_hl_update_screen(&hl, MODE_GC16, temperature);
delay(500);
epd_poweroff();
delay(1000);

}
`
Also, the delays seem unnecessary for me?

[DavidM42]

I now use the epd_hl_set_all_white method, but the delays reduce some artifacts or graying of the background in my testing.
Maybe they can be avoided with further changes to the driving code here

[vroland]

Thanks for the example, so far everything works with platformio. I noticed one issue where the text drawn after 30 seconds of run time produces weird artefacts. This is because the screen is cleared without setting the framebuffer to white. Could you fix that before the merge?

[DavidM42]

Thanks for the great input. I'm new to electronic paper displays, so I'm thankful for all tips.
I adapted most of your requests, but I still sometimes encounter artefacts. If you have time maybe you can have a look at the reasons for that

[vroland]

Thanks, looks good :)
Yes, there is still a little bit of aliasing after updating the font. This is because I use an approximate waveform, not the matching vendor waveform. With the vendor waveform it looks better, but LilyGO did not publish it in their repository and don't reply to the corresponding issue. I won't publish it myself, because it's unclear if these are copyright-able, and I don't want this repo to be taken down because of it.

[entozoon]

@vroland LilyGo appear to have responded to you and open-sourced their waveform, which is awesome!
I've created a PR if you'd to merge. It's tested and looks great

@DavidM42 Thank you so much for this! Saved me so much time, I can't even.

[DavidM42]

@entozoon I wanted to comment on your PR that I tested it and that it really looks great and sharp with the added waveform 🎉 but it got merged already so here

I'm glad I could help you and my long struggle with this was less of a waste

[entozoon]

Thanks @DavidM42, and yeah I'd have given up without your work. In fact, I'm pretty close again .. lol