e-Paper display no sharp image

Question

I'm driving an e-Paper display with Adafruit Feather nRF52 Bluefruit LE, code mentioned below but not getting any sharp image. The display starts to get dull as soon as the power goes off. Is there anything I can change in code to retain the display's image quality?

Used library: https://github.com/ZinggJM/GxEPD Software : Arduino IDE

#include <GxEPD.h>
#include <GxGDEH0213B73/GxGDEH0213B73.h>  // 2.13" b/w newer panel
#include GxEPD_BitmapExamples

// FreeFonts from Adafruit_GFX
#include <Fonts/FreeMonoBold9pt7b.h>
#include <Fonts/FreeMonoBold12pt7b.h>
#include <Fonts/FreeMonoBold18pt7b.h>
#include <Fonts/FreeMonoBold24pt7b.h>


#include <GxIO/GxIO_SPI/GxIO_SPI.h>
#include <GxIO/GxIO.h>

GxIO_Class io(SPI, /*CS=*/ 4, /*DC=*/ 3, /*RST=*/ 2); // arbitrary selection of 8, 9 selected for default of GxEPD_Class

GxEPD_Class display(io, /*RST=*/ 2, /*BUSY=*/ 5); // default selection of (9), 7

void setup()
{
  Serial.begin(115200);
  Serial.println();
  Serial.println("setup");

  display.init(115200); // enable diagnostic output on Serial

  Serial.println("setup done");
}

void loop()
{
  display.drawPaged(showFontCallback);
  delay(5000);
}

void showFontCallback()
{
  const char* name = "FreeMonoBold9pt7b";
  const GFXfont* f = &FreeMonoBold9pt7b;
  display.fillScreen(GxEPD_WHITE);
  display.setTextColor(GxEPD_BLACK);
  display.setFont(f);
  display.setCursor(0, 0);
  display.println();
  display.println(name);
  display.println(" !\"#$%&'()*+,-./");
  display.println("0123456789:;<=>?");
  display.println("@ABCDEFGHIJKLMNO");
  display.println("PQRSTUVWXYZ[\\]^_");
#if defined(HAS_RED_COLOR)
  display.setTextColor(GxEPD_RED);
#endif
  display.println("`abcdefghijklmno");
  display.println("pqrstuvwxyz{|}~ ");
}

.

Edited: I bought Waveshare Driver-hat separately online not with displays. Datasheet link for the 2.13 display https://drive.google.com/file/d/1ZL9M1V500O0vegqsBbeMTPr0Vli2cNjX/view?usp=sharing

Answer 1

The HAT you use (from Waveshare) is designed to be compatible with Waveshare EPDs (which, as far as I know, are all produced by Good Display, but I don't think they necessarily support all models from Good Display).

The library you use is designed to support EPDs from Good Display (a pretty large list, not sure if all models are supported).

Your EPD is produced by BOE. So unless it is just a rebranded version of one of the Good Display EPDs, chances of it working out of the box are slim.

The first thing is that the driver you chose does not use the right screen resolution (your screen is 212x104, the driver you use is for a screen with 250x128 pixels).

The next thing is that clearly the waveforms and/or signal levels used are not correct. I believe the example should give you black (and red) text on a white background, while you go light-greyish on dark-greyish.

Unless you find a driver in the list of screens of that library that actually works (you seem to say none does), then one will need to build a dedicated driver. It's possible taking an existing one and modifying it a little bit will be enough, though I'm surprised by the amount of code in each driver (hopefully it's just replicated code rather than actually different versions).

The fact that it actually displays something which vaguely ressembles what it should (you can actually see the intended text) is a good sign, but it's difficult to guess what exactly needs to be changed.

Possible things that need to be changed:

• screen size (resolution, in pixels)
• format (seems to be black/white/red rather than black/white or grayscale, though your picture seems to show different grey levels...)
• waveforms (not sure if those actually need to be sent by the MCU in this case)
• pin-out on the FPC
• voltage levels on one or more pins
• other details in the communication protocol

You can compare the data sheet you have with one from GD to see what seems to match or not, but a quick glance through your data sheet tells me there's quite a bit of information missing. Some of the issues are purely software, others would be a hardware issue.

Did you ask them if there was an existing driver from that EPD, or if it's compatible with some other EPD? In addition to waveforms, details of the communication protocol are missing as well.