Get 3-inch e-Paper working on a Nano

Question

Please help!

I purchased a 3-inch e-Paper Display from Waveshare, which appeared to suit my project well. The exemplary little code to show an image was easy to set up and to demonstrate functionality:

#include <SPI.h>
#include "epd3in0g.h"
#include "imagedata.h"

Epd epd;

void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);
  Serial.print("e-Paper init ");
  if (epd.Init() != 0) {
      Serial.print("e-Paper init failed");
      return;
  }

  Serial.print("White \r\n");
  epd.Clear(white);
  delay(2000);

  epd.Init();
  Serial.print("Image \r\n");
  epd.Display(IMAGE_DATA);
  delay(2000);

  epd.Init();
  Serial.print("Small Image \r\n");
  epd.Display_part(IMAGE_DATA, 0 ,0, 168, 400);
  delay(2000);

  epd.Init();
  Serial.print("Clear...\r\n");
  epd.Clear(white);
  delay(2000);

  Serial.print("Goto Sleep...\r\n");
  epd.Sleep();
}

void loop() {

}

I will not just have images displayed, I aim for strings with text and numbers and those partial refreshed. Wild guesses if a

epd.Display_Text('''Hello World''');

might work is pointless. Thus, the existence and usage of possible commands for the epd. appears to me not well documented (or I was unable to find something even after a thoroughly search).

I had a look at other examples using GxEPD libraries and it seemed as a good starting point for me.

Within the GxEPD2 Library it seems a class for 3-inch EPD is missing as it is nowhere declared (I assume there should be something like a GxEPD_300 to set display dimensions etc.).

So, I reckon I need to wrap up something to meet the specs of the 400x168 pixel display but I don't know where to start.

I tried around with the GxEPD_MinimumExample.ino, like

• replacing the display specific lib with the epd3in0g.h from the example
• adjusted the right pins according to the Waveshare Wiki

// GxEPD_MinimumExample by Jean-Marc Zingg

#include <GxEPD.h>

// select the display class to use, only one, copy from GxEPD_Example
//#include <GxGDEH0154D67/GxGDEH0154D67.h>  // 1.54" b/w -> from org. example.
#include "epd3in0g.h" //my 3-inch display

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

// constructor for AVR Arduino, copy from GxEPD_Example else
GxIO_Class io(SPI, /*CS=*/ 10, /*DC=*/ 9, /*RST=*/ 8); // arbitrary selection of 8, 9 selected for default of GxEPD_Class
GxEPD_Class display(io, /*RST=*/ 8, /*BUSY=*/ 7); // default selection of (9), 7

void setup()
{
  display.init();
  display.eraseDisplay();
  // comment out next line to have no or minimal Adafruit_GFX code
  display.drawPaged(drawHelloWorld); // version for AVR using paged drawing, works also on other processors
}

void drawHelloWorld()
{
  display.setTextColor(GxEPD_BLACK);
  display.print("Hello World!");
}

void loop() {};

During the verification prior the upload I get errors pointing back to the libs:

error: 'GxEPD_Class' does not name a type; did you mean 'GxIO_Class'?*

I assume this is because the call to initiate the display is not working.

Thank you for any advice!

Answer 1

Waveshare examples, by and large, suck. They're usually a bunch of register writes, undocumented. I had to write a library for an EPD once - OEM version, which later popped up on Waveshare's website as their own - and the OEM's documentation and code were good enough (just...) to produce a functional library.

Looking at the example for your specific screen, I see it is indeed the usual SendCommand() crap. Although it seems slightly more evolved, with an Epd class. But still, useless.

EPD code is HARD, and requires a lot of information from the manufacturer. And producing a library that handles text is also a little harder to get right.

I don't think trying to transplant their crappy code onto an existing library is going to work. I figure you have two solutions:

• Rewrite a library for this epaper from scratch.
• Half-ass something by adding text handling to their code by converting text to pixels in the buffer, and push that.

In both cases, painful.