RAM Problem with 1.54 inch E-Paper and ATmega328P + GxEPD2

Other Hardware Displays
1

I am a beginner with e-papers and I Need help! I want to display text on a Waveshare E-Paper BW display 1.54 inch with an Arduino UNO. Unfortunately, Waveshare does not have a product name for the display. My simple test program also works conditionally. If I change

#define MAX_DISPLAY_BUFFER_SIZE 400

to

#define MAX_DISPLAY_BUFFER_SIZE 1000

I get strange artifacts - you can see them on the photos.

BUFFER-SIZE-400
BUFFER-SIZE-4001920×1440 278 KB

BUFFER-SIZE-1000
BUFFER-SIZE-10001920×1440 281 KB

I suspect it is a RAM problem. In both cases there seems to be enough free space:

Global variables use 945 bytes (46%) of dynamic memory, leaving 1103 bytes for local variables. Maximum is 2048 bytes.

Global variables use 1545 bytes (75%) of dynamic memory, leaving 503 bytes for local variables. Maximum is 2048 bytes.

My sketch:

#define ENABLE_GxEPD2_GFX 0
#include <GxEPD2_BW.h>
#include <Fonts/FreeSansBold18pt7b.h>

// SPI Arduino UNO
// #define SPI_DIN 11
// #define SPI_CLK 13
#define SPI_CS 10
#define SPI_DC 14    // A0
#define SPI_RST 15   // A1
#define SPI_BUSY 16  // A2

// #define GxEPD2_DRIVER_CLASS GxEPD2_154_GDEY0154D67
#define GxEPD2_DRIVER_CLASS GxEPD2_154_D67

#define MAX_DISPLAY_BUFFER_SIZE 400
//#define MAX_DISPLAY_BUFFER_SIZE 1000

#define MAX_HEIGHT(EPD) (EPD::HEIGHT <= (MAX_DISPLAY_BUFFER_SIZE) / (EPD::WIDTH / 8) ? EPD::HEIGHT : (MAX_DISPLAY_BUFFER_SIZE) / (EPD::WIDTH / 8))
GxEPD2_BW<GxEPD2_DRIVER_CLASS, MAX_HEIGHT(GxEPD2_DRIVER_CLASS)> display(GxEPD2_DRIVER_CLASS(SPI_CS, SPI_DC, SPI_RST, SPI_BUSY));

void setup() {
  display.init(0);
  display.setRotation(3);
  display.setTextColor(GxEPD_BLACK);
  staticScreen();
}


void staticScreen() {
  display.firstPage();
  do {
    display.fillScreen(GxEPD_WHITE);
    display.setCursor(48, 160);
    display.setFont(&FreeSansBold18pt7b);
    display.print("HELLO");
  } while (display.nextPage());
}

void loop() {
}

I look forward to any advice. Manfred

2

500 bytes is not enough memory for the micro to work; it needs about 400 bytes just to "run."
Why do you need to expand the buffer?

3

Try with 800. Like in the examples!

4

Thanks for your reply. I'll use the display for a batterie powered project, so power consum is impotant. I thought more buffer means less cycles in the paged-loop, resulting in less batterie consumption.

5

Thanks for the hint. Didn't notice that.

6

I have found a cause. setFont() shouldn't be called in the page-loop. That was a stupid thing for me to do. Sorry. Manfred

Update:

Excuse me. I think that was a coincidence. I need to reduce the buffer size. Manfred