Example 4: Update Modes

In the previous examples, we learned how to initialise the display, how to write different graphics & text and how to use different graylevels. Now let’s have a look at three different ways how to update an ePaper screen.

Update Modes

The E-Paper library defines the following three update modes EPD_UPD_FULL, EPD_UPD_PART and EPD_MONO. EPD_UPD_FULL is set by default, achieves four graylevels, takes about 800ms and refreshes all pixels. This is the update mode having the best image quality. EPD_UPD_PART is a variant of the previous one but only changing pixels are refreshed. This results in less flickering for the price of a slightly higher pixel to pixel crosstalk. EPD_MONO is again a variant of the previous update mode but only about 250ms long. This allows slightly faster and more responsive updates for the price of supporting only two graylevels (EPD_BLACK and EPD_WHITE). Depending on your application it is recommended to insert a full update EPD_UPD_FULL after a couple of mono updates to increase the image quality.

Demo

Sketch

#include "Adafruit_GFX.h"
#include "PL_microEPD.h"

#define EPD_RST     A0
#define EPD_BUSY    A1
#define EPD_CS      A2

PL_microEPD display(EPD_CS, EPD_RST, EPD_BUSY); 


void setup() {
    SPI.begin();                            // SPI initialisation
    SPI.setBitOrder(MSBFIRST);                 
    SPI.setDataMode(SPI_MODE0); 
    SPI.setClockDivider(SPI_CLOCK_DIV4);
    display.begin();                        // Paperino ePaper initialisation and refresh screen 

    display.setTextSize(2);
    display.println("Update Modes");
    display.setTextSize(1);
    display.println("-Full Update");
    display.println("-Partial Update");          
    display.println("-Partial Mono Update");          
    display.update();                       // Triggers a Full update, 4 GL, 800ms

    delay(4000);
    display.clear();
    display.setTextSize(2);
    display.print("EPD_UPD_FULL");          
    display.update();                       // Triggers a Full update, 4 GL, 800ms
    delay(1000);
    display.setTextSize(1);
    display.print("This is a ");
    display.setTextColor(EPD_WHITE, EPD_BLACK);
    display.println("full update.");
    display.update();                   
    delay(1000);
    display.setTextColor(EPD_BLACK, EPD_WHITE);
    display.println("All pixels are reset no matter whether they are changing or not.");
    display.update();
    delay(2000);
    display.println("Hm, a bit boring, isn't it...?");
    display.update();

    delay(4000);
    display.clear();
    display.setTextSize(2);
    display.print("EPD_UPD_PART");                 
    display.update(EPD_UPD_PART);           // Triggers a Partial update, 4 GL, 800ms
    delay(1000);
    display.setTextSize(1);
    display.print("OK! Now you see ");
    display.setTextColor(EPD_WHITE, EPD_BLACK);
    display.print("partial updates!");
    display.update(EPD_UPD_PART);                
    delay(1000);
    display.setTextColor(EPD_BLACK, EPD_WHITE);
    display.print(" Only changing  pixels are updated. ");
    display.update(EPD_UPD_PART);
    delay(1000);
    display.print("Thisgenerates less flicker  and results in lower    power consumption. ");
    display.update(EPD_UPD_PART);

    delay(4000);
    display.clear();
    display.setTextSize(2);
    display.print("EPD_UPD_MONO");                 
    display.update(EPD_UPD_MONO);           // Triggers a Partial Mono update, 2 GL, 250ms
    delay(1000);
    display.setTextSize(1);
    display.setTextColor(EPD_WHITE, EPD_BLACK);
    display.print("Mono updates");
    display.setTextColor(EPD_BLACK, EPD_WHITE);
    display.print(" allow a bitfaster update rates ");
    display.update(EPD_UPD_MONO);                
    delay(1000);
    display.print("(butsupport only two grey-  levels).");
    display.update(EPD_UPD_MONO);

    delay(1000);
    display.drawRect(9, 51, 125, 14, 0);
    display.update(EPD_UPD_MONO);
    for (int i=1; i<18; i++) {
        display.fillRect(6 + 7*i, 53, 5, 10, 0);
        display.update(EPD_UPD_MONO);
    }
}

void loop() {
}

Congratulation! You now learned the basics of running an ePaper screen. Interested in more? In the next examples we learn how to make use of the integrated accelerometer as a cheap touch emulator.