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I have 4 dot matrix displays, every one of them connected to an i2c and accessible with 0x70, 0x71, 0x72 and 0x73. All these work just fine when I address them apart. What I want to achieve is a scrolling text throughout all 4 displays. How can I do this? Are there any libraries around that already do this? (I did not find any).

Basically, this is my code:

#include <Wire.h>
#include "Adafruit_LEDBackpack.h"
#include "Adafruit_GFX.h"

Adafruit_8x8matrix matrix[4];

void setup() {
  Serial.begin(9600);
  Serial.println("4x(8x8) LED Matrix Test");
  matrix[0].begin(0x70);
  matrix[1].begin(0x71);
  matrix[2].begin(0x72);
  matrix[3].begin(0x73);
}
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This is what I found behind the link @mikael-patel posted, and with a little configuration it does exactly what I want. Basically the scroll()-method handles anything neccessary.

#include <Wire.h>
#include "Adafruit_LEDBackpack.h"
#include "Adafruit_GFX.h"

#define NUM_MATRICES 2
Adafruit_8x8matrix matrix[NUM_MATRICES];

void setup() {
  Serial.begin(9600);
  Serial.println("8x8 LED Matrix Test");

  for(uint8_t m=0; m<NUM_MATRICES; m++) {
    matrix[m].begin(0x70 + m);
    matrix[m].clear();
    matrix[m].setTextSize(1);
    matrix[m].setTextWrap(false);  // we dont want text to wrap so it scrolls nicely
    matrix[m].setTextColor(LED_GREEN);
  }
}

void loop() {
  scroll("Hello World!");
}

void scroll(char* text) {
  int scrollPositions = (strlen(text) * 8) + 32;

  for (int x=(8 * NUM_MATRICES); x>=-scrollPositions; x--) {
   for(uint8_t m=0; m<NUM_MATRICES; m++) {
    matrix[m].clear();
    matrix[m].setCursor((x - (m * 8)), 0);
    matrix[m].print(text);
    matrix[m].writeDisplay();
   }
   delay(80);
  }
}

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