grid.ino

// thanks to https://www.glennklockwood.com/electronics/max7219.html and http://www.gammon.com.au/forum/?id=11516 for help
// and to the data sheet

#include <SPI.h>
#define selectPin D2

#define REG_NOOP 0x00
#define REG_DIGIT_0 0x01
#define REG_DIGIT_1 0x02
#define REG_DIGIT_2 0x03
#define REG_DIGIT_3 0x04
#define REG_DIGIT_4 0x05
#define REG_DIGIT_5 0x06
#define REG_DIGIT_6 0x07
#define REG_DIGIT_7 0x08
#define REG_DECODE_MODE 0x09
#define REG_INTENSITY 0x0A
#define REG_SCAN_LIMIT 0x0B
#define REG_SHUTDOWN 0x0C
#define REG_DISPLAY_TEST 0x0F

SPISettings MaxSpiSettings;

const int IMAGE_WAIT[] = {
  2000,
  1700,
  1000,
  1700,
  2200,
  1000,
};

const byte IMAGES[][8] = {
{
  B01111110,
  B11000011,
  B10011001,
  B10011001,
  B10011001,
  B10100101,
  B10000001,
  B01111110
},{
  B00000000,
  B10111011,
  B10101010,
  B10110010,
  B10101010,
  B10101010,
  B10101011,
  B00000000
},{
  B00000000,
  B00000000,
  B00000000,
  B00000000,
  B00000000,
  B00000000,
  B00000000,
  B00000000
},{
  B00000000,
  B10111011,
  B10101010,
  B10110010,
  B10101010,
  B10101010,
  B10101011,
  B00000000
},{
  B00000000,
  B00000110,
  B00001001,
  B00000001,
  B10100110,
  B10100001,
  B01001001,
  B00000110
},{
  B00000000,
  B00000000,
  B00000000,
  B00000000,
  B00000000,
  B00000000,
  B00000000,
  B00000000
}};
const int IMAGES_LEN = sizeof(IMAGES)/8;

int image = 0;

void setRegister(byte reg, byte value) {
//  Serial.print("  setting 0x");
//  Serial.print(reg, HEX);
//  Serial.print(" to 0x");
//  Serial.print(value, HEX);
//  Serial.println("");

  digitalWrite(selectPin, LOW);
  SPI.beginTransaction(MaxSpiSettings);
  SPI.transfer(reg);
  SPI.transfer(value);
  SPI.endTransaction();
  digitalWrite(selectPin, HIGH);
}

void setup() {
  MaxSpiSettings = SPISettings(1000000, MSBFIRST, SPI_MODE0);
  SPI.begin();

  Serial.begin(115200);

  // enable chip select pin
  pinMode(selectPin, OUTPUT);
  digitalWrite(selectPin, HIGH);

  // wait for output to stabilise before we start using it
  Serial.print("\n");
  Serial.println("waiting");

  Serial.println(0x1 | 0x02, HEX);
  delay(500);

  // set scan limit register
  setRegister(REG_SCAN_LIMIT, 0x07);
  // set decode mode
  setRegister(REG_DECODE_MODE, 0x00);
  // disable display test
  setRegister(REG_DISPLAY_TEST, 0x00);
  // clear display
  for (uint8_t a = 0x00; a < 0x08; ++a) {
    setRegister(a + 0x01, 0x00);
  }
  // set scan limit register
  setRegister(REG_INTENSITY, 0x00);
  // set shutdown register
  setRegister(REG_SHUTDOWN, 0x01);

  // wait a bit
  Serial.println("blanked");
  delay(500);
}

void displayImage(int iNum) {
  Serial.print("Displaying image ");
  Serial.println(iNum);

  byte column;
  for (int x = 0; x < 8; ++x) {
//    setRegister(x + 0x1, IMAGES[iNum][x]);
    column = 0;
    for (int y = 0; y < 8; ++y) {
      column = column | (((IMAGES[iNum][y] >> (7 - x)) & B00000001) << y);
    }
    setRegister(x + 0x1, column);
  }
}

void loop() {
  displayImage(image);

  delay(IMAGE_WAIT[image]);

  if (++image >= IMAGES_LEN) {
    image = 0;
  }
}