Using Timer Interrupt of Arduino Uno

Example to use Timer Interrupt of Arduino Uno.


WalkingLedMatrix.ino

// 2-dimensional array of row pin numbers:
const int row[8] = {
  2, 7, 19, 5, 13, 18, 12, 16
};

// 2-dimensional array of column pin numbers:
const int col[8] = {
  6, 11, 10, 3, 17, 4, 8, 9
};

// 2-dimensional array of pixels:
int pixels[8][8];

int posX = 7;
int posY = 7;
int count = 30;
bool bg = false;

volatile unsigned long lasttime;
volatile unsigned long now;

int timer1_counter;

void setup() {
  Serial.begin(9600);
  
  // initialize the I/O pins as outputs
  // iterate over the pins:
  for (int thisPin = 0; thisPin < 8; thisPin++) {
    // initialize the output pins:
    pinMode(col[thisPin], OUTPUT);
    pinMode(row[thisPin], OUTPUT);
    // take the col pins (i.e. the cathodes) high to ensure that
    // the LEDS are off:
    digitalWrite(col[thisPin], HIGH);
  }

  setupScreen();
  
  // initialize timer1 
  noInterrupts();           // disable all interrupts
  TCCR1A = 0;
  TCCR1B = 0;

  //timer1_counter for 1 sec, with prescaler=256
  //65536 - 16000000/256
  //timer1_counter = 3036;
  //timer1_counter for 0.5 sec, with prescaler=256
  //65536 - 16000000/(256*2)
  //timer1_counter = 34286;
  //timer1_counter for 0.1 sec, with prescaler=256
  //65536 - 16000000/(256*10)
  timer1_counter = 59286;
  
  
  TCNT1 = timer1_counter;   // preload timer
  TCCR1B |= (1 << CS12);    // 256 prescaler 
  TIMSK1 |= (1 << TOIE1);   // enable timer overflow interrupt
  interrupts();             // enable all interrupts
  
  lasttime = millis();

}

ISR(TIMER1_OVF_vect)        // interrupt service routine 
{
  TCNT1 = timer1_counter;   // preload timer

  if(posX--==0){
    posX = 7;
    if(posY--==0){
      posY = 7;
      bg = !bg;
    }
  }
  setupScreen();
  
  now = millis();
  Serial.println(now - lasttime);
  lasttime = now;
}

void loop() {
  refreshScreen();
}

void setupScreen(){
  if(bg){
    //ON all others
    for (int x = 0; x < 8; x++) {
      for (int y = 0; y < 8; y++) {
        pixels[x][y] = LOW;
      }
    }
    
    //OFF current pos
    pixels[posX][posY] = HIGH;
  }else{
    //OFF all others
    for (int x = 0; x < 8; x++) {
      for (int y = 0; y < 8; y++) {
        pixels[x][y] = HIGH;
      }
    }
    
    //ON current pos
    pixels[posX][posY] = LOW;
  }
}

void refreshScreen() {
  // iterate over the rows (anodes):
  for (int thisRow = 0; thisRow < 8; thisRow++) {
    // take the row pin (anode) high:
    digitalWrite(row[thisRow], HIGH);
    // iterate over the cols (cathodes):
    for (int thisCol = 0; thisCol < 8; thisCol++) {
      // get the state of the current pixel;
      int thisPixel = pixels[thisRow][thisCol];
      // when the row is HIGH and the col is LOW,
      // the LED where they meet turns on:
      digitalWrite(col[thisCol], thisPixel);
      // turn the pixel off:
      if (thisPixel == LOW) {
        digitalWrite(col[thisCol], HIGH);
      }
    }
    // take the row pin low to turn off the whole row:
    digitalWrite(row[thisRow], LOW);
  }
}