int t = 500;

void setup() {
  for(int i=1; i < 9; i++){
    pinMode(i, OUTPUT);
  }

}

void loop() {
  for(int i=1; i<5; i++){
    if(i == 1){
      delay(t);
      digitalWrite(1, 1);
      digitalWrite(2, 1);
      delay(t);
      digitalWrite(1, 0);
      digitalWrite(2, 0);
    }
    if(i == 2){
      delay(t);
      digitalWrite(3, 1);
      digitalWrite(4, 1);
      delay(t);
      digitalWrite(3, 0);
      digitalWrite(4, 0);
    }
    if(i == 3){
      delay(t);
      digitalWrite(5, 1);
      digitalWrite(6, 1);
      delay(t);
      digitalWrite(5, 0);
      digitalWrite(6, 0);
    }
    if(i == 4){
      delay(t);
      digitalWrite(7, 1);
      digitalWrite(8, 1);
      delay(t);
      digitalWrite(7, 0);
      digitalWrite(8, 0);
    }
  }
}