int counter = 1;

void setup() {
  DDRD = 0xFF;
  //Serial.begin(115200);
}

void loop() {
  for (int x = 0; x < 7; x++) { // Spremenljivka in vrednost, pogoj, kaj se zgodi s spremenljivko
    PORTD = counter;
    delay(200);
    counter *= 2; // counter = counter * 2
    //Serial.println(counter);
    if (counter > 128) counter = 128; // counter /= 2 | counter = 128
  }
  for (int x = 0; x < 7; x++) {
    PORTD = counter;
    delay(200);
    counter /= 2;
    if (counter < 1) counter = 1;
  }
}