Twinkle, Twinkle, Little Star on a passive buzzer (pin 9), on an Arduino Uno

// Twinkle, Twinkle, Little Star on a passive buzzer on pin 9.
//
//   pin 9 -> the buzzer's + leg; the other leg -> GND
//
// A tune is two lists: which note, and for how long. Each note is a
// frequency in hertz (middle C is 262), and each length is in milliseconds.
// The for loop plays them in order, with a short gap so repeated notes are
// heard as two.

const int BUZZER = 9;

const int C = 262, D = 294, E = 330, F = 349, G = 392, A = 440;

const int melody[] = {C, C, G, G, A, A, G, F, F, E, E, D, D, C};
const int lengths[] = {400, 400, 400, 400, 400, 400, 800, 400, 400, 400, 400, 400, 400, 800};
const int NOTES = sizeof(melody) / sizeof(melody[0]);

void setup() {
  Serial.begin(9600);
  Serial.println("Mokxi Uno: Twinkle, Twinkle, Little Star on pin 9");
}

void loop() {
  for (int i = 0; i < NOTES; i++) {
    tone(BUZZER, melody[i], lengths[i]);
    delay(lengths[i] * 13 / 10);
    noTone(BUZZER);
  }
  delay(1000);
}