// #include "pitches.h"

float noteToFreq(int note) {
  return 220.0 * pow(2.0, note / 12.0);
}

// const int iterFrequency = 62500;
const int iterPeriod = 333;

const uint8_t buzzerPins[] = { 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2 };

const int numTones = sizeof(buzzerPins) / sizeof(buzzerPins[0]);

volatile unsigned long iter = 0;
float freqs[numTones] = {};
int periods[numTones] = {};
bool buzzerStates[numTones] = {};

void setup() {

  for (int i = 0; i < numTones; i++) {
    pinMode(buzzerPins[i], OUTPUT);
    freqs[i] = noteToFreq(i + 3);
    periods[i] = round(1e6 / freqs[i] / iterPeriod);
    buzzerStates[i] = false;
  }

  noInterrupts();
  TCCR1A = 0;
  TCCR1B = 0;
  TCNT1 = 0;
  OCR1A = 249;
  TCCR1B |= (1 << WGM12);
  TCCR1B |= (1 << CS11);
  TIMSK1 |= (1 << OCIE1A);
  interrupts();
}

void loop() {
  
}

ISR(TIMER1_COMPA_vect) {
  iter++;

  for (int i = 0; i < numTones; i++) {
    if (iter % periods[i] == 0 || iter % periods[i] == round(periods[i] / 2)) {
      buzzerStates[i] = !buzzerStates[i];
      digitalWrite(buzzerPins[i], buzzerStates[i]);
    }
  }
}