const byte playPin = 7;
const byte stopPin = 8;
const byte buzzerPin = 4;

enum state {SILENT, BEEPING_ON, BEEPING_OFF} state = SILENT;
unsigned long chrono;
const unsigned long soundOnDuration = 500; // ms
const unsigned long soundOffDuration = 500; // ms


void setup() {
  pinMode(buzzerPin, OUTPUT);
  pinMode(playPin, INPUT_PULLUP);
  pinMode(stopPin, INPUT_PULLUP);
}

void loop() {
  switch (state) {
    case SILENT:
      // we are silent, if we press the play button, then start playing the sound
      if (digitalRead(playPin) == LOW) {
        tone(buzzerPin, 3150);  // start the sound
        chrono = millis();      // note the start time
        state = BEEPING_ON;
      }
      break;

    case BEEPING_ON:
      // the beeping is on, check if we need to stop
      if (digitalRead(stopPin) == LOW) {
        noTone(buzzerPin);
        state = SILENT;
      } else // check if ON duration has elapsed
        if (millis() - chrono >= soundOnDuration) {
          noTone(buzzerPin);
          chrono = millis();      // note the start time
          state = BEEPING_OFF;
        }
      break;

    case BEEPING_OFF:
      // the beeping is off check if we need to stop
      if (digitalRead(stopPin) == LOW) {
        noTone(buzzerPin);
        state = SILENT;
      } else // check if OFF duration has elapsed
        if (millis() - chrono >= soundOffDuration) {
          tone(buzzerPin, 3150);  // start the sound again
          chrono = millis();      // note the start time
          state = BEEPING_ON;
        }
      break;
  }

}