const byte LED_PIN = 23;
const byte INTERRUPT_PIN = 34;
volatile byte state = HIGH;

void setup() {
  Serial.begin(9600);
  pinMode(LED_PIN, OUTPUT);
  pinMode(INTERRUPT_PIN, INPUT_PULLUP);
  attachInterrupt(digitalPinToInterrupt(INTERRUPT_PIN), blink, CHANGE);
}

void loop() {
  digitalWrite(LED_PIN, state);
  while (Serial.available()) {
    // get the new byte:
    char inChar = (char)Serial.read();
    if (inChar == 'Q' || inChar == 'q') {
      detachInterrupt(digitalPinToInterrupt(INTERRUPT_PIN));
      Serial.println("Interrupt disabled");
	  }
	else if (inChar == 'O' || inChar == 'o') {
		  attachInterrupt(digitalPinToInterrupt(INTERRUPT_PIN), blink, CHANGE);
		  Serial.println("Interrupt enabled");
    }
  }
}

void blink() {
  state = !state;
}