volatile bool b = false;
volatile uint32_t debounce;
void setup() {
  pinMode(2, INPUT_PULLUP);
  pinMode(13, OUTPUT);
  digitalWrite(13, LOW);
  attachInterrupt(0, btnIsr, RISING);
}
void btnIsr(){
if (millis() - debounce >= 200 && digitalRead(2)) {
      debounce = millis();
      b = !b;
}
}
void loop() {
  if (b) {
    digitalWrite(13, HIGH);
    delay(500);
    digitalWrite(13, LOW);
    delay(500);
  }
}