const int LED_PIN = 13;
const int LED_PIN2 = 12;
const int INTERRUPT_PIN = 2;
volatile bool ledState = LOW;
volatile bool ledState2 = LOW;
volatile unsigned long zeit = 0;

void setup() {
    pinMode(LED_PIN, OUTPUT);
    pinMode(LED_PIN2, OUTPUT);
    pinMode(INTERRUPT_PIN, INPUT);
    attachInterrupt(digitalPinToInterrupt(INTERRUPT_PIN), myISR, RISING); // trigger when button pressed, but not when released.
}

void loop() {
    digitalWrite(LED_PIN2, ledState2);
    ledState2 = !ledState2;
    delay(200);
}

void myISR() {
    delay(50);
    if (digitalRead(INTERRUPT_PIN) == HIGH && millis() > zeit + 50) {
      ledState = !ledState;
      digitalWrite(LED_PIN, ledState);
      zeit = millis();
    }
    /*
    if(millis() > zeit + 500) {
      ledState = !ledState;
      digitalWrite(LED_PIN, ledState);
      zeit = millis();
    }
    */
    // note: LOW == false == 0, HIGH == true == 1, so inverting the boolean is the same as switching between LOW and HIGH.
}