// https://forum.arduino.cc/t/erste-erfahrungen-mit-interrrupt/1145963/2
// man braucht keinen Interrupt für Timer...


void doSomething() {
  static uint32_t previousMillis = 0;
  if (millis() - previousMillis > 5000) {
    previousMillis = millis();
    Serial.println(F("tu Was"));
  }
}

void blink() {
  static uint32_t previousMillis = 0;
  if (millis() - previousMillis > 500) {
    previousMillis = millis();
    if (digitalRead(13) == LOW) digitalWrite(13, HIGH); else digitalWrite(13, LOW);
  }
}

void setup() {
  Serial.begin(115200);
  pinMode(13, OUTPUT);
}

void loop() {
  doSomething();
  blink();
}