const int switchpin=2;
const unsigned long debouncetime=40;
bool schalter=LOW;
bool merker=LOW;
unsigned long lasttime=0;
const int LED=LED_BUILTIN;

void setup()
{
  pinMode (10, INPUT_PULLUP);
  pinMode (9, OUTPUT);
}

void loop()
{
  if (millis()-lasttime>debouncetime)
  {
    if (digitalRead (10))
    {
      lasttime=millis();
      if (!merker)
      {
        schalter=!schalter;
        merker=HIGH;
      }
    }
    else
    {
      merker=LOW;
    }
  }
  digitalWrite (9,schalter);
}