int triggerPin = 6;
int echoPin = 7;
int speakerPin = 11;
int startPin = 10;
int ledPin = 13;

boolean running = false;
boolean lastButtonState = false;

long time = 0;
long distance = 0;
int loud = 0;

void setup()
{
  Serial.begin(9600);

  pinMode(triggerPin, OUTPUT);
  pinMode(echoPin, INPUT);
  pinMode(speakerPin, OUTPUT);
  pinMode(startPin, INPUT);
  pinMode(ledPin, OUTPUT);
  digitalWrite(ledPin, LOW);
}

boolean debounce(boolean last)
{
   boolean current = digitalRead(startPin);
   if(last != current)
   {
     delay(5);
     current = digitalRead(startPin);
   }
   return current;
}

void loop()
{
  bool currentButtonState = debounce(lastButtonState);
  if(lastButtonState == LOW && currentButtonState == HIGH)
  {
    Serial.println("SWITCHED");
    running = !running;
    digitalWrite(ledPin, running);
  }
  delay(50);

  if(running)
  {
    digitalWrite(triggerPin, LOW);
    delay(5);
    digitalWrite(triggerPin, HIGH);
    delay(10);
    digitalWrite(triggerPin, LOW);
    time = pulseIn(echoPin, HIGH);

    distance = (time/2) / 29.1;

    if(distance >= 500 || distance <= 0)
    {
      Serial.println("Kein Messwert");
      loud = 0;
    }
    else
    {
      loud = map(distance, 1,499,255,0);
      Serial.print(distance);
      Serial.print(" cm");
    }
    analogWrite(speakerPin, loud);
    delay(100);
  }
  else
  {
    analogWrite(speakerPin, 0);
    digitalWrite(ledPin, LOW);
  }

  lastButtonState = currentButtonState;
}