const int trigPin = 9;
  const int echoPin = 10;
  

  const int ledPin3 = 3;

  long duration;
  int distance;
  
  void setup() {
    Serial.begin(9600);
    pinMode(trigPin, OUTPUT);
    pinMode(echoPin, INPUT);

    pinMode(ledPin3, OUTPUT);
  }
  
  void loop() {
    
    digitalWrite(trigPin, LOW);
    delayMicroseconds(2);
    digitalWrite(trigPin, HIGH);
    delayMicroseconds(10);
    digitalWrite(trigPin, LOW);
    
    duration = pulseIn(echoPin, HIGH);
    
    distance = duration * 0.034 / 2;
    
    Serial.print("Vzdialenost: ");
    Serial.print(distance);
    Serial.println(" cm");

    if(distance < 50){
      digitalWrite(ledPin3, HIGH);
    }
    else {
      digitalWrite(ledPin3, LOW);
    }

    delay(1000);
  }