int trigPin = 5;
int echoPin = 18;
int beep = 16;

//define sound speed in cm/uS
float SOUND_SPEED = 0.034;
long duration;
float afstand;

void setup() {
  Serial.begin(115200); // Starts the serial communication
  pinMode(trigPin, OUTPUT); // Sets the trigPin as an Output
  pinMode(echoPin, INPUT); // Sets the echoPin as an Input
}

void loop() {
  digitalWrite(trigPin, LOW);                 // eerst de trigger afzetten
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);                //10µs hoog zetten
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);
  
  duration = pulseIn(echoPin, HIGH);          //lees de tijd tot de echopin de hoog detecteerde
  
  // Calculate the distance
  afstand = duration * SOUND_SPEED/2;
  // Prints the distance in the Serial Monitor
  Serial.print("afstand (cm): ");
  //Serial.println(afstand);
  
  if(afstand<25)
  {
  Serial.println(afstand);
  digitalWrite(beep,HIGH);
  delay(1);
  digitalWrite(beep,LOW);
  delay(1);
  }
  if (afstand<50)
  {
  Serial.println(afstand);
  for (i = 0;i<10,i++)
  {
  digitalWrite(beep,HIGH);
  delay(1);
  digitalWrite(beep,LOW);
  delay(1);
  }
  delay (300);
  if (afstand<100)
  {
  Serial.println(afstand);
 for (i = 0;i<10,i++)
  {
  digitalWrite(beep,HIGH);
  delay(1);
  digitalWrite(beep,LOW);
  delay(1);
  }
  delay (1000);
  }
  else 
  {
      Serial.println(afstand);

  }
  //delay(1000);

}