const byte ledpin = 13;
const byte triggerpin = 9;
const byte echopin = 8;

void setup() {
  pinMode(triggerpin, OUTPUT);
  pinMode(echopin, INPUT);
  Serial.begin(115200);
}

void loop() {
  digitalWrite(triggerpin, LOW);
  delayMicroseconds(2);
  digitalWrite(triggerpin, HIGH);
  delayMicroseconds(6);
  digitalWrite(triggerpin, LOW);

  unsigned long traveltime = pulseIn(echopin, HIGH);
  int distance = (traveltime / 2) * 0.0343;

  Serial.print("Distance in cm: ");
  Serial.println(distance);

  if(distance<100){
    digitalWrite(ledpin, HIGH);
  }
  else{
    digitalWrite(ledpin, LOW);
  }
  
  delay(100);
}