const int LED = 26;
const int TRIG = 5;
const int ECHO = 18;
const int THRESHOLD = 20;

void setup(){
  Serial.begin(115200);
  pinMode(LED, OUTPUT);
  pinMode(TRIG, OUTPUT);
  pinMode(ECHO, INPUT);
}

void loop(){
  digitalWrite(TRIG, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG, LOW);

  long duration = pulseIn(ECHO, HIGH, 30000);
  float distance = duration*0.0343/2;

  Serial.println(distance);
  if(duration>0 && distance<THRESHOLD){
    digitalWrite(LED, HIGH);
  }
  else{
    digitalWrite(LED, LOW);
  }
  delay(100);
}