#define pow 0
#define echo 1
#define trig 2
#define LED 3

void setup() {
  // put your setup code here, to run once:
  pinMode(pow, OUTPUT);
  pinMode(echo, INPUT);
  pinMode(trig, OUTPUT);
  pinMode(LED, OUTPUT);

  digitalWrite(pow, HIGH);
}

void loop() {
  // put your main code here, to run repeatedly:
  digitalWrite(trig, HIGH);
  delayMicroseconds(10);
  digitalWrite(trig, LOW);

  // Read the result:
  int duration = pulseIn(echo, HIGH);
  if(duration/50 < 100){
    digitalWrite(LED, HIGH);
  }

  delay(1000);
  digitalWrite(LED, LOW);
}