#include <NewPing.h>

const int LED_PIN = 3;
const int SR04_TRIG = 10;
const int SR04_ECHO = 11;

const int range = 20;
const int max_dist = 400;

NewPing sonar(SR04_TRIG, SR04_ECHO, max_dist);

void setup()
{
  pinMode(LED_PIN, OUTPUT);

}

void loop()
{
  int distance = 0;
  distance = sonar.ping_cm();

  if (distance <= range)
  {
    digitalWrite(LED_PIN, HIGH);
  }
  else
  {
    digitalWrite(LED_PIN, LOW);
  }
}