#define trig 6
#define echo 7
#define led 12

long duration, distance;
void setup() 
{ 
  pinMode(echo, INPUT);
  pinMode(trig, OUTPUT);
  pinMode(led, OUTPUT);

  Serial.begin(115200);
}
void loop() 
{
  digitalWrite(trig, LOW);
  delayMicroseconds(5);
  digitalWrite(trig, HIGH);
  delayMicroseconds(5);
  digitalWrite(trig, LOW);

  //end triger
  duration=pulseIn(echo, HIGH); //Read echo ultrasonics
  distance=(duration/2)/29.1;   // conver to CM
  if(distance>20)
  {
    digitalWrite(led, LOW);
  }
  else
  {
    digitalWrite(led, HIGH);
  }
  delay(300); 
  //send to monitor
  Serial.println(distance);
}