void setup() {
  // put your setup code here, to run once:
  pinMode(6, OUTPUT);
  pinMode(7, INPUT);
  pinMode(8, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  // put your main code here, to run repeatedly:
  digitalWrite(6, LOW);
  digitalWrite(6, HIGH);
  delayMicroseconds(10);
  digitalWrite(6, LOW);
   float duration = pulseIn(7, HIGH);
  float distanceCm= (duration*0.034)/2;
      Serial.print("Object is at : ");
   Serial.println(distanceCm);
   delay(1000);
   if(distanceCm>20){
     pinMode(8,HIGH);
   }
}