const int US_sensorPin = 7;
const int relayPin = 10;
const int range = 8;   //Range of detection from the sensor in cm
int valRelay = 0;      // variable to store the read value
long relayAction;

void setup() {
  pinMode(relayPin, OUTPUT);
  digitalWrite(relayPin, HIGH); // Default relay should be OFF!
}

void loop() {
  long duration, cm;
  pinMode(US_sensorPin, OUTPUT);
  
  digitalWrite(US_sensorPin, LOW);
  delayMicroseconds(2);
  digitalWrite(US_sensorPin, HIGH);
  delayMicroseconds(5);
  digitalWrite(US_sensorPin, LOW);

  pinMode(US_sensorPin, INPUT);
  duration = pulseIn(US_sensorPin, HIGH);

  cm = microsecondsToCentimeters(duration);
  
  if (cm < range && cm > 1) {
    long new_duration, new_cm;
    pinMode(US_sensorPin, OUTPUT);
    digitalWrite(US_sensorPin, LOW);
    delayMicroseconds(2);
    digitalWrite(US_sensorPin, HIGH);
    delayMicroseconds(5);
    digitalWrite(US_sensorPin, LOW);
    pinMode(US_sensorPin, INPUT);
    new_duration = pulseIn(US_sensorPin, HIGH);

    new_cm = microsecondsToCentimeters(new_duration);

    valRelay = digitalRead(relayPin);   // read the status of input pin
    if (valRelay) {
      relayAction = LOW;
    } else {
      relayAction = HIGH;
    }

    if (new_cm < range && new_cm > 1) {
      digitalWrite(relayPin, relayAction);   // Switch Ralay ON or OFF
      delay(1000);                           // Miliseconds which it waits before does any action again
    }
  }
}
long microsecondsToCentimeters(long microseconds) {
  return microseconds / 29 / 2;

}