const int trigPin = 9;
const int echoPin = 8;
const int RELAY_PIN = 4;
const int LED_PIN= 13;
const int Distance_Thershold= 100;

float duration , distance;

void setup() {
  Serial.begin(9600);
  pinMode(RELAY_PIN, OUTPUT);
  pinMode(trigPin, OUTPUT); 
  pinMode(echoPin, INPUT); 
  pinMode(LED_PIN, OUTPUT);
}


void loop() {
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);
  duration = pulseIn(echoPin, HIGH);
  distance = duration * 0.017; 
  
if( distance < Distance_Thershold)
{
    digitalWrite(LED_PIN, HIGH);
    digitalWrite(RELAY_PIN, HIGH);
  }

else {
    digitalWrite(LED_PIN, LOW);
    digitalWrite(RELAY_PIN, LOW);
  }

  
  Serial.print("Distance: ");
  Serial.print(distance);
  Serial.println(" cm ");
  delay(1000);
}