const int trigPin = 10;
const int echoPin = 9;
const int ledPin = 8;

float duration, distance;
float threshold = 500.00;

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

void loop()
{
  // put your main code here, to run repeatedly:
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  duration = pulseIn(echoPin, HIGH);
  distance = (duration * .0343) / 2.0;

  Serial.print("duration = ");
  Serial.println(duration);
  Serial.print("Distance = ");
  Serial.println(distance);
  Serial.println();

  if(distance >= threshold)
  {
    digitalWrite(ledPin,HIGH);
  }
  else
  {
    digitalWrite(ledPin,LOW);
  }

  delay(1000);
}