int detector = 9; // define the obstacle avoidance sensor interface
int val ;

void setup ()
{
  pinMode(13, OUTPUT);     // Built in Arduino LED
  digitalWrite (13, LOW);
  pinMode (detector, INPUT) ;// define the obstacle avoidance sensor output interface
}
void loop ()
{
  val = digitalRead (detector) ;
  if (val == HIGH) // When the obstacle avoidance sensor detects a signal, LED flashes
  {
    digitalWrite (13, HIGH);
    delay(100);
  }
  else
  {
    digitalWrite (13, LOW);
    delay(100);
  }
}
