const int ProxSensor=3; 

void setup() {                
  pinMode(13, OUTPUT);   
  pinMode(ProxSensor,INPUT); 
}

void loop() {
  
  if(digitalRead(ProxSensor)==HIGH)    
             {
               digitalWrite(13, LOW);  
             }
  else
            {
              digitalWrite(13, HIGH);   
             }
  delay(100);             

}