volatile char *ddrD = 0x2A; // Port D Data Direction Register
volatile char *outD = 0x2B; // Port D Data Register
volatile char *inD  = 0x29; // Port D Input Pins Addres

void setup() {
 
  *ddrD =0x08;  // set pin 3 for output
  *inD = 0x00;  //set the other pas ins as input 

}

void loop() {
  
  volatile char input;
  input = *inD;

  if(input & 0X04 )
  {
    *outD = 0x08; //turn on the led when the sensor detects.
  }    
  
  else
    *outD = 0x00;//turn the led when the sensor does not detects.
  
    

}