volatile bool status=false;
#define FCPU 16000000 //CPU Clock Speed
#define TD .5  //500ms delay before counter overflow
#define PRESCALER 1024
#define RELOAD (65536-FCPU*TD/PRESCALER)

void setup() {
 
 pinMode(3, OUTPUT); 
 digitalWrite(3,status);
 cli(); //Disable Global Interrupt
 TCNT1 = RELOAD; //load the TCNT1 with RELOAD value for 500ms delay //for normal mode operation and pre-scalar of 1024
 TCCR1A = 0x00; TCCR1B = 0b00000101; 
 bitSet(TIMSK1, TOIE1);
 sei(); //Enable Global Interrupt

}

void loop() {
  // There is nothing here 
}

ISR(TIMER1_OVF_vect){
 TCNT1 = RELOAD;
 status=!status;
 digitalWrite(3,status);
}