#define TIMER0_PRESCALER                64
#define TIMER0_FREQUENCY                1000 // Hz

#define PWM_PERIOD_MS                   20                                  //PWM-period in milli seconds
#define TIMER_CLOCKS                    16000000/8                          //prescaled timer clocks per second of timer 1
#define TIMER_CLOCKS_PER_MS             TIMER_CLOCKS/1000
#define TIMER_CLOCKS_PER_PWM_PERIOD     PWM_PERIOD_MS*TIMER_CLOCKS_PER_MS

#define LEFT_POS                        1.00*TIMER_CLOCKS_PER_MS-1          // 1.0 ms for left position
#define MIDDLE_POS                      1.48*TIMER_CLOCKS_PER_MS-1          // 1.5 ms for middle position
#define RIGHT_POS                       2.00*TIMER_CLOCKS_PER_MS-1          // 2.0 ms for right position

#define POS_MIN                         0.57*TIMER_CLOCKS_PER_MS-1
#define POS_MAX                         2.53*TIMER_CLOCKS_PER_MS-1

unsigned int timer0_counter = 0;

void setup()
{
    //CTC-Mode of Timer0
    OCR0A  = 249;
    TCCR0A = (1 << WGM01); //CTC-Mode TOP-Value = OCR0A
    TCCR0B = (1 << CS01) | (1 << CS00); //Prescaler = 64
    TIMSK0 = (1 << OCIE0A);
    TIFR0  = (1 << OCF0A);

    //FAST PWM SETTINGS USING TIMER1
    DDRB |= (1 << PB1);                                     //set PB1 for OC1A to output mode
    TCCR1A = (1 << COM1A1) | (1 << WGM11);                  //Clear OC1A on compare match, set OC1A at BOTTOM value of TCNT1
    TCCR1B = (1 << WGM13) | (1 << WGM12) | (1 << CS11);     //Fast PWM in Mode 14, prescaler = 8
    OCR1A = RIGHT_POS;                                     //Compare value for pulse width equal to servo middle position
    ICR1 = TIMER_CLOCKS_PER_PWM_PERIOD;                     //Top value to set pwm-period

    sei();

}

void loop()
{
}

ISR(TIMER0_COMPA_vect)
{
  if(++timer0_counter == TIMER0_FREQUENCY)
  {
    timer0_counter = 0;
    if(OCR1A == RIGHT_POS)  OCR1A = LEFT_POS;  
    else                    OCR1A = RIGHT_POS;
  }
}