/* function to read out switches */
uint8_t PollSwitch(void)
{
    unsigned int i;
    _Bool ec_bak = autoencode;
    autoencode = FALSE;
    DDRD |= SWITCHES;               // Switches as Output
    SWITCH_ON;                      // Output HIGH for measurement
    ADMUX = (1 << REFS0) | SWITCH;  // AVCC reference with external capacitor
    Sleep(10);

    ADCSRA |= (1 << ADSC);          // Start conversion
    while (!(ADCSRA & (1 << ADIF)));// wait for conversion complete
    ADCSRA |= (1 << ADIF);          // clear ADCIF
    i = ADCL + (ADCH << 8);

    SWITCH_OFF;
    Sleep(5);
    autoencode = ec_bak;

    return ((10240000/i - 10000) * 63 + 5000)/10000;
}

/*!
 * binds switch press to external Interrupt 1
 * catch it with ISR(INT1_vect)
 * see avr-libc documentation for details
 */
void StartSwitch(void)
{
    SWITCH_OFF;
    DDRD &= ~SWITCHES;                  // disable Switches as Input

    Sleep(100); // cool down from pollswitch

    MCUCR &= ~((1 << ISC11) | (1 << ISC10));// Low level generates interrupt
    GICR |= (1 << INT1);                    // Enable external Interrupt 1
}

void StopSwitch(void)
{
    GICR &= ~(1 << INT1);
}