SparkFun Electronics Forum

#include <avr/io.h>
#include <avr/interrupt.h>

#define READ(port,pin) (PIN ## port & (1<<pin)) 
#define INPUT(port,pin) DDR ## port &= ~(1<<pin)
#define OUTPUT(port,pin) DDR ## port |= (1<<pin)
#define CLEAR(port,pin) PORT ## port &= ~(1<<pin)
#define SET(port,pin) PORT ## port |= (1<<pin)
#define TOGGLE(port,pin) PORT ## port ^= (1<<pin)

	volatile unsigned int pWidth;
	volatile unsigned int pStart;
	volatile unsigned int pStop;

int main (void)
{
	INPUT(D,6);	// Input Capture Pin set as input
	SET(D,6);	// Enable pull-up resistor

	OUTPUT(B,0);	// Declare PB0 as output

	TCCR1B = (1<<CS11);	// Set prescaler to 8
	TCCR1B |= (1<<ICES1);	// Input capture in rising edge
	TIMSK = (1<<ICIE1);	// Enable Input Capture interrupt

	pWidth = 1500;

	while(1)
	{
		sei();
		if(pWidth <= 1470)
		{
			PORTB |= (1<<PB0);
		}
		else
		{
			PORTB &= ~(1<<PB0); 
		}
	}
}

ISR(TIMER1_CAPT_vect)
{

	PORTB ^= (1<<PB0);
    pStop = ICR1;
    if (TCCR1B & (1<<ICES1))
	{
        TCCR1B &= ~(1<<ICES1);
        pStart = pStop;
    }
	else
	{
        TCCR1B |= (1<<ICES1);
        pWidth = pStop - pStart;
    } 
}