#include "avr/io.h"
#include "avr/interrupt.h"

int main ( )
{
	DDRB = DDRB |(1<<3);	
	OCR0 = 69;			
	TCCR0 = 0x19;	  
	TIMSK = (1<<OCIE0);	
	sei();			
	while(1);		
	
	return 0;
}

ISR(TIMER0_COMP_vect)
{
	const unsigned char waveTable [] = {24,49,39,34};
	static unsigned char index = 0;

	OCR0 = waveTable[index];
	index ++;

	if(index >= 4)
		index = 0;
}