#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;
  }