int duracion = 250;  
int freqmin = 2000;  
int freqmax = 4000;  

void setup(){
	pinMode(8, OUTPUT); 
}

void loop(){
	int i;
	for (i = freqmin; i<=freqmax; i++){
		tone (8, i, duracion);
	}
	for (i = freqmax; i>=freqmin; i--){
		tone (8, i, duracion);
	}
} 





