Code:

/* Play Melody
 * -----------
 *
 * Program to play melodies stored in an array, it requires to know
 * about timing issues and about how to play tones.
 *
 * The calculation of the tones is made following the mathematical
 * operation:
 *
 * timeHigh = 1/(2 * toneFrequency) = period / 2
 *
 * where the different tones are described as in the table:
 *
 * note frequency period PW (timeHigh) 
 * c 261 Hz 3830 1915 
 * d 294 Hz 3400 1700 
 * e 329 Hz 3038 1519 
 * f 349 Hz 2864 1432 
 * g 392 Hz 2550 1275 
 * a 440 Hz 2272 1136 
 * b 493 Hz 2028 1014 
 * C 523 Hz 1912 956
 *
 * (cleft) 2005 D. Cuartielles for K3
 */

int ledPin = 13;
int potPin = A0;
int speakerOut = 7; 
//byte names[] = {'c', 'd', 'e', 'f', 'g', 'a', 'b', 'C'}; 
//int tones[] = {1915, 1700, 1519, 1432, 1275, 1136, 1014, 956};

byte names[] ={ 'c', 'd', 'e', 'f', 'g', 'a', 'b', 'C', 'D', 'E', 'F', 'G', 'A', 'B'}; 
unsigned int tones[] = { 1915, 1700, 1519, 1432, 1275, 1136, 1014, 956, 852, 759, 716, 639, 568, 506};

byte melody[] = "3F3A3F9E5p3F3A3F5E2p3D3F3D4C2p3D8A8G1p3D8A8G1p3D1p9D8p";

int val = 0;
int count = 0;
int count2 = 0;
int count3 = 0;
int MAX_COUNT = 28;
int statePin = LOW;

void setup() {
// pinMode(ledPin, OUTPUT); 
 pinMode(speakerOut, OUTPUT);
}

void loop() {
 digitalWrite(speakerOut, LOW);
 val = analogRead(potPin); // read value from the sensor
if (val > 0 ){ 
 for (count = 0; count < MAX_COUNT; count++) {
 statePin = !statePin;
 digitalWrite(ledPin, statePin);
 for (count3 = 0; count3 <= (melody[count*2] - 48) * 30; count3++) {
 for (count2=0;count2<15;count2++) {
 if (names[count2] == melody[count*2 + 1]) { 
 digitalWrite(speakerOut,HIGH);
 delayMicroseconds(tones[count2]);
 digitalWrite(speakerOut, LOW);
 delayMicroseconds(tones[count2]);
 } 
 if (melody[count*2 + 1] == 'p') {
 // make a pause of a certain size
 digitalWrite(speakerOut, 0);
 delayMicroseconds(500);
 }
 }
 }
 }
}
}