Tutorial.Melody History

Hide minor edits - Show changes to output

October 18, 2008, at 06:23 PM by David A. Mellis -
Changed lines 1-2 from:
!!Play Melody
to:
!!Melody
October 18, 2008, at 06:22 PM by David A. Mellis -
Added lines 1-78:
!!Play Melody

This example uses a piezo speaker to play melodies. It sends a square wave of the appropriate frequency to the piezo, generating the corresponding tone.

The calculation of the tones is made following the mathematical operation:

timeHigh = period / 2 = 1 / (2 * toneFrequency)

where the different tones are described as in the table:

[@
note frequency period 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
@]

!!!Circuit

Piezos have polarity. Commercial devices are usually have a red (positive) and a black (negative). Connect the red wire digital pin 9 and the black wire to ground. Sometimes it is possible to acquire Piezo elements without a plastic housing, then they will just look like a metallic disc.

[[http://static.flickr.com/31/53523608_3d4268ba68_o.jpg|http://static.flickr.com/31/53523608_3d4268ba68.jpg]]

''A piezo connected to pin 9.''

!!!Code

[@
int speakerPin = 9;

int length = 15; // the number of notes
char notes[] = "ccggaagffeeddc "; // a space represents a rest
int beats[] = { 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 2, 4 };
int tempo = 300;

void playTone(int tone, int duration) {
for (long i = 0; i < duration * 1000L; i += tone * 2) {
digitalWrite(speakerPin, HIGH);
delayMicroseconds(tone);
digitalWrite(speakerPin, LOW);
delayMicroseconds(tone);
}
}

void playNote(char note, int duration) {
char names[] = { 'c', 'd', 'e', 'f', 'g', 'a', 'b', 'C' };
int tones[] = { 1915, 1700, 1519, 1432, 1275, 1136, 1014, 956 };

// play the tone corresponding to the note name
for (int i = 0; i < 8; i++) {
if (names[i] == note) {
playTone(tones[i], duration);
}
}
}

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

void loop() {
for (int i = 0; i < length; i++) {
if (notes[i] == ' ') {
delay(beats[i] * tempo); // rest
} else {
playNote(notes[i], beats[i] * tempo);
}

// pause between notes
delay(tempo / 2);
}
}
@]

Share