Nuts and Volts - August 2009

noises. For us to create a recognizable tune, we need to control the musical notes (tones) and the duration between the notes (beat). For simple tunes, we can live with eight tones (a music octave) each having a specific frequency. Each of these tones has a letter ‘note’ assigned to it by musicians as in Figure 6.

We will keep this as simple as possible and generate these notes using the Arduino library delayMicroseconds function. (A microsecond is 1/1,000,000 second — yes: one millionth of a second — you have heard that computers are fast, haven’t you?)

To generate the ‘c’ note, we create an output waveform (see Figure 7) that turns on and off with a frequency of 261 cycles per second. Each of these on/off cycles occurs in 1/261 of a second or 0.003831 seconds. Since we are dealing with microseconds, we multiply this by 1,000,000 to get 3,831 microseconds per cycle. Since we need to cycle the pin (turn the pin on and off) in that time, we turn it on for 3831/2 = 1,915 microseconds (throwing away the fractional part) and off for 1,915 microseconds giving us a total of 3,830. We lost 1 due to our not wanting to use fractions, but who is going to miss a microsecond?

In the Tunes program, we use a play Tone function that takes the tone and the duration as parameters. A loop repeats the on/off cycle for the note parameter for a length of time in the duration parameter. It might, for instance, turn the speaker on for 1,915 uS and off for 1,915 uS repeating for a full second to give a rather long ‘c’ note. The play Tone function is called by the playNote function that has the job of reading through the tune array to get the next note/duration combination.

Each tune is played by an individual function that contains two arrays: one for the tune notes and one for the tune beat. It calculates the duration from the beats and sends that duration along with the tune note to the playNote function. The playNote function reads through an array of note names and uses that name position in that array to get the number for the microseconds needed to play that note. It then calls play Tone with the tone microseconds and the duration as parameters.

The play Tone uses those parameters to turn the pin connected to the piezo element on and off, thus generating exquisite music like none heard since the last pterodactyl blundered into a fern tree.

Tunes Source Code

The Tunes source code is shown here in TAW abridged from the full code that is available along with the ACW version in Workshop13.zip. It is shortened since there is a lot of repetition in how the tunes are played. Twinkle, Twerdle, Euro Siren, and Beep Beep are in the zip file. AND a note to more experienced programmers: Yes, I know this isn’t the ‘best’ way to do this, but this is instructional code for novices. I have some comments with the zipped code about better ways and I will

SMILEY’S WORKSHOP ☺

show those ways in a future workshop.

/* TAW Tunes
 Joe Pardue May 13, 2009
 based on Arduino example code Melody
 www.arduino.cc/en/Tutorial/Melody
 (cleft) 2005 D. Cuartielles for K3
 */

// define numbers for tunes
#define Twinkle 0
#define Happy_Birthday 1
#define Euro_Siren 2
#define Twerdle 3
#define Beep_Beep 4

// create and intialize global variables
int speakerPin = 9; // pin to drive the piezo
element
int tune = 0; // tune to play

void setup() {
  Serial.begin(9600);
  pinMode(speakerPin, OUTPUT);

 // greetings
  Serial.println(“TAW Tunes”);
  Serial.println(“Enter 0 for Twinkle Twinkle
Little Star”);
  Serial.println(“Enter 1 for Happy Birthday”);
  Serial.println(“Enter 2 for Euro Siren”);
  Serial.println(“Enter 3 for Twerdle Alarm”);
  Serial.println(“Enter 4 for Beep Alarm”);
}

void loop() {
  // check if data has been sent from the
  // computer
  if (Serial.available()) {
 cmdParse(); // if true, get the data and
parse it
  }