Simulated Electronics

/* Play Melody
 * -----------
 *
 * Program to play a simple melody
 *
 * Tones are created by quickly pulsing a speaker on and off
 *   using PWM, to create signature frequencies.
 *



 * Each note has a frequency, created by varying the period of
 *  vibration, measured in microseconds. We'll use pulse-width
 *  modulation (PWM) to create that vibration.

 * We calculate the pulse-width to be half the period; we pulse
 *  the speaker HIGH for

 'pulse-width' micro





seconds, then LOW
 *  for 'pulse-width' microseconds.
 *  This pulsing creates a vibration of the desired frequency.
 *






 * (cleft) 2005 D. Cuartielles for K3
 * Refactoring and comments 2006 clay.shirky@nyu.edu
 * See NOTES in comments at end for possible improvements
 */

// TONES  ==========================================
// Start by defining the relationship between
//       note, period, &  frequency.
#define  c     3830    // 261 Hz
#define  d     3400    // 294 Hz
#define  e     3038    // 329 Hz
#define  f     2864    // 349 Hz
#define  g     2550    // 392 Hz
#define  a     2272    // 440 Hz
#define  b     2028    // 493 Hz
#define  C     1912    // 523 Hz
// Define a special note, 'R', to represent a rest
#define  R     0

// SETUP ============================================
// Set up speaker on a PWM pin (digital 9, 10 or 11)
int speakerOut = 9;
// Do we want debugging on serial out? 1 for yes, 0 for no
int DEBUG = 0;

void setup() {
  pinMode(speakerOut, OUTPUT);
  if (DEBUG) {
    Serial.begin(9600); // Set serial out if we want debugging
  }
}

// MELODY and TIMING  =======================================
//  melody[] is an array of notes, accompanied by beats[],
//  which sets each note's relative length (higher #, longer note)
int melody[] = {  C,  b,  g,  C,  b,   e,  R,  C,  c,  g, a, C };
int beats[]  = { 16, 16, 16,  8,  8,  16, 32, 16, 16, 16, 8, 8 };
int MAX_COUNT = sizeof(melody) / 2; // Melody length, for looping.

// Set overall tempo
long tempo = 10000;
// Set length of pause between notes
int pause = 1000;
// Loop variable to increase Rest length
int rest_count = 100; //<-BLETCHEROUS HACK; See NOTES

// Initialize core variables
int tone_ = 0;
int beat = 0;
long duration  = 0;

// PLAY TONE  ==============================================
// Pulse the speaker to play a tone for a particular duration
void playTone() {
  long elapsed_time = 0;
  if (tone_ > 0) { // if this isn't a Rest beat, while the tone has
    //  played less long than 'duration', pulse speaker HIGH and LOW
    while (elapsed_time < duration) {

      digitalWrite(speakerOut,HIGH);
      delayMicroseconds(tone_ / 2);

      // DOWN
      digitalWrite(speakerOut, LOW);
      delayMicroseconds(tone_ / 2);

      // Keep track of how long we pulsed
      elapsed_time += (tone_);
    }
  }
  else { // Rest beat; loop times delay
    for (int j = 0; j < rest_count; j++) { // See NOTE on rest_count
      delayMicroseconds(duration);  
    }                                
  }                                
}

// LET THE WILD RUMPUS BEGIN =============================
void loop() {
  // Set up a counter to pull from melody[] and beats[]
  for (int i=0; i<MAX_COUNT; i++) {
    tone_ = melody[i];
    beat = beats[i];

    duration = beat * tempo; // Set up timing

    playTone();
    // A pause between notes...
    delayMicroseconds(pause);

    if (DEBUG) { // If debugging, report loop, tone, beat, and duration
      Serial.print(i);
      Serial.print(":");
      Serial.print(beat);
      Serial.print(" ");    
      Serial.print(tone_);
      Serial.print(" ");
      Serial.println(duration);
    }
  }
}

/*
 * NOTES
 * The program purports to hold a tone for 'duration' microseconds.
 *  Lies lies lies! It holds for at least 'duration' microseconds, _plus_
 *  any overhead created by incremeting elapsed_time (could be in excess of
 *  3K microseconds) _plus_ overhead of looping and two digitalWrites()
 *  
 * As a result, a tone of 'duration' plays much more slowly than a rest
 *  of 'duration.' rest_count creates a loop variable to bring 'rest' beats
 *  in line with 'tone' beats of the same length.
 *
 * rest_count will be affected by chip architecture and speed, as well as
 *  overhead from any program mods. Past behavior is no guarantee of future
 *  performance. Your mileage may vary. Light fuse and get away.
 *  
 * This could use a number of enhancements:
 * ADD code to let the programmer specify how many times the melody should
 *     loop before stopping
 * ADD another octave
 * MOVE tempo, pause, and rest_count to #define statements
 * RE-WRITE to include volume, using analogWrite, as with the second program at
 *          http://www.arduino.cc/en/Tutorial/PlayMelody
 * ADD code to make the tempo settable by pot or other input device
 * ADD code to take tempo or volume settable by serial communication
 *          (Requires 0005 or higher.)
 * ADD code to create a tone offset (higer or lower) through pot etc
 * REPLACE random melody with opening bars to 'Smoke on the Water'
 */