Christmas tunes player (will play other tunes too!)

by Tom de Simone 
8th Dec 2009
Get the circuit design and see it in action at http://meatfinish.wordpress.com/2010/12/12/arduino-christmas-tunes-player/
Inspired by the piezo circuit in the awesome oomlout beginner's guide for their Arduino Experimentation Kit (oomlout.com)
This code is licensed as Creative Commons share-alike (http://creativecommons.org/licenses/by-nc-sa/3.0/)

******** TODO: ********
 - Make toggle button work better
 - Redo note frequencies


Instructions
============
User selects 1 of 4 tunes to play by twisting a potentiometer and seeing a corresponding LED light up.
They then press the microswitch to play the selected tune.

If you just want to edit the melodies that are played, the only changes you need to make are in playTune(). This function works by calling parseTune()
with the following parameters:

char notes[]: a string that represents the notes of the song
int beatLength: how long a beat should be, which has a direct effect on tempo. Smaller value -> quicker; bigger -> slower
boolean loopSong: if true, the song will loop indefinitely (until you press the microswitch)

So in order to modify an existing tune, you basically have to modify the above 3 parameters in the call to parseTune();

Each tune is stored as a string of note names and their corresponding durations. Each token in the string can be represented
by the following regex:
 
  ([cdefgabCDEFGAB]#{0,1}[0-9]{1,2})|(,[0-9]{1,2})|\.
  
In other words, you can have a letter which represents the pitch (2 octaves possible: 'c' up to 'b', then 'C' up to 'B'),
followed by a '#' if it is a sharp (there are no flats in this grammar), and then a number representing its duration,
where 4 is a single beat (crotchet or 1/4 note), 2 is half a beat (quaver or 1/8 note), 8 is two beats (minim or 1/2 note) etc.
The duration can be any number from 1-99, but you'll rarely need longer than 16. If 1 (semiquaver or 1/16 note) really isn't
short enough for you, you could always increase the tempo ;)

To add a rest, use a comma (',') and then a number for the rest duration as above.

Finally, VERY IMPORTANT: EVERY tune you write should have a full stop/period ('.') as the last character in the string.
This tells the Arduino that the tune has finished.
  
For example, the following are all valid tokens:

  c2 // play a 'C' note for a duration of 2 (equivalent to a quaver or 1/8 note)
  a#4 // play an 'A#' note for a duration of 4 (equivalent to a crotchet or 1/4 note)
  A#4 // play an 'A#' note an octave higher for a duration of 4 (equivalent to a crotchet or 1/4 note)
  ,8 // a minim (or 1/2 note) rest
  
The following are NOT valid tokens:

  cBd // each of the 3 notes must be followed by a number representing its duration
  ,#6 // a rest cannot be "sharpened"
  
The following is a valid string representing a melody:

  "e4d4c4d4e4e4e4,4d4d4d4,4e4g4g4,4."
  
The following is NOT a valid string representing a melody:
  
  "e4d4c4d4e4e4e4,d4d4d4,4e4g4g4,4"
                 ^                ^

  because one of the rests is missing a duration value, and there is no full stop/period ('.') at the end of the string.
  
For more examples, look at the 4 melodies that are already written inside playTune() !