Wednesday, December 7, 2011

Star Wars Christmas Tree...Now with Sound

A few days ago I posted a set of Christmas tree lights that flashes to the Star Wars theme song.  I initially did not include a sound output intentionally because the tree sits in our dining room and it'd be annoying to have a song playing whenever we had the tree lit.  I decided later that as long as I could turn the sound off, it'd be a fun addition to the project, so I added a small piezo buzzer between pins 8 & 9 of the MSP430 and made the software changes necessary to output the song on the buzzer as well as on the lights.  I soldered a couple female headers onto my protoboard so that I can plug the buzzer in (to have sound) or take it out (for lights only).

In order to add the sound, I had to go back to the music and re-transcribe it with the actual note values (I ignored flats/sharps before because you couldn't really distinguish them on the lights...but it matters more with the sound).  I looked up the frequencies of those notes here.  The notes in the song range in frequency from ~294 Hz to 880 Hz.  I tried to keep the structure of my code as similar to the first version as possible, so the audio PWM is handled in software in the interrupt routine that fires when Timer A reaches the end of its period for the LED PWM.  I bumped up the DCO frequency from 1Mhz to 8Mhz to provide finer resolution for the musical notes, but the rest of the changes are pretty minor.  An updated version of the source code is available at

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