Gerrit sent us a link to his Arduino project that syncs a strand of lights to the beat of the music. He uses Processing to analyze the sound, and an Arduino to control the relay. He plans on upgrading to solid state-relays in the future, along with making an enclosure for safety. Thanks Gerrit!

I used the minim library for processing for beat detection. It takes input from an iPod, detects the beats for it, and then sends commands to the Arduino board to turn on and off a relay switch.

More about Music controlled lights via Arduino

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Arduino Family
Make: Arduino