The lullaby machine is a computer controlled xylophone! It plays songs using a computer and an arduino to drive a set of solenoids.
It can also be driven manually using a computer keyboard. In this mode, you can also record your keys and timing to play back automatically later.
The original reason I wanted to build this was to use it to signal events -- different notes or melodies to signal different online events like a new email, tweet, etc.
It's built from a simple toy xylophone and equipped with one solenoid per key. The solenoids are driven by an arduino. Most of the logic is currently handled by a tethered computer.
Here's a video of it playing the opening to Brahm's Lullaby:
The xylophone can be manually controlled by the computer keyboard. The asdf row maps to C, D, E, F, etc. on the xylophone.
Using the manual control, there's a play/record function. You can capture your manual sequence of keys and timing and have the xylophone repeat it back.