Still a ways to go in unpacking at our new place (and building our light-up costumes) but I found enough time for a small arduino project (and time to blog about it 
).
Our baby is really turning on to his mobile but we did not like the music that the old turning mechanism made nor did we like turning the knob to reload the spinning every 40 seconds.
Arduino+Servo+8.4V battery pack = indefinately turning mobile with no annoying music. Used the Arduino servo "Sweep" library code, modifying it to make the servo turn farther and slower.
Of course twist ties, zip ties, and paper clips do not make safe building materials (not to mention pulling up on the plastic servo arm). Hopefully it stays up until I can find the rest of my tools.
