To make the stars in the background of the Nyan Cat video, I made two long strips of LEDs. The strips consist of six nodes of 5 LED's each, arranged in a star pattern. The six nodes are split in half, and connected with the two-transistor LED alternating circuit in the center.
Here's one of the strips:
Recreating the exact star pattern seen in the Nyan Cat video would have taken 13 LEDs per star, so I simplified it to use only 5. The centers and outsides of the stars are connected to opposite outputs of the LED controlling circuit so that they alternate.
The stars are set up so that consecutive stars around the circumference of the hat have alternate lighting patters - when the inside of one star is lit, the outsides of its neighbors are lit.
Holes for the LEDs were melted through the hat with a soldering iron.
All the wires from the top of the hat (motor, half of the LEDs, battery, audio amplifier power, and audio signal) were routed down the center support, and into the base. They each got their own quick disconnect headers, so that the hat can be taken apart. All the power connections were wired through a toggle switch in the side of the hat.
An old iPod nano, donated by a hallmate, was restored, loaded up with the Nyan Cat song, and set to infinitely repeat. It was fixed to the polycarbonate panel with double sided tape, with it's pause/play button accessible through a hole in the plate.
I wasn't able to scrounge an iPod cable anywhere, so I got a super cheap car charger from the 7-eleven, removed all the casing, and wired it to the hat's battery pack.
Here's the shiny toggle switch. You can see the volume knob for the amplifier off to the right of the hat.
To let sound from the speaker escape better, I made some vents in the top of the hat:
One step I completely forgot to document was the making of the rainbow and the actual cat image. The pieces were scaled from a Nyan Cat GIF, and then printed on the single Athena Cluster color printer on campus. After cutting out the pieces, I realized that I was about an inch short of rainbow. Upon returning to the color printer, I found that in the two hours between my visits, someone had managed to break it. To get it to print, I had another person help me to hold the printer's door closed, so that the switch that tells the printer that the door was open was kept depressed. Anyway, once I printed and cut out all the parts, I laminated them with packing tape.
Here's a final picture: