This is remixed from the Circuit Playground Yo-Yo case by the Ruiz Brothers. Print the case at 100% infill in either ABS or PLA. If you don't have a 3d printer, you can use a service like Shapeways and they'll print one for you and send it over.
The case has a loop near the top where you can thread your necklace cord and a small slot at the bottom for your on/off switch.
