Start by soldering the NeoPixel ring to the Gemma like so:
- GND → GND
- D0 → Data Input
- Vout → Pwr
You'll want to arrange things so that the top of the Gemma (the side with the LEDs, button, switch, USB, and battery connector) faces out from the disc, while the top of the NeoPixel ring (the side with the LEDs on it) can make contact with the disc. It's helpful to lay things out on the disc first to get a sense of what this looks like:
You'll want a little bit of slack in the wire for positioning, but not too much. I wound up with longer wire than I strictly needed.
Push the wires through the NeoPixel ring from the top (the LED side) and solder them from the bottom. Once in place, they should fit in-between the LEDs on the top. I did the same with the Gemma on my first disc, though it might be safer to run them up from underneath and keep the profile lower.
Next, add the vibration switch like so:
GND → One leg of sensor
D1 → Other leg of sensor
The plan is to tuck the sensor in between the Gemma and the NeoPixel ring and apply hot glue, so don't use too much wire. I wound up using the end of a jumper wire for the stiffer leg of the sensor, and putting a bit of heat shrink around a blob of solder on the other, flimsier leg, but this is probably overcomplicated. The main thing is that you want connections which will hold up as the disc is thrown.