Cut a red, black, and white wire about 3" long. Strip a tiny bit off the end of each, and carefully solder the wires into the back of the NeoPixel jewel. This can be a bit fiddly, but it really does work best if you solder from the back.
Trim the wires to about 1.5", just long enough to reach the Gemma's pads without a lot of slack. Strip about 1/4" off this end. Solder the red wire to VOUT, the white wire to D1 and the black wire to G.
Twist the jewel around so it's sitting back to back with the Gemma. It makes such a tidy little package. Plug in your battery. If you've already uploaded your code, the NeoPixels should all light up. Success!
If the NeoPixels don't light up, here are a few things to check:
- Did you solder to the correct pads on the Jewel? Be sure you soldered to IN and not OUT with the white wire.
- Make sure your code specifies that the pixels are on pin D1.
- Be sure the on/off switch on the face of the Gemma is turned on.
- Be sure the battery has charge.
If you're happy using the Gemma's onboard on/off switch, you're done! Go make the hat.
If you want an easier way to turn the hat on and off while you're wearing it, adding a tactile switch is really worth the extra effort.
Trim the leads on your tactile on/off switch until they're about 2" long. Cut both ends off the JST extension cable, also to about 2". Put some heat shrink on each wire.
Solder the black wires of the extension cable right back together (only shorter). Solder each end of the red wires to one of the switch leads. You'll end up with short extension cable with a switch.
Plug the battery into the male end and the female end into the Gemma. Now you can turn your lights on and off by feel.