Solder four colored wires to your 3W LED. These work differently than NeoPixels -- you have one wire for red, one for green, and one for blue, and a power wire as well. The aluminum pads on this LED can be a little tricky to solder to. I found it easiest to tin the wire heavily, then heat the aluminum pad on the LED and press the tinned wire down until it stays.
Be sure you get these wires connected solidly. We'll seal the LED later, but you don't want wires popping off when you bend them.
If needed, solder the included headers onto your PropMaker Wing. Solder the other end of the wires from the LED to the pads marked R, G, B and + near the center of the board. I soldered these on from underneath the PropMaker Wing, so the wires and delicate connections will be sandwiched between the PropMaker Wing and the Feather when everything is assembled.
Next, stack the PropMaker Wing on top of the Feather M4 Express and solder in place. You can use female headers or just solder the PropMaker's headers directly to the Feather.
We're going to use a couple different varieties of heat shrink to encase our electronics in plastic so they're 100% waterproof and dust-proof.
First up: Adhesive Heat Shrink
If you haven't used this stuff, well, it's great. Adhesive heat shrink already comes with hot-melt glue inside, so when you heat it up to shrink it down, the glue melts and makes a super strong, waterproof connection. This stuff is really useful for playa-proofing your electronics.
Shop for Adhesive Heat Shrink on Amazon\
Next up: Clear 1" Heat Shrink
Heat shrink comes in GIANT size! A clear piece of 1" or 3/4" heat shrink sealed with hot glue at the ends will make a slim, cheap, waterproof enclosure for your electronics.
Once it's sealed, it's not easy to update code or fix loose connections, so be 100% sure everything is working the way you want before sealing. But, it is not too hard to remove the plastic for updates or fixes if needed. 99% alcohol will remove hot glue easily and completely, so if you need to get in there you can, without breaking your setup.
Our waterproof battery case doesn't come with a JST connector, so you'll need to solder one on. This connection will be exposed, so we'll double-heat shrink it to make sure it's bulletproof.
Heat-shrink both wires individually, then add a piece of adhesive heat shrink over the top of both connections.
Upload your code if you haven't already, and plug your battery into the Feather. The 3W LED should come on and shine super bright, running a rainbow animation. Wiggle the wires around and make sure nothing comes loose!
Important Note about Power!!
Do NOT leave the battery pack plugged in to the Feather while you also have a USB cord plugged in. The Feather has onboard charging, so it will try to charge your AA batteries, which could result in battery damage and / or Feather damage.
Slip a piece of 3/4" clear heat shrink over the LED, with all wires neatly coming out one side. Squirt a small amount of hot glue inside each end (you need less than you think) and while the glue is wet, use a heat gun to shrink the heat shrink down. Let it dry and trim the edges if needed.
Once everything is completely encased and cooled, give it another test to make sure it's still working reliably. If you need to bust into this thing to repair a loose wire, or if you want to update the code, 99% alcohol will remove the hot glue. Just cut the heat shrink off then soak in alcohol and the glue will peel right off.
The Feather and PropWing are a little trickier to encase, simply because we don't want the reset button getting pressed accidentally by the tight plastic. I carefully added a little hot glue around the edges of the reset button, making sure not to get any IN the button mechanism. This will make a little shelf the case can rest on, so the feather doesn't get accidentally reset. But the plastic is soft enough that I can still press the button if I push hard, and reset the board.
With the battery plugged in, and when you're 100% sure everything works, slide a piece of 1" heat shrink over the Feather and PropMaker Wing. Squirt a little glue in each end and shrink it down. Trim the ends if needed.
Your setup is now fully waterproof! I threw mine in the pool just to test it, and it's still blindingly bright at noontime in full sun! This will drive our fiber optics really well.
The 3W LED will get hot, but not hot enough to melt the glue. I imagine that you could break this if you really tried, but it would take some doing.
Note: this does make a waterproof light, but the battery case doesn't seem to be officially rated for underwater use, so .. I wouldn't put it in water deeper than a couple feet. "Waterproof" and "submersible" are not really the same thing. A battery case with a rating of IP68 would be certified submersible, but there's no offical rating on this one, so go carefully.