Choose a coat that is light in color with a fabric that's light-permeable. I scoured funky thrift stores for white or off-white coats, and found a furry vest for $35 that was almost ideal: warm, with fur trim, but made of a material that diffuses the light fairly well without blocking it too much. While you're shopping, use your phone's flashlight to test how much light shines through a fabric.
Ski jackets and other windbreaker jackets tend to be light-blocking as well, with a tight fabric weave. White fun fur is a great choice, but real fur has a leather backing and will block the light entirely.
Check out this guide on diffusion to see how different fabrics pass light through.
It's helpful if your coat has big pockets where you can put batteries and controllers, but these are fairly easy to add if yours doesn't have them. Even on a coat with pockets, you may want to add inside pockets for the batteries so you still have room for your hands and your stuff in the outside pockets.
I added a fabric pocket on the inside of each side of the vest, since it didn't come with pockets. One will contain the battery and microcontroller, and the other can be used for my stuff.
Open up the lining at the bottom with a thread ripper and hand-sew the pocket through the lining layer only, leaving the lining loose from the main jacket.
Add some velcro or a button or other closure to the top of the pocket or your stuff will fall out and get lost, especially if your lining is silky and slippery (ask me how I know).
LED Layout & Density
In this guide I'll show two different methods for lighting this coat:
1. Fur Trim Border Lights
This is an easy build that doesn't require LED mapping or fancy sewing tricks. It looks great with the standard WLED setup. I used higher density 15mm pitch lights for a beautifully smooth animation, and ended up with around 250 lights to make it all the way around the coat.
2. Light Matrix Panels
This method uses three custom-built light panels sewn inside the body of the coat so the whole thing lights up in a grid. I used lower-density lights with 50mm spacing for the panels. My total number of lights in this strand was 154.
The build is a bit more complicated, but gives us some really cool software options. I used the LED Mapping functionality in WLED to turn the whole coat into a matrix, and now I can show low-resolution animated images on the coat. This really makes the coat next-level -- lights that are mapped can create truly jaw-dropping effects.
Check out this guide for a primer on mapping with WLED. This map won't be a rectangle, so it'll get a bit more complicated and require some mathematical thinking, but the end result is out of this world.
LED Strip Limits: Battery Power & Processing Power
When planning your layout and choosing your lights, take into account the total number of LEDs in your strip. The documentation for WLED recommends keeping each strip to around 500 LEDs. I've had it work with up to 650 in one strip, but it doesn't seem to be as reliable and some of the more complex animations might hang the microcontroller.
You can run up to 3 strips at once on 3 different microcontroller pins, so if you need more than 500 LEDs it's possible to do, but it makes the whole project a lot more complicated.
Battery life is also a consideration. I don't want to carry around a giant battery all night just so my coat stays lit. With 150-200 lights, my coat will run all night with a palm-sized USB battery, as long as I keep the brightness pretty low.
Battery life is really hard to predict, so the best way to figure out the life of your coat is to test it out. Get two batteries, so you have a spare when the first one dies.
Check out this guide on Sipping Power with NeoPixels to learn more about how these LEDs draw power.
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