Secret Project - LED Hoodie Sweatshirt

I’ve been working really hard at getting everything to work and now that is has, I’ve gone ahead and shown you what it looks like (on my last post)

But I wanted to show all the parts I missed before I forget. This isn’t a how-to, just more of a “what I did”.

My niece is turning 15 and I thought she needed a more sophisticated/advanced present this year. What better way to show off her uniqueness than with a walking light show? LEDs were a hit recently in New York fashion too, so this fit perfect.

Every step from beginning to operational:

Grab all the materials needed

Here’s a raw list of materials used in this sweatshirt (at this point in time)

  • Sweatshirt - I picked a Star Wars sweatshirt with R2D2 on it because that’s what my niece likes. And it’s cool as hell too. I got it in white with the idea that the bright NeoPixel light will bounce around and diffuse.
  • Adafruit Gemma - It’s a cheap Arduino clone ($7.95) that runs at 8Mhz. It’s based on the Atmel Attiny85 and is really easy to use using the Arduino IDE. (
  • Sheet of 20 NeoPixels - These are “tab” versions of the NeoPixels whose contacts are sewable via a convenient hole. They come on a PCB sheet together but can be snapped off one at a time. I used a needle nose pliers to snap them off and a sharp scissor to clean off the edges. (
  • 3-Ply Stainless Steel Thread - This stuff is strong. Make sure your scissors are sharp. It’s also a little hard to keep tied down because it likes to unravel itself. I used clear nail polish (as suggested by Adafruit’s Wearables Expert, Becky Stern @bekathwia) but looking back, I think i should have tried super glue. I’ll experiment next time. (
  • Needles - A variety pack of assorted needles to sew with. I didn’t have any so I bought some. (
  • 5 volt, 1 Amp Battery with 4400mAh capacity - I bought 2 of these on sale at Amazon for $10 with free shipping. It’s pretty cool. Each NeoPixel draws 60mA at max brightness and with 20 of them, it draws more than can be supplied. I figured this was ok and the light will be slightly dimmer at higher brightnesses. (
  • USB Mini Cable - I had one so I didn’t have to buy one. Mine is a little longer than I need, so if I had a choice I’d buy a shorter one… in white. (

Make a pocket to house the battery pack

I measured out some extra fabric and cut it.


I wrapped the edges around itself and ironed on a seam so it didn’t move so much while sewing.


I sew the open side of the pocket on the fabric side so the opening doesn’t fray so much.


Then I sew the edges to the sweatshirt on top of the existing pocket (on the inside).



And there we have a finished pocket! It’s bigger than the battery, which is cool because now you can put more than just the battery in your secret pocket.


Sew in the NeoPixels

Sounds simple, and for the most part it is, but it took longer than I anticipated. Also be prepared to constantly stick yourself with the needle if you’re not so good at sewing, like I am.


The stitches show through the outside of the hoodie which isn’t ideal but I didn’t have a choice. The fabric here is a single layer fleece and I would have rather used a double layer cotton so I can stitch to the inner layer to avoid showing on the outside.


I sew in the rails first because those were the easiest. Those are the + and - contacts. They are all connected and they go the entire length of the hoodie.


I sew the + on the NeoPixels to the Vout on the Gemma, and the - to the GND.


The next step was to sew the data line.

This one was a little tricky because they’re not all connected by a single thread. Each NeoPixel is connected to the next by 2 contacts. One NeoPixel’s “OUT” is connected to the other’s “IN”. I don’t have any pictures of this step, but basically you’re sewing from one “IN” to the other’s “OUT”, cut the thread, and do it again for the next set. It gets tedious and you just have to make sure you follow the arrows on the PCB. The arrows point to the next pixel in line until you get to the end.

I started getting frustrated a little and decided to connect all the data lines together, across the LED part of the NeoPixel, then cutting the extra thread later after a quick coat of clear nail polish to hold it together. I should have probably took my time and did each one separately to keep it nice and strong.

Load in the “strandtest” sketch on the Gemma

The Adafruit site is indispensable here. Read the über guide. I configured their strandtest sketch for the Gemma using PIN 0 and 20 NeoPixels. (

Next was the test

And it works!



To Alyssa, if you’re reading this, Happy Birthday!

You can follow me on twitter @victor_butler or tumblr at electricsuds.