Plan, place, and glue your hardware
Outline where you want your hardware with chalk, put your hardware where you want it, and secure in place with a little bit of hot glue. When lining the LEDs up, make sure that the positives and negatives are in line. Also, consider where your lines are going when placing your LEDs. I put these LEDs 1/2 an inch apart.
Sew in and insulate negative line
Connect all negatives to the negative spot on the board. The sewing is very simple, and just link regular sewing, but if you want a more in-depth example of how to sew with conductive thread, check this out.
* Since you glued your pieces down, you don't have to use the thread to sew the pieces to the fabric, simple loop it through the hole about 5 times, or until you think you've made a good connection
Then use the hot glue gun to insulate the thread by going over it with hot glue, then pressing it down with your finger. Lick your finger (or rub it on ice) before you do this, otherwise the glue sticks to your finger and it is better at burning you.
* Pro tip, use a low temp hot glue gun for a burn free experience (;
Sew in and insulate positive line
Use the same technique for sewing in the positive line as you did with the negative line, but follow the diagram. The diagram only has 4 LEDs per pin (hole in the LilyPad), but the physical version has 8 LEDs per pin.
*If you wanted to, you could do less LEDs per pin, or more, but after 8-10, they start to dim, so test it first!
Insulate as you go, and use a multimeter (or an LED tester I made from a 3V battery, alligator clips soldered to a battery holder) to test that your LEDs are getting the electricity that they need, and are able to light up.
Cover hardware with software (fabric!)
To cover the LEDS, hot glue a strip of fabric over the LEDs. Be careful not cover the LED in glue. Then use fabric scissors to snip little holes above the LED. I prefer to glue all the fabric down, and then snip all the holes. If you would like, you can then sew down the sides of the strip of fabric you just glued down. I like how this finished the edge, but isn't required.
For the inside of the shirt, simply glue a strip of fabric in, covering the hot glue parts. This is for the wearers comfort, and is also optional, but certainly recommended.
Solder and Create a pocket for the battery
If your battery pack did not come with a JST connection, the first half of this step is for you! If it did, skip a head a bit. Simply slip on a bit of heat shrink (or later cover in hot glue) connect the positive side of the battery to the positive side of the JST and the negative to the negative, and shrink the heat shrink (or cover in hot glue), and you're done!
Place the battery where you want it. Cut a small piece of fabric larger than the size of your battery, and glue outline of 3 sides of the square to the shirt. Once is dries, you are able to tuck the battery in to the little pocket you created.
Code it to your liking & done!
Heres the code, all it does is turn the LEDs on. Modify to your liking, and enjoy!