I like things that light up. Especially if they're blue. And also necklaces. So, why not combine them?
For this project you will need:
1 resistor (I'm using a 330 ohm resistor, but any value around 100-500 should work with a standard LED)
1 CR2032 battery
small pieces of ultrasuede (or other fabric that doesn't unravel at the edges)
some sort of cord or ribbon
Step 1: Cut the Fabric
Decide what color to use as the base. Fold it in half, and cut a square a bit bigger than your battery. (The fold should be on one side of this square.) Remember that you need room to sew the edges and also thread the cord through.
Next, cut the accent color. You can make it any shape you want, but it needs to be smaller than the square you just cut and big enough to cover the LED leads and the resistor.
Finally, use a big needle to stitch your cord through both layers of fabric from back to front and then front to back. The stitch at the front will hold the pendant closed ensuring that the battery makes a good connection.
Step 2: Prepare the Circuit
Make a small loop in one resistor lead, and wrap the wire around the base of the loop. Cut the extra wire off. (This loop is for sewing conductive thread to.)
Cut the positive LED lead and the other resistor lead fairly short. Solder them together.
Make a loop in the negative LED lead, wrap the wire around the base of the loop, and cut the extra wire off.
Bend the wires such that the loops are flat and the LED Is sticking out. You can also position the resistor relative to the LED to make it fit better under the fabric (this is the accent color). Important: the loop on the resistor needs to be close to the edge of the pendant.
Decide how the fabric shape will be placed on the pendant and where the LED should be. Make a hole in the fabric the right size for the LED to poke through.
Step 3: Wiring Part One
The front of the pendant will connect to the negative side of the battery and the back will connect to the positive side of the battery. This is important! (I tried it the other way around on my first attempt and ended up with a short. Because the edges of the battery are positive, and the thread needs to get from the LED on the front of the pendant around to the back, my negative thread ended up touching the positive edge of the battery.)
Stitch conductive thread through the negative LED loop and through the base fabric. Make sure there's a good amount of thread exposed on the inside of the pendant to make a good connection with the battery.
Pro tip: The thick conductive thread I used doesn't hold knots very well. Put a drop of glue on the knot to stop it from untying.
Next, stitch some thread from right at the edge of the fabric through the loop on the resistor. The stitches should be entirely on the front of the fabric except at the edge so the thread won't contact the negative side of the battery. Don't tie the thread off! Leave a length of thread attached - it will be sewn to the back of the pendant later.
Step 4: Wiring Part Two
Put the LED through the hole in the accent fabric, and sew the fabric in place so that it covers the circuit. I used a contrasting color of thread and a whip stitch, but you can do whatever you want :)
Optional: put a little bit of polyester fiberfill under the accent fabric to pad it so that the resistor doesn't make a bump.
Now, pull the cord tight so that the pendant is folded in half. Take the conductive thread that's attached to the resistor and stitch it across the back of the pendant. I stitched a + to remind me that this is the positive side.
Step 5: Finish the Pendant
Now stitch up the sides of the pendant. Again, you can use any color or stitch that you want. :) However, the seam line should be to the inside of the stitches you made when connecting the conductive thread to the resistor. If you're using a whip stitch like me, the conductive thread will be inside the whip stitches. If you use a straight stitch and leave the edges open, the conductive thread may be visible at the side seam.
Figure out how long you want your necklace, cut the cord off, and tie it in a knot (if you didn't do that already). Or, add a clasp to the ends of the cord.
Finally, insert the battery. In order to get it in, you'll have to pull the cord from inside the pendant to make loops. Remember that the negative side of the battery goes at the front.
And... you're done!
p.s. The only way to turn the pendant off is to take the battery out. If you take the battery out for storage, keep it with the pendant somehow so you have it when you need it.