If you run at night this is for you. This lights up as it gets darker outside on two independent photocells and no micro controller!

Materials

10 x 3mm red LEDs
12 x 3mm white LEDs
2 x PNP 2N3960 -E13 Transistors
2 x 5mm Photocells
1 x 22k Ω resistor (not pictured)
2 x 47k Ω resistor
Battery holder with a switch that holds two 3V batteries
2 x 3.3V batteries
Ribbon wire
~ 1 yard athletic fabric - anything stretchy and breathable
1 yard 1 inch elastic ( I used fold over elastic; its softer. Found at a craft store)
Piece of balsa wood (if you're using a laster cutter)

Tools

Soldering iron (and solder)
Hot glue gun (and hot glue)
Sewing machine (and thread)
A brain (and food)
Optional, but nice: Laser cutter

Skills

Intermediate sewing/pattern making
Beginner soldering
Laser cutting
Patience

Step 1: Solder in LED and Place in Fabric

Laser cut the pattern of your choice into a piece of balsa wood and your fabric.* Then place the LEDs in the wood, making sure they are all the correct directions (the long leg is positive, the short leg is negative), and solder them together with ribbon wire (black (-), red and purple (+)). Check to make sure your solder joints are good and your LEDs light up as you go. When they are all soldered together, trim the tails to about 2 inches long. You can trim the tails to about 2 inches. Then pop into the fabric and hot glue to secure. Do this for all your red LEDs, and repeat for the process for the white LEDs.

* When putting 'normal' LEDs into fabric, I like to cut the shape I want the LEDs to be in into the fabric and into a piece of balsa wood, that way they will fit. This method makes soldering dramatically easier, it makes the electronics a simple, easier to integrate unit, and you avoid all the problems that come with using 'wearable' LEDs and conductive thread; such as exposed electronics (or bulk coverings), and increased resistance due to the thread. If you do not have access to a laser cutter, you can cut tiny holes in the fabric with scissors, or burn tiny holes with a soldering iron. I like the second, because it make a clean hole, but it smells toxic. Once you make the holes by whichever method you choose, put the LEDs in the holes, and follow the method above.

Step 2: Place and Solder the Transistor and Photo Cell

Solder together the transistor (PNP 3906 - 13E) and the photo cell. With the flat side up, solder one leg of the photocell to the left leg of the transistor, and the other to the middle. Solder the resistor to the middle leg after the photocell.The solder the positive line from the LEDs to the far right leg of the transistor (the one that doesn't have anything else soldered to it yet). Then use black ribbon wire to extend the leg that has the resistor, and red to extend the last, (far left) leg. Then cover with hot glue.

** In the photo, each transistor only has 1 47k Ω resistor. When I put it together the first time, the white took all the energy when both strings of LEDs are on, so I had to put a 22k Ω resistor in.

Step 3: Sew Structure

Cover the LEDs and transistor with a piece of fabric. I hot glued this into place because I didn't want the stitching to show up on the other side.

Fold over the top hem in the shape you want. I chose a slight U in the front and straight across in the back. While yours sewing, keep the wires in the tube that is created by the hem. Important! Make sure you have the wires going to the same side as of the body!

Sew up the sides - I marked mine with calk. When you do this, make sure that the LED lines are lining up. It isn't a huge deal if you don't but it might feel/look wonky.

Sew on the straps. Measure out enough elastic to go from where you want the straps in the front to be to where you want them in the back. Personally, I liked crossed straps because they don't fall off my shoulders, but regular (cami style) will still work. Secure these well. If you are crossing them, make sure they are were you want and then sew a little dash down the center so they don't squirm around too much while you move.

Step 4: Solder and Place Battery Pack

On one side of the top, under the armpit area, should be about 4 wires coming out. Join one black wire to the other, so the two strands become one long strand. Leave about 4 inches of slack before the joint so that wearer is still able to stretch the fabric without breaking the wires. Repeat with the positives (the purple and red). Snip the wires to about 2 feet long past the join.

(Not pictured) The battery pack will come with red and black wires. Solder the black wire (negative) from the top to black wire on the battery case, and the red wire (positive) from the top to the red wire on the battery case.

Cover all 4 joints that were just created in hot glue.

Step 5: More Sewing!

Sew wire in seam: Sew another line next to the seam created when you sewed the front and back together, and feed the thread through. Sew together the straps: This simply makes it so they don't slip around.

Create battery pocket: Sew a bit of fabric on three sides on the inside of the top, that will fit the battery and whatever excess wire is about. I made it so the tube the wire was in extended around the bottom of the pocket so you don't see the wire.

Hem it: Pin wherever you want the hem, and sew it with a zig zag stitch.

And you're done!