Half of the work on this project is in concept and planning. Aside from the aforementioned inspiration, I knew that I wanted to utilize the simplest design possible to create the desired effect. This vest will see a lot of activity so I wanted to minimize the failure points and keep components simple.

First, the concept. I knew I wanted to include EL Wire "piping" to accentuate the lines of the vest and that I wanted the stars to twinkle like real stars would. The twinkling effect would have to be random to achieve the perception of real stars, which with the number of stars I was hoping for to be visible at night in the desert, I would need to rely on a design with a lot of pins or one that utilizes multiplexing.

Once I had a concept down, I needed to tackle the brains. For simplicity sake, I considered using 555 timers for the dimming of the LEDs for the twinkling of the stars, but randomizing their timing complicated things. I decided instead to use a microcontroller. My options included the LilyTwinkle, Gemma, LilyPad, Flora, and probably several more. I decided upon the Gemma for a number of reasons including size, familiarity, ease of use, and functionality.

Next I had to figure which LEDs to use. Going back to my edict for the simplest means to achieve effect, I decided against addressable LEDs like Neopixels for the simpler but still "wearable" Sequins. The best way to connect them to the Gemma would be wire, since stainless steel thread was impractical due to their placement and distance. When doing wearables, standard solid core wire isn't ideal, so I went for flexible stranded silicone wire.

To make the whole thing twinkle in a seemingly random pattern with the Gemma, I needed to multiplex to give me more than 3 twinkling options (the Gemma has 3 pins). Now, just using simple multiplexing off of only 3 pins only gives me 6 twinkle options, but I figured with 20 LEDs this was enough. I chose this method above more complicated multiplexing methods to minimize failure points and reduce wiring.

Finally I designed a simple mock-up in 123D Circuits. The diodes are instrumental in making sure that the signal from one pin doesn't "travel backward" throughout the wires to the other pins. It's a little hard to conceptualize from the mock-up, but all multiplexed LEDs need diodes at some point prior to the wires meeting.

I'll spare you the machinations in my brain that made the drawings above possible (more on that in the next step anyway), suffice it to say I determined the placement of each of the 20 LEDs and how each would be distributed. With 20 LEDs that means each combination would be used at least three times. Given that with this design I'm already pushing the limits of the amperage off the 3 GPIO pins, I made sure to balance the drain on the 3 pins as best as I could.