For some time, I've been contemplating how I can make an intelligent, micro-controller-powered necklace, but I hadn't been able to figure out how to make it small enough to be attractive. Even if a microcontroller is small enough to fit in a necklace pendant, the battery to power it usually isn't. Then, I had a revelation: why not store the microcontroller and battery behind my neck/hair, where nobody can see it, and connect the necklace pendant to the microcontroller via a headphone cable? Modern headphone cables might contain 3 or 4 uber-thin wires, so I would be able to move power, ground, and two data lines from the microcontroller behind my neck to the pendant hanging in front. Here, I'll show you a little bit about my experiments with headphone wires for wearables.
Step 1: Parts
Step 2: Step 1: Break out the wires
Measure your neck to determine how long your wire should be. Then cut the headphone wire in half, such that there is NECK_CIRCUMFERENCE/2 wire connected to the headphone jack, and NECK_CIRCUMFERENCE/2 wire of separate headphone cable. I say this about the headphone jack because we'll be using it to control data messages and power on the wires from the microcontroller. Overestimate NECK_CIRCUMFERENCE so that you have some room in case something goes wrong. Strip the wire and see the inner wires as shown above. You might find some structural fibers (the yellow fuzz shown above), which is annoying and gets in the way. Cut it or burn it. Now, the remaining wires are covered in some fiber as well. In their current state, we cannot contact the conductive wires underneath the fiber, so for each fiber-covered-wire, burn the tips for 10 seconds or so until you see silver. This is tough, fume-y, and requires patience.
Step 3: Step 2: Identify connections
Now you should have one headphone wire with its headphone jack in tact. Plug that jack into the female connector you bought, and using a multimeter, identify which prong on the female jack corresponds to which headphone wire. When you've done this, you're almost done! Except...
Step 4: Step 3: Solder and done!
Here, I've soldered the headphone cables to this Adafruit neopixel. This is tough because the headphone wires are hard to solder, so use lots of flux, have patience, and keep backups! In my particular project, I soldered wires from one cable to power and signal, and one of the wires from the second cable to ground. I then used the headphone jack as a clasp for the necklace, as well as a switch to turn it on (Power goes from the battery through the neopixel, out through the headphone wire and back to the ground connection of the battery).
Step 5: Suggestions?
This method isn't the easiest/nicest/prettiest/most stable. Thoughts/feedback/improvements?