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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 über-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

  • 3-4 headphone cables. The larger (radially) the cables, the easier they will be to work with, but they might look more clunky. Best to get a wide variety.
  • Headphone jack breakout. Something like this, although it's a little large.
  • For this project, I'm using an Arduino Micro, but any Arduino will do, and an Adafruit neopixel
  • Solder, cables, breadboard--the usual

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?

love the idea. if you wanted to shrink it more, you could use an attiny85/45/25 and the trinkit librarys from adafruit. that would be.super tiny lol
<p>Awesome idea, think I might try this.</p>
<p>Oh and at the bottom of you post you mention this isn't the easiest or most stable way to do it. What about it are you not happy with?</p><p>I'm thinking you could use a small clip to carry the weight of the battery and micro-controller on the back of your collar. Otherwise your pendant would have to be a bit larger to hide the controller and battery. I would like if Adafruit carried a single coin cell battery holder that was a plastic shell so it would be smaller. But perhaps there is another idea for the Sugru I got.</p>
<p>The wire in the headphone cables is *super* hard to solder, and even when soldered, the connection is definitely tenuous. As for the batter holder, you're right that you could probably make yourself one pretty easily with Sugru. I like your idea to use a clip to hold the microcontroller. It feels a bit awkward to have a microcontroller at the back of one's neck when it's heavier than the pendant</p>
<p>I'm thinking a jewelry setting and a translucent stone in front of the LED. Or perhaps wire wrap the LED to the back. Could cover the back of the LED with something so I don't short it out. Sugru comes to mind for more comfort, and in case there is nickel.</p><p>I have some 'slices' of dyed agate that the light would show through. Or a piece of sanded or colored glass.</p><p>Adafruit also has silicone covered wire that is pretty flexible. Could braid together strands also. Although you would have to buy it and it wouldn't then be as thin as your idea. But it comes in colors.</p><p>You have given me a lot of ideas. Thanks</p>
<p>I like your idea of setting it behind a translucent stone or agate! I was thinking of covering it with a thin piece of wood, but never got around to it. I think I have some of that wire you're talking about... magnet wire? It's also really thin and coated in silicone. Could look neat (if I could ever get the silicone off!). </p>
Will it work with an LED instead? haha
<p>Yup definitely! In that case, you only need two wires, power and ground.</p>
<p>Good!! idea... </p><p>I want to make it too....</p>
looks good :-)<br><br>Question: Does AdaFruit kit come with thr copper ring, or was that separate? Also, whats the battery strategy? Is it detachable so you can use necklace w/ or w/o battery?
For this project, I'm using a &nbsp;<a href="http://www.adafruit.com/products/1570" rel="nofollow">mini lipo</a>. The lipo snaps in with a JST connector, so it is removable. The ring does not come with the AdaFruit kit. I guess you can't tell from the picture, but it's actually laser cut wood.
<p>Nice work!</p>
<p>This is a really cool idea! </p>

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