Cover photo by Anouk Wipprecht
Check out version 2 of this project: LED tattoos that respond to sound and light sensors.
I was just trying to make cool earrings for Maker Faire New York, but my earlobes are too wussy to handle these! So, the two pieces became a pendant and a tattoo. It's a really simple project, electronically, but makes a big impression.
The conductive fabric tape is the COOLEST thing that went into this project! Here's the snap-apart kit I used; it's similar to many LilyPads offered by Sparkfun:
First, solder the "heart" of your circuit: the CR2032 coin-cell battery holder and its switch. (Trust me, you want a switch: it's way easier to turn off a wearable than to change batteries while you're wearing it.)
How you do this depends on the type of kit you have. I made two units and mounted one with the switch on the front of the battery pack, one on the back. I soldered the switch directly to a positive (+) power pin, and then to the conductive fabric tape.
I went snooping around Tinkersphere and found some amazing conductive, sticky-backed fabric tape. I cut two lengths of this, and stuck them down side-by-side on a cardboard surface. (Something more heat-resistant is ideal, but this worked.)
From there, I made evenly-spaced blobs of solder down the length of one tape, and paired them with corresponding blobs on the other piece of tape.
Then, making sure that they would all end up in the correct orientation – and face forward when attached to the battery pack – I soldered down the LEDs, which I'd already tinned. I love sewable LED modules for this, because they already include resistors, plus they have a flat back and a low profile. You can get these from TinyCircuits as well as Adafruit.
For Version 1, I used wire to suspend the battery pack in the middle of a hoop earring. That wire also connected the circuit to the conductive tape; I simply wrapped the wire around the tape (contacting the non-adhesive side), and made a solder blob around the joint.
In the end, this version was too heavy to wear as an earring in my puny earlobes, so I tied it onto my dress and wore it as a pendant, sticking the tapes onto the dress. Still pretty good!
For Version 2, I deployed a piece of instant jewelry I'd brought on the trip. The two-finger ring became a perfect mount point for the battery pack, using some double-sided sticky tape. The tapes helped hold the ring on my hand, too.
It stuck on and didn't short out in 95-degree weather at Maker Faire New York, and I consider that a success! The battery lasted for hours as we wandered the Faire and the city. I will definitely be using this again.
...In fact, I already have! Someone on reddit requested low-light pics/video, so I stuck it back on with double-sided tape. If your skin is especially sensitive, you might want to stick it to something else first, to weaken the tack. As-is, this worked great.