12. Skin Electronics¶

Research & Inspiration¶

This week I wanted to make a skin electronics accessory - something wearable that I knew would be well insulated. I landed on a bracelet.

I was inspired by the concept of thermochromic tattoos from our lecture, as well as the history of mood rings - an accesssory that blew up in the 1970's.

While the colour of a mood ring can kind of correspond to the wearer’s “mood”, the colour of a mood ring is really more indicitive of a change in body temperature - which theortically could correspond to stress level. Mood rings are filled with liquid crystals and when the molecules react to temperature fluctations they reflect different wave lengths of light.

The history of the mood ring is fascinating.

_{Photo Credit: John Olson/Getty Images}

The mood ring was released in 1975 by Josh Reynolds and Maris Ambats and quickly became an overnight sensation - selling $20 million dollars worth in its first year. However, the technology was not pattented, and soon knock-offs flooded the market. The company to file for bankrupcy only two years later.

While the true progenitor of the mood ring is unclear, one of the alleged inventors, Marvin Wernick, claims he invented it years before its commerical release in 1975 after seeing a doctor use a thermochromic temperature measuring tape on a patient. Wernick was interested in biofeedback, i.e. harnessing signals from the body to improve one's health.

This article by History.com goes into further detail about the mood ring's history:

How Mood Rings Became a 1970s Sensation — HISTORY.com

I was also inspired by acrylic and the interesting patterns that can be acheived when it is stacked, having made acrylic cards for my loom last week. So I paired these ideas together.

_{Credit: Corey Moranis}

Concept¶

We didn't have tattoo paper in the lab but we did have two types of premixed thermochromic ink that I'd been hankering to try:

Blue to violet - which activated at 22 degrees Celsius
and Black to Blue - which activated at 25 degrees Celsius.

Ultimately, I tried both, but for my electrical bracelet I opted for the blue to violet. I figured it would be easiest to see the results. At ambient room temperature it was still blue so I knew I only needed to push it two or three degrees.

If it didn't change colour with my skin temperature alone, the heat required to activate it with an electrical circuit wouldn't be much.

In my research, most sources stated that human skin temperature is typically within a range of 24-37 degrees Celsius, except when exposed to more high or low weather conditions.

So I did some research to figure out what material would be best for the inside of the bracelet.

On my first pass, ChatGPT suggested Madeira HC12 or HC 40 conductive thread. It was very concerned with not instructing me to make something dangerous or too powerful.

_{Credit: ChatGPT}

The math indicated I'd be generating only .83mA of current

3V = I x R

3V = I x 36 omhs...

I = V / R

_{Credit: ChatGPT}

... but chatGPT said it was still possible for it to work since I only need to shift the temperature a small amount. I wanted to be optomistic, so I decided to try it.

Design¶

I began the process of designing the bracelet to actually fit on my wrist. I used an existing bangle to know the width needed for my hand to fit through. It was 2.5".

_{Photo Credit: Claire Cavanagh,2025}

I liked the idea of something parametric looking and asymmetrical. I used Rhino to churn out a few ideas.

_{Photo Credit: Claire Cavanagh,2025}

I'd been playing with traces of snake skin in Week 6 for Computational Couture. So I called this my "snake skin bracelet".

_{Snake skin Bracelet: Claire Cavanagh,2025}

The last adjustment was to make sure there were no sharp points to brush against.

_{Photo Credit: Claire Cavanagh,2025}

Next I laser cut them with the Roby Trotec using a:

power of 100
speed of .5
Frequency of 1000HZ

_{Photo Credit: Claire Cavanagh,2025}

And then I painted them with my two types of thermochromic ink to test it out.

_{Photo Credit: Claire Cavanagh,2025}

Because the turning point was so low with the blue ink (again 22 degrees C) I was hoping, in the sunroom, there might be at least some change if I left them for a while to heat up... but nothing happened.

_{Photo Credit: Claire Cavanagh,2025}

So I stared thinking about how I could wire them instead. I came up with this design.

_{Photo Credit: Claire Cavanagh,2025}

The idea was to have a series of stacked acrylic pieces. The circles would be filled with a thermochromic painted tube and a heated wire.

One piece would have a channel for the thread. This thread would interact with the tubes and the battery. The battery would be housed inside one side of the large bottom circles.

_{Photo Credit: Claire Cavanagh,2025}

Laser Trouble...¶

I had a lot of trouble with my files when I imported them to the laser. As a .DFX sometimes my lines would not show up at all or would change shape. You can see this in the battery area in the image below.

_{Photo Credit: Claire Cavanagh,2025}

So I tried changing my DFX files to PDFs. This created different, new illegible lines. So I moved to an .SVG by importing them to Inkscape.

With SVG's the lines were better but the size of my bracelet was thrown off!

_{Photo Credit: Claire Cavanagh,2025}

So with my .SVG I adjusted the battery hole sizes manually in the Ruby Trotec itself. It was close but it still wasn't right ...

20

_{Photo Credit: Claire Cavanagh,2025}

So I went back to .DFX.

AUTOCAD TIP

Something to note about AutoCad - when cutting on lasers and CNC machines etc. sometimes the software has trouble reading splines.

To fix this you need to convert your splines to polylines in AutoCad.

As you see in the top Properties panel the object is labelled "spline"

_{Photo Credit: Claire Cavanagh,2025}

You need to select your spline and type PEDIT in the command bar.
It will ask if you want to turn it into a polyline

_{Photo Credit: Claire Cavanagh,2025}

Click Y for "yes"
Now when you click the line it should say "polyline" in the properties panel where it used to say "spline".

_{Photo Credit: Claire Cavanagh,2025}

Troubleshooting a few other things ...

I also forgot that the channel for my wire needed to be engraved. So I had to add a fill in my file for the Roby Trotect to read it properly. The fill also wasn't showing up in the laser software. Eventually I realized it was because the fill wasn't a true black.

I figured this out by moving my fill away from the black line around it. And I made it true black - consistent with the laser parameters.

_{Photo Credit: Claire Cavanagh,2025}

I consulted the cutting parameters for the laser for a 3/8" acrylic piece, since all my other tests had been 1/4".

_{Photo Credit: Claire Cavanagh,2025}

But in my run, I found these setting didn't totally cut through. Annie told me the laser was a bit older so I needed to make sure I was running 2 passes of cuts.

Finally I got it all working - but in the end I really wasn't happy with the design. It felt too clunky - not something I'd actually wear. I wanted it to be more delicate, so I changed it again.

This was the final design I landed on:

_{Photo Credit: Claire Cavanagh,2025}

Finally I had all my pieces, so I went home. It was time to paint.

Paint and Assembly

I was enjoying the tree-like effect I was getting from smushing the acrylic on the paper. I discovered this effect by accident, so I rolled with it.

_{Photo Credit: Claire Cavanagh,2025}

Now it was time to think about the wiring. I needed to thread it all together with the Madeira HC thread. These are examples of my various parts.

_{Photo Credit: Claire Cavanagh,2025}

Annie suggested instead of many parallel circuits, just have one thread that goes up and down through all the pieces.

It was not easy. Instead of coloured tubes to reinforce the structure, like I'd orignally planned, I was using the small bead-like acrylic centre pieces that otherwise would have been wasted. But with lots of tries and re-tries it worked. I should have stuck with tubes. It would have been more stable and less fiddly.

I also tested the colour change on both bracelets using a hair dryer. The ink did in fact change so I knew it was working. I am holding the piece with my feet with a phone in one hand and a hair dryer in the other ...

_{Photo Credit: Claire Cavanagh,2025}

Left side = non heated, right side = heated

And this was the "snake skin" bracelet under a hair dryer...

_{Photo Credit: Claire Cavanagh,2025}

To double check my circuit, I hooked it up to my week 5 E- textiles project. When I added the thread to the existing circuit, the LED still lit up so I knew the thread worked and the wiring had been a success.

_{Photo Credit: Claire Cavanagh,2025}

I also tested my battery with the multimeter and it was still getting a 3V read.

This image shows how the wire connected to the battery. In this image I also do not have the blue end cap for demonstration purposes, but it sat on the top to obscure the battery and secure the thread.

_{Photo Credit: Claire Cavanagh,2025}

You can't see the full tail of the conductive thread but this was a complete circuit. I maybe saw a very very subtle colour shift but it was hard to tell.

I felt like it wasn't working, but I threaded the outer pieces on top of all the electrical pieces with non conductive thread and secured all the parts to at least see it all assembled.

_{Photo Credit: Claire Cavanagh,2025}

Further research ...¶

In Liza's lecture on wearables in week 9, she suggests tracing paper can be a better substrate than thicker materials - like muslin for example, to see quick dramatic changes.

It's all about getting the right amount of resistance. If it's too low it can cause a short circuit. If it's too high it needs more power.

Maybe the madeira thread wasn't conductive enough for my project. Or maybe the acrylic was just too thick for this small power load.

I wasn't comfortable going above 3V for something so close to my skin - so I was really hoping to get it to work with this size of battery.

Liza had also suggested 500mA to 1amp was needed to heat the paint. So I probably needed something that would produce much more amperage than .83mA

I also think it's important to mention on my second pass with ChatGPT it told me something completely different than what it said at the beginning of the project. It suggest Nichrome was a better choice than conductive thread!

_{Photo Credit: Claire Cavanagh,2025}

Final Thoughts ...¶

So if I were to do this again I would change three things.

I would switch to nichrome wire instead of Madeira HC 12 thread. I would adjust the length of the wire to get me closer to the range of 500mA, and I would wrap it in tubes made out of tracing paper or something thin that gets inserted along the Z axis of the bracelet, instead of using acrylic.

I still have hope on a hot summer's day the bracelet will change colour without any electricity at all.

I also could have made a pendant. When I press hard on the "snake skin " braclet it does change colour as seen in my hairdryer video, although a little more subtly, and I think a pendant close to the chest would have a better effect than the wrist, which is more exposed.

All in all - thermocromic ink is fun to work with. I'd like to push it further when I have more time.

My Autocad Laser files can be found here:

Electric Bracelet

View on Sketchfab

Snake Skin Bracelet

View on Sketchfab