Since the thread needs to carry at least 100mA of current to change the ink’s color and the battery is 3.7 volts, we know that the thread will need to have a resistance of 37 Ω (R = V/I).

Using the multimeter to test the voltage and resistance:

the voltage of the battery: 3.6 volts

the resistance in the trace from battery to switch: 13.2 mΩ

the resistance in the trace from switch back to battery: 9.6 mΩ

total resistance: 22.8 mΩ

So…

I = V/R

I = 3.6 V/  22.8 mΩ

I= 157.9 A

(measured current:  119.3 – 133.4 A)

THE PICNIC:

My initial idea for the fabric was to create a system that would change from solid to checkered when turned on.

However, my first attempt to create a circuit was unsuccessful. I didn’t test the resistance through the length of thread before sewing and I quickly realized that the battery wouldn’t be able to power the circuit.

Sketch:

Setting up:

I first sketched some facial expressions that could be represented using threads.

Then I used a paper box to represent the face.

I then sew the facial feature onto the fabric and the box

Here are the results:

cold hot

Thermobot in action

Details

Voltage: 3.7 V

Resistance: 15.9 Ohms

Current (calculated) : 232 mAmps

Current (measured): ~100 mAmps

I used several n-mosfets and a lilypad microcontroller to control varying sections of the circuit programmatically. A mosfet is a transistor that can be used for switching electronic signals- essentially a voltage controlled gate. By sending a small voltage to the gate pin, a larger voltage can be passed through the drain pin. A pulldown resistor is connected between the gate and the source pin to pull the gate low when no input voltage is being supplied.

(Diagram created by Leah Buechley)

I used 4 n-mosfets to control 4 separate sections of thermochromic pigment by connecting the gate pin of each to a  separate digital pin on the lilypad. I then connected a separate 5v power supply to each individual section of the circuit that corresponded with the sections of the thermochromic pigment.

For programing the lilypad, I assigned each pin a number, and then toggled them on and off using a keyboard inputs via the serial monitor. I had to toggle all of the pins from input to output before switching them on and off, otherwise the voltage supplied by the pins would not be high enough to open the gate for the mosfets. Not sure if this was the ideal solution, but it seemed to work. The code for the project is available here: thermo_swatch.zip

For the current, I calculated the resistance of one of the circuits first:
I added up all of the resistances of the sections of conductive thread. I didn’t include the 10k resistor since the current wouldn’t pass through it when the gate was open.

V= IR
5v =  (14.2 ohms +3.3 ohms +  14.8 ohms) * I
I=  5/32.3
I=0.15 Amps

I*4 = 0.6 Amps total

In my second attempt, I improved the construction by using an embroidery hoop and the stainless steel thread from the supply  instead of the bobbin we were supplied. The hoop kept my fabric flat while stitching so it did not end up crumpled like the sunrise v1.0. The steel thread from the supply has has a resistance of ___ as opposed to the small bobbin’s resistance of _____  so the MIT MechE design was able to generate more power.

I did not have a camera when I was working before I painted the design, so there is no picture. I made the design by drawing my design in pencil and sewing along the lines. I had several loops in my design, but I electrically isolated them by making sure the thread was separated by the fabric at each crossing.  After sewing, I painted the whole surface with a mixture of blue and red paint.

When the thread is electrified by the battery, the “MIT MechE” appears in red against a purple backgroud. The “MIT” part comes out clearly, but the “MechE” is a bit too small to be legible. Some areas have a double wide stich and these areas show up significantly brighter.

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Before painting, I measured the resistance at 10 Ohms, but this value changed when the fabric is pulled taunt.

Voltage: 3.7 V

Resistance: 20.9 Ohms (after painting)

Current (measured): 0.19 Amps

Current (expected): 0.17 Amps

For this assignment, I wanted to accentuate the underside of a series of pleats. I began by stitching a zig-zag along the length of each pleat using stainless steel thread for the bobbin. I then secured the pleats with a straight stitch (using non-conductive thread) on either end. In order to bridge between the pleats such that a continuous electrical current can flow from one conductive stitched line to the next, I hand-stitched from the switch to the first pleat, then again from the end of one pleat perpendicularly across to its neighbor and so forth. The resulting circuit zig-zags from one pleat to the next, arriving at the circuit board and then traveling back to the switch via long hand-stitches.

Final piece (this is a second version) with the switch and circuit board stitched in using stainless steel yarn.

The stainless steel conductive thread (used as the bobbin) is stitched in lines along the fold of the pleat.

The conductive thread is hidden within the pleated folds.

The thermochromic ink is applied to the bobbin side of the stitch, the side with the conductive thread.

Sadly, the color changing did not occur has I had an insufficient amount of current running through the piece. Both my calculations as well as the multimeter readings proved that of the 100 mA required to heat the thread to a warm enough degree, I was only able to muster a weak 67 mA. The multimeter measured an even lower 41.7 mA. It’s likely that I used too much conductive thread (my total resistance = 56.7 ohms) with too little voltage. The voltage required to overcome 56.7 ohms of resistance (with 100 mA of current) is 5.67 volts. It’s also highly likely that my circuit may have been shorting due to either messy connections across the threads or too weak a connection.

Calculations:
The resistance I should not exceed (but did!):
V = I * R
3.7 v = 100 mA * R
37 ohms = R

Resistance per trace: (measured using multimeter)
1. 50.2 ohms
2. 6.5 ohms
Total: 56.7 ohms

Current in piece:
V = I * R
3.8 v = I * 56.7 ohms
67 mA = I …. That’s too low! Needs to be at least 100 mA!

Circuit Description:

This project is a proposal for a reactive wearable. A Hug pushes a button to run current through a circuit heating the contour of a heart on the breast pocket of a shirt.

(2) Traces:
Battery to Swtich =12.2 (m)ohms
Switch to Battery = 8.9 (m)ohms
Total Resistance = 21.1 (m)ohms

(1) Battery: 3.69 Volts

Ohms Law: I=V/R = 3.69Volts/21.1 (m)ohms = 174.9 ampere

Actual Current using MicroMeter: 121-148.2 ampere

Here are some photos:

For the Thermo Paint mixture I used blue and cut it with non thermo red to make a purple. When the current (or any heat) activates the pigment, the blue turns clear and reveals a pure red. It turned out to be extremely close to blood which I suppose is relevant for the concept. Here is the video.

Cardio_Coutore

Video link does not seem to be working at the moment.

I think it could make a fun line of hypercolor details for men’s fashion for the future and will work on refining the stitch pattern and insulation of the circuit to isolate the contour I want to change.

Happy Valentines Day.

Completed small swatch of color changing textile activated by 4V battery.

Here’s a short video of the color changing in action.

________________________________________________________________________________________________________________

::process::

materials:
non-conductive fabric (cotton)
conductive stainless steel thread
3.7V lithium polymer battery
switch
thermochromatic ink

I wanted to create a small pattern of beach pebbles in different colors.
The conductive thread stitches would form the white pressure lines of the pebbles, so when the stitches heat up (with the power from 4V battery), the color of immediate adjacent area next to the conductive thread would turn clear.  First I sketched few different pattern options as well as stitching pattern, then I outlined the selected pattern on the cotton fabric. It is now ready to be sewn. I doubled the conductive thread to make sure the pattern had enough resistance.

With the completed pattern, I took it to the Lab to start applying the thermochromatic paint. The main thermochromatic paint color was blue, so I added just a little bit of other colors to the main blue color to achieve various shades. One thing to remember was not to add too much of other colors to the thermochromatic mixture, otherwise the thermochromatic mixture would get diluted. So below is the first layer of paint applied.

Using the multimeter, I measured the resistance and current within the circuit.

resistance: 11 ohms

given the equation V=IR, anticipated current was:
3.7=11I
I=336 mA

measured current was = 137 mA (much less than calculated)

When I turned on the switch, the color change was so subtle that it was almost unnoticeable. I applied another coat of paint, especially near the stitch area. This time I could definitely read the area near the stitch line turning brighter.

The first step is to estimate the amount of current that will go through the circuit. I laid out an estimated amount of conductive thread needed for the pattern and determined its resistance with the multimeter. The estimated resistance was 17 ohms. Using Ohm’s Law, the current is determined to be 218 mA.

To make sure that the circuit has at least 100mA and to account for practical errors, I double threaded the needle to sew the pattern. Below is the finished stitch work.

Here are some measurements and calculations I took of this project:

battery ~ 3.72v

resistance ~ 11 Ω

calculated I ~ 338 mA

measured I ~ 180 mA

It is interesting that the measured current is so much less than the calculated current. I think one reason could be because the contact points (the button and the power switch)  are sewn on too loosely, making it hard for the current to pass through the circuit.

Here is a link to the video of the textile changing color. The color change is quite faint and subtle, but if you look for it, you can see the blue region becoming more red, first in the middle then the sides.

Because I had some extra time, I decided to make this pattern wearable. I took two pieces of the canvas and put a piece of felt in the center to act as an insulator between the body and the color-changing canvas. then, I sewed some buttons to one side and some yarn on the other, and voilà it becomes a sleeve.

This is the final product.

COLOR CHANGING SUCCESS! (needs a bit of tweaking)

voltage – 3.7

resistance – 39 Ω (goal = 37)

current – .094 A (goal = 0.1)

The story can be depicted here:

Construct a color changing textile using: white cotton fabric, thermochromic ink, stainless steel thread, a switch, and a rechargeable Lithium Polymer battery.

I have illustrated the tools and the process I went through in the following drawings and images…

Thermochromic Ink, Fabric Painting medium, and acrylic paints

Thermochromic Paint

stainless steel thread, a switch, rechargeable Lithium Polymer battery

Stitching done with conductive thread

Cups with paints and fabric medium

Paints after mixing..

Painting over the conductive thread stitching..

Experimenting with the mixing of colors and the effects of temperature

After stitching my circuit and painting it, and leaving it to dry, I tried running current through it to see the color change. Turns out… the color was not changing! Yikes! Now came the troubleshooting that had to be done. With Leah’s advice I checked my battery to ensure there was enough volts in it, and there was. She then pointed out to me that the length of my circuit (the length of stitching) was more than likely too long and that I would need to shorten it. After testing that hypothesis using alligator clips to shorten the run of my circuit, it worked! Color changing was happening.

Photo BEFORE current passes through the thread

Photo AFTER current has started passing through thread... note color change

In the end I decided to reduce the length of my circuit by eliminating two columns of colors (green and red) and let me circuit only pass through the blue paint. I also increased the amount of stitching between the switches to reduce resistance.

This work by Vernelle Noel is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.