A variation on a pressure point interface using black thermochromic ink on a
ring of fluorescent fabric. Glued the fabric and only supply 1,5 volt power.
thermochromic interface
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Tag Archives: thermochromic ink
Screen printing on fabric
Orange and yellow fabric with failed print
I’ve been very lucky with the thermochromic ink. I got a very big discount from Blanken Controls, two liters for the price of one. That was just as well because my first attempt at screen printing has failed. I went to a workshop to get assistance. And after having obtained a screen with the right mesh size I was confident that things would go right. But there were some difficulties.
I want a big and perfect black square printed on the three colours of fluorescent fabric I’ll be using. Each colour representing a gas. I got the nice looking water repellent fabric from HaVeP. Unfortunately it also repels ink… It was hard to get an even print although I did manage to fill the area but it wasn’t even. The red fabric was most successful, it isn’t water repellent. But even there it was hard to get an even area.
I’ve taken some steps to improve the results. HaVeP have kindly send me orange and red fabric that isn’t water repellent. I’ve spoken to another graphic workshop who’ll help me with the printing of the black area. They seemed confident that this is possible and have all the right equipment.
Screen printing
Matsui on the left, Thermostar on the right
This Monday I worked with Peter, a screen printing expert on my reflective strips. We tested two different inks: the Matsui and the ChromaZone.
I bought the Matsui ink in a very nice turquoise blue to be activated at 27 degrees and a black with an activation temperature of 25 degrees.
The Dutch firm Blanken Controls was very kind and send me a sample set of pigments and binders of the ChromaZone ink. I used the black which activates at 31, it came with two different binders which we tried both.
We started with the Matsui. I tried mixing the blue with black but it didn’t give me the rich dark blue I was hoping for. We soon discovered that the ink wasn’t at all opaque. Adding more pigment and printing several layers helped a little but I want a smooth, opaque plane. But neither the blue nor the black was satisfying.
How different it was with the ChromaZone! The first attempt yielded an almost perfect opaque result. There wasn’t any difference between the textile and screen binder as far as I can tell. Applying two layers creates a deep black but when heating with the conductive fabric is does lose a lot of the reflective qualities so I’ll have to settle for one layer, which is enough. After taking a strip with me it does appear to be brittle when it folds.
Yesterday I’ve been hunting for UV protection varnish. It’s had to find for this material and use but I’ll find something. To be continued.
A technical meeting
There was a small group at the meeting last week. Which was nice in the sense that we could all claim Paul (the engineer) for a longer time. Today we all inventoried our current status and needs with regard to the technical part of our projects.
Thermochromic ink
Testing with conductive yarn and thermochromic ink
First I did tests with the thermochromic ink and conductive yarn: to change colour the voltage should be between 6 and 12 and 0,1 ampere. With 6 volt you can change ink above a straight line of yarn for about 6 cm. For longer stretches stitching of the same length can be placed parallel. When the yarn is stitched tightly it is easier to change the colour. Thickness of yarn will make a difference. I’ll have to do some tests. I can use an adaptor to try out different voltages to work with, the ampere value can stay the same.
Arduino
I worked a little on the Arduino program which will be pretty straight forward. I will have to make sure that the sensors have time to heat up before I read the data. It is unclear how many minutes the sensors may stay on. They may deteriorate quickly when they stay turned on too long.
Sensors
Paul is going to work on the schematic for the three analogue sensors. It’s pretty complicated because they use different voltages. We’ll be using a part that will allow us to completely switch them off. It will give us more control and save power. He’ll also calculate the power needed. Most power will go to heating the yarn or wire for changing the colour pattern. Depending on the length of the wires we’ll need more or less power.
Solar power
It is possible to realize the wearable using solar power. The panels will be used to charge batteries and not to power the wearable real-time. Solar power is too instable because I’ll be needing enough power every two minutes to measure and change the display. But it will run independently on it’s own solar panels which makes me very happy. I’ll probably need 6 C batteries to power the wearable which will make it heavy…
Communication
I’ll probably use Bluetooth to communication for talking from the Arduino to the phone. As I can’t find any documentation on serial/USB communication.
No-tech prototypes
Fruitless attempt at working a LED matrix
After trying some work with a LED matrix I decided that is was time to look for a simple way to experiment with the visualisation of the data.
Sketches
There are three routes to take: the stain, the line or the flock route. I’m looking for ways of translating the parameters: colour, length, applied pressure and pressure duration which I’ve used in the paper models. I made a sketch using the same felt-tips as I used for my earlier prototypes.
I made a flock wrist-top with fake LED’s. Two paper ‘buttons’ can be activated to indicate nice or bad smell.
Fake LED flock on wrist
I tried the lines with coloured elastic bands. That worked very nice. But translating that to fake EL-wire it was just too stiff.
Experiments using coloured lines
Then I read a nice article by Joanna Berzowska from XS Labs in this .x-med-a. publication. That was very inspiring in terms of how to approach a wearable and in term of the visualisation. She talks about ‘non-emissive, multi-pixel, fully addressable textile displays’ which are constructed entirely with soft materials like conductive fabric and yarn and thermochromic inks. Besides being completely integrated into the wearable they also have a nice refresh rate (rather slow e.g. 10 seconds to appear and disappear) that matches the speed of the sensors.
I’ve found this video: Electric Plaid: color-change electronic textile from XS Labs that demos the technique. You heat up the yarn with electricity and that heat activates the thermochromic ink. Using a layer of paint underneath the thermo ink you can create different colours.
This video also gives good insight into the process. And a nice article: http://wearables-chootka.blogspot.com/ and another one: http://clemenswinkler.com/skin/?cat=1 where this technique is used.
Here are some designs I made for this technique.
Two types of visualizations
Two other types of visualizations
I’ve tried with copper wire and a piece of fabric with heat sensitive paint that was lying around but I can’t generate any colour changes with it yet.