I’ve been working my ass of this weekend to get the displays working for the video shoot. I had to moderate my goals where the coding is concerned. I couldn’t get it to work the advanced way for three displays. So I chose just to light up an equal number of rings for every display, using the same amount of heating time for every three similar sized rings.
Wiring of the three displays inside the vest
Full of expectation I switched on all the batteries, pressed the demo button and… nothing. Not a thing happened. After some fiddling I got the smallest of one of the displays to heat up. Paul gave me some testing tips so I could test each ring separately. I got the two smallest rings of one display working. No matter what I tried the third or forth ring just wouldn’t light up. As it has become very cramped inside the vest with all the wires I asked my model, Hans, to help me on Sunday with the testing and we would do the video shoot later, when it was fixed.
The cooperation went very well. We tested and re-soldered some of the rings until we had the two smallest rings working for every display. But when it was time for Hans to wear the vest and press the demo button again nothing worked. We went back to just lighting one ring per display and after applying some pressure on the solder points three small rings light up feebly.
By then it was dark and I had to put up a very big lamp to light the room. With the utmost difficulty we got some reasonable shots. But alas the result is very poor.
The innermost ring of the NO2 display lighting up
Conclusion: this is not the way to go with the displays. These are the problems that have become clear:
- The soldered connection between the hard wire and the soft fabric isn’t stable. Often it doesn’t seem to provide enough power
- The fabric doesn’t conduct the power evenly. On some parts I can’t measure any current
- Often I do measure current everywhere but the fabric isn’t heated, *sigh*
- When turning on more rings the current seems to go the ring that is most conductive leaving the other rings with little or no power
- The more rings I try to heat the harder it gets to get even one working
Stepping into bed and removing my electric blanket I got a brain wave. Why not use this technology? I already had tips from Syuzi on this forum but I wanted to test my own set-up first.
After doing some research yesterday I’ve discovered there’re quite some producers of heated clothing. Some of the garments even work on 7 volt batteries. So that must be the way to go. Now I just need an electronics wizard to help me make the right choises.
The last weeks I’ve been very busy building and testing the soft displays which use thermochromic ink.
Aplying the foil and the meager results
First I did some tests with PU foil which might be UV repellent at the TU in Eindhoven. But it reduces the opacity of the ink even more. I also tried working with glue sheets to attach the conductive fabric to the back of the fluorescent fabric. That looks really nice but didn’t work on all the pieces of fabric. On the yellow fabric the two fabrics didn’t glue. With the red fabric I made some construction errors. Firstly I used spay glue to attach the strips to the foil. I shouldn’t have done that. Secondly I made the strips of foil to wide so they stuck to the cardboard on which I was working. I had to use cold glue on both instances. The way to go with this technique is:
- Glue the sheet onto the conductive fabric
- Cut out the strips on a cardboard layer (don’t use too much spay glue)
- Glue the strips to the reflective fabric
The second thing is how to attach the soft fabric to ordinary wires? I wanted to use strands of yarn but they broke even before my first experiment… The yarn deteriorates when is has been heated. I had to heat the glue foils to 150 degrees C. Yarn can’t stand that heat and so every loop (a cold test showed they were a stable connection) I made went up in flames.
So I did some research and ended up at the excellent website ‘KOBAKANT DIY Wearable Technology Documentation’ which devotes an entire chapter to connecting different materials. I discovered that it is possible to solder hard wires to fabric. It’s a nice, solid connection but now I’ve discovered the fabric sometimes doesn’t conduct evenly. I’ll try and repear that with conductive glue I’ve bought. Apparently there’s also a risk of breaking…
Soldered thread and test setup with batteries
I’ve spend a lot of time figuring out the ampere and voltage values needed for the heating of the pieces of conductive fabric. I used two meters, one for ampere and one for voltage while I heated the fabric until it the ink dissolved. Non of the values were the same for any of the strips and the values ranged from 0,38 volt and 2 ampere for the smallest strip to 3,56 volts and 1,82 ampere for the biggest strip. The smaller strips also take far less time to heat up: 10 seconds as opposed to 40 seconds for the biggest strips.
From the above findings my engineer Paul calculated that three D-cell batteries would provide enough power. We decided to go for a constant voltage and adjustable times. This is of course critical because the fabric will burn if the Arduino software hangs. But the conductive fabric seems rather robust.
As for the times and voltages, they are a bit different when I tested with the adaptor. Now all the strips get 3,6 volt and the small ones get a couple of seconds the big ones around 40 seconds.
The ambient temperature also is of great influence on the heating time. The wearable does include a temperature sensor so I will have to read that to calculate heating times.
Finally it will take some programming to have all the strips light up at the same time because the times are so far apart.
I’ve worked together with Mickel on the design of the actual vest. Mickel makes extravagant suits and has a feel for the effect of textile techniques. First we talked through the whole vest and the atmosphere that it should breath. I took all my requisites and net fabric that I ordered online from a firm that makes rucksacks. We made a sketch and decided that the three display colours should reappear as bulky pockets on the sides.
With only two seams Mickel made the vest look a lot more sturdy. We studied some examples of pockets and did some tests. Sewing the actual pocket with extra net pocket and flap proved a lot of work. The result is a bit too overdone to my taste. But unless you make it you can’t tell what will work. Some slight changes will be necessary to achieve the right effect. The actual display is still in its’ infancy where integration in the vest is concerned.
f.l.t.r.: uneven width, too wide, too thin, cutting out paper overlay, right size, result
I have been working on the display elements for all three gasses. I use conductive fabric that will heat up causing the ink to turn transparent. It was quite a research to get the shapes right. The lines have to be the same width everywhere otherwise the current won’t go through the whole strip. They shouldn’t be too wide because there will not be enough resistance to generate heat. Nor should they be too narrow because the fabric will burn. After I found the right width and shape I measured the voltage and ampere values for each strip. They differ quite a lot because each strip varies in size and form. Voltages range from 0,38 to 3,56 volt. Amperes are between 1,82 and 2. Heating times are between 10 and 40 seconds but they are very much depending on the temperature of the environment .
The result should be a nice animation of evenly lit strips of reflective fabric. If it needs some extra stitching remains to be seen. The three displays should be integrated with the same look and feel as the pockets to give it a work wear quality.
Button made out of a zipper
This week I’ve worked on the interface of my air quality vest. I must say I couldn’t decide on how to solve the design of the button and the actual display.
The ‘button’ is my way to interact with the sensors. By indicating if it smells good or bad. The system will measure and send the air quality values when I use the button. But what should the button look like? Thinking really hard I decided I wanted to somehow duplicate the movements you make in real life if it smell good or bad. So opening or squeezing the nostrils. In clothes I suppose the equivalent would be opening or closing a zipper. And that’s how my ‘button’ has turned out.
A logical but rather boring first step
An even bigger challenge is the actual display. How am I going to visualize the sensor data? I took a look at my earlier experiments and actually started build some dummy examples. Some were plain boring, others too far fetched. Then it was easy to see the I’m going to go for the ‘stain’ metaphor. The visual is interesting. I want to line up three circles in different colours. While working I decided to add a scale in silver reflective strip. It’s informative and aesthetical as well.
Dummy example of two 'stains'