Transfering from template to fabric
The last couple of weeks I’ve been continuously working on the wiring of the displays. The first challenge was to prevent the naked wires touching the conductive fabric underneath. In the morning I had another brain wave: I should isolate the wires instead of the fabric. After talking to the salesman in my favourite electronics shop I went home happy because he showed me some nice silicon tubing and cables that I could use. The cable (with its contents removed) was still rather thick. I couldn’t iron it onto the displays. So I went for finer tubing which I could buy from my shop in a nice set with different sizes inside. This wasn’t enough by far so I ordered another five meter online which was only just enough…
I figured out the different amounts of resistance needed for the different ring diameters. The smallest rings now use very thin wire that has a resistance of 44 Ohm per meter. Rings 2 are a resistance of 10 Ohm. Rings 3, 4, 5 and 6 use the 6,9 Ohm wires that I started out with. The two biggest rings are 2,5 Ohm. This way I can keep the heating times together and not make them too long.
Attaching the wires
First I shaped the wires onto a paper template to determine the lengths needed. Then I isolated them and uncoated the end parts of the ones that had a lacquer coating. Then I embroidered the isolated wires onto ordinary fabric making sure that the connection parts were sticking out at the back. Connecting the resistive wire to the common wire using the terminal tubes was not as easy as I expected. It took quite a lot of squeezing and re-squeezing. I secured the connection parts with yarn to make sure they can take a certain amount of pulling. The whole strip of cables I secured with glue from a glue pistol.
The final bottle neck was the code. I’d been struggling with that for weeks. Mainly because the internal workings of the shift register remained unclear to me. I kept thinking that I needed to shift all the positions to get the outmost ring to light up, working with endless loop variations. I finally asked help from Marius again. He is a real hard- and software wizard. First he corrected my code by mail to make the outmost ring light up. It appeared I didn’t need a loop at all. He just pulled the byte values from the array…
As there were also some hardware problems he was kind enough to come over. He rewrote my software (that took me weeks) in 15 minutes! The code is now completely dynamic (and highly compact) using one big loop for all three displays.
We did some measuring and it appeared that the displays, when heating four or more rings on all three displays, use 10 Ampere which the batteries can’t really deliver. They should but they don’t. Which causes the voltage to drop. So I’m considering using a battery from an electric hand tool, a drill for example.
But for now I’m very happy with what I’ve got. It works and the concept is clear. I’m ready for the photo and video shoot upcoming weekend.
Displays in action
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.
Paul explaines how to measure the power used for the heating of the fabric
I’m having a hard time with my wearable. There are different areas where I’m experiencing problems:
- The thermochromic ink deteriorates very fast. Under influence of UV radiation for which I haven’t been able to find a solution. The amount of electricity it needs to heat up is very much depending on the air temperature. Also the width of the strip of fabric (this has to be equal for the whole length) is crucial for successful colour change. So there’s a lot of testing ahead before this will work well. I have switched from reflective strip to using reflective fabric, I wonder if the performance will improve.
Arduino talking to Nokia
- I’ve been talking to a lot of experts lately but Friday last I got a pretty disturbing e-mail from the RIVM which is a leading Dutch centre of expertise and research, it advises and supports policy-makers and professionals in public health and environmental areas. The gases I’m measuring are a good indication of air quality but the sensors I’m using aren’t sensitive enough. I was happy to find gas sensors in the first place but now they appear to be worthless for my purpose.
- Programming the Bluetooth connection has made some progress. I can now connect with the Arduino board and send and receive bytes. Now I’m at the final stage of sending all of my sensor data in a single string to the Nokia. I also have to find out how to let Python check for incoming serial data continuously. Some sort of event listener.
- I keep having trouble using the internal GPS. It seems to break down after I’ve used it once. Only a restart will make it work again.
- On the bright side I’ve made two dummies for my vest. Saturday I worked together with my tailor on my second dummy, using the actual fabric. This gave me a lot of insight in what I want. Discussing it with AnnaMariaCornelia it became clear that I have to take a radical turn to make my vest look like true work ware. I’m really looking forward to designing my vest and make it look sturdy and cool to wear.
The second dummy which at this stage looks too much like an apron
I wasn’t feeling well but as I had so much to discuss I just had to go to last Saturdays’ workshop. A tailor was coming and Paul would also be there to help me build my shopping list so I could move on. My head was exploding with all the things that I was still uncertain about going through my mind.
I don’t know anything about tailoring or sewing so it was quite a relief to pose all my question to Michael. He had some nice solutions: I’ll make the fastenings asymmetrical so I can preserve the circles and I’ll sew a box to the outside of the vest where my sensors will be. It will give a nice sci-fi feel to it and it’s very practical because the sensors need fresh air anyway. He also cut a pattern so things are getting more concrete and (best of all) he’s going to make the vest :)
Diagram of Arduino architecture (Bluetooth is missing)
My meeting with Paul was also very calming for my brain. He immediately started drawing two nice schemes (called architecture), one for all the Arduino in and out pins and one for the power supply. Why didn’t I think of that… There are enough i/o pins on the Arduino to fit my project. I’m going to work with the Arduino Mini Pro and the BlueSMiRF Gold Bluetooth module.
As for the power we’ll need 7+ volts to power everything. So six AA batteries should suffice. All that’s needed is a set of amplifiers to boost the Ampere value for heating the conductive fabric. I’ll make a test with the largest circle so Paul has an indication and can start working on a design. These amplifiers should be placed as close a possible to the display to prevent energy loss.
Finally we’ll have to organize the sensor tangle and make it easy to plug in and out. I want to separate the display and the sensor part so I can wash the display if that’s needed.
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.
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.
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.
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.
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…
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.