Non-emissive displays v2

Transfering from template to fabric

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

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

Displays in action

Breakthrough

I’ve been doing a lot of testing with heating my thermochromic ink with resistive wire. And I’ve had some great results, to my relief.
First I had an almost two hour call with Marius, another electronics genius who helped me with the hardware on one of my other projects: www.collectingsilence.org. He pointed me in the right direction on which materials to buy.

Then I just started cutting up the wires, measuring and heating them. The wires heat up very quickly using much less energy than the former solution. At my electronic shop in town they sold wire at a resistance of 6,9 Ohm per meter. This works great for the medium size rings. The bigger ones need less resistance, the smaller ones more. So I ordered some different values online. This way I can use three D-cell batteries for all rings, still two less then in my previous setup.

wires

six resistive wires applied to interfacing

To be on the safe side I made a dummy display with six rings and checked if I can light the rings at once, which I could! I almost cried when I saw the result, just as I want it to be. Finally.

working_display

six ring test display

tube

small tubes for connections

For the connections I’m going to use a naked terminal tube. That way I don’t need to solder avoiding the risk of breaking or melting of the connection or destroying the displays. You do need a special pair of tongs to apply the tubes.

Because I don’t have the time to re-do the three displays I want to use iron-on nonwoven interfacing to apply the wires to the back of the existing displays. The only problem with this solution is that the conductive fabric interferes with the wires causing overheating… I’ve tried putting a layer of Iron-on Nonwoven interfacing between the wires and fabric. this works but I feel it’s a bit vulnerable. The interfacing is thin and burns quickly. So I’m hoping to find a better solution.

Display hell

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

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

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.

Closure

Michael finishing the vest

Michael finishing the vest

I’m working towards the closure of the demo version. The tailor had finished last week and most of the wiring was done. With all the custom print boards the vest has turned out rather stiff and armour like. Not very comfortable… The boards are a little bigger than expected and the flat cables that connect the boards are also a bit rigid. I’ll have to fold them and perhaps use some glue to make them stay compact and flat.

Me working on the wiring, photo taken by Richard

Me working on the wiring, photo taken by Richard

I had to attach the last few wires connecting the buttons and the nice switch I made for the 7.2 Volt battery pack. I still don’t know what I did wrong but as soon as I switched on this battery pack I started smelling something, I looked at the battery pack and it was melting! Well, some wires were definitely crossed… I decided to call my friend Richard, a programmer and electronic engineer, to help me with the final wiring and the code for driving three displays instead of just one. He was very kind to help me on a Saturday.
We had everything connected and had uploaded the program which worked. Instead of the conductive fabric rings we used the board with LEDs for testing purposes. But alas non of the LEDs would turn on. Wanting to check the serial monitor while running the program we kept the FTDI board for uploading attached to the Arduino whilst also connecting the 6 AA batteries. Again a bad smell and smoke. I’d fried my FTDI board. But I only discovered that later when I tried to upload the improved software for three displays. So I had to order a new one which again held up my progress for two days. The gentleman from the shop said I’d also ruined my Arduino but that turned out not to be the case. I took the opportunity to improve the wiring and make all the pins pluggable.

Now I’ve got everything set up right. I’ve adjusted my code to make the status LED blink every time bytes are send. The software works but at some point there’s a problem with the hardware. I’ll be paying Paul a final visit tomorrow to sort this out. Then I can work on the code again and do a simple video on Saturday.

Test set-up with Arduino Mini and LED boards

Test set-up with Arduino Mini and LED boards

I made some recordings earlier this week but it is just too cold to film. The batteries die very fast. Another thing I’ve discovered is that it’s very hard/impossible to heat up the bigger rings when the temperature is below say 15 degrees. I’ll have to postpone the recordings until spring comes.

Death by deadline?

I’m on the train to Den Bosch to meet my tailor and finish the fabric side of the vest. At least, I hope so because the deadline is fixed. This weekend, weather permitting, I’ll be shooting the video. The demo version of the vest must be working then.

The last couple of weeks I’ve been working on the displays. Trying to figure out why some of the rings wouldn’t light up properly. I’ve discovered that it’s a power issue. The engineer now has another theory: by forcing the power to make a circle the whole ring will light up. I’ll be picking up the new print boards he has etched and the displays and I will have to restart testing the times and power needed. Also I’ll have to work on the rings, cutting them in two and soldering at new points.

Working on the code with Pauls custom made print boards

Working on the code with Pauls custom made print boards

In the mean time I’ll have to finish the software driving the displays. Its’ function is to display a fake low and high pollution for all three gasses using random numbers in every occasion after the wearer pushes a hidden button. Putting it down in one line of text it looks so simple but I’ve been working on it for a week. Trying to grasp the concept of shift registers and working  with a row of LEDs as stand-in for the displays. I’ve got the random low and high working for one gas. I’m rather proud of my solution for bridging the difference in times between the small and the big rings.

if (millis() – previous_millis >= co_times_array[l]-co_times_array[l-1] ){
   Serial.println(“array time “);
   Serial.println(co_times_array[l]-co_times_array[l-1]);
   // update l
   l–;
   // turn on next LED
   data += data_array[l]; // increment the bytes
   my_shiftout(data);
   // reset
   previous_millis = millis();
}

With this code the outer most rings, with the longest heating time, get power first. The program counts backwards so that in the end all rings are lit up and are switched of simultaneously. The final step is driving all three displays simultaneously, each with their own random amount of rings and timing. I’m working on that at the moment. All times should be corrected depending on the temperature. I’ll probably work on that after the video shoot.

I’m on my way back from Den Bosch. Michael, my tailor, worked very hard all day. We’re nearly finished. It’s looking very nice, although a bit big for me. Right now the decorations are very prominent, pushing the displays to the background a bit. I’m very curious to see how this balance will be once the displays work.

Putting together the vest in Michaels shop

Putting together the vest in Michaels shop

But it’s just so good to see it coming together. Thursday we’ll be finishing the sewing and put the wiring together. Some tests will be necessary too. Then the finishing touches on Friday and then the video in the weekend. I keep my fingers crossed for the weather…