week10.md

10. E-Textiles and Wearables II

Lookit! My heating pad powered with a 9V battery, transistor controlled by an ATtiny (details below), Loes Bogers, 2019

Soft speaker controlled by ATtiny85, Loes Bogers, 2019

Results

• I made four coils that an be used as speaker coils or as heating pad, and controlled them with an Attiny85, both in a speaker circuit and as a heating pad
• I made some swatches that I dyed with thermochromic pigments

For the week I decided to make a number of coils that I could use both as a speaker and as a heating pad. Even the code turned out to be exactly the same which was really interesting to realise :) Simple principles with 1001 applications, that's beauty right there. I loved going into the bare bones of the physics of electronics this week, I think this is how electronics should be taught to anyone, so we can understand how material properties and laws of physics interact and how you can bend them a little to achieve interesting results and expressions.

##Soft Speakers

Making a jack connector and soldering the amp board

I started of by making a jack connector connected to a mono amp board following the tutorial Liza mentioned. I added some shrink tube to insulate the wires inside the metal cylinder. I soldered the amp board together and turned the volume knob on the board up to max with a tiny screwdriver. The board used is an Adafruit Mono 2.5W Class D audio amplifier and Liza describes how to make this jack connector here.

Jack plug soldered to a Mono Amp, Loes Bogers, 2019

Designing & Fabricating coils

What makes for a good coil? I guess I will be able to answer this question at the end of the week haha. But we received the parameters to play with. I spent most of the week figuring out and puzzling what makes for a good membrane. It seems to be something light that doesn't let air through. So cellophane or cling film was mentioned by Anastasia, but I also got really good results from a fake leather swatch interestingly enough, not so light but pretty airtight.

Variables

• Coil tightness: The tighter the coil, the louder. (It will be since it will have a stronger magnetic field.)
• Material: You can hear noise because the sound waves vibrate off the material. How stiff or thick the material is effects the loudness.
• Magnet size The larger the magnet, the louder the volume. You can combine many small magnets or just get a big one BUT be careful - neodymium magnets are very strong.
• Magnet placement The volume will be louder the closer the magnet is to the center of the coil.

Liza's instructions to design a coil for needlepointing

Draw a coil on your fabric or paper. It can be any shape you like. Thread your needle with one strand of conductive thread. You can run wax over the end to get it through the hole. Tie a knot 5-6 inches from the end. Come up through the center of the piece of fabric. Stitch around the coil, making sure the conductive thread lines do not touch each other. Make sure the extra 5-6 inches of thread does not get sewn into the coil! We need to keep them separate.

Lasercutting and heat'n bond

I decided to also try lasercutting a coil from conductive fabric that I could attach with heat 'n bond, since I hadn't tried that yet. So I designed a simple spiral in rhino that I tweaked a little in illustrator. I forgot to design the leads to the edge of the swatch though, so I had to add pieces at the end and solder them together to ensure a good connection.

• Rhino: Spiral
• Illustrator: offset, add extra lines.

I designed lines of the spiral to be 3mm thick so I could still handle them. Too thin would be crazy. Then I tried to figure out how to work with conductive textile (I missed the first e-textiles week). This tutorial and Bela and Bea's documentation helped a lot!

Preparing the conductive textile by ironing on heat 'n bond, Loes Bogers, 2019

I ironed the heat 'n bond to the conductive fabric before laser cutting (I put a little piece of cotton canvas over it to prevent the plastic melting to the iron. I kept the backing paper during the lasercutting and cut with laser cutter at Speed 100/Power 20. I had to tape it down a few times to keep it from burning. I then carefully ironed the coil to the textile. And finally I added a soldering braid from the back by making a little cut in the center so I could connect to both sides of the coil. A stuck a bit of tape on the back to prevent shorts.

Trying to prevent the coil from going everywhere, Loes Bogers, 2019

I had to cut off a few windings because I couldn't get them on neatly. So it's a relatively small and weak coil. But it works! You have to get close but you can clearly hear the music with a stack of 5-10 magnets.

Lasercutting and needlepointing

I cut the same spiral shape but without the offset. Instead I just cut the line with a dotted pattern that I can follow with a conductive thread. This coil has a lot more windings so I'm pretty hopeful about these.

Troubleshooting the coil

The speaker made a very low sound, which is to be expected, since it has only 7 windings on the coil and I could only make them so tight. Making the coil trace thinner of leaving less offset would have made it impossible to transfer onto textile without shorting the traces somewhere.

What I did do was turn the volume on the mono amp all the way up. Added a few more magnets that I put below the coil instead of on top, giving the membrane (textile) a little more space to vibrate). I also used the multimeter to check the resistance in the coil. I couldn't get a stable reading easily so checked the two connections in my coil: one in the center where i connect a desoldering braid via the back, and one at the edge of the coil on the outside to make the other connection with a crocodile clip. I forgot to design it like that so just ironed on an extra piece, but the connection was less strong.

I soldered these connections to ensure a good flow of the current. Below a video of the technique. I heat the lycra a little by holding the iron just above the fabric, and then for a split second I touch the solder and conductive fabric, enough to flow. Super quick though or the lycra burns.

I checked again with the multimeter, now I could get a stable reading of 17.7 ohm across. Which I will use for the Thermochromic circuit in which this coil will feature as a heating pad. I embroidered the number on for reference.

I had to solder all the coils because threads broke etcetera etcetera. Lots of soldering-on-textiles practice involved this week.

Four coils this week: clockwise from top left: laser cut conductive textile on lycra (17.7 ohm, 8 windings), conductive thread on cotton canvas (16.6 ohm, 19 windings, conductive thread on fake leather (17.2 ohm, 19 windings), crocheted copper wire laced with wool (5.5 ohm), Loes Bogers, 2019

Testing the different coils-as-speaker

1. The hand-threaded black cotton canvas coil swatch - winner of the week! Nice audible sound even when your ear is not on the pad
2. The hand-threaded red fake leather coil swatch - also pretty good!
3. The lasercut lycra coil - very low sound but audible with a cup or by getting very close
4. The crochet copper wire - it basically has not membrane to help make the air particles move! So I tried a weaving technique to integrate a bit of wool to help the coil move air and make audible sounds. I broke a lead in the process, will fix later.

The crochet copper wire coil/heating pad (left), with added wool yarn to act as membrane (right), Loes Bogers, 2019

Controlling a soft speaker with an ATtiny85

The code I wrote for the headpad controlled by Attiny (see below) works unchanged for the speaker as well. The mono-jack connector is connected to a device playing music, and only when pin 3 writes HIGH, the amp gets 5V and the speaker will work.

const int buttonPin = 2;     // the number of the pushbutton pin
const int ledPin =  0;      // the number of the LED pin
const int speakerPin = 3;    // pin 3 connected to 5V of mono amp

int buttonState = 0;         // variable for reading the pushbutton status

void setup() {
  pinMode(ledPin, OUTPUT);
  pinMode(buttonPin, INPUT);
  pinMode(speakerPin, OUTPUT);

}

void loop() {
  buttonState = digitalRead(buttonPin);

  if (buttonState == HIGH) {
    digitalWrite(ledPin, HIGH);
    digitalWrite(speakerPin, HIGH);

  } else {
    digitalWrite(ledPin, LOW);
    digitalWrite(speakerPin, LOW);
  }
}

Code for heatpad OR speaker circuit with ATtiny85, Loes Bogers, 2019