9. E-Textiles and Wearables II#
Inspiration#
Wifi Tapestry from R Vijgen on Vimeo.
This week I got inspired by the “WIFI Tapestry” by Richard Vijgen. I wanted to recreate a tapestry made with threads covered by thermochromic ink but he time wasn’t enought.
AtTiny Swatch | Cirquit with mosfet | Shape Memory Alloy flower | Heating element | Thermochromic ink on natual dyed cotton canvas
AtTiny#
Last time we did e-textiles we used an Arduino Uno, these week we used the ATtiny, a tiny microcontroller which is less powerful than the Uno, but it’s more practical for us.
Drivers#
Arduino as programmer#
The ATtiny can’t be connected directly to a computer to upload sketches, but we can use the Arduino Uno as a programmer This just means putting the ATtiny onto a breadboard, and using a few jumper cables to connect it to the Uno. IMMAGINE BREADBOARD
Steps:#
- Program the Arduino to be a programmer
- Connect the Attiny85
- Select board (attiny85 (internal 8MHz)) and port
- Select programmer: Arduino as ISP
- Burn bootloader
- Upload your code
Paper cirquit#
What you need:#
- A piece of thick paper or card
- Copper tape (preferably the kind with conductive adhesive)
- A piece of regular tape
- A MOSFET (ours was an IRF530)
- Soldering iron and solder
- Pliers to bend the legs of the MOSFET
- Optional 9V battery clip if you plan on using a 9V battery as a power supply
How to make it#
- Apply the copper tape in the pattern shown below. Make sure to use a piece of regular tape to insulate the middle and left MOSFET traces from each other.
- Carefully use the pliers to bend the legs of the MOSFET so that they are far enough apart from each other that the copper traces won’t touch, and so that the MOSFET can lie flat on the paper.
- Solder the MOSFET legs and the 9V battery clip to the copper tape.
The mosfet#
Heating takes a LOT of power - current to be specific. Arduino pins cannot provide the power we need to warm a heating element. We can’t draw more than 40mA from a pin. We have to construct a circuit that will let us use a secondary power source. Thanks to transistors, we can do this.
ATtiny swatch#
Actuator 1: Thermochromic ink#
Thermochromic ink is a type of dye that changes color when temperatures increase or decrease. Once they reach a temperature, the inks become colorless.
1st apptempt thermochromic ink application2nd apptempt thermochromic ink application
Thermochromic ink: How it works#
The Thermochromic ink changes is color when the temperature changes.It is possible to activate this change trought the body heat, the room temperature or using the heat generated by electricity by running current through a heating element.
Jessica and I used a thermochromic ink that is black below 27°C and translucent above 27°C.
The resistance#
As said before it is possible to generate heat runningrunning current through a heating element.
What it means? When an electric current passes through a conductor, this will produce a quantity of heat directly proportional to its resistance, to the current that circulates and time. This is called Joul effect.
So we need a conductive material that has just the right amount of resistance. Too high and it won’t change. Too low and you might create a short circuit.
We can use the Ohm’s law to calculate the right amount of current we will draw from a power source depending on its resistance.
Actuator 2: Shape Memory Alloy#
Shape memory alloys are metals that change shape when they are heated to a certain temp. They behave like regular metals when cool and return to preset shape when heated.
There are two types of SMA: - Untrained flexinol will contract by 10% of its length when heat is applied. - Trained flexinol also contracts by 10% but has been “trained” into a shape through a heating process. When heated, it will return to the shape you trained it to.Shape Memory Alloy: How it works#
There are three parameters that influence the success of the project: - Material Substrates. Generally any lighter weight paper or fabric will yield best results. For example, paper, cotton, etc (not polyester!). - Diameter Size. The higher the diameter of the wire, the more power you will need to change its state. - Length. The resistance increases as the length increases.
Useful links#
- Fritzing: for creating conding diagram
- Thermochromic ink
- Kobakant: How to get what you want
- Liza Stark slides
- Emma Pareschi slides
Joul effect#
Love, share, download the code here!#
/*Irene Caretti, 26 nov 2018
* Input(swatch) and Output(led) circuit ATtiny
*/
int led_pin = 1;
int sw_pin = 2;
int sw_value = 0;
void setup() {
// put your setup code here, to run once:
pinMode(led_pin, OUTPUT);
pinMode(sw_pin, INPUT);
Serial.begin(9600);
}
void loop() {
// put your main code here, to run repeatedly:
sw_value = digitalRead(sw_pin);
Serial.println(sw_value);
if(sw_value == LOW){
digitalWrite(led_pin,LOW); //
Serial.println("the switch is pushed, the Led is off");
} else {
digitalWrite(led_pin, HIGH); //sw not pushed(not closed light on)
Serial.println("the switch not is pushed, the Led is on");
}
}
/*Irene Caretti, 26 nov 2018
* Heating element Thermochromic ink. ATtiny
*/
int heater=1;
void setup() {
// put your setup code here, to run once:
pinMode(heater,OUTPUT);
}
void loop() {
// put your main code here, to run repeatedly:
digitalWrite(heater,HIGH);
delay(100);
digitalWrite(heater,HIGH);
delay(100);
}
/*Irene Caretti, 26 nov 2018
* Heating element Shape Memory Alloy. ATtiny
*/
int heater=1;
void setup() {
// put your setup code here, to run once:
pinMode(heater,OUTPUT);
}
void loop() {
// put your main code here, to run repeatedly:
digitalWrite(heater,HIGH);
delay(100);
digitalWrite(heater,HIGH);
delay(100);
}