E-textiles¶

1. Objective¶

Weekly assignment

Learning outcomes

Research skills: the participant has acquired knowledge through references or replicating existing projects
Design skills: the participant understands how to produce soft circuits and sensors
Fabrication skills: Learn how to embed electronics on fabrics, study soft-hard connections
Process skills: Anyone can go through the workflow, understand it and reproduce it
Final outcome: The assignment is assembled and either complete or tested

Student checklist

Build at least one digital and one analogue soft sensor, using different materials and techniques.
Document the sensor project as well as the readings got using the AnalogRead of Arduino
Integrate the two soft sensors into one or two textile swatches using hard soft connections
Document the circuit and its schematic
Document your swatches / samples
Upload your arduino code as text
Upload a small video of the swatches functioning

2. References, research & inspiration¶

Coming from an electronics background, this was an amusing subject to work with, although the concepts were the same as they've always been; their expression and applications were completely new to me. Hence, I spent a lot of my time exploring https://howtogetwhatyouwant.at/ and understanding the nature of the new material and their implementation

Insert htgwyw image

Liza Stark's work and Jessica’s session on the e-textile continuity tester were a good starting point. In the end, I decided to check out the new material I found: the velostat sheet.

For some reason, my mind was going back to the wearable tech route. The Second skin by Rachel Freire and Connextyle by Jessica Marsch were great implementations of it. As the primary objective of the assignment was to create one digital and one analog sensor, I decided to start with a basic switch and then control some mood lighting using NeoPixels with velostat.

Insert ref photo of second skin and other refs

3. The Plan¶

The plan for the week is to first get to understand the new materials like conductive thread and velostat and then use them with copper tape and any other conductors.

Step 1 - Swatch of Basic switch using a button on the shirt or item of clothing
Step 2 - Pressure sensitive swatch using velostat.
Step 3 - Neopixel wearable patch.

4. The Process¶

Digital Sensor / On-Off Switch¶

connection diagram - button patch - arduino

button swatch

To test the mechanism, I used some leftover pieces of felt from earlier. One piece is used to stitch a cloth button to it. One modification I did was to stick some copper tape on the bottom of the button. In hindsight, using metallic buttons would have been easier. The button and the buttonhole is stitched with conductive thread and then connected to a continuity tester patch or to an arduino searching for digital input.

// this constant won't change:
const int buttonPin = 2;  // the pin that the pushbutton is attached to
const int ledPin = 13;    // the pin that the LED is attached to


// Variables will change:
int buttonPushCounter = 0;  // counter for the number of button presses
int buttonState = 0;        // current state of the button
int lastButtonState = 0;    // previous state of the button


void setup() {
  // initialize the button pin as a input:
  pinMode(buttonPin, INPUT);
  // initialize the LED as an output:
  pinMode(ledPin, OUTPUT);
  // initialize serial communication:
  Serial.begin(9600);
}




void loop() {
  // read the pushbutton input pin:
  buttonState = digitalRead(buttonPin);


  // compare the buttonState to its previous state
  if (buttonState != lastButtonState) {
    // if the state has changed, increment the counter
    if (buttonState == HIGH) {
      // if the current state is HIGH then the button went from off to on:
      buttonPushCounter++;
      Serial.println("on");
      Serial.print("number of button pushes: ");
      Serial.println(buttonPushCounter);
    } else {
      // if the current state is LOW then the button went from on to off:
      Serial.println("off");
    }
    // Delay a little bit to avoid bouncing
    delay(50);
  }
  // save the current state as the last state, for next time through the loop
  lastButtonState = buttonState;




  // turns on the LED every four button pushes by checking the modulo of the
  // button push counter. the modulo function gives you the remainder of the
  // division of two numbers:
  if (buttonPushCounter % 4 == 0) {
    digitalWrite(ledPin, HIGH);
  } else {
    digitalWrite(ledPin, LOW);
  }
}

This code is a preinstalled code is arduino IDE, Under File > Examples > 2. Digital > StateChangeDetection.

For basic on off detection, go to File > Examples > 1. Basics > DigitalReadSerial. This program provides a continuous tracking of the sensor, while the code mentioned above only detects it when it turns ON or OFF (changes state).

This setup can be used as the Main Power Switch for e-textile circuits.

Analog Sensor Using Velostat¶

The Velostat is a pressure sensitive resistive material. The initial idea for using velostat was in fact to make a flex sensor, but soon I found out that the material does not like to really stretch and undergoes plastic deformation. It not only changes its dimensions, but also the resistance permanently. There must be other ways to make it into a flex sensor, a support material, a particular way to cut etc. which I would like to try, but for now, it was time for plan B, to create a pressure sensitive pad.

I sandwiched a thin strip of velostat, between two pieces of felt and stuck the three together using double sided tape. Additionally, I connected velostat to the arduino using some conductive thread. This temporary assembly is to understand the sensitivity of the sensor through the felt. To check the readings I used another example code - File > 1. Basics > AnalogReadSerial. This provides a gradient output between 1 to 1023 which can be used to trigger multiple outputs and gradient outputs in return.