Stretch Sensor

IMG_1297

We tried three different stretch sensors made from resistive fabric. One was only the fabric, one was the knitted fabric, and the last was crocheted fabric. Our tests showed that the fabric on its own can be easily overstretched and does not return to its original length afterwards. The knitted sensor seemed to be working most accurately.

Here you see the knitted sensor applied to the arm:

relaked - knitted
relaxed – knitted
stretched - knitted
stretched – knitted

 

 

 

 

 

 

 

 

 

 

And here is the Lilypad Graph:

knitted graph

the peaks show the arm being relaxed

here is the crocheted sensor:

crocheted relaxed
relaxed – crocheted
stretched -crocheted
stretched -crocheted

 

 

 

 

 

 

 

 

 

 

and its graph:

stretch2

the peaks show the arm being stretched

 

and here is the piece of fabric:

relaxed - single
relaxed – single
stretched - single
stretched – single

 

 

 

 

 

 

 

 

 

 

and the graph:

stretch3

the peaks correspond to the arm being stretched.

 

The crocheted and the simple fabric increase resistance when stretched, whereas the knitted sensor decreases in resistance when being stretched, this is most probably due to the different grain (fadenlauf) in the fabric.

And here is a data table forĀ  different stretch lengths and their Lilypad values:

3cm 5cm 6cm 7cm 10cm 14cm
Knitted 300 570 600 632 520
Crocheted 100 270 325 340 390
Simple 90 140 185

and here are the values in Ohm, so the calculated resistance:

3cm 5cm 6cm 7cm 10cm 14cm
Knitted 4150 122500 14200 16200 10300
Crocheted 1090 3600 4650 5000 6200
Simple 1590 2200

The code used was the Arduino example sketch for Analog read (AnalogReadSerial). It looks like this:

void setup() {
// initialize serial communication at 9600 bits per second:
Serial.begin(9600);
}

// the loop routine runs over and over again forever:
void loop() {
// read the input on analog pin 0:
int sensorValue = analogRead(A0);
// print out the value you read:
Serial.println(sensorValue);
delay(1); // delay in between reads for stability
}

The formula used to turn the numbers gained with the AnalogRead into the resistance is this one:
U = 5 * AnalogNumber/1023;
R = 10000 * U/(5-U);