Workshop: Artificial Skins and Bones

This is a workshop for the 2015/16 WS project course “Artificial Skins and Bones”
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Part 1 – Sensors

Resistive Sensors

Some materials change its electrical resistance as they get manipulated (pressure, stretch, light..). By measuring its change in resistance, it can be used to sense its environment or interaction applied to them.

The analog input pins on microcontroller measures incoming voltage. Therefor we need to connect the resistive sensors as voltage divider to cause change in voltage when its electrical resistance changes.

“In electronics, a voltage divider is a passive linear circuit that produces an output voltage (Vout) that is a fraction of its input voltage (Vin). Voltage division is the result of distributing the input voltage among the components of the divider. A simple example of a voltage divider is two resistors connected in series, with the input voltage applied across the resistor pair and the output voltage emerging from the connection between them.”
(from https://en.wikipedia.org/wiki/Voltage_divider)

The voltage measured (Vout) follows this formula:
Vout=Vin*(Z2/(Z1+Z2))
(from https://www.arduino.cc/en/Tutorial/AnalogInput)

Potentiometer

“A potentiometer, informally a pot, is a three-terminal resistor with a sliding contact that forms an adjustable voltage divider. If only two terminals are used, one end and the wiper, it acts as a variable resistor or rheostat.”
(from http://en.wikipedia.org/wiki/Potentiometer)

Inside of a potentiometer

Now, if we use eeonyx resistive material (carbon enforced non-woven fabric) as resistive material in potentiometer, we can create our own potentiometer.

http://elab-kh-berlin.de/elab/wp-content/uploads/2015/10/eeonyx_pot-1024x690.jpg 1024w, http://elab-kh-berlin.de/elab/wp-content/uploads/2015/10/eeonyx_pot-534x360.jpg 534w" sizes="(max-width: 300px) 100vw, 300px" />
Make the connection as above and upload the Arduino/File/Examples/Basics/AnalogReadSerial sketch to your Arduino. Open the SerialMonitor and see how the sensor input value changes

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Vout=Vin*(R2/(R1+R2))

The eeonyx material is also piezoreistive. It changes its resistance when pressured. Check with Multimeter what are the resistance range of the material when it is pressured.
Now, we can use this material as resistive pressure sensor.

http://elab-kh-berlin.de/elab/wp-content/uploads/2015/10/eeonyx_pot3-1024x656.jpg 1024w, http://elab-kh-berlin.de/elab/wp-content/uploads/2015/10/eeonyx_pot3-562x360.jpg 562w" sizes="(max-width: 300px) 100vw, 300px" />

http://elab-kh-berlin.de/elab/wp-content/uploads/2015/10/eeonyx_pot4-1024x775.jpg 1024w, http://elab-kh-berlin.de/elab/wp-content/uploads/2015/10/eeonyx_pot4-476x360.jpg 476w" sizes="(max-width: 300px) 100vw, 300px" />
In this case, R1 (the sensor) changes its resistance as you manipulate it, but the R2 (the fixed resister) does not. You have to find the right sized resister to make a voltage divider.
Vout=Vin*(R2/(R1+R2))

Contact Switches

Contact Switches (i.e. pushbutton) are digital sensors that gives 2 state (on/off, 5V/0V).

Pull Up Resister
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So, let’s make the above connection with crocodile clips
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Try the example sketch: File/ Examples/ Digital/ Basics/ DigitalReadSerial

Capacitive Sensing

Capacitive sensing is also an interesting technique of sensing.
“capacitive sensing is a technology, based on capacitive coupling, that takes human body capacitance as input. Capacitive sensors detect anything that is conductive or has a dielectric different from that of air.” (from Wikipedia)
The nice thing about the capacitive sensing is that you need only one connection to a sensor (electrode), and any conductive material can be made into a sensor. Also, the user does not have to touch the electrode. It can be covered with another types of materials.

There is a very nice library and tutorial on capacitive sensing with Arudino. Go to the following link and try it >> http://playground.arduino.cc/Main/CapacitiveSensor?from=Main.CapSense

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Part 2 – Materials

copper conductive fabric

Shieldex® Kassel
Company: Statex
Characteristics: Corrosion proof copper-silver plated polyamide ripstop fabric, < 0.03 Ohms/cm2 surface resistivity. Can be cut with laser cutter. You can also apply solder.

silver stretch conductive fabric

Shieldex® Technik-tex P130
Company: Statex
Characteristics: Silver plated knitted fabric, 78% Polyamide + 22% Elastomer plated with 99% pure silver, < 2 Ohms/cm2 surface resistivity. example:
Lasercut Fabric Breakout

Resistive carbon coated fabric

Eeonyx NW-SLPA 20k, MA-3-12
Company: Eeonyx
Characteristics: Resistive material (20k), non woven, can be used to make pressure or bend sensor
example:
Stretchy Traces
example:
Pressure sensor

Resistive carbon coated stretch fabric

Eeonyx
Company: Eeonyx
Characteristics: Resistive material, stretchy in both direction, can be used to make stretch sensor
example:
Fabric Stretch Sensors

Resistive carbon fused plastic
Velostat
Company: 3M
Characteristics: Resistive material, good for making pressure or bend sensor with. Very cheap.

example:
Neoprene Bend Sensor

silver plated conductive thread
Elitex Fadenmaterial Art Nr. 235/34 PA/Ag
company: Imbut GmbH
Characteristic: silver conductive thread (100% polyamid beschichtet mit silber

example:
Neoprene Bend Sensor

copper conductive thread
High Flex 3981
company: Karl Grimm
Characteristic: Very conductive, Solder-able, good for making circuit connections

example:
Machine-Sewing Solderable Traces

stainless steel thread
Bekinox VN 12.3.2.175S.HT
Company: Bekaert
Characteristics: Stainless steel yarn, good for heating use, plied

conductive yarn
Nm10/3 conductive yarn
Company: plug and wear
Characteristics: Nm10/3 conductive yarn, 80% polyester 20% stainless steel, light grey, Surface resistance < 100000ohm

example:
circular knit stretch sensors

conductive wool
Bekinox W12/18
company: Bekaert
Characteristic: Wool fiber mixed with stainless steel fiber, Suitable for felting

example:
felted pressure sensor

Paper and ink

copper tape
Copper Tape 5mm
Characteristic: Adhesive on the back, good to make connections for paper circuits.

example:
paper electronics.

conductive ink (carbon)
Electric Paint – 50 mL + 10 mL
company : Bare Conductive
Characteristic:carbon based conductive ink. It has some resistance, so not very good to make a circuit with. It can be applied on paper or on skin. You can also use silkscreen to print. Water soluble. Good to make contact sensor or capacitive sensor with.

copper ink
CuPro-Cote™ PAINT
company : LessEMF
Characteristic:very conductive. It can be used to make a circuit with. It can be applied on paper or on fabric. Not suitable for screen printing.
example:
Screen printed capacitive sensor on paper

Exercise:
Use Conductive fabric material and make
-resistive sensor
-contact switch
-capacitive sensor

Traces Techniques

Iron-on Fusible
Iron-on Fusible applied on conductive fabric, cut with Laser cutter to make fabric circuit
http://www.kobakant.at/DIY/?p=2672

Iron-on Fusible applied on stretch conductive fabric to make Stretchy Traces
http://www.kobakant.at/DIY/?p=1300

Stitches
Hand stitched circuit connection with conductive thread. Bead is used to isolate the cross section.

Karl-Grimm thread used as Bobbin thread on the sewing machine creating Solderable Traces
http://www.kobakant.at/DIY/?p=3395

Paper circuit
Jie Qi has many nice examples on paper electronics.
http://technolojie.com/category/featured-projects/

Screen printed capacitive sensor on paper
http://etextile-summercamp.org/2014/screen-printing-circuits/

Sensor examples

Pressure sensor
http://www.kobakant.at/DIY/?p=4619

Neoprene Bend Sensor
http://www.kobakant.at/DIY/?p=20

Fabric Stretch Sensors
http://www.kobakant.at/DIY/?p=210

circular knit stretch sensors
http://www.kobakant.at/DIY/?p=2108

felted pressure sensor
http://www.kobakant.at/DIY/?p=3089

Stroke Sensor
http://www.kobakant.at/DIY/?p=792

PomPom sensor
http://www.kobakant.at/DIY/?p=2028

You can find many examples of eTextile sensors here
http://www.kobakant.at/DIY/?cat=26

Actuators

Fabric Speakers
Create a coil with conductive thread, copper wire or conductive fabric onto a fabric, place a magnet in the middle and apply sound signal to the coil. It starts to vibrate the membrane and you can hear the sound playing back.
http://www.kobakant.at/DIY/?p=2936

SMA (shape memory alloy)
SMA are metal compounds capable of converting thermal energy into mechanical energy. They can be mechanically deformed and through a thermal stimulus they display the ability to return to their pre-memorized shape.