This is a workshop for the 2015/16 WS project course “Artificial Skins and Bones”
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.
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
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.
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
So, let’s make the above connection with crocodile clips
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
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.
Thermochromic ink and heat-able traces
Thermochromic ink is an ink that changes its color (color to transparent) when exposed to certain temperature.
By using stainless steel thread as heat element, you can create electrically controllable color changing surface.
You can find many examples of eTextile actuators here
http://www.kobakant.at/DIY/?cat=28