University of Illinois researchers explain how they make their conductive ink on this step-by-step tutorial.

(via Boing Boing)

The Resistor JelTone is an edible toy piano created by NYC Resistor members Ranjit Bhatnagar, Astrida Valigorsky, Mimi Hui and myself for the Jello Mold Competition.

As part of our experiments we realized that jello and fruit, which contain a lot of water, are conductive. Embedded in each jello/fruit key is a sterling silver pin (food safe) connected to an Arduino microcontroller underneath the piano’s base. Below the piano’s case is another sterling silver pin. With this setup, the JelTone can either be played with a metal utensil connected to the Arduino, gloves enhanced with conductive thread, or bare hands by touching both a key and the piano’s case.

If you’d like to make your own, you can get the project files, code and instructions from Thingiverse.

Shown below in its fruit and jello versions. Both JelTones were exhibited on June 25th at the 2011 Solid Sound Festival, Mass MoCA and at the Jello Mold Competition (where it was awarded the creativity prize and was both played and eaten by the exhibit visitors).

LED Dragon Kite by Jie Qi

Jie Qi, from MIT’s High-Low Tech group, posted a couple really nice tutorials on how to combine paper, electronics and smart materials to create beautiful objects.

The LED dragon kite: http://hlt.media.mit.edu/?p=1414
SMA origami crane: http://hlt.media.mit.edu/?p=1448

Heat Reactive Materials
Heat reactive materials change state, shape and/or color when exposed to temperatures above ambient. Naturally, many materials change state, eg. melt, at high temperatures. What’s special about some of them that their state, shape and/or color can be altered at relatively low temperatures (provided through hot water, body heat, hair dryers, ambient heaters, ovens, or just a hot summer day), making them easy to use and suitable for DIY projects. In this post I’ll go over polymorph, shape memory polymers and heat-shrink materials.

:: polymorph
:: shape memory polymers
:: heat-shrink (tubing and thread)
:: suppliers

Polymorph, aka polycaprolactone, is a biodegradable polyester with a low melting point of around 60ºC (140ºF). It can be heated with just hot water then molded by hand or cast. Once it cools to room temperature, polymorph becomes a hard, nylon-like plastic, which can be reheated and reshaped any number of times.

“Molding a Handle” tutorial by Inventables

Polymorph is extremely easy to use. Start by filling a container with very hot water. Add some polymorph granules and wait until they turn clear and cluster together. At this point, the polymorph is ready to be shaped. Scoop it out of the hot water bath (with tongs or something like that) and shape it by hand or press it into a mold (see video above). Once molded let the polymorph cool completely - you’ll know it’s ready when it turns back to solid white. You can also melt polymorph with a hair dryer or a heat gun, but avoid using flames (such as a lighter) as this will blacken the material. Powdered pigments such as this one can be used to color polymorph.

ECCEROBOT with polymorph ‘bones’ (images by France Cadet)

Shape Memory Polymers (SMP) can be re-shaped when exposed to heat and will retain this new shape after cooling down. But once exposed again to the change-over temperature the polymer will revert back to its original shape. The physical properties, behavior and change-over temperature vary greatly from SMP to SMP. According to Wikipedia:

SMPs can retain two or sometimes three shapes, and the transition between those is induced by temperature. In addition to temperature change, the shape change of SMPs can also be triggered by an electric or magnetic field, light or solution. As well as polymers in general, SMPs also cover a wide property-range from stable to biodegradable, from soft to hard, and from elastic to rigid, depending on the structural units that constitute the SMP. SMPs include thermoplastic and thermoset (covalently cross-linked) polymeric materials.

Shape memory plastic sheet (image by Inventables)

Shape memory polymers have been finding several industrial applications, such as CRG’s Smart Mandrels:

When heated above the transition temperature, the mandrel becomes elastic and can easily be molded into a desired shape. Once cooled, the material will become rigid and retain the new shape. The mandrel can then be filament wound and the resulting part cured on the mandrel. Heating the mandrel above its transition temperature after the part is cured makes the mandrel elastic again and easily extractable from the part. Because of the mandrel’s shape memory properties, it can be returned to its original tubular shape and reused.

Heat-Shrink Tubing is manufactured from a thermoplastic (such as nylon or polyolefin) which shrinks when exposed to heat. It’s used mostly to insulate wires, connections, joints and terminals in electrical engineering. According to Wikipedia:

According to the exact material used, there are two ways that heat shrink may work. If the material contains many monomers, then when the tubing is heated the monomers polymerise. This increases the density of the material as the monomers become bonded together, therefore taking up less space. Accordingly, the volume of the material shrinks. Heat shrink can also be expansion-based. This process involves producing the tubing as normal, heating it to just above the polymer’s crystalline melting point and mechanically stretching the tubing (often by inflating it with a gas); finally, it is rapidly cooled. Later, when heated, the tubing will relax back to the un-expanded size. The material is often cross-linked through the use of electron beams, peroxides, or moisture. This cross-linking helps to make the tubing maintain its shape, both before and after shrinking. For external use, heat shrink tubing often has a UV stabilizer added.

Heat-shrink tubing

To use simply run the wires, or whatever you wish to enclose/insulate, through the heat-shrink tubing and then apply heat with a heat-gun or lighter, this will cause the tubing to shrink and mold itself around the wires. This shape change is irreversible, i.e. once shrank it’s not possible to revert the tubing back to its original shape.

Heat-Shrink Thread, which is made of polyester, looks and sews just like regular thread but when exposed to heat (176ºC/350ºF) shrinks 10 to 30% (depending on composition). To use, start by stitching normally and then apply heat with a household iron. See Erica’s Craft and Sewing Center for detailed instructions (clicking on the image of the thread will open a PDF with instructions)

Heat-shrink thread and textile perfboard (image by Plug & Wear)

Suppliers
Erica’s Craft and Sewing Center (US): heat-shrink thread
Inventables (US) :: shape memory polymers (sheets and strips), hand moldable plastic (aka polymorph)
Mindsets (UK): polymorph, shape memory polymer
Plug & Wear (Italy): heat-shrink thread
* Polymorph and heat-shrink tubing are common crafts and electronics materials and can be found in a variety of online stores.

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Heat Reactive Materials
Heat reactive materials change state, shape and/or color when exposed to temperatures above ambient. Naturally, many materials change shape, eg. melt, at high temperatures. What’s special about some of them is that their state, shape and/or color can be altered at relatively low temperatures (provided through hot water, body heat, hair dryers, ambient heaters, ovens, or just a hot summer day), making them easy to use and suitable for DIY projects. In this post I’ll go over thermochromic pigments and a few materials they have been incorporated into, namely paint, fabric, film and glass.

Thermochromic Pigments change color when exposed to heat and turn back to their original color when the temperature drops again. According to TEP:

Most thermochromic materials are based on liquid crystal technology. At specific temperatures the liquid crystals re-orientate to produce an apparent change of colour. The liquid crystal material itself is micro-encapsulated - i.e., contained within microscopic spherical capsules typically just 10 microns in diameter. Billions of these capsules are mixed with a suitable base to make thermochromic printing ink or, for example, plastics destined for injection molding.

These pigments can be mixed with an acrylic base or screen printing ink. At room temperature the pigment appears in its original color, but at temperatures between 27° and 30°C (80° to 86°F) this color disappears, eg, if a black pigment is applied to a white surface, the surface turns from black to white at the change-over temperature. When mixed with an acrylic base each pigment will turn instead into the color of the acrylic base or color blender, eg., if a blue pigment is mixed with a yellow acrylic base the resulting color will be green, but at the change-over temperature the blue will disappear and the green will turn into yellow. The ratio of acrylic base to coloring pigment depends entirely on the application and density of color required. For a detailed explanation of the functioning and applications of thermochromic pigments see the TEP Smart Colors info sheet (PDF) and this little demo animation.

Shi Yuan’s thermochromic wallpaper

Temperature-Sensitive Glass results from the application of thermochromic pigments to glass tiles which change color based on ambient, body or water temperature:

The textured glass surface layer protects and highlights the color-change film on the tile. The base color of the tile can match almost any color, and the temperature change point can be fit to the user’s environment and requirements. The dynamic color change begins at the selected activation temperature and shimmers through three phases, one with each 6–10° rise in temperature. Once the temperature peak is passed, the base color returns and remains the same until the temperature drops.
(source: Inventables)

Temperature-sensitive glass tile (image by Inventables)

Thermochromic Film has adhesive on one side and thermochromic ink on the other. The film is normally black but changes to bright green/blue at temperatures between 29.4 and 33°C (84º - 91º F). Due to its low change-over temperatures, touching a piece of thermochromic film for a few seconds will cause the contact area to change color - it can also be used with nichrome or any other heat source.

Thermochromic film (image by Mindsets)

Suppliers
Body Faders (US) :: thermochromic fabric
Inventables (US) :: thermochromic fabric, thermochromic film, temperature-sensitive glass tiles
Mindsets (UK): thermochromic pigments, thermochromic film
Paint with Pearl (US) :: thermochromic pigment powder

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The Open Hardware Summit (OHS) invites submissions for the second annual summit, to be held on September 15, 2011 in New York City. The Open Hardware Summit is a venue to present, discuss, and learn about open hardware of all kinds. The summit examines open hardware and its relation to other issues, such as software, design, business, and law. We are seeking submissions for talks, breakout sessions, and demos from individuals and groups working with open hardware and related areas. Submissions are due by June 24, 2011. Notification of accepted proposals will happen by August 1st.

Since the first Open Hardware Summit in 2010, we have seen the open hardware movement continue to flourish. The Open-Source Hardware Definition was announced, the OSHW logo was selected by a popular vote, an open source oil spill cleaning robot got more than $33,000 in crowd funding, Google adopted the open hardware movement’s biggest success story, Arduino, as its platform and our very own keynote speaker, Limor Fried, was featured on the front page of Wired Magazine – to name a few. Needless to say, open hardware is getting BIG.

Head over to the Open Hardware Summit website for more details on submissions.

Empa’s EAP propelled airship with Dielectric Elastomer (DE) actuators as muscles.

SketchChair, a project by Tiago Rorke and Greg Saul of Diatom, is an “open-source software tool that allows anyone to easily design and build their own digitally fabricated furniture:”

The SketchChair software allows anybody to take part in the process of designing and building their own chairs. The program lets users design chairs using a simple 2d drawing interface, automatically generating the structure of a chair and testing its stability. Users can simulate sitting on a chair with a customizable figure of themselves, in order to test and refine the chair to ensure it will comfortably support them.

The software automatically generates cutting profiles for the chairs, which can then be used to make physical SketchChairs. Using a cnc router, laser cutter or paper cutter, these parts can be cut from any suitable flat sheet material, and then easily assembled by hand.

We have launched SketchChair as a Kickstarter campaign, to try and raise funds to complete the software and release the source code, and to start building an online community of people creating, sharing and editing designs.

photochromic pigments from mindsets

UV reactive materials, which initially have an off-white appearance, change to bright colors when exposed to UV rays (sunlight or a UV lamp) and revert to their original pale color when away from UV light. The basis for these materials are photochromic pigments which can be mixed with an acrylic base and then applied as normal paint. The more dilute the pigment, the less dramatic the color change.

acrylic base to orange photochromic pigment ratio tests ran by a student of the Aix-en-Provence (France) Art School

Besides pigments, which can be used to make color-changing paints, photochromic materials are also available in the shapes of sewing and embroidering thread, plastic goods such as beads and buttons, and nail polish. Naturally it’s also possible to produce photochromic fabrics, but I haven’t been able to find them as raw materials in retail shops.

photochromic thread and beads (indoors and outdoors)

What is it exactly?
According to Wikipedia:

Photochromism does not have a rigorous definition, but is usually used to describe compounds that undergo a reversible photochemical reaction where an absorption band in the visible part of the electromagnetic spectrum changes dramatically in strength or wavelength. In many cases, an absorbance band is present in only one form. The degree of change required for a photochemical reaction to be dubbed “photochromic” is that which appears dramatic by eye, but in essence there is no dividing line between photochromic reactions and other photochemistry.

Suppliers
:: Mindsets (UK): photochromic pigments and sewing thread
:: Solar Active (USA): UV reactive sewing and embroidering thread, plastic goods (beads, buttons, etc.), nail polish

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As the name indicates, electrotextiles are textiles with electrical properties. They’re mostly used for electromagnetic shielding, anti-static and heating purposes, and also for soft circuits: electric circuits or sensors made out of a combination of special fabrics, threads, yarns and electronic components.

:: conductive fabrics
:: conductive threads & yarns
:: special electrotextiles
:: related materials
:: starter kit
:: electrotextiles tutorials by openMaterials
:: learning resources
:: main suppliers

Conductive Fabrics
Fabrics with electrical properties made by blending or coating textiles with copper and/or nickel and/or silver fibers. They’re available in many textures, weaves and combination of materials. Stores such as Plug & Wear, Mindsets and Less EMF sell kits with a sample of each of their conductive fabrics. These samples provide an excellent way to get a hands-on feel for and test the properties of each material in order to find the right one for your project before acquiring it in a larger quantity. There are many types of conductive fabrics and you can find an extensive (though not comprehensive) list on the oM wiki. Here I will only describe some of my favorites.

:: Shieldit Super (iron-on conductive fabric) from Less EMF: a single side conductive fabric made of polyester substrate, nickel and copper. The back side is covered with a non-conductive hot melt adhesive, which activates at 130ºC (266ºF), meaning that it can be ironed on to another fabric, wood, glass or paper. This fabric is a pretty good conductor, easy to apply and thus perfect for making longer connections between components. It can also be cut and sewn like ordinary fabric. 230 g/m², 0.17 mm thick. UL 94V-0 level flame retardant. RoHS Compliant. Gray, 14 inch wide.

:: Electrolycra from Mindsets: looks and feels like ordinary lycra but it’s highly conductive. Its conductivity in one direction depends on how tightly it is stretched - if you pull it the resistance increases and then drops again when stretched even tighter. When cut into a thin strip, the material also warms up when current is passed through it and can thus provide the basis of a heated garment. A 6V battery will cause an appreciable warming effect. Resistivity: 5 ohms per 100mm, increasing to 20 ohms when stretched to 150mm. If the material is turned through 90º and stretched the resistance drops to 2.5 ohms.

:: Knitted Superlight Conductive Fabric from Plug & Wear: an extremely light and transparent conductive fabric, only 190 g per sq.m. It allows air flow and is easy to cut with scissors. It can also be sewn with a standard sewing machine or soldered to. Hand washable. Material: tin copper. Resistivity: 0.1 Ohm per square. Width: 1000 mm (39″), thickness: 1 mm (.039″), max working temperature: 150°C (302°F), weight: 190 g per sq.m.

:: Conductive Aluminum Laminated Fabric from Plug & Wear: a single side conductive (the shiny side) laminate made of aluminum foil and fiberglass reinforced polypropylene tape. It’s easy to cut with scissors and it can be sewn with a standard sewing machine, but it’s very stiff and calling it a fabric is a bit of a stretch. In fact it feels a lot more like a thick aluminum foil which makes it perfect for paper projects. In a recent openMaterials workshop, a group of students cut it into an beautifully intricate shape and used as a touch sensor on the cover of a book. Width: 650 mm (25.5″); thickness: 156 micron; max working temperature: 45°C (113°F); weight: 185 g per sq.m.

:: Velostat: a film made of opaque, volume-conductive, carbon-impregnated polyolefin. The resistivity of velostat decreases when pressured. When sandwiched between two conductive layers, it has a wonderful range for making pressure and bend sensors. Depending on the project, more than one layer of velostat might be necessary, eg. I used 3 layers of velostat to make a pressure sensor that gradually lights up a few strands of EL wire. Thickness: 100 microns; width: 91 cm (36″). Volume resistivity < 500 Ohms/cm. Color: black.

Conductive Threads & Yarns

Conductive threads are made of a combination of either cotton or polyester with alloys of several conductive materials such as silver, copper, tin and nickel. Just as most conductive fabrics, conductive thread is uninsulated making it excellent to connect electronic components to each other or to other electrotextiles. In order to ensure proper connection it should be sewn very tight and with more loops than normally used with regular thread. After some time, conductive thread tends to fray and the stitches to become loose. For this reason I often coat my conductive thread connections with a bit of Wire Glue. Wire glue takes several hours to cure so this coating should only be done after you’re done with all the sewing.

There are several kinds of conductive thread, with significant differences in terms of conductivity/resistivity and fraying, but they are commonly sold in two qualities: 2-ply and 4-ply. The 4-ply contains twice as much metal as the 2-ply, making it more conductive, but it’s also thicker making it harder to thread and sew with. For this reason I usually keep a set of sewing needles with large eyes. The How to Get What You Want and Fashioning Technology websites have some excellent overviews and comparisons of the conductive threads available in the market.

The resistivity of all conductive threads increases drastically with length, making them inappropriate for long connections. For this reason, consider making long connections with ribbons of a good conductive fabric and using the thread only to sew the electronic components to the conductive fabric.

The highly resistive (<1000 Ohm/10cm) silver plated thread offered by Less EMF (cat. #A1226) is good for embroidering fixed or variable resistors.

Conductive yarns are usually made of a combination of polyurethane and inox steel fiber. The resistivity of some yarns increases when the knitted piece is stretched. Again, see How to Get What You Want for great information on conductive yarn.

Special Electrotextiles
:: Textile Perfboard: a fabric base with interlaced rows of thin metal wire.

:: Pressure and Bend Sensitive Fabrics, Tapes and Buttons: made of a layer of insulating knitted or resistive fabric sandwiched between two layers of knitted conductive fabric.

:: Textile Water/Wetness Sensor: detects water by changing its resistance from an open circuit to a few megaohms.

:: EL Wire Tapes: knitted tapes with strands of EL wire weaved into them.

:: Hook and Loop Fastener: similar to velcro but conductive.

Related Materials
:: Wire Glue: even though originally created to replace solder on the connection of electronic components, wire glue is a great material for working with electrotextiles as well. I use it to coat conductive thread knots to prevent them from fraying and also to attach metal snaps to metals that can’t be soldered to.

:: EL Wire: can be basted, woven into or otherwise applied to your soft circuits for illumination.

:: Quantum Tunnelling Composite (QTC): an interesting pressure sensitive material for making textile control pads and keyboards.

:: Metal Sewing Materials: almost all metal sewing supplies, such as snaps and zippers, are conductive and can be used in conjunction with electrotextiles. See oM’s connecting hardware & softwear on soft(er) circuits blog post for some examples.

:: SMD Components: SMD battery holders, LEDs, etc that have flat metal pads are also great for soft circuits. You can solder or wire glue metal snaps or metal rings on these pads to attach them to your circuit.

Starter Kit
I’m often asked what are the first materials one should get to start making soft circuits. Here’s a suggestion for a starter kit:

:: Conductive thread
:: Iron-on conductive fabric or another non-stretch conductive fabric*
:: Stretch conductive fabric*
:: Velostat*
:: Assorted LEDs
:: CR2025 or CR2032 lithium batteries
:: SMD lithium battery holder with flat pads such as this one
:: Non-conductive fabric (felt is my favorite)
:: Sewing supplies: thread, metal snaps, needles with large eyes, needle threader
* Most electrotextiles stores sell conductive fabric sample kits, you can just try one of those instead of buying a larger quantity of the stretch and non-strech conductive fabrics.

Electrotextiles Tutorials by openMaterials
:: Connecting Hardware & Softwear on Soft(er) Circuits
:: Light Up Handshake Glove

Learning Resources
There are many resources for learning how to use electrotextiles. One of the most useful and complete, from a materials and experimentation point of view, is Kobakant’s How to Get What You Want - make sure to check out the sensors and conductive materials sections.

:: Websites w/ Tutorials
Fashioning Technology
How to Get What You Want
Lynne Bruning’s Techniques
Plug & Wear
Plusea
Soft Circuits Saturdays
Sternlab

:: Books w/ Tutorials
Fashion Geek by Diana Eng
Fashionable Technology by Sabine Seymour
Fashioning Technology by Syuzi Pakhchya
Open Softwear by Tony Olsson, David Gaetano, Jonas Odhner, Samson Wiklund
Switch Craft by Alison Lewis

:: Other Interesting Websites
3lectromode
Talk2MyShirt

Main Suppliers
:: Less EMF (USA): conductive fabrics, resistive thread, hook and loop fastener, textile pressure sensitive switches, fabric potentiometer kit

:: Mindsets (formerly MUTR) (UK): conductive fabrics & thread, but make sure to also check out the materials > smart materials section

:: Plug & Wear (Italy): conductive fabrics, textile perfboards, pressure sensitive fabrics, tapes and buttons, textile water/wetness sensor, conductive thread and yarns, EL wire, EL wire tapes

:: Sparkfun (USA): several types of conductive thread

Share your knowledge
If you’d like to contribute content or corrections regarding electrotextiles, please use the comment form below.

>> about the materials 101 series.