Knitting Wire Swatches, Yarn Burn Tests

I'm developing a method to machine knit and solder copper wire, resulting in a flexible and conductive textile. Here are some of my test swatches, all knitted on my Brother 940 knitting machine in my new studio space. The swatches are knitted with 3 strands of 34 AWG wire, held together as a single strand.

In order to mix non-conductive fibers with the wire, I've conducted heat tests on traditional yarns like acrylic, wool, silk, and cotton. I'm interested in finding textiles that can withstand the heat of a soldering iron for the 2-3 seconds necessary to make a solid joint. So far, silk and cotton are the clear winners (and now I have a great excuse to buy luxury yarn!).

Security Blanket

I'm showing work in the "Concealed Carry" show at Experimental Station this month.
The show is a response to the new Firearm Conceal Carry law that went into effect January 1.

My work, "Security Blanket", features a knitted image of a gun, embedded with conductive fibers. Touching the trigger "triggers" a (very loud) audio recording of a gun shot. The piece uses capacitive sensing with an Arduino, and I'm excited to be working with this technology, as my students have expressed interest in it, and I plan to introduce a unit in my class on it soon.

The show opening is tonight from 5-8pm. Experimental Station is located at 6100 S. Blackstone Ave, at the edge of the Univ of Chicago campus.
The exhibit will be accompanied by two public conversations on the new law, led by former Chicago Public Radio host Steve Edwards.


Embedded Speakers



I've been working on a design for simple, efficient speakers that can easily be embedded in textiles. Pictured are two of my working prototypes. The one above is knitted, and uses hand-made paper. The one below is a no-frills version that I'll use to illustrate the design concept here.


[ETA 6/4/14  Here is a video of several speakers in action, taken at a speaker-making workshop I led in March.]


This speaker consists of four pieces of magnet wire, glued between two pieces of paper, positioned precisely over a magnet from a hard drive. The 4 pieces of wire are soldered together at both ends so that they carry audio signal from a small amplifier in parallel. The wires are placed just over the mid-section of the magnet. 

This creates an effective speaker because hard drive magnets are dipolar. The broad face of the magnet has both a north and south pole. (Most bar magnets have just one pole per side, and aren't as effective for a flat speaker design.) Additionally, hard drive magnets are extremely strong.

When the wire is placed directly over the boundary between the magnet's two poles (i.e. the red line on the paper rests on the red line on the magnet), it produces a clearly audible speaker.

How and Why It Works

Electric current running through a copper wire produces an electromagnetic field. If this wire is placed in a magnetic field, it experiences physical force.

The directions of the current, the magnetic field, and the physical force are all perpendicular to each other. A good way to remember this is Fleming’s left-hand rule, which uses your left hand as a mnemonic.

image: Jfmelero

The thumb, forefinger, and middle finger are held perpendicular to each other, forming an x, y, and z axis. The first finger is the magnetic field (B), flowing from north (knuckles) to south (the fingertip). The middle finger is the electric current (I) traveling from positive (the knuckles) to negative (the fingertip). The thumb is the physical force (F), the direction the wire moves.

You can see this principle at work in a conventional speaker:

image: Tony DiMauro

The coil of wire (“voice coil”) fits into a circular slot, the sides of which are a magnet.

The middle piece is the north pole, and the outer ring is the south. So the magnetic fields run perpendicular through the coil, with the result that it pushes out, in the direction of the cone. Very efficient!

Flattening the Speaker

A coil is great for speakers, but not particularly flat, as it sticks out perpendicular to the resonator.

So I started with a straight length of wire, glued between two pieces of paper. I centered it between the two very powerful poles on the face of the hard drive magnet. I attached a resonator, the paper, so the wire vibrates the resonator, which vibrates the air much better than a piece of wire. The result is an audible speaker. (The wire-between-two-magnetic-poles will look familiar to those who know the work of sound artist Alvin Lucier.)

However, one piece of wire doesn’t move the paper very much. To increase the volume, I attached several pieces of wire, glued parallel to each other across the paper. I also sent the current running through the wires in parallel (this is very important for increasing volume). Now all the wires vibrate the paper in sync.

My development of this design is on-going, and I am currently refining my knitting machine fabrication techniques. Stay tuned for more documentation.

References:

Hannah Perner-Wilson's Kobakant - resource for e-textiles

Karla Spiluttini and Piem Wirtz at V.2 - a previous knitted-speaker project

Jess Rowland -  foil-and-paper speakers using parallel wiring

Dr. Dominique Cheenne - my Columbia College colleague who suggested I look at planar speakers as an alternative model for embedded speakers

LaFolia Loudspeaker Project - a site for diy planar speakers

Magnepan - manufacturers of the first planar speaker, Magneplanar, invented in 1969 by Jim Winey

Orlando Visit: FamiLab

I'm in Orlando for the holidays, so Saturday I decided to check out the local makerspace, FamiLab. Met some great makers who showed me the space and some awesome projects. Also learned that FamiLab stands for Four A.M. Lab, not Family-Lab. Big difference!

David "Pocky" Sikes has an RFID chip implanted in each hand. He's wired an Arduino into his motorcycle, so it turns on with a swipe of his hand. His front door knows the difference between his left hand and right hand, so it locks or unlocks depending on whether he's coming or going.

Craft/Work Show and my first Instructables


My work has been accepted to the Craft/Work show, to open at Beauty & Brawn Gallery in April, 2014.  They're interested in my knitted speakers, a project I hope to document here soon. I'm looking forward to working with the Craft/Work artists, and connecting with a community that embraces textiles.  I work in a department of audio engineers and I make a lot of work at the hackerspace Pumping Station: One. They're both great places with strong "engineering" cultures.  They're also both over 80% male. So when I started experimenting with knitting machines in 2012, seeking ways to knit e-textiles, I thought it'd be a great way to connect to a historically female community. However, when I started giving knitting machine workshops at PS:1, I was a little surprised that most of the people who signed up were guys. (In hindsight, it makes sense, given the membership demographics.)

The Clamshell Stompbox: Adding Code

Playing around with the clamshell stompbox, I used two sketches included in the Arduino examples to turn it into a functioning switch.

To make a momentary push-button switch, I used the sketch, “IfStatementConditional”, found in the “Control” examples.  

This sketch was meant for a potentiometer, so I treated the clamshell stompbox as one half of the potentiometer, and used a fixed resistor for the other half.

The Clamshell Stompbox: Part 1

This is a DIY variable resistor I designed as an interface for live performance-- like a stompbox.

Resistance ranges from 0 to about 20k ohms. It's very sensitive to slight changes in pressure. If you want subtle manipulation, I'd recommend using your hands. But with an Arduino, you can use big jumps in resistance as an on/off switch-- perfect for foot-powered control! The important thing is that it can take a beating, as long as the solder points are protected.