HOW TO GET WHAT YOU WANT

Circular Knit Stretch Sensors

Use of a circular knitting machine to knit a circular stretch sensor from combinations of conductive and non-conductive yarns.

In the cases of the Inox steel fiber blend yarns, the stretch sensing is due to the structure of the conductive yarn which is made up of lots of short steel fibers mixed with polyester. Even without knitting the yarn into a structure you can use it as a stretch sensor by simply pulling it taught or relaxing it. But the yarn is not very strong and easy to tear. The knit structure allows you to accumulate more yarn and thus more resistance in less length and also by combining the conductive yarn with regular yarn you can gauge the sensitivity of the sensor by choosing a thicker or thinner yarn - thicker yarn gets more in the way of the conductive yarn making extra contact through the knitted loop structure. Plus knitting creates the stretchy structure giving you some natural tangible feedback.

Video of the circular knit stretch sensor collection using an arduino board with an Atmega 168, using internal pull-up resistors and graph application written in Processing.

>> Download higher quality video (262MB)

#1) New conductive yarn obtained from Plug and Wear (more info soon)
#2) Nm 10/3 20% Inox, 80% PET knit with regular white yarn from Schoeller-Wool
#3) Nm 50/2 20% Inox, 80% PET knit with regular white yarn from Schoeller-Wool
#4) Nm 50/2 40% Inox, 60% PET knit with regular white yarn from Schoeller-Wool
#5) Nm 25/1 100% Inox steel fiber knit with regular white yarn from Schoeller-Wool
#6) Nm 20/2 30% Inox, 70% Laine wool pure from Wera-Tech
#7) Nm 20/2 30% Inox, 70% Laine wool knit with regular white yarn from Wera-Tech
#8) 117/17 2ply silver plated Nylon conductive thread from Sparkfun and LessEMF
#9) 66/22 3ply 110 PET silver plated Nylon conductive thread from LessEMF

Video showing stretch sensing properties of the individual conductive yarns used in the above shown video in the knit structures.

>> Download higher quality video (421MB)

Conductive yarns

Conductive yarn is currently hard to come by, but hopefully soon online shops like www.plugandwear.com and www.sparkfun.com will offer such yarns in various thicknesses, conductivity and at a good price and amount.
The conductive yarns (and conductive threads) used in these examples are listed bellow.

Circular knitting machines

Circular knitting machines range from 20-250$ in price and differ in diameter, number of needles and spacing of needles. Spool or wire knitters have only four needles and resemble manual knitting dolls, while the knitting machines resemble manual knitting wheels or looms.

Make your own

The following Instructable covers the making of a circular knit stretch sensor with a with the following models of circular and spool knitting machines:
- Play Go Knit Knit (17 Euro from Amazon Germany)
- Singer Spool Knitter (19$ from Amazon USA)

>> Instructable