A few test stictches on Bekaert fabric were made to determine the resistivity with regards to stitch type and change in length of stretch was determined. My Brother LS-2125sewing machine had 10 types of stitches, so I tried them all.
The thread would break every so often, due to the thread on the reel having variable tension on it, and being quite thick. I sewed with the thread on the spool, instead of the bobbin because I found that it jammed less (although the thread broke). I also switched to a thinner needle for lightweight fabrics, rather than the standard size #40 needle. Resistivity increased with amount of thread, so close stitches resulted in higher resistivity, but less change in resistance when stretched. Stitches that had more contact points were less likely to rip out when the fabric was stretched beyond a few inches. Although a "stretch stitch" , which had 3 points of contact along each zig zag, was prefered for minimal threads coming out of the fabric, it did not give the best dynamic range. However, I also favored the #4 wide zigzag stitch, which seemed to have the greatest dynamic range.
The result was a piece of fabric approximately 7.5" x 9" with stitches running down all four sdes
The fabric controller was designed to support how people interacts with fabrics. We pull on hems, push shirts under other clothes, and might even scrunch them up to toss a piece of fabric into the hamper. I built a portable frame that would support these interactions.
At first, I had planed for a stand-up interaction, thinking about curtains that hang or stand-up displays. Upon realizing the integration of different capabilities (moving from sewing area to electronics bench to testing area, I realized the need to start with something portable for ease of testing).
So I made a tabletop frame that allows the fabric to be tensioned between the four corners. The fabric stands off the tabletop at 2.5", with leads at each of the four corners. The main consideration was unimpeded access to the fabric. Another consideration is that the feel and access of the fabric should be unimpeded by the electronics.
The resistance of each side measured approximately 10MOhms at rest, and increased when stretched. I made a voltage divider so that the change in resistance would be transduced into voltage. I built a follower circuit to sense the change in voltage for each leg. Here is one circuit diagram, representative of each leg. The fabric was the lower leg of a 1:10 voltage divider. The change in voltage was typicallly between 4.7V-3V. Due to the closeness of the input voltage to the rails,Matt Malinowski helped me find the right op-amp for the job, an LMC6482 which had a high common-mode range.
here is the circuit breadboard. The four strain readings are being taken on the righ side of the board.
The circuit on the left side is for the conductive fabric part of the project, which I will explain later. Unfortunately, the conductive fabric triangle didn't work very well and had many noise problems.
II am a novice to PD, but I had an initial notion that stretching the fabric sideways might map to reverb, or speed of some musical piece. Meanwhile, stretching the fabric vertically should map to volume. I found a patch that allowed me to load a music snippet and alter the speed and volume.
For the other side, I had pitch of an "interrupting" zing noise mapped to the top, and the volume of that interrupting noise was on the right. Click below to open up a bigger window of the patch.