Well, I’ve finally come up with a good material to use for sensors, and a good way to attach the wire leads to the fabric, and a good way to attach the sensors to the glove. Finally. Here is the short version:
- Material: stretch conductive fabric (Cat. #251 from LessEMF)
- Wire attachment: wire glue followed with a bead of 5-minute or 30-minute epoxy
- Sensor attachment: sewing with regular or conductive thread
Honestly, I don’t think conductive thread is necessary because the material is so incredibly conductive itself. Unless you sew all over the surface with non-conductive thread, you really probably aren’t going to have any problem at all.
I came to the above conclusion about the material because it excels at every single property necessary for touch sensors except solderability. It’s thin, stretchy, easy to sew through, and insanely conductive, particularly when you touch two pieces together. Many of the materials I tested were perfectly conductive between two points on the same piece of material, but pressing two separate pieces of material together didn’t result in an electrical short. Since the glove is entirely built around the concept of touching sensors together, this is obviously a critical problem.
The boringly labeled “stretch conductive fabric” is made mostly of nylon and achieves its conductivity because the nylon is silver-plated. That’s why it so expensive, but as I calculated in the last post, even one linear foot (~$60) of material cut from a bolt of that stuff would make sensors for about 50 gloves. That’s not prohibitive at all, really.
Of course, after deciding to use a fabric that I can’t solder wire to, I had to come up with a way to reliably attach a wire to it while maintaining conductivity. The answer to this problem turned out to be a thin application of wire glue first, and then another thin application of epoxy to add strength. The wire glue is great for conductivity, but very poor at holding something in place under stress.
The perfect joint is achieved by applying only a very small amount of wire glue, since the somewhat porous nature of the fabric actually allows it to flow through to the bottom. You really don’t need a whole lot, since the real work will be done by the epoxy. The wire glue is really only there to make sure the epoxy doesn’t somehow separate the wire from the fabric. After the wire glue is dry (give it an hour or so), mix up a small glob of epoxy and apply a small bead with a toothpick or something similar. Flatter is better, since the thicker it is, the more raised the sensor will be on that corner.
One other note: the fabric is conductive on both sides and through the center. Therefore, I put the wire on the back side to leave the front entirely open for maximum available area. It also looks nicer that way. The fabric has a shiny side (the front) and a less shiny side (the back), and seems to have a slight natural curl such that the front is convex and the back is concave. Hopefully that’s enough info for anyone to figure out which is which. See if you can tell from the picture above.
Now I need to actually try to attach one of the sensors to the glove to see if I can actually do it. The most sew-ish thing I’ve ever done before was a cross-stitch project about 10 years ago. We’ll see how it goes. I was going to try an iron-on double-sided adhesive strip, but the LessEMF fabric description very clearly states “DO NOT IRON.” So I guess that’s out.