This week I focused a lot on building the actual wearable sensor for my final project. So, I logged as many hours as I could on the sewing machine. This sewing machine, by the way, is by far the most complicated machine on the ITP floor in my opinion.
Monday night, my wife, Marina, joined me on the floor, and we tried to figure out the sewing machine together. We brought some old pillow cases to use as practice material, and together we were able to get the thing going.
Marina showing off the complexity of the Juki HZL-F600
Initially we were using regular thread just to get the hang of the sewing machine, which took better part of Monday night. But, by the end of the night I was feeling pretty comfortable on the machine more or less. The next hurdle was getting the conductive thread onto a spool that will actually fit into the sewing machine. If only there were some kind of powered, spinning device on the ITP floor….
How to transfer conductive thread to a sewing machine like a boss
The drill! I was very proud of this problem solving moment. It worked perfectly. I got a spool of conductive thread, and then I put it in the machine and spooled a bobbin of conductive thread for the underside of the stitch, and I was ready to sew some circuits.
I decided to use my newfound sewing skills on my fabrication project, which was to build an enclosure. So I wired up a switch and a battery on the underside of a piece of wood from the Free Store (AKA Junk Shelf), and I completed the circuit on top by sewing conductive thread on an old pillow case.
Cool right? Wrong. It doesn’t work. You can read about it at this link.
As frustrating as it was, this was a very important learning opportunity for building the wearable fetal kick sensor. The sewn circuit’s conductivity falls off with the length of the circuit. Some possibilities for why this is:
The conductive thread I used isn’t as conductive as I thought.
The pillow case that I sewed onto has conductive properties and is dispersing my voltage.
Relating to the first point, it’s possible that the thread is still good enough for a circuit, but the zig-zag stitch I used effectively makes the circuit something like 50 times longer than it looks. So a tighter stitch that makes contact with itself could also help.
Originally I tried the stitch mentioned in #3. It’s also the same stitch Kobakant uses in their stretchy pressure matrix example. But, it was almost impossible (at least with my skill level) to sew that stitch onto the stretchy pillow case material I was using.
Some takeaways on what to do for next week. I will make a wearable sensor prototype by Thursday next week and have it connected to a P5 sketch. However, for now I will hold off on sewing the whole conductive matrix. For now, I can use conductive iron-on fabric to make my matrix that will save a ton of time and be more reliably conductive. By the way, this solution was Marina’s idea at like 1:30 in the morning when I got home after an evening of being frustrated with soft circuits. If I have time once I have my sensor and sketch working, I’ll take another crack at sewing it proper, but for now I think I will have to revert to simpler, more reliable materials.