Why Knitted Circuits?

(a knitted circuit board, ready for soldering.)

The short answer is, I can't sew.

The long answer....

E-textile platforms are based on designing materials to fit textile fabrication methods, resulting in conductive thread and components mounted on PCBs designed especially for sewing (for example, the Flora platform).  Perfect for experienced sewers interested in soft wearables.

However, the conductive threads often used for e-textiles can be unstable as conductors. Silver-plated thread oxidizes over time and becomes non-conductive, something I discovered after buying a large spool and leaving it out for months. (If you have some, store it in an airtight bag.) Stainless steel thread does not have this problem, but it does have higher resistance.

Creating solid connections with the thread presents another challenge.  It requires hand-sewing skill, stitching the thread through the component lead multiple times, knotting tightly, and adding glue for security. The whole process makes me want to reach for my soldering iron.

But... the conductive thread widely available in the US is not solderable. Conductive threads made with polyester or nylon wilt or melt under heat. Solderable conductive thread is available in Europe, made with Kevlar. The minimum purchase, a kilogram, starts around 60 euro, from the company, Karl Grimm & Co. With shipping, you can expect to pay over $100. One of the creators of the phenomenal e-textiles resource, How to Get What You Want, Hannah Perner-Wilson, sells small spools of the Karl-Grimm conductive thread reasonably-priced on Etsy, but it's still not cheap enough for me to create artistic-experiments-with-abandon.

Additionally, conductive thread introduces resistance to the circuit-- it just doesn't conduct as well as the copper wire used in conventional circuits. Arduino-based circuits can compensate for this, but I'd like to build circuits using conventional components, as well.  So I'm investigating how to apply textile techniques to conventional electronic materials. After much research, I've developed a tool-box of methods around my favorite skills of soldering and machine knitting. I'm documenting my methods here, as they evolve.

This approach is not for everyone. I've taught a number of basic knitting machine workshops at Pumping Station: One, and some people love it, some people, not so much. Even if you can machine knit, machine-knitting wire is an advanced technique.  I don't recommend trying it until you're comfortable working with "difficult" yarns like cotton and silk. But once you do get the hang of it, knitting PCBs is soooo easy.....
2 responses
I am going to have to come over to you at some point and get a class in this, sounds fascinating. Do you have any videos posted of these threads in action?
Sounds awesome, I'd love to share it with you. No videos yet, but that's a great idea. I'll see what I can do.