Soft Sensing HW

For our last homework assignment, I wanted to make my breath sensor a little nicer. Luckily, Alexandra was around to give me a refresher on how to use the sewing machine, and showed me a neat trick that keeps the conductive thread on the underside of the fabric, and therefore unexposed:


front, back

I then used this technique to sew along the length of the straps, and used another trick Alexandra showed me to sew terminals for alligator clips:

Then I added velcro at the ends of the straps:

When it came to actually test on a person, the analog read range was quite small, so I had to map the min and max reads to the digital write range to make the LED fade discernible:

Apparently, there are no alligator clips at ITP, so I had to improvise with wire, copper tape, and paper clips.

Soft Sensing Day 2

As we were all intrigued by the possibilities of conductive thread, our “research group” decided to explore making the stroke sensor we saw on How to Get What You Want.

Instead of using a piece of conductive fabric on the backside, we opted to use the Eeonyx StaTex Conductive Fiber as filling for an amorphous plushie. This way, it would be able to detect pressure as well. So many fun things!

Here we are, hard at work:

Not pictured: Alan, who was doing the documenting. Thanks Alan!

Here’s what we ended up with:

Soft Sensors Day 1

For the materials testing lab, Erin and I were able to experiment with different conductive materials: Velostat, Eeonyx Pressure Sensing Fabric, Eeonyx Stretch Sensing Fabric, and Eeonyx Conductive Fiber.

Velostat and the pressure sensing fabric needed to be “sandwiched” in a non-conductive material, with conductive terminals for power and ground to be connected to the multimeter; the stretch sensing fabric and conductive fiber only needed to be clamped with alligator clips.

At rest, the velostat had a resistance of 24.5k. To test it, we 1) applied pressure, which yielded a resistance of ~26k, 2) bend it, which yielded a resistance of ~30k, and 3) twisted it, which yielded a resistance of 35k.

The pressure sensing fabric had a resistance of about 3.5k at rest. To test it, we 1) applied pressure, which yielded a resistance of ~3.1k, 2) bent it, which yielded a resistance of ~2.5k, and 3) twisted it, which yielded a resistance of 2.2k.

The stretch fabric had a resistance of ~140k at rest. When we 1) applied pressure, the resistance dropped to ~129k, 2) stretched it, the resistance dropped to ~95k, and 3) twisted it, the resistance dropped to 123k.

The conductive fiber had a resistance of ~2.2k at rest. When we pressed it, it dropped to a value of 1.5k.


 

When we convened for our group exploration, one of our group members had an idea that she wanted to work on alone, so we ended up doing our own thing in close proximity to each other.

I’d never worked with a stretch sensor before, so I attempted to integrate it into a chest strap to make a breath tracker. Since we were limited on time and resources, I quickly sewed together an extremely rough prototype:

I had initially used the grey mystery fabric—since there was more of it—but it didn’t yield very good results: the analog read ranged only from 1014 at a relaxed state, to 1016 at a fully stretched state, using a 220ohm resistor.

The Eeonyx fabric was much more responsive, giving an analog reading from 870 in a relaxed state, to 950 in a fully stretched state, using a 1M ohm resistor.