The project is alive and functioning — the final fabrication of the piezoresistive pressure matrix that I made out of pajamas, conductive fabric and velostat (piezoresistive material). After staying up soldering the protoboard and sewing to wires with conductive thread until 6am Wednesday night, we finally got to play test this thing the next day.
Unfortunately, there was a problem with the audio of the screen recording, but nonetheless, this is the visualization of actual baby kicks. Click here to read more about the visualization.
We ran into some fabrication problems. With one exception, I had been testing almost exclusively layed out on a table, which behaves very differently than when it’s on a person. We were having trouble getting good readings, and I think it was fundamentally due to the way she was wearing it. Last time we tested it, when it had a bunch of alligator clips dangling from it, we fastened it using a back support belt. I think what happened is that Marina grew significantly since then, and it doesn’t work as well any more. It still fits, but it fits differently.
At any rate, Marina had the brilliant innovation of sewing washers onto either side of the sensor, and using lace to tie it up in the back. Velostat, the resistive material in the middle of the conductive sandwich that makes this whole thing work is strikingly similar to a contractor bag. It’s plastic-y and rigid. This makes it difficult to attach it evenly over a round surface like a pregnant lady’s belly. The beauty of the corset approach is that the tightness is variable, creating a much better fit, and generating significantly better readings. The washers Marina used were actually left over from a previous fabrication project (click here to see it).
Marina sewing washers to make the sensor into a corset.
Here are some more notes on the fabrication. First and foremost, this was my first soldered circuit, which I’m very proud of, and I think it’s beautiful.
I used ribbon wires at David Rios’s suggestion to tidy up the connections between the sensor and the microcontroller. But then I had to attach them to the soft fabric somehow. So I had to spend some more time with my old friend conductive thread. I sewed the ribbon wire tips to the conductive fabric with conductive thread by turning the ends of the wire into little circles, and then I hot glued over it to prevent any shorts.
The original wearable design that I actually presented to class was a little different than the version I mentioned above with the corset lace tighteners. My original idea was to attach it to a shirt with Velcro, but in the end, the data coming out of that version sucked. Here is what it looked like.
That’s it for now, but in the very near future I will be adding some Winter Show documentation here.