At the end of August, I built and delivered the first version of this tool. The build process took about 30-40 hours, much of it because each pressure pad was hand-sewn. This could easily be reduced by 50-60% with a machine, and reduced further with different designs. Because it was going to be used by a family member 1500 miles away, I needed the first build to be very resilient, so it may be a bit overbuilt.
In general, the build is well documented in the project steps. I had an issue with one pad, where it had a significant difference in resistance, which was odd, considering 5 other pads of the same size were quite close. Upon examination, I found that the internal piece of Velostat had shifted, allowing some of the thread to contact directly. I ripped out the stitching that held in the Velostat, and one side of the outside stitching, replaced the internal component, and sewed it back up.
The second issue was when mounting the pads on a 2' x 4' piece of MDF using DAP contact cement, I pulled one of the tails off of a pad, requiring another removal of a seam, replacement and re-solder, and closing back up, ensuring to add plenty of strain relief in the stitching. This leads me to want to experiment with using loops of wire within the pad, instead of conductive thread. If this works, it would further reduce the complexity and solder joints, which are points of failure.
After coating the MDF with contact cement and applying the pads based on the user's foot size, I covered the entire panel with a large piece of Neoprene. This provided protection for the wires coming off each pad and gave the product a more finished look. It would be worth evaluating if this top-sheet should be used as an element of the pressure pads to again reduce the amount of material and effort.
With the construction complete, I tuned the analog pin definitions in the software to match the pad locations on the panel, and delivered the controller.
Within a few minutes, the user was able to use the controller to move the mouse, bring up a web browser, and navigate to a social networking site. Considering he has not been able to do this on his own for over 6 months, it was amazing to see him gain this element of autonomy back. Typing using the on-screen keyboard was difficult, we may need to modify the software or Accessibility settings to accommodate.
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