Monday, January 16, 2012

New Hand Support Promising

This afternoon, my wife and I learned how fun it is to sew two pieces of 2mm neoprene material together using a common household sewing machine.  It took a few trys, but eventually we got the tention setup right and learned a few techniques along the way.  4mm of neoprene is taller than the gap under the sewing machines presser foot, so it can be challenging.  The new hand support is done.  It looks and works great.  It is filled with the sand and clay mixture and isn't leaking out.  I couldn't be happier with the way it came out with a solid feel, yet moldable to fit your hand.  The outside is 100% covered in Velro type loop that accepts normal Velcro hook.  I pasted some "industrial strength" Velcro hook on the back of all the buttons and put them on there.  They hold quite nice to the outside of the hand support and allow their removal and  re-installation to the new hand support over and over again until you get each button in exactly the right place.  We went with a very conservative stitch path that is pretty much just a rectangle and straight stitch.  The next version will have a bit more curves and design flare with a zigzag stitch now that we know we can sew it. One of the secrets ended up being the use of tissue paper both above and below the neoprene to help it slip under the presser foot and feed.  The neoprene by itself is quite stubborn and wants to hang up, causing it not to feed through the machine.  Another tip learned is to stick the neoprene parts to be sewn together with double stick carpet tape.  Pinning them together just doesn't work since the material is so thick.

One of these days I'll get around to posting some actual pictures, but my desk is just a mess with all the tools, wires and so on, so I have been reluctant. 

Next up is the creation of the grounding patch that will sit atop the hand support.  I received the small sample size Medtex180 material from SparkFun last week.  It looks and behaves much like regular spandex type material with a nice shiny gleen on one side.  I plan to use a small metal gromet that I bought at the local fabrics store poked through the material and hammered down nice and tight to make a soldering point.  That should make a good solid connection without the requirement of an adhesive.

After the grounding conductive material is in place is to migrate the Teensy board from the breadboard over to its place on the hand support.  I wanted to be sure we got the hand support nailed down before I started figuring out where the Teensy board would reside.  In order to do this, I'll need to design a soldering template that will help me add some tiny 0603 size capacitors to all of the analog pins (11 of them) on the underside of the Teensy board; each run to ground.  Using low value capacitors (100pF - 490pF) really helps make the capacitance touch events much more responsive and repeatable.  While I can reliably detect touches without them, the are a little slower without the capacitors in place.  I plan to glue them down with the hot glue gun to give them structural support to stay attached, in addition to being soldered to each pin the grounding wire running between all of them.  They will all be covered over with a piece of Velcro hook that will hold the Teensy board to the hand support so nobody will know they are there.

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