The following updated video shows the data visualization from all four inputs. And calculates the position of the nail. As you can see it is not perfect, but you can also see that it does kind of work >>
This is the original video using the finger cap >>
Instead of attaching the Vdd or Vcc to the finger, one could also have it as a continuous conductive layer mounted underneath or above the knit, separated by perforated foam. Although this minimizes resolution to the number of perforations, it does free the user from the additional step having to wear the finger cap. But in this case I consciously wanted to test this method for a future project idea.
The knit does not need to be kept on a flat surface, I just did this for demonstration purposes and the next Instructable will show how this method can be used to turn the whole glove into a touchpad. And then hopefully the whole body, though the problem I have to solve here is how to isolate against the knit interfering with the measurable continuous resistance by touching back on itself.
Step 1: Materials and Tools
- Conductive acrylonitrile stretch glove from http://www.all-spec.com
also see http://cnmat.berkeley.edu/resource/conductive_gloves
- Conductive copper tape with conductive adhesive by 3M http://www.3m.com/
also see http://cnmat.berkeley.edu/resource/conductive_tape_conductive_adhesive
- Ni/Cu Fabric Tape with conductive adhesive from LessEMF http://www.lessemf.com/fabric.html
also see http://cnmat.berkeley.edu/resource/ni_cu_fabric_tape
- Solderable perfboard with copper line pattern from All Electronics http://www.allelectronics.com/
- Male and female headers from Sparkfun http://www.sparkfun.com/
- Ribbon cable
- 4x20K resistors
- Thin, flexible wire
- Double-sided sticky tape
- Stretch conductive fabric from http://www.lessemf.com
also see http://cnmat.berkeley.edu/resource/stretch_conductive_fabric
- Fusible interfacing from local fabric store or
also see http://www.shoppellon.com
- Stretch fabric (jersey)
- Arduino and USB cable from Sparkfun http://www.sparkfun.com/
- Arduino software free for download from http://www.arduino.cc/
- Processing software free for download from http://processing.org/
- Sewing needle
- Wire clippers
- Wire strippers
- Soldering iron and solder
Step 2: Preparing Touchpad Surface
To mount this piece of knit, which likes to roll up on itself, I cut a piece of cardboard, about 2cm larger than the knit all around and mounted it on some strips of squishy double-sided sticky tape. The reason I chose to use squishy tape was only because it was the only kind I had that day, but I also thought it could be nice than a hard surface and to some extent the surface is even pressure sensitive, since the harder one presses, the better the electrical connection becomes. Increasing electricity flow equally to all measuring points.
Before sticking the knit to the tape I connected 4 wires to the corners of the cardboard by stripping their ends and simply fastening them down underneath a small corner of copper tape that has conductive adhesive.
Step 3: Connecting the Touchpad
Step 4: Sewing Conductive Finger Cap
Step 5: Soldering Pulldown Resistors
Cut a 6 x 7 hole piece of perfboard (copper lines running the shorter, 6 hole, length). Cut a row of 7 female headers and solder them to the first row of 7 holes. Solder 20K resistors between the third hole and each of the 4 holes next to it. Also see photos for instruction.
Solder the ends of all four (red) cables coming from the corners of your knit touchpad to the other end of the perfboard so that each input runs to the ground through a resistor. Solder the (red) wire coming form the finger cap to one of the two leftover holes on the perfboard that does not pass through a resistor and goes directly to the header. To connect this version to your Arduino you will need to use a piece of rainbow wire that connects things in the right way. The inputs from the four corners should go to your first four analog inputs. The header that is connected to the other end of all the resistors should go to your GND and the header that goes directly to your finger cap should connect to the +5V. See photos!
Cut a 6 x 9 hole piece of perfboard (copper lines running the shorter, 6 hole, length). Cut a row of 4 male headers and solder them to the first four holes in the row of 9 holes. Cut 2 male headers and solder them to the last two holes in the same row of 9 holes. Solder 20K resistors between each of the 4 male headers and the closest of the two male headers - these match up with your Arduino board. Solder the ends of all four (red) cables coming from the corners of your knit touchpad to the other end of the perfboard so that each input runs into a resistor. Solder the (red) wire coming form the finger cap to the left over header in the corner. Now this should fit directly on top of your Arduino and should be able to plug the male headers sticking out of your perfboard into the first 4 analog inputs and the two headers should plug into your GND and +5V. See sketch!