This knit touchpad is possible due to the properties of the anti-static gloves, which are sold for handling sensitive electronic components. The glove is knit from stretchy fibers that also include resistive yarn (poorly conductive). Because of the way the fibers in knits travel from one side to the other, from top to bottom, the resistive yarn travels it doubles back on itself in a way that maintains the resistive connection even when the knit is cut (interrupted). The surface thus has a unique resistance at any point when measuring from at least three points. In this demonstration I chose to measure from all four corners.
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.