I'm trying to build something quite challenging and seem to be getting nowhere. Maybe you'll help. I'd like to detect a touch of two naked fingers with no materials or sensors in between (simple capacitive sensors won't work here). It's a design idea and I'm not very skilled engineer so I have no idea if it's even possible.
Here's a simplified sketch of a hand:
The original idea was this: There's an electrode on each finger and small current is running through from A to B. When fingers touch, current starts passing through the SHORTER GREEN path as well (it may not be apparent but it will be always a shorter by at least ~1cm). But it turns out looking for changes in resistance / current seems to be going nowhere. It's not reliable because the biggest changes in resistance come from contacts between the skin and electrodes. It won't ever be perfect, electrodes move, user sweats, temperatures change, etc. Compared to this, the changes in resistance caused by a shorter path are insignificant. But the contact may be good enough for something else (it would be fine for a simple capacitive touch switch).
I'm now thinking that maybe I could measure the distance between the two contacts somehow by sending some signal from A and reading it at B. Just looking at the time of propagation of charge imo won't be possible because I won't be able to do this fast enough to get at least a millimeter resolution.
The problem could be really described as detecting whether the shorter green path is being used or not.
(We could add more electrodes on the fingers somewhere along the blue path but not along the green path.)
Do you think something like EDM (http://jerrymahun.com/library/Distance/a.htm) could help here? Any other ideas?