Swingman wrote:
On 1/20/2011 9:33 AM, dpb wrote:
Swingman wrote:
On 1/19/2011 10:14 PM, CW wrote:

Hot dogs are pretty moist. When he demonstrated it with his finger,
he soaks
in water first. When woodworking, my hands get dry as a bone. Try a dry
finger.

Doesn't it use capacitance as the switch mechanism?

With capacitance touch switches a dry finger shouldn't make much
practical difference, otherwise you would not get a stylus to work
effectively on a capacitance touch screen.

The question then is why doesn't it trip on dry lumber and there's the
override for using it with PT lumber that is wet?

Something about moisture content increasing the lumbers dialectric
properties (involving dielectric constant) as an insulator and affecting
the ultimate "capacitance" of the human body and the blade as conductors??

Shheeeesh ... haven't taken physics in almost 50 years and "capacitance"
was one of those properties that you thought you had a handle on until
you tried to expound on what you thought you knew (and nothing,
apparently, has changed in the interim). :-)

I do remember that it was always the exact opposite of intuitive,
especially when using an example like the capacitance of the human body,
and a door knob, as conductors generating a spark when being separated
by a dielectric medium like "dry" air, and why it changed with "moist" air.
....

Never did touch on the specifics of the body capacitance so I don't have
a feel at all on it; wasn't in the NE curriculum...

It is related to the makeup of the body tissue which is mostly water I'm
pretty certain, but afaik it is not dependent on actual moisture on the
surface (altho I'm certain that would undoubtedly increase the sensitivity).

AFAIK, the touch screens are active, not passive sensors...

I did a little (as in very little ) search for some internet physics
that could be applicable but found nothing of any real value--the
wikipedia articles on related subjects are subs only and very poor ones
at that. A couple of the proximity sensor data sheets were pretty good
on the active sensors, but didn't find anything on a passive sensor that
seemed as if might be something similar to the Sawstop technology...

'Tis still a puzzle --

"There are more things in heaven and earth, Horatio,
Than are dreamt of in your philosophy..." -- Will the Speare

pretty well summed it up...

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