Dean S. Messing wrote:


I took think the pad is a wee bit sensitive to the touch when I'm
banging away at the keyboard. Sometimes my thumb will brush it and
(at least w/in emacs) the "point" will just to where the cursor sits
and I'm now entering text in the wrong place. Thank goodness for the
powerful "undo" features of emacs. Solution: thumbs up!


Touchpads are misnamed; they don't require touch. There's some kind of
proximity detector involved.





(I also learned to type on my mom's old Remington, with the green
plastic keys. What a great old piece of machinery!)


Imperials were rather popular in my youth. At the bank, at certain times
of the day, we queued for the NCR full-keyboard adding machine. We
became adept at adding in our head, two columns of digits at once. I
started a week after we went to decimal currency, I have no idea how
they managed LSD.




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John

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John Summerfield wrote:
: Dean S. Messing wrote:
:
: > I took think the pad is a wee bit sensitive to the touch when I'm
: > banging away at the keyboard. Sometimes my thumb will brush it and
: > (at least w/in emacs) the "point" will just to where the cursor sits
: > and I'm now entering text in the wrong place. Thank goodness for the
: > powerful "undo" features of emacs. Solution: thumbs up!
:
: Touchpads are misnamed; they don't require touch. There's some kind of
: proximity detector involved.

I believe it is a capacitive sensor and depends on the Dielectric
Constant of the material between the pad and one's finger. I just did
several little experiments to check. (I'm a scientist, after all :-)

First, I took my finger and put it really close to the pad w/o
touching it. No cursor motion. (Air has a small dielectric constant.)
Then I took a thin piece of paper and tried to move the cursor by
sliding finger over paper. No go unless I pressed very hard. Paper
is pretty incompressible so I don't think it was that my finger was
getting closer. Rather the surface area of the contact was increasing
so the capacitive effect was greater the harder I pressed.

Interestingly, through a much thicker envelope glue label, my finger
had no trouble moving the cursor at normal pressure. My guess is that
the glue in between the label and the backing has a high
Dielec. Const.

Finally, I used my finger nail. Being an insulator, it had no effect
even pressing hard.

As an aside to this aside, I once worked for a company that took
security very seriously. They had RFID-activated doors installed all
over their laboratory to keep the secrets in and the intruders out.

Problem was that each door had (on the inside) a capacitive "rail"
that one could push against to open the door normally from the inside.
These were double doors with a small space between them. I wondered
one day if a wire coat hanger, bent like a hook, with me touching one
bare end from the insecure side and the other bare end through the
space touching the railing would release the lock. Voila! So much
for the $50K or so they spent on internal building security.

Ain't physics fun?

<snip>

Dean

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Dean S. Messing wrote:

John Summerfield wrote:


owerful "undo" features of emacs. Solution: thumbs up!
:
: Touchpads are misnamed; they don't require touch. There's some kind of
: proximity detector involved.


I believe it is a capacitive sensor and depends on the Dielectric
Constant of the material between the pad and one's finger. I just did
several little experiments to check. (I'm a scientist, after all :-)

grumble grumble[1]



First, I took my finger and put it really close to the pad w/o
touching it. No cursor motion. (Air has a small dielectric constant.)
Then I took a thin piece of paper and tried to move the cursor by
sliding finger over paper. No go unless I pressed very hard. Paper
is pretty incompressible so I don't think it was that my finger was
getting closer. Rather the surface area of the contact was increasing
so the capacitive effect was greater the harder I pressed.

Interestingly, through a much thicker envelope glue label, my finger
had no trouble moving the cursor at normal pressure. My guess is that
the glue in between the label and the backing has a high
Dielec. Const.

Finally, I used my finger nail. Being an insulator, it had no effect
even pressing hard.



I previously test on a G4 17" powerbook running OS X (I don't recall
whether Panther or Tiger). I could move the cursor without touching the
touchpad.


Now I have a G4 15" powerbook running Tiger. I can (just) touch the
touchpad, sliding across the surface with my finger, not moving the cursor.


Non-ferrous metals seem to work much the same as fingers. Side of SATA
cable works. Plastics (polystyrene packaging, Faber-Castell fluoro pen)
and cardboard don't work. Neither does some insulated wire (about the
size of wirewrap wire).


[1]
Daughter was a (just-graduated) scientist, working as a Research
Assistant on a project involving Alzheimer's at http://www.mhri.edu.au.
The lead got his Ph D, the grant ran out and she needed a job. She got
one, doing data entry for an insurance company. She's doing well for
herself in insurance (she talks to the board), but I wish the country
paid its scientists well, we need science more than we need good
insurance professionals.



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Cheers
John

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On Fri, 2007-12-14 at 06:48 +0900, John Summerfield wrote:
> Touchpads are misnamed; they don't require touch. There's some kind of
> proximity detector involved.

;-) Yes, I've seen that too. I'll be using my keyboard with nothing,
at all, anywhere near the touchpad, and suddenly I'm no longer typing
what I thought I was typing.

I'm inclined to think mine's upset by the varying electric field that
surrounds a body.

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Jan Brosius wrote:
Hello, I plan to buy a notebook. This is my first notebook. Besides
Windows I'd like to install also fedora 8.
Can anyone tell me if fedora recognizes the touchpad of the notebook.
If so does fedora also recognise an additional USB mouse?


Any help appreciated
Jan


Thanks to all of you. I wouldn't like to miss fedora. Fedora is a great OS

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On Friday 14 December 2007, Jan Brosius wrote:
> Jan Brosius wrote:
> > Hello, I plan to buy a notebook. This is my first notebook. Besides
> > Windows I'd like to install also fedora 8.

> Thanks to all of you. I wouldn't like to miss fedora. Fedora is a great OS

Also be sure to take a look at the Fedora-Laptops mailing list.
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