[NTLK] Newton touchscreen

[Frank Gruendel]

> It would appear as though the polyester forms a sort of "paper"
> for the MessagePad.  Meaning that when you write on the polyester,
> the conductive coating that resides underneath then picks up the
> pen strokes. The top glass pane below -that- doesn't do much apart
> providing a hard surface on which to write. 

> Is that an accurate picture of how the top two layers of the MP130's
> display work?  Or do I have the wrong end of the stick*?

No, it isn't, and no, you don't. Your picture is almost correct, except
for...

All Newtons and eMates come with a resistive touchscreen. There's a flexible
layer of conducting polyester bonded to a conducting glass pane. When you
tap on the screen, the polyester touches the glass and completes a circuit.
This circuit ends in two leads each for the horizontal and the vertical
position. The leads are connected to the mainboard. Depending on where you
tap, the resistance across the vertical and the horizontal leads will be
different. This is how the Newton mainboard figures out where the tap was.

Since (just like everything on this world except for wifes) touchscreens
come with tolerances, the horizontal and vertical resistance for a
particular location will slightly differ between different Newtons. This is
why you have to calibrate the screen.

Cheers

Frank

-- Newton software and hardware at http://www.pda-soft.de