On Tue, Feb 22, 2000 at 01:46:37AM -0000, Peter Pachla wrote:
> >....concluded that while the 150 wasn't that bad, touch screens
> >were not all that they were cracked up to be....
> >....it resulted in a sort of fatigue that was called "gorilla
> >arm"....
>
> Quite, I can believe it. I recall messing around with a light pen on my
> Atari back around 1984, nice idea but my arm would soon start to ache if I
> used it a lot....so I gave up on it (but then this is the man who hates
> function keys above the keyboard as he can't operate them with the little
> finger of his left hand (lazy or what!?)).
I really like the Sun "Starfire" concept. It's very pie-in-the-sky
at this point... but basically you sit in front of a giant screen whose
lower 18" is horizontal, like a desk, and curves upwards and inwards
like a baseball backstop. The entire thing is a touchscreen and scanner
also; any paper you lay on the surface becomes an electronic document
with no further intervention. You can work on the horizontal surface
to reduce arm fatigue but also drag reference materials or large windows
of other kinds up onto the vertical part of the display. So it would
seem to be the best of both worlds (vertical monitor for easy reading,
combined with a horizontal work surface like a drafting table). This
was never built of course, they did a "video prototype". I've seen the
video once but it has become available retail so I ordered a copy to see
it again.
Once wireless touchscreen "web pads" become more commonplace we may see
people using those to operate a big-screen display remotely; the pad can
display user-interface elements while the big-screen shows what you're
actually working on. You can position it however it's most comfortable.
> How did the touch screen operate then, infra red beams?
There have been a variety of touchscreen and pen type devices over the
years. The most common ones now are the resistive and capacitive types;
both involve a film coating over the CRT. With the resistive one, there
are two layers with some kind of grid of transparent resistive traces;
and the pressure of your finger causes them to come into more intimate
contact, lowering the resistance between the two traces which cross at
that point. The resistance is proportional to the pressure, and this
is handy in some applications. With the capacitive type, the presence
of your finger changes the capacitance and this gets detected, but these
screens are not pressure-sensitive. You can also use a stylus that has
a similar effect on the capacitance, but not a hard-tipped one. There
is also the Surface Acoustic Wave (SAW) variety, which (I think) somehow uses
ultrasound to detect very slight deformations in the glass as you press
your finger against it; this type is also pressure-sensitive. There
have been infrared beam touchscreens but those tend to be lower-resolution.
It detects your finger breaking a pair of crossing beams. And of course
there's the old lightpen trick. There is a hardware register somewhere
which has a pointer to the VRAM memory location where the color value for
the current dot (or character) being painted is coming from; so when the
pen detects that the phosphor dot under it has just been lit up by the
electron gun, simply go check that pointer to determine what the
coordinates of that dot are. I imagine high-persistence phosphors probably
interfere with the ability of this method to work very well. And
there is another kind of touchscreen that is simply a base that you
set a conventional monitor on. I believe it detects a force differential
between several strain gauges; as you push on the screen, the weight
distribution on the base changes in proportion to where you're pushing
and how hard. But it's been a while since I've seen material on this
kind and I've never seen an actual unit. I'd bet the calibration
would be somewhat finicky.
For use with a stylus, the additional options are RF-based. Some of
them require the stylus (or puck, in the case of a digitizing board) to
be powered and emitting a low-power radio signal. It's picked up by
a criss-crossing grid of circuit board traces behind the screen, which
act as antennae, and the signal strength gives it a clue to where the
pen is located. An advantage of this method is that you can move the
cursor without physical contact. My Dauphin DTR-1 uses this type of
digitizer, and I can move the cursor with the pen up to 1/2" or so away
from the screen. Pressing it down is equivalent to a mouse click.
The disadvantage is that the pen must be powered, with batteries in
the case of the DTR-1 or else tethered to the machine in other cases.
There are also RF-type pens that are passive; the machine emits RF
and the pen acts as a transponder to relay it back. My IBM 730T
Thinkpad uses an unpowered type of pen but I haven't opened it up to
see if the detector is just a grid of circuit board traces or something
more.
I believe the Newton and other practical PDAs like the Palm probably
use resistive screens, because they work with your finger as well
as the stylus (but with less precision), and the stylus is just a chunk
of plastic.
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Received on Tue Feb 22 2000 - 20:30:17 GMT