Digest Number 508
Archiver
Posts: 46,084
> Message: 17
> Date: Fri, 2 Mar 2001 14:37:23 -0600
> From: "Al Williams" <alw@a...>
> Subject: RE: Touch-screen technology?
> There are three main ways this is done that I know of.
> 1) Capacitive sensors in the screen (expensive).
> 2) Light beams.
> 3) Sound waves.
> Someone has a patent on #3 and I've never actually seen it done. The idea
is
> they send a ultrasonic chirp down one edge of the screen. Baffles direct
> some of it back to a sensor. When your finger gets in the way, it shows
up
> as a missing return pulse. Of course that only gives you one axis. But
you
> can double it and only have 2 emitters and two sensors:
> Detect
\
\
\
> | |
> | |
> | X |
> | | |
> | | |
> Emit
/
/
/
> The classic way is to use an array of IR emitters and sensors. The old
HP150
> did it that way. You just criss cross the screen with light beams and
watch
> for sensors to go dark. Cheap enough but there are a few catches.
Resolution
> is poor for one thing. The other is to avoid ambient light problems you
need
> to put the sensors in a hole that points right at the emitter. The HP150
had
> a bezel that had little holes in it. But, the little holes would fill up
> with crud and become unusable. We'd snap the bezels off, take them in the
> lab, and shoot them with air from the little shop air vents we had with
the
> anti static deionizer head. Then they'd be good as new for a month or so.
> Have you considered a light pen? The idea there is to monitor a photo
> detector for a light change. We used to make these for the RCA 1802 ELF
by
> hooking an CdS cell up and then "scanning" the (pitiful) graphics
display.
> Say you had 4 objects on the screen, a circle, a rectangle, a square, and
a
> triangle. When you push a button, the program would dim each figure and
> watch to see if the pen's sensor drops. If it does that's the one you are
> over. You do the scan quickly so it is hard to notice. If you are really
> clever, the push button is built into the pen so when press it on the
screen
> it triggers a scan. If you use a phototransistor or diode and a lens you
can
> get pretty good resolution.
> Real controlers use a raster scan to do this (the original PC could take
a
> light pen). I always though light pens would catch on -- better than a
mouse
> if you ask me (except for the difficulty with high resolution). Oh well,
> I've always been anti-mouse.
> Regards,
> Al Williams
> AWC
> * 8 channels of PWM: http://www.al-williams.com/awce/pak5.htm
The classic problem with light pens on "consumer" systems was originally
described as the "gorilla arm" syndrome. It was found that the human arm
tires out very quickly trying to use a light pen on a vertical surface.
There was a time I didn't believe this was true, but experimenting with
rolling my own raster scan routines on a (<showing-age-mode-flag>=ON)
Commodore 64 (the VIC-20 was too slow and the TRS-80 mod 1 was too
cumbersome to bit-twiddle a "wedge" into) convinced me. This was
especially true of fine motor movements required when there are small hit
areas or "action"-type inputs (draw a circle around your choice), which is
why you typically will not find more than a half-dozen selections on an
average sized touch screen.
Oh, and yeah, I worked with the Apple II, Mac, TI 99-4/A, Interact, Amiga,
ZX-80, Atari 400 and Commodore 128 as well. It's hard to believe that so
much fun technology has passed by so quickly. Now it's the Stamp and PIC.
<nostalgia-flag>=OFF
We now return you to your regularly scheduled good stuff.
\
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If you received this in error, please contact the sender and
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> Date: Fri, 2 Mar 2001 14:37:23 -0600
> From: "Al Williams" <alw@a...>
> Subject: RE: Touch-screen technology?
> There are three main ways this is done that I know of.
> 1) Capacitive sensors in the screen (expensive).
> 2) Light beams.
> 3) Sound waves.
> Someone has a patent on #3 and I've never actually seen it done. The idea
is
> they send a ultrasonic chirp down one edge of the screen. Baffles direct
> some of it back to a sensor. When your finger gets in the way, it shows
up
> as a missing return pulse. Of course that only gives you one axis. But
you
> can double it and only have 2 emitters and two sensors:
> Detect
\
\
\
> | |
> | |
> | X |
> | | |
> | | |
> Emit
/
/
/
> The classic way is to use an array of IR emitters and sensors. The old
HP150
> did it that way. You just criss cross the screen with light beams and
watch
> for sensors to go dark. Cheap enough but there are a few catches.
Resolution
> is poor for one thing. The other is to avoid ambient light problems you
need
> to put the sensors in a hole that points right at the emitter. The HP150
had
> a bezel that had little holes in it. But, the little holes would fill up
> with crud and become unusable. We'd snap the bezels off, take them in the
> lab, and shoot them with air from the little shop air vents we had with
the
> anti static deionizer head. Then they'd be good as new for a month or so.
> Have you considered a light pen? The idea there is to monitor a photo
> detector for a light change. We used to make these for the RCA 1802 ELF
by
> hooking an CdS cell up and then "scanning" the (pitiful) graphics
display.
> Say you had 4 objects on the screen, a circle, a rectangle, a square, and
a
> triangle. When you push a button, the program would dim each figure and
> watch to see if the pen's sensor drops. If it does that's the one you are
> over. You do the scan quickly so it is hard to notice. If you are really
> clever, the push button is built into the pen so when press it on the
screen
> it triggers a scan. If you use a phototransistor or diode and a lens you
can
> get pretty good resolution.
> Real controlers use a raster scan to do this (the original PC could take
a
> light pen). I always though light pens would catch on -- better than a
mouse
> if you ask me (except for the difficulty with high resolution). Oh well,
> I've always been anti-mouse.
> Regards,
> Al Williams
> AWC
> * 8 channels of PWM: http://www.al-williams.com/awce/pak5.htm
The classic problem with light pens on "consumer" systems was originally
described as the "gorilla arm" syndrome. It was found that the human arm
tires out very quickly trying to use a light pen on a vertical surface.
There was a time I didn't believe this was true, but experimenting with
rolling my own raster scan routines on a (<showing-age-mode-flag>=ON)
Commodore 64 (the VIC-20 was too slow and the TRS-80 mod 1 was too
cumbersome to bit-twiddle a "wedge" into) convinced me. This was
especially true of fine motor movements required when there are small hit
areas or "action"-type inputs (draw a circle around your choice), which is
why you typically will not find more than a half-dozen selections on an
average sized touch screen.
Oh, and yeah, I worked with the Apple II, Mac, TI 99-4/A, Interact, Amiga,
ZX-80, Atari 400 and Commodore 128 as well. It's hard to believe that so
much fun technology has passed by so quickly. Now it's the Stamp and PIC.
<nostalgia-flag>=OFF
We now return you to your regularly scheduled good stuff.
\
The information transmitted is intended only for the person
or entity to which it is addressed and may contain confidential
and/or privileged material. If you are not the intended
recipient of this message you are hereby notified that any use,
review, retransmission, dissemination, distribution, reproduction
or any action taken in reliance upon this message is prohibited.
If you received this in error, please contact the sender and
delete the material from any computer. Any views expressed
in this message are those of the individual sender and may
not necessarily reflect the views of the company.
\