Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!elroy.jpl.nasa.gov!decwrl!mcnc!rti!mozart!sasrer
From: sasrer@unx.sas.com (Rodney Radford)
Newsgroups: sci.electronics
Subject: Re: touch screen for crt display?
Message-ID: <1991May20.153737.18381@unx.sas.com>
Date: 20 May 91 15:37:37 GMT
References: <1656@fs1.ee.ubc.ca> <1991May18.025326.375@ddsw1.MCS.COM>
Organization: SAS Institute Inc.
Lines: 48

In article <1991May18.025326.375@ddsw1.MCS.COM> whos@ddsw1.MCS.COM (Ben Feen) writes:
>In article <1656@fs1.ee.ubc.ca> jthornto@ee.ubc.ca (Johan Thornton) writes:
>>Does anyone know either
>>
>>- where to get 
>>- how to build
>>
>>a clear touch screen to fit over a monitor.  It doesn't have to have
>>to have very high resolution--4 by 4 would be ok.
>>
>>One idea I had was to run some small wires across the screen and essentially
>>use the classic capacitive touch-switch circuit.
>>
>
>Touch screens are not touch-operated, or at least the HP screens I've seen
>aren't.  They are based on small transmitters and sensors around the
>screen's border.  When you interrupt the beams crossing the screen, the
>computer knows the X-Y  coord's of your finger.  The wires idea is cute, but
>there are two problems:
>
>1:  You'd have to prevent the "X" wires from shorting with the "Y" wires,
>but still have them close enough to touch two at once.
>2:  Who wants wires on their screen?
>

I have a surplus touch sensitive terminal from an old Plato educational 
system that used the idea of "X" and "Y" wires that were shorted together
when you press at (or near) their intersection. The terminal I have has
a 16x16 resolution giving 256 specific touch points. And no, you can't
see the small wires (their are very thin - near the size of human hair).

The display was given to me, and I have not done anything with it yet, other
than play with the builtin in test program. As you press each of the 256 
areas, a portion of the screen toggles on/off so you can verify that it
works OK. The screen resolution is 512x512 black&white. The only problem
is that it uses a non-standard bit-stream protocol (I have no specs on
the software that controlled it but the person who gave it to me thought 
that is was a 17bit in, 21bit out serialized format!!).

This equipment is now junk, but it was 'state of the art' only a few years
ago when I saw it demo'ed at the Worlds Fair in Knoxville. My how things 
change....

-- 
+-----------------------------------------------------------------------------+
| Rodney E. Radford        Computer Graphics Imaging    sasrer@unx.sas.com    |
| (919) 677-8000           SAS Institute, Inc.                                |
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