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Versatile Input Device and Technology for CRT Terminal

IP.com Disclosure Number: IPCOM000102281D
Original Publication Date: 1990-Nov-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 3 page(s) / 115K

Publishing Venue

IBM

Related People

Chang, IF: AUTHOR

Abstract

An input technology utilizing the intrinsic CRT raster-scanning characteristics is described herein. Taking advantage of a well-known light-trapping (light-guide) effect, a simple detection is implemented to provide either light pen input or touch input. Both light pen input and touch input are incorporated in one device which is very desirable in CRT terminals.

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Versatile Input Device and Technology for CRT Terminal

       An input technology utilizing the intrinsic CRT
raster-scanning characteristics is described herein.  Taking
advantage of a well-known light-trapping (light-guide) effect, a
simple detection is implemented to provide either light pen input or
touch input.  Both light pen input and touch input are incorporated
in one device which is very desirable in CRT terminals.

      Fig. 1 provides a schematic description of the basic concepts
involved.  The basic concept is to use an intrinsic CRT raster scan
to generate light signals for input detection.  This is different
from traditional light pens in that it can determine position
information in regions where there is no light image.  Thus, this
light pen input can be implemented as a true position input device,
like tablets. As shown in Fig. 1, one makes use of the unused border
of the CRT screen 10 to generate a series of light pulses for light
pen 16 using the intrinsic CRT raster scan 12.  In a novel display
terminal, one could deposit stripes 14 of a different phosphor such
as IR phosphors, as shown in Fig. 2, to make the light detection in
infrared.  Under normal raster scan these phosphor stripes will
provide a long unambiguous start light pulse train with pulse
duration and separation chosen to give horizontal position accuracy
in the light pen detection mode.  This long pulse train is followed
by short pulse trains occurring at line scan frequency identifiable
in pairs separated by the normal flyback time.  These pulse pairs can
provide vertical position accuracy in the light pen detection mode.
Finally the bottom stripe will again give a long light pulse train
which may be redundant or be used to make more accurate horizontal
position selection when correlated with the top pulse train.

      To facilitate light pen detection, it is more desirable to use
fast decay IR phosphors; however, even with long persistent visible
phosphor emission, one can use a two-threshold detection scheme to
determine the horizontal position accurately.  A soft lens with an
appropriate index to match the CRT faceplate can be added onto the
light pen to enhance the signal/noise ratio.

      This concept can also be applied to touch input.  Fig. 2 shows
a touch input scheme where detectors 20 are mounted on the edge of
the CRT faceplate 22 (in principle four detectors at four corners can
easily resolve all positions on the screen).  The light sensed will
be decreased by the finger touching the CRT glass plate by an amount
proportional to d square divided by (x square pl...