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Description  |
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BACKGROUND OF THE INVENTION
This invention relates to entering information into, and displaying
information from a data processor.
One device for displaying such information is the well-known liquid crystal
display (LCD) which has a special liquid crystal material held between two
parallel glass faces. The liquid crystal material temporarily changes its
molecular structure, and thus its appearance, when subjected to an
electrical field. Appropriately shaped transparent electrodes printed on
the glass faces establish such an electrical field in the liquid crystal
material to form a desired image, such as numbers representing the time of
day.
One device for entering information into a data processor is a touch pad on
which the user "writes" either with his finger, a pen, or a special
purpose stylus. Corresponding electrical signals are generated by one of
several techniques, including electromagnetic induction, variable
capacitance, make-and-break switching, or grids of parallel infrared
beams. Some touch pads have soft membrane surfaces which must be depressed
to be activated.
The computer may be arranged so that whatever is "written" on the pad is
immediately displayed back to the user on the computer's CRT display.
Another data entry technique is the light pen which senses the time at
which light appears at a selected spot on a scanned display screen as an
indication of the location of the spot.
SUMMARY OF THE INVENTION
In general, the invention features apparatus for both entering input
information into and displaying output information from a data processor,
and which has imaging means including a plurality of elements each with a
visual characteristic which depends on electrical stimulation of the
element and is visible at a writing surface; the imaging means also
includes conductive means arranged to deliver electrical stimulation to
the elements; the imaging means is arranged to produce electrical
manifestations at the conductive means in response to writing stimuli; and
the apparatus also includes circuitry for delivering electrical signals to
the conductive means to form an image of the output information visible at
the writing surface and for converting the electrical manifestations to a
digital form representative of the input information.
In preferred embodiments the elements comprise a fluid (e.g., liquid
crystalline material) contained between the writing surface and a support
layer parallel to and spaced from the writing surface; the conductive
means includes a pair of electrodes associated with each element in such a
way that the electrical manifestations correspond to changes in
conductance of the element resulting from the stimuli; the writing surface
is a resilient layer which is written on at locations corresponding to the
input information; the conductive means includes sets of row conductors
and column conductors which intersect to define locations corresponding to
the elements; the circuitry includes driver circuitry which scans the row
and column conductors to form the image and sensor circuitry which senses
the electrical manifestations; and the apparatus also includes control
circuitry for interlacing the operation of the driver and sensor
circuitries.
The invention permits entering information and viewing an image
simultaneously at the same writing surface. The device is thin enough to
sit conveniently on a desk top. Information can be entered and displayed
at the same time without flickering of the image.
DESCRIPTION OF THE PREFERRED EMBODIMENT
We first briefly describe the drawings. Drawings
FIG. 1 is an isometric view of a touch pad, partially broken away.
FIG. 2 is an enlarged cross-sectional view (at 2--2 in FIG. 1) of the pad
sandwich of the pad of FIG. 1, not to scale.
FIG. 3 is an equivalent circuit diagram corresponding to a representative
portion of the pad sandwich and related electronics.
FIG. 4 is a block diagram of the control circuitry of FIG. 3.
STRUCTURE
Referring to FIG. 1, touch pad 10 has a large (e.g., 81/2".times.11")
exposed resilient writing surface 12 for writing with a finger or stylus
15.
Referring to FIG. 2, surface 12 is part of a pad sandwich 14 which includes
a flexible, resilient, transparent plastic upper layer 30 spaced apart
(e.g., with a spacing of 5 microns) from and parallel to a flexible
plastic lower layer 32 to define a cavity 34 between them. A conventional
liquid crystal material is held within the cavity by sealing together the
upper and lower layers 30, 32 along the peripheral edges of sandwich 14
(not shown). The flexibility and resilience of layer 30 are such that
pressing at a point on the surface (e.g., 17) will deform layer 30 in a
localized region at the point of pressure, with the deformed region
returning to its original position after the pressing stops. Layers 30, 32
are kept spaced apart either by a matrix of resilient supporting pillars
inserted between them or by selection of a liquid crystal material having
appropriate physical characteristics.
The bottom surface 36 of layer 30 is imprinted (by conventional thin-film
technology) with a series of closely spaced (e.g., with a spacing of
0.005"), parallel, transparent, conductors 38 of a kind conventionally
used in LCD displays. The top surface 40 of layer 32 is likewise imprinted
with a series of closely spaced (e.g., with a spacing of 0.010"),
parallel, transparent conductors 42. Only one conductor 42 appears on FIG.
2. Conductors 42 run along the length of pad 10 and conductors 38 along
its width, thus forming a grid defining a matrix of pixels (display
elements) on surface 12, each pixel being defined by the intersecting pair
of conductors 38, 42 which underlie that pixel. For example, pixel 44 is
defined by a particular conductor 46 of the conductors 38, and a
particular one of the conductors 42.
Referring to FIG. 3, conductors 42 can be viewed as forming rows and
conductors 38 as forming columns in an equivalent circuit diagram. At each
pixel location is shown an imaginary discrete circuit element 50 which
represents the electrical characteristic of a localized path between the
particular row and column conductors 38, 42, associated with that pixel.
The electrical characteristic of each such element 50 is indicated (by
means of an arrow) as variable to reflect the fact that when surface 12 is
depressed at a pixel location, the resulting local physical deformation of
layer 30 with respect to layer 32 will produce a change in the electrical
characteristic. For example, the resulting localized reduction in distance
between layers 30, 32 may increase the capacitance or decrease the
resistance (or a combination of the two) between the associated top and
bottom conductors 38, 42 depending on the materials and physical
construction of pad 10. Whatever its precise character, the electrical
change in the local path between conductors 38, 42, may be called a change
in conductance.
For information display purposes, each row conductor 42 is connected to a
conventional source driver 52 (e.g., type HD44780 or HD44100 available
from Hitachi) for feeding current to the conductor. The source drivers 52
are all connected to control circuitry 54 for selectively triggering
appropriate ones of the drivers 52. Control circuitry 54 is also connected
to a set of conventional sink display drivers 56 (e.g., type HD44100H or
HD44780 available from Hitachi). Each sink display driver 56 is in turn
connected to one of the column conductors 38 for sinking current from the
corresponding conductor when triggered by control circuitry 54.
For information input purposes, control circuitry 54 is also connected to a
set of input sensors 60 (e.g., type MC14049UB available from Motorola).
Each input sensor 60 is in turn connected to one of the column conductors
38 for sensing an electrical value related to the conductance of various
ones of the elements 50 connected to the conductor, such conductances
being indicative of which elements 50 are being subjected to pressure.
Each sensor 60 can be of the type having CMOS inverter gates which detect
whether the sensed voltage appearing across an element 50 as a result of
the pressure of stylus 15 is greater than a threshold voltage of the gate.
Each sensor 60 also includes a voltage comparator circuit (e.g., type
.mu.A3302 available from Fairchild) for allowing the detection of
differential voltage levels, for a purpose discussed below.
Referring to FIG. 4, control circuitry 54 includes a column selector which
accepts bits from particular sensors 60 (indicating which elements 50 are
being subjected to pressure) and delivers display bits to sink drivers 56
(corresponding to an image to be displayed) as dictated by trigger signals
provided from an interlace controller 72. Any output bit from a selected
sensor 60 is passed from column selector 70 back to controller 72. Control
circuitry 54 also includes a row selector 74 which delivers display bits
to source drivers 52 likewise based on trigger signals from controller 72.
Controller 72 interleaves the displaying of pixels of an image specified
by the data processor with the reading of entered information which is
passed back to the data processor, all via line 22.
Referring again to FIG. 1, the source drivers 52, sink display drivers 56,
control circuitry 54, and sensors 60 are all included in electronic
circuitry 18, mounted in housing 16. Conductors 38 and 42 are connected
via leads 20 to circuitry 18.
A cable 22 enables control circuitry 54 to send and receive information
bits to and from the data processor, corresponding to pixels which are to
be displayed or input information which is to be read.
Operation
The pad is capable of simultaneously displaying output information from a
data processor and receiving input information represented by pressure of
stylus 15 at various points on surface 12 (e.g., the points along a line
62, FIG. 1).
Displaying an image is accomplished in the conventional way for LCDs. Each
of the pixels corresponding to the output information is darkened by
establishing an electrical field across the liquid crystal material
between the two conductors associated with that pixel. The field is
established by triggering the corresponding source and sink drivers 52,
56. The field temporarily alters the molecular alignment of the liquid
crystal material at the pixel, causing it to appear darker. An entire
image is generated by rapidly triggering in succession (that is, scanning)
the appropriate sink display drivers 56 while one of the source drivers 52
is triggered, then repeating the process while another one of the other
source drivers is triggered, and so on. By repeating the scanning process
(refreshing the image) at a high rate of repetition, the image is seen
without interruption.
Because the number of pixels defined by conductors 38, 42 is large, the
time required to refresh a displayed image is likely to be long.
Furthermore, the refresh cycles must follow each other with little
intervening dead time to produce a flicker-free image. As a result,
insufficient time may be available between refresh cycles to completely
scan all elements 50 to determine which, if any, are being subjected to
pressure by stylus 15. Instead controller 72 concurrently interlaces the
displaying of pixels 44 with the reading of elements 50 in order to
accomplish both in about the same time that would otherwise be required
for displaying alone.
The concurrent interlacing is accomplished as follows. First a given row
conductor 42 is activated by triggering the corresponding driver 52. While
that row conductor 42 is activated, each sensor 60 is triggered in turn to
read the elements 50 along row conductor 42. If a pixel 44 is also to be
displayed at the same intersection between the active row conductor 42,
and the column conductor 38 associated with the triggered sensor 60, then
the corresponding sink driver 56 is triggered at the same time; if that
pixel is not to be displayed, that corresponding sink driver is not
triggered. Sensor 60 is arranged to sense pressure at the element 50
corresponding to that pixel whether or not that pixel is simultaneously
being displayed. If that pixel is being displayed, the field used to cause
the display may itself induce changes in the conductance of the
corresponding element 50 similar to the changes produced by pressure on
that element. In that case, the output of the source driver 52 is then
used as an input to the voltage comparator circuit of sensor 60 to offset
the effect of the drive voltage, thus permitting the sensor to detect that
element 50 is being pressed.
Once all elements 50 have been scanned, the cycle is repeated.
The displayed information can be the same as, or different from, the input
information. When the displayed and input information are the same, the
pad allows the user to see immediately on the pad what he has just
written. The device is thin enough to sit conveniently on a desk top with
the writing surface facing up. Information can be entered and displayed at
the same time without flickering of the image.
Other embodiments are within the following claims.
For example, the interlacing can be accomplished by an offset technique in
which the triggered sensor 60 is in the adjacent column to the column in
which the sink driver 56 is potentially triggered. In that case, the
sensors 60 will always be sensing elements 50 corresponding to undisplayed
pixels. However, the total scanning time required for both image
displaying and reading will be one column longer in duration for each row
scanned because of the offsetting of the reading and displaying
operations.
The multiple sensors 60 could be replaced by a single sensor connected via
a multiplexing switch (e.g., type MC14051B available from Motorola) to
each of the columns to be sensed. The multiplexing switch would then be
controlled by control circuitry 54.
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