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BACKGROUND
1. FIELD OF THE INVENTION
This invention relates generally to practical
display units for electronic directories and like electronic
tabulations for public viewing; and more particularly to a
display unit for an electronically controlled directory that
employs a liquid-crystal display.
2. PRIOR ART
Directories are commonly posted in the public
lobbies of business buildings, apartment houses, multiple-
building condo-
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t' minimum complexes, and other multiple-occupant facilities. In
2 secured facilities, the entries in such directories often
include room or suite numbers, or other numbers for use With an
4 adjacent telephone or intercom in contacting individual occu-
pants to gain admission.
In a few large facilities, in recent years, hand-lettered
or movable-letter directories have given way to electronic
systems that are much easier to revise. Such systeAS eliminate
tedious manual reshuffling of placards or letters to keep
entries in alphabetical order and to accommodate subdivision or
11 consolidation of occupant suites.
12 Although they are an enormous improvement over manual
13 directories, the electronic systems have suffered from a major
14 limitation in their use of cathode-ray-tube (CRT) display
units. Such video display units, in the forms currently
t6~ encountered in commercial practice, have several well-known
drawbacks.
The drawbacks of CRT displays include image instability,
poor resolution and (particularly in bright light) poor con-
trast. Instability of the image, ranging from minor flicker to
21 , vertical roll, can make reading the information on the screen
22 difficult.
23 Poor resolution severely limits the number of entries that
24 can be displayed simultaneously on a screen of moderate size.
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This strategy sometimes leads to very large screens that
2 visually dominate a lobby.
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tive, because the CRT or video colors inject an incongruously
gaudy element into a fine decor.
CRT displays are particularly troublesome in
brightly lit environments such as outdoors and in lobbies
surrounded by large windows that admit brilliant sunlight. In
these circumstances, contrast can be so inadequate that the
displays are almost completely unreadable.
Moreover, CRT displays are relatively expensive. In
large formats they are too deep (front to back) for
straightforward mounting in a wall -- and so require provision
of a free-standing or recessed support structure enclosure two
or three feet deep. Because of their evacuated-chamber
construction, they are also relatively fragile and
inordinately subject to vandalism.
Other display types -- light-emitting diode (LED)
and liquid-crystal displays (LCD) -- are known for use with
electronic information processors. Before introduction of our
directories disclosed earlier, LCD displays were not effective
or in common use for directories or other large electronic
tabulations for public viewing; we shall explain some reasons
for this shortly.
Most LEDs require relatively bulky apparatus for
each character to be displayed. Furthermore LEDs are quite
dim, and in the few very-small-screen outdoor applications
where they have been used (such as some automatic-teller
machines)
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they are extremely hard to read -- even when elaborately
2 shaded. A larger LED array such as required for a directory
3 would be prohibitively difficult to shade effectively and would
be inordinately expensive.
Under ideal conditions, liquid-crystal displays are capa-
6 ble of excellent contrast and resolution, are plainly readable
even in the brightest light, and are readily backlighted for
nighttime use. Their use also results in a far less expensive
and much more compact product package. LCDs are accordingly
excellent for directories and the like, and the LCD directories
11 disclosed in the above-mentioned parent applications have been
12 very successful; but LCDs do have important limitations.
13 An LCD has a display medium -- the liquid-crystal fluid
14 itself -- and a structure which contains the fluid. Tn at
least some commercial LCDs this structure typically includes
16~ two planar pieces of material with the medium sandwiched
between them. At least the piece on the viewing side of the
sandwich, which in this document we will call the LCD "face,"
19 ordinarily is transparent glass or plastic.
Electrodes are formedon the opposed interior surfaces of
21, this sandwich. These electrodes too are ordinarily transparent
22 on at least the a a side. One elecErode material is intrinsic
23 tin oxide.
24 Both the fluid glass are very sensitive to temper-
and the
ature. (It may be recalledthat the early applications of
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1 liquid-crystal displays were as novelty items, particularly
including thermometers.)
3 If the temperature of the glass rises beyond certain
4 relatively narrow limits, the display develops dark spots, or
the entire display may actually turn dark. As we understand
6 it, this darkening is due to an expansion of the cell gap
7 within the glass. The black characters or other symbols then
8 fail to stand out well against the darkening background.
On the other hand, if the temperature falls too much, the
changing of characters begins to be very slow, an effect which
11 is said to be related to increasing viscosity of the medium.
12 As temperature decreases further the display blushes a differ-
13 ent color (e-, pink) -- this time due to contraction of the
14 cell gap -- and again becomes unreadable.
Directory applications would call for use of the larger
16~ graphic LCDs, and also for a type of medium known as "super-
17 twist" fluid. This kind of fluid provides far superior con-
18 trast and hence significantly better readability. The large
19 LCDs, however, and especially those using supertwist fluid, are
particularly sensitive to temperature.
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temperature-sensitive. LCD wristwatches also take advantage of
2 the wearer's limited temperature tolerance, and heat conduction
3 to and from the wearer's body, to limit the severity of temper-
4 atures to which the display is exposed.
Even under such relatively protected conditions, fading
6 and blushing of wristwatch displays is well known to athletes
and workers whose activities reach the anticipated design
8 limits of the watches.
LCDs are also used for many usually indoor applications
such as calculators and laptop,computers. Here too they are
11 typically used in temperature-controlled environments, or if
12 they are found to malfunction can generally be moved into such
13 environments.
14 Operation of large LCDs is subject. to temperature problems
in lobbies and other indoor entryways, as well as outdoors, if
16~ the locations receive intense sunlight. Temperature rise in
11 such areas sometimes outstrips the capabilities of a building
18 air-conditioning system, and can be severe enough to degrade
19 the performance of an LCD.
If the LCD is inside a case, and protected from vandals by
21, an unbreakable window, as is desirable in our application, the
22 temperature problem can be aggravated much further. This is
23 due to a "greenhouse" effect, in which air trapped between the
24 window and the LCD becomes extremely hot, much like the interi-
or of a car left shut on a hot day.
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A related problem of LCD temperature sensitivity
involves a voltage that is applied to the display medium to
control the contrast of the characters relative to the
background screen. The necessary voltage for proper contrast
varies very strongly and nonlinearly with temperature.
Thus, as the temperature to which the LCD is exposed
changes (e-q., between day and night), the LCD contrast
requires constant adjustment to prevent characters from
disappearing or otherwise becoming illegible. A very
nonlinear relationship between the voltage and the temperature
renders the problem of automatic contrast-control technique
far from straightforward.
For whatever reason, LCDs were not used in sizable
directory-type displays before introduction of our own earlier
units. Those units in fact dealt very effectively with all
the problems described above, and those described in the
following paragraphs of this section as well; and were
accorded a most favorable commercial reception.
They have, however, left some room for further
refinement in that they require cooling fans and power to
drive the fans. Our earlier units also require relatively
expensive case construction to provide effective ventilation
fans, plena and holes while deterring vandalism and theft.
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1 The use of ventilation fans also draws dirt into the case
with the ventilating air. Flow of dirty air through the unit
produces an objectionable accumulation of dirt on the inside
4 surface of the window and on the LCD face, a particular annoy-
ence near construction sites.
Moreover, because of significant temperature gradients
7 within the case, in our earlier units, we found it necessary to
position in the LCD-face region -- just inside the window --
9 the temperature sensor needed to develop a temperature-compen-
sating voltage for contrast control. This required relatively
11 costly and awkward cabling to the sensor from the circuit board
~2 at the rear of the display-unit case.
14 We will return now to more general discussion of electron-
is directories and the like.
16~ Another problem arises in configuration of such devices
11 when outdoor or bright-lobby applications are involved. That
18 is the problem of controlling reflections at glass or plastic ,
19 surfaces of the display unit.
Such reflections of the viewing person -- and of objects
21. around. and behind that person, become confused with the dis-
22 played characters, making the display very hard to read. When
23 sufficiently bright, these reflections actually obscure the
24 displayed characters.
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1 ' As a verbal shorthand we shall refer to these confusing
2 and obscuring reflections collectively as "glare." Such glare
3 can be controlled to a certain extent by providing a matte
4 finish on the screen itself, provided that the electronic
display screen (such as a CRT screen) is directly exposed to
6 the viewing person. Direct exposure of the display screen is
7 accordingly a conventional teaching of the prior art.
This conventional teaching, however, severely limits the
9 use of electronic directories since it makes them susceptible
to vandalism. Direct exposure of the display screen makes it
11 easy for a vandal to break the screen or damage the display
12 unit.
13 Hence there is a conflict between the direct exposure
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that is reflected at a glass or plastic surface, however, is
light not used to develop visible LCD characters -- and, in
fact, is light that creates reflections which compete with the
already diminished LCD characters.
Thus, again, even if there had been a suggestion of
LCD use in electronic directories, such a suggestion would
have been particularly likely to meet with immediate rejection
in view of the relatively adverse glare-related properties of
LCDs.
Our own earlier units, resolved glare problems
satisfactorily by use of coatings applied to the window as
well as the face of the LCD display. Again, this solution to
the glare problem was found entirely satisfactory except for
the cost of the coatings.
Finally, even though the electronic directory
systems currently available are far more convenient in terms
of entering and deleting names than the movable-letter or
placard directories, before introduction of our units they
still required local procedures for entries or revisions --
either at the system itself or through a computer close by.
This arrangement was very inconvenient for buildings with off-
site property management, especially when tenant turnover was
high and frequent directory changes required.
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All of the above limitations resulted in the relatively
limited use of electronic directories before the advent of
commercial units corresponding to our inventions. As can now
4 be seen, the prior art failed to provide an adequate display
system for directories and the like, particularly for use out
6 of doors and in lobbies or other entryways subject to intense
sunlight.
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concave instrument-panel window, with a small overhang of the
instrument panel that shades the window from steeply inclined
rays of direct sunlight. If the driver's eyes are in a
relatively narrow range of positions evidently contemplated by
the system designers, such a window reflects the inside of the
overhang, rather than the driver's own image, into the
driver's eyes.
In practice, however, as used in automotive
applications the curved window works only if the driver's eyes
are in rather exactly the design position -- as to both height
and fore/aft distance -- behind the steering wheel. If the
driver sits too far forward or sits too tall, relative to
design expectations, the driver's view of the instruments is
confused by superimposed parts of the driver's own image, or
light from the sky or objects behind the driver.
viewers of directories are not subject to standing
or sitting in such a constrained fashion. Accordingly the
glare-elimination problem is substantially more severe in
relation to directories.
SUMMARY OF THE INVENTION
The invention provides a display unit for an
electronic directory that is exposed to sunlight; said display
unit comprising: a case including a front wall; a liquid-
crystal display mounted within the case and comprising a face
for displaying directory information in the form of a
directory; an aperture defined in the front wall for viewing
the display face; a hood mounted to the front wall of the
case, extending outward therefrom at the aperture and
dimensioned to shade substantially the entire aperture from
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sunlight at midday; said hood having an undersurface; an
external window mounted to the case to protect the liquid-
crystal display; said window being shaped, disposed and
oriented to reflect into a viewer's eyes substantially only
the undersurface of the hood, if the viewer looks at the LCD
from in front of the LCD; and solid-state digital electronic
circuitry, electrically interconnected with the liquid-crystal
display, for electronically storing directory information and
for controlling the liquid-crystal display unit to
automatically exhibit stored directory information in the form
of a directory having multiple listings in an alphabetical or
like order or in classified groupings.
The invention also provides a display unit for an
electronic directory that is exposed to sunlight; said display
unit comprising: a case including a front wall; a liquid-
crystal display mounted within the case and comprising a face
for displaying directory information in the form of a
directory; an aperture defined in the front wall for viewing
the display face; a substantially cylindrical window mounted
to the case at the aperture to protect the liquid-crystal
display; a hood mounted to the front wall of the case,
extending outward from the front wall of the case beyond the
center of curvature of the substantially cylindrical window;
and solid-state digital electronic circuitry, electrically
interconnected with the liquid-crystal display, for
electronically storing directory information and for
controlling the liquid-crystal display unit to automatically
exhibit stored directory information in the form of a
directory having multiple listings in an alphabetical or like
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order or in classified groupings.
The invention further provides a vandalism-resistant
display unit for an electronic directory, comprising: a
substantially vandalism-resistant case including a front wall;
a liquid-crystal display, mounted within the case, and having
a display medium and a structure for containing the display
medium; the liquid-crystal display structure comprising a face
disposed in front of the medium, for displaying directory
information outdoors in the form of a directory; means for
protecting the liquid-crystal display against vandalism and
for maintaining the temperature of the liquid-crystal display
medium and structure between practical operating limits for
the display, notwithstanding ambient temperature and humidity
variations over generally normal ranges for at least the
temperature zones, and even if the display unit is placed to
receive direct sunlight when the sun is out; the protecting
and temperature-maintaining means comprising: an external
window mounted to the case in the front wall to protect the
liquid-crystal display, and means for reducing glare from the
window and reducing solar heat loading into the case through
the window, said glare-and-heat-loading reducing means
comprising: (i) a hood mounted to the front wall of the
case, extending outward therefrom above the window, and
dimensioned to shade substantially the entire window from
sunlight at least at mid-day, said hood having an underside,
(ii) configuration of the window in a curved shape, generally
concave upward and outward, to reflect into a viewer's eyes
only light from the underside of the hood, if the viewer looks
at the LCD from in front of the LCD; and solid-state digital
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electronic circuitry, electrically interconnected with the
liquid-crystal display, for electronically storing directory
information and for controlling the liquid-crystal display
unit to automatically exhibit stored directory information in
the form of a directory having multiple listings in an
alphabetical or like order or in classified groupings.
Generally throughout this document including the
appended claims we intend such phrases as "shade from
sunlight", "reflect all sunlight", "receives no reflected
sunlight" etc. to refer only to rays of sunlight received
directly from the sun in primary straight-line paths.
Further, by phrases such as "reflect all sunlight" and
"reflected sunlight" we refer only to specular reflection of
that directly received sunlight.
Of course sunlight approaches our apparatus not only
directly but also by reflection from the ground and from
nearby buildings, plants and people -- and even from the sky.
Furthermore the transmissive window of our apparatus, like
every surface (even a mirror surface) scatters much light as
well as reflecting specularly. Except where otherwise clear
from the context: (1) from our references to sunlight we
explicitly exclude light thus approaching indirectly; and (2)
from our references to directions of reflection we explicitly
exclude
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1 We regard these two properties of the window as mutually
2 independent, in accordance with correspondingly independent
claims appended hereto. As will become clear, however,Ithese
4 two aspects of the invention are amenable to being practiced
together, and we do prefer to practice the invention with both.
6
The foregoing may be a description or definition of the
present invention in its broadest or most general terms. Even
in such general or broad forms, however, as can now be seen the
invention resolves the previously outlined problems of the
11 prior art.
12 In particular heat loading is substantially eliminated
13 because the direct rays of the sun are entirely deterred from
14 striking the window at least at midday when heat loading is of
primary significance. At those times, the window directly
16~ receives substantially no sunlight to reflect.
At other times, direct sunlight can strike the window, but
18 at those times sunlight is not as intense. Moreover, much of
it is reflected outward from the window rather than being
admitted to the case.
21 We have tested units in accordance with our invention in
22 desert temperatures up to 46 'C (115' F), and with no ventila-
23 tion fans or even ventilation holes. Remarkably, in these
24 tests there was no blush of the LCD display.
17
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In addition we have found that with this system the
temperature distribution within the case is more homogenous, to
such an extent that we can reposition -- onto the circuit board
4 at the rear of the case -- the temperature sensor that is used
to develop a temperature-compensated voltage to control the
6 LCD. This repositioning allows us to eliminate the previously
required costly and awkward cabling between the circuit board
and the LCD-face region.
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images. Using a substantially cylindrical-form window has at
2 least one and possibly two further advantages:
First, it can be shown geometrically that with a suitably
4 oriented cylindrical-segmental window it is possible to virtu-
ally guarantee -- subject to some qualifications that will be
6 presented in a later section of this document -- that a viewer
7 who looks at the LCD from in front of the LCD can see only one
8 reflection: that of the undersurface of the top section of the
9 hood.
To obtain this condition, if the window at its top edge is
11 substantially tangent to the front wall of the case: (1) the
'12 top section of the hood should be made to extend outward from
13 the front wall of the case beyond the center of curvature of
~4 the cylindrical segment that is the window -- or in other
words, the hood top section should extend from the front wall
of the case by a distance just greater than the radius of
curvature of the window -- and (2) that radius should be equal
to the sum of the squares of the viewing-aperture height a_ and
bottom hood-section length b, divided by twice the latter
length: (as+ bs)/2_b.
(By "suitably oriented", however, we do not mean to imply
22 that the window at its top edge must be substantially tangent
23 to the front wall of the case. To the contrary, the desired
24 effect can be obtained with a shorter hood if the upper edge of
the window is canted back to a nonvertical orientation; howev-
19
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er, this solution does tend to restrict viewing from lower
2 angles.)
We do prefer that the hood extend outward by at least the
4 window radius, and as will be recalled this is part of the
second independent major aspect of the invention. This condi-
tion optimizes the efficacy of glare reduction by intercepting
at the hood undersurface rays corresponding to the reflection
of the viewer's line of sight.
Although this condition is easily satisfied, we have
discovered that the limitations of the glare-reducing curved
11 window in automotive applications are due to failure to observe
12 this requirement. When the hood is not long enough, light from
13 the sky above the viewer's head is more readily reflected into
~4 the viewer's eyes if the viewer's head is not precisely in the
~5 design position; and this is just what happens in the automo-
tive situation.
The second, or possible second, advantage of cylindrical
windows relates to another geometrical property: very general-
ly speaking, a cylindrical window tends to reflect sunlight
20 incident on the window to certain portions of the hood under-
2~ surface, and tends to reflect the viewer's gaze to different
22 portions of the hood undersurface. As will be shown later,
23 this selectivity is not absolute, rather being variable with
24 time of day, height and position of the viewer, and portion of
25 the LCD display being viewed.
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Nevertheless these phenomena are present and significant
2 -- and tend to make the viewer's lines of sight congruent, by
reflection at the window surface, with portions of the hood
4 undersurface that are not strongly illuminated. The less
strongly illuminated are superimposed reflections from a
6 window, in general, the less confusion with objects viewed
7 directly by transmission through the window.
As a practical matter, we are not certain just how much
advantage is conferred in this way, because our invention works
very well even without this effect. More specifically, at
least if the hood undersurface is a dark color and not reflec-
12 tive, even brightly illuminated portions do not ordinarily
13 cause significant -- or usually even noticeable -- confusing
~4 reflections.
~5 It is possible, however, that under special circumstances
a further important improvement in glare reduction may result
from this differentiation between areas of the hood that are
strongly illuminated and areas that are reflected into the
19 viewer's line of sight. In particular the benefits of this
effect may be important if the hood undersurface becomes very
21. dusty (particularly if the dust is light in color), or if the
22 site is subject to incidence of sunlight at very shallow angles
23 (as when no building, tree etc. is present to block the light
24 from the rising or setting sun).
21
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1 We are not scientists and cannot fully assess the practi-
2 cal significance of all the theoretically available benefits of
our invention. We have found, however, that it works and it
4 works well.
Although the invention in its broad general forms as
7 described above thus provides very significant advances rela-
8 tive to the prior art, nevertheless for greatest enjoyment of
9 the benefits of the invention it is preferably practiced in
conjunction with certain other features or characteristics
11 which enhance its benefits. For example, we prefer that the
12 display unit further comprise a glare-reducing material applied
13 on the liquid-crystal display (but not on the window).
14 With respect to the invention in its above-mentioned
" ' st aspect" -- which is to say, characterizing the invention
16~ simply in terms of reflecting to the viewer only portions of
the underside of the hood -- we also consider it preferable
18 that the window be curved. A planar window can be used, but a
19 curved window is preferred because the hood length can be
relatively shorter, the window itself is mechanically stronger,
21 , and more importantly the readability of the display unit is
22 extended to lower viewing angles.
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window be substantially vertical, in otherwordssubstan-
or
2 tially tangent to the front wall the case.The bottom of
of
3 the window is thus projected outwardfrom planeof the
the
4 front wall.
Preferably the hood structure too is extended outward from
6 the bottom of the aperture (or if preferred from some point
below the bottom of the aperture) to meet and support the
8 bottom of the window. Side panels of the hood structure
interconnect and stabilize the top and bottom hood sections,
and also provide surfaces for holding the window in place.
For best resistance to vandals, we prefer to configure the
~2 hood in a strengthening folded rectangular form, using stain-
13 less steel, with an internal curved track or retainer on each
~4 of the inward-facing lateral panels to hold the window. We
prefer to make the window of Lexan'" -- a brand of extremely
16~ tough polycarbonate -- heat-formed to the desired curvature
described above. The folded steel hood and curved Lexan window
18 mechanically reinforce each other very effectively.
Whether the window is cylindrical or not, we consider it
preferable that the window reflect:
21
22 - substantially all directly received sunlight upward and
outward to the hood, and
24
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1 - a viewer's own image upward and outward to the underside
2 of the hood (rather than back toward the viewer), and
4 - outward to a viewer only light from a portion of the hood
that receives no reflected sunlight near midday.
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In addition, preferably the underside of the hood -- what
the viewer sees due to reflection at the window -- is a very
dark color, ideally black, and has a matte finish or is other-
1U wise given minimum reflectance. The surface in any event
11 should not be not bright enough to make its reflection at the
12 window noticeable, in comparison with the LCD characters seen
13 through the window.
14 As already suggested, we prefer to retain the use of a
15 temperature sensor, as in our earlier units, for monitoring the
temperature of the LCD medium to permit automatic adjustment of
the LCD contrast-control voltage. Because temperature varia-
tion within the case is greatly reduced by our present inven-
tion, however, as mentioned above the sensor now can be located
20 directly on the electronics circuit board, thereby rendering
21. the apparatus simpler and less costly.
22 The sensor controls the contrast-control voltage through a
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23 voltage-adjusting circuit that includes an analog-to-digital
24 ("A/D") temperature-conversion stage and a digital electronic
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memory. This memory holds a lookup table for establishing
2 desired contrast-control voltages for various temperatures.
3 After some experimentation we have come to prefer this
system because the voltage requirement varies strongly with
temperature, particularly toward the extremes of the tempera-
6 ture operating range, and is difficult to represent in closed
form as by a formula. We prefer to include A/D conversion of
temperature because representing the voltage-temperature
relationship with an analog circuit is relatively difficult and
expensive.
» Because that relationship is difficult to represent in
~2 closed form as by a formula, we prefer to use a look-up table.
~3 This approach has the added benefit of allowing us to easily
change the relationship to account for differences in display
~5 lots or even different displays we might subsequently use.
We also prefer to provide a heater for raising the LCD
temperature, and to provide "heater-controlling means" for
operating the heater only when needed. The heater-controlling
means are also responsive to temperature.
20 The LCD face may be guarded against glare by either a
2~ matte finish or an antireflection coating as suggested in our
22 previous applications. For this purpose we now prefer a matte-
23 surfaced film with a multilayer antireflection coating, avail-
24 able from Optical Coating Laboratories Inc., Santa Rosa, Cali-
25 fornia as its type HEA2000.
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1 Fig. Z is an interior side elevation, partly in section,
2 of the Fig. 1 embodiment of the invention;
3 Fig. 2A is a like elevation showing geometrical construc-
4 tion lines representing various light rays related to the
glare-reduction and heat-load-reduction characteristics of the
invention;
7 Fig. 3 is a front elevation of the same embodiment;
Fig. 4 is a block diagram of the programming processing
flow for the system and shows the different programming devices
that can be used along with the major electronic components
11 used to process their input'; and
12 Fig. 5 is a picture of our handheld programmer -- one of
13 the devices used to program the system manually at the system.
14
16~ DETAILED DESCRIPTION OF TfIE PREFERRED EMBODIMENTS
17
18 As seen in Figs. 1 and 2, the preferred embodiment of our
19 display unit has a case 101 that includes a front panel 107.
The case 101 also includes a rear wall 103, left and right side
21 walls 104, 105, a ceiling 106, and a floor 107. We prefer to
22 make the front panel stainless steel and the case painted cold-
23 rolled steel.
24 The front panel 102 is hinged to the right wall 105, and
provided with a keyed lock 107 that engages a strike groove
27
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1 formed in the left wall 104 to secure the front panel firmly
2 against the rear parts 103-106 of the case. Formed in the
3 front panel 102 are a viewing port 111, louvres 112 and an
4 array of twelve small square access holes 113, a small hole 114
and a larger hole 115.
The louvres 112 are provided for transmission of sound
from an audio speaker 203 (Fig. 2) that is mounted behind the
8 front panel 102. The square access holes 113 accommodate
9 twelve pushbuttons of a standard telephone-type pushbutton
array 116. The small hole 114 allows for transmission of sound
11 to a microphone 204 (Fig. Z) that is mounted directly behind
12 the hole. The larger hole 115 is for installation of a post-
13 office key lock. If this lock is not used, a plug fills the
14 hole.
The hood structure 131 projects forward (from the front "'
16~ wall 102 of the case) at the bottom of the window aperture 139,
17 as well as at the top. Fig. 1 shows that the top and bottom
18 hood sections 132, 133 are interconnected by tapered side
1,9 panels 134, 135 for strength and some exclusion of laterally
approaching ambient light.
21 . Securely mounted in tracks 136 carried on inward-facing
22 lateral surfaces 134, 135 of the hood 131 is the polycarbonate
23 viewing window 117, which carries no antireflection coating.
24 Behind the window 117 is an LCD 120, preferably six to eighteen
rows of twenty-six to forty characters each. A bezel 137
28
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1 inside the case, within the boundary of the viewing aperture
2 139, guards the edges of the LCD face 120. The bezel, integral
3 with the LCD, wraps around the top, bottom and sides of the LCD
4 and accordingly is seen face-on in Fig. 2 as well as Fig. 1.
As previously explained, the window 117 is preferably
6 curved -- and more specifically concave upward and outward, and
7 preferably substantially cylindrical -- to reduce "glare" (as
8 defined above) sufficiently that the LCD 120 can be read. The
9 latter function is particularly important when the LCD is
facing away from the incident sunlight.
11 When that is so, the person attempting to read the LCD is
12 facing into the sun, and is brightly illuminated. Under these
13 circumstances the reflected image of the person's own face and
14 surroundings, as would be seen in a generally an window,
could be extremely bright and could almost.totally obscure the
16~ LCD. (In our earlier units this problem was overcome by
17 provision of an antireflection coating.)
18 As to the detailed geometry of the hood (and window), our
19 research revealed a family of different solutions. These can
be described using the assumption that the window 117 should be
21 substantially vertical at its top edge 119. We believe that
22 this assumption tends to minimize the size of the window and
23 the hood.
24 As one extreme solution (not illustrated), the top section
of the hood can be minimized in length by making the top and
29
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1 bottom sections (corresponding to 132, 133 in the illustrated
2 embodiment) equal in length, and selecting a window curvature
3 that brings the outward bottom edge of the window into tangency
4 with the bottom section of the hood. This solution is objec-
tionable in that the bottom characters of the display would not
6 be readily visible to people whose eyes would be at a low level
7 relative to the display.
That includes not only children and other relatively short
people, but also wheelchair users, automobile drive-up directo
ry users, etc. Furthermore, even for users who would be able
11 to look directly into the device -- for example, along an ;;.<
12 essentially horizontal line of sight -- the equal lengths of
13 top and bottom sections would produce a sort of tunnel effect
14 that would be unpleasant.
At the other extreme, in purest mathematical principle the
16~ window would be entirely flat (radius of curvature infinite),
the bottom section of the hood zero length, and the top section
18 accordingly of infinite length. Of course a hood of great
length would be impractical or at least very uneconomic.
An intermediate solution of optimum economics can be
21, selected using certain other needed input parameters: (1) the
22 aperture height a of the display to be used, (2) the vertical
23 and horizontal distances from the bottom edge of the case
24 aperture to the bottom line of characters of the display, and
(3) the assumed vertical and horizontal distances from that
~~ii~~3~
1 line of characters to the lowest eye position which is to be
2 accommodated.
3 Items (2) and (3) suffice to permit straightforward
4 calculation of the greatest permissible bottom-section length _b
of the hood. That distance _b in conjunction with item (1), the
aperture height a_ -- and the assumption of window verticality
at the top of the aperture -- permit similar calculation of the
8 radius of curvature of the window using the formula presented
9 earlier.
That radius in turn yields the forward extension of the
11 top section of the hood: the hood length should be just
12 greater than the radius, or to put it another way the top
13 section 132 of the hood extends just beyond the center of
14 curvature 118 (Fig. 2A). As will now be clear, different
display sizes and different installation arrangements call for
16~ different window curvatures and thus different hood configura
tions and sizes.
18
19 We shall offer next a discussion of the selective reflec-
tion effects mentioned earlier in this document. As stated in
21 . that discussion, we are not yet certain how important these
22 effects are in practical operation of our invention.
23 Fig. ZA shows that very steeply angled rays 141 of direct
24 midday sunlight either are captured by the hood top section 132
or miss the apparatus entirely. Rays 142 incident near midday
31
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1 rays from the LCD (but not necessarily through the topmost part
2 of the window from the bezel) will be confused only with light
3 reflected from relatively rearward regions 154 of the hood
4 underside 132. We give that surface a black matte finish so
that most of the illumination that does reach those rearward
regions 154 is absorbed, and much of the small residual is
scattered omnidirectionally -- so that very little light is
8 scattered from area 149 within the pencil 153, 152 to compete
9 with rays 151 from the LCD.
Thus for a viewer looking horizontally at the center of
11 the LCD, glare is substantially eliminated. It is also readily
12 seen from study of the drawing that there is no angle of view,
13 for any eye position outside the hood, Lhat allows specular
14 reflection at the window into the viewer's eyes from the sky or
any other background source
16~ It remains to consider whether there is any angle of view
at which information in rays from the LCD can be confused by
18 light reflected from the most intensely illuminated forward
19 portions 145 of the hood undersurface 132. Because the hood
24 top section 132 extends just beyond the window center of curva-
21 , ture 118, and in specular reflection the incident and reflected
22 rays form equal angles about the radius to the point (or in
23 this case line) of reflection, the brightest reflected illumi-
24 nation -- ordinarily occurring at midday -- strikes the under-
side of the hood just behind the center of curvature.
33
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1 In order for the viewer's eye to receive, by reflection
2 from the same surface, light from that most-intensely illumi-
3 nated region, the viewer's eye would have to be positioned
4 along the path of incidence -- which is to say, with the ..;,4,..w
viewer's head partially within the hood. If the viewer is in
that position, the viewer's head will obstruct much or all
(depending on the width of ,the display) of the incoming sun- , -
light under'consideration; and to the extent that any incoming
sunlight remains troublesome the viewer will perceive that this
situation can be eliminated by moving just slightly away from
11 the apparatus.
12 At times ear midday, when incoming sunlight is intermedi-
13 ate between the illustrated steep and shallow paths 142 and
14 146, that light is reflected to generally forward-to-intermedi-
ate regions of the hood. If the viewer in position 161 of Fig.
16~ 2A looks at the forwardmost lower edge of the window, the
17 viewer may be able to see some of those regions'; however, that
part of the window will appear to be be ow the bottom edge of
the LCD, and therefore will not make any part of the LCD hard
to read.
21 As the viewer in position 161 looks instead at the bottom
22 edge of the LCD, through the point marked 155 in the drawing,
23 the point along the hood which is imaged in confusion with the
24 LCD is shifted rearward of the area that is illuminated by
reflected sunlight. If the viewer looks at any portion of the
34
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1 Resulting dimensions for our most highly preferred embodi-
ment, which we believe makes an ideal working tradeoff for
various field applications, appear in a tabulation several
4 paragraphs below.
Our earlier units employed six metal extenders, spaced
along the top and bottom edges of the viewing port, to stand
the LCD off from the rear surface of the front panel and
9 thereby define an air space between the viewing window and the
LCD. This provision was satisfactory except for the relatively
11 small additional or differential cost of, making the case deep
12 enough (ie., large enough in the front-to-back direction) to
13 accommodate this space -- and the corresponding cost of accom-
14 modating the case with this added depth. If desired the case
may be made shallower to exploit the potential saving that
16~ results from eliminating the air-space requirement in accor-
dance with the present invention.
~;1=ii~~~~
1 we believe that an LCD with a different bezel or no bezel could
2 serve as well.
3 The display can be operated from a microprocessor or even
4 a personal computer or other microcomputer, in very generally
conventional fashion. We prefer, however, to use novel elec-
6 tronics and software which we have developed. These additional
subsystems optimize the performance of the display as part of a
8 novel programmable electronic directory system, as will be
9 described shortly.
Mounted to the system circuit board (rather than immedi-
11 ately behind the window as in prior forms of our apparatus) is
12 a thermistor element 123. As in our earlier apparatus, this
13 thermistor is excited and monitored by portions of the elec-
14 tropic circuitry 211 within the case 101, and the resulting
temperature information is used to control the LCD contrast
16' voltage.
A small strip.heater 212 is advantageously mounted behind
18 the LCD 120. Also as in our earlier units, this heater too is
19 temperature-controlled but need not be made responsive to the
thermistor 123. The heater element itself is self regulating:
21. its resistance increases with temperature, tending to reduce
22 heat output. The heater can be a twelve-volt d. c. model CDH
23 00310 commercially available from Midwest Components, Inc. of
24 Muskegon, Michigan.
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Approximate dimensions of the
apparatus are collected
2 below.
3 ~m nches
4
case 101 height 53~ 21
width 42 16.5
7 depth 11 4.3
8
port 111 height 17~ 6.9
' width 27,~ 10.8
11
12 window 117 height (when
13 flat) 18 7.1
14 radius of
curvature 21 g,3
16~ width 27 10.6
17 thickness 0.3 0.13
18
19 hood width 27 10.7
height 17~' 6.8
21 depth 21 8.3
23 Thus our inve ntion encompasses
several important
innova-
24 tions relating provision of a high-resolution,
to high-con-
trast, essentiallyglare-free display electronic directo-
for
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ries and the like. It is particularly advantageous in outdoor
installations, and in building entries or lobbies where temper-
ature and brightness of illumination are not well controlled.
4
Our invention further encompasses important innovations in
a programmable electronic directory system. These innovations
will be described herebelow.
s;._I..1 ~~cl~
1 Figure 4 gives an overview of the
programming processing
2 flow and shows the different programming devices that can be
3 used along with the major electronic components used to process
4 their input. Local programming is generally done using a
handheld programmer of our own design (pictured in Fig, 5)
6 which plugs directly into the system electronics via ribbon
cable. The programmer is an alphanumeric membrane keypad that
8 simply provides contact closure output. As a result, it is
9 extremely rugged, very thin, small sized, and very inexpensive.
As can be seen from the graphics on the keypad, it as well
11 as our system can do substantially more than provide for an
12 electronic directory. In one of its forms, the system can be a
13 complete access control system providing for both occupant and
14 visitor access control, using card or code entry for occupants
and telephone entry for visitors. In this system configuration,
16~ the electronic directory would normally be part of the tele-
phone entry function for visitor access control. The microphone
18 and the speaker are for communications between the visitor and
19 the person being contacted in the building whose name is listed
on the electronic directory. This system configuration is,
21 however, only one form in which the electronic directory could
22 be used and in no way is intended to limit the scope of our
23 claims.
24 The 12-button keypad, which also provides simple contact
closure output, can also be used to program the system locally.
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date a wide range of devices. The serial ASCII data that enter
2 through the RS-232 connection proceed to a UART (Universal
3 Asynchronous Receiver Transmitter), which converts the serial
4 data to parallel data -- and also has a hardware interrupt to
alert the microprocessor that it has data. We use Exar 88C681
6 UART. The microprocessor handles these data in the same way as
those from the handheld programmer and keypad, except that it
8 displays these data on the device connected to the RS-232 port
(~. the video screen that is part of the terminal).
The RS-232 port also
provides a means of remote program-
ming in that a modem can be connected to the RS-232 port and
'12 thus allow communications with the system over the telephone
13 lines from a remote location having a modem and terminal. Our
~4 system also has an onboard modem chip (Rockwell RC224AT), which
eliminates the need for an outboard modem. An outboard modem
16~ would be used only if a baud data transmission rate faster than
» 2400 were desired. A "dumb" terminal, as opposed to a personal
~8 computer (PC), can be used in either instance, since all the
necessary intelligence resides in our system.
The serial ASCII data from the onboard modem is sent to a
2~ UART and then to the microprocessor. Data entries and system
22 prompts are sent back to the modem -- which then transmits them
23 over the telephone line to the modem and terminal at the remote
24 location, where they are displayed on the video screen.
42
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1 from a common input source -- in this case the unknown type of
2 telephone call being answered.
We accomplish this by using an active hybrid circuit. The
4 hybrid is an analog three-port circuit design having an input
port, an output port, and an input/output port that enables
6 concurrent testing for either an incoming modem signal or a
DTMF signal. Outputs of the modem transmitter and voice chip
are fed to the input port and both the modem receiver and the
DTMF receiver inputs are connected to the output port of the
hybrid. The telephone-line interface feeds signals both into
11 and out of the input/output port of the active hybrid.
12 When the system is called, it senses the ring signal on
13 the line and integrates these occurrences over a period of time
14 to avoid spuriously answering on noise pulses. The system then
answers by seizing the line and, after a 2.2 second delay,
16~ answers in English speech by saying, "Hello."
The system then presents the modem answering tone and
listens concurrently for either an origination tone from a
possible modem originating station or a DTMF tone. If an
origination tone from a modem is detected, the unit will ignore
21 subsequent DTMF tones during the same session. Conversely, if
22 a DTMF tone is detected, the unit turns off its modem answering
23 tone, ignores any subsequent modem frequencies, and obeys only
24 the incoming DTMF commands.
44
..x~~)
Another feature of the active hybrid is cancellation of
leakage between the input port (transmitter output) and the
output port (receiver input). This is accomplished by mathe-
4 matical relationships that are inherent in the design.
i :i0~~2
Our system allows these data to be retrieved when the
2 system is in the programming mode, either locally or remotely,
3 by display on the system LCD, a printer, or a terminal, depend-
4 ing on the programming mode as discussed earlier. The chip we
use for the transaction buffer memory is an RCA 6264 eight-
h thousand byte RAM or a RCA 62256 thirty-two thousand byte RAM.
The size depends on the maximum number of transactions to be
retained.
We have also created a software program on floppy disc
that allows the data in the transaction buffer to be sorted
11 after it is retrieved. Sorting can be by date, time, source
12 and type of transaction; and by code used, name, and action
13 taken. Thus, a user can focus in more narrowly on the specific
14 transactions he wishes to review.
The program also allows the programmed information stored
16~ in the system EEPROM memory (e-R., names on the directory,
codes, telephone numbers, etc.) to be downloaded to a floppy
18 disc. Thus, a backup disc file of the system memory can be
maintained.
This is a particularly attractive feature with directory
21 , units having the capacity for a large number of names, where
22 loss of the system memory (e-R.~,, due to lightning strike)
23 would necessitate reprogramming many names. With this floppy-
24 disc program, the names on the backup disc file can simply be
uploaded to the affected system once it is back in commission.
46
'<~~s~a3~
This floppy-disc program can be used in any IBM-compatible
2 PC with DOS 2.0 or higher. The PC can be connected directly to
3 the system via RS-232 connection or can communicate with the
system via modem -- since the floppy-disc program includes the
terminal-emulation and communications software necessary for a
PC to be able to communicate via modem.
It will be understood that the foregoing disclosure is
intended to be merely exemplary, and not to limit the scope of
the invention -- which is to be determined by reference to the
f0 appended claims.
47
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