Liquid Crystal Bar Graph Display

Abstract

An analog display in the form of a plurality of bar graphs is provided by an arrangement of horizontally extending graphic electrode strips cooperating with vertically disposed and mutually discrete common electrode strips and a film of liquid crystal material confined between the electrodes. Selected groups of the horizontal graphic electrode strips are energized in accordance with the magnitude of a bidirectionally varying signal, and a selected one or more of the common electrodes are concurrently energized to selectively display the several bar graphs in a time shared arrangement.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to display devices of the liquid crystal type and, more particularly, concerns a liquid crystal display of information in an analog form.

2. Description of Prior Art

Liquid crystal displays are widely employed for presenting patterns of numbers or letters. The common alphanumeric or numeric liquid crystal display employs a group of electrodes deposited in a pattern that allows selected ones of the electrodes to be energized together with a back electrode that is common to all of the elements of the electrode pattern. The pattern of front electrodes selected for energization activates an interposed thin film of confined liquid crystal material to provide a readily visible display. Although the numeric and alphanumeric liquid crystal display devices are quite satisfactory, in many instances analog displays are necessary or desirable. In particular, analog displays in the form of bar graphs are highly desirable. This type of analog display deivce is readily adaptable to operations which require quick, easy reference by an operator such as display of aircraft engine parameters and the like. The extent of the movable end of the bar graph may be readily correlated with indicia permanently located on the face of the display to thereby directly identify ranges of operating conditions from normal to marginal to failure or emergency. For these and other reasons, an analog display is often preferred.

Accordingly, it is an object of the present invention to employ liquid crystal display techniques to provide an analog display. Herein, the term liquid crystal is to be interpreted to include suspended liquid and other similar materials and technologies.

Reference is hereby made to the co-pending application of L. E. Tannas, Jr., et al, entitled Liquid Crystal Display, filed Feb. 28, 1973, bearing U.S. Ser. No. 337,258, as well as to the co-pending continuation application of R. Chang et al, entitled Nematic Liquid Crystal Compositions, filed Oct. 12, 1972, bearing U.S. Ser. No. 297,172, each of which applications has been assigned to the common assignee. The cross-reference is made to these applications in order to incorporate the teachings thereof in this application.

SUMMARY OF THE INVENTION

An improved display device utilizing techniques currently used in providing liquid crystal type displays. First and second plates, sealed together by a suitable sealer form a container or chamber between the plates. Electrodes are placed on each of the plates. In particular, a plurality of relatively large common electrodes are placed on the inner surface of one of the plates. A plurality of relatively smaller electrodes are placed on the other plate. The electrodes are generally oriented transverse to each other. Control circuitry is provided to selectively energize various ones of each of said plurality of electrodes in order to provide a variable display indicator. Thus, an analog type display is provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of one embodiment of the multiple bar graph display of the present invention.

FIG. 2 is an exploded and enlarged cross-sectional view taken generally along the line 2--2 of the display shown in FIG. 1.

FIG. 3 is a diagram illustrating electrical connections and positioning of the electrodes of the display of FIGS. 1 and 2.

DETAILED DESCRIPTION

Referring concurrently to FIGS. 1 through 3, a front plate 10 is sealed, in spaced relation, to a back plate 12 by means of sealing strips 14. Typically, plates 10 and 12 are transparent glass and strip 14 is glass frit or other suitable spacing and sealing means. A chamber 100 is provided between the opposed inner faces of the plates and within strip 14. In a preferred embodiment, plate 10 is wider than plate 12 whereby plate 10 extends beyond two sides of plate 12. A liquid crystal material (not shown) is retained in chamber 100. Deposited upon the inner surface of front plate 10, within the space defined by chamber 100, are first and second rows of horizontally extending graphic electrode strips generally designated at 16 and 18 (FIGS. 2 and 3).

The external surface of the front glass plate 10 has imprinted thereon suitable legends, scaling indicia and color patterns indicated generally as 10a (FIG. 2) to complete the visual display afforded by the described electrode pattern.

Imprinted upon the outer surface of the front glass plate are identifications of the several bar graphs, such as, for example, the term "OIL" and the letters "P" and "T" for graphs 30 and 32, to indicate oil pressure and temperature, respectively. Also imprinted on the face of the front plate 10 and directly over the graph itself are the various numbers indicating the values of the pattern displayed. If desired, color coded strips 30a and 32a may also be formed on the face of the display. Typically, the color coded strips may be used for indicating red at extremely low and extremely high oil pressures; green at an intermediate pressure in the vicinity of 75; and yellow for a pressure of roughly 25-60. Obviously, the colors chosen and the extent of each color are matters of choice and design, according to the particular display employed.

Also shown in the exemplary display of FIG. 1 are graphs 34 and 36 bearing legends identifying these parameters as cylinder head temperature (CHT) and exhaust gas temperature (EGT), thus providing a display typical of those used with aircraft engines. Each of bar graphs 34 and 36 will have appropriate color strips indicating safe or normal (green), emergency (red) or marginal (yellow) operating conditions. These imprinted legends are designated generally by reference numeral 10a as in FIG. 2.

In one embodiment, electrode strips in row 16 are separated from the electrode strips in row 18 by a distance represented by isolating space 20. A strip of insulating material similar to sealer 14 may be inserted in space 20. Each electrode strip of row 16 is connected to a separate conductor portion 16a. Similarly, each electrode strip of row 18 is connected to a separate conductor portion 18a. The conductor portions 16a and 18a extend beneath the spacer sealer strips 14 and along the inner surface of that portion of the front plate 10 that extends laterally beyond the edges of back plate 12. Conductor portions 16a and 18a are arranged at opposite sides of chamber 100. The arrangement of laterally extending side portions of front plate 10 and conductors 16a and 18a facilitates connection to external circuitry to be described hereinafter.

Each row of graphic electrode strips comprises a plurality of mutually discrete, but closely spaced, strips which are generally parallel to each other and extend transverse to the extent of the pattern collectively formed by the strips. Thus, each row of strips can delineate a substantially vertically extending bar pattern formed by a number of mutually discrete horizontally extending strips. The display is, effectively, an analog appearing display, although actually achieved by a number of energized electrode strips. The strips may be so closely spaced that there is little or no visually detectable demarcation between liquid crystal areas energized by adjacent strips rendering the appearance of a continuous display when all horizontal strips below the indicated value are energized. Of course, the electronic control circuitry could be so configured that only a single horizontal electrode strip is energized at the reading to be indicated thereby simulating a needle type display.

FIG. 3 illustrates the pattern of strips of the rows 16 and 18. For example, row 16 comprises a plurality of individual strips 16.1, 16.2 and so forth which may include any desired number, for example 40. Each of the strips 16.1, 16.2, has an associated conductor portion 16.1a, 16.2a. Similarly, the row of strips 18 includes a suitable number of horizontally extending strips collectively forming the bar graph pattern illustrated in FIG. 3. The horizontal strips in FIG. 3 are designed for 2:1 multiplexing. That is, two common electrodes have to be controlled relative to one electrode strip. The horizontal strips could extend across the four independent common electrodes if so desired, but 4:1 multiplexing would be necessary.

Deposited upon the inner surface of the back plate 12 in continuous vertically extending bar patterns are common electrodes 22, 24, 26 and 28. These common electrodes are illustrated in FIG. 3 as overlying the rows 16, 18 of graphic electrode strips. The first pair of common electrodes 22, 24 together are substantially coextensive with the full vertical extent of the row of graphic electrode strips 16. However, the two common electrodes are laterally spaced apart along line 29. Accordingly, each common electrode 22 and 24 overlies a portion, e.g., one-half, of each of the electrode strips of row 16. In particular, outer common electrode 22 overlies the outer portion of the electrode strips of row 16 and inner common electrode 24 overlies the inner portion of each of the electrode strips of row 16. However, it should be noted that outer common electrode 22 terminates laterally near the outer edges of the graphic electrode strips, but does not overlie the conductor portions 16.1a, 16.2a and so forth.

Similarly, common electrodes 26, 28 collectively are substantially coextensive with row 18 of graphic electrode strips. Each of common electrodes 26 and 28 is mutually spaced from the other. Outer electrode 28 has the laterally outward edge near the outer edges of all the electrode strips of row 18. In effect, each graphic electrode strip terminates at an edge of a corresponding common electrode, although each strip includes a conductor portion integral therewith. However, because the conductor portions 16a, 18a and the like extend beyond the edges of the common electrode, there is no liquid crystal material interposed between a pair of electrodes. Therefore, application of a signal to conductor portions 16a or 18a will not activate the liquid crystal material and cause a display thereby.

Manufacture and assembly of glass plates, electrodes and insertion of liquid crystal material confined between the plates may be performed with conventional techniques. Briefly, the electrode patterns and the patterns of conductors are formed on the glass plates of a transparent tin oxide by suitable masking and/or silk-screen techniques. The spacer, sealer may be a glass frit fused to the peripheral edges of the back plate and to mating portions of the front plate, providing suitable channels to allow cleaning of the chamber formed between the spaced and sealed plates. Vacuum filling of the chamber with a thin film of a suitable liquid crystal material is then accomplished through the aforesaid channels. Various types of liquid crystal materials are described in the prior art and in the above-mentioned copending applications.

A thin film of confined nematic liquid crystal material, as is well known, is substantially transparent to light when at least one of the electrodes is unenergized. When electrodes on the front and back plates are concurrently energized to provide an electrical potential across an interposed portion of liquid crystal material, the latter is activated over the area thereof that is directly between the electrically energized electrode portions. The activated material scatters light to provide an opalescent effect. Accordingly, if a common electrode, e.g., common electrode 22, is energized and, concurrently, the lowermost strip 16.1 of row 16 is energized, a thin opalescent horizontal line is produced. This opalescent line has a width or vertical extent (as viewed in FIG. 3) equal to the width of the strip 16.1, and a horizontal extent equal to the width of common electrode 22. Moreover, the opalescent line will exhibit a strong visual contrast with the remainder of the display. Similarly, if the lower two strips 16.1 and 16.2 are energized concurrently with energization of the common electrode 22, the liquid crystal material between the energized electrodes is activated. According to one embodiment of the invention, as will be described hereinafter, strips 16 are energized in groups of consecutive strips, always including the lowermost strip 16.1 and including a number of strips proportional to a magnitude that is to be displayed. Accordingly, a vertically extending portion of the common electrode 22 (when this is energized together with the strips of graphic electrode 16) will activate a vertical length of the adjacent nematic liquid having a height equal to the number of graphic electrode strips energized.

If common electrode 24 is energized and electrode 22 is not, then an opalescent display having a vertical extent, as viewed in FIG. 3, will appear in the second bar graph pattern that is delineated by the common electrode 24. Similarly, common electrodes 26 and/or 28 may be caused to cooperate with energized electrode strips of the row 18, whereby third and fourth bar graphs may be individually displayed. Each of these bar graphs will have an opalescent vertical extent according to the number of electrode strips that are energized at any given instant.

The arrangement of electrode bar graph patterns is such as to provide for mutually discrete vertically extending bar graph areas, respectively identified by numerals 30, 32, 34 and 36 in FIG. 1. Each of these graph areas is essentially coextensive with a respective one of common electrodes 22, 24, 26 and 28. As previously stated, FIG. 1 is a perspective view from the front of front plate 10. FIG. 3 is a view from the back of the front plate and shows the back (or common) electrode pattern overlying the graphic electrode rows. FIG. 3 illustrates the overlapping arrangement of certain common electrodes and certain portions of the rows of graphic electrode strips.

The bar graph display shown in FIG. 1 provides a visual indication of various conditions or parameters sensed by parameter detecting transducers 38, 40, 42, and 44, shown in FIG. 3. Transducers 38 and 40 provide analog signals having magnitudes proportional to the conditions sensed thereby, e.g., exhaust gas temperature and cylinder head temperature, respectively. These analog signals are fed to multiplexer 46 which provides output signals on common line 48 in accordance with timing signals from timer 56. The signals on line 48 represent the analog values sensed by transducers 38 and 40. The signals on line 48 are in sequence or time shared relation as controlled by multiplexer 46. These signals are fed to analog-to-digital converter 50 which provides digital signals to decoder 52. The digital signals are representative of the analog signals from the transducers. Decoder 52 has a plurality of output leads collectively indicated at 54. Leads 54 are selectively enabled in accordance with the output signals from converter 50. The number of output leads 54 is equal to the number of electrode strips of row 18. These leads are individually connected to separate conductor portions of the electrode strips. A timer 56 feeds timing signals to multiplexer 46 to cause the latter to sequentially transmit the analog signals from transducers 38 and 40, respectively. Timer 56 also supplies timing signals via lead 58 to gating circuit 60. Gating circuit 60 selectively transfers a signal from A.C. source 62, via leads G1, G2 G3 and G4, to common electrodes 28, 26, 24 and 22, respectively. Source 62 produces the energizing signal that, in one embodiment, is fed via selectively enabled leads of decoder 52 to the electrode strips of row 18. The arrangement of timing signals from timer 52 to gating circuit 60 and multiplexer 46 is such that multiplexer 46 transmits signals from transducer 40 to analog to digital converter 50 while gating circuit 60 energizes common electrode 28 via line G1. Converter 50 operates upon the signals from multiplexer 46 and supplies a digitized value of the analog signal detected by transducer 40 to the decoder 52. Decoder 52 supplies energizing signals to the electrode strips of row 18. Thus, the concurrent energization of common electrode 28 and strips of row 18 determines that only exhaust gas temperature is displayed at graph 36.

At a different interval of the timer, multiplexer 46 is permitted to feed the output signal from transducer 38 to analog to digital converter 50 which causes decoder 52 to energize a group of graphic electrode strips in row 18 representative of the value of sensed cylinder head temperature. Concurrently, gating circuit 60 is permitted to provide energization to common electrode 26 via line G2. Line G1 and common electrode 28 are not energized at this time or energized in phase. Thus, only cylinder head temperature bar graph 34 is made opalescent.

Similarly, analog signals from transducers 42 and 44, respesenting magnitude of detected oil pressure and temperature, alternately appear at the output of second multiplexer 64 and are fed, in sequence, to second analog to digital converter 66 to operate a second decoder 68. Decoder 68 selectively feeds energy from source 62 to conductors of graphic electrode strips in row 16. Again, timer 56 synchronizes operation of multiplexer 64 with gating circuitry 60. Thus, when analog to digital converter 66 presents a digitized version of the analog signal detected by transducer 42, gating circuit 60 will permit energization of common electrode 22 via lead G4. Likewise, when the analog to digital converter 66 energizes decoder 68 with a digitized signal representing the analog signal detected by transducer 44, timer 56 will permit gating circuit 60 to energize common electrode 24 via lead G3.

The overall sequence of gating energization may provide sequential energization of the four bar graphs, one at a time. For example, graph 30, graph 32, graph 34 and graph 36 may each be energized for a discrete interval of time and then de-energized, whereupon the next graph is energized. However, with the arrangement shown, viz. graphic electrode strip rows 16 and 18 are common to a pair of common electrodes with separate multiplexers, converters and decoders, the timing of one pair of graphs, such as graphs 30 and 32, need not be synchronized with the timing of the second pair of graphs 34, 36. Accordingly, graphs 30 and 34 may be energized simultaneously and graphs 32 and 36 may be energized simultaneously in some desirable chronological relation. For example, common electrodes 28 and 24 may be energized at a given instant, and suitable groups of the first and second rows of graphic electrode strips 18 and 16 may be likewise energized by the appropriate one of the pair of transducers assigned thereto.

Where all four graphs are multiplexed (a 4:1 multiplexing), that is, sequentially at a separate instant of time, the multiplexer, analog to digital converter and decoder need not be duplicated. This last mentioned arrangement would employ a single four-channel multiplexer, a single analog to digital converter and single decoder. The decoder output leads in such case are connected to electrode strips of both rows 16 and 18.

The arrangement illustrated in FIG. 3, wherein two rows of graphic electrode strips are provided with each row being employed for two bar graphs, enables simultaneous display of one of the pair of graphs of row 16 and one of the pair of graphs of row 18. If deemed necessary or desirable, the electrode strips of rows 16 and 18 may be made continuous, i.e., not separated as at isolating space 20 of FIG. 2. With each of the strips of rows 16 and 18 extending entirely across all four common electrodes, the common electrodes must be sequentially energized. Thus, each bar graph can be activated about 25 percent of the time. Relaxation rates of the liquid crystal material (i.e., time required for the material to return to its inactive state upon termination of its electrical energization) may be such as to require discrete rows 16 and 18 of graphic electrode strips illustrated herein. In addition, duplication of multiplexer, analog to digital converter and decoder may be necessary so as to provide a longer active time for each of the graphs. The arrangement of FIG. 3 is preferred for such situations.

As is well known, liquid crystal displays may be of either the transmissive or reflective type. In the transmissive type, both the electrodes on the front plate and the electrodes on the back plate are made of a transparent material, such as tin oxide, and light is transmitted from behind the display through the thin film of liquid crystal material to the viewer who is positioned in front of the front plate. In the reflective type, the common electrode which is formed on the inner surface of the back plate is made of a reflective material, for example gold, and light is transmitted from the front of the display through the front plate, through the liquid crystal material, and reflected from the back electrode to the viewer positioned in front of the front plate.

Principles of the present invention may be applied to either a reflective or transmissive display.

In an exemplary arrangement employing forty graphic electrode strips, each having a width (vertical extent as viewed in FIG. 3) of 90 mils and each spaced from an adjacent strip by 10 mils, the total height of the bar graphs may be about 4 inches, the display having a total width of 2 inches or less for all four bar graphs.

The described arrangement provides a display that vividly presents analog information in a readily readable bar graph form, requiring little power and minimized space. These attributes of the display are extremely useful in aircraft, automotive or other applications wherein small size and easy readability to the operator are desired.

The foregoing detailed description is to be clearly understood as given by way of illustration and example only, the spirit and scope of this invention being limited solely by the appended claims.

Claims

What is claimed is:

1. A display comprising

a panel including first and second plates,

a layer of liquid crystal material confined between said plates,

common electrode means on said first plate,

a plurality of discrete electrode strips arranged on said second plate in a pattern to collectively delineate a continuous bar extending normal to the extent of individual ones of said strips,

means for electrically energizing said common electrode means,

means for electrically energizing one or more of said electrode strips whereby the energized electrode strips will visually express the value of an analog signal by activating a portion of said confined liquid crystal layer along a length of said bar pattern,

a first transducer for developing a first variable analog signal,

a second transducer for developing a second variable analog signal,

said means for electrically energizing said electrode strips including a multiplexer responsive to signals fed from said first and second transducers for energizing groups containing a number of strips substantially proportional to the signals fed from said transducers to said multiplexer,

said common electrode means comprising first and second discrete common electrodes each extending the full length of said bar pattern and each having a width less than the full extent of said individual electrode strips, and

means for alternately energizing said common electrodes in synchronism with said multiplexer.

2. The display of claim 1 wherein

said common electrode means includes first and second discrete common electrodes each extending in a direction normal to the extent of individual ones of said electrode strips,

each of said discrete common electrodes having the length of said bar pattern and a width of a fraction of the length of said electrode strips,

said means for electrically energizing said electrode strips comprising means for energizing different electrode strips in accordance with different analog signals,

said means for energizing said common electrode means comprising means for energizing said first and second common electrodes in synchronism with the energization of said electrode strips in accordance with said analog signals.

3. The display of claim 1 wherein, said display includes a scale positioned in proximity to said bar pattern and having indicia extending along said bar, said scale includes a plurality of strips of different colors respectively indicating different conditions of the values displayed.

4. The display of claim 1 wherein each of a group of said strips extends continuously from an intermediate portion of said second plate to an edge of said second plate for connection with said strip energizing means, and including

a second plurality of discrete electrode strips arranged in a pattern to collectively delineate a second continuous bar extending normal to the extent of individual ones of said second plurality of electrodes strips,

said second continuous bar being positioned adjacent to said first continuous bar, each of the strips of said second plurality of electrode means extending from said intermediate portion of said second plate to a second edge of said second plate,

means connected to said second plurality of electrode means at said second edge for energizing one or more of said second plurality of electrode strips,

second common electrode means on said first plate oppositely disposed with respect to said second bar pattern, and

means for electrically energizing said second common electrode means.

5. The display of claim 4 wherein each strip of said first graphic electrode means extends continuously for the width of both said first and second common electrodes.

6. The display of claim 4, wherein said second graphic electrode means is electrically isolated from said first-mentioned graphic electrode means.

7. A parameter display comprising

first and second glass plates and a liquid crystal material confined between said plates,

first and second mutually discrete common electrodes extending substantially continuously in a bar pattern on said first plate,

graphic electrode means on said second plate,

said graphic electrode means comprising a plurality of mutually discrete, adjacent and parallel electrode strips each extending continuously across the width of both of said common electrodes to an edge of said second plate,

said graphic electrode means collectively delineating first and second continuous bars, each congruent with a respective one of said common electrodes,

means for receiving first and second bidirectionally variable analog signals,

means responsive to said analog signals for electrically energizing said electrode strips in alternate groups of adjacent strips,

said groups including a number of strips that varies in either sense in accordance with alternate ones of said analog signals,

means for alternately energizing said first and second common electrodes,

means for synchronizing the alternate energization of said common electrodes with the alternate energization of said groups of graphic electrode strips in accordance with said first and second bidirectionally variable analog signals,

third and fourth common electrodes on said first plate each extending for the length of said first and second common electrodes and being insulated relative to each other and to said first and second common electrodes, second graphic electrode means electrically isolated from said first-mentioned graphic electrode means and comprising a plurality of mutually discrete, adjacent and mutually parallel electrode strips arranged in a pattern congruent with both of said third and fourth common electrodes to collectively delineate third and fourth continuous bars congruent to said third and fourth common electrodes, respectively,

means for receiving third and fourth analog signals,

means for electrically energizing the electrode strips of said second graphic electrode means in alternate groups of adjacent strips,

said groups including a number of strips that varies in either sense in accordance with said third and fourth analog signals alternately,

means for electrically energizing said third and fourth common electrodes alternately in synchronism with the energization of said alternate groups of strips of said second graphic electrode means in accordance with said third and fourth analog signals, respectively,

electrode strips of said first graphic electrode means extending to a first edge of said second plate for external electrical connection, and

electrode strips of said second graphic electrode means extending to a second edge of said second plate for external electrical connection.