GB2148571A - Meter for providing L.C.D. display of measured quantities - Google Patents

Abstract

There is disclosed a meter which comprises a transparent back plate (14), a transparent front plate (13) spaced from the back plate to define a space (15) therebetween, liquid crystal display material filling the space (15) and being of such a type as to be rendered transparent upon application of an electrical potential across the material, an electrically conductive film (19) applied to an inner face of the back plate (14) in a predetermined pattern or array. an electrically conductive film (18) applied to an inner face of the front plate (13) in a further predetermined pattern or array, and electronic control means connected to the patterns of the films (18, 19) on the front and back plates in such a way as to provide energisation across predetermined areas of the films in dependence upon the specific measured quantity which is to be displayed. The electrically conductive film (18) on the inner face of the front plate (13) is light transmissive and is preferably made of indium/tin oxide. The electrically conductive film (19) on the inner face of the back plate (14) is light reflective, and preferably comprises a transflective surface coating made of, for example, gold or silver. <IMAGE>

Description

SPECIFICATION Liquid crystal display meter This invention relates generally to a liquid crystal display meter, and has been developed primarily with a view to provide an improved meter to replace currently available designs of moving coiltype meter.

In particular, the present invention seeks to provide an improved construction of meter having better L.C.D. display of measured quantities than is currently available in L.C.D., and which is particularly suitable to replace the type of display provided by conventional moving coil type instruments.

In conventional L.C.D. instruments and apparatus, a glass sandwich is provided having a back plate and a front plate which are spaced apart to define a space which is filled with liquid crystal display material. Electrically conductive films are applied to the inner faces of the glass plates, the films being arranged in predetermined patterns or arrays to suit the type of display to be provided. Electronic control circuitry is connected to the conductive films, so as to energise predetermined points or regions thereof, thereby to provide a potential across the plates and through the L.C.D. material at regions corresponding to the display information to be provided.Usually, the L.C.D. material is of a "twisted mnematic type, in which the material is light transmissive when no potential is applied across the material, but becomes opaque or non-transmissive at regions in which a potential is applied thereacross. In this way, upon application of appropriate control signals to the conductive patterns on the plates, appropriate visual information can be displayed.

The visual information to be displayed at the front plate is normally obtained via an arrangement of polarised light filters arranged on top of the front plate. The conductive films on the inner faces of the glass plates are usually light transmissive i.e.

normally permit of the order of 95% of impinging light to pass therethrough. Accordingly, surrounding light impinging on the known L.C.D. devices passes through the front plate, the film on the inner surf ace thereof, the L.C.D. material, the conductive film on the inner face of the back plate, and the back plate itself. This incident light is then reflected from a reflective surface which is applied on the outer face of the back plate, so as to pass through the back plate, the film thereon, the L.C.D. material, the film on the front plate, the front plate and then through the polarized filters. In the regions where a potential has been applied, the L.C.D. material will be opaque, thereby providing a visual display in that the display information will appear black or dark against a white or light coloured surrounding.

The present invention seeks to improve the known L.C.D devices, by rendering it unnecessary to provide the polarised light filter arrangements, and also the reflective surface on the outer face of the back plate. The polarised light filter arrangement does not always provide satisfactory operating performance.

According to one aspect of the invention there is provided a meter for providing L.C.D.

display of measured quantities and comprising a transparent back plate, a transparent front plate spaced from the back plate to define a space therebetween, liquid crystal display material filling said space and being of such a type as to be rendered transparent upon application of an electrical potential across the material, an electrically conductive film applied to an inner face of the back plate in a predetermined pattern or array, an electrically conductive film applied to an inner face of the front plate in a further predetermined pattern or array, and electronic control means connected to the patterns of the films on the front and back plates in such a way as to provide energisation across predetermined areas of the films in dependence upon the specific measured quantity which is to be displayed, in which the electrically conductive film on the inner lace of the front plate is light transmissive and the electrically conductive film on the inner face of the back plate is light reflective.

The electrically conductive film applied to the inner face of the back plate may comprise any suitable transflective surface coating made of, for example, gold or silver. In a preferred arrangement, a gold film is applied, which provides a yellow display of measured information, set against a black or dark surrounding. The yellow display is achieved in the relevant predetermined area, in that the L.C.D material will be rendered light transmissive in this area upon application of a potential across the L.C.D material in this area via the electronic control means and its connections to the films on the front and back plates.

This will provide a meter which will provide a striking visual display i.e. which is particularly clear to read, being yellow on black, and would be particularly useful in environments in which a clear display is vital, despite difficult surrounding environments from a lighting point of view.

It is preferred that the transflective surface coating should be partly light transmissive e.g. 90% reflective and 10% transmissive. In this case, when the incident light upon the front plate of the meter is insufficient to provide a satisfactory visual display, upon reflection from the transflective surface coating, or if a brighter display is required in given conditions, some means of illumination may be provided along the outer face i.e.

below the back plate, which can pass through the partly transmissive (10%) film on the inner face of the back plate.

The liquid crystal display material used in the meter may take any suitable commercially available form, provided it is of such a type as to be rendered transparent upon application of an electrical potential across the material. The preferred material is known as dyed phase change According to a further aspect of the invention there is provided a meter for providing L.C.D. display of measured quantities and comprising a transparent back plate, a transparent front plate spaced from the back plate to define a space therebetween, liquid crystal display material filling said space and being of such a type as to be rendered transparent upon application of an electrical potential across the material, an electrically conductive film applied in a predetermined array upon an inner face of the back plate, an electrically conductive film applied in a further predetermined array upon an inner face of the front plate, electronic control means connected to the film arrays upon the front and back plates so as to be capable of providing energisation across predetermined areas of the films in dependence upon the specific measured quantity which is to be displayed, in which the arrays of electrically conductive films on the front and back plates are such as to provide first and second types of L.C.D. display, the first type simulating a movable pointer type of moving coil meter display and the second type providing a corresponding digital display simultaneously therewith.

In the further aspect of the invention, the electrically conductive film on the front plate is substantially light transmissive, whereas it is preferred that the electrically conductive film on the back plate is a transflective surface coating i.e. is at least mainly light reflective.

The film on the front plate is preferably indium/tin oxide, and the transflective surface coating on the back plate is preferably a gold film, though silver and other transflective and electrically conductive material may be used.

One embodiment of liquid crystal display meter according to the invention will now be described in detail, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a schematic illustration of the L.C.D. meter, indicating two different types of display which can be provided simultaneously, namely a simulation of a movable pointer of a moving coil instrument and a simultaneous separate digital display; Figure 2 is an illustration of the two types of L.C.D. display provided by the meter; Figure 3 is a plan view of a segmental layout of an electrically conductive film applied to an inner face of a front plate of the meter; Figure 4 is a plan view of an electrically conductive film applied to an inner face of a back plate of the meter; Figure 5 is a schematic side illustration of the front and back plates of the meter; and Figure 6 is a schematic circuit diagram of an electrical control circuit for controlling the L.C.D. display.

Referring now to Figures 1 and 2 of the drawings, there is shown a meter for provid ing dual types of L.C.D. displays. The first type is designated generally by reference numeral 10 and comprises a simulation of a movable pointer of a conventional moving coil type meter. The second type is designated by reference numeral 11 which provides a simultaneous digital display of corresponding values, the types 10 and 11 being provided on a single display face 1 2 of the meter.

Referring now to Figure 5, there is shown in schematic illustration an L.C.D. sandwich which comprises a transparent front plate 1 3 and a transparent back plate 14 defining a space 1 5 which is filled with liquid crystal display material. The L.C.D. material is of such a type as to be rendered transparent upon application of an electrical potential across the material, and is preferably of the type known as dyed phase change, L.C.D.

material. Unlike conventional constructions of L.C.D. display, there is no provision of polarized light filters at the outer face 1 6 of the front plate 1 3. Also, unlike the conventional constructions, there is no provision of a reflective coating on the outer or back face 1 7 of the back plate 14. Usually, the front and back plates 1 3 and 14 will be glass plates.

On the inner face of the front plate 1 3 there is provided an electrically conductive film 18 arranged in a predetermined pattern or array.

On the inner face of the back plate 14 there is an electrically conductive film 1 9 arranged in another predetermined pattern or array. The arrangements of the films 18 and 1 9 are shown in more detail in Figures 3 and 4 respectively, and will be described in more detail below with reference thereto.

In Figure 6, there is shown a circuit diagram of electronic control means for controlling the operation of the L.C.D. display provided by the meter. The electronic control means is connected to the two different patterns o f the films 18 and 1 9 so as to provide energisation across predetermined areas of the films in dependence upon the specific measured quantity which is to be displayed. Energisation across the L.C.D. material at any predetermined region will result in the L.C.D.

material in that region becoming light transmissive, whereas the remaining L.C.D.

material surrounding that region will remain nontransmissive. Accordingly, a visual display will be provided in the energised region.

Referring to Figure 3, the pattern or array of the electrically conductive film 1 8 is shown in more detail so as to provide simultaneously the two types of display 10 and 11. The film 18 is an indium/tin oxide coating, and is applied in such a way as to be substantially light transmissive i.e. light incident upon the front face 1 2 (Figure 1) of the meter can pass through the front plate 1 3 and the film 18, before subsequent passage through the L.C.D.

material.

The pattern or array of the electrically conductive film 1 9 is shown in more detail in Figure 4, and comprises a transflective surface coating whereby the film 1 9 is at least mainly light reflective. Thus, the film 1 9 serves a dual function, which is considered to be unique in L.C.D. displays. Thus, the film 19 serves as a means for application of an electrical potential at predetermined points or regions across an L.C.D. material, but also functions to reflect incident light (which passes through front plate 13, film 1 8 and the L.C.D.

material) back through the L.C.D. material and the front plate 1 5. Assuming that an electrical potential has been applied across a predermined area of the L.C.D. material, incident light will be reflected from the film 1 9 through the L.C.D. material in this area to provide a visual display with a dark surround in adjoining (non-energised) regions.

Any suitable transflective surface coating may be applied e.g. a silver coating, to form the film 19, though it is preferred that a gold film is applied at the necessary density to provide transflective properties. It is preferred that the gold film is applied so as to be only 10% transmissive and 90% reflective. When gold is used, this provides a yellow visual display against a black surrounding, which is a particularly striking display. This will be of particular use in environments, in which a clear display is essential.

The film 1 8 shown in Figure 3 and the film 1 9 shown in Figure 4 combine to provide a composite visual display as shown in Figure 2.

The pattern or array of the film 1 9 shown in Figure 4 is composed of six separate planes, and the pattern or array of the film 1 8 shown in Figure 3 is divided into 59 segments which cooperate with the planes of the film 1 9 in the manner described below.

The application of an electrical potential between plane number 1 (see Figure 4) on the back plate and segment number 1 (see Figure 3) of film 1 8 will cause segment number 1 to be energised and thereby the L.C.D.

material underlying this region will change from an opaque state to a transparent state.

Incident light can therefore pass straight through the cell construction shown in Figure 5, to be reflected back from film 1 9 and provide a corresponding visual display (10, 11). If the potential is removed from segment number 1 and is applied to segment number 2 (while back plane number 1 remains energised), segment number 2 will now be energised and the corresponding region of the L.C.D. material will become transparent. This sequence of operation < can be carried on up to segment number 10.

In order to energise segment number "1"1 í of the fiim 18, the connection to segment number 10 is maintained, but the connection from the back plane number i of film 1 9 is transferred to back plane number 2. Segment number 1 2 can be energised by maintaining the connection to back plane number 2, and moving the other connection to what was segment number 9. Thus, segments numbers 1 to 10 use back plane number 1 in ascending order, segments 1 1 to 2G use back plane number 2 in decending order, this sequence being repeated through the successive planes up to the full 59 segments provided by the arrangement which is illustrated.All switching of the connection to the segments and the back planes will be carried out by electronic control means known per se.

The number of segments and back planes may be altered from the arrangement illustrated, which is a 270 arc having 59 segments. One preferred alternative will have a 250 array and only 50 segments.

The use of a gold film to provide the transflective surface coating for film 1 9 provides a gold back plane which gives a yellow on-black display from incident ambient light.

However, during low light conditions, or if it is desired to provide an enhanced visual display, a light source may be placed behind the back plate a 14, to boost the visual display.

This is possible by reason of the face that the transflective coating is preferably " G% light transmissive so that the light from the light source can pass through back plate 14 and the film 19, and then through the energised region (s) of the L.C.D. material, to emerge as the dual visual display from the front plate 13.

The electronic driving circuit is shown sche matically in Figure 6. Practical details of preferred electronic driving arrangements which may be used are shown in more detail in U.K.

patent No. 200179at.

Claims (11)

1. A meter for providing L.C.D. display of measured quantities and comprising a transparent back plate. a transparent front plate spaced from the back plate to define a space therebetween, liquid crystal display material filling said space and being of such a type as to be rendered transparent upon application of an electrical potential across the material, an electrically conductive L film applied to an inner face of the back plate in a predetermined pattern or array. an electrically conductive film applied to an inner face of the front plate in a further predetermined pattern or array, and electronic control means connected to the patterns of the films on the front and back plates in such a array as to provide energisation across predetermined areas of the films in dependence upon the specific measured quantity which is to be displayed, in which the electrically conductive film on the inner face of the front plate is light transmissive and the electrically conductive film on the inner face of the back plate is light reflective.

2. A meter according to claim 1, in which the electrically conductive film applied to the inner face of the back plate comprises a transflective surface coating.

3. A meter according to claim 2, in which the transflective surface coating is made of gold or silver.

4. A meter according to claim 3, in which the gold surface coating is applied in the form of a gold film which provides a yellow display of measured information, to be set against a black or dark surrounding.

5. A meter according to any one of claims 2 to 4, in which the transflective surface coating is partly light transmissive.

6. A meter according to claim 5, in which the transflective surface coating is 90% reflective and 10% transmissive.

7. A meter according to any one of the preceding claims, in which the liquid crystal display material is material of the type known as dyed phase change material.

8. A meter for providing L.C.D. display of measured quantities and comprising a transparent back plate, a transparent front plate spaced from the back plate to define a space therebetween, liquid crystal display material filling said space and being of such a type as to be rendered transparent upon application of an electrical potential across the material, an electrically conductive film applied in a predetermined array upon an inner face of the back plate, an electrically conductive film applied in a further predetermined array upon an inner face of the front plate, electronic control means connected to the film arrays upon the front and back plate so as to be capable of providing energisation across predetermined areas of the films in dependence upon the specific measured quantity which is to be displayed, in which the arrays of electrically conductive films on the front and back plates are such as to provide first and second types of L.C.D. display, the first type simulating a movable pointer type of moving coil meter display and the second type providing a corresponding digital display simultaneously therewith.

9. A meter according to claim 8, in which the electrically conductive film on the front plate is substantially light transmissive.

10. A meter according to claim 9, in which the electrically conductive film on the back plate is a transflective surface coating.

11. A meter according to claim 9 or 10, in which the electrically conductive film on the front plate is indium/tin oxide, and the transflective surface coating on the back plate is a gold film, silver or other transflective and electrically conductive material.

1 2. A meter according to claim 1 and substantially as hereinbefore described with reference to, and as shown in the accompanying drawings.

1 3. A meter according to claim 8 and substantially as hereinbefore described with reference to, and as shown in the accompanying drawings.