GB1599667A

GB1599667A - Electrooptical analogue display with reduced connections

Info

Publication number: GB1599667A
Application number: GB19887/77A
Authority: GB
Original assignee: Murrell N J
Current assignee: Murrell N J
Priority date: 1977-05-12
Filing date: 1977-05-12
Publication date: 1981-10-07
Also published as: DE2820326A1; IT7823353A0; NL7805194A; FR2390793A2; IT1113178B; FR2390793B2; CA1112463A; JPS53140997A

Description

(54) ELECTRO-OPTICAL ANALOGUE DISPLAY WITH REDUCED CONNECTIONS (71) I, NICHOLAS JOHN MURRELL, a British Subject, of 23 The Wynd, Dalgety Bay, Fife, Scotland, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to an analogue display device comprising an electrooptical system such as a liquid crystal system and an electronic drive circuit for energising electrodes disposed on opposite faces of the electro-optical system and relates particularly to a display device suitable for the simultaneous display of three variables.

A display device of this character is described in my British Patent Specification No. 1,472,260, which concerns a time-piece in which the display device simulates the hour and minute hands of a conventional watch or clock and also provides an analogue display of seconds. Reference is made to Specification No. 1.472,260 for a description of the types of electro-optical system which can be used and the ways in which individual radial bars selected by the electronic circuit can be made visible relative to other parts of the display to indicate by their angular position the hours, minutes and seconds.

It has now been appreciated that a display device as described in Specification No.

1,472.260 can also be applied to the display of other sets of three variables instead of the hours, minutes and seconds required to be shown by a time piece. For example the variables displayed on an aircraft instrument might be the nominal heading, the wind direction. and the actual heading or for a motor vehicle instrument could be speed, temperature. and fuel level. Thus the present invention is concerned broadly with a display device for the display of three variables comprising an electro-optical system having on one face a plurality of bar electrodes radiating from a central point and on the other face two concentric electrodes, the electrodes being connected to an electronic drive circuit constructed to select a bar electrode in conjunction with the inner of the concentric electrodes for display of the first variable, a bar electrode in conjunction with the outer of the concentric electrodes for display of the second variable, and a bar electrode in conjunction with both of the concentric electrodes for display of the third variable, the magnitudes of the variables being shown by the angular position of the selected bar electrodes. Such a display device will be called hereafter a display device of the type defined.

In a display device of the type defined, especially if it is to be made of small overall dimensions, for example as a wrist watch, it is important to reduce as far as possible the number of connections between the electronic drive circuit and the electro-optical system both because the available space is limited and because the making of such connections adds significantly to the cost of manufacture. The time-piece described in Specification No. 1,472,260 represented a considerable advance in this direction because a complete display of hours, minutes, and seconds could be achieved with only sixty connections to the bar electrodes and two connections to the concentric electrodes.

A further reduction would however be desirable if it could be achieved without degrading the quality of the display.

It is true that in British Patent Specification No. 1,464,976 there is described an electronic time-piece with a liquid crystal display device in which the number of connections between the display device and the electronic circuit is reduced to twentyfour. This is achieved by dividing sixty electrodes into twelve blocks of five and connecting together the corresponding electrodes of the twelve blocks so that only five connections are necessary to the electronic circuit, while a further twelve connections are made to twelve electrode segments on the opposite face of the display device each of which is common to the five electrodes ofone block. Twelve electrodes for the hour display are similarly divided into tbur blocks of three, requiring a further seven connections. This however does not provide for any seconds display and moreover the minutes display is cumulative, that is to say as successive electrodes are turned on those previously turned on remain on. Apart from the difficulty of reading such a display, which is quite different from the hands of a conventional watch, it increases the time for which the liquid crystal system is energized and thereby reduces its overall life-time.

In accordance with the present invention there is provided a display device of the type defined wherein the concentric electrodes are divided into segments such that groups of bar electrodes forming sectors of the display cooperate respectively with an inner segment and an outer segment for each sector and wherein the bar electrodes of one sector are connected directly in reverse order to the bar electrodes of another sector, the electronic circuit being constructed to select a segment or segments in the required sector and to change the order of selection of the bar electrodes in accordance with the sector selected.

Thus the connections between the bar electrodes follow a similar pattern to that described in Specification No. 1,464,976. The reversal of the order of the electrodes occurs because the connections are to be made on a flat surface and crossing over of the connectors has therefore to be avoided. However the use of the electronic circuit to compensate for this reversal makes it possible to select any required bar electrode in conjunction with one or both of the associated segments to achieve in a timepiece a complete hours, minutes, and seconds display while using, for example, only 22 connections if there are five groups of twelve bar electrodes or six groups of ten bar electrodes, with in the first case ten segment connections and twelve bar connections or in the second case twelve segment connections and ten bar electrode connections.

The invention will now be described in more detail with the aid of an example illustrated in the accompanying drawings, in which: Fig. I is a block circuit diagram of a display device in accordance with the invention intended primarily for use a time-piece but showing also the modifications necessary for display of three independent measured variables, Fig. 2 is a diagram of the layout and connections of the electrodes of the electrooptical system for the display device of Fig.

1. and Figs. 3 and 4 show the actual pattern of electrodes and connections on the two faces of the electro-optical system when this is a liquid crystal system.

The circuit shown in Fig. I is similar in many respects to the circuit shown in Fig. 3 of Specification No. 1,472,260 and for ease of reference the same reference numerals have been used for the corresponding elements in the two Figures. The circuit is controlled by a time base in the form of a crystal oscillator 21. Pulses from the oscillator 21 pass to a 16stage divider 22 which delivers one pulse per second to a seconds counter 23. The seconds counter in turn delivers one pulse per minute to a minutes counter 24, which delivers twelve pulses per hour to an hours counter 25. The outputs of the counters 23, 24 and 25 are fed in binary coded decimal form to a multiplexer consisting of switching units 26, 27, 28 and 29 which receive pairs of inputs from the counters as shown. The switching units 26 to 29 are controlled by a data display selection circuit 30 which receives pulses from the divider 22 at the muliplex frequency and by means of a divide-by-3 divider delivers in turn a "seconds" output on line 31, a "minutes" output on lines 31 and 32, and an "hours" output on line 32. These outputs are also delivered to a segment drive circuit 33 which controls the energization of the appropriate electrode segment in a liquid crystal display system 34.

The outputs of the switching units 28 and 29 are passed to decoding units 40 and 41 which convert the signals from binary coded decimal to one of sixty, the unit 40 having outputs 0 to 9 and the unit 41 having outputs 00, 10, 20, 30, 40, and 50. The output of the decoding unit 41 is passed to the segment drive circuit 33 to select the appropriate sector of the display and also controls an inverter 42 which reverses the order of the outputs of the decoding unit 40 according as an odd or even sector of the display is selected. These outputs from the unit 40, by way of a bar driver circuit 43, control the energization of the ten bar electrodes in the selected sector. An A.C. square wave generator 39 driven at multiplex frequency by signals from the divider 22 provides the alternating field required between opposite electrodes of the liquid crystal display system 34.

The multiplex frequency from the divider 22, which may for example be 40 Hz. is applied to the selection circuit 30 which switches the multiplexer between the seconds, minutes, and hours counters 23, 24 and 25 and at the same time, in the segment drive 33, selects the appropriate segments for display of seconds, minutes, and hours. As time advances or the variables change the seconds counter 23 steps on and the output from unit 40 causes different bar electrodes in one sector to be selected in turn, after which the output from unit 41 may change to select another sector, by switching to a different set of connections between the segment drive 33 and the electrode segments of the display system 34. At the same time the inverter 42 is operated if necessary to reverse the sequence of the outputs from unit 40 so that the bar electrodes after an odd/even change of sector are selected in reverse order, thus compensating for the physical reversal of the electrodes resulting from the manner of their connection, which will now be described.

The layout diagram of Fig. 2 shows a display system divided into six sectors defined by inner electrode segments 44A to 44F and outer electrode segments 45A to 45F. In each sector there are ten bar electrodes labelled A0 to A9. B0 to B9, and so on.

It will be understood that the inner and outer electrode segments are on one face of a liquid crystal device while the bar electrodes are on the opposite face. The bar electrodes of sector A are connected at their outer ends to respective terminals TO to T9 and at their inner ends to respective bar electrodes of sector B. However. to avoid any cross-over of the connectors it will be seen that the bar electrodes of sector B are connected in the reverse order. that is B9 to AO. B8 to Al, and so on with BO connected to A9. The connections are made at the outer ends of the bar electrodes between those of sector B and those of sector C. the order again being reversed. However it will be seen that B9 and CO are directly connected at their inner ends.

This form of S connection, alternately at the inner and outer ends. is continued throughout the six sectors so that. for example, the terminal T3 is connected in series with bar electrodes A3. B6. C3, D6, E3, and F6.

In addition to the terminals TO to T9, terminals Sl to S12 are provided, which are connected to the electrode segments 44A to 44F and 45A to 45F as shown. There are thus a total of 10 bar terminals and 12 segment terminals to which connections must be made from the electronic circuit of Fig. 1.

Twelve segment electrodes with their associated connection leads are shown in printed circuit form in Fig. 3. Whereas in Fig. 2 the terminals are all arranged along one edge of the display. Figs. 3 and 4 show an arrangement with terminals along two opposite edges and in which corresponding bar electrodes are not connected in series throughout all the sectors but are simply grouped in pairs with central connections. Thus in Fig. 4 there are ten bar electrode terminals TO to T9 connected to the bar electrodes A0 to A9 but it will be noted that the connection of TO to A0 is in fact by way of electrode F9 while the connection of T9 is through electrode BO.

The bar electrodes AO to A9 are connected respectively with electrodes B9 to BO; Similarly CO to C9 are connected respectively with D9 to DO and EO to E9 with F9 to F0.

Additionally, there is a central connection between A0, B9, CO, D9, E0. and F9.

Additional terminals LO to L8 are connected directly to bar electrodes FO to F8, respectively, and similarly at the opposite edge of the array there are terminals MO to M9 connected respectively to bar electrodes CO to C9 and terminals N 1 to N9 connected respectively to electrodes D1 to D8 and EO; By external connections between selected terminals it is then possible to ensure that the same signal is applied to corresponding bar electrodes in all six sectors. For example tlie terminals T1, L8 and M1 and/or N8 are connected to a common point so that electrodes Al, B8, C1, D8, El, andF8 receive the same signal.

Fig. 4 additionally shows terminals S1 to S12 for connection to the segment electrodes 44E, 45F, 44F, 45A, 44A, 45B, 44B, 45C, 44C, 45D, 44D, and 45E respectively. These terminals are placed for convenience on the same board as the other terminals and connections are made from them across the liquid crystal unit to the conductors on the board which carries the segment electrodes.

WHAT I CLAIM IS: 1. A display device of the type defined wherein the concentric electrodes are divided into segments such that groups of bar electrodes forming sectors of the display cooperate respectively with an inner segment and an outer segment for each sector and wherein the bar electrodes of one sector are connected directly in reverse order to the bar electrodes of another sector, the electronic circuit being constructed to select a segment or segments in the required sector and to change the order of selection of the bar electrodes in accordance with the sector selected.

2. A display device as claimed in claim 1 wherein there are six sectors and connections formed at the centre of the display between the bar electrodes of each of three pairs of adjacent sectors, a set of first terminals along one edge of the display connected to the ends of bar electrodes from two adjacent but unconnected sectors and a set of second terminals along the opposite edge of the display connected to bar electrodes of the third pair of sectors.

3. A display device as claimed in claim 2 in which the bar electrodes and their interconnections are in printed circuit form.

4. A display device as claimed in any of the preceding claims for display of hours, seconds. and minutes as the first, second, and third variables wherein there are six groups of ten bar electrodes and six segments in each of the concentric electrodes.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. from unit 40 causes different bar electrodes in one sector to be selected in turn, after which the output from unit 41 may change to select another sector, by switching to a different set of connections between the segment drive 33 and the electrode segments of the display system 34. At the same time the inverter 42 is operated if necessary to reverse the sequence of the outputs from unit 40 so that the bar electrodes after an odd/even change of sector are selected in reverse order, thus compensating for the physical reversal of the electrodes resulting from the manner of their connection, which will now be described. The layout diagram of Fig. 2 shows a display system divided into six sectors defined by inner electrode segments 44A to 44F and outer electrode segments 45A to 45F. In each sector there are ten bar electrodes labelled A0 to A9. B0 to B9, and so on. It will be understood that the inner and outer electrode segments are on one face of a liquid crystal device while the bar electrodes are on the opposite face. The bar electrodes of sector A are connected at their outer ends to respective terminals TO to T9 and at their inner ends to respective bar electrodes of sector B. However. to avoid any cross-over of the connectors it will be seen that the bar electrodes of sector B are connected in the reverse order. that is B9 to AO. B8 to Al, and so on with BO connected to A9. The connections are made at the outer ends of the bar electrodes between those of sector B and those of sector C. the order again being reversed. However it will be seen that B9 and CO are directly connected at their inner ends. This form of S connection, alternately at the inner and outer ends. is continued throughout the six sectors so that. for example, the terminal T3 is connected in series with bar electrodes A3. B6. C3, D6, E3, and F6. In addition to the terminals TO to T9, terminals Sl to S12 are provided, which are connected to the electrode segments 44A to 44F and 45A to 45F as shown. There are thus a total of 10 bar terminals and 12 segment terminals to which connections must be made from the electronic circuit of Fig. 1. Twelve segment electrodes with their associated connection leads are shown in printed circuit form in Fig. 3. Whereas in Fig. 2 the terminals are all arranged along one edge of the display. Figs. 3 and 4 show an arrangement with terminals along two opposite edges and in which corresponding bar electrodes are not connected in series throughout all the sectors but are simply grouped in pairs with central connections. Thus in Fig. 4 there are ten bar electrode terminals TO to T9 connected to the bar electrodes A0 to A9 but it will be noted that the connection of TO to A0 is in fact by way of electrode F9 while the connection of T9 is through electrode BO. The bar electrodes AO to A9 are connected respectively with electrodes B9 to BO; Similarly CO to C9 are connected respectively with D9 to DO and EO to E9 with F9 to F0. Additionally, there is a central connection between A0, B9, CO, D9, E0. and F9. Additional terminals LO to L8 are connected directly to bar electrodes FO to F8, respectively, and similarly at the opposite edge of the array there are terminals MO to M9 connected respectively to bar electrodes CO to C9 and terminals N 1 to N9 connected respectively to electrodes D1 to D8 and EO; By external connections between selected terminals it is then possible to ensure that the same signal is applied to corresponding bar electrodes in all six sectors. For example tlie terminals T1, L8 and M1 and/or N8 are connected to a common point so that electrodes Al, B8, C1, D8, El, andF8 receive the same signal. Fig. 4 additionally shows terminals S1 to S12 for connection to the segment electrodes 44E, 45F, 44F, 45A, 44A, 45B, 44B, 45C, 44C, 45D, 44D, and 45E respectively. These terminals are placed for convenience on the same board as the other terminals and connections are made from them across the liquid crystal unit to the conductors on the board which carries the segment electrodes. WHAT I CLAIM IS:

1. A display device of the type defined wherein the concentric electrodes are divided into segments such that groups of bar electrodes forming sectors of the display cooperate respectively with an inner segment and an outer segment for each sector and wherein the bar electrodes of one sector are connected directly in reverse order to the bar electrodes of another sector, the electronic circuit being constructed to select a segment or segments in the required sector and to change the order of selection of the bar electrodes in accordance with the sector selected.

5. A display device as claimed in any of

the preceding claims in which the electronic circuit comprises a bar selection and drive circuit for energizing any selected electrode of each of the groups, a segment drive circuit for energizing the inner segment, the outer segment, or both segments in any selected sector, a sector selector arranged to connect the segment drive circuit to the selected sector, the sector selector also being connected to the bar selection and drive circuit by way of an inverter to reverse the order of the outputs to the bar electrodes on switching from one sector to an adjacent sector.

6. A display device as claimed in claim 5 including a data display selection circuit whose output is connected to the segment drive circuit and also to a multiplexer for applying stored signals representing the values of the three variables to the bar selection and drive circuit and the sector selector, the data display selection circuit switching rapidly and repeatedly between inner segment, outer segment, and both segments and at the same time selecting the corresponding variable by means of the multiplexer.

7. A display device for the display of three variables substantially as described with reference to the accompanying drawings.