ELECTRONIC KEYBOARD AND KEYTOPS THEREFOR

ELECTRONIC KEYBOARD AND KEYTOPS THEREFOR

The present invention relates to electronic keyboards and, in particular, to the keytops of the keys of such a keyboard.

In known electronic keyboards, the function of each key is generally indicated by a visual designation such as a character inscribed or stamped on the keytop- In certain applications it may be desired to alter the function of one or more keys of the keyboard, with the result that, to avoid confusion,- the visual designation of the keys concerned must also be changed. At present this involves either physically changing the relevant keytops or, more crudely, sticking a label over the keytop designations to be changed. Where a large number ^'of keys is involved or where the frequency of change of key designation is high, neither of the above two procedures is very practical.

It is an object of the present invention to provide an electronic keyboard in which the visual designations given to the keys can be readily changed.

According to one aspect of the present invention,

^~:display being energisable to display a selected one of a plurality of characters for the purpose of providing a visual designation of current function of the associated key, the keyboard further comprising electronic control means for controlling the energisation of said display, and connection means connecting said electronic control means to each said display.

Preferably each said electronic display is a liquid crystal display of dot matrix form (for example 9 rows by 7 columns) , the dots being selectively energisable to represent^" most currently used characters or symbols.

In use of the keyboard, the electronic control means causes the keytop displays to display a desired set of characters . This displayed character set can be readily altered by appropriately instructing the electronic control means to change the energisations of the displays. The electronic control means will generally comprise a memory device storing the required display energisation patterns for one or more character setsr in this case it is only necessary to instruct the control means as to the identity of a new character set it is desired to display in order to bring about the desired change. Instruction of the electronic control means may, for example, be effected via a particular key of the keyboard. The memory device is, for example, a programmable read only memory (PROM) containing several character sets, further such sets being available by interchanging the PROM device for another one. *

The said connection means connecting the keytop displays and the electronic control means, advantageously includes, for each key, a flexible connector having one part carried by the key top and a cooperating part carried on a printed circuit board mounting the keys. The connector part carried by the key top is electrically connected to the keytop display while the connector part carried by the printed circuit board is electrically connected to the electronic control means which preferably take the form of one or more integrated circuits mounted on the circuit board.

According to another aspect of the present invention, -there is provided a keytop for keys of an electronic

An electronic-keyboard key embodying the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which:

Figure 1 is a perspective view of the key and of a printed circuit board on which the key is to be mounted, the Figure also showing in block diagram form, control electronics used to control an electronic display incorporated in the key;

Figure 2 is an enlarged cross-section through the key, the switch components of the key being omitted for the sake of clarity;

Figure 3 is a.plan view of a liquid crystal display incorporated in the keytop of the key;

Figure 4 is a section on line IV-IV of Figure 3;

Figure 5 is a section on line V-V of Figure 3;

Figure 6 is a view similar to Figure 3 but of an alternative embodiment of the liquid crystal display,

Figure 7 is a perspective view of a retaining collar of the key, and

_^Figure 8 is a cross-section similar to Figure 2, but showing an alternative key structure.

To be described hereinafter is one key 10 (see Figure 1) of an electronic keyboard which comprises a plurality of substantially identical keys. These keys are mounted on a printed circuit board 11 and so far as their key switching action is concerned, the keys are of standard form; for this reason the details of the key switches will not be described. Thus in Figure 2 although the keytop 12 of the key 10 has been illustrated, the key switch normally housed inside the keytop 12 has not been shown. One suitable form of key switch for the keyboard keys is that of the "Keyboard Component System" (Trade Mark) marketed by Chromerics of Wobur , Massachusetts, U.S.A.

Referring now in detail to the drawings, the key shown in Figures 1 and 2 comprises a keytop 12 incorporating an upwardly-facing liquid crystal display 13. At its lower end, the keytop 12 carries the female part 14 of a flexible connector, the male part 15 of which is mounted on the circuit board 11. The male and female connector parts 15, 14 are arranged to snap engage with each other upon the keytop 12 being pressed into place over the structure of the key switch (not shown) . The connector 14, 15 serves to connect the liquid crystal display 13 to controlling electronics mounted on the printed circuit board 11.

When the keytop 12 is in place (see Figure 2) , its side opposite the flexible connector 14, 15 rests on a cushion 16 which permits the key 10 to be depressed (with flexing about the connector) to operate the key switch.

As shown in Figure 3, the liquid crystal display 13 is of dot matrix form having sixty-three dots 17 arranged in nine rows and seven columns. The display 13 comprises two plates 18 and 19 the uppermost one 18 of which is transparent. The undersurface of the upper plate 18 is formed with nine channels 21 (Figure 5) extending in the column direction of the dot matrix, while the lower plate 19 is formed in its upper surface with seven channels

20 (Fig. 4) extending in the row direction of the dot matrix. The plates 18 and 19 are sealingly joined together with their channels containing a suitable known form of liquid crystal composition. The "dots" of the display matrix lie at the channel intersections. Selective energisation of the matrix dots (that is, the application of an electric field thereacross) is effected, by means of transparent conductive tracks carried by the plates 18 and 19 in alignment with the column channels 21 and the row channels 20 respectively. In order to provide for external connection to these conductive tracks, each track terminates in a respective edge connector contact 22 (shown hatched in Figure 3 for clarity) . Since the contacts 22 are most conveniently made on the underside of the plate 18 and on the upper surface of the plate 19, these plates 18 and 19 are staggered with respect to one another to leave the edge portion of one side of each plate free for the contacts 22. The nine. column contacts 22 are thus arranged downwardly facing along the projecting side of the upper plate 18 while the seven row contacts are arranged upwardly facing on the projecting side of the lower plate 19. In an .alternative embodiment (see Figure 6), in order to enable, the areas of the contacts 22 to be made as large as possible, the plates 18 and 19 are staggered such that two adjacent sides of each plate project beyond the other plate and the contacts 22 corresponding to the matrix columns are divided four and five between opposite exposed edge portions of the plates 18 and 19, while the contacts 22 corresponding to the matrix rows are divided four and three between the corresponding opposite edge portions of the plates 18 and 19.

Typical dimensions for the form of display 13- illustrated in Figure 3 are an overall size of 10.25 mm x 12.25 mm with gaps of 0.20 mm between channels 20 and 21, the width of the channels and associated conductive tracks being 0.70 mm.

The liquid display 13 is arranged to seat within the top of the _.keytop 12 which is preferably formed by injection moulding techniques. To retain the display

13 in position, a retaining collar 25 (see Figures 2 and 6) is arranged to snap engage with the keytop 12, for which purpose the keytop is formed with a resilient lip 26 m The retaining collar 25 is formed with a central transparent plate 27 which serves as a protective covering for the display 13. The general shape of the collar 25 is such that the top of the key has a concave form.

Embedded within the keytop 12 are sixteen leads 28 which extend up from the female flexible-connector part

14 carried by the keytop 12, towards the display 13 to make contact with respective ones of the contacts 22 of the display. Nine of the leads 28 terminate in contacts disposed directly beneath respective ones of the downwardly facing contacts 22 carried by the plate 18; these lead contacts are not visible in Figure 2 but ^" extend leftwards in a line from the illustrated lead 28 in a different but parellel plane to that of the

Figure. Electrical connection between the lead contacts and the contacts 22 is effected either directly (with the downward retaining pressure exerted by the collar 25 ensuring good contact therebetween) or with the imposition-of a conducting gasket (not shown) such as is marketed by Chomerics under the Trade Mark "Cho-nector" The other seven leads 28 extend up to the level of the - collar 25 in regions directly opposite respective ones of the upwardly facing contacts 22 of the plate 19.

If all the contacts 22 were to be arranged downwardly facing on the plate 18, the provision of bridging contacts 31 carried by the collar 25 would of course be unnecessary.

The male part of the flexible connector 15 can either be directly connected to tracks printed on the printed circuit board 11 or, as is indicated in Figure 2 , may be connected to leads 33 embedded in the board 11, these leads in turn being connected to printed circuit tracks on the board.

Figure 8 shows an alternative form of key structure in which the keytop 12 is snap-mounted on a post 40 for limited sliding movement sufficient to cause operation of the key contacts via a pressure pad 41 carried by the circuit board 11. Connection of the leads 33 to the liquid crystal display 13 is effected via a sixteen-conductor flexible connection strip

42 extending from.a snap connector 43 inside the keytop 12 to a snap connector 44 making contact with projecting terminations 45 of the leads 33. The snap connector

43 makes direct contact with the contacts of the liquid crystal display 13 and can be of any suitable form.

The key top 12 can be internally formed to facilitate . the location of the snap connector 43.

The control electronics used to control the energisation ^•of the row and column tracks of the display 13, and ^" thus the character formed on the display, basically comprises the following three components : 1) a memory unit 50 (see Figure 1) containing the row and column energisation patterns required to produce the characters of one or more character sets ; 2) driver circuits 51 arranged to energise the display 13 in dependence on the energisation data stored in the memory unit 50; and 3) a control unit 52 for controlling the output of data from the memory unit 50 to the driver circuits 51.

The control electronics is of course arranged to control the energisation of the displays 13 of all the keys 10 making up the keyboard and, as is standard practice with multiple displays , multiplexing is adopted to reduce the number of outputs from the control electronics. Three possible arrangements of the control electronics will be briefly outlined below; the precise implementation details of these arrangements will be apparent to those skilled in the relevant art and therefore a detailed exposition of the electronics will not be given herein.

^! In a first arrangement, the memory unit 50 only contains energisation pattern data for a single, fixed, character set with the association of each key 10 with a ^"character of that set being also fixed. With such an arrangement, the energisation pattern data output from - ^" the memory unit 50. is invariant in content and order between successive multiplexing cycles so that the control unit 52 can be very simple. In an electronic keyboard implemented with control electronics of this form, the memory unit 50 preferably takes the form of a read-only memory (ROM) in a plug-in integrated

- circuit package so that change of the displayed character set only requires the ROM to be changed.

-In a second arrangement of the control electronics , the memory unit 50 is pre-programmed with the energisation pattern data for two or more character sets and, again, the association of each key 16 with a character of that set is fixed. This arrangement is very similar to the first except that now the control unit 52 must be instructed as to which of the two or more memorised character sets is to be displayed. Instruction of the control unit 52 can be effected either under operator control using a dedicated input switch 53 (see Figure 1) or a designated one of the keyboard keys , or under the control of a microprocessor or other computing device with which the keyboard is associated. As with the first arrangement, the memory unit 50 preferably comprises plug-in ROM's which can be replaced to vary the available character sets.

In a third arrangement, the control electronics is very similar to that of the first arrangement except that the memory unit 50 is of the type which can be both repeatedly written into and read from during operation. The energisation pattern data held in the memory unit 60 is loaded in from an external source (for example, a controlling microprocessor) and can be changed at any time. Such an arrangement is very versatile since it enables the designation of any one or. more keys 10 to be changed without affecting the remaining key designations. Of course it will be appreciated that the energisation pattern data fed to the memory unit 50 has still to be stored somewhere in the overall system, the selection and transmission of this data to the memory unit 50 being initiated by an instruction to put up a particular character on a particular key display. The necessary control and memory devices required to re-programme the memory unit can, of course, be incorporated in the control electronics provided on the board 11. From the foregoing it will be appreciated that the described form of keyboard key enables an electronic keyboard to be provided which can be set to display variable layouts and/or different languages and alternative symbols in response to a single user instruction or operation. This facility permits a keyboard to be used for a variety of functions, with appropriate key representations being displayed in accordance with user requirements. Electronic keyboards of this form have application in computer terminals, video displays, typewriters and similar equipment where data is to be entered manually.