GB2128336A - Proximity control switching panels - Google Patents

Abstract

In proximity control switching panels including switching capacitors (e.g. 11, 12) each of which comprises a command electrode capacitor plate (not shown) behind which is arranged at least one slave electrode capacitor plate (3, 4), and conductive input and output connectors e.g. 115 for connecting each slave electrode plate to a voltage source and/or output signal monitoring circuitry, difficulties can arise in the reliable detection of the level of the output signals used to effect switching. To alleviate this problem, said slave electrode plates and associated connectors are constituted by conductive coatings deposited on an insulating support (8), and for a plurality of said capacitors the slave electrodes and their associated connectors are so arranged on the support that when their capacitors are connected to a common voltage source, output signals from those capacitors all have values lying on one side of a threshold value when the command electrodes of those capacitors are in actuated condition, and all have values lying on the other side of such threshold value when their command electrodes are in unactuated condition. <IMAGE>

Description

SPECIFICATION Proximity responsive switching panels This invention relates to a proximity control switching panel including switching capacitors each of which comprises a command electrode capacitor plate behind which is arranged at least one slave electrode capacitor plate, and conductive input and output connectors for connecting each slave electrode plate to a voltage source and/or output signal monitoring circuitry.

Such panels are useful for a wide variety of purposes, for example as data input keyboards for typewriter, printer, computer or telephone operation or as part of a control system for domestic cookers or elevators.

The panels may take various forms. The command and slave electrodes may be applied to the different sides of a single dielectric sheet or onto different dielectric sheets. Each capacitor may have a single slave electrode or an input slave electrode and an output slave electrode. The command electrodes may be exposed to touch or covered by a thin insulating coating.

The operation of such switching panels is well known. When a command electrode plate is actuated, the coupling between the plates of that capacitor is modified so as to modify the level of an output signal and this modification is monitored by detecting circuitry and used to effect some desired switching function.

A particular problem can under some circumstances arise in the reliable detection of such modifications in the levels of the output signals. This problem arises because of crosscapacitance effects between the various connectors and slave electrode plates, and its effects may be particularly acute in the case, for example, of a multiplex circuit arrangement in which at least two output signals are directed to the same input of the detecting circuitry.

It is an object of the present invention to alleviate this problem.

The present invention provides a proximity control switching panel including switching capacitors each of which comprises a command electrode capacitor plate behind which is arranged at least one slave electrode capacitor plate, and conductive input and output connectors for connecting each slave electrode plate to a voltage source and/or output signal monitoring circuitry, characterised in that said slave electrodes and associated connectors are constituted by conductive coatings deposited on an insulating support, and in that for a plurality of said capacitors, the slave electrodes and their associated connectors are so arranged on the support that when their capacitors are connected to a common voltage source, output signals from those capacitors all have values lying on one side of a threshold value when the command electrodes of those capacitors are in actuated condition, and all have values lying on the other side of such threshold value when their command electrodes are in unactuated condition.

The present invention has the advantage that the output monitoring circuitry to be associated with such a panel can be simplified, either in its construction or in its setting up. For example when the outputs of the capacitors are fed to different threshold detectors, all these detectors may be pre-set to the same threshold value. Alternatively, a single threshold detector may be used.

The problem which the present invention is intended to alleviate is particularly acute when one or more of the following circumstances obtains: the slave electrodes lie between a vitreous backing sheet and the command electrodes; said plurality of capacitors comprises a rectangular array which is at least three by three, for example three by four or four by four or larger; each of said plurality of capacitors has a pair of slave electrodes of which one is an input electrode arranged for connection to a voltage source common to all such capacitors and the other is an output electrode arranged for connection to pulse detector circuitry; the input slave electrodes are interconnected on the support by their associated connectors; and the invention is accordingly particularly applicable in those circumstances.

In preferred embodiments of the invention, conductive coating material is applied to said support so as to increase cross capacitance between at least one selected slave electrode and/or output connector and a neighbouring conductive element. The or each slave electrode and/or output connector so selected will be one having an otherwise low capacitive crosscoupling, and the adoption of this preferred feature of the invention introduces an increased cross-coupling of the selected electrode and/or connector. In this way it is possible to compensate for undesired cross-coupling of other, unselected electrodes and/or connectors to give the desired output signals.

It is perhaps surprising that the disadvantageous effects of capacitive crosscoupling in certain capacitors should be reduced by introducing further cross-couplings rather than by reducing the undesired cross-couplings, but in practice this is found most convenient, inter alia because of constraints on the space which the panel may occupy.

One way of achieving this result is to ensure that selected pairs of input and output slave electrodes are deposited closer together than other pairs of slave electrodes as is preferred. This introduces an increased cross-coupling between those selected pairs of electrodes as compared with the others.

Also, by depositing such a pair of slave electrode closer together, it is possible to enlarge the gap between that pair of slave electrodes and an adjacent pair. This is especially useful at the borders of a said array where an output connector from the centre of the array must pass between two pairs of slave electrodes.

By enlarging the gap between those pairs of electrodes, an output connector can be led through further away from any input electrode bordering that gap so that cross-coupling between them is reduced. It is accordingly preferred that such selected more closely spaced pairs of electrodes should comprise at least some of the pairs of slave electrodes cf capacitors located at the edge of such array. Whether this particular feature is present or not, it is for a similar reason preferred that the or each output connector from the or a central column or row of the array which passes between input and output slave electrodes of an outer column or row of the array is arranged to pass closer to such output electrode than to such input electrode.

Alternatively or in addition, it is preferred that at least one selected connector should include at least one local change in direction thereby to induce additional capacitive coupling of that connector (and its associated slave electrode) with a neighbouring slave electrode and/or with a connector associated with a neighbouring slave electrode, and/or to induce additional electrical resistance in that selected capacitor. Each such selected connector is preferably an output connector, and the said neighbouring slave electrode is preferably the input electrode paired with the output electrode from which that connector leads.

Another alternative or additional preferred feature of some embodiments of the invention is that at least one selected connector has a conductive line branching therefrom to induce additional capacitive coupling of that connector (and its associated slave electrode) with a neighbouring slave electrode.

A further alternative or additional preferred feature is that at least one selected slave electrode has a conductive line branching therefrom to induce additional capacitive coupling of its associated selected slave electrode with a neighbouring slave electrode and/or of that associated selected slave electrode with a said connector associated with a neighbouring slave electrode.

By appropriate selection of connector(s) and/or slave electrode(s), such additional coupling can be arranged to modify output signals from the different capacitors so that a common threshold can be set for the output signals originating with all of the capacitors.

Advantageously, at least some of said associated and neighbouring pairs of slave electrodes form one or more said pairs of input and output electrodes. In this way, the output signal modification achieved by the additional cross-coupling will be substantially confined to the capacitors of which such pairs are a part, so that signal modification for individual capacitors is simplified.

Best results have been achieved in embodiments in which the or each such conductive branch line branches from an input connector or an input slave electrode.

Another way of achieving a common threshold as between operative and inoperative conditions of the command electrodes of the various capacitors is to reduce the size of at least one slave electrode (preferably an output electrode) as compared with neighbouring slave electrodes.

Preferably the or all such smaller output electrode(s) is or are surrounded by other slave electrodes on the support.

In other preferred embodiments of the invention, the or at least one such smaller electrode is an input electrode which is not wholly surrounded by the other slave electrodes on the support.

The invention is particularly applicable where all slave electrodes are deposited on a common support, for example a vitreous support, which may be the same as or different from the support on which the command electrodes are deposited.

The conductive coatings forming the electrode plates and connectors and conductive lines where present are preferably conductive metal oxide coatings, for example coatings of doped tin oxide.

The invention includes a proximity control switching system including a panel as herein defined and comprising a voltage source (preferably a pulse generator) connected to each input connector and, connected to said output connectors, monitoring circuitry comprising threshold means for sequentially monitoring the output from different output connectors and for identifying the switching capacitor from which the output is being monitored at any given time.

Various preferred embodiments of the present invention will now be described with reference to the accompanying drawings in which: Figures 1 and 2 illustrate levels of various output signals; Figures 3 and 4 are cross sectiona! views of two embodiments of panel according to the invention: Figures 5 to 8 illustrate various ways in which the slave electrodes and their connectors can be deposited in accordance with the invention; Figure 9 is a bock diagram illustrating the use of a panel according to the invention; Figure 10 is a further illustration of the deposition of slave electrodes and their connectors, and Figure 11 is a second block diagram illustrating the use of the panel illustrated in Figure 10.

Figures 1 and 2 illustrate schematically the levels of pairs of output pulses from two capacitor switches. Output pulse A comes from a first capacitor in which a command electrode plate is in the unactuated condition, and pulse B from the same capacitor when its command electrode plate is touched or closely approached to render it operative. The amplitudes of these pulses are indicated at Va and Vb respectively. Output pulses C and D come from a second capacitor respectively when the command electrode plate is in unactuated and in actuated condition. The amplitudes of these pulses are indicated at Vc and Vd.

In the circumstances illustrated in Figure 1 , the range Va to Vb over which pulse amplitude from the first capacitor is changed lies wholly outside the range Vc to Vd over which pulses from the second capacitor have their amplitudes modified.

Accordingly no common switching threshold can be set for these capacitors. The invention seeks to remedy this problem by arranging capacitor slave plates on their support in such a manner that there is an overlap in such modification ranges, for example as shown in Figure 2, in which case a single switching threshold can be set with a value between Vc and Vb.

In Figure 3 a sheet of glass 1 which may be tempered has a pattern of command electrodes 2 deposited on its front face, and a pattern of slave electrodes, input electrodes 3 and output electrodes 4, together with associated connectors (not shown). Each command electrode 2 and its associated pair of input and output slave electrodes 3, 4 constitutes a switching capacitor 5 of which two are shown in the drawing. A backing sheet 6 also of glass is bonded to the rear face of the first sheet 1 over the slave electrodes by a layer of adhesive material 7.

Figure 4 shows a modified panel in which similar integers are accorded the same reference numerals. The difference between the two panels is that in the Figure 4 embodiment the slave electrodes 3, 4 (and their associated connectors) are deposited not on the rear face of the front sheet 1, but on the front face of the backing sheet 6. An advantage of this arrangement is that the front glass sheet 1 no longer needs to be coated on both sides.

Other modifications may be made to the form of the panel, for example as described with reference to any of Figures 1, 2 and 5 of co-pending British Application No. 2 090 979.

The idea underlying the invention is manifest in the pattern in which slave electrodes and associated connectors are deposited on their support, whether this be a front sheer 1 as in Figure 3 or a backing sh-eet 6 as shown in Figure 4, or indeed with some slave electrodes on one such sheet and others on another.

Examples of such patterns are illustrated-in Figures 5 to 8, in each of which all the slave electrodes 3, 4 are deposited as doped tin oxide coatings on a vitreous support 8. The various connectors and conductive lines (where present) are also formed by tin oxide coatings. Input and output terminals 9, 10 are provided, and these are conveniently formed by metallising portions of the support 8 or, and preferably, by depositing bodies of conductive enamel so as to facilitate solder connection of circuit wiring.

In Figures 5 to 8, pairs of input 3 and output 4 slave electrodes are deposited in a four-by-four rectangular array for a panel having up to sixteen switches. Of course if less than sixteen switches are required, the signals from appropriate output terminals 10 are left unused. These sixteen pairs of slave electrodes 3, 4 are numbered, from the top left, 11 to 26, as shown in Figures 5 and 8, though not all the reference numbers are shown in all the drawings.

A common input connector 27 has elements which extend from the input terminals 9 to each of the input electrodes 3 of pairs 23, 26 and thence via input electrodes 3 of pairs 24, 25 respectively to meet in the centre of the bottom row of the array. An element of the input connector 27 leads up the array and is joined via branch connectors to each of the other input electrodes 3. An output connector leads from each output electrode 4 to its individual output terminal 10.

Specific features of the embodiments illustrated in Figures 5 to-8 will now be adverted to with reference to the individual Figures, and in this description, the various output connectors, where specifically referred to, will be allotted a three digit reference numeral consisting of the reference numeral of the slave electrode pair from which they lead to which the number of the appropriate Figure is suffixed.

In Figure 5, the electrode plates 3, 4 are all of substantially the same size, and the various pairs are uniformly spaced: In switching capacitors of the type illustrated there is a problem caused by unwanted capacitive cross-coupling- between the input 3 and output 4 electrode plates of any pair.

An output connector such as 1 65 leading from one of the electrode pairs 1 6 in the centre of the array must clearly pass between electrode plates at the edge of the array, and a further problem arises because of unwanted cross-coupling between that connector 1 65 and the input electrode 3 of electrode pair 11 next to which it passes. In fact there will also be some crosscoupling between that connector 1 65 and the output electrode 4 of electrode pair 1 5 next to which it passes, but this is of comparatively minor significance. A similar situation obtains in the case of output connectors 175,205, 215, 245 and 255 respectively leading from the output electrodes 4 of electrode pairs 17-, 20, 21, 24 and 25 also in the centre columns of the array.These problems give rise to the undesirable reiative levels of output signals illustrated in Figure 1.

In accordance with the invention, the various output connectors are deposited in an appropriate way to compensate, at least in part, for differences in output signal levels as between the different output capacitors, so as to bring about the situation described with reference to Figure 2. This is particularly noticeable in the case of the output connectors from the output electrodes in the two outer columns of the array. It will be noted that each of these connectors, indicated respectively at 115, 145, 155, 185, 195,225,235 and 265 undergoes at least one local change in direction so that, in particular, its course passes close to the input electrode 3 associated with the output electrode 4 from which it leads. In addition, output connectors 235 and 265 pass close to elements of the input connector 27. Also it will be noted that a conductive extension 28 branches from the input connector 27 at the upper centre of the array between electrode pairs 12 and 1 3 whose output connectors 125, 135 do not pass next to any input electrode. The effect of the arrangement illustrated is to provide increased cross-coupling between the output connector or output electrode of each of these pairs 11 to 15, 18, 19, 22, 23 and 26 and the input electrode 3 of the respective pairs and/or the input connector, so that output signals from those electrode pairs are modified in the same sense as the output signals from electrode pairs 16, 17, 20, 21,24 and 25 and thus bring about the situation described with reference to Figure 2.

Figure 6 shows an embodiment similar to that of Figure 5 in which further compensatory features are introduced. In Figure 6, the spacing between the slave electrodes 3, 4 of each pair is uniform, output connectors 116, 146, 156, 186, 196, 226, 236 and 266 from output electrodes 4 in the outer columns undergo local changes in direction to provide additional cross-coupling with their respectively associated input electrodes 3, and a conductive extension 28 branching from the input connector provides additional cross-coupling between the input and output electrodes 3, 4 of electrode pairs 12, 13: these features follow Figure 5.

An additional feature shown in Figure 6 is that output connector 166, leading from one of the electrode pairs 1 6 in the centre columns of the array is redirected so that instead of passing midway between input electrode 3 of pair 11 and output electrode 4 of pair 1 5 at the edge of the array (compare Figure 5), it passes much closer to the output electrode 4 of pair 1 5. Thus output connector 166 is spaced further from the input electrode 3 of pair 11 so that undesirable crosscoupling between them is reduced and hence the output signal from electrode pair 1 6 is modified.

Output connectors 176, 206, 216, 246 and 256 are similarly redirected to reduce their crosscoupling with input electrodes 3 next to which they pass.

Instead of, or in addition to, redirecting those output connectors, cross-coupling between them and the input electrodes 3 of pairs 11, 14, 15, 18, 19 and 22 can be reduced by reducing the area of those input electrodes 3 by comparison with the other slave electrodes on the support. This feature is also illustrated in Figure 6, and will again have a modifying effect on the levels of the output signals from the panel.

In Figure 7, as in Figure 6, output connectors (here indicated at 167, 177, 207, 217, 247 and 257) from electrode pairs 16, 17, 20, 21,24 and 25 are redirected to pass further away from the input electrodes 3 respectively of electrode pairs 11,14,15,18, 19 and 22, and those input electrodes 3 are of reduced area as compared with all the other slave electrodes.

In Figure 7, this distancing of output connectors such as 1 67 from adjacent input electrodes 3 such as that of pair 11 is further enhanced by reducing the gap between the input and output electrodes 3, 4 of those same electrode pairs 11, 14, 1 5, 18, 19and22.

The embodiment illustrated in Figure 7 also includes a number of conductive lines branching out from the input network comprising input connector 27 and extension 28 and the input electrodes 3. A branch 29 projects to either side of the end of the conductive extension 28 to increase capacitive cross-coupling between the output electrodes 4 of electrode pairs 12, 13 and their respective input electrodes. Electrode pair 11 is provided with two conductive branch lines 30, 31.

The first of these, 30, branches out from the input connector element leading to its input electrode 3 and provides additional capacitive cross-coupling between that input electrode 3 and its paired output electrode 4. The second conductive line 31 branches out from the input electrode 3 itself, to run parallel to the output connector 117 of its paired output electrode 4 to increase capacitive cross-coupling between them. The presence of either or both of these lines 30, 31 will have a modifying effect on output signals from the electrode pair 11.

Electrode pairs 14, 15, 1 8, 19 and 22 have similar conductive branch lines 30, 31.

It will of course be appreciated that any conductive branch line 30, or each of them, could be arranged to lead out from an input electrode 3 instead of the input connector element leading to that electrode.

In Figure 8, as in Figure 7, output connectors (here indicated at 168,178,208,218,248 and 258) from electrode pairs 16, 17,20,21,24 and 25 are redirected further away from the input electrodes 3 respectively of electrode pairs 11, 14, 15, 1 8, 19 and 22 and those input electrodes 3 are displaced upwardly towards their associated output electrodes 4 to reduce the gap between them. As in Figures 5 and 6, conductive extension 28 provides additional cross-coupling between the input and output electrodes 3, 4 of pairs 12,13.

In Figure 8, all the input slave electrodes 3 are of the same size and equal in area to those output slave electrodes 4 which lie at the border of the array, that is to say those of the electrode pairs 11 to 1 5, 1 8, 19, 22, 23 and 26. Slave electrodes 4 of the other electrode pairs 1 6, 17, 20, 21, 24 and 25 are of reduced size (approximately half size).

This modifies the level of the output signal from those electrodes as compared with the remainder.

By virtue of any of the departures from a uniformly sized and spaced layout of slave electrodes and conductors described with reference to Figures 5 to 8, a closer agreement between the levels of output signals from the various output electrodes can be achieved and this permits the use of a single threshold setting for all the capacitor switches on the panel.

Figure 9 illustrates diagrammatically how a panel according to the invention may be used. The panel (indicated at 33) has its (input) slave electrodes (not shown) fed by a common voltage source 32, preferably a pulse generator or oscillator which may for example be arranged to deliver input pulses with a frequency of 100 kHz.

Output signals from the various switching capacitors on the panel are individually fed to monitoring circuitry 34 where they are suitably passed sequentially to a common threshold detector which is arranged to detect when any switching capacitor is actuated and which is coupled with pulse counter or other means for determining which of the switching capacitors was actuated, so that an appropriate switching signal can be passed to the apparatus being controlled by the panel.

Figure 10 shows a vitreous support 8 which carries pairs of input 3 and output 4 electrodes deposited in two adjacent four-by-four rectangular arrays for a panel having thirty two switches indicated at SO to S31. As before, the input electrodes 3 of each array (the switches SO to S15 and S16 to S31 respectively) are connected to each other and to input terminals 9 by connectors 27a and 27b respectively. The output electrodes 4 of the switches SO to S31 are connected to output terminals 10 by conductors respectively CO to C31 (not all of which are specifically indicated).

In Figure 10 is will be noted that the thirty-two switches SO to S31 are approximately square, that they are substantially evenly spaced in four vertical columns each containing eight switches and that the input 3 and output 4 electrodes of each switch are formed as rectangles separated by a horizontally running space. However unlike the arrangement of Figures 5 to 8, like electrodes of successivç switches in each column are placed adjacent one another. Considering the electrodes in any column, going down from the top, there is one output, two inputs, two outputs, two inputs, two outputs and so on to a single output for the bottom switches S19, S23, S27 and 531.This arrangement enables output connectors C5, C6; C9, C10; C7, C20; Cl 1, C24; C21, C22; C25, C26 from central switches of the array to be led out between output electrodes 4 of outer switches rather than adjacent an input electrode of an outer switch. Thus for example output connectors C5, C6 of switches S5, S6 are led out between the output electrodes 4 of switches S1 and S2. This renders output signals from switches S5, S6 less susceptible to noise due to cross capacitance with input circuit elements.

In order to compensate for differences in levels of output pulses from the various switches compensatory features are provided in respect of those switches in the two outer columns.

Thus, the input and output electrodes 3, 4 of those switches S1, S14, S17 and S30 whose input electrodes 3 are directly connected to input terminals 9 are reduced in area as compared with the electrodes of the two central columns, and the electrodes 3, 4 of switches SO, S1 5, S16 and S31 are also reduced in area. The last mentioned four switches are adjacent the input electrodes 3 of the other four switches of reduced electrode area. This compensatory feature acts to reduce the total capacitance of these eight switches which would otherwise be higher due to the fact that output connectors CO, C1, C14, C15 and C16, C17, C30, C31 are respectively adjacent the input connectors 27a and 27b.

The other switches in the two outer columns are those designated S2, S3, S12, S13, S18, S19, S28 and 529 and the input and output electrodes of these switches have substantially the same area as the switches in the two centre columns.

The input electrode of each of these other outer switches is provided with a conductive line 31 (compare Figure 7) which branches out to run parallel to the output connector of that switch.

This compensatory feature acts to increase the cross-capacitance thereto and thus the total capacitance of these switches which is small because their output connectors areishort and because they are remote from the input connectors.

Figure 11 illustrates the connection of switches SO,S1...S15andS16,S17...S31 toan interface circuit 35 arranged to deliver a binary encoded output at output terminals U, W, X, Y, Z.

Series of scanning clock pulses are fed alternatively from the interface circuit 35 respectively along the connector 27a to the first sixteen switches SO to S15 and along connector 27b to the second sixteen switches S16 to S31.

The first sixteen switches SO, S1 ... S15 are connected by their output connectors CO, C1 ...

C15 respectively to input terminals IA, IB .. IP of the interface circuit 35. The second sixteen switches S16, S17 S31 are also connected respectively to the sixteen input terminals IA, IB . . IP of the interface circuit 35. When one of the thirty-two switches is touched, a modified signal is delivered to the appropriate input terminal and a signal is then passed through the interface circuit to the appropriate output terminal(s) U, W, X, Y, Z.

Distinction between the two switches connected to any given input terminal IA, IB . IP is by synchronisation with the scanning clock pulses.

When a multiplex arrangement as illustrated in Figure 11 is used, and one or more of the switches SO to S31 is not connected to any input terminal of the interface circuit 35 because it is not desired to make use of that switch or those switches, or because a smaller switch panel is used, for example a twenty-four switch panel, then each "missing" switch should be replaced by a capacitor wired in between the appropriate scanning clock output and the appropriate input terminal of the interface circuit. Alternatively if any input terminal is wholly idle, it may be connected to a voltage source so that the terminal always registers as though switches were connected thereto and were untouched.

It will be appreciated that in such a multiplex circuit arrangement the requirement for substantial equalisation of switch output pulses in the untouched. and in the touched conditions respectively is more stringent than when each switch passes pulses to its own circuit input.

Claims (22)

1. A proximity control switching panel including switching capacitors each of which comprises a command electrode capacitor plate behind which is arranged at least one slave electrode capacitor plate, and conductive input and output connectors for connecting each slave electrode plate to a voltage source and/or output signal monitoring circuitry, characterised in that said slave electrodes and associated connectors are constituted by conductive coatings deposited on an insulating support, and in that for a plurality of said capacitors, the slave electrodes and their associated connectors are so arranged on the support that when their capacitors are connected to a common voltage source, output signals from those capacitors all have values lying on one side of a threshold value when the command electrodes of those capacitors are in actuated condition, and all have values lying on the other side of such threshold value when their command electrodes are in unactuated condition.

2. A panel according to Claim 1, wherein said slave electrodes lie between a vitreous backing sheet and said command electrodes.

3. A panel according to Claim 1 or 2, wherein said plurality of capacitors comprises a rectangular array which is at least three by three.

4. A panel according to any preceding claim, wherein each of said plurality of capacitors has a pair of slave electrodes of which one is an input electrode arranged for connection to a voltage source common to all such capacitors and the other is an output electrode arranged for connection to signal monitoring circuitry.

5. A panel according to Claim 4, wherein the input slave electrodes are interconnected on the support by their associated connectors.

6. A panel according to any preceding claim, wherein conductive coating material is applied to said support so as to increase cross capacitance between at least one selected slave electrode and/or output connector and a neighbouring conductive element.

7. A panel according to Claim 4 or 5 and Claim 6 wherein selected pairs of input and output slave electrodes are deposited closer together than other pairs of slave electrodes.

8. A panel according to Claim 3 and any of Claims 4 to 7 wherein the or each output connector from the or a central column or row of the array which passes between input and output slave electrodes of an outer column or row of the array is arranged to pass closer to such output electrode than to such input electrode.

9. A panel according to any preceding claim, wherein at least one selected connector includes local changes in direction thereby to induce additional capacitive coupling of that connector (and its associated slave electrode) with a neighbouring slave electrode and/or with a connector associated with a neighbouring slave electrode, and/or to induce additional electrical resistance in that selected connector.

1 0. A panel according to Claim 9, wherein the or each said selected connector is an output connector.

11. A panel according to any preceding claim, wherein at least one selected connector has a conductive line branching therefrom to induce additional capacitive coupling of that connector (and its associated slave electrode) with a neighbouring slave electrode.

12. A panel according to any preceding claim, wherein at least one selected slave electrode has a conductive line branching therefrom to induce additional capacitive coupling of its associated selected slave electrode with a neighbouring slave electrode, and/or of that associated selected slave electrode with a said connector associated with a neighbouring slave electrode.

13. A panel according to any of Claims 4 to 8 and any of Claims 9 to 12, wherein the or at least some of said associated and neighbouring pairs of slave electrodes form one or more said pairs of input and output electrodes.

14. A panel according to any of Claims 4 to 8 and any of Claims 11 to 13, wherein the or each such conductive branch line branches from an input connector or an input slave electrode.

1 5. A panel according to any preceding claims, wherein at least one slave electrode is of reduced size as compared with neighbouring slave electrodes.

1 6. A panel according to any of Claims 5 to 8 and Claim 14, wherein the or at least one such smaller electrode is an output electrode.

17. A panel according to Claim 16, wherein the or all such smaller output electrode(s) is or are surrounded by other slave electrodes on the support.

1 8. A panel according to any of Claims 5 to 8 and Claim 15, wherein the or at least one such smaller electrode is an input electrode which is not wholly surrounded by other slave electrodes on the support.

1 9. A panel according to any preceding claim, wherein said slave electrodes are deposited on a common support.

20. A panel according to Claim 19, wherein said support is a vitreous support.

21. A panel according to any preceding claim, wherein said conductive coatings are conductive metal oxide coatings.

22. A proximity control switching system including a panel according to any preceding claim, and comprising a voltage source connected to each input connector and, connected to said output connectors, monitoring circuitry comprising threshold means for sequentially monitoring the output from different output connectors and for identifying the switching capacitor from which the output is being monitored at any given time.