Note: Descriptions are shown in the official language in which they were submitted.
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SWITCH/DISPLAY UNITS
The present invention relates to switch/display units.
British Patent Specification No 2002522 discloses a
touch switch with integral electro-luminescent
display. This switch may be arranged so that the
switch, or a legend on the switch, is illuminated upon
actuation of the switch. The illuminated area of the
switch is defined by an insulating mask which controls
the area of excitation of a layer of phosphor. The
area that may be illuminated would therefore be fixed
when the switch is manufactured and the switch is
consequently suitable to control only one function.
The present invention provides a switch/display unit in
which the display may be varied electronically, thus
providing a programmable multi-function switch.
According to one aspect of the present invention, a
switch/display unit comprises; a transparent
dielectric panel; a first set of elongate parallel
electrode~ formed from transparent conductive material
on the rear surface of said dielectric panel; a layer
of phosphor in contact with said first set of
electrodes; a second set of parallel elongate
1;2190S2
electrodes mounted in contac~ with the rear sur~ace of
the layer of phosphor, the second set of electrodes
being inclined to the first set of electrodes, so that
the electrodes of one set overlap ~hose of the other
set to form a dot matrix; and a transparent conductive
layer formed in front of the dielectric panel and
overlying the first set of electrodes.
The conductive layer in front of the dielectric panel
may be formed on the front surface of the panel. With
this form of construction, the conductive layer will
capacitively couple the electrodes on the rear surface
of the panel. This capacitive coupling may be modified
by applying an electrical load to the conductive layer
by, for example, touching or earthing the conductive
layer, and this change in coupling may be used to
produce a signal for switching purposes. Altern-
atively, the conductive layer may be spaced from the
front surface of the dielectric panel, but arranged so
that it may be moved into engagement with the panel.
With this arrangement, initially electrodes on the rear
surface of the panel will not be coupled capacitively
to any great extent, but will be coupled when the
conductive layer is moved into contact with the panel.
Again this change in coupling may be used to produce
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a signal for switching purposes.
For swi~ching purposes, the first set of electrodes may
be divided into two groups. Read pulses may be applied
to one of these groups of electrodes by means of
suitable circuitry. The other group of electrodes may
be connected to circuity capable of sensing the change
in signal on this group of electrodes, due to the
change in capacitive coupling between the groups of
electrodes when the switch is actuated, and initiating
a switching action in respect to that change. Altern-
atively, additional electrodes may be provided on the
rear surface of the dielectric panel to take over the
function of one or the other of the groups of elec-
trodes, so that for example read pulses may be applied
to the whole set of electrodes on the rear face of the
dielectric panel and a separate electrode may be used
for sensing purposes.
For illumination purposes, pulses of one polarity are
applied to one or more of the electrodes of the first
set of electrodes and pulses of opposite polarity are
applied to one or more of the electrodes in the second
set of electrodes. Where a pulsed electrode of the
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first set overlies a puls~d electrode of the second
set, a potential is applied across the intermediate
layer of phosphor sufficient to excite the phosphor and
cause illumination at that point. The required symbol
or legend may thus be built up from illuminated dots,
by pulsing the appropriate electrodes in each set of
electrodes. Typically the first and second sets of
elongate electrodes may contain between 20 and 40
electrodes per centimetre.
The read pulses tha~ are applied to the electrodes for
switching purposes, may typically be as low as 10 volts
and may be of either polarity. It is however convenient
to use the same circuitry for applying the read pulses
and the illumination control pulses to the set of the
electrodes on the rear face of the dielectric panel.
The read pulses are applied at intervals between
illumination pulses. For example, the minimum potential
difference required to cause the phosphor layer to
luminesce is, typically from 80 to 120 volts.
Illùmination pulses of from ~40 to +60 volts are
consequently applied to the appropriate electrodes of
one set of electrodes and pulses of from -40 to -60
volts applied to the appropriate electrodes of the
other set of electrodes. These pulses would typically
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be of 10 to 30 microsecond duration at a frequency of
from 0.5 to 2 kHz. Read pulses of the same amplitude
as the illumination pulses (i.e. +40 to +60 volts)
would be applied to all the electrodes of the first set
of electrodes or group of the first set of electrodes,
between the illumination pulses. These pulses would
typically be of 10 microsecond duration at a frequency
of 500 Hz.
Various embodiments of the invention are now described,
by way of example only, with reference to the
accompanying drawings, in which :-
Figure 1 illustrates diagrammatrically in exploded
view, a switch/display unit formed in
accordance with the present invention;
Figure 2 shows a sectional side elevation of the
~witch/display unit illustrated in Figure l;
Figure 3 shows a sectional view along the line III-III
shown in Figure 2;
Figure 4 shows a view similar to that shown in Figure
3, illustrating a modified switch/display
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unit;
Figures 5 and 6 illustrate diagrammatically in
sectional side elevation, modifications to the
switch/display units illustrated in Figures 1
to 4;
Figure 7 illustrates diagrammatically in sectional side
elevation a further form of switch/display
unit formed in accordance with the present
invention, and
Figure ~ shows a similar view to that shown in Figures
3 and 4, illustrating a 2 x 6 array of
switch/display units formed in accordance
with the present invention.
The switch/display unit illustrated in Figures 1 to 3
comprises a panel 10 made of transparent dielectric
material, for example qlass. A set of transparent
elongate parallel electrodes 11, made from electrically
conductive material such as tin oxide, are applied to
th~ rear surface of the panel 10. A transparent layer
12 of conductive material is applied to the front
surface of panel 10, so that it overlies the set of
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electrodes 11 on the rear surface of the panel 10.
A layer of phosphor 13 is applied to the rear of the
set of electrodes 11 and a second set of elongate
parallel electrodes 14, are applied to the rear surface
of the phosphor layer 13. The second set of electrodes
14 are arranged so that they extend at right angles to
the first set of electrodes 11, each electrode of one
set thus overlapping all the electrodes of the other
set, to form a dot matrix.
As illustrated in Figure 3, electrodes 11 are provided
with input connections 15 which may be connected to
circuitry suitable for applying a voltage pulse
individual~y to each electrode. Electrodes 14 are
provided with similar input connections (not shown) by
which they may be connected to circuitry for applying
a voltage pulse of opposite polarity to those applied
to electrodes 11, individually to each electrode 14.
Typically, the phosphor layer used will have an
illumination threshold of from 80 to 120 volts and the
voltage pulse applied to electrodes 11 may be from 40
to 60 volts while the pulses applied to electrodes 14
may be from -40 to -60 volts.
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If pulses are applied to one electrode in each of the
sets 11 and 14, a potential of from 80 to 120 volts
will be applied across the layer 13 of phosphor, at the
point where those electrodes 11 and 14 overlap. This
potential will excite that portion of the phosphor
layer 13 and produce an illuminated dot. By applying
pulses simultaneously to the appropriate electrodes in
each set of electrodes 11 and 14, the plurality of dots
may be illuminated to form a legend or symbol. The
legend or symbol may be altered by applying pulses to
different electrodes in the sets 11 and 14. Typically,
these illumination pulses will have a duration of from
10 to 30 microseconds and be applied to the electrodes
at a frequency of 0.5 to 2 kHz, while the display is
illuminated.
To provide switch means the set of electrodes 11 are
divided into two groups X and Y, as shown in Figure 3.
The group Y is provided with a set of output
connections 16 by which they may be connected to
suitable sensing circuitry. Read pulses may now be
applied simultaneously to all the electrodes 11 in
group X and these will be coupled capacitively, via the
conductive layer 12, to the electrodes 11 in group Y
and an output pulse will consequently be transmitted to
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the electrodes 11 in group Y. This output pulse may be
detected by the sensing circuit. To actuate the
switch, an electrical load is applied to the conductive
layer 12 by, for example, a person touching the
conductive layer 12. This load will reduce the
capacitive coupling between groups X and Y of the set
of electrodes 11 and will-thus reduce the signal on the
electrodes 11 in group Y. This reduction in signal may
be detected by the sensing circuit and used to effect
switching.
For convenience, the circuitry to apply illumination
pulses to electrodes 11, may also be used to apply the
read pulses, but instead of pulsing individual
electrodes 11 as required for illumination purposes, it
will be arranged to pulse all the electrodes 11 in
group X simultaneously. These~ read pulses will be
applied in between the illumination pulses and will
typically be of the order of 10 microsecond duration at
a frequency of 500 Hz. As no pulse will be applied to
the electrodes 14 when the read pulses are applied to
the electrodes 11, the potential across the phosphor
layer will not reach the illumination threshold and
consequently the display will not be affected.
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10 .
The switch/display unit described above pr~vides a
display which may be varied as desired. The switch may
consequently be used as a programmable multi-functional
switch, the display being arranged to change in
response to actuation of the switch or in response to
actuation of other switches in, for example, an array
of similar switch/display units.
Instead of dividing the set of electrodes 11 into two
groups X and Y as described above, an additional
electrode 20 may be provided on the rear surface of
panel 10 as illustrated in Figure 4. The phosphor
layer 13 and second set of parallel electrodes 14 are
applied to the rear of the first set of electrodes 11
and the display is operated in the manner described
above.
However, for switching purposes, read pulses are
applied simultaneously to all the electrodes 11 in the
set. The conductive layer 12 is extended, so that it
overlies both the set of electrodes 11 and the
electrode 20 and this couples the electrodes 11
to the electrode 20. Electrode 20 i8 connected to a
suitable sensing circuit, so that the change in signal,
~; 25 when a load is applied to the conductive layer 12, can
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be detected and switching initiated as described above.
A further guard electrode 21 is provided on the rear
surface of panel 10 between the set of electrodes 11
and electrode 20. This guard electrode 21 is connected
to earth so as to minimise direct coupling of the
electrodes 11 with electrode 20.
The switch/display units described above may be
modified as illustrated in Figure 5, by positioning a
transparent, resilient conductive membrane 40 in front
of the conductive layer 12, said membrane 40 being
spaced from the conductive layer 12 by means of
insulative spacers 41. This modified switch/display
unit is actuated by a person depressing the membrane 40
until it comes into contact with the conductive layer
12. The conductive layer 12 will then be connected to
earth through the membrane 40 and the person touching
the membrane, and the resulting electrical load on the
conductive layer 12 will cause a reduction in the
capacitive coupling of the switch, in the manner
described above. The movement of the membrane 40 will
provide a tactile feedback to the person operaLing the
switch The membrane 40 may be moulded to form a
bubble or blister formation over the conductive layer
12, so that when depressed it will move into engagement
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12.
with the conducti~e layer with a snap action feel.
These bubble or blister formations may also serve to
separate the membrane 40 from the conductive layer 12,
in place of the spacers 41.
In the switch illustrated in Figure 6, a membrane 45 is
formed from transparent non-conductive resilient
plastics material, and is moulded tO provide a bubble
or blister formation 46 which overlies and is separated
from the conductive layer 12. The inner surface of the
membrane 45 is provided with a transparent conductive
coating 4a t this coating 48 being connected to earth.
When this switch is actuated by depressing the blister
formation 46, the conductive layer 12 is connected
directly to earth via coating 48. The resulting change
in capacitance will consequently be independent of the
person actuating the switch and will give a more
consistent change in signal when the switch is
actuated. Furthermore. ~his form of switch may be
. 20 actuated by nonconductive implements.
When pressure is removed from the blister formation 46
it will snap back away from the conductive layer 12, so
that the capacitive characteristics of the switch will
2~ revert to their original values when the switch is not
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actuated.
The central portion of the blister formation 46 may be
formed with a lens 47, through which the display will
be magnified.
In the switch/display unit illustrated in Figure 7,
the arrangement of the sets of electrodes 11 and 14 and
phosphor layer 13, on the rear of the dielectric panel
10, is the same as that disclosed with reference to
Figures 1 to 3. However, instead of forming a
conductive layer 12 on the front surface of the panel
10, a conductive coating 52 is provided on the rear
surface of a blister formation 51 formed in a
transparent, resilient non-conductive membrane 50
positioned in front of the panel 10 so that it overlies
the set of electrodes 11 and is spaced from the front
surface of panel 10. The conductive layer 52 is
electrically isolated. With this construction, there
will be little or no coupling between the groups X and
Y of electrodes 11 when the switch is in its
non-actuated condition. Consequently when read pulses
are applied to electrodes 11 in group X, there will be
no or only a very small output pulse on the electrodes
11 in group Y. However, when the blister formation 51
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is depressed so that the coating 52 engages the upper
surface of panel 10, the electrodes 11 in ~roups X and
Y will be coupled capacitively through the coating 52.
A read pulse applied to the electrodes 11 in group X
will now produce an output pulse of significant
amplitude on the electrodes 11 in group Y and this
pulse may be used to initiate switching.
This form of switch, in which the conductive layer 52
is spaced from the front surface of the dielectric
panel 10, may be used with other arrangements of
electrodes on the rear surface of the dielectric panel
10, for example, in the form described with reference
to Figure 4.
The switches described above may be used individually
or several such switches may be used together.
However, this form of construction is suitable for
producing an array of switch/display units on a single
panel, as illustrated in Figure 8. This figure shows a
2 by 6 array of switch/display units, two rows of six
switch/display units being formed on a dielectric panel
30. Two sets of transparent elongate electrodes 31
are provided on the rear face of the panel 30. Two
rows of six separate transparent electrodes 32 are also
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formed on the rear face of the panel 30, between the
sets of the electrodes 31. Each set of electrodes 31
is capacitively coupled to the adjacent row of
electrodes 32 by means of individual transparent
conductive layers 33 formed on the front surface of
panel 30. Fach conductive layer 33 overlies a
different one of the electrodes 32 and a portion of the
adjacent set of electrodes 31. As described above, the
two sets of electrodes 31 may be connected to circuitry
for applying read pulses, while the electrodes 32 may
be connected to suitable sensing circuitry. ~he
application of an electrical load to one of the
conductive layers 33 will alter the coupling between
the set of electrodes 31 and electrode 32 covered by
that conductive layer 33 and the change in signal on
the electrode 32 can be sensed to effect a switching
action appropriate to that switch.
A phosphor layer is applied to the rear surface of the
electrodes 31 and 32 and two further sets of parallel
elongate electrodes are applied to the rear face of the
phosphor layer, in the manner described above. The
display means of each switch can thus be controlled by
applying pulses to the appropriate electrodes on either
side of the phosphor layer, as described with reference
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16.
to the individual switch/display units.
Similarly, switches of the form described with
reference to Figure 7 may be formed into an array.
The switch/display units of such arrays may be provided
with resilient membranes in the manne~s described with
reference to Figures 5 to 7. In such arrays the
membranes for each switch will preferably be formed as
a single sheet, for example as a sheet moulded with
individual blister formations 46 or 51 for each switch.
Where the membrane has a conductive coating, as
described with reference to Figures 6 and 7, this too
may be formed as a single coatins over the whole of the
sheet.
Various modifications may be made without departing from
the invention. For example, with the array of
switch/display units, the two sets of electrodes 31 on
the rear surface of the panel 30 may alternatively be
arranged vertically in the manner indicated in Figure 4.
With arrays of switch/display units of the type
described above, the units may be multiplexed ur.der the
control of a microprocessor, as described in British
Patent No 2059657.
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17.
Finally, it should be noted that the accompanying
drawings are diagrammatic illustrations only. They are
not intended to indicate the relative dimensions and
particularly thicknesses of the components. Typically
the dielectric panel 10 will be of the order of 3mm
thick the phosphor layer 13 of the order of 40 microns
thick, and the various electrodes 11, 14, 20, 21, 31,
32 and conductive layers 12, 33 of the order of 0.05
microns thicX.
