United States Patent [19]
`Binstead
`
`US006137427A
`[11] Patent Number:
`[45] Date of Patent:
`
`6,137,427
`*Oct. 24, 2000
`
`[54] MULTIPLE INPUT PROXIMITY DETECTOR
`AND TOUCHPAD SYSTEM
`
`[76]
`
`Inventor: Ronald Peter Binstead, 15 Seely Road,
`Radford, Nottingham, United Kingdom,
`GB NG7 1NU
`
`Notice:
`
`This patent is subject to a terminal dis
`claimer.
`
`Appl. No.:
`
`Filed:
`
`09/179,489
`Oct. 27, 1998
`
`Related US. Application Data
`
`[63]
`
`Continuation of application No. 08/718,356, Oct. 3, 1996,
`Pat. No. 5,844,506, Which is a continuation of application
`No. PCT/GB95/00767, Apr. 5, 1995.
`Foreign Application Priority Data
`
`[30]
`Apr. 5, 1994 [GB]
`[51]
`[52]
`
`United Kingdom ................. .. 9406702
`
`Int. Cl.7 ................................................... .. H03K 17/94
`US. Cl. ............................ .. 341/33; 341/34; 345/173;
`345/174
`Field of Search ................................ .. 341/33, 34, 20;
`345/173, 174
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`[58]
`
`[56]
`
`5,459,463 10/1995 GruaZ et a1. ............................ .. 341/33
`
`FOREIGN PATENT DOCUMENTS
`
`0078676A 5/1983 European Pat. Off. .
`0609021A 8/1994 European Pat. Off. .
`3910977A 10/1990 Germany .
`
`Primary Examiner—Michael Horabik
`Assistant Examiner—Timothy Edwards, Jr.
`Attorney, Agent, or Firm—Cahill Sutton & Thomas, P.L.C.
`
`[57]
`
`ABSTRACT
`
`Atouchpad is formed of an electrically insulating membrane
`(10) With a ?rst series of spaced apart conductors (12) on a
`?rst face of membrane (10) and a second series of spaced
`apart conductors (14) on or proximal thereto, in Which there
`is no electrical contact betWeen the ?rst and second series of
`conductors (12, 14) Each conductor in the ?rst and second
`series of conductors is sensitive to the proximity of a ?nger
`to modify the capacitance of the proximate conductor to
`detect the presence of the ?nger positioned close to that
`conductor. A scanning system operative to sample one of the
`conductors in turn from both the ?rst and second series of
`conductors (12, 14) in order to measure and store a capaci
`tance value associated With that respective conductor. The
`scanning system is operative to maintain all conductors
`(12-n, 14-n) at a common potential equal to the potential of
`the conductor being sampled When the remaining conductors
`are not actively being sampled by the scanning system.
`
`4,686,332
`
`8/1987
`
`Greanias et al. ........................ .. 178/19
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`25 Claims, 9 Drawing Sheets
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`U.S. Patent
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`Oct. 24,2000
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`U.S. Patent
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`U.S. Patent
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`0a. 24, 2000
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`U.S. Patent
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`0a. 24, 2000
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`U.S. Patent
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`0a. 24, 2000
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`1
`MULTIPLE INPUT PROXIMITY DETECTOR
`AND TOUCHPAD SYSTEM
`
`The present application is a continuation of an applica
`tion entitled “MULTIPLE INPUT PROXIMITY DETEC
`TOR AND TOUCHPAD SYSTEMS”, ?led Oct. 3, 1996 and
`assigned Ser. No. 08/718,356, now US. Pat. No. 5,844,506
`Which is a national application based upon British PCT
`Application entitled “MULTIPLE INPUT PROXIMITY
`DETECTOR AND TOUCHPAD SYSTEM”, assigned Ser.
`No. PCT/GB95/00767, ?led Apr. 5, 1995, claiming priority
`to a British application entitled “MULTIPLE INPUT
`PROXIMITY DETECTOR AND TOUCHPAD SYSTEM”,
`?led May 4, 1994 and assigned Ser. No. 94067022, all of
`Which applications describe and claim inventions made by
`the present inventor.
`The present invention relates to a multiple input prox
`imity detector/touchpad system Which may comprise, for
`example, a keypad array, digitising tablet, touchscreen or an
`electronic mouse Which may be operated through a variable
`thickness of glass or other dielectric medium, and more
`particularly to the design of a multiple input proximity
`detector/touchpad system in Which a large matrix of keys or
`a large touch sensitive area may be formed using the
`superposition of, for example, orthogonally arranged con
`ducting elements. The conducting elements, and the elec
`tronic scanning system to service the conducting elements
`are particularly arranged to obtain optimiZed sensitivity.
`In European Patent No. EP-0185671 there is described a
`touch operated keyboard for attachment to one face of a
`sheet of glass comprising a plurality of keypads disposed
`adjacent each other in a desired pattern, together With
`interrogation means for assessing the condition of the
`keypads, indicating When a keypad, or keypads have been
`operated by a user, and an electronic scanning and process
`ing system for providing means for threshold value genera
`tion and drift compensation.
`The threshold value generation means is operative to
`determine repeatedly at predetermined intervals the required
`capacitance level associated With any keypad in order to
`indicate that that keypad has been operated by a user.
`The drift compensation means is operative to offset
`variations in capacitance caused by varying background
`conditions.
`The present invention is directed toWards the construc
`tion of a multiple input proximity detector/touchpad system,
`Which may comprise a keypad array, digitising tablet, touch
`screen or an electronic mouse, Wherein the position of a
`user’s ?nger or other object touching, or in close proximity
`to the “touch sensitive” surface area, hereinafter referred to
`as a touchpad, is determined by means of the capacitive
`effect of that ?nger on multiple conductor elements
`(hereinafter referred to as a keystroke), and to the optimi
`sation of sensitivity of the touchpad, particularly When the
`touch sensitive area becomes relatively large. It is intended
`that throughout the present speci?cation, reference to a
`“?nger” is intended to include any object that Would exert
`sufficient capacitive in?uence to be detected by the touch
`pad.
`It should be noted that the activation of a “keypad” or
`area of the touchpad can be achieved Without pressure on, or
`even Without physical contact With, the surface of the
`touchpad, although in normal mode of operation, the user’s
`?nger Would contact the touchpad surface or a surface
`associated thereWith.
`Other knoWn types of touchpad, such as membrane
`sWitches having tWo sets of conductors face to face, require
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`the use of pressure on tWo conducting elements at an
`intersection of those conducting elements. Pairs of conduct
`ing elements may be scanned in systematic manner to
`determine Which, if any, intersection has been pressed.
`Disadvantages of this system are that there are moving parts
`(eg. the upper surface presented to the user’s ?nger) Which
`can therefore be subject to damage, and also that the
`positioning of the user’s ?nger must coincide With the
`conducting element intersection. This method employs a set
`of driver conductors and a set of sensing conductors.
`The present invention, hoWever, uses only sensing con
`ductors and has no moving parts. It can thus be Well
`protected from damage by users by the glass or other
`dielectric medium covering the touchpad. The electronic
`scanning of the conducting elements requires connection to
`only one element at a time, and all other elements can be
`placed in condition to reduce interference When not being
`scanned. The present invention further permits detection of
`the user’s ?nger at any point on the touchpad’s active
`surface, and the electronic scanning mechanism could be
`arranged to assign predetermined areas of the touchpad to be
`interpreted as discrete keypads, or “boxes”.
`Of fundamental importance to such a touchpad system is
`the sensitivity of the apparatus to the proximity of a ?nger
`When compared With normal variations in capacitance. This
`ensures reliable indication of an intentional “keystroke” as
`previously described, and the determination With a high
`degree of accuracy of the position of that ?nger. The position
`of the ?nger may be a digital representation of Which “box”
`or predetermined area of the touchpad has been activated
`from a set of possible boxes, or predetermined areas, or
`alternatively an analogue representation of the position by,
`for example, x-y coordinates.
`The present invention is further directed toWards the
`achievement of this required sensitivity, by a number of
`alternative embodiments Which may be used separately or in
`conjunction With one another.
`Applications of such a touchpad are many and diverse,
`for example:
`as a touchscreen interface for a computer system the
`keyboard being located immediately in front of a
`display unit Which may be, for example, a cathode ray
`tube or liquid crystal display;
`a cash till keypad, Where there Would normally be many
`buttons for speci?c or different types of merchandise
`(the present invention is particularly suited to this
`application Where the till operator is likely to have dirty
`or greasy hands, since the invention can provide a
`smooth glass for the keypad surface Which is easily
`Wiped clean);
`as an equivalent to a “mouse” input device to a computer
`system Where the screen cursor is moved by moving
`one’s ?nger across the surface of a touchpad;
`as a standard layout keyboard for use in a hostile envi
`ronment;
`as many discrete proximity sensing keys.
`In the environment of a cathode ray tube, or other static-or
`interference-generating device, it may be necessary to pro
`tect the touchpad from such static by knoWn means, for
`example a transparent earthing shield. Alternatively, an
`actively driven back plane may be used.
`In a general aspect the present invention provides a
`multiple input proximity detector in Which the juxtaposition
`of tWo or more independent sensor inputs are used to
`determine the proximity of a ?nger, such detection only
`being accepted as valid When all the sensor inputs indicate
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`a valid detection, Where such inputs may be juxtaposed next
`to a range of other inputs in unique combination such that
`When any one combination gives a true detection for all its
`individual inputs, a unique valid detection is determined.
`According to the present invention there is provided a
`touchpad comprising an electrically insulating membrane
`With a ?rst series of spaced apart conductors on a ?rst face
`of the membrane and a second series of spaced apart
`conductors on or proximal thereto, in Which there is no
`electrical contact betWeen the ?rst and second series of
`conductors, each conductor in said series being sensitive to
`the proximity of a ?nger to modify the capacitance of said
`conductor to detect the presence of said ?nger positioned
`close to that conductor. Preferably the ?rst and second
`conductors comprise ?ne Wires preferably of a siZe betWeen
`10 to 25 microns to be substantially invisible When the
`touchpad is used as a touchscreen.
`Embodiments of the present invention Will noW be
`described by Way of example With reference to the accom
`panying draWings in Which:
`FIG. 1 shoWs in plan vieW a touchpad according to the
`present invention;
`FIGS. 2a, 2b and 2c shoW in alternative embodiments
`cross-sections through the touchpad of FIG. 1, not to scale;
`FIGS. 3a and 3b shoW embodiments of intersection points
`of tWo conducting elements;
`FIG. 4 shoWs in plan vieW an embodiment of the present
`invention suitable for a large area touchpad With multiple
`conducting elements;
`FIG. 5 shoWs in cross-section an embodiment of the
`present invention in Which connections can be made
`betWeen conducting elements;
`FIG. 6 shoWs a small part of a touchpad surface;
`FIG. 7 shoWs a part of a touchpad surface indicating an
`embodiment of the invention in Which multiple keypad areas
`are assigned to each intersection;
`FIG. 8 shoWs schematically an embodiment of scanning
`apparatus suitable for use With the touchpad;
`FIG. 9 shoWs a pattern of conductor elements suitable for
`use in the style of a standard typeWriter keyboard layout; and
`FIG. 10 shoWs a pattern of conductor elements demon
`strating one embodiment of a multiplexed touchpad.
`With reference to FIGS. 1 and 2a, and according to one
`embodiment of the invention, there is provided a thin
`dielectric ?lm 10 on Which is deposited on one face by an
`appropriate technique such as screen printing or similar
`lithographic process, a pattern of electrically conducting
`material forming a ?rst series of parallel conductor elements
`12 With appropriate connections at one or both ends. On the
`other face of the thin dielectric ?lm 10, by a similar
`technique, there is provided a pattern of electrically con
`ducting material forming a second series of parallel conduc
`tor elements 14 With appropriate connections at one or both
`ends Which are orthogonal to, but not in electrical contact
`With the ?rst series. The ?rst and second series of conductor
`elements thus form a plurality of intersections 20. Appro
`priate material for these conductor elements 12, 14 is, for
`example, silver-based conducting ink. If the conductor ele
`ments are to be of loW visibility Where the touchpad is being
`used in front of a display system, then indium oxide is an
`appropriate material.
`In other embodiments, the ?rst and second series of
`conductor elements need not be parallel, nor is it necessary
`for the ?rst and second series of conductor elements to be
`mutually orthogonal. The second series of conductor ele
`ments may be deposited onto a second thin dielectric ?lm,
`the second ?lm being superimposed on the ?rst dielectric
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`?lm in order to achieve similar effect of separation of the
`?rst and second series of conductor elements by a dielectric
`layer.
`It is also possible to effect the superposition of the
`conducting elements in other Ways. For example, in FIG. 2b
`the ?rst series of conductor elements 12 may be deposited
`onto the thin dielectric ?lm 10 and an insulating layer 13
`deposited thereupon. The second series of conducting ele
`ments 14 may then be deposited over the insulating layer.
`Thus, the insulating layer 13 forms a membrane structure
`betWeen the ?rst and second series of conducting elements.
`The insulating layer 13 need not, hoWever, be continuous
`over the entire touchpad surface: it is only necessary to
`insulate the intersections of the ?rst and second series of
`conductor elements. In FIG. 2c, this arrangement is shoWn,
`Where small regions of insulating material 13‘ are deposited
`over the ?rst series of conducting elements 12 at the pro
`posed intersection points. The second series of conductor
`elements 14 may then be deposited. In this instance, the
`small regions of insulating material 13‘ in conjunction With
`the dielectric ?lm 10 form a membrane structure separating
`the ?rst and second series of conductor elements.
`Connection to the conductor elements 12 and the conduc
`tor elements 14 is made by further conducting elements 32,
`34 respectively deposited and/or de?ned in similar manner
`to conductor elements 12, 14. A connection to the touchpad
`scanning system is made by connector 30 using an appro
`priate connection system.
`In the embodiments of FIGS. 1 and 2a—2c, the Width 16
`of the conductor elements 12 and 14 is small compared With
`the inter-element spacing 18. If the conducting material
`being used to form conductor elements 12, 14 is of loW
`conductivity, an alternative pattern of conductor element
`may be used as described later.
`In another embodiment, the inter-element spacing 18 need
`not be identical for each adjacent pair of conductor elements.
`The sensitivity of the touchpad and its immunity to
`extraneous interference has been found to be enhanced by
`the encapsulation of the dielectric ?lm 10 and conducting
`elements 12, 14, 32, 34 in a dielectric laminate 50, as shoWn
`in FIGS. 2a—2c The dielectric laminate may be a plastic ?lm,
`and can be formed using Well knoWn techniques such as heat
`sealing. This provides a constant dielectric environment in
`the immediate proximity of the conductor elements, elimi
`nates the in?uence of moisture Which might otherWise be
`present on the conductor elements, and further improves the
`robustness of the apparatus.
`High sensitivity to changes in capacitance of a conductor
`element or group of conductor elements caused by the
`proximity of a ?nger or other object is achieved by mini
`mising the cross-coupled capacitance betWeen the conductor
`elements 12 and the conductor elements 14. This can be
`achieved in one embodiment by the use of highly conductive
`material (such as silver) and the forming of conductor
`elements Which have a very narroW Width 16 When com
`pared to the conductor spacing 18 as previously described,
`such that the capacitance of the intersections 20 is small. In
`the event that it is desirable that a loWer conductivity
`material be used (eg indium oxide), or that the dimensions
`of the touchpad become suf?ciently large such that there is
`substantial resistance along a conductor element, then alter
`native patterns may be considered such as those embodied in
`FIGS. 3a and 3b.
`In FIG. 3a, Where the conductor elements have a more
`substantial Width 22, at the intersections 20 the Width 24 is
`greatly reduced.
`In FIG. 3b, the conductor elements 12 and 14 maintain
`full Width 22, but the second conductor element 14 has a
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`“Window” area 28 Which has no conductive material. This
`“Window” allows the necessary capacitive link to the ?rst
`conductive element 12. The WindoW area 28 need not be
`completely open. As indicated by dotted line 29, an area of
`conductor material electrically isolated from the second
`conductor element 14 can in fact be left Within the WindoW
`28 and still provide the necessary capacitive link to the ?rst
`conductor element 12.
`The relative thicknesses of the conductor elements thus
`can be varied to suit the conductivity of the material being
`used, the length of the tracks, and other constraining factors.
`It is noted that the smaller Width tracks can result in better
`resolution and higher speed of operation, but use of the
`Wider tracks can be acceptable for loWer resolution, less
`sensitive or sloWer requirements.
`In another embodiment, the sensitivity to changes in
`capacitance caused by the proximity of a ?nger or other
`object to a large area touchpad is enhanced by connecting
`several conductor elements 12, 14 together in groups as
`embodied in FIG. 4. This particular embodiment is preferred
`Where the required positional resolution of a keystroke can
`be compromised in favour of an increased area of touchpad.
`This particular embodiment confers upon the apparatus the
`additional bene?t that damage to one of the conductor
`elements 12 or 14 causing a break in that element does not
`affect the performance of the system, provided that the
`connection of each group of elements at both ends is made,
`as shoWn in the embodiment of FIG. 4. If a ?ne Wire is used
`to detect a large area then the Wire should be Zig-Zagged over
`that area. The Wire could be Zig-Zagged With %—1/5th of an
`inch spacing.
`If required, the conductor elements can be electrically
`connected to elements on the opposite face of the dielectric
`?lm 10 by the provision of appropriately placed holes 36 in
`the dielectric ?lm as shoWn in FIGS. 4 and 5, ?lled With
`conductive material through Which, for example, conductor
`element 12 is connected to conductor element 32 in order
`that connector 30 is only required to make contact to one
`face of the dielectric ?lm 10. Such a system may also be
`used to form “underpasses” for the conductor elements if
`required on particularly complex conductor patterns. These
`“underpasses” may be used to effect the intersection points
`of the ?rst series of conductor elements 12 and the second
`series of conductor elements 14.
`It is further noted that Where conductor elements are used
`Which have signi?cant resistance along the length thereof, it
`is possible to minimise the impact this has by providing
`conductor elements 32,34 to contact both ends of conductor
`elements 12,14 respectively. It is further possible to provide
`conductor elements 32,34 in high-conductivity material, and
`conductor elements in the loWer conductivity material, the
`elements being coupled together in knoWn manner.
`In a particular embodiment of this invention the required
`sensitivity of the system to changes in capacitance on any
`given element is enhanced by ensuring that all of the
`conductor elements 14-1 .
`.
`. 14-n and 12-1 .
`.
`. 12-n are
`maintained at the same potential (for example ground
`potential, or Vsupply hereinafter referred to as “ground
`potential”) except for the conductor element being sampled.
`The grounding of all conductor elements not being sampled
`greatly reduces the effect of stray capacitance from other
`parts of the touchpad on the element being sampled, thus
`providing a more reliable measure of any capacitive change
`that may have taken place on the conductor element being
`scanned.
`An appropriate system for scanning keyboards, such as
`that described in European Patent No. 0185671 is readily
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`applicable With some modi?cation to this touchpad. In one
`particular embodiment as shoWn in FIG. 8, each of conduc
`tor elements 12-1 to 12-4, and 14-1 to 14-3 is connected at
`one end to a resistor 71 having a high value such as 100
`kohms When compared With the impedance of the detection
`circuit, for example 10 kohms. (The particular values of
`resistance used are exemplary, and may be substantially
`varied according to the con?guration of the system.) Each of
`the resistors is connected to, for example, ground potential.
`The other end of each of conductor elements 12-1 to 12-4,
`and 14-1 to 14-3 is connected in turn via analogue multi
`plexer 75 to Output line 72.
`Where there is signi?cant resistance along the length of
`the conductor elements 12 and 14, improvements in the
`performance of the detection system can be achieved by the
`placing of the resistors 71 at the opposite sides of the
`conductor elements 12 and 14 to that shoWn in FIG. 8. In
`other Words, the resistors are placed at the multiplexer 75 of
`the touchpad and connected to ground or an active ground as
`hereinafter described.
`Output line 72 is connected to the input of a capacitance
`controlled oscillator 85, the output of Which is connected to
`a divide-by-n circuit 90, Which provides the data output on
`line 92. An indexing counter 80, clocked by a remote clock
`on line 82, is operative to control the analogue multiplexer,
`and to reset capacitance controlled oscillator 85 and divide
`by-n circuit 90. Aprocessing means, not shoWn, is operative
`to receive the data from divide-by-n counter on line 92, and
`store it in a plurality of locations, each allocated to a
`particular one of the conductor elements 12 and 14. Divide
`by-n circuit 90 and other components such as indexing
`counter 80 could be provided by means of a suitable
`standard microprocessor.
`The scanning system thus samples each conductor ele
`ment in turn according to the analogue multiplexer
`sequence, and stores each capacitance value in memory.
`These values are compared With reference values from
`earlier scans, and With other capacitance values in the same
`scan from the other conductor elements in order to detect a
`keystroke. Keystrokes must be above a threshold value to be
`valid. By having several threshold values it is possible to
`determine the pressure of key press or distance that the
`?nger is aWay from the key. This may be useful, for
`example, When moving a cursor across a screen and then
`making a selection by pressing harder on a selected point.
`The remaining features of the scanning mechanism are
`Well described in the cited document and Will not be
`discussed further here.
`Detected changes in capacitance on more than one con
`ductor element in any one scanning sequence enables inter
`polation of a keystroke betWeen those conductor elements.
`In the tWo dimensional case, as shoWn in FIG. 6, conductor
`element 14-3, and conductor element 14-4 cross conductor
`elements 12-1 and 12-2. A ?nger or other object at position
`40 can be determined in the X-direction by the relative effect
`on the capacitance of element 14-3 compared With element
`14-4, and in the Y-direction by the relative effect on the
`capacitance of element 12-1 compared With element 12-2. In
`a typical application, conductor elements 12-1,12-2 .
`.
`. 12-n
`and 14-1,14-2 .
`.
`. 14-n Will be sampled by the scanning
`system in a sequential manner. Clearly, the same applies to
`the embodiment of the touchpad Where the conductor ele
`ments are arranged in groups Where the interpolation is
`made betWeen the centre line 45 of each group of conductor
`elements (FIG. 4).
`It Will be clear that the interpolation technique enables not
`only an analogue representation of ?nger position on the
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`6,137,427
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`7
`touchpad to be created, but also allows the use of an
`increased number of “boxes” or predetermined key areas
`60,61 over the number of element intersections, as indicated
`in FIG. 7. Such “boxes” or keypad areas could be arranged
`in any number of con?gurations capable of being resolved
`by the system.
`In an alternative embodiment, an active backplane may be
`incorporated into the touchscreen. For example, a plastic
`sheet upon Which is coated a conductive ?lm is laminated to
`the touchscreen. The output 72 is connected to a unity gain
`non-inverting ampli?er 73. The output of this ampli?er 73 is
`connected to the backplane conductor (not shoWn) Which
`may cover all or part of the keypad. The backplane Will be
`active since the voltage thereon Will vary With the output on
`line 72.
`The backplane could also extend to areas in front of the
`keypad to “shield” keys Which are non-operative.
`The backplane potential thus created could also be suit
`ably connected to maintain all conductors 12-n, 14-n Which
`are not actively being sampled at a common potential equal
`to the active backplane potential rather than the common
`ground potential as previously described herein.
`This can in certain uses of the touchscreen eliminate the
`requirement for a completely conductive backplane ?lm.
`In FIG. 9 there is shoWn an example of an appropriate
`pattern of elements for simulating a keypad con?guration
`such as that normally associated With a typeWriter keyboard.
`This particular embodiment comprises the horiZontal con
`ducting elements 12, vertical conducting elements 14, con
`ducting elements 32, 34 for connection to connector 30 in
`similar manner to the embodiments described With reference
`to the FIGS. 1 and 2. The sensitivity of the system can be
`further enhanced by the addition of further conducting
`elements 42, 44; elements 42 being in electrical connection
`With conducting elements 12, and elements 44 being in
`electrical connection With conducting elements 14, elements
`42 being positioned such that centre of a box de?ned by the
`elements 42 is superimposed on the centre of a box de?ned
`by elements 44, the elements 12, 42 being on one face of the
`thin dielectric ?lm 10, and the elements 14, 44 being on the
`other face of the thin dielectric ?lm 10. The separate
`elements 42, 44 are indicated schematically to the side of the
`draWing of FIG. 9.
`As indicated earlier, the ?rst and second series of con
`ductor elements 12 and 14 need not be deposited on opposite
`faces of the same dielectric membrane, but might be depos
`ited on separate dielectric membranes, With said membranes
`being superimposed one on the other. This principle may be
`extended to include a plurality of membranes, each having
`a separate pattern of conductor elements. These could, for
`example be PCB’s (printed circuit boards) of knoWn type.
`The conductor elements 12,14,32 and 34 could be formed
`from ?ne conducting Wires Which Would preferably be
`insulated by, for example, an enamel coating. The Wires
`12,14 could be alloWed to touch at intersections 20, electri
`cal contact being prevented by the insulating coating.
`Alternatively, the Wires could be arranged on either side of
`a suitable membrane for mounting purposes. The Wires may
`be from 10 to 25 microns in diameter thereby being invisible
`to the naked eye When the invention is used as a touchscreen.
`In a further embodiment of the present invention, particu
`larly an embodiment including, for example, a plurality of
`membranes having conductor elements thereon, multiplex
`ing techniques can be used. Duplicate sets of N small
`touchpads are arranged to form a large touchpad array. This
`array is superimposed upon a larger touchpad With M keys
`(M could be equal to N). The position of a ?nger or other
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`10
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`15
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`25
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`35
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`45
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`55
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`65
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`object proximate to the ?rst touchpad is interpretable by the
`system as a key stroke in any one of N possible positions.
`The second, larger grid pattern is used to determine Which of
`the M possible duplicate key pads has been touched,
`enabling unambiguous determination of the position of the
`?nger.
`With reference to FIG. 10, there is a ?rst grid pattern
`comprising repeating pattern of elements Ato D and W to Z;
`that is to say that all A elements are electrically connected,
`all B elements are electrically connected, and so on. It is thus
`apparent that there Will be four ?rst grid horiZontal connec
`tions A,B,C,D, and four ?rst grid vertical connections W,X,
`Y,Z. A second grid is placed directly over the ?rst grid, the
`second grid having four horiZontal elements With four
`connections a,b,c,d, and four vertical elements With four
`connections W,x,y,Z. A ?nger placed at the position marked
`With a square on the ?rst grid Will be indicated by the ?rst
`grid as interference With elements A and Z. Such interfer
`ence Would be the same for sixteen positions on this grid, but
`the second grid Will indicate interference With elements c
`and b, With c stronger than b, and interference With elements
`x and y, With x stronger than y. This enables unique
`determination of the position of the interfering object. It is
`readily apparent that 256 positions can thus be resolved by
`just 16 electrical connections. If interpolation techniques are
`used, more than 256 positions can be resolved.
`If enamel coated Wires are used then because these are
`insulated from each other a plurality of matrix Wire arrange
`ments can be placed on top of each other Without any
`separating membrane.
`More keys can be determined by duplicating or rearrang
`ing the order of the connections and thus determining the
`unique best and second best values. For example, instead of
`A,B,C,D, as above the order D,A,B,C,D,B, could be used.
`If D gives the best value in the above example and C is
`the second best then it is the second D that has been selected.
`If D gives the best value and A is the second best then it
`is the ?rst D that has been selected.
`This example can be accomplished in a linear or in a grid
`pattern to provide more key positions and thus can be used
`in combination With the interpolation techniques to provide
`even more key positions.
`The grid patterns could be arranged as shoWn in FIG. 10
`to be evenly spaced, but equally each four by four pattern
`(A—D, W—Z) could be arranged, Within reason, at any
`location on the touchpad surface or on another surface thus
`providing 16 separate and distinct four by four arrays. In the
`extreme case, each array could be constructed to be a single
`key, the example shoWn thus providing 256 keys at remote
`locations but not necessarily in a d