United States Patent {191
`Larson
`
`1541 MEMBRANE SWITCH
`[75] Inventor: Willis A. Larson, Wayzata, Minn.
`[73] Assignee: Magic Dot, lnc., Minneapolis, Minn.
`[22] Filed:
`Mar. 29, 1973
`[21] Appl. No.: 346,055
`' Related US. Application Data
`[60] Division of Scr. No. 161.948. July 9. 1971. Pat. No.
`3.737.670. which is a continuation of Scr. No.
`865.760. Oct. 13. 1969. Pat. No. 3.737.670.
`
`[52] US. Cl. ......................... .. 200/159 B; 200/83 N
`[51] Int. Cl. ......................................... .. l-l0lh 13/54
`[58] Field of Search ............ .. 200/159 B, 5 A. 83 N;
`340/365 R, 365 A
`
`[56]
`
`2.659.533
`
`References Cited
`UNITED STATES PATENTS
`11/1953 Quinby et a1. ............... .. 200/D1G. 1
`
`3.267233
`3.487.268
`
`8/1966 Basile et a1. . . , . . . . .
`12/1969
`Ljungdell et al....
`
`. . . . . .. 200/83 N
`...... .. 340/365 R
`
`3.600.528
`
`8/1971
`
`Lcposavic . . . . . . .
`
`. . . ,, 200/159 B X
`
`3.688.066
`
`8/1972 Adelson . . . . . .
`
`. . . . . . . .. ZOO/159 B
`
`3.699.294
`3.728.509
`
`340/365 R X
`10/1972 Sudduth ..... ..
`4/1973 Shimojo .................... .. 200/166 C X
`OTHER PUBLICATIONS
`Fazzio. Circular Sequencing Contact. IBM Technical
`Disclosure Bulletin, June 1970, p. 219.
`
`3,879,593
`1111
`[45] Apr. 22, 1975
`
`Primary E.\'aminer—Robert K. Schaeffer
`‘Assistant E.raminer—William .1. Smith
`Attorney. Agent, or F irm——Wicks & Nemer
`
`ABSTRACT
`[ 5 7 ]
`In order to provide a sensitive, touch responsive elec
`tronic membrane switch, a pair of electrodes are dis
`posed in a unique con?guration and are coupled to a
`high gain ampli?er. A membrane, having a conductive
`coating on a side facing the electrodes. is disposed
`over the pair of electrodes to perform a bridging func
`tion when the membrane is pressed against the elec
`trodes to thus cause a positive switching condition at
`the output terminals of the high gain ampli?er. 1n a
`?rst embodiment of the invention, the pair of elec
`trodes comprises a ?rst centrally disposed electrode
`encompassed by a second, circular electrode concen
`trically to. but longitudinally offset from the ?rst elec
`trode. The bridging of the electrodes is sensed and dif
`ferentiated from the substantially in?nite resistance
`normally existing between the two electrodes by the
`hight current gain ampli?cation to provide a sharp
`change in current flow through a load connected to
`the output terminals of the high gain ampli?er. The
`sharply differentiated state of the output terminals of
`the high gain ampli?er may be utilized to control
`switching functions in any manner desired.
`19 Claims, 7 Drawing Figures
`
`A
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`Global Touch Solutions, LLC
`Exhibit 2002
`Microsoft Corp. et al. v. Global Touch Solutions, LLC
`IPR2015-01149
`Page 1 of 7
`
`

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`Global Touch Solutions, LLC
`Exhibit 2002
`Microsoft Corp. et al. v. Global Touch Solutions, LLC
`IPR2015-01149
`Page 2 of 7
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`, PATENTEBAPRZZISYS
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`3,879,593
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`SHEEI 2 BF 2
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`7
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`gjz/
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`4. g ..
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`PIE. 7
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`Global Touch Solutions, LLC
`Exhibit 2002
`Microsoft Corp. et al. v. Global Touch Solutions, LLC
`IPR2015-01149
`Page 3 of 7
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`1
`MEMBRANE SWITCH
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`3,879,593
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`CROSS REFERENCES
`This application is a division of application Ser. No.
`161,948, filed July 9, 1971 now U.S. Pat. No.
`3,737,670, June 5, 1973 which is a continuation of ap
`plication Ser. No. 865,760 ?led Oct. 13, 1969 in the
`name of Willis A. Larson, now U.S. Pat. 3,737,670 is
`sued June 5, 1973.
`This invention relates to electronic switching and,
`more particularly, to apparatus for utilizing a mem
`brane, manually actuated, for providing discrete
`switching phenomena at the output terminals of an
`electronic circuit.
`Prior art manually operated switches generally func
`tion on the mechanical principal of bringing two con
`ductors into physical contact to complete a circuit
`through which current can flow. Because of the me
`chanical nature of the prior art switches, they are sub
`ject to wear and eventual failure as a result of the re
`peated operation of the moving parts, plating of mate
`rial from one contact to the other because of unidirec
`tional current ?ow, pitting, corrosion, and contamina
`tion in the form of accumulated dust, dirt, and chemi
`cal oxides formed by interaction between the contact
`material and the environmental atmosphere.
`In an attempt to obviate the dif?culties encountered
`by mechanical switches, touch responsive switches uti
`lizing body capacitance or skin resistance have been
`proposed. however, these prior art touch responsive
`switches have been either very complex and costly to
`manufacture or somewhat dangerous because the volt
`ages required to operate them are higher than desirable
`such that they have been deemed either impractical or
`useful only in applications in which high cost can be
`justified. Thus, it will be readily appreciated that a
`touch responsive switch which is highly reliable, safe,
`and lends itself to economical mass production would
`be highly desirable. Such a switch would ?nd broad ap
`plication for use with computer terminals, typewriter
`keyboards, calculator keyboards, control panels, and
`such other uses as require the entry of data through a
`primary switching interface unit.
`It is therefore a broad object of thisv invention to pro
`vide an improved touch responsive switch.
`It is a more speci?c object of this invention to pro
`vide a touch responsive switch utilizing a uniquely con
`?gured pair of electrodes coupled to a high gain ampli
`?er.
`It is another object of this invention to provide
`switching element electrodes which are unaffected by
`environmental contamination and which may be easily
`operated even if the operator is wearing gloves.
`These and other objects of the invention are
`achieved, according to an embodiment of the invention
`disclosed and claimed in application Ser. No. 161,948,
`now U.S. Pat. No. 3,737,670, by utilizing, as the oper~
`ated switching element, a pair of electrodes comprising
`a ?rst centrally disposed electrode encompassed by a
`second, circular electrode longitudinally offset from
`the ?rst electrode such that the pair of electrodes sub
`stantially conform to the contour of an operator’s ?n
`ger. When the operator touches the two electrodes, a
`?nite resistance path is set up between the two elec
`trodes, and this condition is detected through the use
`of a high current gain ampli?er whose last stage will
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`reach saturation, or very near saturation, when even a
`relatively high resistance is placed across the electrodes
`to set up low level current ?ow into the input stage of
`the ampli?er. However, when the resistance across the
`electrode is substantially in?nite such that no current
`flows into the input stage, the last stage of the high gain
`ampli?er is cut off. Thus, a load impedance may be
`driven by the ?nal stage of the high gain ampli?er in re
`sponse to the differentiation between the resistance ap
`pearing between the two electrodes when they are
`bridged by galvanic skin resistance and when they are
`not bridged.
`3
`In the embodiment of the invention particularly
`adapted for use in contaminated environments which
`might create a suf?ciently low resistance between the
`two electrodes to set up an arti?cial “touch" condition,
`a membrane provided with a conductive coating on its
`underside is placed over the electrode pair to provide
`a seal against such contamination. When the mem
`brane is pressed downwardly against the electrodes, the
`conductive coating performs the bridging function
`which is sensed through the high gain amplifier.
`The subject matter of the invention is particularly
`pointed out and distinctly claimed in the concluding
`portion of the speci?cation. The invention, however,
`both as to organization and method of operation, may
`best be understood by reference to the following de
`scription taken in connection with the accompanying
`drawings of which:
`FIG. 1 is a perspective view of the switching system
`of the present invention showing the disposition of the
`inner and outer electrodes and housing especially
`adapted for printed circuit board use;
`FIG. 2 is a cross section taken along the lines 2~2 of
`the housing illustrated in FIG. 1;
`FIG. 3 illustrates a slightly altered physical configura
`tion of the housing which renders it particularly suit
`able for panel mount operation;
`FIG. 4 is a cross section taken along the lines 4—4 of
`the housing illustrated in FIG. 3 and also shows the
`manner in which the electronic circuitry associated
`with the electrodo pair may be contained within the
`housing;
`FIG. 5 is a schematic diagram of a rather straight
`forward Darlington ampli?er which provides adequate
`gain to perform the electronic switching initiated by
`bridging the electrodes with galvanic skin resistance;
`FIG. 6 is a schematic diagram of a slightly altered
`Darlington circuit which places more voltage across the
`electrode pair to insure saturation of the ?nal amplifier
`stage; and
`FIG. 7 is a partially cutaway perspective view of a
`con?guration for the electrode housing which is partic
`ularly useful in contaminated environments.
`Referring now to FIGS. 1 and 2, a housing I, which
`may be made of any suitable durable insulating mate
`rial, is shown as it would be utilized with a printed wir
`ing board. A dust seal 3 of foam rubber or the like is
`placed between the ?ange 4 of the housing 1 and a
`panel 5 through which the housing extends for manual
`access.
`As best shown in FIG. I, the electrode pair comprises
`a center electrode 6 and an annular electrode 7 con
`centrically disposed to the center electrode 6, but ex
`tending longitudinally upwardly beyond the uppermost
`limit of the center electrode. The center electrode 6
`and the annular electrode ‘7 are separated and and held
`
`Global Touch Solutions, LLC
`Exhibit 2002
`Microsoft Corp. et al. v. Global Touch Solutions, LLC
`IPR2015-01149
`Page 4 of 7
`
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`in their respective positions by an insulator ring 8. It
`will be observed in FIG. 2 that the insulator ring 8 takes
`the form of a hollow cylinder to provide a chamber 9
`into which the electronic components of the high gain.
`ampli?er may be placed as will be discussed in detail
`below. A'pair of hollow conductors 10 are imbedded in
`the bottom portion of the housing 1 to provide commu
`nication to the chamber 9. These hollow conductors
`permit a pair of leads to be brought from the chamber
`9 to the lower surface of the printed wiring board 2
`where they may be soldered into place in the usual
`manner. The solder will also adhere to the hollow con
`ductors 10 to provide a certain degree of mechanical
`strength in attaching the switching system to the
`printed wiring board 2.
`_
`FIGS. 3 and 4 illustrate a slightly differently configu
`rated housing particularly adapted for panel mounting.
`The retainer clip 11 is utilized to hold the housing 12
`tightly against the panel 13. It will be understood by
`those skilled in the art that the retainer clip 11 could
`be replaced by a nut, provided the lower portion of the
`housing 12 were threaded to receive the nut, or by any
`other suitable method of panel mounting.
`The cross-sectional view of FIG. 4 illustrates an en
`capsulated high d-c current gain amplifier 14 disposed
`within the chamber 15 of the housing 12. The chamber
`15 is ?lled with potting material to provide structural
`strength to the assembly and protection against con
`tamination or other deterioration which could result
`from prolonged exposure to the atmosphere. A current
`_limiting resistor 16 is connected between the center
`electrode 6 and one of the input terminals to the ampli
`?er 14. The annular electrode 7 is connected directly
`to a second input terminal to the amplifier 14. A pair
`of leads 17 are utilized as output terminals to an exter
`nal load and an external power supply as will be dis
`cussed in conjunction with the schematic diagrams of
`FIGS. 5 and 6.
`Referring now to FIG. 5, a basic Darlington amplifier
`circuit is presented which is connected to the electrode
`pair 6 and 7, to an external low voltage d-c power sup
`ply represented by the battery 20, and to a current re
`sponsive load represented by the impedance 21. The
`elements enclosed within the dashed line 22 are con
`tained within the cavity 9 of FIG. 2 or the cavity 15 of
`FIG. 4. It will be observed from an examination of FIG.
`5 that only two leads need extend from the cavity; viz.:
`the negative lead from the power supply 20 to the emit
`ter electrode of transistor Q2 and a lead which is com
`mon to one end of the current responsive load 21, the
`collector electrodes of the transistors Q1 and Q2, and
`the annular electrode 7.
`In operation, when a substantially in?nite resistance
`appears between the electrodes 6 and 7, no current will
`?ow between the electrodes, and both the transistors
`Q1 and Q2 will be cut off such that no appreciable cur
`rent flows through the current responsive load 21. As
`suming the power supply 20 delivers nominally 5 volts
`and the current responsive load 21 to have a nominal
`value of 500 ohms, it has been found that a conductive
`path of as much as 10 megohms between the electrodes
`6 and 7 will permit sufficient current to flow into the
`base electrode of the ampli?er input transistor O1 to
`bring output transistor Q2 into current saturation or
`very close thereto. Inasmuch as it has been shown that
`the galvanic skin resistance can _vary from 20 kilohms
`to 10 megohms, it will be understood that the current
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`passing through the current responsive load 21 can be
`switched from substantially zero to a full nominal value
`by placing the tip of ones ?nger such that the elec
`trodes 6 and 7 are bridged. The basic operation of the
`high gain Darlington ampli?er illustrated in FIG. 5 is
`well known and need not be discussed at length here.
`It may be pointed out, however, that a typical current
`gain for such a con?guration would fall within the
`range of 20,000 to 100,000. As noted briefly above, the
`resistor 16 is placed within the circuit to limit the base
`current to the transistor O1 to a safe level in case the
`electrodes 6 and 7 should be directly shorted with a
`metallic conductor or the like. With high gain transis
`tors, such as 2N3904‘s used with a 5 volt power supply
`and 500 ohm load impedance, the resistor 16 may have
`a value of 1,000 ohms to afford adequate protection for
`the transistor Q1.
`While the circuit of FIG. 5 is entirely adequate for
`most applications, the slightly rearranged circuit of
`FIG. 6 may be used for increased sensitivity. The result
`of placing the current responsive load 21 directly in se
`ries with the transistor O2 in the FIG. 6 con?guration
`is to apply a higher voltage gradiant across the elec
`trodes 6 and 7. Thus, the same resistance brought to
`bear across the electrodes 6 and 7 in the FIG. 6 circuit
`configuration will result in a somewhat higher base cur
`rent to the transistor Q1 than in the FIG. 5 configura
`tion. The resistor 23 may be added optionally to limit
`the voltage to which the operator is exposed in the
`event of a power supply failure which would otherwise
`place a high voltage between the electrodes 6 and 7.
`Such a failure could take the form of a primary to sec
`ondary short in a power supply transformer (not
`shown) which conceivably could expose the operator
`to full line voltage if the resistor 23 were not provided.
`The Darlington configurations of FIG. 5 and FIG. 6
`are presented merely as exemplary of the high gain cir
`cuits which could be utilized. For example, it will be ap
`parent to those skilled in the art that very sensitive ap
`plications might well require three stages of ampli?ca
`tion rather than the two stages depicted. The current
`responsive load 21 can take any form necessary to
`achieve the switching function desired. For example,
`the load 21 may comprise a relay coil or subsequent
`high level electronic switching circuitry and may also
`include readout structure such as an incandescent lamp
`which may be optionally disposed within the housing
`supporting the electrodes 6 and 7 to be used with an
`electronic package permitting pushon-pushoff, latch
`ing, etc. response in addition to the normal momentary
`operation achieved with a simple current responsive
`load 21. Further, those skilled in the digital arts will un
`derstand that it is a simple matter to generate _a multi
`bit alpha-numeric code in response to a change'of state
`of the output stage of the high gain ampli?er.
`Referring back to FIGS. 1 and 4, it is important to re
`alize the signi?cance of the con?guration and dispo
`sition of the center electrode 6 and the annular elec
`trode 7 with respect to one another. if it were possible
`to touch the center electrode 6 without ?rst touching
`the annular electrode 7, the usual alternating voltage
`induced into the operator’s body would cause the
`switching system to turn off and on at the alternating
`frequency, typically 60 Hz. Thus, the center electrode
`6 is depressed below the level of the annular electrode
`7 to assure a good contact of the ?nger with the latter
`before contact is made with the center electrode 6. By
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`Global Touch Solutions, LLC
`Exhibit 2002
`Microsoft Corp. et al. v. Global Touch Solutions, LLC
`IPR2015-01149
`Page 5 of 7
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`?rst contacting the annular electrode 7, the induced a-c
`voltage is harmlessly grounded and a d-c current path
`is set up as soon as the ?nger touches the center elec
`trode 6. it is often important in keyboard use and gen
`eral switching to provide a speci?ed touch threshold
`Touch threshold can be adjusted by varying the depth
`of the center electrode 6 with respect to the outer sur
`face of the annular electrode 7, the deeper the center
`_ electrode with respect to the annular electrode, the
`heavier the touch required to force the ?ngertip into
`contact with both electrodes. Further, by providing the
`center electrode with a hemispheric shape, as depicted
`in FIG. 4, and by providing an inaccessible vertical por
`tion to the annular conductor 7, salts and other con
`tamination deposited from repeated touching of the
`switching with the ?ngers will not be able to set up a
`suf?ciently conductive path to bring about undesired
`activation of the switching system.
`While close attention to the physical con?guration of
`the electrodes 6 and 7 will provide adequate protection
`against inadvertent actuation through interelectrode
`contamination in moderately contaminated environ
`ments, the embodiment of the invention illustrated in
`FIG. 7 affords complete protection in even heavily con
`taminated environments. It will be observed that the
`electrodes 6 and 7 of the FIG. 7 embodiment are mutu
`ally oriented in the same manner as described above.
`However, the electrodes 6 and 7 are completely sealed
`from the environment by a membrane 25 which is pro
`vided with a conductive coating 26 on its inner surface.
`The membrane 25 is sufficiently ?exible to permit de
`flection downwardly such that the conductive coating
`26 will bridge the electrodes 6 and 7 to provide a low
`level current path supplied by the galvanic skin resis
`tance in the previously discussed embodiments. The
`characteristics of the conductive coating 26 may ad
`vantageously be adjusted to provide the current limit
`ing function of the resistor 16 thereby eliminating the
`necessity for the current limiting resistor as a discrete
`component. It will be observed that the FIG. 7 embodi
`ment may be easily actuated even when the operator is
`wearing gloves, and the use of this embodiment may
`therefore be advantageous under certain conditions in
`which the atmosphere is not contaminated, but in
`which the galvanic skin resistance cannot be relied
`upon to perform the bridging function.
`While the principles of the invention have now been
`made clear in an illustrative embodiment, there will be
`immediately obvious to those skilled in the art many
`modi?cations of structure, arrangement, proportions,
`the elements, materials, and components, used in the
`practice of the invention which are particularly
`adapted for speci?c environments and operating re
`quirements without departing from those principles.
`1 claim:
`1. Electrical membrane switch apparatus comprising:
`a housing; first electrode means having a top surface
`and substantially centrally disposed in the housing; sec
`ond annular electrode means having a top surface and
`disposed in the housing and encompassing the ?rst
`electrode means, with the level of the top surface of the
`?rst electrode means vertically spaced from the level of
`the top surface of the second electrode means; and
`elastic membrane means provided with a conductive
`coating on one of its surfaces, the elastic membrane
`means being normally supported by the housing closely
`spaced from, but not touching, the ?rst and second
`
`6
`electrode means, the elastic membrane means being
`adapted to de?ect under pressure such that the con
`ductive coating touches both the ?rst and second elec
`trode means to provide a conductive path therebe
`tween.
`2. The electrical membrane switch apparatus of
`claim 1 wherein the level of the top surface of the sec
`ond electrode means is spaced vertically above the ‘
`level of the top surface of the ?rst electrode means.
`3. Electronic membrane switch apparatus,‘ compris
`ing in combination: insulating media having a top sur
`face; ?rst electrode means immovably arranged with
`the insulating media with the top surface of the ?rst
`electrode means exposed upon the top surface of the
`insulating media; second electrode means immovably
`arranged with the insulating media laterally around and
`about the ?rst electrode means with the top surface of
`the second electrode means exposed upon the top sur
`face of the insulating media laterally from the ?rst elec
`trode means with the level of the top surface of the sec
`ond electrode means vertically spaced from the level of
`the top surface of the ?rst electrode means; elastic
`membrane means disposed in a spaced relation above
`and adjacent to the level of the top surfaces of the elec
`trode means; and conductive means associated with the
`membrane at least on a portion thereof adjacent the
`top surfaces of the electrode means, such that when the
`elastic membrane is deflected toward the top surfaces
`of the electrode means the conductive means contacts
`both the electrode means and provides a conductive
`path therebetween.
`4. The electronic membrane switch apparatus of
`claim 3 wherein the top surface of the ?rst electrode
`means extends from the top surface of insulating media
`and wherein the top surface of the second electrode
`means extends from the top surface of the insulating
`media.
`5. The electronic membrane switch apparatus of
`claim 3, wherein the insulating media includes; space
`for a direct current ampli?er; and coupling means for
`connecting the ?rst and second electrode means to the
`input terminals of any direct current amplifier within
`the space.
`6. The electronic membrane switch apparatus of
`claim 3 including means for coupling the ?rst and sec
`ond electrode means to input terminals of an amplifier.
`7. The electronic membrane switch apparatus of
`claim 3 wherein the vertical spacing between the level
`of the top surface of the ?rst electrode means and the
`level of the top surface of the second electrode means
`is suf?cient to establish a desired touch threshold for
`the switch.
`8. The electrical membrane switch apparatus of
`claim 3 wherein the level of the top surface of the first
`electrode means is spaced vertically below the level of
`the top surface of the second electrode means.
`9. The electronic membrane switch apparatus of
`claim 8 wherein the vertical spacing between the level
`of the top surface of the ?rst electrode means and the
`level of the top surface of the second electrode means
`is suf?cient to establish a desired touch threshold for
`the switch.
`10. The electrical membrane switch apparatus of
`claim 9 wherein the top surface of the ?rst electrode
`means extends from the top surface of insulating media
`and wherein the top surface of the second electrode
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`Exhibit 2002
`Microsoft Corp. et al. v. Global Touch Solutions, LLC
`IPR2015-01149
`Page 6 of 7
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`means extends from the top surface of the insulating
`media.
`11. The electrical membrane switch apparatus of
`claim 8 wherein the top surface of the ?rst electrode
`means extends from the top surface of insulating media
`and wherein the top surface of the second electrode
`means extends from the top surface of the insulating
`media.
`'
`
`12. Electronic membrane switch apparatus, compris
`ing in combination: insulating media having a top sur
`face; ?rst electrode means laterally immovably ar
`ranged with the insulating media with the top surface
`of the first electrode means extending above the top
`surface of the insulating media; second electrode
`means laterally immovably arranged with the insulating
`media and the first electrode means laterally around
`and about, spaced, and insulated from the ?rst elec
`trode means with the top surface of the second elec
`trode means extending above the top surface of the in
`sulating media laterally from the ?rst electrode means
`and such that the level of the top surface of the second
`electrode means is vertically spaced from the level of
`the top surface of the first electrode means; an elastic
`membrane means disposed in a spaced relation above
`and adjacent to the level of the top surface of the elec
`trode means; conductive means associated with the
`membrane means at least on a portion thereof adjacent
`the top surfaces of the electrode means such that when
`the membrane is de?ected toward the top surfaces of
`the electrode means. the conductive means thereon
`contacts both the electrode means and provides a con
`ductive path therebetween; first means for providing an
`electrical connection to the ?rst electrode means; and
`second means for providing an electrical connection to
`the second electrode means.
`13. The electronic membrane switch apparatus of
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`claim 12 wherein the level of the top surface of the sec
`ond electrode means is spaced vertically above the
`level of the top surface of the ?rst electrode means.
`14. The electronic membrane switch apparatus of
`claim 13 wherein the ?rst connection means comprises
`means for providing an electrical connection between
`the ?rst electrode means and the input of a direct cur
`rent ampli?er.
`15. The electronic membrane switch apparatus of
`claim 14 wherein the second connection means com
`prises means for providing an electrical connection be
`tween the second electrode means and_ a means for sup
`plying DC voltage to the direct current ampli?er.
`16. The electronic membrane switch apparatus of
`claim 15 wherein vertical spacing between the level of
`the top surface of the ?rst electrode means and the
`level of the top surface of the second electrode is suffi
`cient to establish a desired touch threshold for the
`switch.
`17. The electronic membrane switch apparatus of
`claim 12 wherein the second connection means com
`prises means for providing an electrical connection be
`tween the second electrode means and a means for sup
`plying DC voltage to the direct current ampli?er.
`18. The electronic membrane switch apparatus of
`claim 12 wherein the vertical spacing between the level
`of the top surface of the ?rst electrode and the level of
`the top surface of the second electrode is sufficient to
`establish a desired touch threshold for the switch.
`19. The electronic membrane switch apparatus of
`claim 12 wherein the ?rst connection means comprises
`means for providing an electrical connection between
`the ?rst electrode means and the input of a direct cur
`rent amplifier.
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`Global Touch Solutions, LLC
`Exhibit 2002
`Microsoft Corp. et al. v. Global Touch Solutions, LLC
`IPR2015-01149
`Page 7 of 7