United States Patent no]
`United States Patent {191
`Larson
`Larson
`
`[54] MEMBRANE SWITCH
`1541 MEMBRANE SWITCH
`Inventor: Willis A. Larson, Wayzata, Minn.
`[75]
`[75] Inventor: Willis A. Larson, Wayzata, Minn.
`[73] Assignee: Magic Dot, Inc., Minneapolis, Minn.
`[73] Assignee: Magic Dot, lnc., Minneapolis, Minn.
`[22] Filed:
`Mar. 29, 1973
`[22] Filed:
`Mar. 29, 1973
`[21] Appl. No.: 346,055
`[21] Appl. No.: 346,055
`Related U.S. Application Data
`' Related US. Application Data
`[60] Division of Ser. No. 161,948, July 9, 1971, Pat. No.
`[60] Division of Scr. No. 161.948. July 9. 1971. Pat. No.
`3,737,670, which is a continuation of Ser. No.
`3.737.670. which is a continuation of Scr. No.
`865,760, Oct. 13, 1969, Pat. No. 3,737,670.
`865.760. Oct. 13. 1969. Pat. No. 3.737.670.
`
`[52] U.S. CI
`. 200/159 B; 200/83 N
`[52] US. Cl. ......................... .. 200/159 B; 200/83 N
`[ 5 1 ]
`I n t . C I
`HOlh 13/54
`[51] Int. Cl. ......................................... .. l-l0lh 13/54
`[ 5 8 ] F i e l d o f S e a r c h
`200/159 B, 5 A, 83 N;
`[58] Field of Search ............ .. 200/159 B, 5 A. 83 N;
`340/365 R, 365 A
`340/365 R, 365 A
`
`[56]
`[56]
`
`3 , 8 7 9 , 5 9 3
`i n ]
`3,879,593
`1111
`[45] Apr. 22, 1975
`[45] Apr. 22, 1975
`
`Primary Examiner—Robert K. Schaeffer
`Primary E.\'aminer—Robert K. Schaeffer
`Assistant Examiner—William J. Smith
`‘Assistant E.raminer—William .1. Smith
`Attorney, Agent, or Finn—Wicks & Nemer
`Attorney. Agent, or F irm——Wicks & Nemer
`
`[57]
`ABSTRACT
`ABSTRACT
`[ 5 7 ]
`In order to provide a sensitive, touch responsive elec­
`In order to provide a sensitive, touch responsive elec
`tronic membrane switch, a pair of electrodes are dis­
`tronic membrane switch, a pair of electrodes are dis
`posed in a unique configuration and are coupled to a
`posed in a unique con?guration and are coupled to a
`high gain amplifier. A membrane, having a conductive
`high gain ampli?er. A membrane, having a conductive
`coating on a side facing the electrodes, is disposed
`coating on a side facing the electrodes. is disposed
`over the pair of electrodes to perform a bridging func­
`over the pair of electrodes to perform a bridging func
`tion when the membrane is pressed against the elec­
`tion when the membrane is pressed against the elec
`trodes to thus cause a positive switching condition at
`trodes to thus cause a positive switching condition at
`the output terminals of the high gain amplifier. In a
`the output terminals of the high gain ampli?er. 1n a
`first embodiment of the invention, the pair of elec­
`?rst embodiment of the invention, the pair of elec
`trodes comprises a first centrally disposed electrode
`trodes comprises a ?rst centrally disposed electrode
`encompassed by a second, circular electrode concen­
`encompassed by a second, circular electrode concen
`trically to, but longitudinally offset from the first elec­
`trically to. but longitudinally offset from the ?rst elec
`trode. The bridging of the electrodes is sensed and dif­
`trode. The bridging of the electrodes is sensed and dif
`ferentiated from the substantially infinite resistance
`ferentiated from the substantially in?nite resistance
`normally existing between the two electrodes by the
`normally existing between the two electrodes by the
`hight current gain amplification to provide a sharp
`hight current gain ampli?cation to provide a sharp
`change in current flow through a load connected to
`change in current flow through a load connected to
`the output terminals of the high gain amplifier. The
`the output terminals of the high gain ampli?er. The
`sharply differentiated state of the output terminals of
`sharply differentiated state of the output terminals of
`the high gain amplifier may be utilized to control
`the high gain ampli?er may be utilized to control
`switching functions in any manner desired.
`switching functions in any manner desired.
`19 Claims, 7 Drawing Figures
`19 Claims, 7 Drawing Figures
`
`8/1971
`
`Lcposavic . . . . . . .
`
`. . . ,, 200/159 B X
`
`8/1972 Adelson . . . . . .
`
`. . . . . . . .. ZOO/159 B
`
`26
`
`&
`
`7
`
`A
`
`2,659,533
`2.659.533
`3,267,233
`3.267233
`3,487,268
`3.487.268
`3,600,528
`3,688,066
`3,699,294
`3.699.294
`3,728,509
`3.728.509
`
`3.600.528
`
`3.688.066
`
`References Cited
`References Cited
`UNITED STATES PATENTS
`UNITED STATES PATENTS
`.. 200/DIG. 1
`11/1953 Quinbyetal
`11/1953 Quinby et a1. ............... .. 200/D1G. 1
`200/83 N
`8/1966 Basile et al
`8/1966 Basile et a1. . . , . . . . .
`. . . . . .. 200/83 N
`... 340/365 R
`12/1969 Ljungdell et al
`12/1969
`Ljungdell et al....
`...... .. 340/365 R
`200/159 B X
`8/1971 Leposavic
`... 200/159 B
`8/1972 Adelson
`340/365 R X
`10/1972 Sudduth
`340/365 R X
`10/1972 Sudduth ..... ..
`200/166 C X
`4/1973 Shimojo
`4/1973 Shimojo .................... .. 200/166 C X
`OTHER PUBLICATIONS
`OTHER PUBLICATIONS
`Fazzio, Circular Sequencing Contact, IBM Technical
`Fazzio. Circular Sequencing Contact. IBM Technical
`Disclosure Bulletin, June 1970, p. 219.
`Disclosure Bulletin, June 1970, p. 219.
`
`GLOBAL EX. 2004
`Microsoft Corporation, et al. v. Global Touch Solutions, LLC
`IPR2015-01151
`
`

`
`PATENTED APR 2 21975
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`3,879,593
`3,879,593
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`1
`1
`MEMBRANE SWITCH
`MEMBRANE SWITCH
`
`2
`reach saturation, or very near saturation, when even a
`reach saturation, or very near saturation, when even a
`relatively high resistance is placed across the electrodes
`relatively high resistance is placed across the electrodes
`to set up low level current flow into the input stage of
`to set up low level current ?ow into the input stage of
`CROSS REFERENCES
`CROSS REFERENCES
`the amplifier. However, when the resistance across the
`the ampli?er. However, when the resistance across the
`This application is a division of application Ser. No. 5 electrode is substantially infinite such that no current
`This application is a division of application Ser. No.
`electrode is substantially in?nite such that no current
`161,948, filed July 9, 1971 now U.S. Pat. No.
`flows into the input stage, the last stage of the high gain
`161,948, filed July 9, 1971 now U.S. Pat. No.
`flows into the input stage, the last stage of the high gain
`3,737,670, June 5, 1973 which is a continuation of ap­
`amplifier is cut off. Thus, a load impedance may be
`3,737,670, June 5, 1973 which is a continuation of ap
`ampli?er is cut off. Thus, a load impedance may be
`plication Ser. No. 865,760 filed Oct. 13, 1969 in the
`driven by the final stage of the high gain amplifier in re­
`plication Ser. No. 865,760 ?led Oct. 13, 1969 in the
`driven by the ?nal stage of the high gain ampli?er in re
`name of Willis A. Larson, now U.S. Pat. 3,737,670 is­
`sponse to the differentiation between the resistance ap-
`name of Willis A. Larson, now U.S. Pat. 3,737,670 is
`sponse to the differentiation between the resistance ap
`sued June 5, 1973.
`10 pearing between the two electrodes when they are
`sued June 5, 1973.
`10
`pearing between the two electrodes when they are
`This invention relates to electronic switching and,
`bridged by galvanic skin resistance and when they are
`This invention relates to electronic switching and,
`bridged by galvanic skin resistance and when they are
`more particularly, to apparatus for utilizing a mem­
`not bridged.
`more particularly, to apparatus for utilizing a mem
`not bridged.
`3
`brane, manually actuated, for providing discrete
`In the embodiment of the invention particularly
`brane, manually actuated, for providing discrete
`In the embodiment of the invention particularly
`switching phenomena at the output terminals of an
`adapted for use in contaminated environmehts which
`switching phenomena at the output terminals of an
`adapted for use in contaminated environments which
`electronic circuit.
`15 might create a sufficiently low resistance between the
`electronic circuit.
`might create a suf?ciently low resistance between the
`Prior art manually operated switches generally func­
`two electrodes to set up an artificial "touch" condition,
`Prior art manually operated switches generally func
`two electrodes to set up an arti?cial “touch" condition,
`tion on the mechanical principal of bringing two con­
`a membrane provided with a conductive coating on its
`tion on the mechanical principal of bringing two con
`a membrane provided with a conductive coating on its
`ductors into physical contact to complete a circuit
`underside is placed over the electrode pair to provide
`ductors into physical contact to complete a circuit
`underside is placed over the electrode pair to provide
`through which current can flow. Because of the me­
`a seal against such contamination. When the mem-
`through which current can flow. Because of the me
`a seal against such contamination. When the mem
`chanical nature of the prior art switches, they are sub- 20 brane is pressed downwardly against the electrodes, the
`chanical nature of the prior art switches, they are sub
`brane is pressed downwardly against the electrodes, the
`ject to wear and eventual failure as a result of the re­
`conductive coating performs the bridging function
`conductive coating performs the bridging function
`ject to wear and eventual failure as a result of the re
`peated operation of the moving parts, plating of mate­
`which is sensed through the high gain amplifier.
`peated operation of the moving parts, plating of mate
`which is sensed through the high gain amplifier.
`rial from one contact to the other because of unidirec-
`The subject matter of the invention is particularly
`rial from one contact to the other because of unidirec
`The subject matter of the invention is particularly
`tional current flow, pitting, corrosion, and contamina­
`pointed out and distinctly claimed in the concluding
`tional current ?ow, pitting, corrosion, and contamina
`pointed out and distinctly claimed in the concluding
`tion in the form of accumulated dust, dirt, and chemi- 25 portion of the specification. The invention, however,
`25
`tion in the form of accumulated dust, dirt, and chemi
`portion of the speci?cation. The invention, however,
`cal oxides formed by interaction between the contact
`both as to organization and method of operation, may
`cal oxides formed by interaction between the contact
`both as to organization and method of operation, may
`material and the environmental atmosphere.
`best be understood by reference to the following de­
`material and the environmental atmosphere.
`best be understood by reference to the following de
`In an attempt to obviate the difficulties encountered
`scription taken in connection with the accompanying
`In an attempt to obviate the dif?culties encountered
`scription taken in connection with the accompanying
`by mechanical switches, touch responsive switches uti­
`drawings of which:
`by mechanical switches, touch responsive switches uti
`drawings of which:
`lizing body capacitance or skin resistance have been 30
`FIG. 1 is a perspective view of the switching system
`30
`lizing body capacitance or skin resistance have been
`FIG. 1 is a perspective view of the switching system
`proposed, however, these prior art touch responsive
`of the present invention showing the disposition of the
`proposed. however, these prior art touch responsive
`of the present invention showing the disposition of the
`switches have been either very complex and costly to
`inner and outer electrodes and housing especially
`switches have been either very complex and costly to
`inner and outer electrodes and housing especially
`manufacture or somewhat dangerous because the volt­
`adapted for printed circuit board use;
`manufacture or somewhat dangerous because the volt
`adapted for printed circuit board use;
`ages required to operate them are higher than desirable
`FIG. 2 is a cross section taken along the lines 2—2 of
`ages required to operate them are higher than desirable
`FIG. 2 is a cross section taken along the lines 2~2 of
`such that they have been deemed either impractical or
`the housing illustrated in FIG. 1;
`such that they have been deemed either impractical or
`the housing illustrated in FIG. 1;
`useful only in applications in which high cost can be
`FIG. 3 illustrates a slightly altered physical configura­
`useful only in applications in which high cost can be
`FIG. 3 illustrates a slightly altered physical configura
`justified. Thus, it will be readily appreciated that a
`tion of the housing which renders it particularly suit­
`justified. Thus, it will be readily appreciated that a
`tion of the housing which renders it particularly suit
`touch responsive switch which is highly reliable, safe,
`able for panel mount operation;
`touch responsive switch which is highly reliable, safe,
`able for panel mount operation;
`and lends itself to economical mass production would
`FIG. 4 is a cross section taken along the lines 4—4 of
`and lends itself to economical mass production would
`FIG. 4 is a cross section taken along the lines 4—4 of
`be highly desirable. Such a switch would find broad ap­
`the housing illustrated in FIG. 3 and also shows the
`be highly desirable. Such a switch would ?nd broad ap
`the housing illustrated in FIG. 3 and also shows the
`plication for use with computer terminals, typewriter
`manner in which the electronic circuitry associated
`plication for use with computer terminals, typewriter
`manner in which the electronic circuitry associated
`keyboards, calculator keyboards, control panels, and
`with the electrodo pair may be contained within the
`keyboards, calculator keyboards, control panels, and
`with the electrodo pair may be contained within the
`housing;
`such other uses as require the entry of data through a
`housing;
`such other uses as require the entry of data through a
`FIG. 5 is a schematic diagram of a rather straight­
`primary switching interface unit.
`primary switching interface unit.
`FIG. 5 is a schematic diagram of a rather straight
`45
`It is therefore a broad object of this invention to pro­
`forward Darlington amplifier which provides adequate
`forward Darlington ampli?er which provides adequate
`It is therefore a broad object of thisv invention to pro
`vide an improved touch responsive switch.
`gain to perform the electronic switching initiated by
`vide an improved touch responsive switch.
`gain to perform the electronic switching initiated by
`It is a more specific object of this invention to pro­
`bridging the electrodes with galvanic skin resistance;
`It is a more speci?c object of this invention to pro
`bridging the electrodes with galvanic skin resistance;
`vide a touch responsive switch utilizing a uniquely con­
`FIG. 6 is a schematic diagram of a slightly altered
`vide a touch responsive switch utilizing a uniquely con
`FIG. 6 is a schematic diagram of a slightly altered
`figured pair of electrodes coupled to a high gain ampli­
`Darlington circuit which places more voltage across the
`?gured pair of electrodes coupled to a high gain ampli
`Darlington circuit which places more voltage across the
`50
`electrode pair to insure saturation of the final amplifier
`fier.
`?er.
`electrode pair to insure saturation of the ?nal amplifier
`stage; and
`It is another object of this invention to provide
`It is another object of this invention to provide
`stage; and
`switching element electrodes which are unaffected by
`FIG. 7 is a partially cutaway perspective view of a
`switching element electrodes which are unaffected by
`FIG. 7 is a partially cutaway perspective view of a
`environmental contamination and which may be easily
`configuration for the electrode housing which is partic­
`environmental contamination and which may be easily
`con?guration for the electrode housing which is partic
`operated even if the operator is wearing gloves.
`ularly useful in contaminated environments.
`operated even if the operator is wearing gloves.
`ularly useful in contaminated environments.
`55
`55
`These and other objects of the
`invention are
`Referring now to FIGS. 1 and 2, a housing 1, which
`These and other objects of the invention are
`Referring now to FIGS. 1 and 2, a housing I, which
`achieved, according to an embodiment of the invention
`may be made of any suitable durable insulating mate­
`achieved, according to an embodiment of the invention
`may be made of any suitable durable insulating mate
`disclosed and claimed in application Ser. No. 161,948,
`rial, is shown as it would be utilized with a printed wir­
`disclosed and claimed in application Ser. No. 161,948,
`rial, is shown as it would be utilized with a printed wir
`now U.S. Pat. No. 3,737,670, by utilizing, as the oper­
`ing board. A dust seal 3 of foam rubber or the like is
`now U.S. Pat. No. 3,737,670, by utilizing, as the oper~
`ing board. A dust seal 3 of foam rubber or the like is
`placed between the flange 4 of the housing 1 and a
`ated switching element, a pair of electrodes comprising
`ated switching element, a pair of electrodes comprising
`placed between the ?ange 4 of the housing 1 and a
`60
`60
`panel 5 through which the housing extends for manual
`a first centrally disposed electrode encompassed by a
`a ?rst centrally disposed electrode encompassed by a
`panel 5 through which the housing extends for manual
`access.
`second, circular electrode longitudinally offset from
`second, circular electrode longitudinally offset from
`access.
`As best shown in FIG. 1, the electrode pair comprises
`the first electrode such that the pair of electrodes sub­
`the ?rst electrode such that the pair of electrodes sub
`As best shown in FIG. I, the electrode pair comprises
`a center electrode 6 and an annular electrode 7 con­
`stantially conform to the contour of an operator's fin­
`stantially conform to the contour of an operator’s ?n
`a center electrode 6 and an annular electrode 7 con
`centrically disposed to the center electrode 6, but ex­
`ger. When the operator touches the two electrodes, a
`ger. When the operator touches the two electrodes, a
`centrically disposed to the center electrode 6, but ex
`65
`65
`tending longitudinally upwardly beyond the uppermost
`finite resistance path is set up between the two elec­
`tending longitudinally upwardly beyond the uppermost
`?nite resistance path is set up between the two elec
`limit of the center electrode. The center electrode 6
`trodes, and this condition is detected through the use
`trodes, and this condition is detected through the use
`limit of the center electrode. The center electrode 6
`and the annular electrode 7 are separated and and held
`of a high current gain amplifier whose last stage will
`of a high current gain ampli?er whose last stage will
`and the annular electrode ‘7 are separated and and held
`
`35
`35
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`3
`4
`4
`3
`in their respective positions by an insulator ring 8. It
`passing through the current responsive load 21 can be
`passing through the current responsive load 21 can be
`in their respective positions by an insulator ring 8. It
`will be observed in FIG. 2 that the insulator ring 8 takes
`switched from substantially zero to a full nominal value
`switched from substantially zero to a full nominal value
`will be observed in FIG. 2 that the insulator ring 8 takes
`the form of a hollow cylinder to provide a chamber 9
`by placing the tip of ones finger such that the elec­
`by placing the tip of ones ?nger such that the elec
`the form of a hollow cylinder to provide a chamber 9
`into which the electronic components of the high gain
`trodes 6 and 7 are bridged. The basic operation of the
`trodes 6 and 7 are bridged. The basic operation of the
`into which the electronic components of the high gain.
`amplifier may be placed as will be discussed in detail 5 high gain Darlington amplifier illustrated in FIG. 5 is
`high gain Darlington ampli?er illustrated in FIG. 5 is
`ampli?er may be placed as will be discussed in detail
`below. A pair of hollow conductors 10 are imbedded in
`well known and need not be discussed at length here.
`well known and need not be discussed at length here.
`below. A'pair of hollow conductors 10 are imbedded in
`the bottom portion of the housing 1 to provide commu­
`It may be pointed out, however, that a typical current
`It may be pointed out, however, that a typical current
`the bottom portion of the housing 1 to provide commu
`nication to the chamber 9. These hollow conductors
`gain for such a configuration would fall within the
`gain for such a con?guration would fall within the
`nication to the chamber 9. These hollow conductors
`permit a pair of leads to be brought from the chamber
`range of 20,000 to 100,000. As noted briefly above, the
`range of 20,000 to 100,000. As noted briefly above, the
`permit a pair of leads to be brought from the chamber
`9 to the lower surface of the printed wiring board 2 10 resistor 16 is placed within the circuit to limit the base
`resistor 16 is placed within the circuit to limit the base
`9 to the lower surface of the printed wiring board 2
`current to the transistor Q1 to a safe level in case the
`where they may be soldered into place in the usual
`where they may be soldered into place in the usual
`current to the transistor O1 to a safe level in case the
`manner. The solder will also adhere to the hollow con­
`electrodes 6 and 7 should be directly shorted with a
`electrodes 6 and 7 should be directly shorted with a
`manner. The solder will also adhere to the hollow con
`ductors 10 to provide a certain degree of mechanical
`metallic conductor or the like. With high gain transis­
`metallic conductor or the like. With high gain transis
`ductors 10 to provide a certain degree of mechanical
`tors, such as 2N3904's used with a 5 volt power supply
`strength in attaching the switching system to the
`strength in attaching the switching system to the
`tors, such as 2N3904‘s used with a 5 volt power supply
`15 and 500 ohm load impedance, the resistor 16 may have
`printed wiring board 2.
`and 500 ohm load impedance, the resistor 16 may have
`printed wiring board 2.
`_
`a value of 1,000 ohms to afford adequate protection for
`FIGS. 3 and 4 illustrate a slightly differently configu­
`a value of 1,000 ohms to afford adequate protection for
`FIGS. 3 and 4 illustrate a slightly differently configu
`the transistor Ql.
`rated housing particularly adapted for panel mounting.
`rated housing particularly adapted for panel mounting.
`the transistor Q1.
`While the circuit of FIG. 5 is entirely adequate for
`The retainer clip 11 is utilized to hold the housing 12
`While the circuit of FIG. 5 is entirely adequate for
`The retainer clip 11 is utilized to hold the housing 12
`tightly against the panel 13. It will be understood by
`most applications, the slightly rearranged circuit of
`most applications, the slightly rearranged circuit of
`tightly against the panel 13. It will be understood by
`those skilled in the art that the retainer clip 11 could 20 FIG. 6 may be used for increased sensitivity. The result
`FIG. 6 may be used for increased sensitivity. The result
`those skilled in the art that the retainer clip 11 could
`be replaced by a nut, provided the lower portion of the
`of placing the current responsive load 21 directly in se­
`of placing the current responsive load 21 directly in se
`be replaced by a nut, provided the lower portion of the
`housing 12 were threaded to receive the nut, or by any
`ries with the transistor Q2 in the FIG. 6 configuration
`ries with the transistor O2 in the FIG. 6 con?guration
`housing 12 were threaded to receive the nut, or by any
`is to apply a higher voltage gradiant across the elec­
`other suitable method of panel mounting.
`is to apply a higher voltage gradiant across the elec
`other suitable method of panel mounting.
`trodes 6 and 7. Thus, the same resistance brought to
`The cross-sectional view of FIG. 4 illustrates an en-
`trodes 6 and 7. Thus, the same resistance brought to
`The cross-sectional view of FIG. 4 illustrates an en
`capsulated high d-c current gain amplifier 14 disposed 25 bear across the electrodes 6 and 7 in the FIG. 6 circuit
`25
`capsulated high d-c current gain amplifier 14 disposed
`bear across the electrodes 6 and 7 in the FIG. 6 circuit
`within the chamber 15 of the housing 12. The chamber
`configuration will result in a somewhat higher base cur­
`configuration will result in a somewhat higher base cur
`within the chamber 15 of the housing 12. The chamber
`rent to the transistor Ql than in the FIG. 5 configura­
`15 is filled with potting material to provide structural
`rent to the transistor Q1 than in the FIG. 5 configura
`15 is ?lled with potting material to provide structural
`strength to the assembly and protection against con­
`tion. The resistor 23 may be added optionally to limit
`tion. The resistor 23 may be added optionally to limit
`strength to the assembly and protection against con
`tamination or other deterioration which could result
`the voltage to which the operator is exposed in the
`the voltage to which the operator is exposed in the
`tamination or other deterioration which could result
`from prolonged exposure to the atmosphere. A current 30 event of a power supply failure which would otherwise
`30
`event of a power supply failure which would otherwise
`from prolonged exposure to the atmosphere. A current
`limiting resistor 16 is connected between the center
`place a high voltage between the electrodes 6 and 7.
`place a high voltage between the electrodes 6 and 7.
`_limiting resistor 16 is connected between the center
`electrode 6 and one of the input terminals to the ampli­
`Such a failure could take the form of a primary to sec­
`Such a failure could take the form of a primary to sec
`electrode 6 and one of the input terminals to the ampli
`ondary short in a power supply transformer (not
`fier 14. The annular electrode 7 is connected directly
`ondary short in a power supply transformer (not
`?er 14. The annular electrode 7 is connected directly
`shown) which conceivably could expose the operator
`to a second input terminal to the amplifier 14. A pair
`shown) which conceivably could expose the operator
`to a second input terminal to the amplifier 14. A pair
`to full line voltage if the resistor 23 were not provided.
`of leads 17 are utilized as output terminals to an exter­
`to full line voltage if the resistor 23 were not provided.
`of leads 17 are utilized as output terminals to an exter
`nal load and an external power supply as will be dis­
`The Darlington configurations of FIG. 5 and FIG. 6
`The Darlington configurations of FIG. 5 and FIG. 6
`nal load and an external power supply as will be dis
`are presented merely as exemplary of the high gain cir­
`cussed in conjunction with the schematic diagrams of
`are presented merely as exemplary of the high gain cir
`cussed in conjunction with the schematic diagrams of
`cuits which could be utilized. For example, it will be ap­
`FIGS. 5 and 6.
`cuits which could be utilized. For example, it will be ap
`FIGS. 5 and 6.
`Referring now to FIG. 5, a basic Darlington amplifier
`parent to those skilled in the art that very sensitive ap­
`parent to those skilled in the art that very sensitive ap
`Referring now to FIG. 5, a basic Darlington amplifier
`circuit is presented which is connected to the electrode
`plications might well require three stages of amplifica­
`plications might well require three stages of ampli?ca
`circuit is presented which is connected to the electrode
`tion rather than the two stages depicted. The current
`pair 6 and 7, to an external low voltage d-c power sup­
`tion rather than the two stages depicted. The current
`pair 6 and 7, to an external low voltage d-c power sup
`responsive load 21 can take any form necessary to
`ply represented by the battery 20, and to a current re­
`responsive load 21 can take any form necessary to
`ply represented by the battery 20, and to a current re
`sponsive load represented by the impedance 21. The
`achieve the switching function desired. For example,
`achieve the switching function desired. For example,
`sponsive load represented by the impedance 21. The
`elements enclosed within the dashed line 22 are con­
`the load 21 may comprise a relay coil or subsequent
`the load 21 may comprise a relay coil or subsequent
`elements enclosed within the dashed line 22 are con
`tained within the cavity 9 of FIG. 2 or the cavity 15 of
`high level electronic switching circuitry and may also
`high level electronic switching circuitry and may also
`tained within the cavity 9 of FIG. 2 or the cavity 15 of
`FIG. 4. It will be observed from an examination of FIG.
`include readout structure such as an incandescent lamp
`include readout structure such as an incandescent lamp
`FIG. 4. It will be observed from an examination of FIG.
`5 that only two leads need extend from the cavity; viz.:
`which may be optionally disposed within the housing
`which may be optionally disposed within the housing
`5 that only two leads need extend from the cavity; viz.:
`the negative lead from the power supply 20 to the emit­
`supporting the electrodes 6 and 7 to be used with an
`supporting the electrodes 6 and 7 to be used with an
`the negative lead from the power supply 20 to the emit
`ter electrode of transistor Q2 and a lead which is com­
`electronic package permitting pushon-pushoff, latch­
`electronic package permitting pushon-pushoff, latch
`ter electrode of transistor Q2 and a lead which is com
`mon to one end of the current responsive load 21, the
`ing, etc. response in addition to the normal momentary
`ing, etc. response in addition to the normal momentary
`mon to one end of the current responsive load 21, the
`operation achieved with a simple current responsive
`collector electrodes of the transistors Ql and Q2, and
`operation achieved with a simple current responsive
`collector electrodes of the transistors Q1 and Q2, and
`load 21. Further, those skilled in the digital arts will un­
`the annular electrode 7.
`load 21. Further, those skilled in the digital arts will un
`the annular electrode 7.
`derstand that it is a simple matter to generate a multi-
`In operation, when a substantially infinite resistance
`derstand that it is a simple matter to generate _a multi
`In operation, when a substantially in?nite resistance
`appears between the electrodes 6 and 7, no current will
`bit alpha-numeric code in response to a change of state
`bit alpha-numeric code in response to a change'of state
`appears between the electrodes 6 and 7, no current will
`of the output stage of the high gain amplifier.
`flow between the electrodes, and both the transistors
`of the output stage of the high gain ampli?er.
`?ow between the electrodes, and both the transistors
`Referring back to FIGS. 1 and 4, it is important to re­
`Ql and Q2 will be cut off such that no appreciable cur­
`Referring back to FIGS. 1 and 4, it is important to re
`Q1 and Q2 will be cut off such that no appreciable cur
`alize the significance of the configuration and dispo­
`rent flows through the current responsive load 21. As­
`alize the signi?cance of the con?guration and dispo
`rent flows through the current responsive load 21. As
`sition of the center electrode 6 and the annular elec-
`suming the power supply 20 delivers nominally 5 volts
`sition of the center electrode 6 and the annular elec
`suming the power supply 20 delivers nominally 5 volts
`trode 7 with respect to one another, if it were possible
`and the current responsive load 21 to have a nominal
`trode 7 with respect to one another. if it were possible
`and the current responsive load 21 to have a nominal
`to touch the center electrode 6 without first touching
`value of 500 ohms, it has been found that a conductive
`to touch the center electrode 6 without ?rst touching
`value of 500 ohms, it has been found that a conductive
`the annular electrode 7, the usual alternating voltage
`path of as much as 10 megohms between the electrodes
`the annular electrode 7, the usual alternating voltage
`path of as much as 10 megohms between the electrodes
`induced into the operator's body would cause the
`6 and 7 will permit sufficient current to flow into the
`induced into the operator’s body would cause the
`6 and 7 will permit sufficient current to flow into the
`base electrode of the amplifier input transistor Ql to
`switching system to turn off and on at the alternating
`switching syst