US3564541A

US3564541A - Switching mechanism

Info

Publication number: US3564541A
Application number: US783959A
Authority: US
Inventors: Donald C Gove
Original assignee: IKOR Inc
Current assignee: IKOR Inc
Priority date: 1967-01-05
Filing date: 1968-12-16
Publication date: 1971-02-16
Anticipated expiration: 1988-02-16
Also published as: GB1151299A; DE1537946A1; US3419697A; DE1537946B2

Abstract

THE FOLLOWING SPECIFICATION DESCRIBERS A SWITCH IN WHICH ONE OR MORE CONDUCTIVE TRANSMISSION BARS ARE CONNECTABLE TO AN INPUT TERMINAL AND ONE OR MORE DISCRETE, CONDUCTIVE RECEIVING STRIPS ARE EACH CONNECTABLE TO AN OUTPUT TERMINAL. THE INPUT TERMINAL IS INTENDED TO BE CONNECTED TO A SOURCE OF A SIGNAL OF CHANGING POTENTIAL, AND IN ONE FORM IS CONNECTABE TO THE TRANSMISSION BARS BY A COMMUTATING DEVICE. IN SUCH CASE, A SINGLE LARGE RECEIVING STRIP CAN BE USED DIRECTLY CONNECTED TO THE OUTPUT TERMINAL. IN ANOTHER FORM, THE INPUT TERMINAL IS DIRECTLY CONNECTED TO A SINGLE TRANSMISSION BAR AND A NUMBER OF RECEIVING STRIPS ARE CONNECTABLE THROUGH COMMUTATION TO THE OUTPUT TERMINAL. A MANUALLY ENGAGEABLE KEY IN THE FORM OF AN ELECTROSTATIC SHIELDING ELEMENT IS NORMALLY INTERPOSED BETWEEN THE TRANSMISSION AND RECEIVING ELEMENTS SO AS TO PREVENT CAPACITIVE COUPLING OF THE SIGNAL FROM OCCURRING BETWEEN THE TRANSMISSION AND RECEIVING ELEMENTS. THE KEY IS MOVABLE TO A POSITION AT WHICH APERTURES IN THE KEY PERMIT COUPLING AND THUS SWITCHING TO OCCUR. THE KEY CAN, BE VIRTUE OF THE NUMBER AND PLCEMENT OF APERTURES IN IT, DIRECTLY ENCODE THE SIGNAL INTO A GIVEN NUMERIAL FORM DEFINED BY SELECTIVE ENERGIZATION OF THE INPUT TERMINALS, AND HENCE FORMS A BASIC ELEMENT FOR A MULTIPLE KEY KEYBOARD.

Description

D. C. GQVE SWITCHING MECHANISM Feb. 16, 1971 2 Sheets-Sheet 1 Filed Dec. 16, 1968 DONALD a GUI/E INVENTOR.

BY Sm ATTORNEY Feb. 16, 1971 D V 3,564,541

SWITCHING MECHANISM Filed Dec. 16, 1968 2 Sheets-Sheet 2 SHIFT A REGISTER SHIFT CONDITION REGISTER CONDITION W IIIIAIIIII I ,IIIL

.r F G! E; A

DONALD C GUI/E IINVENTOR.

RM} S I ATTORNEY COMM - COMM.

OSC.

FIG. 7.

United States Patent Int. Cl. -G08c 9/02 US. Cl. 340365 6 Claims ABSTRACT OF THE DISCLOSURE The following specification describes a switch in which one or more conductive transmission bars are connectable to an input terminal and one or more discrete, conductive receiving strips are each connectable to an output terminal. The input terminal is intended to be connected to a source of a signal of changing potential, and in one form is connectable to the transmission bars by a commutating device. In such case, a single large receiving stri can be used directly connected to the output terminal. In another form, the input terminal is directly connected to a single transmission bar and a number of receiving strips are connectable through commutation to the output terminal. A manually engageable key in the form of an electrostatic shielding element is normally interposed between the transmission and receiving elements so as to prevent capacitive coupling of the signal from occurring between the transmission and receiving elements. The key is movable to a position at which apertures in the key permit coupling and thus switching to occur. The key can, by virtue of the number and placement of apertures in it, directly encode the signal into a given numerical form defined by selective energization of the input terminals, and hence forms a basic element for a multiple key keyboard.

This application is a continuation-in-part of copending application Ser. No. 607,563 filed Jan. 5, 1967 now U.S. Pat. 3,419,697.

This invention relates to an electrical switching device and more particularly to novel switching means adapted for multiple keyboard switching.

As is well known, the typical electronic calculator operates on the basis of a numerical or logical system other than decimal because of the difficulty in manipulating decimal notation or multivalued logic. However, because data is most generally in decimal form, a manually manipulated input key-board to a calculator is usually designed to accept information in decimal terms. Hence, the device usually requires means for coding the decimal input data into another numerical system (typically binary) more suited for machine usage.

A usual input keyboard comprises a plurality of keys, each connected to operate a mechanical switch. The state of the keyboard switches is converted to an appropriately coded signal either by using cross-bar switches in which the coding is directly accomplished, or by using simple mechanical switches with auxiliary apparatus such as a diode matrix to achieve coding. The portion of the mechanical switch moved manually usually is a currentcarrying element, hence the latter must be insulated so that the operator is not exposed to the current. Of course, in either type of switch there are a number of other problems posed by its mechanical construction. For example, mechanical contact switching tends to be noisy, being subject to switching transients and contact bounce. Mechanical contact switches also tend to Wear at the contact surfaces and hence have limited life and reliability.

The present invention, therefore, has as a principal ice object the provision of novel switching means particularly adapted to provide signal encoding Without the above noted problems characteristic of mechanical contact switches.

Another object of the present invention is to provide switching means 'with increased reliability because switching is achieved substantially without contact arcing, bounce, or wear.

Yet another object of the present invention is to achieve direct encoding of a value into serial form Without employing diode matrices or the like. Briefly, to accomplish these and other objects, the present invention is embodied in a three-element switch intended to switch only changing potentials. The switch comprises a first element having a signal transmitting surface, a second element having a signal receiving surface, the two elements being disposed so that an interspace is provided between the twofacing surfaces. The third element is an electrically conductive electrostatic shield disposed between the receiving and transmitting surfaces. It will be apparent that when the first element is connected to a source of changing potential, the presence of an electrostatic shield between the receiving and transmitting surfaces will prevent the occurrence of any capacitive coupling of the signal at the transmitting surface with the receiving surface. Therefore,

the shield has a configuration such that a portion thereof is not electrically conductive but presents a dielectric aperture through which capacitive coupling of respective surfaces can be achieved. At least one of the elements is movable with respect to the others so that coupling is effected only in a predetermined relative position of the three elements and preferably in no other position. Thus, the output of the switch is uniquely related to the nature and position of transmitting and receiving surfaces and dielectric apertures so that direct coding by the switch is readily accomplished. Where the transmission surfaces are all simultaneously enerigized, the output is a parallel coded signal. A system of this type, disclosed in said copending application, therefore would normally require a multiplicity of signal conditioners such as amplifiers, drivers and the like for each switch.

However, often it is desirable to provide the output code in serial rather than parallel form. Such a serial system requires, of course, but one output channel requiring but a single signal conditioning means. The present invention is therefore an improvement on the aforesaid coding system in that it inherently provides serial rather than parallel encoding.

Other objects of the invention will in part be obvious and will in part appear hereinafter. The invention accordingly comprises the apparatus possessing the construction, combination of elements, and arrangement of parts which are exemplified in the following detailed-disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the present invention, reference should be had to the following detailed description taken in connection with the accompanying drawings, wherein:

FIG. 1 is a schematic perspective view partly in fragment of an assembled switch embodying the principles of the present invention FIG. 2 is an exploded perspective showing the relation and details of a number of the elements of the switch of FIG. 1;

FIG. 3 is a partial cross-section of a portion of the embodiment of FIG. 1 taken along the line 33;

FIG. 4 is a schematic perspective view showing the relation of a number of selected elements of the embodiment of FIG. 1 when the switch is in a conducting position;

FIG. 5 is a schematic representation showing the elements of FIG. 4 when the switch is in a non-conducting position;

FIG. 6 is a schematic circuit diagram, partly in block form, showing an embodiment of the present invention useful for multiple signal encoding, and

FIG. 7 is yet another schematic circuit diagram, partly in block form, showing another signal encoding system.

As previously noted, the switching means of the present invention is intended to connect input and output terminals through a capacitive coupling phenomenon, and hence requires that the signal at the input terminal be a changing potential, i.e., a smoothly changing potential, such as an oscillating Voltage, or a step-change such as is found with a pulse train input or the like.

Referring now to FIGS. 1-3, there is shown one embodiment of the present invention comprising reception element having at least one elongated slab 22 of an electrically conductive material such as copper or the like. One surface of the slab bears an electrically insulating element 24, for example of an enamel or other dielectric material. Another thin layer of electrically conductive material 26 overlies insulating layer 24. One or more areas of slab 22 are devoid of both

layers

24 and 26 such that there is at least one discrete, exposed, uninsulated surface portion 28 of the electrically-conductive material of slab 22, Le. an aperture through to the

layers

24 and 26. Where there are more than one uninsulated portion 28, each such surface portion is spaced apart and separated from the others by the presence of the intervening structure of

layers

24 and 26. Obviously, all uninsulated surface portions 28 are electrically connected to one another through the body of slab 22. Means, such as lead 29, are provided for connecting slab 22 to an output terminal. Layer 26 is preferably connected to a system ground and hence provides electrostatic shielding with respect to the other areas of the surface of slab 22, directly underlying layer 26.

Spaced from element 20 is transmission element 30 which typically comprises elongated support means in the form of insulating substrate 32, for example of glass or glass-epoxy resin. Mounted on a surface of substrate 32 so as to be in register with each surface portion 28 (i.e., in facing relation across the interspace between transmission element 20 and reception element 30) is a corresponding, electrically-conductive element, for example flat metallic strip 34. If more than one such strip is required because there is more than one surface portion 28, the strips are spaced from one another and are held electrically insulated from one another by substrate 32.

In a preferred embodiment,

elements

20 and 30 are fixedly mounted with respect to one another so that each surface portion 28 is in fixed register with a corresponding strip 34. Mounted for movement between and spaced from both

elements

20 and 30 is electrostatic shielding means 36 preferably formed of an electrically-conductive material and having at least one aperture 38 therein. Aperture 38 can simply be a hole which contains a dielectric material such as a vacuum, air or even a solid dielectric, as desired. Where the facing surfaces of the transmission and reception elements are substantially planar, the electrostatic shield can simply be a flat metallic plate with one or more apertures 38 appropriately placed, as will appear hereinafter.

Shielding means 36 is preferably mounted for movement within the interspace between

elements

20 and 30* such that in a unique position of the shield, every aperture 38 lies between a corresponding registered pair of a surface portion 28 and a strip 34, thereby permitting any changing potential on the latter to be capacitively coupled to its registered portion 28. Preferably, in all other positions to which the shield is movable, the electricallyconductive material of the shield is interposed between the registered pair or pairs. Because shielding means 36 is also connected to ground, it is apparent that it will constitute an electrostatic shield preventing capacitive coupling when interposed between a registered pair.

A switch of the present invention, particularly adapted for use as a keyboard switch, is as shown in FIGS. 1 and 2 wherein reception element 20 is a slab formed in a U-shape such that the surface bearing layers 24 and 26 is on the outside of the U. Element 20 is fixedly mounted at the base of the U upon a support such as plate 40. As shown in FIG. 2, a number of surface portions 28 are provided as perforations extending through layers 24and 26 to expose the electrically conductive material of slab 22. It will be recognized that because of the U- shape of element 20, there are two outwardly facing surfaces, each of which may bear one or more surface portions 28. Consequently, opposite each arm of the U-shape of element 20' is a corresponding transmission element 30 provided with a plurality of strips 34. For each surface portion 28 of element 20 there is at least one registered corresponding strip 34. Each of the elements 30 is also fixedly mounted on base 40 in proper relationship to the outwardly facing surfaces of element 20.

The switch of FIGS. 1 and 2 also includes electrostatic shielding means 36 in the form of a metallic strip bent to form a U, dimensioned so as to fit outside element 20 but inside the interspace between element 20 and ele ment 30. Element 36 is mounted for movement within the interspace between element 20 and element 30 in the following manner: there is provided top plate 42 having a central aperture 43 into which shielding means 36 is slidably mounted. Means (not shown) are included for mounting plate 42 in a substantially fixed, parallel relation with plate 40. Rigidly mounted on the inside of the base of the U-shape of means 36 and extending substantially centrally between and parallel to the arms of the U-shape thereof is pin 44. Slidably mounted on pin 44 is bar 46 which extends substantially perpendicularly to pin 44 and is dimensioned to be longer than the width of shielding means 36, and, therefore, extends outwardly from the bight of the U-shape of the latter so as to be engageable with edge portions of the periphery of aperture 43 in plate 42. Resilient means such as spring 48 is mounted about pin 44, one end of spring 48 being anchored at the distal end of the pin, the other end of spring 48 being anchored on bar 46 adjacent the pin. Manually engageable button 50, typically intended to bear on its top surface a numerical or other indicium, is affixed to the outside of the base of the U-shape of shielding means 36.

As shown assembled in FIG. 1, when shielding means 36 is positioned in aperture 43 of plate 42 such that bar 46 engages the top surface of plate 42, spring 48 serves to retain shielding means 36 in a normal position wherein (as schematically shown in FIG. 5 apertures 38 in shielding means 36 are completely out of alignment with any registered surface portion 28 and strip 34. In this normal position of the shielding means, the electrically conductive body of the shield is interposed between each registered pair of surface portions 28 and strips 34. When button 50 is subjected to manual pressure so as to force the shield to move downwardly through the interspace between

elements

20 and 30, because one end of spring 48 is fixedly positioned by the engagement of bar 46 and plate 42, the other end of the spring moves with pin 44, and the spring is placed under tension. Of course, upon release of pressure on button 50, the spring will tend to restore shielding means 36 to its normal position.

For convenience in manufacture, each of transmission elements 30 is preferably provided in an embodiment such as that shown in FIGS. 1 and 2, wherein each element 30 has the same plurality of strips 34 thereon, each strip corresponding for example to a specific whole power of a radix of a numerical code. Thus, as shown for the sake of illustration in FIGS. 4 and 5, element 30 bears four strips, 34A, 34B, 34C, and 34D, each having its own,

individual input lead, respectively, 52A, 52B, 52C, and 52D. Now, it can be assumed for example that only one arm of the U-shape of reception element bears two surface portions respectively identified in FIGS. 4 and 5 as 28A and 28C registered with

corresponding strips

34A and 34C. Element 20 is coupled to output lead 29. It will be seen from FIGS. 4 and 5 that when shielding means 36 is in its normal position, electrically-conductive material of the body of the latter lies wholly between portion 28A and strip 34A and between portion 24C and strip'34C. Shielding means 36, as shown, includes a pair of dielectric apertures identified respectively as 38A and 38C. The latter apertures are disposed so that when shielding means 36 is moved to a switching position as shown in FIG. 4, the dielectric apertures then lie respectively between registered portions 28A and strip 34A and registered portion 28C and strip 34C and therefore permit any changing potential signal on only either

strip

34C or 34A to be capacitively coupled to element 20. In order to insure that there is only one unique position at which this can occur, inasmuch as there may be a plurality of surface portions and corresponding dielectric apertures, portions 28 and apertures 38 are disposed respectively on element 20 and shielding means 36 such that no surface portions are regstered with any aperture in any other position of the shielding means. This caa be accomplished by distributing the dielectric apertures on the shielding means along lines perpendicular to the direction of motion of the latter so that when the shielding means is moved in that direction, each dielectric aperture sweeps out a unique path with respect to the transmisson element, and not more than one surface portion 28 lies within each such unique path.

In the example given, it can further be assumed that each switch is intended to code a particular corresponding decimal numeral into its binary equivalent, and that the shielding means of the switch shown in FIGS. 4 and 5 bears or is identified by the decimal indicium 5. In such case, leads 52A-D respectively constitute inputs corresponding to the binary 1, 2, 4 and 8 values. If now a changing potential is impressed in sequence on leads 52A- D in order when the shielding means is in its pormal position where capacitive coupling occurs between

surface portion

28A and 28C and

corresponding strips

34A and 34C and leads 52A-D are then sequentially energized, the signals will only appear where coupling occurs. Because these are respectively the binary 1 and 4 values, it will be seen that the act of depressing the shield to its conductive coupling position and then commutating the input leads automatically provides the correct serial binary coded signal at the output terminals of the switch, i.e. 0101. Where, as shown in FIGS. 1 and 2, there is essentially a double switching mechanism due to the trim arms of the U-shape of element 20 and shielding means 36, the output can be coded into a number havng twice as many places as it can with but a single pair of transmission and reception surfaces.

The configuration of the three basic elements is not particularly important. For example, the surfaces can be curved, corrugated, or the like, provided, of course, that there is a proper path allowed for the motion of the shielding means between the transmission and reception elements and the latter are close enough to one another to permit capacitive coupling. The number and placement of surface portions, dielectric apertures and receiving strips required depend, naturally, upon the particular encoding scheme used. For example, the switch can be used to convert demimal to serial bianry, to serial excess-three binary, to serial reflected binary, to select but a few of the many codes available. It will further be appreciated that while in the embodiment described the electrostatic shielding means itself is movable, and the transmission and reception elements are fixed, other embodiments can be made in which the transmission element or the reception element is movable while the other two 6 elements are fixed. However, the embodiment shown has a distinct advantage in that the movable element, being grounded, does not carry any substantial current when the switch is conducting, and this aspect constitutes a distinct safety feature. The provision of

layers

24 and 26 insure that signals can only be coupled when the shield is in its transmitting position.

Because the switching means heretofore described is capable of providing direct encoding, a multiple key keyboard can be readily formed using a number of such switching means. Thus, there is shown in FIG. 6 a simplified schematic diagram of such a keyboard limited to two such switches for the sake of simplicity. The embodiment of FIG. '6 includes a source of changing potential, such as sinusoidal oscillator 52, and two switches shown generally at 54 and 56. The two switches are the same in that they all include (identified only in switch 54 as exemplary) a reception element or bar 60, a shielding element or key 62, and plurality of four transmission elements or strips 64A, 64B, 64C and 64D. All of the transmission elements of the switches are connectable to oscillator 52 in sequence by commutating device '66, and all keys 62 are grounded.

The two switches differ only in the number and position of dielectric apertures which are disposed in the respective shielding elements or keys 62. For example, one can assume that the key 62 of switch 54 is identified by or coded to represent the decimal numeral 3, key 62 of switch 56 being representative of the decimal numeral 4. The switches can, for example, encode these demical numerals directly into serial binary outputs while the appropriate keys are depressed. To encode a single demical number in binary notation requires only four transmission elements or strips. Key 62 of switch 54 will then include two apertures intended to permit coupling of the signals sequentially applied to

strips

64A and 64B, representing binary l and binary 2, to the reception bar. Key 62 of switch 56 will have but one aperture to permit the corresponding 64C strip (representing binary 4) to be coupled to its reception bar.

Input strips 64A are connected to one another, 64B are connected to one another, and so forth, so that the operation of commutating device 66 results in all

strips

64A, 64B, 64C and 64D being momentarily energized and deenergized in sequence. All reception elements or bars 60 are electrically connected to one another to provide a single output line which is fed to amplifier 68, and thence through a signal conditioning device 70 to some storage means such as shift register 72.

In operation, it will be seen that if key 62 of switch 54 is depressed to its operative position and commutator 66 turns, the latter first connects and then disconnects the output of oscillator 62 in sequence to

strips

64A, 64B, 64C and 64D. The successive signals imposed on

strips

64A and 64B will appear as pulses coupled in that order to the input of amplifier 68; but because no apertures exist with respect .to srips 64C and 64D, there will be an absence of signals for the commutation periods of those strips. Thus, a sequential series of pulses and no pulses will be produced representing 1100; this signal, in binary notation with the least significant digit to the left (in reverse order), represents decimal value 3. This signal, appropriately conditioned as by filtering, wave-shaping and the like for entry into digital equipment by the usual signal conditioning device 70, can then be entered in serial form into shift register 72 for storage.

Obviously, the embodiment described in FIG. 6 is highly simplified in that no timing system is included. However, a variety of timing systems can be employed with the basic concepts. For example, a typical modification of the spstem of FIG. 6 is shown in FIG. 7 wherein like numerals indicate like parts. It will be seen in FIG. 7, particularly, that an additional channel or input strip 64R has been added to each switch and consequently each switch contains an additional corresponding output bar 60R (identified only in connection with one switch, considered exemplary). In such case, the shielding element or key 62 in everyswitch includes an additional aperture positioned to couple each input strip 64R with its corresponding output bar 60R when the key is in operative position. The outputs of all 60R strips are connected to respective inputs of AND gate 74 and also the respective inputs of OR gate 76. The output of AND gate 74 is connected through an inverter amplifier 78 to an input of AND gate 80, another input of the latter being connected to the output of OR gate 76. The output of OR gate 80 is connected to a start control terminal 82 of commutator 66. Additionally, all of strips 64A to 64D inclusive are connected to inputs of OR gate 84. The output of the latter is connected to timing control input terminal 86 of shift register 72.

in the operation of the device of FIG. 7, commutator 66 will normally connect the output of oscillator 52 to input 64R. unless a key is depressed to permit the signal onstrip 64R to be coupled to bar 60R, commutator 66 A will not initiate any additional switching signals. However,

when one or more keys are depressed so that a signal is sensed on any bar 60R, this signal is fed through OR gate 76 to an input of AND gate 80. If more than one of the 60R bars are connected to the input of AND gate 74, the latter will produce an inhibit signal which when inverted by inverter 78 disables gate 80 so as to prevent commutating device 66 from starting a switching sequence. If, however, only one 60R bar is energized, there will be no inhibit signal from gate 74 and inverter 78 thus provides an enabling signal to gate 80 so that commutating device 66 will then operate to sequentially switch or apply momentary signals from oscillator 52 to bars 60A-64D in order. It will be seen that this sequence of signals is also fed by gate 84 to the control input terminal 86 of shift register 72 so that for every sequential input signal impressed on the input strips 64A to 64D, regardless of whether or not coupling occurs, register 72 will shift appropriately thus insuring the proper serial spacing of output signals from the switches through amplifier 68 and detector 70.

-It will be apparent to those skilled in the art that a large number of modifications can be made on the basic concept without departing from the scope of the invention. For example, each key can include a plurality of input strips and like plurality of output bars, and simultaneous commutation provided for both input and output signals. A large number of other logical gating schemes can be employed to handle the read, inhibit, and timing functions desirable in using a group of switches of the present invention in connection with a multiple key control.

Since certain changes may be made in the above apparatus without departing from the scope of the invention herein involved it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted in an illustrative and not in a limiting sense.

What is claimed is:

1. Device for switching a changing potential, comprising in combination;

transmitting means defining a surface having a number of discrete, spaced-apart, electrically conductive surface portions all connectable sequentially to the source of said potential;

receiver means defining a second surface spaced a fixed distance from the surface of said transmitting means, said second surface being electrically conductive; and electrically conductive shield means having at least one dielectric aperture therein and being disposed within the interspace between and spaced from both 'of said surfaces; said surface portions, elements and apertures being disposed witlrat least one of said means being movable with respect to the others so that there is a relative and unique position of said means wherein each said aperture is positioned to permit capacitive coupling to be effected between a corresponding one of said surface portions and said second surface, all other positions pf all of said means being such that said shield provides electrostatic shielding preventing capacitive coupling from occurring between any of said surface portions and said second surface.

2. A device for switching as defined in claim 1 wherein said shield means is said one of said means, which is movable with respect to the others, and including means for releasably maintaining said shield means in one of said other positions.

3. A device for switching as defined in claim 1 including a third electrically conductive surface positioned with respect to said transmitting means so one of said apertures can be positioned to effect capacitive coupling with one of said surface portions whenever any other surface portions is capacitively coupled through a corresponding aperture to said second surface.

4. Keyboard device for switching a changing potential comprising, in combination;

a plurality of switches each having transmitting means defining a surface having a number of discrete, spaced apart, electrically conductive surface portions connectable to the source of said potential, and receiver .means defining a second and electrically conductive surface spaced a fixed distance from the surface of said transmitting means;

means for sequentially connecting each of said surface portions momentarily to said source of potential;

each of said switches having an electrically conductive shield means disposed between and spaced from the respective surfaces of said transmitting and receiver means of said each switch, each of said shield means having a number of apertures therethrough, the combination of number and position of said apertures being unique for each of said shield means;

for each of. said switches said surface portions, elements and apertures being disposed with at least one of said means being movable with respect to the others so that there is a relative and unique position of said means wherein each said aperture is positioned to permit capacitive coupling to be effected between a corresponding one of said surface portions and said second surface, all other positions of all of said means being such that said shield provides electrostatic shielding preventing capacitive coupling from occurring between any of said surface portions and said second surface.

5. Keyboard device as defined in claim 4 wherein each of said second surfaces is electrically connected to one another so as to provide a single output channel.

6. Keyboard device as defined in claim 4 wherein each of said third surfaces are electrically connected through logical gating means so as to inhibit said means for sequentially connecting from operating unless capacitive coupling of any surface portion with its corresponding second surface is occurring in only one of said switches.

v References Cited UNITED STATES PATENTS 3,293,640 12/1966 Chalfin 340-365 THOMAS B. HABECKER, Primary Examiner US. Cl. X.R.