US3731015A

US3731015A - Control keyboard switch with cantilevered contact and diode matrix array

Info

Publication number: US3731015A
Application number: US00144606A
Authority: US
Inventors: J Brady
Original assignee: UNIVERSAL TECHNOLOGY
Current assignee: UNIVERSAL TECHNOLOGY; UNIVERSAL TECHNOLOGY INC US
Priority date: 1971-05-18
Filing date: 1971-05-18
Publication date: 1973-05-01
Anticipated expiration: 1990-05-01

Abstract

A low profile keyboard unit including an etched circuit board and a plurality of keyboard switches mounted on one surface thereof. Individual switches include housings configured to carry in self-contained fashion up to ten diodes plus a resistor, the leads from these elements being passed through holes in the board and flow soldered at the back side of the board.

Description

United States Patent 1 1 Brady 1 1 May 1, 1973 154 CONTROL KEYBOARD SWITCH WITH 3,290,553 12 1966 Sapy ..317 101 CE CANTILEVERED CONTACT AND 3,605,063 9/1971 Stewart ..317/101 CE x 3,290,439 12/1966 Willcox et a1 ..200/5 A X DIODE MATRIX ARRAY 3,240,885 3/1966 Grunfelder et a1. ..200/5 A [75] Inventor: John FQBrady, Clifton, NJ. 1,226,971 5/1917 Hart ..200/166 SD UX 3,584,162 6/1971 KrakinowskL. ..200/S A [731 Asslgflecgnjwersal Techmhgy Inc-1 Verona, 3,627,935 12 1971 Spievak ..2o0 s A x [22] Filed; May 18 1971 Primary Examiner--J. R. Scott An0rneyDean S. Edmonds et a1. [21] App]. No.: 144,606

' I [57] ABSTRACT U-S. Cl. A, A A low profile keyboard unit including an etched ir- [51] hit. Cl. ..H0lh 13/52 cuit board and a plurality f keyboard Switches Fleld Search 5 6 R, mounted on one surface thereof. Individual switches 200/6 6 6 159 159 A, 166 include housings configured to carry in self-contained 159 317/101 101 101 101 fashion up to ten diodes plus a resistor, the leads from CE these elements being passed through holes in the board and flow soldered at the back side of the board. [56] References Cited I v 18 Claims, 5 Drawing Figures UNITED STATES PATENTS 3,551,616 12/1970 Juliusberger et al ..3l7/l0l CE X Patented May 1,1973 I 3,731,015

3 Sheets-Sheet 1 v INVENTOR JOHN F. BRADY Wm 9.9,1M

ATTORNEYS .Patentd May 1, 1973 3 Sheets-Sheet 2 INVENTOR JOHN F. BRADY ATTORNEYS- CONTROL KEYBOARD SWITCH WITH CANTILEVERED CONTACT AND DIODE MATRIX ARRAY BACKGROUND OF INVENTION This invention relates generally to electrical keyboards and more specifically relates to the multiple switch type of keyboard commonly employed at computer terminals or similar environments whereat operator communication with an electronic system occurs.

Electric keyboards featuring an array of individual key switches have been in use for many years. Such keyboards have, for example, long been utilized in electric typewriters, in which environment activation of the individual keys effects striking of the type face-bearing elements against the typewriter platen. In still more recent years, in consequence of the enormous proliferation in data processing and communications systems, increased interest in keyboards and in the switches utilized therewith has been evident. This has occurred by virtue of the fact that communication with the cited systems is commonly effected through a manually operated keyboard. In particular an operator desiring to enter information into the system or query the system with respect to information already stored therein, will manually depress appropriate keys at the keyboard to enter data or initiate development of desired information.

In the electronic systems referred to a central problem has been that of incorporating into the keyboard at commercially reasonable costs, sufficient flexibility to assure full control functions. While it is in theory always possible to associate sufficient logic circuitry with the keyboard to assure, for example, that depressing of a selected key will provide properly encoded signals to activate a desired function, such results are often achieved by complex and expensive means, and more importantly by means that add to the difficulty of assembling the keyboard.

In accordance with the foregoing it may be regarded as an object of the present invention, to provide a keyboard for computer terminal installations or the like, which is of relatively low cost construction and yet incorporates a wide range of control functions therein.

It is a further object of the invention, to provide an electrical control keyboard capable of providing a wide range of encoded outputs for interacting with a data processing or display system or the like, which keyboard is of such construction as to enable assembly thereof in a simple, inexpensive, and expeditious manner.

It is a further object of the present invention, to provide a keyboard for computer terminal installations or the like, which incorporates encoding functions in such a manner as to enable low profile configurations in the apparatus incorporating the keyboard.

SUMMARY OF INVENTION Now in accordance with the present invention, the foregoing objects, and others as will become apparent in the course of the ensuing specification, are achieved in a construction including an etched circuit board and a plurality of low profile keyboard switches mounted against one surface thereof. The etched circuit board carries a plurality of generally parallel conductive tracks at the front and back surfaces thereof, and at inthe cross sectional view of FIG. 1A, includes an insulatdividual switch positions plated holes are provided which connect to selected tracks. The switch housing is configured to carry in completely self-contained fashion up to 10 diodes plus a resistor, the arrangement of these elements being such that direct connection to the holes of the underlying circuit board is readily made, thereby facilitating assembly of a keyboard having complete encoding and control functions associated therewith.

BRIEF DESCRIPTION OF DRAWINGS The invention is diagrammatically illustrated, by way of example, in the drawings appended thereto, in which:

FIG. 1 is an isometric, exploded view of a portion of a keyboard in accordance with the invention;

FIG. 1A is a cross sectional view of the circuit board portion depicted in FIG. 1, taken along the line 1-1 therein;

FIG. 2 is an isometric, cutaway view of the switch portion of FIG. 1, showing elements of the switch in their assembled relationship; and

FIGS. 3 and 3A are respectively, partial front and rear plan views of portions of the circuit board utilized with the present invention.

DESCRIPTION OF PREFERRED EMBODIMENT In FIG. 1 an isometric, exploded view appears, of a keyboard 2 in accordance with the present invention. The keyboard 2 is seen to include a switch 1 and an underlying circuit board 4. The latter, as may be seen in ing board having a pattern 111 of conductive lines on both sides thereof and a plurality of drilled holes 112 which are provided with plated conductive surfacing 113. The manner in which interconnection of switch 1 to pattern 111 is effected, and other specifics of the circuit board 4, will be further discussed herein below in connection with the showings of FIGS. 3 and 3A.

The switch 1 itself is seen to include generally a housing 3, key top 11, and plunger 9, all molded or otherwise formed of a nonconductive plastic such as nylon or the like, and a pair of electrically conductive elements in the form of a contact plate 5 and a contact leaf 7. The housing 3 is a generally box-shaped member, the interior of which is formed with a plate support platform 41 which is stepped outwardly at one end thereof to define a leaf support ledge 43. A channel 45 is present in platform 41 and is defined, as shown in FIG. 2, by a cylindrical plunger support passage 47 which extends part of the way through housing 3 and then enlarges to a cylindrical bore 48. The latter flares out to an enlarged radius where it terminates at the back of housing 3, thereby defining a shoulder 50. A pair of

ears

40, 42 are formed as partial arcs about channel 45. An adjoining channel 49 is formed in leaf support ledge 43 and is seen to be in communication with the forward part of passage 47. Bore 48 at the rear of housing 3 is closed by a spring plate 22, which is formed of plastic or the like and is received at shoulder 50.

Housing 3 is provided with a plurality of cylindrical passages 33 and with a single transversely elongated passage 53, all of which extend completelythrough the housing to open at the back end thereof. The passages 33 with the exception of the passage identified as 33a are used to carry diodes 35 therein. It is evident that when such diodes are nested in passages 33, the leads 35a and 35b thereof are accessible for connection at both ends of passage 33. The excepted passage, 33a, is utilized for nesting the metal contact pin 19 which via its lead 19a permits external common connection to contact plate 5. The elongated passage 53 is also seen to be adapted for receipt therein in side-by-side fashion of both a diode and a resistor. In a representative application of the present switch, up to diodes and 1 resistor may actually be present in housing 3, with connection to underlying circuit board 4 being directly effected at the exposed leads of the electrical components such as at 35b. This large number of selfcontained diodes means in practice that the switch 1 can typically be used to provide a very full range of control and encoding in the keyboard in which it is incorporated. Typically, for example, sufficient switched connections are available to provide encoding for up to 7 bit numbers (including an additional bit for parity), plus additional switched connections for roll-over, shift inhibit, and control inhibit functions.

The metallic contact plate 5 is seen in FIG. 1 to be adapted to rest upon platform 41 with the two protruding bosses 55 and 57 passing through aligned holes 59 and 61 in the plate. A series of circular holes 39 and an elongate slot 63 are present in plate 5, these elements being upon assembly registrable with the various underlying passages in housing 3. In similar fashion the rectangular opening 65 registers with channel 45 in the housing. A tab 67 at the bottom of plate 5 assists in positioning the plate during assembly and closes the forward part of channel 49.

Contact leaf 7, as is seen in FIG. 1, is a metallic, leaflike structure, typically formed of a thin gauge spring steel. It is a single, unit stamped structure, including a base portion 69 which is bifurcated into the

branches

23 and 25, the branches in turn being trifurcated at their adjacent but noncontacting end portions into sets of three contact fingers 23a, 23b, 23c and 25a, 25b, 25c. Each individual contact finger is seen to be relatively independently displaceable transverse to the general plane of leaf 7. It will also be seen that each of the fingers 23a, 25a, etc., are bent downwardly at their midpoints 70 so that the ends thereof are normally displaced somewhat in the direction of plate 5.

It is seen that when the various elements are assembled in switch 1, the base portion 69 of leaf 7 rests upon ledge 43 with the bosses 71 and 73 of the ledge protruding through

circular holes

75 and 77 in the leaf. An additional circular hole 79 in the leaf permits passage of the contact pin 21 (the head thereof being held at the leaf) through an aligned passage 81 in housing 3. It will be clear that when plate 5 and leaf 7 are mounted in housing 3 the leaf 7 is only supported at its base 69, with

branches

23 and 25 being cantilevered over the spaced plate 5.

Contact between the contact leaf 7 and plate 5 is effected by an operators depressing key top 11. The interior of the key top 11 is formed with a cavity (not explicitly shown) adapted to receive end portion 91 of plunger 9 therein.

The plunger 9 may conveniently be molded (of plastic or the like) as a single unit. It includes, in addition to end portion 91 and cross rib 92, a pad portion 93, and a foot portion 95. The latter, which is approximately cylindrical in shape, is adapted to pass through the openings 97 and 65 of contact leaf 7 and contact plate 5, and into channel 47 of housing 3. Portion 95 includes a longitudinal slot 99 extending along one side thereof. Slot 99 cooperates with a key way 100 extending into housing 3 from the edge of car 42 to the back of passage 47, so as to assure that even when plunger 9 is at its most withdrawn position, very little wobble is evidenced at key top 11. Foot portion 95 terminates in a tip 102 which is heat flattened after passage through retaining washer 106 to prevent withdrawal of plunger 9 from the housing A return spring 17 bears against spring plate 22; spring 17, as key top 11 is depressed, is compressed, and provides a restoring force via washer 106 for returning the key top to its original position.

By examing FIG. 1 in conjunction with the cutaway isometric view of FIG. 2, it may be seen that plunger 9 is provided on side 101 of foot portion 95, with a depressed flattened portion 29 adapted to receive a portion of the tactile ball 13 therein. The showing of FIG. 2 depicts the switch 1 of FIG. 1 rotated 90 in a counterclockwise direction. Tactile ball 13 is a small plastic or metallic ball of radius larger than the height of the shoulder 104 defined (FIG. 3) between portion 29 and the unflattened portion of foot 9. Ball 13 is biased into contact with face 101 by the tactile spring 15 nested in cavity 103 of housing 3. The cutaway view of FIG. 2 depicts the switch 1 in its normal, undepressed condition. Thus it is seen that under these circumstances tactile ball 13 is firmly seated upon flat 29 and against shoulder 104, and in combination with the restoring force provided by spring 17, offers considerable resistance to downward movement of plunger 9, in that such movement cannot occur until ball 13 is displaced away from the stop provided by shoulder 104. Upon the operators continuing to increase his finger pressure upon key 11, however, a threshold level is reached upon which ball 13 suddenly moves outwardly from flat 29 and over shoulder 104, in consequency of which a sudden precipitous drop in resistance to movement of the key occurs.

The sequence of events described, has several very important consequences in the present invention. Firstly, it will be evident that a most excellent tactile feedback is present for the keyboard operator, in that the latter may most readily sense the sudden disengagement of tactile ball 13 and has a clear indication of key depression. Secondly, the comparatively high threshold force required to displace ball 13 eliminates the phenomenom of teasing" whereby an operator may play with a key and accidentally activate it. Thirdly, once sufficient force is applied to displace the ball 13, the resistance drops so suddenly that much excess force is then present, assuring a complete driving home of plunger 9 to provide a clear hit" on the switch.

Actual electrical contact in switch 1 is then brought about by pad 93'bearing against fingers 23a, 23b, 23c, and 25a, 25b, 250. Such action is evident both from the exploded view of FIG. 1 and the cutaway view of FIG. 2. It will also be evident from these views that as the pad 93 advances, flexure occurs in both the

branches

23,25, and in the fingers 23a, 23b, 23c, and 25a, 25b, 25c, in turn advancing these elements toward plate 5. It

will also be clear that the tips of the six fingers will make initial contact with plate 5, but that as plunger 9 advances further, flexure of branches and fingers will laterally displace the points of contact in a continuing wiping action.

It is important to appreciate that the six fingers, 23a, 250, etc. provide six separate contact points for the closing of the switch. Not only is the conta t resistance in such an arrangement quite low, but moreover the reliability of operation is much enhanced by the largely independent movement and contact made by the individual fingers. In addition, as has been previously pointed out, the ensuing contact between fingers and plate 5 is a wiping contact produced by a continuing impulse, in consequence of which exceedingly little bounce can occur as the switch circuit is closed.

As has previously been indicated a principal advantage of the present invention derives from the simplistic manner in which assembly may be effected for a keyboard unit yet retaining full control capabilities. This aspect of the invention may be best understood by I consideringin conjunction with FIG. 1, the plan views of FIGS. 3 and 3A. These latter views depict on an enlarged scale,

portions

115 and 117 of circuit board 4, taken from respectively opposite sides of board 4.

Portions

115 and 117 are actually back-to-back elements of board 4, which is to say that the points designated X and Y in FIG. 3, will on the actual circuit board overlie the points designated X and Y in FIG. 3A.

The portions 1 l5 and l 17 of circuit board 4 shown in FIGS. 3 and 3A, represent, it will be appreciated, only a fraction of the entire circuit board present in a full kevboard. Thus, in this connection, a dotted outline 119 appears in FIG. 3, representing the approximate mounted perimeter of a switch such as switch 1 in FIG. 1; and a dotted outline 119A appears in FIG. 3A representing the relation of the approximate mounted perimeter of the same switch to portion 117 of circuit board 4. It will be readily apparent that the mounting positions for but four such switches are set forth in FIGS. 3 and 3A. In a typical keyboard a total of 61 such positions may actually be present, four parallel rows of mounting positions being utilized to accommodate this totality. Portions of but two such rows, 120 and 121 are shown in FIGS. 3 and 3A, in that the connection scheme and mode of operation of theinvention is fully evident from the limited depiction.

The conductive patterns 111 on circuit board 4 are established by conventional photoetching techniques. In particular, beginning with an insulating board 110 clad on each face with a copper layer, a photoresist is applied and appropriate exposure to actinic radiation effected so as upon etching to leave the desired conductive pattern. Drilled holes are then formed, as at 122, which holes are then plated as at 113 in 'FIG. 1A so that leads inserted therethrough may be connected to portions of pattern 111 which in turn are connected to selected holes.

It will be specifically appreciated that each mounting

row

120, 121, etc. is defined on portion 115 of board 4 by a series of generally parallel conductive tracks 123, a further series of parallel conductive tracks 125 being present on the underlying portion 117 of the board. It will be seen that eight such tracks 123 are present in each such row; five such tracks are within the perimeter 119 and an additional six tracks underlie the perimeter 119 on the opposite side (FIG. 3A) of board 4 so that a total of l 1 rows are actually accessible for direct connection to the pins such as 35b projecting from diode and resistor elements positioned in housing 3 of switch 1 and contact pins such as pin 21.

The scheme of connection for the various diode and resistor elements should now be clear. In particular, examination of portions and 117 in FIGS. 3 and 3A will establish that each conductively plated hole at a mounting position is electrically connected to at least one of the

parallel tracks

123, 125, and that each such track in turn connects to one of a plurality of conductive lines 127 at the border of board 4. Thus, for example, a hole 129 is connected to the conductive line 130 via the track 131 on board portion 115, and thence through plated hole 133 and track 132 on portion 117 to plated hole 134. Conductive lines 127, in turn, include terminal points 135 whereat connections may be effected for other components of the computer terminal incorporating the present keyboard.

In a typical application line 136 may serve as a ground and line 137 as a source of V+ voltage. These two lines are seen to be connected respectively to

pins

138 and 139. Depending on the particular grouping of diodes in a given switch 1, it will thus be clear that since the leads 35a (FIG. 1) of the several diodes are connected to contact plate 5, closing of the switch contacts will cause signals to appear at such of terminals 135 as are electrically adjoined to the circuit through diode (or resistor) contacts with

tracks

123 and 125. Depending therefore on the number and arrangement of diodes, differing groupings of signals appear at the terminals 135, and the signal groupings in terms of presence or absence of an output at the several terminals may be associated with a given letter, symbol, or so forth. That is to say that with the representative eleven lines 127, up to 11 bits of information can be presented upon depressing of a single key in the keyboard 2, and the bit sequence may be associated by any standard encoding technique with given symbols, graphics, or so forth.

It will be appreciated that all that is necessary to achieve initial installation or replacement of a given switch 1, is to place such switch with its properly protruding leads (such as lead 35b in FIG. 1) upon its appropriate position on the keyboard. The leads then pass through the several conductively plated holes of the keyboard, and the switch is then rendered fast to the keyboard by simply soldering the leads to adjacent points at the holes. Where a large group of switches is attached at a single time, such soldering may be effected in a single operation, by standard methods such as by dip soldering.

While the present invention has been particularly described in terms of a specific embodiment thereof, it will be evident in view of the present disclosure, that numerous variations upon the invention are now enabled to those skilled in the art, which variations are properly within the true scope of the present teaching. Accordingly, the invention is to be broadly construed, and limited only by the scope and spirit of the claims now appended hereto.

I claim:

1. A keyboard unit comprising in combination:

a circuit board including a plurality of generally parallel conductive tracks at least one of which is connectable to a source of input potential, a plurality of conductively plated holes formed through said board and connected to said tracks, and a series of output terminals connected to said tracks; plurality of keyboard switches mounted on said board over said holes, each of said switches including an individual housing, a fixed conductive plate therein, a movable contact, actuating means for moving said movable contact into engagement with said fixed conductive plate, and space for carrying similarly shaped switching diodes; and

plurality of diodes, at least one diode being mounted in each keyboard switch, each diode having a pair of leads one of which protrudes from said housing, passes directly through a hole in the circuit board and is joined to the hole boundary to form an electrical connection to one of said conductive tracks and the other of which is connected to the fixed conductive plate of the keyboard switch in which it is mounted, whereby signals may be established at the output terminals upon operation of the actuating means in accordance with the arrangement and number of diodes in said keyboard switch.

2. Apparatus in accordance with claim 1 wherein said conductive tracks and the overlying switches are arranged in a plurality of parallel rows.

3. Apparatus in accordance with claim 1, wherein said conductive tracks are present on both sides of said board, and at least some of the tracks on opposite sides of said board are electrically connected to one another through said conductively surfaced holes.

4. Apparatus in accordance with claim 3 wherein at least of said tracks underlie each switch, whereby direct connection to at least an equal number of said switching diodes is enabled.

5. Apparatus in accordance with claim 4 wherein each diode in a keyboard switch is connected to a different underlying track.

6. Apparatus in accordance with claim 1 wherein:

the movable contact is supported in cantilevered fashion in its housing, said movable contact being positioned approximately in parallel spaced relationship to said fixed conductive plate; and

the actuating means comprises plunger means movable into said housing in a direction transverse to the plane of said movable contact, said plunger means being adapted upon said movement to bear upon said movable contact and displace the cantilevered portion thereof into contact with said fixed conductive plate to close the keyboard switch.

7. Apparatus in accordance with claim 6 wherein said movable contact comprises a generally flattened member having a base portion and a pair of branch portions extending from said base portion and in turn branching into multiple contact fingers, said movable contact being supported in said housing at said base portion, said branch portions being cantilevered over said fixed conductive plate.

8. Apparatus in accordance with claim 7 wherein the base portion, the branch portions and contact fingers surround and define an opening in said movable contact.

9. Apparatus in accordance with claim 8 wherein said plunger means bears on said contact fingers to displace them into contact with said fixed conductive plate.

10. Apparatus in accordance with claim 2 wherein the base portion, the branch portions and the finger portions of said movable contact surround and define an opening in said contact, an opening being present in said fixed conductive plate, and a plunger support passage being present in said housing, and wherein said plunger includes a foot portion adapted to pass through said openings and into said passage of'said housing and a laterally extending pad portion which presses against said fingers of said movable contact to effect said displacement thereof as said pad contacts said movable contact.

'11. Apparatus in accordance with claim 10, wherein said foot is of generally cylindrical shape, said depressed portion thereon comprising a flat on said cylinder, the said tactile ball resting against the shoulder defined between said flat and the remaining portion of said cylinder when said plunger is in an undepressed condition. l2. Apparatus in accordance with claim 10, wherein said plunger support passage includes a keyway extending longitudinally therein and said plunger foot .includes a longitudinal slot for engaging said keyway and steadying I the lateral movement of said plunger, whereby to reduce wobble at said key top.

13. Apparatus-in accordance with claim 6, further including a key top interconnected with said plunger means to effect said displacement thereof upon operator pressure. i a

14. Apparatus in accordance with claim 7, further including a return springcompressible by said displacement of said plunger means to provide a restoring force for returning said plunger to its original position.

15. Apparatus in accordance with claim 6, wherein said housing is formed with a transverse platform for supporting said contact plate, said platform being stepped upwardly at an end thereof to define a narrow support ledge for the base portion of said contact leaf.

16, Apparatus in accordance with claim 6 wherein the source of input potential is connected to the movable contact.

17. Apparatus in accordance with claim 6 wherein:

said movable contact comprises a member having a base portion, a branch portion extending from said base portion, and multiple contact fingers connected to said branch portion and cantilevered over said fixed conductive plate; and said plunger means bears on said contact fingers to displace them into contact with said fixed conduc tive plate.

18. Apparatus in accordance with claim 6, wherein said plunger means carries a depressed portion-on a face thereof parallel to the direction of said displacement, and wherein said switch further includes a tactile ball and a tactile spring nested in said housing for biasing said ball against said plunger face, said spring and ball being nested at a position such that when the plunger is in an undepressed position the tactile ball rests in said depressed portion and thereby provides a resistive force to displacement of said plunger, sufficient force upon said plunger acting to move said plunger and displace said ball outwardly from said depressed portion whereby to suddenly reduce the said resistive force and provide tactile indication to the operator of movement of said plunger.

Claims

1. A keyboard unit comprising in combination: a circuit board including a plurality of generally parallel conductive tracks at least one of which is connectable to a source of input potential, a plurality of conductively plated holes formed through said board and connected to said tracks, and a series of output terminals connected to said tracks; a plurality of keyboard switches mounted on said board over said holes, each of said switches including an individual housing, a fixed conductive plate therein, a movable contact, actuating means for moving said movable contact into engagement with said fixed conductive plate, and space for carrying similarly shaped switching diodes; and a plurality of diodes, at least one diode being mounted in each keyboard switch, each diode having a pair of leads one of which protrudes from said housing, passes directly through a hole in the circuit board and is joined to the hole boundary to form an electrical connection to one of said conductive tracks and the other of which is connected to the fixed conductive plate of the keyboard switch in which it is mounted, whereby signals may be established at the output terminals upon operation of the actuating means in accordance with the arrangement and number of diodes in said keyboard switch.

4. Apparatus in accordance with claim 3 wherein at least 10 of said tracks underlie each switch, whereby direct connection to at least an equal number of said switching diodes is enabled.

6. Apparatus in accordance with claim 1 wherein: the movable contact is supported in cantilevered fashion in its housing, said movable contact being positioned approximately in parallel spaced relationship to said fixed conductive plate; and the actuating means comprises plunger means movable into said housing in a direction transverse to the plane of said movable contact, said plunger meanS being adapted upon said movement to bear upon said movable contact and displace the cantilevered portion thereof into contact with said fixed conductive plate to close the keyboard switch.

10. Apparatus in accordance with claim 2 wherein the base portion, the branch portions and the finger portions of said movable contact surround and define an opening in said contact, an opening being present in said fixed conductive plate, and a plunger support passage being present in said housing, and wherein said plunger includes a foot portion adapted to pass through said openings and into said passage of said housing and a laterally extending pad portion which presses against said fingers of said movable contact to effect said displacement thereof as said pad contacts said movable contact.

11. Apparatus in accordance with claim 10, wherein said foot is of generally cylindrical shape, said depressed portion thereon comprising a flat on said cylinder, the said tactile ball resting against the shoulder defined between said flat and the remaining portion of said cylinder when said plunger is in an undepressed condition.

12. Apparatus in accordance with claim 10, wherein said plunger support passage includes a keyway extending longitudinally therein and said plunger foot includes a longitudinal slot for engaging said keyway and steadying the lateral movement of said plunger, whereby to reduce wobble at said key top.

13. Apparatus in accordance with claim 6, further including a key top interconnected with said plunger means to effect said displacement thereof upon operator pressure.

14. Apparatus in accordance with claim 7, further including a return spring compressible by said displacement of said plunger means to provide a restoring force for returning said plunger to its original position.

16. Apparatus in accordance with claim 6 wherein the source of input potential is connected to the movable contact.

17. Apparatus in accordance with claim 6 wherein: said movable contact comprises a member having a base portion, a branch portion extending from said base portion, and multiple contact fingers connected to said branch portion and cantilevered over said fixed conductive plate; and said plunger means bears on said contact fingers to displace them into contact with said fixed conductive plate.

18. Apparatus in accordance with claim 6, wherein said plunger means carries a depressed portion on a face thereof parallel to the direction of said displacement, and wherein said switch further includes a tactile ball and a tactile spring nested in said housing for biasing said ball against said plunger face, said spring and ball being nested at a position such that when the plunger is in an undepressed position the tactile ball rests in said depressed portion and thereby provides a resistive force to displacement of said plunger, sufficient force upon said plunger acting to move said plunger and displace said ball outwardly from said depressed portion whereby to suddenly reduce the said resistivE force and provide tactile indication to the operator of movement of said plunger.