US3284584A

US3284584A - Adjustable switching apparatus comprising resilient means biasing movable plate structure

Info

Publication number: US3284584A
Application number: US483686A
Authority: US
Inventors: Didyk Witalij
Original assignee: Zenith Radio Corp
Current assignee: Zenith Electronics LLC
Priority date: 1965-08-30
Filing date: 1965-08-30
Publication date: 1966-11-08
Anticipated expiration: 1983-11-08

Description

Nov. 8, 1966 W. ADJUSTABLE SWITCHING APPARATUS COMPRISING RESILIENT MEANS Filed Aug. 50, 1965 Hail MICROPHONE 2 COIL H PNP IL 1| TELEPHONE "T PICKUP COIL BIASING MOVABLE PLATE STRUCTURE 2 Sheets-Sheet 1 II" Amplifiers 0 nd Sound Reproducer Nov. 8, 1966 w DIDYK 3,284,584

ADJUSTABLE SWITCHING APPAlATUS COMPRISING RESILIENT MEANS BIASING MOVABLE PLATE STRUCTURE Filed Aug. 30, 1965 2 Sheets-Sheet 9 United States Patent ADJUSTABLE SWITCHING APPARATUS COMPRIS- ING RESILIENT MEANS BIASING MOVABLE PLATE STRUCTURE Witalij Didyk, Chicago, 11]., assignor t0 Zenith Radio Corporation, Chicago, 111., a corporation of Delaware Filed Aug. 30, 1965, Ser. No. 483,686 6 Claims. (Cl. 200-11) This invention relates in general to adjustable switching apparatus and more particularly to a novel switching arrangement for selectively connecting, by means of a movable contact, one fixed contact to another fixed contact. The switching apparatus lends itself to miniaturization and is particularly useful when incorporated in a small, compact hearing aid where space is at a premium; hence, the invention will be described in that environment.

While current adjustable switches, suitable for employment in small electronic devices such as hearing aids, are considerably smaller and more compact than switches of yesteryear, it is an object of this invention to miniaturize them to a still greater extent. The switching arrangement of the present invention may be made with extremely small dimensions, and yet it is capable of simultaneously performing several indepedent switching functions. Moreover, the novel switch of the present invention exhibits economy and reliability advantages over the previous switching mechanisms.

It is, therefore, an object of the present invention to provide a new and improved switching apparatus.

It is another object to provide a novel adjustable switching device which simultaneously effects switching of a number of separate and independent circuits.

An adjustable switching apparatus, constructed in accordance with one aspect of the invention, comprises a first substantially flat contact assembly having on one side thereof at least one fixed switch contact, and a second substantially flat contact assembly, spaced apart from and parallel to the first contact assembly, having at least one fixed switch contact on the side adjacent the fixed contact of the first contact assembly. There is a plural-position adjustable contact assembly movable between and in a path parallel to the first and second contact assemblies. The adjustable contact assembly includes a movable switch contact which, in at least one of the positions of the adjustable assembly, engages and electrically interconnects the fixed contacts of the first and second contact assemblies. There is also resilient means for urging one of the first and second contact assemblies toward the other.

The features of this invention which are believed to be new are set forth with particu'arity in the appended claims. The invention, together with further objects and advantages thereof, may best be understood, however, by reference to the following description in conjunction with the accompanying drawings in which:

FIGURE 1 schematically illustrates a hearing aid circuit which includes several individual adjustable switches all of which are combined in the switching apparatus of the present invention; and,

FIGURES 2-61) are various detailed views of a switching apparatus embodying the invention and which may be employed to perform all of the switching functions of the switches of the hearing aid circuit of FIGURE 1.

Turning now to FIGURE 1, the hearing aid there represented is a transistorized instrument of miniature form, being constructed for example within a temple bar of an eyeglass frame or being assembled in a tiny structure to be supported behind or even within the ear of the wearer. Alternatively, the hearing aid may be of the body type in which all of the components of the aid, with the exception of the earphone sound reproducer, are mounted within a case which may be supported by the clothing or held in a pocket of the wearer; the earphone receiver would, of course, be attached to an earmold inserted in the wearers ear. Since the physical structure of the aid, with the exception of the novel switching apparatus to be described, may be entirely conventional, it has not been illustrated.

The hearing aid of FIGURE 1 comprises a magnetic microphone schematically shown merely as a coil 10, having one terminal connected to the base 11 of a conventional PNP type junction transistor 12. The other terminal of the microphone is connected to one side of a telephone pickup coil 16 which, when brought in close proximity to the receiver coil of a conventional telephone such that the two coils are inductively coupled together, produces an audio electrical signal which is substantially a replica of the audio electrical signal supplied to the receiver coil. The other side of coil 16 is coupled through a pair of series connected capacitors 17 and 18 to a plane of reference potential, such as ground. The emitter 13 of transistor 12 is also connected to ground.

The junction of

coils

16 and 16 is connected via a conductor 21 to the movable contact 22 of a four-position switch A having four fixed or stationary contacts 24-27 to which movable contact 22 connects in switch positions 1-4 respectively.

Stationary contacts

24, 25 and 27 are joined together and are then connected by Way of a conductor 28 to the junction of coil 16 and capacitor 17. With this arrangement, when switch A is positioned in any one of its

positions

1, 2 or 4, movable contact 22 electrically interconnects

conductors

21 and 28 to short out telephone pickup coil 16. Stationary contact 26,

which is engaged by movable contact 22 in position 3 of' switch A, connects over a conductor 29 to base 11 of transistor 12. A conductor 31 connects the movable cont act 32 of another four-position switch B to ground. This switch has four fixed contacts 34-37 which are individually engaged by movable contact 32 in switch positions 1-4 respectively. Fixed

contacts

34, 36 and 37, to which movable contact 32 connects in

positions

1, 3 and 4 respectively, are joined together and are then connected over a conductor 38 to the junction of capacitors 17 and 18. Hence, when switch B is established in any one of its

positions

1, 3 or 4 movable contact 32 connects conductor 31 to conductor 38, thereby shorting out capacitor 18.

Collector 14 of transistor 12 connects to the junction of telephone pickup coil 16 and capacitor 17 through a biasing resistor 42. The collector is also coupled through a load resistor 43 to a conductor 51 which in turn is connected to the movable contact 52 of a four-position switch C which has four fixed contacts 5457 to which the movable contact connects in positions 1-4 respectively. Stationary contacts 55-57 are connected in common and are then coupled via a conductor 58 to the negative terminal of a unidirectional potential source, the positive terminal of which is grounded. When switch C is established in any one of positions 2-4, movable contact 52 couples conductor 51 to conductor 58 in order to apply operating and bias potentials to transistor 12. When switch C is so positioned, transistor 12 and its associated circuitry constitute a conventional amplifying stage for audio signals.

Collector 14 is also coupled through a DC. blocking condenser 62 to one input terminal of apparatus shown in FIGURE 1 by the single block 63 designated amplifiers and sound reproducer, the other input terminal of which is grounded. Block 63 preferably contains two stages of amplification plus a sound reproducer in the form of an earphone or air conduction receiver for delivering amplified acoustic energy. Switches A, B and C are ganged to operate in unison as illustrated by the dashed construction line 64.

Patented Nov. 8, 1966 When the switches are established in their first position, which is the OFF position, operating and bias potentials are not applied to transistor 12 and thus no amplification takes place. Of course, while it has not been shown, it is contemplated that conductor 51 will be connected to the amplifiers of unit 63- in order that switch C controls the application of operating potentials to those amplifiers. In position 1, switch A shorts out coil 16 while switch B shorts out capacitor 18, but this is of no concern since stgae 12 is not functioning anyway.

When switches A, B and C are now simultaneously positioned to their respective positions 2, switch A starts out coil 16, switch B removes the short from capacitor 18, and switch C applies operating and bias potentials to all of the amplifying stages. The input circuit of transistor 12 thus includs the series arrangement of the base-emitter conduction path, microphone coil 10, and capacitors 17 and 18. Any acoustic signal picked up by microphone is therefore converted to an electrical signal, representative of the acoustic energy, for application between base 11 and emitter 13 of transistor 12. The signal is amplified in that transistor in normal fashion, and an amplified replica is applied to unit 63 where it is further amplified to develop a signal suitbale for driving the sound output transducer.

With capacitor 18 included in the input circuit of transistor 12, the low frequency response of the hearing aid is reduced. For that reason, position 2 of the switches may be designated the microphone-low cut position. It has been found that by employing a 1.0 ,ufd. condenser for con-denser 17 and a .01 ,ufd. condenser for condenser 18 excellent tone or frequency control is obtained.

When switches A, B and C are established in their respective positions 3, switch A connects conductor 21 to conductor 29 to short out microphone coil 10, switch B connects conductor 31 to conductor 38 to short out capacitor 18, while switch C again completes the energizing circuit for applying operating potentials to the amplifying system. The input circuit of transistor 12 now includes the series arrangement of the base-emitter conduction path, telephone pickup coil 16 and capacitor 17. If a telephone receiver coil is now inductively coupled to pickup coil 16, any electrical signal supplied to the receiver coil will be induced in telpehone pickup coil 16 and the amplifying stages of the hearing aid will be driven thereby. Hence, the third position of the switches may be designated the telephone pickup position. With capacitor 18 shorted out, the low frequency response of the hearing aid is enhanced.

Finally, when the switches are concurrently positioned to their respective fourth positions, switch A again shorts out pickup coil 16 and substitutes microphone 10, switch B again shorts out capacitor 18, while switch C again completes the energizing circuit for the amplifying stages. The input circuit of transistor 12 now includes the series arrangement of the base-emitter conduction path, microphone 10 and capacitor 17 and thus any acoustic energy picked up by the microphone is converted to an electrical signal, amplified, and then supplied to the output reproducer. Since condenser 18 is shorted out, which enhances the low frequency response of the hearing aid, the fourth position the switches is designated the microphone-full response position.

All of the switching functions performed by switches A, B and C may be achieved by the switching apparatus constructed in accordance with the invention and shown in FIGURE 2, detailed views of parts of which are shown in FIGURES 3-6a Since the required switching functions involve selective interconnections as between

conductors

21, 28, 29, 31, 38, 51 and 58, those conductors are attached to the switching arrangement of FIGURES 2-6b and bear the identical reference numbers. Since miniaturized electronic devices very often include printed circuits, it is convenient to mount applicants switching apparatus on such a printed circuit board. In fact, partof the switching arrangement may constitute a printed circuit which occupies the area of the board over which the switching device is mounted.

More specifically, in the illustrated embodiment of the invention a sheet 65 of insulating material has affixed thereto, on one of its sides (the top side as viewed in FIGURE 3), a pattern of metallic conductive areas 6669. Insulating sheet 65 may be a printed circuit board on which most, if not all, of the components schematically shown in FIGURE 1 are supported and electrically interconnected. The portion of sheet 65 illustrated herein may merely be an extension or one corner of the printed circuit board. Conductive areas 66-69 (best shown in FIGURE 6a) constitute fixed switch contacts and may be mounted to insulating sheet 65 in any appropriate manner. For example, the fixed contacts may be affixed by any well-known printing technique, such as the silk screening process, or for that matter by any of the customary stencilling, etching, or the like, operations.

Conductors

58, 38, 28 and 29 are electrically connected, such as by soldering, to metallic contact surfaces 66, 67, 68, and 69 respectively. Insulating member 65, and the contacts attached thereto, provide a first substantially flat contact assembly having on one side thereof a plurality of fixed switch contacts.

A shaft 71, which has a reduced diameter section inserted into an aperture of insulating panel 65, is supported by that panel and is rigidly secured thereto by the expedient of a nut 72. A rotatable insulating disc or rotor 75 is journalled on shaft 71 for rotation over fixed contacts 66-69. A portion of the periphery of the rotor is rimmed to extend below insulating sheet 65, see FIG-

URES

2 and 3. In this way, the partial rim provides a pair of stop shoulders 77, 78 which engage sections or surfaces 81. and 82 respectively of panel member 65 (see FIGURE 4) to limit the extent of rotation of disc 75.

Another insulating sheet or panel member 83 is slidably mounted over shaft 71 on top of disc 75. Insulating sheet 83 has a pattern of conductive metallic areas 84-86 on its side adjacent disc 75 (see FIGURE 6b) which constitute fixed switch contacts and which may be mounted on panel member 83 in any convenient manner such as by one of the techniques suggested hereinbefore in connection with the mounting of conductive areas 6669 on insulating member 65. The stationary switch contact surfaces 84, 85 and 86 are electrically connected, such as by soldering, to

conductors

51, 31 and 21 respectively. Sheet 83 and contacts 84-86 provide a second substantially fiat contact assembly, spaced apart from and parallel to the first contact assembly 65459, having a plurality of fixed contacts on the side adjacent the fixed contacts of the first assembly.

Insulating rotor 75 has a series of three equally spaced apertures or channels on its periphery apart) each of which extends from one side of the rotor to the other and accommodates a respective one of three movable

metallic contact pins

22a, 32a, and 52a. These pins are freely and slidably mounted within their associated channels and each has a length dimension which is greater than the thickness of disc 75 in order to engage the fixed contacts on

sheets

65 and 83. The three

contact pins

22a, 32a, and 52a essentially correspond to

movable contacts

22, 32 and 52, respectively, of the switches shown in FIGURE 1.

Since insulating member 83 is not rigidly secured to shaft 71, it is free to move in the direction of the axis of the shaft. A spiral spring 89 is located between the hexagonal head of shaft 71 and the top surface of insulating sheet 83 in order to urge sheet 83 downward toward insulating sheet 65. In this way, there will be constant pressure of the fixed contacts of both

members

65 and 83 against the

movable contact pins

22a, 32a, and 52a. One end of a stud 91 is rigidly secured to insulating member 65 while the other end protrudes through an aperture 92 of ininsulating member 83 against any substantial movement in a direction other than along the axis of shaft 71.

Insulating disc 75 has an integrally formed projection or tab portion 93, a surface of which is serrated, to facilitate convenient adjustment of the switching apparatus by the wearer. The disc has four distinct positions and establishment of the disc in those positions is aided by a detent spring 94 (shown by itself in FIGURE 5) which mates with four notches on the periphery of insulating disc 75, as best seen in FIGURE 4.

All of the small circular areas designated by the numbers 1-4 in FIGURES 6a and 6b illustrate the positions of

contact pins

22a, 32a, and 52a in the four different positions of the switching apparatus. More specifically, in all four positions one end of pin 22a (the upper end as viewed in FIGURE 3) engages and electrically connects to fixed contact 86 and consequently to conductor 21, while in all but position 3 the other or lower end of pin 22a engages and electrically connects to fixed contact 68 and consequently to conductor 28. In the third position, the lower end of pin 22a engages and connects to fixed contact 69 which is connected to conductor 29. It is thus apparent that pin 22a and fixed

contacts

86, 68 and 69 perform all of the switching functions of switch A of FIGURE 1. For that reason, those fixed contacts are designated A in FIGURES 6a and 6b.

The upper end of contact pin 32a engages fixed contact 85, and is thus connected to lead 31, in all four positions while the lower end of that pin mates with fixed contact 67 to connect to conductor 38 in each of

positions

1, 3 and 4. In the second position, there is no fixed contact connected to the lower end of pin 32a. Hence, contact pin 32a and fixed

contacts

85 and 67 perform the functions of switch B. Those fixed contacts are therefore designated B in FIGURES 6a and 6b.

The upper end of pin 52a mates with and connects to conductor surface 84, and consequently to conductor 51, while the lower end of pin 52a connects to fixed contact 66, and thus lead 58, in

positions

2, 3 and 4. There is no fixed contact that connects with the lower end of pin 52a in the first or OFF position.

Fixed contacts

84 and 66 and movable contact 52a therefore serve the functions of switch C; the fixed contacts in FIGURES 6a and 6b are labeled accordingly.

Of course, providing spring 89 to bias insulating

sheets

83 and 65 toward each other insures that even though the contact pins wear down and their length dimensions decrease, the pins will still firmly engage the fixed contacts to establish good electrical connections. Moreover, even if each of the three contact pins has a slightly different' length dimension, there will still be proper mating since the apertures of insulating member 83 through which shaft 71 and stud 91 extend are large enough to permit a slight tilting of board 83. The three pins define a plane and this plane does not have to be perpendicular to the axis of shaft 71 which would be the case if the pins are uneven. Of course, since the pins are free to slide within their.associated apertures, the lower ends of

pins

22a, 32a and 52a (as viewed in FIGURE 3) will always be even and pressed against the fixed contacts of board 65.

The invention therefore provides an extremely compact switching arrangement which achieves a variety of different and independent switching functions in a very small space. By way of summary, the adjustable switching apparatus comprises a first substantially fiat contact assembly (the printed circuit board shown in FIGURE 6a) having on one side thereof a plurality of fixed

switch contacts

66, 67, 68 and 69. There is a second substantially flat contact assembly (the printed circuit board shown in FIGURE 6b), spaced apart from and parallel to the first contact assembly, having a plurality of fixed

switch contacts

8d, 85 and 86 on the side adjacent the fixed contacts of the first contact assembly. Rotatable disc 75 and

contact pins

22a, 32a and 52a provide a plural-position adjustable contact assembly movable between and in a path parallel to the first and second contact assemblies and including a plurality of movable switch contacts insulated from each other and each of which, in at least one of the positions of the adjustable contact assembly, electrically connects a fixed contact of the first assembly to a fixed contact of the second assembly. Spiral spring 89 constitutes resilient means for urging one of the first and second contact assemblies toward the other.

While a particular embodiment of the invention has been shown and described, modifications may be made, and it is intended in the appended claims to cover all such modifications as may fall within the true spirit and scope of the invention.

I claim:

1. Adjustable switching apparatus comprising:

a first insulating sheet to which is affixed on one side thereof at least one fixed conductive switch contact;

a second insulating sheet to which is affixed on one side thereof at least one fixed conductive switch contact;

a rotatable insulating disc having an aperture which extends therethrough from one side to the other;

means including a shaft for supporting and aligning said first and second insulating sheets and said disc in parallel spaced apart relation such that said disc isv journalled on said shaft between said first and second insulating sheets for rotation as between at least a plurality of different discrete positions and the sides of said insulating sheets, to which said fixed contacts are afiixed, are adjacent each other;

said insulating disc having a manual control tab extending in a direction perpendicular to its axis of rotation to facilitate adjustment from one position to the next and also having a plurality of detent notches on its periphery corresponding to the plurality of different positions of said disc;

a movable contact pin retained in said aperture of said rotatable insulating disc and, in at least one position of said disc, engaging .and electrically interconnecting the fixed contacts of said first and second insulating sheets;

a resilient detent which mates with a different notch on the periphery of said insulating disc in each different position of said disc;

and resilient means for urging one of said first and second insulating sheets toward the other.

2. Adinstable switching apparatus comprising:

a second insulating sheet to which is afiixed on one side thereof at least one fixed conductive switch contact;

means including a shaft for supporting and aligning said first and second insulating sheets and said disc in parallel spaced apart relation such that said disc is journalled on said shaft between said first and second insulating sheets for rotation as between at least a plurality of different discrete positions and the sides of said sheets, to which said fixed contacts are afiixed, are adjacent each other;

said insulating disc having a manual control tab extending in a direction perpendicular to its axis of totation to facilitate adjustment from one position to the next and also having a plurality of detent notches on its periphery corresponding to the plurality of different positions of said disc;

a movable contact pin retained in said aperture of said rotatable insulating disc and, in at least one position of said disc, engaging and electrically interconnecting the fixed contacts of said first and second insulating sheets;

and resilient means including a spiral spring connected to said shaft and said first insulating sheet for urging said first sheet toward said second sheet thereby to bias said fixed contacts toward said contact pin.

3. Adjustable switching apparatus comprising:

a first insulating sheet to which is afiixed on one side thereof first and second fixed conductive switch contacts;

a second insulating sheet to which is affixed on one side thereof first and second-fixed conductive switch contacts;

a rotatable insulating disc having first and second spaced apart apertures each of which extends through said dis-c from one side to the other;

means including a shaft for supporting and aligning said first and second insulating sheets and said disc in parallel spaced apart relation such that said disc is journalled on said shaft between said first and second insulating sheets for rotation as between at least a plurality of different discrete positions and the sides of said sheets, to which said fixed contacts are affixed, are adjacent each other;

first and second movable contact pins retained in said first and second apertures respectively and, in at least one position of said disc, said first contact pin electrically connects said first contact of said first sheet to said first contact of said second sheet while said second contact pin electrically connects said second contact of said first sheet to said second contact of said second sheet;

and resilientmeans for urging one of said insulating sheets toward the other.

4. Adjustable switching apparatus comprising:

a first insulating sheet to which is afiixed on one side thereof first, second and third fixed conductive switch contacts;

a second insulating sheet to which is affixed on one side thereof first, second and third fixed conductive switch contacts;

a rotatable insulating disc having first, second and third spaced apart apertures each of which extends through said disc from one side to the other;

means including a shaft for supporting and aligning said first and second insulating sheets in parallel spaced apart relation such that said disc is journalled on said shaft between said first and second insulating sheets for rotation as between at least a plurality of different discrete positions and the sides of said sheets, to which said fixed contacts are affixed, are adjacent each other;

first, second and third movable contact pins retained in said first, second and third'apertures respectively and, in at least one position of said disc, said first n t p n elec rical y connects said fir t cont t of said first sheet to said first contact of said second sheet while said second contact pin electrically connects said second contact of said first sheet to said second contact of said second sheet and said third Contact pin electrically connects said third contact of said first sheet to said third contact of said second sheet;

a resilient detent which mates with a difierent notch on the periphery of said insulating disc in each different position of said disc;

and resilient means for urging one of said insulating sheets toward the other.

5. Adjustable switching apparatus comprising:

a first substantially fiat contact assembly to which is aflixed on one side thereof a fixed conductive switch contact;

a second substantially fiat contact assembly to which is afiixed on one side thereof a plurality of fixed conductive switch contacts;

a plural-position adjustable contact assembly including a rotatable insulating disc, at least one movable conductive switch contact retained by said disc, a plurality of detent notches on the periphery of said disc corresponding to the plurality of different positions of said adjustable contact assembly, and a manual control tab on said disc and extending in a direction perpendicular to its axis of rotation;

means including a shaft for supporting and aligning said contact assemblies in parallel spaced apart relation with the sides of said first and second assemblies to which said fixed contacts are affixed being adjacent each other and separated by said adjustable contact assembly adjustment of which is facilitated by manipulation of said manual control tab, said movable switch contact in one position of said adjustable contact assembly engaging and electrically interconnecting the fixed contact of said first assembly and one of the fixed contacts of said second assembly and in another position engaging and electrically interconnecting the fixed contact of said first assembly and another of the fixed contacts of said second assemy;

a resilient detent which mates with a different notch on the periphery of said insulating disc in each different position of said adjustable contact assembly;

and resilient means for urging one of said first and sec and contact assemblies toward the other.

6. Adjustable switching apparatus according to claim 5 in which said first contact assembly includes a plurality of fixed conductive switch contacts, and said adjustable contact assembly includes a plurality of movable contacts insulated from each other and each of which, in at least one of the positions of said adjustable contact assembly, electrically connects a fixed contact of said first assembly to a fixed contact of said second assembly.

References Cited by the Examiner UNITED STATES PATENTS 1,832,869 11/1931 Macy ZOO-11 X 2,010,741 8/1935 Sullender 200-11 X 2,432,067 12/1947 Morse 200ll FOREIGN PATENTS 893,208 6/1958 Great Britain.

ROBERT K. SCHAEFER, Primary Examiner.

KATHLEEN H. CLAFFY, Examiner.

J, R. SCOTT, Assistant Examiner.

Claims

1. ADJUSTABLE SWITCHING APPARATUS COMPRISING: A FIRST INSULATING SHEET OF WHICH IS AFFIXED ON ONE SIDE THEREOF AT LEAST ONE FIXED CONDUCTIVE SWITCH CONTACT; A SECOND INSULATING SHEET OF WHICH IS AFFIXED ON ONE SIDE THEREOF AT LEAST ONE FIXED CONDUCTIVE SWITCH CONTACT; A ROTATABLE INSULATING DISC HAVING AN APERTURE WHICH EXTENDS THERETHROUGH FROM ONE SIDE TO THE OTHER; MEANS INCLUDING A SHAFT FOR SUPPORTING SAND ALIGNING SAID FIRST AND SECOND INSULATING SHEETS AND SAID DISC IN PARALLEL SPACED APART RELATION SUCH THAT SAID DISC IS JOURNALLED ON SAID SHAFT BETWEEN SAID FIRST AND SECOND INSULATING SHEETS FOR ROTATION AS BETWEEN AT LEAST A PLURALITY OF DIFFERENT DISCRETE POSITIONS AND THE SIDES OF SAID INSULATING SHEETS, TO WHICH SAID FIXED CONTACTS ARE AFFIXED, ARE ADJACENT EACH OTHER; SAID INSULATING DISC HAVING A MANUAL CONTROL TAB EXTENDING IN A DIRECTION PERPENDICULAR TO ITS AXIS OF ROTATION TO FACILITATE ADJUSTMENT FROM ONE POSITION TO THE NEXT AND ALSO HAVING A PLURALITY OF DETENT NOTCHES ON ITS PERIPHERY CORRESPONDING TO THE PLURALITY OF DIFFERENT POSITIONS OF SAID DISC; A MOVABLE CONTACT PIN RETAINED IN SAID APERTURE OF SAID ROTATABLE INSULATING DISC AND, IN AT LEAST ONE POSITION OF SAID DISC, ENGAGING AND ELECTRICALLY INTERCONNECTING THE FIXED CONTACTS OF SAID FIRST AND SECOND INSULATING SHEETS; A RESILIENT DETENT WHICH MATES WITH A DIFFERENT NOTCH ON THE PERIPHERY OF SAID INSULATING DISC IN EACH DIFFERENT POSITION OF SAID DISC; AND RESILIENT MEANS FOR URGING ONE OF SAID FIRST AND SECOND INSULATING SHEETS TOWARD THE OTHER.