US3845447A

US3845447A - Variable resistor

Info

Publication number: US3845447A
Application number: US00408105A
Authority: US
Inventors: T Ashiya; M Nagami; Y Watanabe
Original assignee: Sony Corp
Current assignee: Sony Corp
Priority date: 1972-10-24
Filing date: 1973-10-19
Publication date: 1974-10-29
Anticipated expiration: 1991-10-29
Also published as: BR7308319D0; NL178285B; GB1415805A; FR2204019B1; DE2353083A1; NL7314630A; NL178285C; DE2353083C2; IT998932B; FR2204019A1; JPS5313002Y2; JPS4977445U; CA989030A

Abstract

A variable resistor comprising a resistor element, a slide contact member in sliding engagement with said resistor element, and switch means actuated by said slide contact member. The switching means connects one end of the resistor element to ground or to an open circuit terminal when slide contact engages the other end of the resistor element.

Description

United States Patent [191 Oct. 29, 1974 Ashiya et a1.

VARIABLE RESISTOR Q Inventors: Takechika Ashiya, Kawasaki; Masaru Nagami, Yokohama; Yoshimi Watanabe, Tokyo, all of Japan Assignee: Sony Corporation, Tokyo, Japan Filed: Oct. 19, 1973 Appl. No.: 408,105

Foreign Application Priority Data Oct. 24, 1972 Japan 47-122924 US. Cl 338/200, 307/156, 323/80, 330/30, 33'8/128, 338/172, 338/202 Int. Cl 1101c 9/08 Field of Search 338/200, 201, 198, 191, 338/185,178,128,129,131,179, 92, 95, 120, 127, 162, 172, 173, 174, 190, 202; 323/63, 80, 94; 307/98, 156, 42, 43; 333/6; 317/99; 330/185, 191, 144, 147, 30, 69, 74,

[56] References Cited UNITED STATES PATENTS 1,931,799 10/1933 Hunter 323/80 X 2,783,397 2/1957 Lauson 338/128 2,942,221 6/1960 Di Girolamo, 338/200 3,047,825 7/1962 Biltz 338/172 3,375,446 3/1968 Guyton 338/198 X 3,587,027 6/1971 Gerwitz 338/198 X 3,629,775 12/1971 Kindred 338/128 3,633,146 1/1972 Sasaki et a1 338/200 X.

Primary Examiner-Bruce A. Reynolds Attorney, Agent, or Firm-Hill, Gross, Simpson, Van Santen, Steadman, Chiara & Simpson [57] ABSTRACT A variable resistor comprising a resistor element, a slide contact member in sliding engagement with said resistor element, and switch means actuated by said slide contact member. The switching means connects one end of the resistor element to ground or to an open circuit terminal when slide contact engages the other end of the resistor element.

7 Claims, 12 Drawing Figures VARIABLE RESISTOR BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to a variable resistor, and more particularly to a variable resistor with a slide contact member engageable with a resistor element which receives two different signals applied to opposite ends of the resistor element so as to derive from the slide contact member either of the two different signals or alternatively a mixture of the two signals.

2. Description of the Prior Art FIG. 1 shows a mixing circuit in which a conventional variable resistor 1 is employed. The variable resistor 1 consists of a resistor element In and a slide contact member 6. Contact points 11 and 1.2 are provided at opposite ends of the resistor element la and a microphone amplifier 2 is connected to contact 11 and an equalizer amplifier 3 (which will be hereinafter referred as to an E amplifier) is connected to contact 12. The amplifiers may be supplied with audio signals, respectively. Thus, signals from a microphone or other device are applied to the

amplifiers

2 and 3 for amplification, delivery to an output terminal 4 through slide contact member 6, as a selected single signal or a mixed signal.

As the slide contact member 6 moves on the resistor element la, the output signal is adjusted. When the slide contact member 6 moves tocontact point 11, the signal from the microphone amplifier 2 is delivered directly unattenuated to the output terminal 4 without passing through the resistor element 1a. When slide contact 6 engages contact point 12, the signal from E0 amplifier 3 is passed unattenuated to output terminal 4. When slide contact 6 is at an intermediate point e between

contact points

11 and 12, a mixture of the two input signals is supplied to output terminal 4.

In prior art devices according to FIG. 1, there is a defeet in that if the resistance value of the resistor element la is not selected large enough as compared with the output impedances of the microphone amplifier 2 or the EQ amplifier 3, separation of the two signals fed to the contact points '11 and 12 cannot be satisfactorily achieved even if the slide contact member 6 engages the

contact points

11 and 12.

Further, when the slide contact member 6 is positioned at intermediate or mid-point c, it is necessary that the resistance value of the resistor element la be small as compared with the input impedance of a device which may be connected to the output terminal 4 so as to avoid the attenuation waveguide the output signal; otherwise, the separation characteristics between the two signals, when the slide contact member 6 is positioned at the

contact point

11 or 12, will be deteriorated.

SUMMARY OF THE INVENTION An object of this invention is to provide an improved variable resistor with a switching means.

Another object of this invention is to provide an improved variable resistor which comprises a resistor element, a slide contact means movable on the resistor element, and a switch means which is controlled by movement of the slide contact means relative to the resistor elements so as to ground or open circuit, one end of the resistor element when the slide contact means reaches the other end of the resistor element, whereby the signal separation characteristic between two applied signals is improved.

A further object of this invention is to provide a variable resistor for use as a mixing circuit which mixes two different signals.

A yet further object of this invention is to provide a variable resistor for use as a mixing circuit which mixes a two-channel signal with a signal from a microphone.

The other objects, features and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram showing a mixing circuit using prior art variable resistor;

FIG. 2 is a side plan view showing an embodiment of the variable resistor according to this invention;

FIGS. 3A, 3B and 3C are respectively plan views of parts used in the variable resistor depicted in FIG. 2;

FIG. 4 is a circuit diagram showing an example of a mixing circuit in which the variable resistor of this invention is used;

FIG. 5 is a circuit diagram showing a two-channel stereophonic reproducing apparatus in which the variable resistor of this invention is used;

FIG. 6 is a circuit diagram showing another example of a mixing circuit in which the variable resistor of this invention is employed;

FIG. 7 is a perspective view showing another example of the variable resistor according to this invention; and

FIGS. 8A, 8B and 8C are respectively schematic diagrams for explaining the variable resistor shown in FIG.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of this invention is shown in FIGS. 2-l2 in which the same reference numerals used in FIG. 1 designate similar elements.

The variable resistor I of this invention consists of the resistor element la and a slide contact member 6 engageable with the resistor element la as in the case of FIG. 1. In this invention, when the slide contact member 6 approaches or contacts the contact point 11 of the resistor element 1a, its other contact point 12 will be opened or grounded by a switching means, and when the slide contact member 6 approaches or contacts the other contact point 12 of the resistor element la, the other contact point 11 will be opened or grounded by a switching means.

In FIGS. 2, 3A, 3B and 3C, reference numeral 7 indicates a rotary shaft made of insulating material which has attached thereto at its one end a knob 7a and is rotatably supported by disc-

like substrates

8, 9 and 10. The resistor element la is ring-shaped with a gap and is coaxially mounted on the substrate 8. The

contact points

11 and 12 are provided at the opposite ends of the resistor element la and are in electrical contact therewith. The output terminals of the microphone amplifier 2 and EQ amplifier 3 are connected to the

contact points

11 and 12, respectively. The conductive slide member 6 has one end fixed to the rotary shaft 7 and its other end is in slide contact with resistor element la. Member 6 also engages the

contact points

11 and 12 at its end travel to produce a composite signal from the outputs of the microphone and

EQ amplifiers

2 and 3 or alternatively their signals separately if the position of the slide contact member 6 engages

contact points

11 and 12. A flexible lead can be connected between contact member 6 and output terminal 4.

A connecting member is made of conductive material and is similar to the resistor body la in shape being ring-shaped with a gap. Member 15 is mounted on the disc-shaped substrate 9 coaxially with the rotary shaft 7. A contact point 17 is electrically connected to one end of the connecting member 15. A contact point 18 is mounted adjacent the other end of the connecting member 15 but is electrically insulated from member 15. Contact point 18 is connected to ground by a suitable conductor and the contact point 17 is connected to the contact point 11 by a suitable conductor. A slide member 23 made of conductive material has one end fixed to the rotary shaft 7 and its other end slides on the connecting member 15 and at its end travel

bridges connecting points

17 and 18 through connecting member 15.

A connecting member 16 of ring-shaped with a gap and which is made of conductive material is mounted on the substrate 10 coaxially with the rotary shaft 7. A contact point is connected to the connecting member 16 at one end and is positioned to be opposite to contact point 17. Contact point 20 is connected to contact point 12 by a suitable conductor. Adjacent the other end of the connecting member 16, a contact point 19 is mounted and it is electrically isolated from the connecting member 16 and is to ground by a suitable conductor. A slide contact member 24made of conductive material has one end fixed to the rotary shaft 7 and its other end bridges the connecting member 16 and

contact points

19 and 20 through connecting member 16.

FIG. 4 shows an example of a mixing circuit in which the variable resistor 1 according to the present invention is employed. The slide contact member 6 is connected to the output terminal and the

contact points

11 and 12 are connected to the microphone and

EQ amplifiers

2 and 3, respectively.

With the present invention constructed as above described, if the knob 7a is rotated in the direction indicated by the arrow 0 in FIG. 2, the

slide contact members

6, 23 and 24 will be rotated together in direction a as shown in FIG. 3. At the extreme counter-clockwise position slide contact member 6 contacts contact point 11 which connects the microphone amplifier 2' to the output terminal 4 through only the slide contact member 6. Also at this position. the slide contact member 24 and connecting member 16 are connected to contact point 19 which short-circuits them to ground. The E0 amplifier 3 is also grounded under this condition. If the knob 7a is rotated clockwise relative to FIGS. 3A, 3B and 3C the

slide contact members

6, 23 and 24 will rotate together and at the end position slide contact member 6 contacts contact point 12 which connects the EQ amplifier 3 to the output terminal 4 directly only through the slide contact member 6; Also at this position, slide contact member 23 short-circuits connecting member 15 and the grounded contact point 18. This grounds the microphone amplifier 2.

If the knob 7a is rotated to a position intermediate such as mid-point c on the resistor element 1a as shown in FIG. 4, the

slide contact members

6, 23 and 24 will be positioned intermediate or at the mid-point on members la, 15 and 16, and the output signals from the microphone and

EQ amplifiers

2 and 3 will be mixed and furnished to the output erminal 4.

As described above, with this invention when the slide contact member 6 is rotated to contact either

contact point

11 or 12, the signal from the microphone amplifier 2 or the EQ amplifier 3 will be, respectively, delivered to the output terminal 4 without attenuation. Thus, separation of the two signals is obtained. When the slide contact member 6 is positioned at an intermediate or mid-point c, the output signals from the

amplifiers

2 and 3 will be mixed through the resistor body la and delivered to the output terminal 4 in amounts proportional to the position of contact 6. The resistance value of the variable resistor la is selected based only on the objective to obtain desired mixture of the two signals and its resistance value can be reduced as compared with resistors of the prior art.

In the above example, the

substrates

8, 9 and 10 are illustrated as separate elements, but it is apparent that they can be integrally formed if desired.

FIG. 5 illustrates an example in which the variable resistor of this invention is used in a two-channel stereophonic reproduction apparatus.

A description will be given of the left channel (L- channel) of the two channels system. The output signal from an E0 amplifier 2L which amplifies the L-channel phono signal is applied to a contact point 11L which is connected to one end of a resistor element 1L of a variable resistor according to this invention. The output from a microphone amplifier 3 is applied to a contact point 12L at the other end of the resistor element lLa. A slide contact member 6L makes wiper contact with resistor 1L and is connected to an L-channel output terminal 4L. The structure and schematic similar to that illustrated in FIGS. 3A, 3B, 3C and 4 may be used. In FIG. 5, contact points 17L, 18L, 19L, 20L and slide contact members 23L, 24L correspond with

contact points

17, 18, 19, and 20 and the

slide members

23, 24 shown in FIG. 4 and operate similarly. That is, when the slide contact member 6L moves upward in FIG. 5 to contact point 11L, the output signal from the microphone amplifier 3 is connected to ground because it is short-circuited by slide contact member 24L which engages contact point 19L and hence only the output signal from the L-channel EQ amplifier 2L is delivered to the output terminal 4L. However, when the slide contact member 6L moves downward in FIG. 5 to engage contact point 12L and the output signal from the EQ amplifier 2L is grounded because slide contact 23L engages grounded contact point,l8L and hence only the output signal from the microphone amplifier 3 is delivered to the output terminal 41.. When the slide contact member 6L is intermediate between the contact points 11L and 12L, an output signal which is a mixture of the signals from the microphone amplifier 3 and the EQ amplifier 2L is delivered to the output termianl 4L. Thus, when the slide contact member 6L contacts either of the contact points 11L or 12L, only one of the output signals from the amplifiers will be delivered to the output terminal 4L. The separation between the signals is substantially enhanced.

The right channel (R-channel) is constructed and operates substantially the same as the L-channel, and the description is omitted for the sake of brevity. The corresponding elements shown in FIG. 5 are identified by the same reference numerals as for the left channel except L is changed to R.

In the above-described embodiments when the slide contact member approaches one end of the resistor element. the other end of the resistor element is grounded as shown in FIGS. 4 and 5. However, it is also possible to improve the separation between signals with a structure such that when the slide member approaches one end of the resistor element. the other end of the resistor element is open-circuited. For this structure, the variable resistor la of the present invention is connected as shown in FIG. 6. The output terminal of the microphone amplifier 2 is connected to the slide contact member 23. Contact point 17 is connected to the contact point 11. Contact point 18 is left opened and is not grounded as in FIG. 4. The output terminal of EO amplifier 3 is connected to the slide contact member 24. Contact point 20 is connected to contact point 12. Contact point 19 is left open and is not grounded as in FIG. 4. Slide contact member 6 is connected to the output terminal 4.

In FIG. 6. when the slide contact member 6 moves upward relative the FIG. 6 and engages contact point 11, the output signal from the microphone amplifier 2 is transmitted to the output terminal 4 through the slide contact member 23, contact points 17, 11, and the slide contact member 6 and does not pass through the resistor element la. At the same time, the output signal from the EQ amplifier 3 is not furnished to the output terminal because the slide contact 24 engages open contact point 19. Under this condition, contact member 24 does not bridge connection member 16 and contact point 19, but engages only contact point 19. When slide contact 6 moves downward relative to the FIG. and engages contact point 12, the output signal from the EQ amplifier 3 is transmitted to the output terminal 4 through the slide contact member 24, contact points 20, 12 and slide contact 6 without passing through the resistor element la. The output signal from the microphone amplifier 2 is not passed to the output terminal 4 because slide contact member 23 engages contact point 18 which is an open circuit. Under this condition, contact member 23 does not bridge connection member 15 and contact point 18, but engages only contact point 18.

Thus, separation between the signals can also be improved with the embodiment shown in FIG. 6.

In FIG. 6, when slide contact member 6 engages resistor element intermediate between contact points 1] and 12, the output signal from the microphone amplifier 2 is transmitted through slide contact member 23, a part of connecting member (refer to FIG. 3B), the connecting points 17, '11, the upper part of the resistor element la relative to the FIG. and the slide contact member 6 to the output terminal 4. The output signal from the EQ'amplifier 3 is transmitted through slide contact member 24, a part of connecting member 16 (refer to FIG. 3C). the connecting

points

20, 12, the lower part of resistor element 1a relative to the FIG. and the slide contact member 6 to the output terminal 4. In this case the output signals from the

amplifiers

2 and 3 are mixed in accordance with the position of the slide contact member 6 on the resistor element la and delivered to the output terminal 4.

Thus, in the FIG. 6 embodiment in which when the slide contact member 6 contacts one end of the resistor element 1a and the other end is opened circuit, the same results to that obtained by the embodiment in FIG. 4 can be obtained.

A further example of this invention is shown in FIGS. 7 and 8 in which the same elements as those shown in FIGS. 4 and 6 are designated by the same numerals.

A cam 31 which has a projection 31a is fixed to one end of the rotary shaft 7 which passes through the substrate 8. A switch 32 consists of a movable contact 32a and fixed contacts 32b and 32c is mounted so that the movable contact can be actuated by the cam 31. The movable contact 32a of the switch 32 is grounded. FIGS. 8A -8C show the connections of the FIG. 7 structure. When the knob 7a is rotated either clockwise or counterclockwise, the movable contact 32a of the switch 32 is moved by cam 31a to contact a first fixed contact 32b (refer to FIG. 8A) or another fixed contact 320 (refer to FIG. 8C). At these limits of travel. the slide contact member 6 engages either

contact point

11 or 12. When the movablecontact 32a does not engage either of the fixed contact points 32b and 320, the slide contact member 6 engages resistor element la between the contact points 11 and 12 (refer to FIG. 8B). Thus, when the slide contact member 6 engages one of the contact points 11 and 12, the output signal from a particular amplifier connected to one of the contact points 11 and 12 is grounded. When the slide contact member 6 is intermediate on the resistor element 1a, the movable contact 32a does not contact either of the fixed contacts 32b and 320, and an output signal which is from both the amplifiers 2 and 3 (not shown in FIGS. 7 and 8) will be produced and delivered to the output terminal 4. It may be possible to provide a detent mechanism on rotary shaft 7 so that movable contact 320 makes positive contact with the fixed contact 32b or 320 as projection 31a of the cam 31 engages contact 320. This will assure that the movable contact 32a positively engages

contact point

11 or 12. It is seen that the example shown in FIGS. 7 and 8A8C produces the same results as those obtained by the other embodiments.

It will be apparent that many modifications and variations could be effected by those skilled in the art without departing from the spirit and scope of the novel concepts of the present invention.

We claim as our invention:

1. A variable resistor comprising:

a. a resistor element having first and second terminals;

b. a conductive slide means mounted for slide contact with said resistor element and said first and second terminals; and

c. switch means controlled by the position of said slide means and operative to ground one of said first and second terminals of said resistor element when said slide means engages the other one of said first and second terminals of said resistor element.

2. A variable resistor comprising: a. a resistor element having first and second terminals;

b. an electrical conductive slide means mounted for slide contact with said resistor element and said first and second terminals; and

c. switch means controlled by the position of said slide means and operable to open the connection between one of said first and second terminals and said resistor element when said slide means engages the other one of said first and second terminals.

3. A variable resistor comprising:

a. a resistor element having first and second terminals, a first input signal source applied to said first terminal, a second input signal source applied to said second terminal;

b. electrical conductive slide means mounted to slide on said resistor element between said first and second terminals, an output terminal for delivering at least one of said first and second signal or a mixed signal of said input signals connected to said slide means; and

c. switch means controlled by the position of said slide means and operative to ground one of said first and second input signals when said slide means engages one of said first and second terminals and to ground the other one of said first and second input signals when said slide means engages the other one of said first and second terminals.

4. A variable resistor comprising:

a. a resistor element having first and second terminals, a first input signal applied to said first terminal, a second input signal applied to said second terminal;

b. an electrical conductive slide means mounted to slide on said resistor element between said first and second terminals, said slide means supplied at least one of said first and second input signals or a mixture thereof from said resistor element depending on the position of said slide means; and

c. switch means controlled by the movement of said slide means and operative to disconnect one of said first and second input signals from said slide means when said slide means engages one of said first or second terminals.

5. A variable resistor comprising:

a. a first resistor element having first and second terminals;

b. a first electrical conductive slide means mounted to slide on said resistor element between said first and second terminals;

0. a second resistor element having third and fourth terminals;

d. a second electrical conductive slide means mounted to slide on said second resistor element between said third and fourth terminals;

e. first input signal means connected to said first terminal of said first resistor element;

f. second input signal means connected to said fourth terminal of said second resistor body;

g. third input signal means connected to said second and third terminals;

h. a first output signal terminal connected to said first slide means and receiving at least one of said input signals from said first and third input signal means or a mixture depending upon the position of said first slide means;

i. a second output signal terminal means connected to said second slide means and receiving at least one of input signals from said third and fourth input signal means or a mixture depending upon the position of said second slide means;

j. first switch means controlled by movement of said first slide means and operative to ground one of said first and second terminals of said first resistor element when said first slide means engages the other of said first and second terminals; and

k. second switch means controlled by movement of said second slide means and operative to ground one of said third and fourth terminals of said second resistor element when said second slide means engages the other of said third and fourth terminals.

6. A variable resistor comprising:

a. a first substrate;

b. a rotary shaft rotatably supported by said first substrate;

c. a resistor element generally ring-shaped formed with a gap mounted on said first substrate around said rotary shaft, said resistor element having first and second contact points at opposite ends;

d. a first slide means with one end attached to said rotary shaft and slidable on said resistor element between said first and second contact points;

e. a second substrate rotatably supporting said rotary shaft;

f. a first connecting member generally ring-shaped with a gap mounted on said second substrate around said rotary shaft, said first connecting member having a third contact point at one end thereof;

g. a fourth grounded contact point mounted on said second substrate adjacent the other end of said first connecting member and electrically isolated from said first connecting member;

h. second slide means with one end attached to said rotary shaft and slidable on said first connecting member between said third and fourth contact points i. a third substrate rotatably supporting said rotary shaft;

j. a second connecting member generally ring-shaped with a gap mounted on said third substrate around said rotary shaft, said second connecting member having a fifth contact on one end corresponding to the position of said third contact relative to rotation of said rotary shaft;

k. a sixth grounded contact point mounted on said second substrate adjacent the other end of said second connecting member and electrically isolated from said second connecting member;

1. third slide means with one end fixed to said rotary shaft and slidable on said second connecting member between said fifth and sixth contact points; and

said switch means is a cam switch having at least three contact points one of which is grounded, and said cam switch controlled by the position of said slide means.

Claims

1. A variable resistor comprising: a. a resistor element having first and second terminals; b. a conductive slide means mounted for slide contact with said resistor element and said first and second terminals; and c. switch means controlled by the position of said slide means and operative to ground one of said first and second terminals of said resistor element when said slide means engages the other one of said first and second terminals of said resistor element.

2. A variable resistor comprising: a. a resistor element having first and second terminals; b. an electrical conductive slide means mounted for slide contact with said resistor element and said first and second terminals; and c. switch means controlled by the position of said slide means and operable to open the connection between one of said first and second terminals and said resistor element when said slide means engages the other one of said first and second terminals.

3. A variable resistor comprising: a. a resistor element having first and second terminals, a first input signal source applied to said first terminal, a second input signal source applied to said second terminal; b. electrical conductive slide means mounted to slide on said resistor element between said first and second terminals, an output terminal for delivering at least one of said first and second signal or a mixed signal of said input signals connected to said slide means; and c. switch means controlled by the position of said slide means and operative to ground one of said first and second input signals when said slide means engages one of said first and second terminals and to ground the other one of said first and second input signals when said slide means engages the other one of said first and second terminals.

4. A variable resistor comprising: a. a resistor element having first and second terminals, a first input signal applied to said first terminal, a second input signal applied to said second terminal; b. an electrical conductive slide means mounted to slide on said resistor element between said first and second terminals, said slide means supplied at least one of said first and second input signals or a mixture thereof from said resistor element depending on the position of said slide means; and c. switch means controlled by the movement of said slide means and operative to disconnect one of said first and second input signals from said slide means when said slide means engages one of said first or second terminals.

5. A variable resistor comprising: a. a first resistor element having first and second terminals; b. a first electrical conductive slide means mounted to slide on said resistor element between said first and second terminals; c. a second resistor element having third and fourth terminals; d. a second electrical conductive slide means mounted to slide on said second resistor element between said third and fourth terminals; e. first input signal means connected to said first terminal of said first resistor elemenT; f. second input signal means connected to said fourth terminal of said second resistor body; g. third input signal means connected to said second and third terminals; h. a first output signal terminal connected to said first slide means and receiving at least one of said input signals from said first and third input signal means or a mixture depending upon the position of said first slide means; i. a second output signal terminal means connected to said second slide means and receiving at least one of input signals from said third and fourth input signal means or a mixture depending upon the position of said second slide means; j. first switch means controlled by movement of said first slide means and operative to ground one of said first and second terminals of said first resistor element when said first slide means engages the other of said first and second terminals; and k. second switch means controlled by movement of said second slide means and operative to ground one of said third and fourth terminals of said second resistor element when said second slide means engages the other of said third and fourth terminals.

6. A variable resistor comprising: a. a first substrate; b. a rotary shaft rotatably supported by said first substrate; c. a resistor element generally ring-shaped formed with a gap mounted on said first substrate around said rotary shaft, said resistor element having first and second contact points at opposite ends; d. a first slide means with one end attached to said rotary shaft and slidable on said resistor element between said first and second contact points; e. a second substrate rotatably supporting said rotary shaft; f. a first connecting member generally ring-shaped with a gap mounted on said second substrate around said rotary shaft, said first connecting member having a third contact point at one end thereof; g. a fourth grounded contact point mounted on said second substrate adjacent the other end of said first connecting member and electrically isolated from said first connecting member; h. second slide means with one end attached to said rotary shaft and slidable on said first connecting member between said third and fourth contact points, i. a third substrate rotatably supporting said rotary shaft; j. a second connecting member generally ring-shaped with a gap mounted on said third substrate around said rotary shaft, said second connecting member having a fifth contact on one end corresponding to the position of said third contact relative to rotation of said rotary shaft; k. a sixth grounded contact point mounted on said second substrate adjacent the other end of said second connecting member and electrically isolated from said second connecting member; l. third slide means with one end fixed to said rotary shaft and slidable on said second connecting member between said fifth and sixth contact points; and m. means connecting said first contact point with said third contact point and said second contact point with said sixth contact point.

7. A variable resistor according to claim 3, wherein said switch means is a cam switch having at least three contact points one of which is grounded, and said cam switch controlled by the position of said slide means.