US 3772486 A
A relatively thin layer of conducting metal laminated to an insulating baseboard is divided into at least one array of uniformly sized and spaced electrically conducting contact segments insulated from each other by narrow separations extending the entire thickness of the metal down to the insulating base. At least one of the separations is contiguous to all the contact segments in the array. A provision is made for a spring contact member to be movable along the center line of the contiguous separation in physical engagement with the metal on either side thereof. In one embodiment of the invention, there are identical contact segments on either side of the contiguous separation, so that electrical connection is made between consecutive pairs of contacts as result of movement of the spring contact member. In another embodiment, there are electrical contact segments on one side of the contiguous separation but a continuous collector strip on the other side thereof, so that electrical connection is made from selected contact segments to the collector strip.
Description (OCR text may contain errors)
United States Patent 1 Wilentchik [451 Nov. 13, 1973 SIDE SELECTOR SWITCH WITH SEGMENTED TERMINALS AND COLLECTOR MEANS  Inventor: Jerzy J. Wilentchik, 222 Lake Ave.,
Yonkers, N.Y. 10701  Filed: Jan. 17, 1972  Appl. No.: 218,086
 U.S. Cl.....' 200/16 C  Int. Cl. H0lh 15/00  Field of Search 200/16 C, 16 D, 166 BA,
200/11 TW, 11 DA, 16 C, 16 D  References Cited UNITED STATES PATENTS 3,308,250 3/1967 Field et al 200/16 D 2,874,237 2/1959 Shlesinger, .lr. 200/166 BA X 3,582,578 6/1971 Lockard 200/16 D 3,089,923 5/1963 Wright..... 200/11 TW X 3,643,042 2/1972 Gratz 200/16 D 2,347,735 5/1944 Coyne 200/166 BA UX 2,453,498 11/1948 Crowley 200/16 D 2,487,199 ll/1949 Titcomb 200/16 C 3,362,004 l/l968 Bang 200/166 BA X 3,639,706 2/1972 Purdy 200/166 BA Primary Examiner-.1 R. Scott Attorney-Charles E. Temko  ABSTRACT A relatively thin layer of conducting metal laminated to an insulating baseboard is divided into at least one array of uniformly sized and spaced electrically conducting contact segments insulated from each other by narrow separations extending the entire thickness of the metal down to the insulating base. At least one of the separations is contiguous to all the contact segments in the array. A provision is made for a spring contact member to be movable along the center line of the contiguous separation in physical engagement with the metal on either side thereof. In one embodiment of the invention, there are identical contact segments on either side of the contiguous separation, so that electrical connection is made between consecutive pairsof contacts as result of movement of the spring contact member. In another embodiment, there are electrical contact segments on one side of the contiguous separation but a continuous collector strip on the other side thereof, so that electrical connection is made from selected contact segments to the collector strip.
The spring member and the individual contact segments and collectors are enclosed in a housing. An actuator accessible from outside of the housing provides the means for displacing the spring contact member along the center of the contiguous separation in steps corresponding to the spacing of the Contact segments and for positioning it at each step in the center of a respective contact segment.
Means are provided for making external electrical connection to the individual contact segments and to the collector strips.
This arrangement lends itself to a great flexibility as either single or multiple arrays can be provided in any one baseboard and can be controlled either independently by respective actuators or jointly by a single actuator. Furthermore, said arrays can be arrayed in either linear or circular fashion.
Indicator means are provided optionally in the housing and in the actuator to identify the position of the spring member in relation to individual contacts.
18 Claims, 13 Drawing Figures PATENTEDHUY 13 1975 3772.486
SHEET EEF 3 ,3; 4 a 2&-
SIDE SELECTOR SWITCH WITH SEGMENTED TERMINALS AND COLLECTOR MEANS The invention relates to improvements in the design, construction, manufacture and use of an electric selector switch. Although there are other methods of building a selector switch, this method offers the following distinct advantages over the existing art: lower internal resistance, smaller size, simplicity of design, lower manufacturing cost, convenience of application.
To illustrate the wide scope of application of the invention, both its linear and rotary motion embodiments are described herein.
The invention provides basically, a selector switch employing a matrix made of copper laminated epoxy baseboard operating in conjunction with a wiping contact in form of a contact spring. This simple design employs fewer assembly parts and results in a lower manufacturing cost as well as smaller overall size. A further object of the invention is an extremely low and stable internal resistance, namely on the order of l milliohm vs. 100 milliohm in conventional switch designs.
Printed circuit matrix is used presently in thumbwheel design swtiches, but because ofvarious considerations, most of the copper in the printed circuit deck is etched away and the current carrying copper paths from input to output terminals are relatively long, narrow, thin and tortuous lines resulting in internal switch resistance on the order of 50 100 milliohms. Since the current carrying copper paths are curves, the only economical way of producing them in conventional designs is by etching excess copper away either by a chemical and/or by a photographic process. The etching process requires that the copper be fairly thin (usually under 0.003 inch) and this requirement alone is largely responsible for the relatively high internal resistance of switches employing printed circuit decks. In contrast, the switch in this specification employs all the available copper in the deck except for thin straight line separations between respective contacts which results in the retention of over 80 percent of the original copper against less than 30 percent in conventional thumbwheel switch designs. To effect these straight line separations a machine shop process of grinding or milling is substituted for etching. Consequently the boards have copper thickness of 0.010 0.030 inch instead of conventional 0.0025 inch, which results in a substantial decrease of internal resistance of the various switch contact sections. In addition, the design of the wiping contact arm provides for a considerably shorter path of current flow, thus, further reducing the internal switch resistance. As result of those improvements the described switch design permits the reduction of internal resistance from conventional value of 10 to 100 milliohms to less than 1 milliohm. Th lowering of switch resistance results in a highly improved overall switch performance and in increased current carrying capacity.
The invention is explained with the aid of the following drawings:
FIG. 1 is a front view of a two pole switch contact deck in a linear embodiment of the invention.
FIG. 1a. is a partly broken view ofa modified contact deck of FIG. 1.
FIG. 2. is a sectional. view of the switch assembly taken along lines 2 2 of FIG. 3. including printed circuit deck of FIG. 1.
FIG. 2a. is a partly broken view of a modified contact arrangement according to the invention.
FIG. 3. is a front view of the linear embodiment of the switch according to the invention.
FIG. 3a. is a partly broken front view of the tape in embodiment of FIGS. 1 5.
FIG. 4 is a sectional view of the switch taken along lines 4 4 of FIG. 2.
FIG. 5 is a rear view of the contact carriage less contact springs taken along lines 5 5 of FIG. 2.
FIG. 5a. is a sectional view of the carriage less contact springs taken along lines 5a 5a in FIG. 5.
FIG. 6 is a view of a modified switch front panel with readout instead of tape according to the invention.
FIG. 7 is a view of switch contact deck in a single pole rotary embodiment of my invention.
FIG. 8 is a partly broken sectional view of a two section rotary embodiment of the switch according to the invention.
FIG. 9. is a sectional view taken along lines 9 9 of FIG. 8.
Reference is made first to FIGS. 1 6 of the drawings portraying a linear embodiment of a two pole switch, according to the invention. FIG. 1 shows an epoxy baseboard 12 having a relatively thin layer of copper contact segments 13 bonded by a suitable adhesive or deposited by a chemical process to one of its large surfacesnBaseboard materials other than epoxy, such as phenolic, mellamine, etc. can be also employed. Boards comprising layer of copper bonded to plastic are known in the art and are used extensively in printed circuit applications. The copper contact segments 13 is divided into a plurality of mutually insulated, current conducting contact sections by means of evenly spaced, parallel grooves 17 extending from both outside edges of the baseboard towards the center and by grooves 14a, 14b and at right angle to the grooves 17. The grooves 17 intersect with respective grooves 14a and 1411 but do not extend to the groove 14c. The first and the last grooves 17, identified as 17-1 extend the entire width of the baseboard 12 and intersect with the groove 14b. & 14c. The grooves 14a, 14b and 140, 17 and 17-1 are provided by a mechanical process (milling or grinding), and because of their narrow width, on the order of 0.010 inch, are shown by single and not by double lines in the drawings of this specification. Those grooves extend in depth the entire thickness of the copper contact segments 13 down to the plastic layer of baseboard 12 and act as insulation between respective current conducting sections. Thus, the board 12 is divided into adjacent, even sized rectangle shaped sections 16a on its left, sections 16b similar to sections 16a on its right and into L shaped sections 15a and 15b located between the center groove 14c, respective groovesl4a and 14b, respective edges of the baseboard 12 and the grooves 17 and 17-1. Each of the sections 15a, 15b and 16a and 16b is provided with a relatively short slot 11 at the lower edges of the baseboard 12 into which an external conductor or components lead can be inserted and soldered in place. To prevent the solder from extending over the grooves 17 between adjacent section 16a or 16b, the grooves 17 can be slit part way to form slots 11a similar to slots 11 but slightly longer which is shown in FIG. la. This pro vides a definite separation between the various conducting sectionsand prevents their inadvertent connec tions by solder.
An alternative method of making external electrical connections to the sections 16a and 16b (not shown) would be by drilling holes thru the baseboard 12 and thru the copper contact segments 13 at approximate location corresponding to the center of respective sections 16a and 16b; placing externally protruding copper leads in the drilled holes; soldering them to the sections 16a and 16b and then cleaning excess solder by grinding or sanding. To provide firm solder connection, the holes thru copper contact segments 13 may be flared with wider opening on the copper side so that solder may surround the lead from every direction and prevent loosening. As further precaution, the copper leads protruding from the baseboard 12 may be epoxied thereto to prevent loosening from twisting.
Referring now to FIGS. 2, 3 and 4, the baseboard 12 is a part of a six walled enclosure comprising a front panel 23, the rear panel 12 and a rectangle shaped four sided platic tube 22 which can be molded or fabricated. The front wall of the tube 22 is provided with a recess 22a (shown in FIG. 2) to accept the front panel 23 which is made from a suitable metal or from a copper laminated plastic similar to the baseboard 12. The panels 12 and 23 are held at a fixed distance from one another by means of a pair of eyelets 18 provided with respective spacers, and also by means of the tube 22. The switch can be fastened to panel or table by means of screws (not shown) thru the eyelets 18.
A slot 25 having its center line opposite the center line of the groove 140 is milled or stamped out in the center of the panel 23 and acts as a guide for an internal contact carriage 27 (shown in FIG. 2) made of insulating material such as epoxy or phenolic. The carriage 27 also shown in more detail in FIG. 4, and 5a, is provided with a pair of spring loaded balls 28 engaging holes 34 in the panel 23 and acting as detent, with a pair of wiping contacts consisting of a pair of compressed helical springs 32a and 32b and with a pair of press fitted pins 29 protruding laterally thru the slot 25 and press fitted into respective blind holes in an actuator 33 mounted on them externally. The dimensions of the carriage 27 are such that it fits with minimum clearance in the tube 22 between the panels 12 and 23.
The diameter of the pins 29 is slightly smaller than the width of the slot 25 to permit a free sliding motion of the carriage 27 along the slot 25. The wiper contacts 32a and 32b sit in respective blind holes 31, the latter located in such manner that their centers are directly opposite the respective center lines of grooves 144 and 14b. The outside diameters of the springs 32a and 32b are smaller than the width of respective contact sections 16a and 16b but considerably larger than the width of respective grooves 14a, 14b and 17. In its normal stationary position, the spring 32a located centrally on the groove 14a halfway between a'pair of grooves 17, exerts pressure on respective contact sections 16a and a thus connecting then electrically together without touching section 15b (shown by dotted lines in FIG. 1). The elongated contact sections 15a and 15b are referred to as Collectors". As the spring 32a is displaced along the center line of the groove 14a, consecutive sections 16a become connected to and then disconnected from the collector 15a. Similar considerations apply to spring 32b and contact sections 15b and 16b. In stationary position of the carriage 27, the current flows from the contact 16a via fractional length of a coil of wire in the spring 32a located across a respective groove 14a between two adjacent grooves 17 to the collector 15a. Similar consideration apply to spring 32b in regard to the contact section 16b. It is understood that the coils of wire in springs 32a and 32b in contact with the copper 13 may be ground flat in order to exert an even pressure on the contact 15a 16a, 15b 16b and that the clearance between the slider 27 and the baseboard 12 is minimal so that coils cannot become entrapped between the slider 27 and the baseboard 12. The material for the springs 32a and 32b can be any spring tempered conductor, such as phosphor bronze, berillium copper, stainless steel or precious metal. Since the length of the spring wire thru which the current flows is approximately 0.010 inches, its electrical resistance is nil for all practical purposes. The contacts 15a, 15b, 16a and 16b are dimensioned in such a manner as to make their electrical resistance negligible. As result of this design, internal resistances on the order of 1 milliohm can be obtained. It will be understood that the principle of a helical spring exerting pressure on two adjacent surfaces and connecting them electrically with a minimum of electrical resistance is not limited to linear motion switches shown in FIGS. 1 6, but can be applied to rotary switches, thumbwheel switches, toggle switches and universally to any switching or circuit breaking problem where two even height surfaces are to be electrically connected and disconnected. I
The slider design presented in reference to FIGS. 1 5 is of Make before Break variety (two adjacent contacts 16a or 16b are temporarily shorted when the spring 32a or 32b passes from one section to the next). Break before MakeTdeSign (no shorting of adjacent sections) is also possible and can be realized by making the grooves 17 wider than the outside diameter of respective springs 32a and 32b, filling them with liquid epoxy, which hardens upon application and then grinding or sanding excess expoy off until uniform sliding surface is obtained.
In order to position the springs 32a and 32b in the center of respective sections 16a and 16b the following detent mechanism is employed: holes 34 of a diameter that is somewhat smaller than the diameter of respective balls 28 but somewhat larger than the width of the slot 25 are drilled along the center of the slot 25. The spacing of the holes 34 is equal to the distance of any two adjacent sections 16a center to center. A pair of blind holes 35 is provided in the contact carriage 27 spaced one from another by a distance equivalent to the distance of two adjacent sections 16a center to center.
A helical spring 36 and a ball 28 is placed in each of the holes 35. The springs 36 push respective balls 28 into the holes 34, the latter located in regard to contacts16a and 16b in such manner that when the balls 28 are in the center of the holes 34, the springs 32a and 32b are in the center of the respective contacts 16a and 16b. From the above description, it will be clear to those skilled in the art that as the contact carriage 27 is moved along the slot 25 by the actuator 33, the balls 28 willengage yieldingly the holes 34 and position respective wiper springs 32a and 32b at the center of respective contact sections 16a and 16b. It will be further understood that the holes 34 could be located anywhere along the panel 23 and not 'necessarily on the groove 25 provided the holes 35 in the carriage 27 are located opposite the holes 34. The maximum travel of the carriage 27 can be controlled by pins 29 hitting the extremities 30 of the slot 25.
Referring now to FIGS. 1, 2 and 3,a pair of round rods 41 made of brass or other suitable material, equal or having diameter smaller than the distance between the panels 12 and 23 is attached by suitable means such as epoxy cement, solder or pins (not shown) to the panel 12 between the grooves 17-1 and the eyelets 18. Each of the rods 41 hasa circular centrally located recess 42 to guide tape 44 made from mylar or from some other flexible but stretch resistant material marked alongside with numerals 26. The spacing center to center of adjacent numerals 26 seen in FIG. 3a is the same as spacing center to center of adjacent contacts 16a and 16b. FIG. 2 shows that the tape 44 is attached to the slider 27 by piercing its ends with the pins 29, however, other suitable expedients such as adhesive can be employed for that purpose. Thus, the tape 44 is formed into a loop, with rods 41 serving as guides.
Referring now to FIG. 2, 4, 5 and 5a, it is seen that the two sides of the slider 27 opposite the panels 12 and 23 have respective center grooves 46, slightly wider than the width of the tape 44 for guiding it and for permitting its free movement in relation to slider 27 during adjustment. Referring to FIG. 3. window 45 provided in the upper central portion of the panel 23 above the slot 25 permits the readout of the numerals 26 of the tape 44. The position and the dimensions of the window 45 and the size of the numerals 26 are such that in any stationary position of the slider 27, only one whole numeral representing a specific slider position appears in the center of the window 45.
In a modified arrangement shown in FIG. 6, the window 45, the tape 44, the grooves 46 in the slider carriage 27, and the rods 41 are eliminated and, the position identifying numerals 40 are imprinted on the front panel 23 along the length of the slot 25 to be read against the center of the actuator 33. All the other assembly parts remain the same as described in reference to FIG. 1 5, except that the panel 23 may have to be made wider to accomodate. the numerals 40.
' Referring back to FIG. 3, it is seen'that the panel 23 is slightly shorter and considerably narrower than the panel 12 exposing grooves 11 so that the solder connections can be made to them. The panel 23 mounted in the recessed portion 22a of the tube 22 is pressed towards the baseboard 12 by the eyelets 18 resulting in the tube 22 enclosing and protecting the slider mechanism and the contact surfaces from dust and dirt and particularly from solder and solder fluxes originating from soldering component leads and wires in the grooves ll 1. The manner in which components 20 (only one shown) may be mounted in the back of the panel 12 with their leads soldered inrespective grooves 11 is shown in FIG. 1 and 2.
The linear embodiment of the invention described in FIGS. 1 6 of this specification is a two pole selector switch. Single pole switches employ structure identical to the two pole structure except that contact sections 15b and 16b and the spring 32b are omitted. It will be further understood by anyone skilled in the art, that the switch is not limited to contact pattern and slider design shown in respective FIGS. 1 and 5. Thus, for instance, the slider carriage 27 could be provided with more than two wipers for multi-pole applications, or conversely switch matrix could be as shown in FIG. 2a. with grooves 17 extending the entire width of the baseboard 12 and a wiper spring travelling along the center of the groove 140 to connect directly together respective sections 16a and 16b. In such an arrangement, the collector 15a and 15b are altogether eliminated.
Reference is made now to FIGS. 7, 8 and 9 of the drawings portraying a rotary embodiment of my inveniton. Referring first to FIG. 7, there is shown an epoxy or phenolic disc 51 having layer of copper 52 bonded to one of its surfaces. The copper 52 is divided into 12 mutually insulated, conducting sections 53 by means of radial grooves 54 spaced 30 apart extending from the outside rim of the disc 51 to a ring shaped groove 55 concentric with discs 51 outside diameter enclosing a circularly shaped copper section 67. The grooves 54 and 55 provided by either a mechanical process (milling or grinding) or by etching with acid, extend in depth the entire thickness of the copper 52 down to the insulating base 51. Because of their narrow width (approx. 0.010 inch), the grooves 54 and 55 are shown in FIG. 7 as single and not as double lines. One of the sections 53 referred to as 53a is connected electrically to the section 67 by means of a solder bridge applied across the groove 55 between the above sections. The solder is sanded down so that it does not protrude and interfere with mechanical performance of movable assembly parts. The sections 53 and 53a are provided with respective slots 65 analogous to slots 11 in FIGS. 1 and In, for placing external wires therein before soldering them to the copper 52.
Referring now to FIG. 8, there is shown a helical spring 56 inserted into a blind round hole 57 in an insulating disc 58, the latter adapted to be rotated about it axis between the copper 52 in the disc 51 and the front panel 66 of the housing 61. The center of the hole 57 is located directly opposite the center of the groove 55 in FIG. 7 or in different words, when rotor 58 rotates around its axis supported in the hole 69 of the disc 58, the center of hole 57 describes a circle which is equal and parallel to the center line of the circular groove 55.
In a free and uncompressed state before assembly, the spring 56 protrudes out of the hole 57 but when compressed against the disc 51, it exerts pressure on copper 52 on both sides of the circular groove 55, thus connecting the section 67 to one of the sections 53. As the rotor 58 is rotated about its axis by a shaft 63, the spring 56 is moved in a circular motion along the center of the groove 55, thus connecting the various sections 53 to the collector ring 67 and to the output section 53a. The diameter of the spring 56 is smaller than the distance between two adjacent grooves 54 measured along the groove 55. The operation is analogous to the embodiment of FIGS. 1 6 in which sections 16a and 16b become connected to respective slip rings 15a and 15b by the springs 32a and 32b except that the action is rotary instead of linear. The rotor 58 is supported bearing wise in a ring 60 made of steel or other suitable material, press fitted internally into insulating housing 61 which is attached to the disc 51 by means of three eyelets 62, apart thru holes 81 in the disc 51 (only one eyelet 62 is shown in FIG. 8). The copper 52 around the eyelets 62 is chamfered to prevent electrical connection.
Referring to FIG. 9, the ring 60 has 12 holes 68 drilled in it 30 apart and the rotor 58 has two blind radial holes 69 drilled in it apart. A pair of compressed, helical springs 71 and a pair of balls 72 of a slightly larger diameter than the holes 68 are placed in respective holes 69, the balls 72 being pushed outwardly by springs 71 into respective holes 68. The ring 60 is aligned with regard to the disc 51 in such manner that when the balls 72 engage respective holes 68, the spring 56 is situated in the center of section 53, between two grooves 54. It will be clear to those skilled in the art that the interaction of balls 72'and the holes 68 produces a detent effect for positioning the wiper spring 56 in the center of respective sections 53 Referring back to FIG. 8, the rotor 58 has a peripheral groove 75. A pin 76 press fitted into a radial hole in the rotor 58 protrudes into the groove 75 from within the rotor 58. The pin 76 acts to limit the rotation of the rotor 58 to a specified are by means of two stop pins 77 (one one seen in FlG. 8) press fitted into radial holes drilled thru the housing 61 and the ring 60, protruding into the center of the groove 75. It will be apparent to those skilled in the art that the rotation of the rotor 58 will be limited to a specified are by the collision of the pin 76 against either one of the pins 77. A window 73 can be drilled or stamped out in the front panel 66 and numerals O 11 imprinted about the face of the rotor 58 at such location that they appear in sequence in the window 73 relative to rotors rotation to provide numeric readout of rotor position. The housing 61 is held tightly to the disc 51 by eyelets 62 thus preventing solder and solder fluxes from penetrating inside and interfering with the functioning of the spring 56. The com-- mon terminal is provided by the section 53a which has been soldered to the collector ring 67. The rotor 58 is rotated within the rings 60 by means of a shaft 63 protruding thru a center bore 50 in the front panel 66. Referring again to FIG. 9, the shaft 63 has a pair of slots 63a 180 apart, and the rotor 58 has two round pins 78 of a diameter slightly smaller than the width of the slots 63a extending into the slots 63a for entraining the rotor 58. The slight amount of play between the pins 78 and the slots 63a will have no effect on switch performance because of detented motion of the rotor 58. The expedient of pins 78 entering slots 63a can be used to control several switch assemblies 74 by a common shaft 63 which is shown in FIGS. 8, there two switches 73 are held together by means of screws (not shown) thru their respective eyelets 62. Additional switches 74 can be added to this assembly by fitting their respective pins 78 into the slots 63a of the shaft 63 and by lining the eyelets 62 of one switch 74 with those of the next switch.
What is claimed is:
1. An electric switching device comprising in combination a thin layer of electrically conducting metal laininated to an insulating baseboard divided into at least one array of uniformly sized and spaced contact segments insulated from each other by narrow separations extending the entire thickness of the metal down to the insulating baseboard at least one of said separations being contiguous to all the contact segments in said array; a contact member including at least one spring, the end of which forms contact surfaces located astride and movable along the center line of said contiguous separation in physicial engagement with said metal on either side thereof; a housing for enclosing said contact member; an actuator accessible from outside of said housing for displacing said contact member along the contiguous separation; a detent mechanism for moving the contact member in steps corresponding to the spacing of said contact segments and for positioning said contact member at each step in the center of a respective contact segment; and means for making external connections to said individual contact segments and to said contact member.
2. The combination according to claim 1 wherein (the) said contact segments are located on either side of said contiguous separations, are of even height and wherein an electrical connection is made between consecutive pairs of segments as result of movement of the spring contact member.
3. The combination according to claim 1 wherein said contact segments are on one side of said contiguous separation; a continuous collector strip on the other side thereof; wherein said contact segments and said collector strip are of even height; and wherein selected contact segments are connected to said collector strip as result of movement of said spring contact memher.
4. The combination according to claim 3 wherein said contact member is conducting helical spring.
5. The combination according to claim 4, including a guide means in said housing for guiding the contact member along said contiguous separation.
6. The combination according to claim 5 where said guide means is straight slot in said housing and wherein said contact segments and the separations contiguous to the segments extend parallelly to the slot.
7. The combination according-to claim 5, wherein said guide means is a round bore in the center of said housing and wherien said contact segments and the separation contiguous to said segments extend in a circle.
8. The combination according to claim 5 including a printed tape readout, said housing having a window, a printed tape attached to the contact member and guide means for guiding the tape under said window relative to displacement of said contact member.
9. The combination according to claim 1, wherein said contiguous separation is air.
10. The combination according to claim 1 wherein said contiguous separation is a non-conducting plastic of height coextensive with said contact segments.
11. Structure in accordance with claim 1, wherein the separation between adjacent contact segments is non-conducting plastic.
12. Ari electric switching device comprising in combination a pair of contact surfaces of even height separated electrically from one another by a narrow separation; an electrically conducting spring located astride said separation having an outside diameter larger than the width of said separation; means for pressing (the) said spring against both contact surfaces for the purpose of electrically connecting them and externally accessible actuator means for moving said spring and for breaking the electrical connection between said surfaces.
13. The combination according to claim 12, whereby one of said contact surfaces comprises a plurality of uniformly sized and spaced, mutually insulated continuous tabs, and whereby the other of said contact surfaces is a continuous collector strip contiguous to the tabs.
14. The combination according to claim 13, including a detent mechanism for positioning said spring in the center of respective tabs; a housing for enclosing said spring, contact surfaces and detent mechanism; guide means in said housing for guiding said spring alongside the path of insulation in conductive engagement with both contact surfaces; indicator means for determining the position of said actuator, and externally accessible terminals connected electrically to respective contact tabs and said collector strip.
15. A device according to claim 14, where both contact surfaces are a part of a baseboard comprising insulator and conductor plates bonded together; whereby the conductor plate is divided by grooves of even height defining mutually insulated contacts.
16. A device according to claim 15 wherein the guide means is a straight slot in the housing, wherein the con-