GB1592283A - Switch contact mechanism for a calculator type keyboard - Google Patents

Description

(54) SWITCH CONTACT MECHANISM FOR A CALCULATOR TYPE KEYBOARD (71) We, RCA CORPORATION, a Corporation organized under the laws of the State of Delaware, United States of America, of 30 Rockefeller Plaza, City and State of New York, 10020, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to switch contact mechanisms for calculator type keyboards. Calculator type keyboards are utilized for a variety of computation and control functions. For example, they have been utilized in a television receiver to permit a viewer to select a particular channel and control such functions as volume, color and tint. Such an application is described in the "XL-100 Color Television-The CTC-74 and CTC-8 1 Chassis" training manual published by the RCA Corporation, Indianapolis, Indiana.

A calculator type keyboard includes an array of push buttons. Typically each push button corresponds to a decimal digit or command. It is often desired that a calculator type keyboard include switch contact mechanisms which are capable of directly converting decimal digits and commands into binary coded representations rather than indirectly by means of a logic circuit encoder so as to simplify its structure and reduce its cost. To directly encode all the decimal digits from 0 to 9 in, for example, the well-known and often employed binary coded decimal (BCD) format, it is necessary that at least one of the switch contact mechanisms associated with decimal digits be capable of actuating at least three contact closures when it is operated. In addition, it may be desirable to provide a contact which is closed after the closures of the code contacts in order to generate a signal signifying that data has been correctly entered and is ready for further processing.

Further, it is desirable that a push-button switch contact mechanism with direct encoding features be capable of being simply and economically manufactured and incorporated in a calculator type keyboard, provide a tactile indication of its operation to an operator, and include self-cleaning contacts.

Where the contact elements comprise flat surfaces which contact each other without a wiping action, it may be necessary to coat their surfaces with a precious metal such as gold or silver. This is costly. Furthermore, even with such a coating, should foreign matter become lodged between the surfaces ,of the two contact elements, no contact closure will occur because there is no wiping action available to dislodge the foreign matter.

So that foreign matter cannot readily be lodged between two contact surfaces, one of the contact surfaces may be provided with a raised portion. A switch contact mechanism including a contact with a raised portion is described, for example, in United States Patent 3,886,341. However, because of the manner in which these raised portions are formed, e.g., by bending or otherwise deforming a separate piece of metal, they cannot be readily employed with contacts which comprise conductors of a printed circuit board.

United States Patent 3,952,174 discloses an array of solid concave disks, each connected to a thin sheet of conductive material so that they may readily be incorporated into a keyboard. As a disk is depressed it deflects in an "oil-canning" action thereby providing an operator with a tactile indication of its operation. However, because these switch mechanisms are arranged to make contact with only a single conductor, they are not useful for direct binary encoding. Furthermore, because the only motion permitted by the solid disk is along its axis, this switch mechanism does not provide a self-cleaning action.

United States patent 3,941,964 issued in the name of Alan C. Yoder on March 2, 1976 discloses a calculator type keyboard with individually mounted push-button switch mechanisms which, it is there stated, may be utilized to generate binary coded signals. Each switch mechanism includes a snap action diaphragm switch element having a center contact dimple with outward extending leg members and contact portions inwardly positioned with respect to the leg members. In order to support the diaphragm and provide code contacts at least some of the leg members of each switch mechanism engage terminal pads on the surface of an insulative board. When the switch mechanism is operated the normally opened contact portions are closed and code signals are applied to the terminal pads which engage the leg members. Therefore, to prevent the erroneous application of code signals to the terminal pads which engage leg members of other switch members, each switch mechanism must be electrically isolated from the others and cannot be connected by a common web member. Because the switch mechanisms of the Yoder patent are separate units, they require individual placement and therefore are not well suited to being readily and quickly incorporated in a keyboard.

Moreover, because in Yoder the legs are not part of the snap action diaphragm and are unsupported by a surrounding web, they do not contribute to any oil-canning effect. Still further, the oil canning deflection of the snap action diaphragm itself is inhibited by the center contact dimple.

In accordance with the present invention, a switch apparatus which may be utilized in a calculator type keyboard and which can be designed to have an "oil-canning" action comprises a generally planar conductive web, a dielectric board carrying contact pads, and an intermediate dielectric spacer.

At least one switch contact mechanism formed as an integral part of said web includes support arms extending inwardly from the periphery of an aperture in the web to intersect in a crisscross configuration. A portion only of said crisscross configuration is contoured away from the plane of the web in a dome-like shape so that portions of said support arms lie in the plane of the web.

Contact blades extend outwardly from the intersection of said support arms, with bridge members connecting the outer ends of said contact blades to adjacent portions of said support arms. The dielectric substrate has at least one group of conductor pads, which are respectively in general alignment with the outer ends of the contact blades of the switch contact mechanism. The dielectric spacer has at least one aperture in general alignment with the web aperture and dimensioned so that the planar portions of said support arms extend over the periphery of the aperture of said spacer. The thickness of the spacer is such that the outer ends of said contact blades can engage their respective conductor pads upon depression of said dome-like portion.

In the accompanying drawings: Figure 1 is an exploded isometric view of a portion of a calculator type keyboard embodying switch contact mechanisms constructed in accordance with the present invention; Figure la is a detail view of a portion of the switch contact mechanism of Figure 1; Figure lb is an exploded detail view of a portion of a contact structure which may be employed in the switch contact mechanism of Figure 1; Figure Ic is a cross-sectional view taken along the line A-A of the contact structure of Figure Ib; Figures 2a, 2b, 2c, 3a, 3b, 3c, 4a, 4b and 4c are cross-sectional views of the switch contact mechanism and associated portions of the keyboard of Figure 1 in various operating positions; Figure 5 is a table indicating the binary coded representations produced by the operation of various switch contact mechanisms of Figure 1; and Figures 6 and 7 are detail and crosssectional views of various other contact structures which may be employed in the switch contact mechanism of Figure 1.

In the keyboard of Figure 1, three apertures 10a, lOb and 10c are provided through a body 12 for three push buttons (not shown). For clarity of drawing, only urging shafts 14a, 14b and 14c of the push buttons are shown. A flexible fluid and dust shield 16 is located beneath body 12 having guide holes 18a, 18b, 18c and 18d in axial alignment with guide pins 20a, 20b, 20c and 20d. Beneath fluid and dust shield 16 there is located a conductive web 22 partitioned into an array of switch contact mechanisms 24a, 24b and 24c. Each switch contact mechanism 24a, 24b and 24c is axially aligned with urging shafts 14a, 14b and 14c.

Web 22 also includes guide holes 26a, 26b, 26c and 26d in axial alignment with guide pins 20a, 20b, 20c and 20d. Beneath web 22 there is located a nonconductive spacer 28 having apertures 30a, 30b and 30c in general alignment with switch contact mechanism 24a, 24b and 24c. Spacer 28 also includes guide holes 32a, 32b, 32c and 32d in axial alignment with guide pins 20a, 20b, 20c and 20d. Beneath spacer 28 there is located a circuit board 34 comprising a dielectric material 36 upon which are formed conductors ending in contact pads arranged in groups 38a, 38b and 38c in general alignment with switch contact mechanisms 24a, 24b and 24c of conductive web 22.

Circuit board 34 includes guide holes 40a, 40b, 40c and 40d in axial alignement with guide pins 20a, 20b, 20c and 20d. Guide pins 20a, 20b, 20c and 20d have ends 42a, 42b, 42c and 42d, the bottom tips of which fit into guide holes 40a, 40b, 40c and 40d of circuit board 34. The length of the ends 42a, 42b, 42c and 42d of guide pins 20a, 20b, 20c and 20d are selected so that conductive web 22 and spacer 28 are snugly but not immovably held between the bottom ends of guide pins 20a, 20b, 20c and 20d and the top surface of circuit board 34 for the reasons set forth below.

Although body 12 includes walls and other support members which form the complete structure of the keyboard, these portions have been omitted from Figure 1 to more clearly show the present switch contact mechanism.

Because each of the switch contact mechanisms 24a, 24b and 24c are identical, only switch contact mechanism 24a and its associated contact pad group 38a will be described in detail. Concurrent reference to Figures 1 and la should now be made.

Switch contact mechanism 24a includes support arms 44a and 44b which extend diagonally inward from the corners of the periphery 46 of a square cutout portion of web 22 and intersect in a crisscross configuration. The intersection of support arms 44a and 44b is in axial alignment with shaft 14a. A portion 45 of the crisscross configuration inward of periphery 46 of the cutout portion is contoured to form a domelike shape, the extent of which is defined by a border 60. The remaining portions of support arms 44a and 44b lie in the plane of web 22. Contact blades or fingers 48a, 48b, 48c and 48d extend radially outward from the intersection of support arms 44a and 44b between adjacent portions thereof. The outer ends of contact blades 48a, 48b, 48c and 48d are connected by bridge members 50 to the portions of support arms 44a and 44b adjacent them. The tips of contact blades 48a, 48b, 48c and 48d extend slightly beyond bridge members 50. Contact points or dimples 62a, 62b, 62c and 62d directed downwardly toward circuit board 34, are formed on the tips of contact blades 48a, 48b, 48c and 48d.

Referring now to Figures 1 and lb, associated contact pad group 38a is comprised of contact pads 54a, 54b, 54c and 54d in alignment with contact points 62a, 62b, 62c and 62b of contact blades 48a, 48b, 48c and 48d of switch contact mechanism 24a and a center contact pad 56 in alignment with the apex of the dome-like shape 45 of switch contact mechanism 24a.

The conductors may be formed in a variety of wellknown ways. For example, printed conductors may be formed by chemically removing conductor material from a conductor (e.g., copper) clad dielectric board in predetermined areas where the conductor material is not protected by a solvent resistant coating previously printed on the board in accordance with a mask. The printed conductors may also be made by an additive process whereby conductor material (e.g., copper) is chemically or electrochemically deposited on an unclad dielectric board in predetermined areas previously printed on the board in accordance with a mask.

A crater-like depression 74 with a raised rim 76 is formed in center conductor pad 56 by striking conductor pad 56 with a punch having a generally spherical head. As is seen in the cross-sectional view of Figure Ic, taken in the direction of section lines A-A of Figure lb, the punch is struck with sufficient force so that as the conductor and dielectric material at the center of the crater 74 is forced downward, surrounding conductor and dielectric material is displaced upward to form rim 76 having a relatively sharp edge above the surface of conductor 56.

The operation of the switch contact mechanism 24a will best be understood by reference to Figures 2a-2c, 3a-3c and 4a--4e which are cross-sectional views taken in the direction of section lines 2-2, 3-3 and 44 of Figure la. It will be understood that shaft 14a is depressed to various degrees to provide the deflections shown in Figures 2a-2c, 3a-3c and 4a 4c. In Figures 2a, 3a and 4a, the normal or rest position of switch contact mechanism 24a is shown. In Figures 2b, 3b and 4b switch contact mechanism 24a is shown after the application of a force sufficient to bring contact blades 48a--48d into contact with conductor pads 54a-54d. Contact points 62a-62d of contact blades 48a-48d make contact with conductor pads 54a-54d essentially at the same time. This is so because bridge members 50 insure that contact blades 48and move downward toward circuit board 34 together. To further enhance this uniformity of contact closure, periphery 60 of dome-like portion 45 is radially inward from periphery 46 of the cutout portion of the web 22 from which support arms 44a and 44b extend inwardly.

Periphery 46 of the cutout portion of web 22 is substantially juxtaposed with periphery 66 of aperture 30a of spacer 28. Therefore, support arms 44a and 44b are able to bend at periphery 46. As a result, contact blades 48a48d come into contact with conductor pads 54a--54d before there is any significant "oil canning" deflection of dome-like portion 45 of switch contact mechanism 24a, as will be explained, which may otherwise prevent one or more of contact blades 48a48d from making contact with its respective contact pad 54a-54d.

While it may be thought that the spoked wheel-like structure of switch contact mechanism 24a may be completely filled in with material to form a solid dome with contact blades extending from its periphery, it has been found in such a solid configuration that one or more of the contact blades can lift from its respective contact pad while other contact blades are still in contact with their respective contact pads because of its rigidity. This may be understood by considering the difficulty of trying to balance a four legged table with uneven legs.

Figures 2c, 3c and 4c show the position of switch contact mechanism 24a when it is fully depressed. It is shown that the apex of dome-like portions 45 is in contact with the raised rim 76 of crater-like depression 76 of center conductor pad 56. At this point of the operation, the apex of the dome-like portion has passed through the plane of the top surface of spacer 28 thereby producing an "oil canning" effect. The "oil canning" takes place after contact blades 48a48d have made contact with conductor pads 54a-54d. As switch contact mechanism 24a is further depressed, dome-like portion 45 trys to flatten out causing support arms 44and to be forced outwardly away from the apex. This causes web 22 to try to expand. However, since web 22 is constrained in the form of a closed loop by end portions 68 and 70, it cannot expand and instead deflects into a reverse curvature contour along with dome-like portion 45 to produce an "oil canning" effect as shown in Figures 2c, 3c and 4c. When the "oil canning" takes place, the operator feels a sudden release of the stresses in switch mechanism 24a, sometimes called a "snap action", at his fingertip providing him with a tactile indication that the switching action is taking place.

It has been found desirable to enhance the "oil canning" effect, to permit end Dortions 68 and 70 of switch contact mechanisms 24a, 24b and 24c to lift up slightly, as shown in Figure 2c, 3c and 4c, when switch contact mechanisms 24a, 24b and 24c are depressed. To this end, in the embodiment of Figure 1, guide holes 26a26d of web 22 are located in the center of the areas on each side of switches 24a, 24b and 24c to receive guide pins 20a-20d so that end portion 68 of web 22 can lift up during the operation of switch contact mechanisms 24a, 24b and 24c. Furthermore, guide pins 20a-20d are dimensioned so that their end portions 42a-42d allow end portions 70 of web 22 to move slightly in the vertical direction.

To provide some degree of mechanical isolation between switch contact mechanism 24a, 24b and 24c without completely separating them, cutouts 58 are desirably located at the ends of the boundary lines between switch contact mechanisms 24a, 24b and 24c. Completely separated switch contact mechanisms are undesirable since they require individual manufacture and placement thereby increasing the cost of the keyboard.

Moreover, separate switch contact mechanisms may become dislodged requiring the keyboard to be repaired.

Because of cutouts 58, the respective outer portions 68 of web 22 bordering each switch contact mechanism 24a, 24b and 24c may separately lift up during its operation without interference from the structure of the adjacent switch contact mechanism.

Figures 2c, 3c and 4c also show that contact blades 48a-48d have been maintained in contact with contact pads 54a-54d although contact points 62an624.

of contact blades 48a-48d have been longitudinally moved with respect to their positions shown in Figures 2b, 3b and 4b across the surfaces of pads 54a-54d. This longitudinal movement cleans the contact areas and insures.relatively low electrical contact resistances for a relatively large number of switch operations. Furthermore, by comparing Figures 2c, 3c and 4c with Figures 2b, 3b and 4b, it is seen that a last contact, i.e., the one associated with center conducto'r pad 56, is closed only after the closure of all the other contacts. Such an arrangement is desirable since it may be utilized to generate a flag signal indicating that all other contacts are closed, in response to which data can be reliably entered. Although there is no wiping action available to clean the contact areas of the apex of the dome-like shape and conductor.

pad 56, these contact areas remain relatively clean because foreign matter such as a dirt particle cannot readily be supported by the relatively sharp edge of rim 76.

Furthermore, with a given amount of pressure, the relatively sharp edge of rim 76 provides a relatively low contact resistance in comparison with the broader areas of flat or smoothly curved contact surfaces conventionally employed because of the relatively greater unit pressure, i.e.

pressure per unit of area, associated with rim 76, in addition to the performance advantages of crater-like contact 74, it is noted that it is simply and economically formed in the manner set forth above without having to deform and then mount a separate conductor.

Bridge members 50 are dimensioned so that they are rigid enough to insure that all of the contact blades 48a48d make and maintain contact with conductor pads 54a54d before the apex of the dome-like shape makes contact with center conductor pad 56, yet flexible enough to permit contact points 62a-62d to wipe across conductor pads 54a-54d.

Although the switch contact mechanisms of web 22 are arranged in a row array, a rectangular array of switch contact mechanisms may also be constructed in accordance with the present invention. In this case, it is desirable that cutouts similar to 58 be located at the ends of the boundaries between switch contact mechanisms in the row direction as well as in the column direction.

The table of Figure 5 indicates a format of binary signals which may be used to encode the decimal digits between 0 and 9. An "X" represents a contact closure between a contact of a switch contact mechanism and a respective conductor. Conductors A, B, C and D are associated with particular BCD code positions: A with 20=1; B with 21=2; C with 22=4; and D with 23=8. Up to 3 of the conductors A, B, C and D may be positioned to be contacted by contact blades of a switch contact mechanism.

Conductor G is coupled to a source of fixed potential such as ground or +5 VDC and is positioned to be contacted by at least one contact blade of a switch contact mechanism. Conductor F is associated with the generation of a flag signal to indicate that all of the contact blades of a switch contact mechanism have made contact with their respective conductors so that data may be entered and is positioned to be contacted by the apex of the dome-like shape.

Assuming that switch contact mechanism 24a corresponds to decimal digit 5, switch contact mechanism 24b corresponds to decimal digit 6 and switch contact mechanism 24c corresponds to decimal digit 7, conductors A, B, C, D, F and G may be arranged as shown in Figure 1 to provide the BCD and flag signals for the decimal digits 5, 6 and 7. With this arrangement, assuming that conductor G is coupled to +5 VDC, when switch contact mechanism 24a is depressed, + 5VDC level (i.e., a logic "high") is applied to conductors A and C.

Thereafter, when the apex of dome-like portion 45 contacts center conductor 56, a flag signal is generated.

It will be noted that because the fixed potential is applied to the BCD code conductors upon the closure of an appropriate conductor blade and conductor G, it is not necessary to wire web 22 to the source of fixed potential, thereby reducing the discrete wiring utilized in the keyboard.

Under these conditions, only three contact blades are available for generating the BCD signals. However, since only a maximum of three closures (for decimal digit 7) are needed to represent the decimal digits in BCD format, this is satisfactory. Should it be desired to additionally generate signals representing the decimal digits from 10 to 16, the contact blade associated with conductor G could be used as a fourth code contact blade. In this case, web 22 should be wired to the source of fixed potential.

In Figures 6 and 7 there are shown other contact structures having crater-like portions with the performance and manufacturing advantages set forth with respect to crater-like contact 74 of Figures 1 and lb. In Figure 6 and Figure 6a, which is a cross-sectional view taken in the direction of section lines A-A of Figure 6, there is shown a crater-like contact structure 74 formed by striking conductor pad 56 with a punch having a chisel type head with sufficient force so that as a depression below the surface of conductor pad 56 is produced, conductor and dielectric material is upwardly displaced to produce knife-like edge 68 above the surface of conductor pad 56. By altering the force and the shape of the chisel head of the punch, two knife-like contact edges may be produced. In Figures 7 and 7a, there is shown a star-like contact structure having a plurality of radially disposed crater-like depressions each of which has a raised knife-like contact edge 78. This contact structure may be formed by striking conductor pad 56 with a punch having a plurality of radially disposed chisel members at its head.

WHAT WE CLAIM IS: 1. A switch apparatus comprising: a generally planar conductive web; at least one switch contact mechanism formed as an integral part of said web including support arms extending inwardly from the periphery of an aperture in the web to intersect in a crisscross configuration; a portion only of said crisscross configuration being contoured away from the plane of the web in a dome-like shape so that portions of said support arms lie in the plane of said web; contact blades extending outwardly from the intersection of said support arms; and bridge members connecting the outer ends of said contact blades to adjacent portions of said support arms; a dielectric board having at least one group of contact pads, the pads of said group being respectively in general alignment with the outer ends of the contact blades of said switch contact mechanism; and

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (18)

**WARNING** start of CLMS field may overlap end of DESC **. without having to deform and then mount a separate conductor. Bridge members 50 are dimensioned so that they are rigid enough to insure that all of the contact blades 48a48d make and maintain contact with conductor pads 54a54d before the apex of the dome-like shape makes contact with center conductor pad 56, yet flexible enough to permit contact points 62a-62d to wipe across conductor pads 54a-54d. Although the switch contact mechanisms of web 22 are arranged in a row array, a rectangular array of switch contact mechanisms may also be constructed in accordance with the present invention. In this case, it is desirable that cutouts similar to 58 be located at the ends of the boundaries between switch contact mechanisms in the row direction as well as in the column direction. The table of Figure 5 indicates a format of binary signals which may be used to encode the decimal digits between 0 and 9. An "X" represents a contact closure between a contact of a switch contact mechanism and a respective conductor. Conductors A, B, C and D are associated with particular BCD code positions: A with 20=1; B with 21=2; C with 22=4; and D with 23=8. Up to 3 of the conductors A, B, C and D may be positioned to be contacted by contact blades of a switch contact mechanism. Conductor G is coupled to a source of fixed potential such as ground or +5 VDC and is positioned to be contacted by at least one contact blade of a switch contact mechanism. Conductor F is associated with the generation of a flag signal to indicate that all of the contact blades of a switch contact mechanism have made contact with their respective conductors so that data may be entered and is positioned to be contacted by the apex of the dome-like shape. Assuming that switch contact mechanism 24a corresponds to decimal digit 5, switch contact mechanism 24b corresponds to decimal digit 6 and switch contact mechanism 24c corresponds to decimal digit 7, conductors A, B, C, D, F and G may be arranged as shown in Figure 1 to provide the BCD and flag signals for the decimal digits 5, 6 and 7. With this arrangement, assuming that conductor G is coupled to +5 VDC, when switch contact mechanism 24a is depressed, + 5VDC level (i.e., a logic "high") is applied to conductors A and C. Thereafter, when the apex of dome-like portion 45 contacts center conductor 56, a flag signal is generated. It will be noted that because the fixed potential is applied to the BCD code conductors upon the closure of an appropriate conductor blade and conductor G, it is not necessary to wire web 22 to the source of fixed potential, thereby reducing the discrete wiring utilized in the keyboard. Under these conditions, only three contact blades are available for generating the BCD signals. However, since only a maximum of three closures (for decimal digit 7) are needed to represent the decimal digits in BCD format, this is satisfactory. Should it be desired to additionally generate signals representing the decimal digits from 10 to 16, the contact blade associated with conductor G could be used as a fourth code contact blade. In this case, web 22 should be wired to the source of fixed potential. In Figures 6 and 7 there are shown other contact structures having crater-like portions with the performance and manufacturing advantages set forth with respect to crater-like contact 74 of Figures 1 and lb. In Figure 6 and Figure 6a, which is a cross-sectional view taken in the direction of section lines A-A of Figure 6, there is shown a crater-like contact structure 74 formed by striking conductor pad 56 with a punch having a chisel type head with sufficient force so that as a depression below the surface of conductor pad 56 is produced, conductor and dielectric material is upwardly displaced to produce knife-like edge 68 above the surface of conductor pad 56. By altering the force and the shape of the chisel head of the punch, two knife-like contact edges may be produced. In Figures 7 and 7a, there is shown a star-like contact structure having a plurality of radially disposed crater-like depressions each of which has a raised knife-like contact edge 78. This contact structure may be formed by striking conductor pad 56 with a punch having a plurality of radially disposed chisel members at its head. WHAT WE CLAIM IS:

1. A switch apparatus comprising: a generally planar conductive web; at least one switch contact mechanism formed as an integral part of said web including support arms extending inwardly from the periphery of an aperture in the web to intersect in a crisscross configuration; a portion only of said crisscross configuration being contoured away from the plane of the web in a dome-like shape so that portions of said support arms lie in the plane of said web; contact blades extending outwardly from the intersection of said support arms; and bridge members connecting the outer ends of said contact blades to adjacent portions of said support arms; a dielectric board having at least one group of contact pads, the pads of said group being respectively in general alignment with the outer ends of the contact blades of said switch contact mechanism; and

a dielectric spacer located between said web and said board and having at least one aperture in general alignment with the aperture of said web and dimensioned so that the planar portions of said support arms extend over the periphery of the aperture of said spacer, the thickness of said spacer being such that the outer ends of said contact blades can engage their respective conductor pads upon depression of said dome-like portion.

2. Apparatus as recited in Claim 1 wherein said web includes an array of at least two of said switch contact mechanisms co-operating with a like number of contact pad groups on said dielectric board, said switch contact mechanisms being partitioned from one another by a boundary area having ends terminating in a cutout portion of said' web so as to provide a degree of mechanical isolation between said switch contact mechanisms.

3. Apparatus as recited in Claim 2 wherein holding means are located between said switch contact mechanisms in said boundary area.

4. Apparatus as recited in Claim 3 wherein said holding means snugly but not immovably holds said web in contact with said spacer so that said web may move slightly in a direction generally perpendicular to the plane of said board during the operation of said switch contact mechanism.

5. Apparatus as recited in Claim 3 or 4 wherein said holding means includes a guide pin extending in a generally perpendicular direction from said board to be received by a guide hole located in said web between said switch contact mechanisms, said guide pin having a portion with a length dimensioned to permit movement of said web in a predetermined range in the direction of the axis of said guide pin.

6. Apparatus as recited in any preceding Claim wherein contact points are formed in the outer ends of said contact blades.

7. Apparatus as recited in any preceding Claim wherein at least one of said contact pads in the or at least one said group thereof is coupled to a conductor for carrying a binary code signal.

8. Apparatus as recited in any preceding Claim wherein one of said contact pads in the or at least one group thereof is available for coupling to a source of fixed potential.

9. Apparatus as recited in any preceding Claim wherein the or at least one said group of contact pads has a center contact pad in alignment with the apex of and contactable by said dome-like shaped portion of the cooperating contact mechanism.

10. Apparatus as recited in Claim 8 wherein said center contact pad is coupled to a conductor for carrying a flag signal in response to that pad being contacted by the dome-like shaped portion of the cooperating switching mechanism, said flag signal indicating that all of said contact blades of that mechanism have made contact with their respective contact pads.

11. Apparatus as recited in Claim 9 or 10 wherein a crater-like depression is formed in said center contact pad with a raised edge portion above the surface of said conductor to form a fixed contact member having a relatively sharp contact area.

12. Apparatus as recited in Claim 11 wherein said edge portion is a generally circular rim.

13. Apparatus as recited in Claim 11 wherein said edge portion is generally straight.

14. Apparatus as recited in Claim 11 wherein said raised edge portion comprises a plurality of straight edges radially disposed to form a star-like pattern.

15. Apparatus as recited in any of Claims 11--14 wherein said center contact pad comprises a conductor formed on the dielectric board and punched with sufficient force to produce said crater-like depression and raised edge portion.

16. Apparatus as recited in any of Claims 11--15 wherein the apex of said dome-like shaped portion is positioned to contact said edge portion.

17. Apparatus as recited in any of Claims 11--16 wherein said dielectric board includes at least a second conductor positioned to be contacted by one of said contact blades before said edge portion is contacted.

18. A switch apparatus substantially as hereinbefore described with reference to the accompanying drawings.