U.S. patent number 3,796,843 [Application Number 05/320,147] was granted by the patent office on 1974-03-12 for calculator keyboard switch with disc spring contact and printed circuit board.
This patent grant is currently assigned to Bomar Instrument Corporation. Invention is credited to Gilbert H. Durkee, Per G. Wareberg, Alan C. Yoder.
United States Patent |
3,796,843 |
Durkee , et al. |
March 12, 1974 |
**Please see images for:
( Certificate of Correction ) ** |
CALCULATOR KEYBOARD SWITCH WITH DISC SPRING CONTACT AND PRINTED
CIRCUIT BOARD
Abstract
A keyboard switch assembly including a printed circuit board
having four switch terminals on one side of the board, three of the
terminals being arranged in a triangle and the fourth disposed
within the triangle. Conductors on the one side of the board are
respectively joined to the interior terminal and at least one of
the three terminals. A conductive, generally triangular,
snap-acting dome switch member is provided having arcuate apices,
projections being respectively formed from the apices and
respectively engaging the three terminals thereby spacing the
periphery of the switch element from the one surface of the printed
circuit board and the conductors thereon, at least the conductor
connected to the interior terminal extending under the dome. The
switch element has a fourth protection formed from the interior of
the dome adjacent the center thereof which is in registry with the
interior terminal and engages that terminal when the dome is
deflected thereby completing an electrical circuit between the
three terminals and the interior terminal. A layer of insulating
material covers the conductors exclusive of the terminals. A sheet
of insulating material covers the insulating layer and has an
opening therein which receives and locates the switch member.
Another sheet of insulating material covers the first sheet and the
switch member. A plate covers the second insulating sheet and has
an opening therein which receives a push button in registry with
the switch element, depression of the push button actuating the
dome of the switch member to a non-overcenter, deflected position
in which the interior projection on the dome engages the interior
switch terminal.
Inventors: |
Durkee; Gilbert H. (Fort Wayne,
IN), Wareberg; Per G. (Fort Wayne, IN), Yoder; Alan
C. (Fort Wayne, IN) |
Assignee: |
Bomar Instrument Corporation
(Ft. Wayne, IN)
|
Family
ID: |
23245080 |
Appl.
No.: |
05/320,147 |
Filed: |
January 2, 1973 |
Current U.S.
Class: |
200/5A; 200/279;
200/513 |
Current CPC
Class: |
H01H
13/785 (20130101); H01H 13/7006 (20130101); H01H
2231/002 (20130101); H01H 2227/026 (20130101); H01H
2209/032 (20130101); H01H 2203/04 (20130101); H01H
2201/026 (20130101); H01H 2229/016 (20130101); H01H
2203/042 (20130101); H01H 2205/024 (20130101); H01H
2229/026 (20130101); H01H 2229/014 (20130101) |
Current International
Class: |
H01H
13/70 (20060101); H01h 013/52 () |
Field of
Search: |
;200/1R,5R,5A,52R,DIG.1,159R,159B,166BH ;340/365A |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Scott; James R.
Claims
1. In a keyboard switch assembly including a push button manually
actuable from an inactive to a switch-actuating position, and a
conductive switch member including a resilient element actuated by
said push button from a normal to a deflected position and
resiliently returning to its normal position upon removal of force
from said bush button, the improvement comprising an insulative
board having opposite surfaces, one only of said surfaces having
first and second elongated conductors thereon, said first conductor
including a first switch terminal portion and said second conductor
including a second switch terminal portion, said conductors and
terminal portions being generally coplanar, said switch element
being positioned in facing relationship with said one surface and
said conductors, said switch element having first and second spaced
contact areas thereon, said first contact area engaging said first
terminal portion, said second contact area being in registry with
said second terminal portion and engaging the same when said
element is in said deflected position thereby electrically
connecting said first and second terminal portions, and mean for
holding said push button, switch member
2. The assembly of claim 1 further comprising a layer of
insulating
3. The assembly of claim 2 wherein said element is a snap-acting
dome, said second contact area being at the center of said dome,
said one surface of said board having a third conductor thereon at
least partially surrounding said second terminal portion, closely
spaced therefrom and generally coplanar therewith, the area of said
dome surrounding said second contact area engaging the insulation
covering said third conductor upon further deflection of said dome
following engagement of said second contact area with said second
terminal portion thereby to protect said second contact
4. The assembly of claim 1 wherein said one surface of said board
has at least a third conductor thereon intermediate and spaced from
said first and second conductors and generally coplanar therewith,
said third conductor extending under said element from a location
on said one surface remote therefrom, said element in its deflected
position being spaced from said third conductor, there being no
electrical connection between said
5. The assembly of claim 4 wherein said element is a snap-acting
dome, said second contact area being at the center of said dome,
said third conductor being intermediate said first and second
terminal portions and generally
6. The assembly of claim 1 wherein said one surface of said board
has a third conductor thereon at least partially surrounding said
second terminal portion, spaced therefrom and generally coplanar
therewith, the area of said element surrounding said second contact
area engaging said third conductor upon further deflection of said
element following engagement of said second contact with said
second terminal portion
7. The assembly of claim 1 wherein a section of at least said
second conductor extends under said element from a location on said
one surface
8. The assembly of claim 1 wherein said element is a snap-acting
dome, said
9. The assembly of claim 8 wherein said second contact area
comprises a
10. The assembly of claim 8 further comprising third, fourth and
fifth switch terminals on said one surface of said board, said
third through fifth terminals and said first terminal portion being
arranged in a rectangle with said second terminal portion in the
interior therof, said first contact area comprising a first
projection formed from said dome adjacent the periphery thereof,
said dome having second, third and fourth projections formed
therefrom adjacent the periphery thereof and respectively engaging
said third, fourth and fifth switch terminals, said projections
spacing the periphery of said dome from said one surface of said
board and said conductor, said second contact area comprising a
fifth
11. The assembly of claim 10 wherein said switch element is
generally rectangular with arcuate corners coaxial with the center
of said dome,
12. The assembly of claim 8 wherein said first contact area
comprises a projection on said switch element spacing the periphery
of said dome from
13. The assembly of claim 12 wherein said projection is formed from
said
14. The assembly of claim 13 wherein said switch member includes a
flat portion joined to the periphery of said dome, said projection
being formed
15. The assembly of claim 8 further comprising third and fourth
switch terminals on said one surface of said board, said third and
fourth terminals and said first terminal portion being arranged in
a triangle with said second terminal portion in the interior
thereof, said first contact area comprising a first projection
formed from said dome adjacent the periphery thereof, said dome
having second and third projections formed therefrom adjacent the
periphery thereof and respectively engaging said third and fourth
switch terminals, said projections spacing the periphery of said
dome from said one surface of said board and said conductors, said
second contact area comprising a fourth projection formed
16. The assembly of claim 15 wherein said switch element generally
triangular with arcuate apices coaxial with the center of said
dome, said
17. The assembly of claim 16 wherein said holding means comprises a
layer of insulating material covering said conductors excluding
said terminal portions and terminals, a first sheet of insulating
material covering said layer and having an opening therein
receiving said switch element and conforming thereto for locating
the same, a second sheet of insulating material covering said first
sheet and switch element, and a plate member covering said second
sheet and having an opening therein receiving said push button,
said push button acting on said dome through said second
18. The assembly of claim 16 wherein a section of at least said
second conductor extends under said dome from a location on said
one surface remote therefrom, said one surface of said board having
a third conductor thereon at least partially surrounding said
second terminal portion, spaced thereon and generally coplanar
therewith, said conductors exclusive of said terminal portions
having a layer of insulating material thereon, the area of said
dome surrounding said fourth projection engaging the insulation
covering said third conductor upon further deflection of said dome
following engagement of said second contact area with said
second
19. The assembly of claim 18 wherein said third conductor
completely surrounds said second terminal portion and is joined to
said second
20. The assembly of claim 18 wherein said third conductor partially
surrounds said second terminal portion and is joined to a fourth
conductor
21. The assembly of claim 18 wherein said first conductor is joined
to at
22. The assembly of claim 18 wherein said board has a fourth
conductor thereon which extends under said dome.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to a keyboard switch assembly of
the type used in electronic calculator apparatus.
2. Description of the Prior Art
Keyboard switches have been provided employing a conductive
snap-acting dome member as the switch element, such keyboard
switches being shown for example in U.S. Pat. Nos. 3,643,041 and
3,684,842, German Pat. Nos. 486,212 and 1,806,241, and IBM
Technical Disclosure Bulletin No. 12, Vol. 7, May. 1965, p. 1,168
entitled "Snap-Action Membrane Switch Keyboard." Another keyboard
switch assembly of the same general type manufactured by Texas
Instruments Incorporated employes a printed circuit board having
conductors on one surface thereof, staples extending through the
board from the other surface to the one surface and being soldered
to selected conductors thereon. and snap-acting domes cooperating
with the portions of the staples on the other side of the board to
perform the switching function. Yet another type of keyboard switch
manufactured by Colorodo Instruments Corp. incorporates a printed
circuit board having conductors on both surfaces thereof, the board
having plated openings extending therethrough connected to certain
conductors, and snap-acting domes cooperating with the plated
openings to perform the switching function.
SUMMARY OF THE INVENTION
The keyboard switch assemblies of the type described above known to
the present applicants employ some combination of double sided
printed circuit boards, soldered connections, and/or a conductive
ground plate in addition to a printed circuit board, these features
complicating assembly thus adding appreciably to the cost. It is
therefore desirable to provide a keyboard switch assembly of the
general type described above which utilizes a single sided printed
circuit board and which does not require soldered connections or an
additional conductive ground plate.
The present invention, in its broader aspects, is embodied in a
keyboard switch assembly including a push button manually actuable
from an inactive to a switch-actuating position, and a conductive
switch member including a resilient element actuated by the push
button from a normal to a deflected position, and comprises an
insulative board having opposite surfaces with one of the surfaces
having first and second conductors thereon, the first conductor
including a first switch terminal portion and the second conductor
including a second switch terminal portion. The switch element
faces the one surface of the printed circuit board and the
conductors and has a first contact area thereon spaced from the
center area of the element, the first contact area engaging the
first terminal portion. The center area of the element forms a
second contact area in registry with the second terminal portion
and engaging the same when the element is in its deflected position
thereby electrically connecting the first and second terminal
portions and their respective conductors.
It is accordingly an object of the invention to provide an improved
keyboard switch assembly.
Another object of the invention is to provide an improved keyboard
switch assembly of the type employing a conductive snap-acting dome
member as the switch element.
A further object of the invention is to provide an improved
keyboard switch assembly of the type employing a snap-acting dome
member as the switch element in which a single sided printed
circuit board is utilized and soldered connections and/or
conductive ground plates are eliminated.
The abovementioned and other features and objects of this invention
and the manner of attaining them will become more apparent and the
invention itself will be best understood by reference to the
following description of an embodiment of the invention taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic illustration of a simplified, two-by-two XY
keyboard switching matrix;
FIG. 2 is a top view showing an insulative board with XY conductors
and switch terminals thereon arranged in a pattern in accordance
with the invention to provide the keyboard switch matrix of FIG.
1;
FIG. 3 is a cross-sectional view taken generally along the line
2--2 of FIG. 2 and showing the basic switching element employed in
the invention;
FIG. 4 is top view, partly broken away, showing the preferred
embodiment of the improved keyboard switch assembly of the
invention;
FIG. 5 is a cross-sectional view taken along the line 5--5 of FIG.
4;
FIG. 6 is an enlarged fragmentary view showing a portion of the
printed circuit board employed in the preferred embodiment;
FIG. 7 is a cross-sectional view taken along the line 7--7 of FIG.
6;
FIG. 8 is a top view showing the snap-acting dome switch member
employed in the preferred embodiment;
FIG. 9 is a fragmentary view showing the configuration of one of
the openings in the switch element retaining member;
FIG. 10 is a fragmentary, exploded perspective view further showing
the preferred embodiment of the invention;
FIG. 11 is a fragmentary cross-sectional view showing another
embodiment of the invention:
FIG. 12 is a top view of the switch element employed in the
embodiment of FIG. 11.
FIG. 13 is a top view of a modified form of the switch element
shown in FIGS. 11 and 12; and
FIG. 14 is a top view of a modified form of the switch element
shown in FIGS. 4-10.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In general, a keyboard switch assembly for an electronic device,
such as a calculator, can be considered to be an XY grid or matrix
of conductors with the X conductors insulated from the Y
conductors, a particular function being identified by making
electrical contact between a selected X conductor and a selected Y
conductor. Referring to FIG. 1 of the drawing, a simplified,
two-by-two switching matrix is shown comprising X.sub.1 and X.sub.2
conductors respectively insulated from Y.sub.1 and Y.sub.2
conductors, the switching functions being performed by switches
S.sub.1 - S.sub.4. It will be understood that the number of X or Y
conductors in the keyboard matrix can be any integer equal to or
larger than one, and that the number of possible switching
functions is equal to the product of the number of X conductors and
the number of Y conductors. Momentary contact push button switches
are customarily employed to make the necessary contact between the
X and Y lines.
The Texas Instruments keyboard switch assembly referred to above
employs a single sided printed circuit board with the requisite
insulation at the XY crossovers being provided by conducting
U-shaped staples extending through the board with their legs
soldered to the conductors on one side and their bight portions
engaging the other side of the board. The Colorado Instruments
keyboard switch assembly referred to employs a two-sided printed
circuit board with the X conductors on one side thereof and the Y
conductors on the other, plated through-holes being used to provide
X contacts on the same side of the board as the Y contacts. In both
of those assemblies, the printed circuit board serves as an
insulator between the X and Y conductors with staples or plated
through-holes being used to bring the X and Y contact points to the
switching side of the board.
In the keyboard switch assembly of the present invention, the
thickness of the printed circuit board is not used as an insulator
between the X and Y conductors, there being no conductors extending
through the board to provide electrical contact from one side to
the other. Referring now to FIGS. 2 and 3, in accordance with the
invention an insulative board 1 is provided having X and Y
conductors secured to the switching side thereof, the conductors
being arranged in a pattern and having terminal portions 2, 3
arranged to cooperate with the respective switching elements S so
as to make contact between selected X and Y conductors without
touching other conductors.
Switching elements S are formed of conductive, resilient material,
each switching element S having edge or peripheral contact areas 5
engaging one or more Y terminal portions 2 and having a normal
position, as shown in solid lines in FIG. 3, with it center contact
area 6 spaced from a respective X terminal portion 3, switching
element 4 also being spaced from other X and/or Y conductors, as
shown. Upon application of a downward force on switching element 4,
as shown by arrow 7, such as that applied by manual actuation of a
push button, switching element 4 is deflected to a position as
shown in dashed lines at 4a with its center contact area 6 making
contact with a respective X terminal portion 3 thus electrically
connecting the respective X and Y conductors. It will be observed
that in its deflected position, switching switching element 4 does
not contact the other conductors, such as conductors Y.sub.1
therebeneath. Upon release of the downward force 7, switching
element 4 resiliently returns to its normal position thus breaking
the electrical connection between the respective X and Y
conductors.
In FIG. 2, the orientation of switching elements S with the
respective X and Y terminal portions is shown in dashed lines. For
example, switching element S1 may be of the type shown in FIG. 13,
switching element S2 may be of the type shown in FIGS. 4-10,
switching element S3 may be the type shown in FIG. 14, and
switching element S4 may be the type shown in FIGS. 11 and 12, it
being understood that all switching elements in a given keyboard
switch assembly will generally have the same configuration.
Referring now to FIGS. 4 through 10 of the drawings, the preferred
embodiment of the improved keyboard switch assembly of the
invention, generally indicated at 10, comprises single sided
printed circuit board 12, snap-acting dome switch members 14,
insulative switch member retaining sheet 16, insulative cover sheet
18, cover member 20, and push buttons 22. Switch members 14 and
insulative sheets 16, 18 are sandwiched between printed circuit
board 12 and cover member 20 and the keyboard switch assembly is
held in assembled relation by rivets 24. The illustrated embodiment
of keyboard switch assembly 10 is intended for use in an electronic
calculator.
While keyboard switch assembly 10 incorporates a plurality of
switching sub-assemblies 28 each comprising one push button 22, one
snap-acting dome switch member 14, and associated switch terminals
and conductors on upper surface 26 of printed circuit board 12,
each of the switching sub-assemblies is similar and functionally
identical and thus description of one such subassembly 28 will
suffice.
Referring now particularly to FIGS. 6 and 7, printed circuit board
12 comprises a sheet of rigid plastic material having one surface
26 copper clad, the conductors and terminals on surface 26 being
formed by photo-engraving techniques as is well known to those
skilled in the art. Each switching sub-assembly 28 comprises three
switch terminals 30 on surface 26 and disposed in an equilateral
triangle, and a center switch terminal 32 on surface 26 disposed in
the center of the triangle formed by outer terminals 30. In the
particular switching sub-assembly 28-1 shown in FIG. 6, two of the
outer terminals 30-1 and 30-2 are connected by conductor 34 on
upper surface 26 of board 12, terminal 30-2 having another
conductor 36 on upper surface 26 connected thereto. Due to the
geometry of the conductor pattern on the upper surface 26 of board
12, terminal 30-3 of switching sub-assembly 28-1 does not have a
conductor connected thereto however, in other of the switching
sub-assemblies 29, all three of the switching terminals 30 may be
connected by one conductor. In the particular circuit board pattern
shown outer terminal 30-3' of switching sub-assembly 28-2 is also
connected to conductor 34.
Central terminal 32 of switching assembly 28-1 is connected by
conductor 38 on upper surface 26 to external terminal 40. The other
conductors on upper surface 26 of board 12, such as conductors 42,
44 and 46 which pass through the triangle defined by outer
terminals 30 of switching assembly 28-1, connect other external
terminals to the terminals of other switching sub-assemblies.
Conductor 48 on upper surface 26 of board 12 partially surrounds
central terminal 32 of switching sub-assembly 28-1 being spaced
therefrom and from conductor 38. In the particular printed circuit
pattern shown, conductor 48 is connected in conductor 50 on upper
surface 26 of board 12 which connects external terminal 52 to a
terminal of another switching subassembly 28. In other switching
sub-assemblies, such as subassembly 28-2, conductor 48' completely
surrounds central terminal 32' and is connected to conductor 38' on
upper surface 26 which connects central terminal 32' to external
terminal 54.
Referring now particularly to FIG. 7, upper surface 26 of printed
circuit board 12 and the conductors thereon are covered with a thin
layer 56 of insulating material, terminals 30, 32 being masked
during application of insulative coating 56 so that the terminals
are not so-coated. Terminals 30, 32 are preferably plated, such as
by plating with gold over nickel, as at 58.
While the conductors, terminals, insulative layer 56, and plating
58 are shown for purposes of illustration in FIGS. 5 and 7 as
having appreciable thickness, it will be understood that actually
these elements are very thin.
Referring now additionally to FIG. 8, in the preferred embodiment,
snap-acting dome switch member 15 has a generally triangular
configuration with apices 60 whicn are arcuately curved about
center 62, apices defining flat sides 62 therebetween. Switch
member 14 may also be said to be generally circular with portions
removed to form chords 62 between arcuate portions 60. Projections
or dimples 64 are formed downwardly from apices 60 and a center
projection or dimple 66 is formed projecting into the interior of
the dome.
Snap-acting dome switch member 14 of switching sub-assembly 28-1 is
disposed over and facing upper surface 26 of board 12, conductors
34-48, and center terminal 32, outer projections 64 respectively
engaging outer terminals 30 and thus spacing the periphery of
switch member 14 above the conductors and terminals, as best seen
in FIG. 7. Center projection 66 is in registry with and spaced from
center terminal 32 in the normal position of snap-acting dome
switch member 14, as shown in solid lines in FIG. 7. Application of
a downward force on switch member 14, as shown by an arrow 68, will
deflect member 14 from its normal position to a non-overcenter
position, as shown in dashed lines at 70, in which center
projection 66 engages center contact 32 thereby electrically
connecting center contact 32 to outer contacts 30 to complete the
desired electrical circuit.
Conductor 48 partially surrounding center terminal 32 (or 48'
completely surrounding center terminal 32'), and its insulative
coating 56, forms a pad preventing damage to center projection 66
on snap-acting dome switch member 14, i.e., application of
excessive force in direction 68 on switch member 14 will cause the
area surrounding projection 66 to move into engagement with the
insulation covering conductor 48 thus preventing further downward
movement of the dome and damage to projection 66.
Retaining sheet 16, which covers insulative layer 56 on upper
surface 26 of circuit board 12, is formed of a sheet of relatively
thin flexible insulating material and has openings 72 therein which
respectively receive and locate snap-acting dome switch members 14,
openings 72 generally conforming to the configuration of switch
members 14 but having cut-out portions 74 respectively aligned with
projections 64 whicn respectively expose portions of outer
terminals 30 (FIG. 9).
Cover sheet 18 is formed of an imperforate sheet of relatively
thin, flexible insulating material and covers retaining sheet 16
and switch members 14. Cover member 20 covers sheet 18 and has
openings 76 therein which receive push buttons 22. Each push button
22 has an X-shaped projection 78 formed on its bottom surface 80,
projection 78 being in registry with center projection 66 of the
respective switch member 14. Projection 78 engages the area of
cover sheet 18 over center projection 66 but normally applies no
force thereto other than what little force is attributable to its
own weight which is insufficient to deflect switch member 14 to its
actuated position 70. Application of manual finger pressure on a
particular push button 22 results in the application of force in
direction 68 through cover sheet 18 on the respective snap-acting
dome switch member 14 thereby actuating the switch member to its
non-overcenter, deflected position 70 to perform the desired
switching function. Upon release of manual finger pressure on push
button 22, the respective switch member 14 resiliently returns to
its normal position thus opening the circuit previously established
and returning the respective push button 22 to its normal, inactive
position.
Referring now to FIG. 11 in which like elements are indicated by
like reference numerals and similar elements by primed reference
numerals, here, each switching sub-assembly 28' comprises center
terminal 32 on upper surface 26 of printed circuit board 12 and a
single outer terminal 30' also on upper surface 26, center terminal
32 and outer terminal 30' being connected by conductors (not shown)
on upper surface 26 to external terminals (also not shown). Sheet
82 formed of relatively thin insulating material covers upper
surface 26 and conductors 84 thereon and has openings 86, 88
respectively exposing terminals 30', 32.
In this embodiment, snap-acting dome switch member 14' has a
generally rectangular configuration with flat portion 90 integrally
joined to the periphery of domed portion 92. Projection 64' is
formed from flat portion 90 and projection 66 is formed from the
center area of dome 92.
Flat portion 90 of switch member 14' is supported on the upper
surface of insulator 82 with projection 64' extending through
opening 86 and engaging terminal 30', and with projection 66 in
registry with opening 88 and terminal 32. Insulative retaining
member 16 covers insulator 82 and has openings 72' therein which
receive and locate switch members 14', openings 72' conforming to
the rectangular configuration of switch members 14'.
Cover sheet 18 covers retaining member 16 and cover member 20 (not
shown in FIG. 11) in turn covers cover sheet 18 and has openings 76
therein which receive and locate push buttons 22.
The switching action of the embodiment of FIGS. 11 and 12 is
virtually identical to that of FIGS. 4-10, i.e., application of
manual finger pressure on a push button 22 causes X-shaped
projection 78 to apply downward force on the center area of a
respective dome 92 through cover sheet 18 thereby actuating doem 92
from its normal position, as shown in FIG. 11, to its
non-overcenter, deflected position in which projection 66 extends
through opening 88 in insulator 82 and engages center contact 32
thereby to provide the switching function.
Referring now to FIG. 13 in which like elements are indicated by
like reference numbers and similar elements by primed reference
numerals, a modification of the switch element of FIGS. 11 and 12
is shown having an additional contact projection 65 formed in flat
portion 90 on the opposite side of domed portion 92 from projection
64'.
Referring now to FIG. 14 in which like elements are again indicated
by like reference numerals and similar elements by double primed
reference numbers, a modification of the switching element 14 shown
in FIGS. 4-10 is shown (referring particularly to FIG. 8) in which
domed switching element 14" has a generally rectangular
configuration with arcuate corners 60" joined by straight sides
62", contact projections or dimples 64 being formed in corners 60".
It will be observed that switching element 14" may be formed by
cutting straight edges 62" from a circular snap-acting dome.
While snap-acting dome switching elements have been shown in the
preferred embodiment, it will be understood that the audible and
tactile feedback provided by the "oil canning" action of a dome is
not required for the switching function and that other types of
switching elements can be employed; the basic requirement of the
switching element is that it be capable of being depressed to
complete a circuit between respective X and Y lines, have the
required memory or resilience to return to its initial position
upon removal of the actuating force, and have a configuration which
will make the required electrical connection between a selected XY
conductor pair when depressed without touching other conductors
interconnecting contact points for other switches on the same
board. While an insulating coating or layer is disclosed covering
the circuitry other than the terminal portions, such an insulative
coating or layer is not a requirement since with proper arrangement
of the conductive pattern and proper switch element deflection
characteristics, the insulating coating can be eliminated.
The switching element configuration shown in FIGS. 8 and 14 is
preferred since the provision of three or four apices or corners
with contact projections or dimples therein provides resting points
for the dome around the periphery thereof, the intermediate flat
sides cut from the dome insuring proper alignment of the contact
projections by the dome retaining sheet 16.
While the printed circuit board has been shown and described, it
will be readily understood that the XY conductors can be secured to
one surface of an insulative board by means other than
photo-engraving.
While there have been described above the principles of this
invention in connection with specific apparatus, it is to be
clearly understood that this description is made only by way of
example and not as a limitation to the scope of the invention.
* * * * *