Illuminated keyboard

An apparatus for illuminating keyboard or individual switches in which a conventional plastic contact actuator member is fabricated of translucent material so that it may function additionally as a conductor and diffuser of light. A lamp source is positioned in the center of a conventional dome-printed circuit switch within holes provided in the metal contact domes and the substrate of the switch. The actuator includes a cylindrical lower hood portion having a recess in the center thereof permitting it to receive the lamp source upon switch actuation.

BACKGROUND OF THE INVENTION 
This invention relates to illuminated keyboards of the type commonly 
employed in a variety of applications including computers and calculators, 
games, control devices, and numerous electrical appliances. In particular, 
this invention discloses a straightforward and economical illuminated 
keyboard adaptable to continuous keyboard illumination or illumination 
only upon actuation of a given keyboard switch. 
Prior keyboards have been complex and often require a separate wafer or 
other member to conduct and diffuse the light to the keyboard surface. The 
keyboard of this invention, however, utilizes no separate or additional 
components, except the lamp itself, to provide versatile illuminating 
capability. 
This economical design is accomplished by combining a light source, which 
is integrally mounted within a dome switch, with a novel plastic switch 
actuator cap that performs a double function. First, the cap functions in 
a conventional manner to transmit the actuation force to the contacts 
below and, second, the cap receives light from a small incandescent lamp 
thereby conducting and diffusing the light over the cap or "button" 
surface. Thus, it can be seen that no additional hardware is required to 
effect illumination of this keyboard. 
An object of this invention, therefore, is to provide an illuminated 
keyboard switch of economical design. 
Another object of this invention resides in the provision of an illuminated 
keyboard containing few additional components as compared with similar 
non-illuminated keyboards. 
Yet another object is to provide an illuminated keyboard switch in which a 
plastic actuator cap functions also to conduct and diffuse the light from 
an illuminating lamp source to the switch surface.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIGS. 1 and 2 illustrate a typical keyboard employing the illumination 
principles of this invention. The keyboard shown contains twelve identical 
key switches arranged into a three column, four row matrix of the form 
commonly utilized in telephone tone signaling applications. The principles 
taught herein, however, may be applied equally to other keyboard 
configurations or to the illumination of individually packaged switch 
units. 
A molded plastic housing 10 forms a chassis into which the switches are 
secured. Parallel flanges 11 for mounting the keyboard unit are provided 
along two opposing sides of housing 10. The large center portion of 
housing 10 forms a rectangular actuator cap retaining and switch mounting 
frame 12 which is raised above the level of the flanges so as to create a 
corresponding rectangular space 13 into which a printed circuit switch 
assembly 14 is fitted. Twelve holes 15 are provided through frame 12, each 
hole being positioned and centered directly above a corresponding switch 
located on the printed circuit switch assembly 14. 
The printed circuit switch assembly 14 consists of a rigid printed circuit 
substrate 16, such as glass epoxy, upon which top and bottom metallized 
foil patterns are etched or plated. These metallized foil patterns form 
the basic contact surfaces 17 and 18 of the twelve switches comprising 
assembly 14 and all necessary interconnecting runners 24 and 25. Twenty 
equally spaced pins 26 are positioned along the lower edge of printed 
circuit substrate 16 forming an electrical connector thereon. Connector 
pins 26 are connected by foil runners 24 and 25 to respective switch 
contacts 17 and 18 and to lamps 27. 
Small holes 28 of approximately 3/32 inch diameter are provided through 
printed circuit substrate 16 at the center of each switch into which a 
small incandescent lamp 27 is placed. Each lamp is mounted by its wire 
leads and soldered to adjacent foil pads on the bottom of substrate 16. 
The lamps may extend above the upper surface of substrate 16, as discussed 
below, to assure proper coupling of the light from lamps 27 into actuator 
caps 29. 
FIGS. 3 and 4 illustrate a dome switch of the type employed on switch 
assembly 14. A circular inner contact 17, having a hole 30 in the center 
thereof through which lamp 27 may protrude, and an annular outer contact 
ring 18 are formed on the top surface of substrate 16 at each switch 
location. Plated-through hole 31 and runner 24 connect inner contact 17 
with a respective connector pin 26. Similarly, connection is made to the 
outer contact ring 18 by upper surface runner 25. 
A circular dome-shaped conductive and resilient contact element 32, 
generally referred to as a dome, is positioned over outer ring 18 and 
centered thereon. Dome 32 is dimensioned so that its outer perimeter rests 
entirely within the contact area of outer ring 18. Dome 32 is fabricated 
of conventional material having the requisite resilient and conductive 
properties. A thin sheet of electrically insulative material 33, having 
lineal dimensions somewhat greater than the diameter of dome 32 and with a 
central opening therethrough at least the size of a hole 34 in the dome, 
is positioned over dome 32 and attached by adhesive to the dome and to 
substrate 16 thereby restraining dome 32 in the above described position. 
A second and generally identical dome is positioned directly above the 
first dome and restrained by a second sheet of insulative material. (The 
second dome and insulative sheet are not shown in the figures for 
clarity.) This second or upper dome augments the first or lower dome 32 
and functions to provide the necessary switch spring return and to secure 
the desired "tactile" touch upon switch actuation. Both dome members 
contain holes 34 through which lamp 27 may protrude. These holes 34 do not 
materially weaken or affect the proper resilient action of domes 32. 
Switch assembly 14, upon which twelve of the above described switches are 
formed, is rigidly secured to frame 12 by self-tapping screws which extend 
through holes provided in substrate 16 into corresponding holes in frame 
12. An actuator cap 29 is positioned in each frame hole 15 and rests upon 
the respective switch domes 32 so that upper surface 35 of the cap is 
level or slightly raised with respect to the top of frame 12. Each 
actuator cap 29 includes a cylindrical lower hood portion 36 having a 
recess 37 of sufficient dimension therein to permit the unrestricted entry 
of associated lamp 27 as may be required upon switch actuation. 
Lamps 27 are positioned in respective holes 28 and mounted by associated 
leads to interconnecting runners and pads 24 on the bottom surface of 
substrate 16. Lamps 27 may extend substantially above substrate 16, as 
illustrated in FIG. 4, to assure adequate coupling of the light from each 
lamp into its respective actuator cap 29 when the actuator is depressed to 
trip the dome switch aligned therewith. 
Actuator caps 29 are molded from a nylon or plastic material having 
translucent properties which permit the light from lamps 27 positioned 
below or within the hood portions 36 of actuator caps 29 to be conducted 
to, and evenly diffused over, the entire upper actuator surfaces 35. In 
this manner the circular profile of each switch is clearly visible when 
viewed from above. While actuator caps of circular cross section are 
shown, it shall be understood that actuators of any convenient style and 
dimension as, for example, square or polygonal, are contemplated by this 
invention. 
A translucent plastic or polyester sheet 38 or other similar material is 
affixed to the upper frame surface 39. This sheet functions to contain 
actuator caps 29 and may be screened with appropriate designs, logos, and 
key switch numbers or other designations 40. Thus, a readily visible means 
of keyswitch identification is available merely by screening opaque key 
designations or indicia 40 above respective actuator caps 29. 
Mechanical and electrical operation of the switches of this keyboard is 
illustrated by FIGS. 4a and 4b. FIG. 4a shows a switch as it appears, 
generally, when not being actuated. Dome 32 forms an electrical contact 
along its perimeter with outer contact ring 18 but, due to its curved or 
domed shape, remains elevated above inner contact 17 and, therefore, not 
in contact with that surface. An electrical "open circuit" results. 
Actuation of the switch is accomplished by the application of a downward 
force upon actuator cap 29. This force is transmitted through this rigid 
cap generally to the center portion of the upper dome, thereby deforming 
and indenting both upper and lower domes 32 until contact is achieved with 
inner contact 17 as shown in FIG. 4b. In this position, an electrical 
connection is formed between inner contact 17 and outer contact ring 18 
through the lower metallic contact dome 32. The switch is electrically 
"closed" and remains so until removal of the downward actuation force at 
which instant the resilient domes "snap" back to their original 
non-indented shape. This electrically opens the switch and urges the 
actuator cap 29 upwardly to its pre-activated position. 
A second embodiment is illustrated in FIG. 5 which differs principally in 
that the overlay is omitted and the actuator caps are exposed to the user. 
In this embodiment an annular flange 50 is provided along the lower 
perimeter of actuator cap 51 which slidably seats within an annular corner 
groove 52 defined by annular surfaces 53 and 54 formed in mounting frame 
55. 
In the absence of an external force of actuation, the internal spring force 
of resilient dome 56 urges actuator cap 51 upwardly until flange 50 
contacts surface 53 of corner groove 52. This interference precludes 
further upward movement of actuator cap 51, thereby retaining this cap 
within the keyboard assembly. 
This self-retaining feature obviates the requirement for a translucent 
actuator retaining sheet such as shown in FIG. 2 at 38 and, typically, 
none are employed in keyboards of this design. Without such a sheet, 
actuator caps 51 may either protrude above the top surface of frame 55 or 
remain substantially flush with this surface in accordance with design 
criteria not important to this invention. Individual actuator caps 51 may 
be screened or otherwise marked with appropriate key designations or 
indicia 57 as described above. In all other material respects, the 
illumination and switch operation of this embodiment is the same as that 
described above. 
From the foregoing, it can be appreciated that this invention pertains to 
an economical and versatile technique for illuminating keyboard switches 
of the dome type requiring no additional components except the lamp 
itself. This is made possible by the novel design of actuator cap 29 (51) 
in combination with a dome switch into which a lamp 27 has been integrally 
placed. By providing a hole through the center of an otherwise 
conventional dome switch and by positioning a lamp 27 therein, the 
actuator 29 (51) of this invention functions in a dual capacity not only 
as a conventional actuation force interface element, but also as a 
conductor and diffuser of the light emanating from the lamp integrally 
contained within such dome switch. Thus, little added complexity, 
components, or expense is necessary to create dome switch keyboard 
illumination when the teachings of this invention are utilized. 
It will be understood that modifications and variations may be effected 
without departing from the scope of the novel concepts of the present 
invention and that this application is to be limited only by the scope of 
the appended claims.