3591749 is referenced by 52 patents and cites 4 patents.

A printed circuit keyboard having contacts thereon with leads from the contacts passing through the board and connected to conductors on the underside of the board. A ground plane in the form of a conductive sheet is positioned above the contacts and biased out of contact therefrom. This sheet could be Mylar plated with nickel. The Mylar sheet is positioned over an apertured member aligned with the contacts to provide the biasing. The Mylar is sufficiently taut so that only one contact can be positioned against the depressed Mylar sheet at one time. A cellophane or other member can be placed over the Mylar and aligned with the apertures to provide numeric indicators for the keyboard.

Title
Printed circuit keyboard
Application Number
04/823,658
Publication Number
3591749
Application Date
May 12, 1969
Publication Date
July 6, 1971
Inventor
Comstock James Martin
Assignee
The Singer Company
IPC
H01h 03/12
H01h 09/16
H04M 01/23
H01H 13/702
H01H 13/70
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