Disclosed is a capacitance keyboard switching device comprising a fixed electrode formed on one surface of a first insulating film, a movable electrode formed on one surface of a second insulating film, a spacer interposed between the first and second insulating films and provided with a switching opening...http://www.google.de/patents/US4736076?utm_source=gb-gplus-sharePatent US4736076 - Capacitance switching device for keyboard
