A pusher formed of a rubber material, a click plate, a membrane switch which serves as a second step switch, a reinforcing plate, a membrane sheet on which a plurality of first step switches are formed, a key operation base and a knob are sequentially assembled into a case. The knob includes a plurality...http://www.google.com/patents/US20040200699?utm_source=gb-gplus-sharePatent US20040200699 - Depression responsive switch unit
