Key input device

A key input device comprising:

• an upper casing provided with an upper flat plate portion having a large number of penetrating holes formed therein;
• a lower casing cooperating with said upper casing to form a receiving chamber;
• a printed circuit board disposed in said receiving chamber and fixed to at least one of said upper and lower casings, said printed circuit board having a flat upper surface with a plurality of pairs of printed contact electrodes thereon;
• a plurality of keytops disposed between said upper casing and said printed circuit board within said receiving chamber, each of said keytops having a keytop main body movable up and down with respect to said upper flat plate portion of said upper casing, and an engaging portion projecting sidewards from said keytop main body so as to be engageable with a peripheral edge portion of the penetrating hole through which the keytop extends, said engaging portion being engageable with the peripheral edge portion at a lower surface of said upper flat plate portion;
• a plurality of contact electrodes each fixed to a lower portion of a corresponding one of said keytops so as to be movable in accordance with the vertical movement of said corresponding keytops;
• and
• a plurality of elastic members each disposed between a corresponding one of said keytops and said printed circuit board for biasing the respective keytops upwardly, a lower end of said elastic member being supported by the flat upper surface of said printed circuit board, and an upper end of said elastic member pushing said keytop upwardly, thereby enabling said contact electrode fixed to said keytop to be spaced at a position upwardly from said printed contact electrodes.