Multilayer capacitive keyboard membrane.

摘要

The membrane is a sandwich of three dielectric layers 3, 5, 4 bonded together by adhesive films 21 with openings 22 in the intermediate layer 5 at each key position. Conductive pads 8, 18 on the inner surface of the outer layers 3, 4 face each other across the opening 22 and register with a conductive pad 20 on the outer surface of the layer 4. The pads 8 are connected in columns by conductive tracks 24 to a pulse generator 38 which pulses the columns sequentially. The pads 20 are connected in rows by conductive tracks 28 to a multipled analog to digital converter 42. The capacitance at a key position is made up of the fixed capacitance between the pads 18, 20 on the layer 4 and the capacitance between the opposed pads 8, 18, which is increased by local pressure on the layer 3.