Membrane type keyboard for e.g. calculator - uses piezoelectric membrane to connect upper and lower conducting strips through holes in upper strips

摘要

The keyboard comprises a lower printed circuit board, an upper printed circuit board, and a covering flexible plastic material which has piezoelectric properties. On the lower printed circuit board conducting strips lie in parallel columns. The upper printed circuit board has printed strips perpendicular to the strips on the lower printed circuit board. There are holes in the upper board to allow the piezo- electric membrane to make contact with both the upper strips and the lower strips when pushed by a finger. A CMOS circuit detects the change at each of the strips and provides the required coding. In addition an audible or visual signal of a successful entry is given.