Key array

Claim 1

A keyboard for initiating switching functions, said keyboard comprising: electrical signal output means; a plurality of mechanically operated depressable keys arranged in a rectangular array of rows and columns, the exposed top surfaces of said keys lying in a substantially common plane and having visual symbols thereon, each said symbol being allocated only to a group of four keys in a square arrangement of mutually adjacent keys and appearing at the area of mutual adjacency in such manner that each crosspoint of the gaps between keys in the key rows and keys in the key columns is allocated to one symbol and each symbol is allocated to one crosspoint; individual means for producing a key signal coupled to alternating ones of said keys in each row and in each column in a checkerboard fashion, said key signal resulting from downward motion of each said key, each said group of four keys including two diagonally adjacent keys coupled to respective key signal producing means, at least some of the keys in each group being part of another adjacent group of four keys; and means coupled between said electrical signal output means and said two key signal producing means in each said group for combining said key signals in an AND function to provide an output signal from said electrical signal output means corresponding to said symbol at the crosspoint of gaps of said four keys in a group, said output signal occurring only when the mutually adjacent keys at a crosspoint are depressed, including said two key signal producing means; whereby depression of less than all of the keys at a crosspoint will not produce an output signal and misoperation of the keys to produce an output signal is highly unlikely.