Printed circuit manual keyboard - uses wire loops bridged by conducting membrane to give matrix coding

摘要

The keyboard comprises a printed circuit (1) with tracks (2x, 2y) arranged to give two electric supplies in an A Y matrix format with wire loops (4x,4y) placed at each track intersection. An insulating board (5), thicker than the height of the loops and having holes (6) surrounding each pair of loops, supports a conducting membrane (7) over which a flexible plastic layer (8) with the characters (9) marked on it is placed. Pressure on the surface causes the conducting membrane (7) to bridge the two wire loops (for example 4x, 4y) causing a disturbance between the two electric supplies and the ends of the X and Y conductors affected by the closure. Logic circuits detect this change and generate the code corresp. to the pressed character.