Membrane switch assembly

Claim 1

A membrane switch assembly (10) comprised of a base substrate (12) and at least one flexible layer (16) separated from each other by spacing means (20), the spacing means (20) having a plurality of openings (22) therein constituting switch sites, the internal surfaces (14,18) of layers (12,16) adjacent the spacing means having a pattern of conductive switch contacts (28,28') thereon, the switch contacts (28,28') on the surfaces (14,18 ) being aligned with the openings (22) in the spacing means (20), the membrane switch assembly (10) being characterised in that: the conductive switch contacts (28,28') on each surface (14,18 ) are interconnected in series along a single conductive path (24,24'), the contacts (28,28') of the series are spaced along the respective single paths so that in each path the value of impedance (30,30') existing between successive switch contacts (28,28') bears a regular relationship to the impedance of the path to the succeeding and/or from the preceding switch contact, the change in impedance between each pair of adjacent switch contacts being uniformly incremental along the path whereby, when an electrical circuit is complete by applying force to the flexible layer (16) to bring together the conductive switch contacts (28,28') of the substrate (12) and flexible layer (16), the resulting total impedance is essentially equal to the sum of the unit values of the impedance means along the circuit path formed by the closed switch.