Encoded keyboard switch

Claim 1

An encoded keyboard switch assembly, said switch assembly being a substantially flat panel-like member having a top surface and having a plurality of key positions on the top surface, the switch assembly being characterized in that: each of said key positions has a key top and a first associated membrane switch beneath said key top so that depression of said key top closes said first associated membrane switch, each first associated membrane switch having opposed first and second switch contacts, said first switch contacts being commonly connected to a first common external conductor extending from said switch assembly, said second switch contacts having output conductors extending therefrom, said output conductors extending to external signal conductors, said second switch contacts are selectively connected to each other by encoding conductors in accordance with a predetermined encoding scheme, at least some of said second switch contacts and at least some of said first switch contacts being multi-pole contacts, said multi-pole contacts being preselected to achieve said encoding scheme, each of said key positions has a second associated membrane switch beneath, and in alignment with, said first associated membrane switch, said second associated membrane switches having third switch contacts which are commonly connected to a second common external conductor, said second associated membrane switches having fourth contacts which are commonly connected to a common internal conductor, said common internal conductor being commonly connected to said first contacts of said first associated membrane switches, said switch assembly comprising first, second, third and fourth sections of flexible film, said sections being stacked beneath said top surface with said first section adjacent to said top surface, each of said first membrane switches being on the opposed surfaces of said first and second sections with said first switch contacts and said first common external conductor being on said first section and with said second switch contacts and said encoding conductors being on said second section, each of said second membrane switches being on the opposed surfaces of said third and fourth sections with said third switch contacts and said second common external conductor being on said third section, and with said fourth switch contacts and said common internal conductor being on said fourth sections whereby, upon depression of one of said key tops, the first associated membrane switch beneath said one key top is closed and subsequently the second associated membrane switch is closed, and after closure of said second associated membrane switch, output signals are transmitted through said external signal conductors in accordance with said encoding scheme.