Encoded keyboard switch

An encoded keyboard switch of the type comprising a single sheet of flexible insulating material which has been folded along fold lines to produce a stack of four sections of film in parallel aligned relationship, the stack comprising a first section, a second section, a third section, and a fourth section, the first and second sections having opposed surfaces on which there are provided a plurality of first switch sites, the third and fourth sections having opposed surfaces on which there are provided a plurality of second switch sites, each first switch site being in alignment with a second switch site, first switch electrodes on the opposed surfaces of the first and second sections at first switch sites, second switch electrodes on the opposed surfaces of the third and fourth sections at second switch sites, a common ground conductor and a plurality of signal bit conductors on the opposed surfaces, selected conductors extending across the folds of the single sheet, and a tail extending from the sheet, the signal bit conductors and the ground conductor extending onto the tail, the switch assembly being characterized in that:

• selected first switch sites and selected second switch sites are electrically isolated from the signal bit conductors and from the common ground conductor,
• selected second switch electrodes on the second section are two pole electrodes and all switch electrodes on the first, third and fourth sections are single pole electrodes,
• all second switch electrodes on the third section and selected first switch electrodes on the first section are connected to the common ground conductor, and
• the routing of the signal bit conductors is in accordance with an encoding scheme which produces a unique signal in the bit conductors on the tail when a specific switch site on the first section is depressed, the signal being a multi-bit signal and being produced in a plurality of signal bit conductors on the tail when some switch sites are depressed and being a single bit signal and being produced in a single signal bit conductor on the tail when other switch sites are depressed whereby, upon depression of the first section at a location above a predetermined first switch site, the opposed surfaces of the predetermined first switch site will be moved into contact with each other, and thereafter the opposed surfaces of the second switch site which is beneath the predetermined first switch site will be moved into contact with each other, and a unique signal will be produced by a circuit extending from the ground conductor on the tail through signal bit conductors to at least one signal bit conductor on the tail, and when the unique signal is a multi-bit signal, the circuit will not be completed by the ground conductor until all of the switch electrodes required for the production of the multi-bit signal have been electrically connected to each other.