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General Instrument S700 Series

S700 series is a type of foam-and-foil switch from General Instrument. Described in US patents 4453198 and 4454562 (both filed on the 15th of September, 1982), it was introduced by 1983.

The patents report that it uses a “telescoping” plunger to provide overtravel and hysteresis. The entire point of using a foam pad in foam and foil switches is for overtravel, but this switch appears to want extra overtravel by having a “telescoping” plunger (in reality, the foam holder can move relative to the plunger) in addition to the foam pad.

The method by which hysteresis is achieved is covered in the earlier of the two patents, and is not at all clear.

The foam material is given as “typically … urethane foam”, and metallised Mylar is given as a possible material for the foil sheet.