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KBK update for Monday, 3rd January

The mystery of Key Tronic’s “Butterfly” switches can finally be laid to rest … for the most part, at least. One of the staff involved with the design has confirmed my suspicion that that switch depicted in US patent 4209819 “Capacitive keyswitch” is indeed the “Butterfly” type. The “Butterfly” name presumably stems from the shape and motion of the movable capacitor plate. “Butterfly” was to be a fully-discrete capacitive switch, soldered to a PCB, with the variable capacitor entirely contained within the switch housing; the design would have no foam pad, which (in theory at least) would avoid the increase in force associated with compression of the overtravel pad.

The finer details, and the rationale for abandoning the design may never be known. The principal inventor—Ewald E. “Sig” Seignemartin—passed away in 2012, and the person who confirmed the patent is not at liberty to disclose details as he left Key Tronic many years ago. We only know that the “Butterfly” type never entered production.

For whatever reason, Key Tronic decided to continue down the foam pad route, introducing the discrete plate-mounted switch module design instead.

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