KBK update for Thursday, 16th April
In August last year I bought some Micro Switch 1PB871 switches. I included a 1PB2001 in the order purely for the sake of illustrating the Micro Switch PB page. 1PB2001 is a combination of an SM basic switch (“microswitch”) and a 2ED “untimed pulse contact buffer circuit”. The latter is a special circuit that provides debouncing, so that the switch unit can drive logic circuits directly. I never paid it that much attention until I started looking into sensing and encoding in more detail. The 1966 Bulletin ED contains the circuit diagram and, after some pondering, I can see what they did. (Those who are more electronics-inclined would find it obvious.) Micro Switch took advantage of the presence of both normally-open (NO) and normally closed (NC) terminals on a basic switch, to drive a flip-flop. Operating the switch activates the flip-flop, which remains active until the switch is released, and the normally-closed current clears it. This way, the bounce period is ignored as the flip-flop remains active throughout. This principle can be extended to any switch series with NO-NC as a supported configuration, including Cherry keyboard switches from the 70s.
Additionally, I found a brief PDF on datasheetarchive.com that finally confirms that Fujitsu FES-8 and FES-9 effectively differ only in profile. Aside from a brief overview of the family characteristics and some hard-to-see photographs, that is all the detail provided.