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The Siemens ST is a switch from Siemens that precedes the Siemens STB "Schreibtasten" switch family; hence, it was decided to call the series ST at deskthority. We don't know the Siemens name of it.
- 80 g actuation force
- keytravel 6 mm
- contact crosspoint type
- 60 mΩ
- typical bounce 1–2 ms, up to 30 ms
- Key feel: the switch has a pronounced tactile event which Siemens called "dem deutlich spürbaren Druckpunkt" which loosely translates to "the clearly noticable pressure point".
The Siemens ST switch was manufactured by Siemens EC division for their own Transdata Terminal keyboards and teletypewriters in the 1970's and 1980's; the Siemens ST switch was not present in the catalogue of preferred parts (Schwerpunkttypen) that Siemens sold to others.
The Siemens ST switch was already used for the Transdata system a year before the Siemens T1000 was introduced. They are mostly associated with these teletypewriters, which were in widespread use and for which a lot of material can still be found on the web, whereas the elusive Transdata terminals had already disappeared in the 1980s.
The Siemens patent, DE2933983 / US4365903, filed in August 1979. The patent is about a modification of the switch, so it is not actual proof of the original switch:
"Luminous-indication key for key boards in office and teleprinting machines. A lockable key for use on electronic keyboards in office typewriters and teleprinters has a receptacle at an upper portion thereof for receiving a light emitting diode which is mounted in a small circuit board which can be snapped into the upper portion of the key and which is supplied current via flexible interlaced wires. A lower portion of the key has a guide element which cooperates with a guide pin carried on a side of the key base for retaining the upper portion of the key in a depressed state after a first actuation thereof, and for allowing return of the upperportion of the key to the original position after a successive actuation thereof."