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Transducer Systems



Transducer Systems, Inc. was an American manufacturer whose product line included keyboards. The origin of the company is unclear, but if they were founded in 1968, then their keyboards would have been amongst their earliest products. Most indications are that the company was called “Transducer Systems, Inc.” although their 1969 magazine advertisement used the name “Transducers Systems, Inc.” seemingly in error.



K-9000-A is TSI’s full-size keyboard design. The only type known is K-9000-A-49, which is a 49-key model identical in design to the Univac 1701 and 1710 keypunch keyboards; the only difference is the lack of keypunch controls along the top. K-9000-A was advertised in Datamation and Computers and Automation in April 1969; it was also depicted in the article Solid state vs electromechanical: three new keyboards in the Electronic Engineer magazine in December 1969.

This keyboard derives its keystroke sensing from proximity transducers; these are small transformers whose output voltage is proportional to the distance between a piece of magnetic material to the exposed tip of the core. (By “magnetic metal” and “magnetic materials” one assumes that the patent would be referring to unmagnetised ferromagnetic materials, rather than permanent magnets, but this is not stated clearly.) Each key station has a proximity transducer which detects the key travel as an analogue reading. Two switch designs are shown in the patent: one uses a leaf spring as the movable magnetic member, and the other uses a flat magnetic disc affixed to the bottom of the plunger, within a discrete switch unit. The patent indicates that the leaf spring in the former type has an “extremely high cycle life”, of 10 million cycles or more, due to its limited motion. As no TSI keyboards are known to have been encountered, we do not know which approach was used for the K-9000-A.

These keyboards also support separate transformer windings per output bit, providing direct encoding in the same manner as that of the original Licon keyboards and of Fort Electronic’s Fero-Snap keyboards.

The patent does not disclose how these switches are read; being analogue, any voltage level can be chosen as the actuation level, and selection of a suitable intermediate level is required for overtravel. The article in Electronic Engineer does say that TTL is used.

Pricing in 1969 for a 1000-piece lot of 50-key K-9000-A keyboards was $75 each unencoded and $150 each encoded.


Little is known about the Mini or “Mini-Line”: they were described in the same April 1969 advertisements as being “Constructed to same high standards and ultra-reliability as the larger keyboard” and were “designed for limited space applications requiring thin line construction.” Although these keypads are nowhere near as flat as a membrane assembly, the size of proximity transducer shown in the patent would not fit inside the depicted design.


Patent Title Filed Published Product
US 3551865 Keyboard switch means 1968-08-20 1970-12-29 Transducer keyboards
US 3594672 Transducer device 1969-07-10 1971-07-20 Output bit encoding


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