FES-5 is a tall click-tactile reed switch from Fujitsu. This design utilises magnetic separation in conjunction with three coil springs. Two springs are placed above the magnet assembly, and apply pressure to the magnet from above. A third spring supports the magnet from below, to return it to its home position when the key is released. The top coil spring has the lowest force, and is compressed first. After a short amount of travel, the second coil spring is engaged, which steepens the force curve considerably. Once the accumulated force in these two springs exceeds that of the magnet and its own spring, the magnet detaches from its keeper, giving a distinct drop in force.
The reed is orientated vertically and placed centrally to the switch, with the magnet and all the springs moving down around it. The same magnet is used for both the tactile feedback and reed operation.
The tactile characteristics appear to be inspired by IBM’s Selectric typewriters. In the Fujitsu Scientific & Technical Journal, the force curve of the new FES-5 switch is overlaid onto that of an “electric typewriter”, whose force curve is similar in form (albeit shorter and simplified) to that of the IBM Selectric Composer:
It is possible that the original Selectric force curve is simpler, but this is not presently available.
No FES-5 keyboards have been encountered yet. It appears to have been introduced in 1972, before being superseded around 1976 by FES-8 Series.
- Ryohei Kinoshita, Masao Hiyane, Masatoshi Kubo: Reliabiltiy and Application of Magnet Driven Reed Switch; Fujitsu Scientific & Technical Journal vol. 8 no. 4, pp. 169–191 (1972)