Alps AKC series
AKC is an Alps Electric keypad and keyswitch series found advertised in 1972, designed for desktop calculators and control panels. The single switch option is the “spring bridge” type found in some old calculators. The switch was advertised alongside AKM series, and unfortunately the advertisement did not depict or describe AKM clearly. The temporary term “spring bridge” itself covers both the old metal-top switches (confirmed to be AKC series) plus the all-plastic switches that are identical inside.
The term “spring bridge” arises from the design of switch contacts: a gold-plated coil spring that is fitted laterally across the plunger is slid down a PCB until it spans a pair of exposed pads. This spring is exceptionally delicate and prone to damage from handling. This PCB protrudes from the bottom of the switch, providing solder points; this same arrangement was used with some Mitsumi switches, such as that used for Shift Lock on the early Commodore 64 keyboards. The design does not make room for an internal return spring, so an external return spring is used, as with capacitive switches.
The keycap mount is a square hole, across which a metal rod is positioned. The keycap has a pair of prongs that snaps extremely tightly onto this rod. The switches could also be used with adapters to provide a more conventional keystem mount, such as with the Monroe 1405 calculator. The switch shell comprises three parts: a body, a lid with a large circular hole for the plunger, and a metal frame that snaps onto the body, securing the lid to the shell and the switch to the mounting plate. A simpler version moulded entirely from plastic was also produced, and the series of this switch is not known; the remainder of the parts of this version are identical.
No clearly-identifiable patent has been found from Alps, but US patent 4418252 “Key switch assembly” filed in 1982 by Phillip R. Daigle depicts a different switch that operates on the same principle.
- Monroe 1405 calculator keypad (PCB code CH34134A)
- Calculator keypad with PCB code CH34149B: see below
All-plastic style, not matching the AKC advertisement:
- Olympia CD 102 (PCB code CH34136B?)
The following photographs of an unidentified keypad with PCB code CH34149B were provided by Deepak Kandepet:
The following photos show the all-plastic version, the series of which is not known. These parts were bought NOS from STRONIC in France, and are of unknown origin.