Alps AKC series
AKC is an Alps Electric keyswitch series introduced by 1972, designed for desktop calculators and control panels, and later used in full-travel keyboards. AKC covers at least one type of “spring bridge” type.
AKC and AKM were advertised together in Electronics magazine in November 1972, and were described as follows:
- 4-block keyboard switch AKM Series
- Mechanical contact point keyboard switch AKC Series
The advertisement does not clearly differentiate between AKM and AKC, calling both types “switch”. AKC itself is described as follows:
This keyboard switch incorporates our own coil-spring contact point as well as the independent one-key unit feature for free key arrangements.
It would appear the single switch unit is AKC, and AKM represents a modular keypad assembly system built around these switches, although this is not wholly certain due to the poor translation from Japanese to English in the advertisement. AKB denotes conventional data entry keyboards that at one point appear to have been built around AKC switches, and as the boxes for these described them as “Alps Keyboard Switch for Micro Computer”, it would appear that the term “switch” was being used incorrectly in the advertisement.
AKC is confirmed to refer to at least one metal-top type (the advertised design is not quite the same as that shown below); there is no information yet to indicate whether the all-plastic type was part of AKC.
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.
The following switch specification was taken from an advertisement in 1976 for AKB-3000 Series keyboards, which “[use] coil spring contact mechanism [switches]”:
|Travel||0.138±0.02″ (3.5±0.5 mm)|
|Actuating force||2.6±0.65 oz (60±15 g)|
|Rated load||DC 12 V 0.1 A|
|Contact resistance||500 mΩ max|
|Bounce time||2 ms max|
|Rated life||5 million cycles|
- 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 Olivetti Logos 42-a PD calculator 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.