Datanetics DC-50 series
|This article requires additional photographic illustration|
|Tactile force||3.0 oz (84 gf)|
|Peak force||ca. 3.8 oz (110 gf)|
|Pretravel||0.110±0.015″ (2.79±0.38 mm)|
|Switch mount||Fixing screw|
Datanetics DC-50 series was the first discrete switch module from Datanetics, initiated in 1972 and fully introduced by 1973. The lower profile DC-60 series followed the same year. DC-50 series was still on sale in 1981 side-by-side with DC-60. According to Apple technical documentation from September 1985, "Datanetics keyboards and keyswitches are no longer supported and replacement parts can no longer be ordered"; DC-60 appeared to still be in available in 1990 (used by Fluke in the Y1700 Keyboard), but it appears that DC-50 went end of life by 1985.
The switch is subtly tactile; the force curve is linear, with a small increase in force of approximately 10 gf directly before actuation, followed by a drop of 0.2 oz (6 gf). The total depth of the tactile curve is around 0.5 mm of travel.
The two defining features of the design are a sealed Mylar-metal sandwich contact assembly, and hysteresis. The hysteresis overlap is 0.040″, or 1.02 mm, which is around twice the length of the tactile curve. The switch contacts are formed as a sealed unit to protect them from contaminants and damage; as Datanetics licensed their diaphragm technology to Futaba, this may account for the Futaba complicated linear switch which is also noted for a sealed contact unit.
The switch shell accepts two contact assembly units, allowing for a DPST arrangement. Support for a latching mechanism was achieved by welding a latching track unit onto the outside of the switch, with a wire connected to the keycap; the switch is otherwise unchanged.
The slider has a large cruciform cross-section, atop which sits a heptagonal or octagonal platform bearing a much smaller cross. The slider is white. The shell is typically black; switches with dark green shells exist but none have been seen in a finished product. The key stem can be either straight or slanted to 12°.
The switch modules are fairly tall, with the shell standing at a fraction under 17 mm high; by comparison, Alps SKCL/SKCM and Cherry MX switches are around 11 mm tall. There are no plate mounting clips; instead, the switches are instead secured using BT self-tapping screws (maximum size #2), for which two screw holes are provided.
The contact assembly in DC-50 is a sealed metal–plastic sandwich. The contact assembly is based on Datanetics elastic diaphragm array, but is not a true membrane system as the contacts are strips of metal instead of traces printed onto plastic. The contacts are nonetheless the thickness of membrane sheets. The layers of the assembly are as follows:
- Stainless steel backing plate, 0.09 mm thick, with a transparent blue coating applied
- Cadmium copper alloy stationary switch contact, a strip of metal 1.37 mm wide and 0.06 mm thick; the ends are stamped with a curved cross section and tinned to form the switch terminals
- Mylar spacer membrane, 0.13 mm thick
- Movable switch contact, identical to the stationary contact but facing the opposite direction
- Mylar protective cover, 0.07 mm thick
A plastic actuator is placed in front of the contact assembly, containing a prong that applies pressure to the front metal strip in a manner similar to a membrane keyboard or an Alps switchplate. The slider does not engage directly on this actuator. Between the slider and the actuator is a leaf spring, 0.1 mm thick, folded such that the centre presses against the actuator and the ends press against the slider. Hooks in the slider push this leaf spring downwards during the down stroke, and upwards during the return stroke. The hooks are spaced further apart than the length of the spring, which causes a delay in engagement in each direction. When the slider is pressed down, it travels 1 mm before engaging the leaf spring. When the leaf spring's centre point reaches the tip of the actuator prong, it pushes the prong outwards and closes the contacts. When the slider is released, the lower hook doesn't engage the leaf spring from below until 1 mm of upwards motion has occurred, providing the hysteresis.
Despite this feature, it is still possible to tease the switch. The cause is not known, but it may be that the pressure from the actuator prong is sufficient to push the leaf spring upwards. This switch is unusual and potentially unique in being a metal contact switch that provides hysteresis without any sound being generated.
A very small lip on the actuator, just above the free end of the prong, appears to be the source of the tactility.
Known part numbers include:
|DC-51-01||SPST||Momentary||—||DC-60 brochure (1974)|
|DC-51-03||SPST||Alternate||—||DC-60 brochure (1974)|
|DC-51-04||DPST||Momentary||—||DC-60 brochure (1974)|
|DC-51-11||SPST||Alternate||Higher force||Meryl Miller|
|DC-51-41||SPST||Momentary||Illuminated||DC-60 brochure (1974)|
|DC-51-43||SPST||Alternate||Illuminated||DC-60 brochure (1974)|
|DC-51-44||DPST||Momentary||Illuminated||DC-60 brochure (1974)|
All parts defined above have a 0° stem; 12° angled key stem was cited in the 1974 DC-50 brochure as an option, as was a high force return spring.
- ABT The KeyPad (straight keystem)
- Apple 1 computer (angled keystem)
- Early Apple II/II Plus
- Earlier Krown Porta-printer keyboards (straight keystem)
- Some Volker Craig VC404 keyboards (straight keystem; momentary and latching)
- Fisher Differential Counter Model 111 (straight keystem)
This is the rare green version of the switch. Normally the shell is black.
- Datanetics DC-50 Series Key Switches brochure (November 1974)
- Datanetics DC Series Data Entry Keyboards (1973 or 1976)
- ITT Datanetics DC-50/DC-60 Key Switches brochure (1981)
- Internet Archive — Apple II Technical Procedures: Appendix A Keyboard and Keyswitch Replacement (September 1985)
- Imgur — Ripster's Vintage Switch Guide: Datanetics
- Correspondence with Meryl Miller, former Datanetics employee
- (Blogspot) The Apple 1 Computer 1976 — Datanetics Keyboard Assembly Complete Retrieved 2015-07-25.
- Mike's Hobby Home Page — Datanetics Keyboard Retrieved 2015-07-25.
- Mike's Hobby Home Page — Apple II Retrieved 2015-07-25.
- Danny Nguyen — Modding MX Stems onto Vintage Datanetics Keycaps