Editing Datanetics DC-50 series

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{{infobox dswitch
| image name        = 
| contact mechanism = 
| manufacturer      = [[Datanetics]]
| product code      = 
| switch type       = Tactile
| switch mount      = [[Fixing screw]]
| introduced        = 1973
| patents           = [http://www.google.com/patents/US3777090 US3777090] (1972)
| pretravel         = 0.110±0.015″ (2.79±0.38 mm)
| travel            = 0.180±0.010″ (4.57±0.25 mm)
| tactile force     = 3.0 oz (84 gf)
| peak force        = ca. 3.8 oz (110 gf)
| lifetime          = 100M
}}

'''Datanetics DC-50 series''' was the first discrete switch module from [[Datanetics]], initiated in 1972 and fully introduced by 1973. The lower profile [[Datanetics DC-60 series|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.<ref name="Apple_II" />

==Design==
The switch is subtly tactile 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<ref name="green" /> 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 [[Apple III]] at one stage used double action DC-50 switches for the arrow keys. These switches (Apple part 705-0012) have yet to be seen, and were not listed in Datanetics brochures.

===Contact assembly===
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

The 1972 press release gives Kapton as the diaphragm material, while the 1974 brochure cites Mylar. The press release also gives the lifetime as 50 million, unlike the 100 million given in the brochure. Kapton appears to be the brown material used in some of the prototype contact assemblies, with Mylar being the colourless transparent material.

[[File:Datanetics DC-50 contact assembly.svg|centre]]

===Operation===
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.

[[File:Datanetics DC-50 operation.svg|centre]]

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.

==Variants==
The structure of DC-50 part numbers remains unclear. While DC-60 parts began with both DC-61 and DC-62, all known DC-50 part numbers begin DC-51. DC-51-0''x'' appears to be non-illuminated, 0° keystem. DC-51-4''x'' covers illuminated switches. Product literature only gives 12° keystems and increased force as options, and the part numbers are never cited. Apple used DC-50-3''x'', which appears to be the 12° keystem option. The increased force option may be covered under DC-51-1''x'', although these break the pattern of 0''x'' and 4''x''.

Known types include:

{| class="wikitable row-headings"
! Part no. !! Contacts !! Action    !! Keystem || Force  || Features     !! Source
|-
| DC-51-01 || SPST     || Momentary || 0°      ||        ||              || DC-50 brochure (1974)
|-
| DC-51-03 || SPST     || Alternate || 0°      ||        ||              || DC-50 brochure (1974)
|-
| DC-51-04 || DPST     || Momentary || 0°      ||        ||              || DC-50 brochure (1974)
|-
| DC-51-11 || SPST     || Alternate ||         || Higher ||              || Meryl Miller<ref name="meryl" />
|-
| DC-51-31 || SPST     || Momentary || 12°     ||        ||              || [[Apple II]] and [[Apple III]] service manuals
|-
| DC-51-35 || SPST     || Momentary || 12°     || 3.5 oz ||              || [[Apple II]] service manual
|-
| DC-51-41 || SPST     || Momentary || 0°      ||        || Illuminated  || DC-50 brochure (1974)
|-
| DC-51-43 || SPST     || Alternate || 0°      ||        || Illuminated  || DC-50 brochure (1974)
|-
| DC-51-44 || DPST     || Momentary || 0°      ||        || Illuminated  || DC-50 brochure (1974)
|-
| ?        || SPST     || Momentary || 12°?    || 9 oz   ||              || Apple II service manual
|-
| ?        || Dual     || Double    ||         ||        ||              || Apple III service manual
|-
| DC-51-90 || N/A      || Immovable || 0°/12°? ||        || Illuminated  || Apple II service manual
|}

The 9 oz and double-action types were not listed with Datanetics part numbers, suggesting that they may have been custom parts ordered by Apple.

==Keyboards==
* [[ABT The KeyPad]] (straight keystem)
* Some keyboards made for the Apple 1 computer<ref name="BS-Apple-1" /> (angled keystem)<ref name="Willegal-1" />
* Original [[Apple II]] computers<ref name="Willegal-II" />
* Original [[Apple III]] computers
* Earlier [[Krown Porta-printer]] keyboards (straight keystem)
* Some [[Volker Craig VC404]] keyboards (straight keystem; momentary and latching)

==Other equipment==
* Fisher Differential Counter Model 111 (straight keystem)<ref name="Fisher" />

==Gallery==
<gallery widths=250 heights=187>
File:DC-50 illuminated and alternate action.jpg     | Illuminated and alternate action variants
File:Datanetics DC-50 keyswitch assembly.jpg        | Switch assembly in the factory: actuator leaf spring is being fitted using a special jig
File:Datanetics DC-50 series contact assemblies.jpg | Production and prototype contact assemblies, and actuators; the brown material will be Kapton
File:Datanetics DC-50 keyswitches in trays.jpg      | Assembled switches in the factory
File:Datanetics DC-50 -- shell, halves.jpg          | The shell is made from two identical halves; these are new parts never assembled
File:Datanetics DC-50 -- shell, insides.jpg         | Shell halves, insides
File:Datanetics DC-50 -- shell, outsides.jpg        | Shell halves, outsides
</gallery>

===DC-51-01===
This is the rare green version of the switch. Normally the shell is black.

<gallery widths=250 heights=187>
File:Datanetics DC-51-01 -- disassembled, outside views.jpg | Disassembled, outside views
File:Datanetics DC-51-01 -- disassembled, inside views.jpg  | Disassembled, inside views
</gallery>

==Specifications==
*[[:File:Bumpas and Jones -- Datanetics DC-50 press release, 1972-09-14.pdf|Datanetics DC-50 press release]] (September 1972)
*[[:File:Datanetics DC-50 Series Key Switches.pdf|Datanetics DC-50 Series Key Switches brochure]] (November 1974)
*[[:File:Datanetics DC Series Data Entry Keyboards.pdf|Datanetics DC Series Data Entry Keyboards]] (1973 or 1976)
*[[:File:ITT Datanetics DC-50 and DC-60 Key Switches.pdf|ITT Datanetics DC-50/DC-60 Key Switches brochure]] (1981)

==References==
<references>
<ref name="Willegal-1">Mike's Hobby Home Page — [http://www.willegal.net/appleii/apple1-datanetics.htm Datanetics Keyboard] Retrieved 2015-07-25.</ref>
<ref name="Willegal-II">Mike's Hobby Home Page — [http://www.willegal.net/appleii/early-a2-keyboards.htm Apple II] Retrieved 2015-07-25.</ref>
<ref name="BS-Apple-1">(Blogspot) The Apple 1 Computer 1976 — [http://www.willegal.net/appleii/early-a2-keyboards.htm Datanetics Keyboard Assembly Complete] Retrieved 2015-07-25.</ref>
<ref name="meryl">Correspondence with Meryl Miller, former Datanetics employee</ref>
<ref name="Apple_II">Internet Archive — [https://ia601300.us.archive.org/26/items/AppleIITechnicalProceduresAppendixAKeyboardAndKeyswitchReplacement/keyswitches.pdf Apple II Technical Procedures: Appendix A Keyboard and Keyswitch Replacement] (September 1985)</ref>
<ref name="green">Imgur — [http://imgur.com/a/t4Smx Ripster's Vintage Switch Guide: Datanetics]</ref> <!-- Ugh please find an alternative :( -->
<ref name="Fisher">Danny Nguyen — [http://hexwire.com/mx-stem-mod-of-vintage-datanetics-keycaps/ Modding MX Stems onto Vintage Datanetics Keycaps]</ref>
</references>

[[Category:Datanetics switches]]
[[Category:Metal contact switches]]
[[Category:Tactile switches]]
[[Category:List of all keyboard switches]]