Editing Datanetics DC-50 series (section)

==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.