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Datanetics DC-60

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Overview

DC-60 is a family of tactile mechanical keyboard switches introduced by Datanetics in 1973, the same year in which they also introduced DC-50. In practice, all discovered examples to date appear to be the undocumented linear design.

Specifications

The specifications differed between the 1975 brochure and the 1981 brochure, and between the latter and the 1985 advertisement in Electronic Engineers Master catalogue. Where the specifications changed, all values are given below.

The force ratings are all for the tactile type, as documentation of the linear type has never been found.

Contact materials Stainless steel with gold inlay
Preload 1.4 oz (40 gf)
Operating force 2.5 oz (71 gf) momentary
3.5 oz (99 gf) alternate action
Total travel force 3 oz (85 gf)
Pretravel 0.070±0.015″ (1.78±0.3 mm)
Total travel 0.125±0.010″ (3.18±0.25 mm)
Contact resistance 1 Ω max (100 mΩ typical) (1975, 1981)
150 mΩ max (1985)
Contact bounce 2 ms max (0.5 ms typical) (1975)
5 ms max (0.5 ms typical) (1981)
0.5 max nominal (1985)
Rated lifetime Momentary:
10 M (1975)
15 M (1981)
20 M (1985)
Alternate action: 50,000 (1981)
Current rating 100 mA (1975, 1981)
50 mA switching (1985)
Voltage range 0.5–300 V DC (1975, 1981)
30 V DC max (1985)
Volt–amp range 5 to 200 mVA (1975, 1981)
Minimum spacing 58″ (15.87 mm)

Characteristics

DC-60 switches have the contacts in the centre and are thus single pole only. Momentary and alternate action is provided. The 1981 brochure indicates that LED illumination was possible, but such a switch has never been seen.

Profile

DC-60 switches were produced in three profiles: “low profile”, “lower profile” and “lowest profile”. The three profiles are illustrated below:

In the 1975 catalogue the product range covered “low profile” and “standard profile”, with distances from the PCB to the top of the plunger of 0.660″ (16.76 mm) and 0.775″ (16.77 mm) respectively. By 1981, these had been renamed to “lowest profile” and “lower profile” and were joined by a taller version now itself referred to as “low profile”, with a height of 0.831″ (21.10 mm). The 1981 catalogue incorrectly reports the lower-profile type to be 19.18 mm tall.

In ITT Schadow’s 1983 advertisement in Electronic Engineer Magazine (see under documentation below), the lowest-profile models (DC61-01 and DC61-02) are stated to be DIN-compliant, being “among the lowest profile module Key Switches ever built”, a claim that stands in stark contrast with Cherry M8 and RAFI RS 74 and 76 which are both distinctly smaller, with RS 74 being also almost a decade older.

Tactility

Official documentation for DC-60 indicates that these switches are tactile. The force curve is linear up to the tactile point, at which point there is a decrease in force of around 6.5 grams according to the force curve. Based on Meryl’s sample tactile switch, the perceived reduction in force feels like it is several times that amount. The lack of peak in the force curve gives the switch an unobstructed feel, but with a very clearly-defined tactile point. The end result is very effective.

The force curve from the 1975 brochure is as follows:

The position of the pretravel line at 0.07″ is in the wrong place. The same graph was included in the 1981 catalogue without any corrections. Inspection of the internal parts would suggest that the contacts would close at possibly more like half way down the tactile drop.

In practice, most DC-60 switches discovered to date have been found to be linear. Sandy’s page on the Fluke Y1700 keyboard indicates that the switches are linear. Likewise, Jacob Alexander described the switches in that keyboard as “Fluke Linear Switch?” in his Fluke Y1700 Keyboard Flickr album. Switches resembling DC-61-02 sold in China are also linear.

The method by which the tactility is provided is not conclusively understood. Meryl Miller provided two assembled DC-60 switches: DC-61-03 (lower profile tactile) and a linear switch in lowest profile. An x-ray of both switches side by side seems to depict that they are structurally identical inside:

DC-60 x-ray comparison

(The two switches were probably meant to face the same way, but the x-ray process ended up far harder than expected, with this being one final attempt at getting it right.)

Meryl also provided an unassembled DC-60 switch. Testing with these parts and those of a cut-open linear switch from China demonstrates that the contacts are responsible for the tactile feel. The step in the contacts is what provides downward force on the separator bar when the tactile point is reached. However, this step is still present even in linear switches. The most likely explanation appears to be that the level of tactility is set by the angle of the stepped contact at rest. Compare the following photograph, that shows tactile contacts on the left, and linear contacts on the right:

Sample tactile parts (left) and linear parts (right)

The switch on the left is Meryl’s tactile sample that was never assembled. The switch on the right is a lowest-profile linear type bought new old stock from China; this seems to be made on worn tooling.

In the linear design, the stepped contact is upright, while on the tactile version it is leaned to the left. It may be that in the linear version, the separator bar moves the straight contact, and in the tactile version the separator bar moves the stepped contact. Careful selection of the angles of the contacts should allow tuning of the tactile force. The x-ray likely shows the same appearance in both switches because a released switch will always hold each contact at the same angle; a second x-ray was needed that depicted each switch in the pressed position to capture how much each contact moved.

It should be possible to prove this from examination, but even after cutting away part of a plunger to get a clearer view of the contacts, it is still not possible to reliably observe how each one moves during switch operation.

Alternate action

The alternate action mechanism is very similar to that of DC-50. To accommodate the latching wire, there is a sloped cutaway on one side of the switch, and a small notch at the top. A small portion of the momentary linear switches purchased from AliExpress have the alternate action shell instead of the momentary shell.

The position of the alternate action wire at the top of the plunger means that the lowest-profile type was momentary earlier: it was not possible to fit a keycap if the alternate action wire was present.

Models

Only a small number of model numbers (“dash” numbers in Datanetics terminology) are known. Only the standard models were listed in the brochures, and these types are all tactile. Although the majority of discovered examples appear to be linear, the existence of linear DC-60 is not something that Meryl Miller became aware of before he left Datanetics in 1979, although he did obtain a sample of a linear type. One other model number is known from the Oxygen Electronics website, and they refuse to sell any.

It appears that the lowest profile plungers were colourless, the lower profile plungers were black and the low profile (tallest) plungers were grey. HP however had brown plungers in their switches, made to the tallest profile. These can be seen in the HP 9825A.

Also listed for sale on AliExpress was a cream slider version with a smaller keystem that appears to be MX mount. terrycherry at Deskthority obtained some, but never reported on their characteristics.

Model Action Profile Guide posts Source Brochures NSN
DC-61-01 Momentary Lowest Present Brochures 1975, 1981
DC-61-02 Momentary Lowest Absent Brochures 1975, 1981
DC-61-03 Momentary Lower Present Brochures 1975, 1981 5930-01-213-0318
DC-61-04 Momentary Lower Absent Brochures 1975, 1981
DC-61-05 Momentary Low Present Brochures 1981
DC-61-06 Momentary Low Absent Brochures 1981 5930-01-135-4015
DC-61-24 Oxygen Electronics
DC-62-03 Alternate Lower Present Brochures 1981 5930-01-212-7965
DC-62-04 Alternate Lower Absent Brochures 1981
DC-62-05 Alternate Low Present Brochures 1981
DC-62-06 Alternate Low Absent Brochures 1981

Cherry M1

Sometime around 1979, it appears that Hewlett-Packard commissioned Cherry to produce a switch with the same dimensions as the tallest DC-60 type. This Cherry type is M1 (or M11). As M1 is linear, the suggestion is that the DC-60 switches in HP keyboards were also linear.

Documentation

Meryl Miller provided two separate DC-60 brochures. These have been donated to the National Museum of American History Library who provided higher quality scans.

See also