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Controls Research BI-PAC


Controls Research BI-PAC is a mechanical switch type whose switch contacts are a pair of concentric coil springs. The wider outer spring has the top end formed into a horizontal bar, and as it is pressed down by the plunger, it makes contact with the top of the inner spring. The springs form the solder terminals. Overtravel is achieved when the inner spring is also compressed.

In an article in Electronics magazine in September 1972, Bi-pac switches are said to be “used in most American-made calculators”, with customer including Eldorado, Commodore, Master Calculator and Garrett Comtronics. In addition to their use in calculators and point-of-sale equipment, they were also used in full-size keyboards.

The switches are formed into blocks that are almost identical in layout to Key Tronic and Maxi-Switch switches. The switch blocks and inner workings are illustrated in Electronic Design magazine in 1972 [ED1972-FOK], under the name “Bi-Pac”. In September 1972, the switch block sizes were given as four, five and six-key units.

US patent 3773996 “Pushbutton switch with coil spring contacts” filed in 1971 covers the design, and describes a means for it to provide tactile (“snap-action”) feedback; British patent 1345831 was also filed, in May 1972.

The series name is spelt “Bi-pac”, “Bi-Pac” or “BI-PAC” depending on the source. In Electronic Design magazine in 1972, “BI-PAC” is used in the body text, and “Bi-Pac” in the image caption. Official advertisements and the HAL DKB-2010 manual use “BI-PAC”, while the 1971 Electronic Design written advertisement and 1972 Electronics article use “Bi-pac”.


The specifications below have been collected from the various advertisements. There is no document that lists all of the specifications collectively.

Travel 0.15″ (3.8 mm)
Operating force “light touch”
Rated lifetime 50 million (September 1971)
10 million (September 1972)
Bounce time 5 ms max.


There are two known designs of BI-PAC switch. In the type depicted in Electronics magazine in 1972, the visible portion of the plunger is entirely square in section; there is a small wall around each plunger aperture. This design is found in the MCM/70 keyboard. A second design has a cylindrical plunger with a square section on top that holds the keycap. The second design was used in the HAL DKB-2010.


Examination of switch modules suggests the following part numbers:

Part Type Known markings
T00-663 4-unit, second type T00-663- 20-73- (HAL DKB-2010)
T00-729 1-unit, second type T00-729 31-74 (HAL DKB-2010)

The final two portions of the markings appear to be the week and year.

The HAL DKB-2010 keyboard has 1-, 2-, 3- and 4-unit modules. The part numbers for the 2- and 3-unit modules are not visible in any photographs.


There are only two confirmed examples in full-size keyboards:

In [ED1972-FOK] a complete calculator keypad is shown, that uses BI-PAC switches. A very similar CRC keypad was used in the Summit 3114, with the main difference being a slightly different key arrangement.

Two stock BI-PAC keyboard models are depicted in advertisments listed under Documentation below.


All material was scanned by Bitsavers unless otherwise noted.