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”|
50 million (September 1971)
10 million (September 1972)
|Bounce time||5 ms max.|
There are only two confirmed examples in full-size keyboards:
- Micro Computer Machines MCM/70 keyboard, assembled in Mexico in 1974, and labelled “N10046 REV AP1” and “B30041-1 REV AP1”.
- The HAL DKB-2010 manual, November 1978 reprinting, lists switches S101–S153 as ‘Controls Research “BI-PAC” Keyswitch’ (such a keyboard is in Engicoder’s possession, but the switches are not discrete but rather in the expected blocks) while the keyboard diagram depicts Stackpole Lo-Pro switches as per Jacob Alexander’s example
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.
- BI-PAC advertisement, The Electronic Engineer, Vol. 30 No. 9, September 1971
- Bi-pac advertisement, Electronic Design, November 25 1971, page 91
- ANSI keyboard advertisement, Electronic Design, August 3 1972, page 75
- Keyboard sells in $50 range, Electronics, September 11, 1972, page 173 (scanned by or for WorldRadioHistory.Com)
- ASR-33 keyboard advertisement, Electronics, February 15 1973, page 172 (scanned by or for WorldRadioHistory.Com)