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Cherry Series S31



Series S31 is a type of snap-action switch from Cherry. S31 switches are an adaptation of their earlier Series S30 miniature open switches, with the mains voltage contacts replaced with gold crosspoint contacts for low-energy switching. Like the other “open” switches, the S31 switch has no enclosure; the components are affixed to a piece of thick substrate and are all directly accessible. “Miniature open” switches are simply a smaller version of the larger “open” switches. The “open” design (exposed snap action mechanism on a backing board) has retrospectively gained the nickname of “mousetrap” switch.

In their “Meet the Pro” brochure for keyboard model B70-05AB, Cherry made the following cryptic remark:

The company that first introduced gold crosspoint contacts to snap action switches for low energy solid state circuits. Then, applied this same innovative gold crosspoint technology to keyboards back in 1967.

The meaning of these statements has never been understood. The products introduced in 1967 are highly unlikely to have been M6 switches, which appear to have been introduced around 1971. The strongest contender for this claim is S31 Series miniature open, which had only been seen in the 1973 Switches & Keyboards catalogue. Further investigation has revealed an article from Electronics magazine from August 1968 (see Documentation below), describing Cherry’s then-new “gold-crosspoint series” of low-energy switches: E31 miniature, E63 subminiature, E53 rotary action and S31 open miniature. The article depicts S31, and notes that these low-energy switches are “particularly attractive for desk-top calculators and computers requiring switching at low voltages and currents”. Although the term “computer” is ambiguous (as they could have been destined for control panel buttons), Cherry name a specific product using S31 switches, the Hewlett-Packard 9100A programmable scientific calculator. 68 such switches were used in each unit, more than you would find in some terminal keyboards.

The size of these switches leads to some interesting arrangements to fit them into the keyboard.

S Series

The following S Series open switch subseries are listed in Electronic Engineers Master Catalog 1988–89 Volume 2:

Subseries Current rating
Series S23 5 amps
Series S25 10 amps
Series S30 10 amps
Series S31 0.1 amps

Switch part numbers are not described completely anywhere, but the following details were collated from Cherry Switches & Keyboards Catalog C-73 and the 1988–89 EEM advertisement:


Series: S23 = light force basic open, S25 = basic open, S30 = miniature open, S31 = low energy (gold crosspoint) miniature open
Actuator arm tip angle: 0 = −45°, 2 = horizontal, 6 = slight upturn
Poles/throws: 0 = SPDT (changeover), 1 = SPST NO, 2 = SPST NC
Terminals: P = “PCB” (tubes, narrow type only), W = integral solder, T = horizontal flat solder tags, Z = quick connect

The exact values for actuator arm tip angle may not be consistent between series; the Cherry advertisement in Electronic Engineers Master 1973–74 appears to have contradictory indications.


There are no observed examples that have been confirmed to be Cherry, but the fact that HP used S31 in the 9100A would suggest that the observed HP examples are also Cherry S31. Only the Computer Communications 303 keyboard is a data entry (“QWERTY”) keyboard.


There is a double-throw type that has become known as “01APBSW”. This does not appear to be a Cherry model number and it is not written on the switch. The origin of this term is not known, and it may be a customer part number. “01APBSW” appears to be an S31 series switch.


All documentation was scanned by Bitsavers.