Micro Switch PB Series
PB Series is a general classification of switches from Micro Switch that take the form of pushbuttons built around existing circuits and switches. There is no specific shape, size or style of PB switch. Some include a control circuit (such as a debounce circuit) and others contain only a microswitch. There seems to be a tendency for them to contain SM Series microswitches, but details on these switches are scarce.
PB was not the only series to enclose a microswitch. KS Series—with models 1KS1-T and 1KS3-T at least—also took the form of an actuator assembly enclosing a microswitch. Here, the microswitch is riveted in and cannot be removed for inspection. These two 1KS models appear to be Micro Switch mount, using the same general style of mount adapter as RW (7A1) switches.
Pictured at right are 1PB871 one-shot keyboard switches (using 311SM29 microswitches) and a 1PB2001 assembly containing a Series 2ED untimed pulse contact buffer.
It appears that the range 1PB870–1PB879 was used for switches suitable for keyboards. These are tall clicky switches that contain an SM Series microswitch, which has both a normally-closed (NC) and a normally-open (NO) terminal. The PB switch is a tall plastic housing that contains the plunger and microswitch. The plunger rides on a pair of coil springs, and drives the microswitch’s actuator arm by way of a horizontally-sliding block worked by an arm extending down from the plunger that runs in a slot in the sliding block. This arrangement provides a longer travel distance and overtravel.
At least two types of PB keyboard switch exist: continuous and one-shot. Continuous switches hold the microswitch in its operated position so long as the plunger is held. One-shot switches have a triangular cam track within the slide block that allows the slide block to spring back once the switch has passed the operating point. The design is very similar to that of alternate action switches, but the simpler cam track does not hold the plunger down. One-shot operation was used in Hall effect switches (the sink pulse sensor types) to achieve N-key rollover; here, the reason for one-shot switching is not known, but it could be for the same purpose.
The design is sub-optimal. There is a faint click and tactile event as the microswitch actuates. If a one-shot switch is pressed a short distance further, there is a very strong tactile event and a loud click as the plunger actuator arm passes off the slide block and it is fired back to the start position. The combination of two separate click sounds and two separate tactile points gives it a strange feel and sound.
The keycap mount is very similar design to that of SW and SN switches, but the mount dimensions are smaller and 2SW keycaps fall off.
1PB877 and 1PB878 were used in the following keyboards:
Both of those types use a 311SM29 microswitch. 1PB877 is one-shot and is used for most keys (including space bar); 1PB878 is continuous and is used for keys that the operator will hold down.
In those keyboards, the switches only date back to 1971. The oldest date observed is 6907 on a surplus 1PB871 switch. So far, no examples have been found that pre-date SW Series Hall effect or RW (7A1) reed switches.
Catalogue listing numbers
PB Series catalogue listing numbers are typically prefixed with the number of poles. The prefix may also encode other characteristics. Examples include:
|1PB||Single pole momentary|
|2PB||Double pole momentary|
|3PB||Triple pole momentary|
|4PB||Quadruple pole momentary|
|82PB||Double pole alternate action||“8” (+80)|
|83PB||Triple pole alternate action|
|84PB||Quadruple pole alternate action|
|15PB||Double pole momentary, white plastic button|
|702PB||Double pole momentary, hermetically sealed||“70” (+700)|
|703PB||Triple pole momentary, hermetically sealed|
|704PB||Quadruple pole momentary, hermetically sealed|
The following table gives a small number of examples. The complete PB Series range is outside of the scope of this site.
|1PB81-T2||Series 2ED separate actuator||Light force||Unspecified||None||5930-00-004-1090
|1PB114||Series 401ED separate actuator||Compact||12SM4||None|
|1PB872||Listed but not observed|
|1PB875||Listed but not observed|
|1PB2001||Untimed pulse contact buffer switch
(Series 2ED circuit)
|+5 to +25 V DC, 500 Ω and above||2ED1|
|1PB2002||+5 to +25 V DC, 100–500 Ω||2ED2||5930-00-959-2879|
|1PB2003||−5 to −25 V DC, 500 Ω and above||2ED3|
|1PB2004||−5 to −25 V DC, 100–500 Ω||2ED4|
|1PB3001||Millisecond pulse one-shot switch
(Series 301ED circuit)
|30 ms pulse, 6–20 V DC||301ED1|
|1PB3002||75 ms pulse, 6–20 V DC||301ED2|
|1PB3003||200 ms pulse, 6–20 V DC||301ED3|
|1PB3004||500 ms pulse, 6–20 V DC||301ED4|
|1PB3005||30 ms pulse, 20–55 V DC||301ED5|
|1PB3006||75 ms pulse, 20–55 V DC||301ED6|
|1PB3007||200 ms pulse, 20–55 V DC||301ED7|
|1PB3008||500 ms pulse, 20–55 V DC||301ED8|
|2PB11-T2||Touch feedback switch||2 × SPDT, momentary, black button|
|2PB12-T2||2 × SPDT, momentary, red button|
|2PB13-T2||2 × SPDT, momentary, green button|
|82PB12-T2||2 × SPDT, alternate action, red button|
|3PB13-T2||3 × SPDT, momentary, red button|
|4PB13-T2||4 × SPDT, momentary, red button|
|84PB13-T2||4 × SPDT, alternate action, red button|
|702PB1||Hermetically sealed||2 × SPDT, black button||HM Series||None|
|702PB2||2 × SPDT, red button|
|702PB3||2 × SPDT, green button|
|703PB1||3 × SPDT, black button|
|704PB3||4 × SPDT, green button|