Author Topic: On/On vs On/Off/On Toggles  (Read 1019 times)

DLW

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On/On vs On/Off/On Toggles
« on: November 09, 2018, 08:31:30 AM »
Hello,
Is there a standard nomenclature to know if an SPST/SPDT is On/On or On/Off/On. I can usually tell by looking at the schematic, but this information isn't always available. I wish this information was just specified on the build doc or BOM...

EBK

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Re: On/On vs On/Off/On Toggles
« Reply #1 on: November 09, 2018, 08:38:28 AM »
You've nearly spelled out the nomenclature in your question.

ON-ON
ON-OFF-ON, sometimes called center-off

If the switch is momentary type, parentheses are used around the corresponding ONs and OFFs.

There are also ON-ON-ON DPDT switches, which are very useful and can even be wired as a SP3T.
« Last Edit: November 09, 2018, 08:40:12 AM by EBK »
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DLW

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Re: On/On vs On/Off/On Toggles
« Reply #2 on: November 09, 2018, 08:50:13 AM »
I should have worded my question better... If it only says SPDT in a build doc, how am I supposed to know if I should use an On/On or On/Off/On switch?

Also, is it a safe assumption that SPST will always use an On/On switch?

EBK

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Re: On/On vs On/Off/On Toggles
« Reply #3 on: November 09, 2018, 08:55:38 AM »
If it only says SPDT, it should be on-on.  On-off-on is more of a specialty switch, so it should certainly be spelled out in the docs if it is used.

A SPST is always an on-off switch.  It only has two contacts, so it can't have two on positions.  Although a SPDT is usually used, with only two terminals connected, where a SPST is called for.  In this case, an on-on SPDT makes a good SPST switch.
« Last Edit: November 09, 2018, 08:59:26 AM by EBK »
"There is a pestilence upon this land. Nothing is sacred. Even those who arrange and design shrubberies are under considerable economic stress in this period in history." --Roger the Shrubber

madbean

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Re: On/On vs On/Off/On Toggles
« Reply #4 on: November 09, 2018, 09:10:53 AM »
I should spell it out more clearly (although I think I have in more recent docs). SPDT is always On/On unless otherwise specified.

DLW

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Re: On/On vs On/Off/On Toggles
« Reply #5 on: November 09, 2018, 04:30:10 PM »
Got it. Thanks, guys.