Rotary pot with switch

[breakshift]

I've not used one before and the datasheets aren't clear on how they actually work. I'd like to use a rotary pot with an 'off' position on the counter clockwise side to turn off my circuit. It'll be a volume control (attenuator prior to audio amp) so I'd like to have it also switch the circuit on and off. I've looked at a few but for example the RV170SF:

**broken link removed**

With regard to this datasheet, when you turn it round CCW and into the switched position, does this close a switch between the wiper terminal and the OFF terminal, or does it close the ON and OFF terminals together? I need it to switch two independent terminals so I can use them to connect a battery to the rest of the circuit, independent of the normal pot terminals. I could use a push switch pot but I prefer the rotary concept. I suppose I could use a dual-gang rotary pot with switch and use the second gang to switch the circuit on and off, but there are fewer of them to chose from.

 

[alec_t]

The switch is usually (always?) a single-pole normally-open type entirely independent of the actual 3-terminal pot. Turning the pot knob clockwise closes the switch while the wiper is still at the 'low' end of the pot resistance track.

 

[4pyros]

I need it to switch two independent terminals so I can use them to connect a battery to the rest of the circuit, independent of the normal pot terminals.

As alec_t said they are already to separate circuits.
How ever the pot does not have a true off position just all the way down.
You don't really need an off position for the volume pot do you? as well as the on/off for power.

 

[KeepItSimpleStupid]

The other spec you need to be cognizant of is the tapers. For an audio attenuator, generally you would want an audio, log or type A taper. They are all the same.

See: **broken link removed**

 

[breakshift]

Good, that's what I need then. The diagrams on the data sheets are a bit misleading in my opinion.

No for what I need the pot itself doesn't need to turn off, just the switch. And yep I will use a log taper since this for controlling volume.

Cheers

 

[Dean Huster]

The switch is usually (always?) a single-pole normally-open type entirely independent of the actual 3-terminal pot.

I'd say that the switch is ALWAYS independent of the pot unless you externally wire it otherwise. As for the switch characteristics, I've seen full CCW open, full CCW closed, full CW open, full CW closed; I've seen SPST as well as SPDT and DPST. If you work with Allen-Bradley etc. brands, you can build up whatever you want, including stacking four independent pots or have switches with DPDT or even 4PDT configurations by adding more and more switch modules. The A-B pots that I've harvested over the years have been taken apart and stored that way so that I can build them into whatever I need at the time. That's the beauty of modular pot construction using screws vs. rivets. With lots of pot and/or switch modules, you can end up with a thing that is four inches deep behind the front panel. That's a good reason for digital pots.

 

[breakshift]

What about this one?

https://uk.farnell.com/vishay-sfernice/p16snp103mab15/pot-w-switch-linear-10k-ohm-20/dp/2360073

Expensive, yes, but I like that it's all-included and it looks decent quality. But again the operation mode of the switch is unclear - and in the picture (on the datasheet) it clearly has three terminals, not five. So how can it have a separate switch - very confusing.

 

[4pyros]

What about this one?

https://uk.farnell.com/vishay-sfernice/p16snp103mab15/pot-w-switch-linear-10k-ohm-20/dp/2360073

Expensive, yes, but I like that it's all-included and it looks decent quality. But again the operation mode of the switch is unclear - and in the picture (on the datasheet) it clearly has three terminals, not five. So how can it have a separate switch - very confusing.

From the data sheet
"Actuation in counter clockwise position (between terminal a and terminal b)"
Seems odd not sure how you would use this arrangement to switch power. Maybe on a micro or something, but it will not work for you.

 

[alec_t]

Coincidence?
https://www.electro-tech-online.com/threads/5-leg-potentiometer-in-metal-detector.140940/

 

[breakshift]

From the data sheet
"Actuation in counter clockwise position (between terminal a and terminal b)"
Seems odd not sure how you would use this arrangement to switch power. Maybe on a micro or something, but it will not work for you.

I read the datasheet but don't really understand what that bit means..? So the switch actuation is on the counter clockwise side of the pot, yes, but 'between terminal a and terminal b'? What does that mean?

 

[4pyros]

I read the datasheet but don't really understand what that bit means..? So the switch actuation is on the counter clockwise side of the pot, yes, but 'between terminal a and terminal b'? What does that mean?

It opens and closes a connection between terminal a and terminal b disregarding the fact that they are also used for the potentiometer.

 

[breakshift]

Ah right. Not sure how that'd be useful at all. I suppose if it was important to know that you'd turned the pot right down, the mechanical feel of it switching into place may be useful.