Potentiometer Wiring, does it make a difference?

Thread Starter

SamR

Joined Mar 19, 2019
1,151
I don't think it does, but I had to ask... see attachment.
 

Attachments

Audioguru

Joined Dec 20, 2007
11,251
LTspice cannot find the symbol for a potentiometer.
Please post your schematic instead of the simulation.
 

WBahn

Joined Mar 31, 2012
24,693
I don't open asc files -- too much of a headache for me. Others will and can comment on the particulars of your schematic.

It usually does matter -- sometimes a lot and sometimes not too much. Often how you hook it up determines whether the output signal increases as you turn it clockwise or the other way around. That is often a pretty big difference.

It also depends on whether you are using the pot as a potentiometer, or as a rheostat.

There are a number of issues that can come into play, such as noise pickup or the potential to burn out the pot as you get the wiper to close to one end.
 

Thread Starter

SamR

Joined Mar 19, 2019
1,151
Try this... The potentiometer symbol is an add-on and not a standard out-of-the-box one included w/ the installation.
pot-wiring.png
 
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WBahn

Joined Mar 31, 2012
24,693
What kind of differences are you concerned about? In two of the circuits the wiper will always be at the same potential as the negative terminal of the supply and in the other two it will be at the positive. Is that a difference that matters?

In two of the circuits you have a dangling part of the potentiometer that will act like a noise antenna. Is that a difference that matters?

There's no indication given of which side of the pot the wiper goes to when it is full clockwise. Is that a difference that matters?

If none of these matter and all you care about is the total resistance seen by the supply, without concern as to whether CW rotation increases or decreases the load, then it doesn't matter. Note that it all four circuits you have the potential for high currents when you are at a low resistance value and that can burn out the end of the potentiometer and/or the wiper contact.
 

Thread Starter

SamR

Joined Mar 19, 2019
1,151
I understand about CW and CCW and orientation although I thought CW was supposed to increase resistance. Let me be more specific. Do both ends and the wiper need to be connected or just one end and the wiper. I have encountered the argument before dealing with pots to adjust LCD backlight and it was stated that only the + to one end of the pot and the wiper to the device needed connecting. Is this valid (it obviously works) and are there any problems doing that? Or even connecting the wiper to + and one end to the device. I wouldn't think so, but am I missing something?
 
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eetech00

Joined Jun 8, 2013
1,660
I understand about CW and CCW and orientation. Let me be more specific. Do both ends and the wiper need to be connected or just one end and the wiper. I have encountered the argument before dealing with pots to adjust LCD backlight and it was stated that only the + to one end of the pot and the wiper to the device needed connecting. Is this valid (it obviously works) and are there any problems doing that? Or even connecting the wiper to + and one end to the device. I wouldn't think so, but am I missing something?
As pointed out in post #6.

It depends on the application but all three pins should be connected to something. If one pin is left dangling it can act as a antenna.

eT
 

Thread Starter

SamR

Joined Mar 19, 2019
1,151
In two of the circuits you have a dangling part of the potentiometer that will act like a noise antenna. Is that a difference that matters?
BINGO! That's the answer I needed. Now I understand why both ends are connected. Thank you!
 

crutschow

Joined Mar 14, 2008
23,340
Another consideration is that if one end is left open, any momentary break of the wiper connection will cause an open circuit.
If the wiper is connected to one end, then a break only causes the circuit to go to the pot resistance value, not an open circuit.
 

MisterBill2

Joined Jan 23, 2018
3,873
Please consider that not all potentiometers are linear, by design. Volume control pots have what they call a log-taper, which approximates a constant dB change in volume per unit of rotation. So for those types, which direction matters a lot. Post #5 mentions taper but does not go in to much detail. And post #10 does make a good point about the resistance variations while turning the pot. So usually, For linear devices, the final choice would be which connection delivers the results that you want as it is turned in the direction selected. For non-linear tapers and functions the normal approach is to use the connection that produces the most uniform change per unit of rotation.
 

Audioguru

Joined Dec 20, 2007
11,251
I do not like to see that in all four of your schematics the pots short the V1 power supply, then each pot smokes and burns when its resistance is turned down vey low. None of your pots are used as an adjustable potentiometer(DC or volume control), they are just shown as a shorting rheostat.
 

AnalogKid

Joined Aug 1, 2013
8,103
I understand about CW and CCW and orientation although I thought CW was supposed to increase resistance.
If, in your four schematic, the wiper moves upward with CW rotation, then resistance decreases in #1 and #2, and increases in #3 and #4. It depends entirely on how you connect the device. Hint: an industry standard convention for normal pots and trimpots is that pin 1 is the CCW end, pin 2 is the wiper, and pin 3 is the CW end. If you add pin numbers (or CW and CCW) notations to the two end pins, it is more clear what happens when the wiper turns each way.
Do both ends and the wiper need to be connected or just one end and the wiper.
In a perfect world, just one end. But ...

IF shock or vibration causes the wiper to bounce and momentarily lose contact with the resistive element
OR IF a particulate contaminant gets inside and the wiper loses contact
THEN the impedance at the wiper node jumps to infinity. Depending on the circuit or system, this could be ... exciting.

ak
 

Thread Starter

SamR

Joined Mar 19, 2019
1,151
IF shock or vibration causes the wiper to bounce and momentarily lose contact with the resistive element
OR IF a particulate contaminant gets inside and the wiper loses contact
THEN the impedance at the wiper node jumps to infinity.
Ahhh… Another good reason that I didn't consider. Thanks.
 

Thread Starter

SamR

Joined Mar 19, 2019
1,151
not all potentiometers are linear, by design
Except digipots, but I can program for that. Don't see log pots much anymore. 50+ years ago I built an electronic slide rule using log pots and a beat frequency oscillator. Not very accurate compared to my 12" K&E, but a fun little project. That was before pocket calculators and it was nowhere near pocket size.
 

djsfantasi

Joined Apr 11, 2010
5,600
Except digipots, but I can program for that. Don't see log pots much anymore. 50+ years ago I built an electronic slide rule using log pots and a beat frequency oscillator. Not very accurate compared to my 12" K&E, but a fun little project. That was before pocket calculators and it was nowhere near pocket size.
What about audio taper pots? Another name for log pots. They are necessary in audio circuits for volume setting.
 

Thread Starter

SamR

Joined Mar 19, 2019
1,151
I do not like to see that in all four of your schematics the pots short the V1 power supply, then each pot smokes and burns when its resistance is turned down vey low. None of your pots are used as an adjustable potentiometer(DC or volume control), they are just shown as a shorting rheostat.
It was just a quickie schematic for demo purposes, not something I would use. I have learned to protect against low resistance. Most audio has gone digital so the log pot is becoming scarce (is that the word I want?). I tend to use linear pots (usually a trimmer) as a voltage divider to tweak a timer circuit or to control LED brightness.
 

MisterBill2

Joined Jan 23, 2018
3,873
What about audio taper pots? Another name for log pots. They are necessary in audio circuits for volume setting.
I mentioned that several posts back and it has been diligently ignored. Except to say that nobody uses them any more. Folks need to keep in mind that the real world is all analog and not as linear as many would wish.
 
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