Introduction: Wire a Potentiometer As a Variable Resistor

At some point in an electronics project you might find yourself needing a variable resistor.  Here's how to make one using a potentiometer.

Variable resistors are useful for the following:

adjustable gain of an amplifier
adjustable cutoff frequency of an RC filter
change the brightness of an LED
making measurements with a wheatstone bridge
adjusting the sensitivity of sensors wired in series/parallel to the variable resistor
testing- find the best resistance for your circuit before soldering a non-variable resistor in permanently

Normally, potentiometers are wired as variable voltage dividers:  connect +V to one side, connect the other side to ground, and the middle pin will output a voltage between 0 and +V (fig 2).
However, by only connecting two pins (one outside pin and one center pin) of a potentiometer to your circuit, you can turn a pot into a variable resistor.  Think about it this way: the potentiometer is filled with resistive material and turning the knob changes the amount of this material that the electrons must travel through before leaving the pot.  This means that the maximum resistance of this variable resistor is the total resistance of the pot.  In figure 1 the pot has a total resistance of 10kOhms, so if the pot is turned all the way to the left the resistance between the two black wires is 10kOhms.  If the pot is turned all the way to the right the amount of resistive material between the two black leads drops to zero and the resistance goes to zero as well.  Any position in the middle will give a resistance between 0 and 10kOhms.  If I'd soldered a wire to the left lead instead of the right all of this will flip: turning all the way to the left is 0Ohms and all the way to the right is 10kOhms.

One thing you might want to keep in mind when using this technique is the taper of your pot.  This pot has a B label on it, which means it is a linear taper pot.  This means the resistance of the material inside the pot is uniform for all positions of the knob.  If the knob of the pot is positioned exactly halfway between the two extremes, the resistance between the black wires equals 10kOhm/2 = 5kOhm.  Position the knob halfway between this mid point and the right extreme and the resistance between the two wires equals 10kOhm/4 = 2.5kOhm.  If the wiring is reversed (wires connected to the left and middle pin instead of right and middle) the pot is still linear but the knob positions of 0Ohm and 10kOhms have reversed.
If you have a pot with an A label on it it has a logarithmic taper: the resistive material inside the pot is not uniform.  When you move the knob from the right extreme the resistance changes dramatically then becomes almost constant as you approach the left extreme position.  So if you wire up the right and middle leads (as shown in fig 1) the dramatic change will happen as you approach 0Ohms resistance, but with the left and middle leads connected the dramatic change happens as you approach 10kOhms resistance.  See fig 3 for more detail (from  Depending on what you are doing you may find one preferable over the other


Yesper made it!(author)2017-02-27


Im want to swap two trimpots for one dual-gang potentiometer. The pot is supposed to function as a variable resistor and will need a 22k resistor in series to set a minimum resistance. How am I supposed to wire the dual-gang to have the resistor work on both "gangs"?

dhwolfer made it!(author)2016-11-03

Here is what I need. I am trying to produce a supply that has a variable output of AC from 0 volts all the way up to 120. I would like to wire in a digital display that would actually give what the output of the terminals would be at each stage. For instance, if the POT was turned to say the middle while the input was always 125vac and then watch the output voltage on the digital display until it reaches the voltage I need at the time. I need the full spectrum of 0v to 125vac in because I will be using this as a testing platform for different things. Is there any way to do this cheaply? Thanks. I have not found anything on line that would do this. So I would appreciate your help.

DavidI22 made it!(author)2016-11-04

BTW, the unit listed only has a range of 2.5 to 30 volts so wouldn't work for your 120 volt AC application. Maybe the site has other products that would work?

dhwolfer made it!(author)2016-11-04

What site are you talking about? If you mean the instructables site then I have not found a solution here yet.

DavidI22 made it!(author)2016-11-05

In the comments I gave a link to the meter display with a photo; the web store is called ''. I've ordered from them before, and have found similar parts on ebay and amazon. Good luck!

NickR63 made it!(author)2016-02-24

Is there a way to wire a digital display to this so that it reads resistance if you are doing something remotely? Say if you wire it to force resistance to go up and down, but as you twist the pot, you can't see what your reading is because the device you're checking is in a different room or floor and don't want to have to go back and forth to make sure you're within a tenth of what you need to be. Kind of like one of those small LED voltmeter displays?

DavidI22 made it!(author)2016-02-25

if you just want to measure a voltage, these are inexpensive:

dhwolfer made it!(author)2016-11-04

Do these work with AC or just DC? Thanks

DavidI22 made it!(author)2016-11-04

See the website link I listed for specs; in the comments a user says:

"Used to continuously measure multiple symmetric AC/DC variable power supplies. Precision is good. Adjustment is possible through a micro trimmer I recommend."

ViditG4 made it!(author)2016-09-21

Please help me to make a speed adjustable cpu fan please.

DustyS2 made it!(author)2016-08-07

How can i hook up a single gang b50k potentiometer to my amp? To use as a remote bass knob?

MikeH282 made it!(author)2016-05-16

Looking for a little help. I am doing a demo on Daisy Chain vs T tap wiring. I am getting 4 digital voltmeters. I want 2 to display the input voltage (120) I want one of the others to display slightly less (119) and the other to display 109. I understand basic electricity but don't know how to figure which of the 100s of potentiometer configurations will work for me.

Thanks for your help

AleksandrK11 made it!(author)2016-04-03

Hi. I have a question - is it ok to control DC motor with pot with an A label (audio)?

JorisL1 made it!(author)2015-07-28

I've seen something similar but with 2 pins bridged (one outer and the middle). What's the difference? Thx

DavidI22 made it!(author)2016-02-24

Bridging the outer and middle pins is done as a "failsafe"; see the section of this article:

"When a potentiometer is used as a rheostat, the
“unused” terminal is often connected to the wiper terminal"

Salman+Naveed made it!(author)2015-05-09

This is useful information. Also, it should be noted that a potentiometer cannot be used to slow down a motor or dim an LED.

Lolman4000 made it!(author)2015-05-30

Do you know how I could variably change the speed of a 6v ac motor?

gdomantic made it!(author)2015-05-11

why? :O I'm new to electronics and I have done it.

Salman+Naveed made it!(author)2015-05-12

A potentiometer can slow down a motor to some extent, but still, it can not be used as a speed regulator. A pot with higher maximum resistance will stop the motor when it is just little away from the zero position.

nuggu.subramanyam made it!(author)2014-11-02

may i know why we use variable resistors instead of resistors.for example for one project we need variable resistor and we set at 22k ,and why should we not use resistor of 22k,please give me answer soon

FighterLighter made it!(author)2015-02-22

I don't know if it's too late and you already have an answer to your question, but the only need for a variable resistor instead of a fixed resistor is if a person wants to choose between different resistances.

For your example, if the project calls for a variable resistor, but you only use 22k and no other resistance, you technically could just use a regular fixed resistor. If it's a school project, maybe there will be another use for the variable resistor in the future...?

Goturtlepoop made it!(author)2013-11-02

my pot is wired using the 3 posts....but my unit gets really hot.....can't figure this out

dpowell12 made it!(author)2012-12-23

it won't slow down an AC motor but a simple 6V DC motor it sure will... great info

tutdude98 made it!(author)2012-08-14

I get some pots from old electronics and i didnt know what pins i need to solder to leds and this really helped me

amandaghassaei made it!(author)2012-08-14

great! let me know if you have any questions!

scraptopower made it!(author)2012-08-12

I didn't think there was a "normal" use for pot. They get used in all kinds of different ways.

avionicskypilot777 made it!(author)2012-08-09

Thanks for the lesson. I had always wondered of the difference between an audio and linear potentiometer. I knew they could be used as variable resistors I just didn't know the difference between the two.

verence made it!(author)2012-08-09

Good info.

You might add a word about the amount of load a potentiometer can handle (i.e. next to nothing).

So a warning that potentiometer is NOT the way to slow down a motor would be nice.

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Bio: I'm a grad student at the Center for Bits and Atoms at MIT Media Lab. Before that I worked at Instructables, writing code for ... More »
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