How to use a potentiometer

A potentiometer is a variable resistor. How to use a potentiometer depends on what you want to achieve and I guess for that you need to know what a potentiometer can do. From now on I’ll refer to a potentiometer as a variable resistor.

Potentiometer pin out

How to use a potentiometer pin out

The potentiometer with the clips on the side opened so you can see inside the component.

A variable resistor has three terminals. Like a normal resistor it has a value. A 10K variable resistor will measure 10k across the two outer terminals. The middle connection is the wiper. This moves depending on where the variable resistor is set. If you put a multimeter across one end terminal and the middle wiper and turn the knob you will see the resistance value go from about zero ohms up to about 10K.

How to use a potentiometer inside

With the top removed you can see that the end terminals connect to a circular track. In this case made of carbon. the middle terminal connects to the wiper.

Don’t be surprised if the readings are a bit off as variable resistors are usually made with about a 20% tolerance. When the resistance is at its minimum the resistance between the other end terminal and the middle wiper will be at its maximum. Likewise if the variable resistor is set at the middle you should read about 5K from either end connection to the middle wiper.

How to use a potentiometer wiper

In the picture above you can clearly see the the copper wiper in contact with the carbon track. The transparent plastic is fixed to the wiper and the spindle of the device. 

Linear potentiometer

The above operation refers to a linear resistor. It is the simplest operation to understand. The other common variable resistor is a logarithmic one.

Audio potentiometer

A logarithmic variable resistor is also known as an audio potentiometer. It operates in a similar way to a linear variable resistor but the values will be different along its range of operation. A 10k log variable resistor will still measure 10k at its maximum and about zero at its minimum but it won’t measure 5K at its middle.

If you’ve ever built an audio amplifier and fitted a volume control you may have noticed that it called for a logarithmic variable resistor as opposed to a linear one. What would happen if you fitted a linear one instead? Well it would still affect the volume as it still alters its resistance between minimum and maximum but it would seem that it didn’t alter the volume much at all over half of its range, say between 0 and 5 but then between 5 and 10 it would go from really quiet to really loud. This is because of the way we hear sound. Without wanting to go into too much technical detail a doubling in decibels doesn’t lead to a doubling in sound levels as we hear it. Volume alters logarithmically, hence the logarithmic variable resistor. That’s why it is sometimes referred to as an audio variable resistor.

Sliding potentiometer

Variable resistors are not only rotary. You may come across sliding variable resistors. A long device but the operation is the same. The longer the sliding mechanism the more precise you will be able to control the resistance. They were originally used in sound mixing desks. You may have seen these in recording studios with long lines of them all together to control the volumes of individual sounds.

Dual potentiometer

How to use a potentiometer dual

The picture above shows a dual potentiometer. As you can see it's just two devices on the same spindle.

A dual potentiometer is exactly what it says on the tin. The one control moves two individual variable resistors. They are usual one on top of another with the spindle running down the middle. They just have two sets of terminals and function exactly as two separate devices. What are they used for? Usually when you want two separate things controlled by one device. A stereo amplifier for instance. Its two separate amplifiers for left and right channels and you usually want the one volume control hence a dual variable resistor. As they are usually used for audio they are more commonly logarithmic as well.

Hopefully this article has given you a better idea of how to use a potentiometer by showing you what goes on inside. It's quite a simple device and doesn't take much to fully understand it's operation and uses.