Whether you work or play with electronics, at some point you’re going to want to adjust the behaviour of your circuit with a knob or come across a symbol that looks like this in a schematic diagram.
These two symbols both represent a potentiometer – the first symbol is more common in Europe, the second more so in the United States – and a potentiometer is the most common way to adjust the behaviour of a circuit. But what exactly is this component, how does it work and what are some common uses for it?
What is a potentiometer?
A potentiometer (often referred to as a “pot” informally) is a three-terminal resistor, with two fixed connections at each end of a resistive element and a third “wiper” connection that slides across the surface of the resistive element between the two fixed connections.
This means that the total resistance between the two fixed connections stays the same (10kΩ would be a common value) and the resistance between the wiper and each end varies with the position of the wiper.
*Images courtesy: ITP Physical Computing, Tom Igoe
This position can usually be varied by either rotating a shaft connected to the wiper or sliding a shaft which can move linearly along the length of the resistive element. The “rotary pot” setup is commonly used for volume or balance controls on audio amplifiers – a “linear pot” is more commonly found in faders on a mixing desk.
It is also possible to find “multi-turn” rotary potentiometers which use either a coiled resistive element or a gearing system to allow for more precise adjustment – these are commonly found in precision scientific equipment.
Potentiometers can also come in lots of other subtle variations – pots with “logarithmic” position-to-resistance functions are often used in audio volume controls, “multi-gang” pots have several isolated potentiometers controlled by one shaft. These are useful in stereo audio controls where you want each signal to pass separately through a potentiometer, but to have good volume matching between each channel.
One significant different type of potentiometer is a “trimmer”, or “trim pot”. These are generally smaller devices and are often adjusted using a screwdriver or allen key and tend to not have a shaft. These are commonly hidden inside equipment and used for setting calibration points or adjustments at the factory and are not intended for frequent adjustment.
What are potentiometers for?
As we have already covered, potentiometers are used to control circuit parameters – but what common circuit parameters get controlled this way, and how? Here are a few (very basic) sample schematics to give you some inspiration! None of these circuits is ideal or intended to be built as they are – they simply show how a potentiometer can be used in a real circuit.
1. Audio volume control
This is a very simple audio volume control that’s suitable for adjusting the level of incoming audio from a low-impedance line source before passing it on to further amplification stages. Here, you can see that the full input voltage is applied across terminals 1 and 3 of the volume pot and we tap it out via the wiper.
If we wind the wiper fully towards terminal 1 we will get the full input voltage at the wiper. If we wind it all the way towards terminal 3 we will ground out the wiper and we will hear nothing. At positions in between, we’ll see a scaled down version of the original signal depending on the exact position of the wiper (and the shaft that it is connected to).
Note that for this circuit, because of the way that human hearing works, a logarithmic potentiometer will give the most natural feel to the volume control and allow for the finest control at low volumes.
2. Adjustable frequency generator
In this circuit, we use the potentiometer in a slightly different way. By connecting one of the end terminals to the wiper, we effectively short out the second half of the resistive element. This means that we have effectively created a variable resistor from the potentiometer.
This versatility is the main reason that you only very infrequently see dedicated variable resistors (as manufacturing a potentiometer of the same specification is about as much effort). As you adjust the potentiometer in this circuit, the frequency of the rectangular wave at the output will vary – you could use this to make the basis of a synthesiser!
It’s useful to note the addition of an extra resistor above the potentiometer (or variable resistor, as it is in this circuit). This helps to avoid the circuit behaving strangely when the pot is set to its minimum value by setting a minimum resistance between pins 6 and 7 on the 555. Without this, the resistance between these two pins could get very close to 0, which is not desirable.
3. Input to an Arduino
Sometimes we want to do something more complex using a potentiometer. Perhaps you want to use a potentiometer as an input to a game that you are developing on an Arduino (or similar microcontroller platform). Here, we want to turn the position of the potentiometer into something that our code can use – a number representing the position, perhaps.
One way of doing this is to set the pot up as a potential divider and read the output voltage into the Arduino via one of its analogue input ports. The schematic below shows how to do this – and the tutorial link after takes you to an Arduino learning page with more info and some code to get you started.
Can you use Electric Paint to make a potentiometer?
If you’re interested in understanding more about the fundamentals of potentiometers, one fun idea to try making one of your own. Since our Electric Paint is easy to paint and connect to, it is a useful tool for this sort of exploration.
In fact, we have four tutorials which us our paint as either a potentiometer or a variable resistor – check them out below!
Making a RGB Led Colour Slider
Building a 555 Noise Maker
Noise book by James Walker
Making a potentiometer with Electric Paint
Author: Stefan-Dzisiewski-Smith, Head of Technology