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Electronics Basics – How a Potentiometer Works

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A potentiometer, also referred to as pot, may come in a wide variety of shapes and are used in many applications in your daily life, for example to control the audio volume of the radio.

A pot is a manually adjustable variable resistor with three terminals.

In the figure below you can see some examples of potentiometers.

potentiometers

Symbols

In a circuit diagram, a potentiometer is represented by one of the two symbols below:

Potentiometer symbols

How Does a Potentiometer Work?

A potentiometer has 3 pins. Two terminals (the blue and green) are connected to a resistive element and the third terminal (the black one) is connected to an adjustable wiper.

Fig. 3

The potentiometer can work as a rheostat (variable resistor) or as a voltage divider.

Rheostat

To use the potentiometer as a rheostat, only two pins are used: one outside pin and the center pin. The position of the wiper determines how much resistance the potentiometer is imposing to the circuit, as the figure demonstrates:

Fig. 4

If we have a 10kΩ potentiometer, it means that the maximum resistance of the variable resistor is 10kΩ and the minimum is 0Ω. This means that by changing the wiper position, you get a value between 0Ω and 10kΩ.

Voltage divider

Potentiometers can be used as voltage dividers. To use the potentiometer as a voltage divider, all the three pins are connected. One of the outer pins is connected to the GND, the other to Vcc and the middle pin is the voltage output.

potentiometer

When the potentiometer is used as a voltage divider, the wiper position determines the output voltage.  When you have the potentiometer connected this way, you have the following circuit:

voltage divider

Basically, the voltage divider is used to turn a large voltage into a smaller one.

The output voltage can be calculated using the following equation obtained from Ohm’s Law:

formula voltage divider

Potentiometer Taper

One main concept associated with potentiometers is the taper. The taper is the relationship between the position and the resistance of the potentiometer. The most common types are linear and logarithmic tapers.

Linear potentiometers

The most common form is the simple linear taper. In a linear taper, the relationship between the resistance and the potentiometer position is linear.

This means that if the knob of the potentiometer is at the medium position, the output voltage is half of the voltage throught the potentiometer. See the figure below:

linear

Potentiometers with linear taper are marked with a B.

tipoB

Logarithmic potentiometers

Non-linear tapers are specially used in audio control applications, namely logarithmic tapers (there are also inverse-logarithmic tapers). The relationship between the position and the resistance is shown in the following figure:

log

Potentiometers with logarithmic taper are marked with an A.

tipoA

Wrapping Up

I hope you’ve learn something new today and you’ve found this explanation useful.

If you’d like to know more about electronics basics or if you’d like to start into the world of electronics make sure you check out our Electronics for Beginners eBook.

Thanks for reading,

– Rui and Sara

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