Electronic Circuits

Applications Of Variable Resistors In Electronic Circuits

April 16, 2024

An electronic resistor is one of those electronic components with a wide array of applications in devices we use daily. This is because resistors perform one of the key functions in electronic circuits: controlling the flow of current. 

Have you ever wondered how the volume of your TV changes as soon as you press the volume button on the remote? 

Similarly, how does the speed of certain motors vary? 

These questions might arise occasionally, but we don’t know what exactly happens behind such a simple yet revolutionary phenomenon. Well, next time any such curiosity arises, know that the electronic part responsible for these things is called a variable resistor. 

Let us dive deep into the world of variable resistors and learn about their different applications in our daily lives.

Variable Resistor – Definition

As discussed above, a resistor is an electronic component that controls or resists the flow of current through an electronic circuit and depletes power in the circuit. Ohm’s law is the principle that governs the working of a resistor. 

As its name suggests, a variable resistor can be controlled to control how much current flows through the circuit. The difference between a normal and a variable resistor is that a variable resistor has three terminals instead of two in a normal resistor. The third terminal changes the resistance between zero and a certain value. 

Types Of Variable Resistor

There are several types of variable resistors whose resistance can be varied with respect to different environmental parameters. These types are as follows. 


A potentiometer is one of the most commonly used types of variable resistors. It can be mechanical or digital and is used in circuits where voltage is to be controlled. 

A trimmer potentiometer, or trim pot, is a small potentiometer used to calibrate and tune circuits. A trimpot resistor can be single-turn or multi-turn. When used as variable resistors, they are called preset resistors. 


If current limitation or adjustment of resistance is required, rheostats are the go-to variable resistor. A rheostat is constructed in a similar pattern to a potentiometer. The only difference between the two is that the moving terminal of a rheostat is short-circuited with one of the side terminals. 


This type of variable resistor is temperature-sensitive, and its resistance changes as the temperature value changes. A thermistor has two types: PTC, or positive temperature coefficient thermistor, and NTC, or negative temperature coefficient thermistor. 

PTC thermistors’ resistance is directly proportional to the temperature, whereas an NTC thermistor’s resistance is inversely proportional to the temperature.


A humistor is a variable resistor whose resistance increases or decreases with an increase or decrease in humidity. Many IoT, or Internet of Things, devices use humistors for the detection of changes in the surrounding environment. 

Applications Of Variable Resistor

Variable resistors have a number of useful applications in various electronic devices. Some of the most common applications are discussed below. 

Volume Control

A potentiometer is the variable resistor involved in volume control in electronic devices. A volume control circuit connects a potentiometer and audio signal path in series. Volume control is achieved by changing the resistance of the potentiometer, which adjusts the levels of audio signals. 

A fixed resistor, also called a load resistor, determines the maximum volume level. The potentiometer’s input terminal receives the audio signal, and the output terminal, like an amplifier, connects to the next stage of the circuit. 

Turning the potentiometer to the opposite end of its starting point lowers the resistance between the input and output terminals, increasing the volume level. The resistance of the potentiometer is inversely proportional to the volume. 

Motor Control

Potentiometers and rheostats are the two variable resistors commonly used to control motor speed regulations. However, their functions are different. Potentiometers change the voltage applied to a motor to adjust its speed. The motor, potentiometer, and fixed resistor are connected in series.

The resistance of the potentiometer varies as it is turned. This alters the voltage applied to the motor, thereby changing its speed. Potentiometers are commonly used to control the speed of small DC motors, radio-controlled vehicles, and other low-power applications.

Rheostats regulate the flow of current through a motor, affecting the torque or power output. In the case of rheostats, voltage is kept constant across the circuit, and they are connected in series. Turning the rheostat changes its resistance, which changes the torque or power output by changing the flow of current. Contrary to potentiometers, rheostats are used in high-power motors.

Brightness Control

Potentiometers are also used to control the brightness of a light source. The current flow in the light source is regulated by changing the resistance of the potentiometer, which is connected to a fixed resistor in series. The light brightness changes to dim when the potentiometer is set to maximum resistance, and vice versa.

Temperature Control

Rheostats are used for temperature control. A rheostat resistor regulates the amount of current flowing through a heating element, allowing the temperature of a space to be controlled. In temperature control applications, a rheostat can also control the speed of the fan. 

Signal Amplification

One major application of variable resistors is signal amplification. This is accomplished by adjusting the resistance in the voltage divider circuit. A potentiometer is used to vary resistance and adjust the output voltage level.


Potentiometers help electronic circuits fine-tune their frequency. Radio or audio circuits usually use potentiometers for frequency tuning. Variable resistors are preferred over fixed resistors for tuning purposes because of their ease of use.


Variable resistors have a number of useful applications in our lives, making them an important electronic component. From temperature control to volume control, from signal amplification to controlling motor speed, from brightness control to tuning of signals, variable resistors are everywhere. And when it comes to buying such an important electronic part, there is only one reliable marketplace: Partstack.

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