Potentiometer: A Variable Resistor

This blog post on potentiometers (variable resistors) is an excerpt from Lesson B-10 of our Intro to Robotics program. Level B is the second level in Intro to Robotics and covers working with electronic components (including a variety of sensors), writing intermediate-level code commands in Python, and using a Raspberry Pi to control your electronics projects with the code you write. It contains 575 pages with 18 lessons and 57 projects and activities. Sample lessons and a full scope and sequence for Level B can be found here.

 

A variable resistor is a resistor that can change value based on user input. These devices are also called potentiometers or "pots" for short.

Variable resistors have a rotary knob or slider that changes their internal resistance when a user moves the knob or slider. They are commonly used in audio equipment for volume control, but they can show up in other places like lighting dimmer switches and mechanical joysticks. They can be used any time user input needs to be measured so it can be processed by a circuit or program.

You can also find potentiometers on the circuit boards inside most electronic equipment. If an exact voltage or resistance level is needed for a circuit to function properly, a potentiometer can be added so the circuit can be tuned to operate as intended, without removing and reinstalling resistors of different values.

Variable resistors have many variations, but the most common models have three leads. Two leads are connected to the ends of a resistive track and one lead is connected to a wiper.

The wiper moves up and down the resistive track, changing the resistance between the wiper and each end point. In rotary knob potentiometers the resistive track is wrapped around a circle, but the output is the same. As the wiper moves closer to one end of the resistive track, the resistance between the wiper and that end decreases. Inversely, as the wiper moves further from the other end, the resistance between the wiper and that end increases.

Potentiometer wiper arms diagram

Each different style of potentiometer will have its resistive track and wiper pins in different locations, so refer to the datasheet from the vendor if you're unsure of the pinout. Here is an image of the pinout of the potentiometer included in the Intro to Robotics Level B kit:

Diagram showing specific potentiometer included in kit

 

Breadboard circuit with potentiometer

 

This blog post on potentiometers (variable resistors) is an excerpt from Lesson B-10 of our Intro to Robotics program. Level B is the second level in Intro to Robotics and covers working with electronic components (including a variety of sensors), writing intermediate-level code commands in Python, and using a Raspberry Pi to control your electronics projects with the code you write. It contains 575 pages with 18 lessons and 57 projects and activities. Sample lessons and a full scope and sequence for Level B can be found here.

 

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