In your travels in the world of electronics, however casual, you have most likely encountered the term “PID controller.” In this Digi-Key video, Shawn offers a crystal clear introduction to PID (proportional, integral, derivative) and the science of Control Theory behind it.

In the video, we use an example of a cruise control system in a car. We want to design a mechanism that can maintain a constant speed by controlling the position of the accelerator (gas pedal). PID controllers are a perfect fit for such a system. In fact, most modern cars use PID controllers for cruise control.

A simple, naive approach to designing such a controller is to adjust the process’s input signal based on the set point alone with no feedback. This is known as an “open-loop control system.” This may work in some cases, but most of the time, the output is dependent on other factors (such as road conditions and hill climbs for our cruise control system). As a result, we need to incorporate feedback into our controller.

A “closed-loop control system” measures the actual output of the process and compares it to the set point. The error is the difference between these two values, and it’s used as the input to the controller. The controller looks at that error and makes adjustments as needed to the process’s input.