This book is about using both the Raspberry Pi 4 and the Arduino Uno in PID-based automatic control applications. The book starts with basic theory of the control systems and feedback control. Working and tested projects are given for controlling real-life systems using PID controllers. The open-loop step time response, tuning the PID parameters, and the closedloop time response of the developed systems are discussed together with the block diagrams, circuit diagrams, PID controller algorithms, and the full program listings for both the Raspberry Pi and the Arduino Uno. The projects given in the book aim to teach the theory and applications of PID controllers and can be modified easily as desired for other applications. The projects given for the Raspberry Pi 4 should work with all other models of Raspberry Pi family. The book covers the following topics: > Open-loop and closed-loop control systems > Analog and digital sensors > Transfer functions and continuous-time systems > First-order and second-order system time responses > Discrete-time digital systems > Continuous-time PID controllers > Discrete-time PID controllers > ON-OFF temperature control with Raspberry Pi and Arduino Uno > PID-based temperature control with Raspberry Pi and Arduino Uno > PID-based DC motor control with Raspberry Pi and Arduino Uno > PID-based water level control with Raspberry Pi and Arduino > PID-based LED-LDR brightness control with Raspberry Pi and Arduino Uno The full program listings of all the projects discussed in the book may be downloaded free of charge from the Elektor Store website, www.elektor.com (search for: book title).