This book presents the fundamentals of PLCs and explains in a practical approach how to draw Ladder Logic diagrams to represent PLC design methods for wide variety of automated applications. Building Arduino PLCs starts by explaining how to build and test a simple Arduino-based 5V DC PLC with Arduino hardware and Grove base shield. You'll then learn how to build 12V DC PLC with Arduino hardware, relays, and various passive components. Then the final part of the book will show readers how to control 120v/240V applications with PLCs by enhancing the design with optocouplers and relays. The Arduino development environment, including Arduino UNO, Arduino Ethernet board, Arduino Ethernet shield, and Arduino WiFi shield are also featured in building a set of simple to complex PLCs.