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Introducing PLC Programming in the Digital Logic Course

Digital logic is a foundational class typically offered to electrical engineering, computer engineering and computer science students early in the curriculum. This class typically covers the analysis and design of combinational and sequential circuits. The laboratory portion of the course usually includes design of digital systems using standard combinational and sequential modules. The designed digital systems are described using a hardware description language such as VHDL, simulated using Computer-Aided Design (CAD) tools such as ModelSim, synthesized using CAD tools such as Xilinx, and verified/tested on FPGA boards.

Programmable Logic Controller (PLC) programming is typically covered within a control systems course or an elective later in the curriculum, if at all. Feedback from industrial partners has identified a need to introduce PLC programming as early as possible in the curriculum. For students who are seeking summer internships or co-ops in industry, their training experience will be richer if they have the necessary background in PLC programming beforehand.

Although introducing PLC programming in a digital logic course is unusual, it has been done very smoothly in this work due to the similarities between the two topics. It also benefits students to develop a digital system that interacts with sensors and actuators. A PLC program can be modelled using Finite State Machines (FSM), which is one of the topics that is traditionally covered in the digital logic course.

This paper will describe the PLC lab component has been added to the last two weeks of class. First students work through an introductory lab on PLC programming to introduce them to the PLC hardware, the PLC programming environment and the basics of ladder logic. Next, students are given a request for proposals by a fictitious local government who is interested in installing and controlling a four-way traffic light. Students work on the PLC program to implement different traffic light modes, wire a traffic light prototype to the PLC, find the specifications of a typical PLC that can do the job, write a reply to the request for proposals that includes the following sections: introduction, design details, prototyping and testing results, specifications and bill of material, budget and justification including hourly rate, estimated delivery time and conclusion.