LabVIEW and arduino as a gateway to PLC programming

Abstract

The key topics of an instrumentation and controls course are a) the transducers that convert the phenomenon of interest into a predictable signal b) the actuators that influence the process in question and c) the hardware and software that control these outputs based the measured inputs. Common candidates for these control systems are data acquisition (DAQ) systems, microcontrollers, and programmable logic controllers (PLCs). Outside of the electrical engineering technology curriculum, engineering technology undergraduates at the University of North Carolina at Charlotte do not cover any of these devices until taking a single course junior or senior year. In a graduate course focused on facilities instrumentation and controls, National Instruments DAQ systems, Arduino microcontrollers, i-TRiLOGI ladder logic simulator and Allen Bradley industrial PLCs were introduced in that order to quickly bring students up to speed on the strengths, weaknesses, and suitable applications for each device. The graduate students in the class came from both civil engineering and construction management undergraduate programs. As such, they had limited backgrounds in electronics and programming. This assessment was reflected in an initial course survey where students rated their abilities in electronics theory, electronics hands on, LabVIEW, and MATLAB as being weak, slightly weak, or average (the three lowest categories on the survey). Conversely, they rated their abilities in math and physics as being average, strong, or very strong (the three highest categories on the survey). National Instruments LabVIEW and a NI USB-6009 multifunction DAQ were chosen as a starting platform given the graphical programming environment, readily available tutorials, and integration with the hardware. Students were shown demonstrations involving simple breadboard circuits before the students worked in small groups to replicate and extend the LabVIEW code and breadboard wiring to include both measurements and control circuits. After completing the breadboard exercises with LabVIEW and the USB DAQ, students were introduced to the Arduino 1.0 Integrated Development Environment (IDE) and an Arduino Uno microcontroller. As a high level programming language, students viewed the Arduino sketches as easy to follow given a limited introduction in lecture and access to the Arduino website. The abundance of published sketches made it easy for students to see the versatility of the microcontroller platform and learn common coding structures. Other key skills that were acquired through the Arduino exercises included effective documentation of code, addressing inputs and outputs, and understanding the difference between analog outputs (available on the NI USB DAQ) and the emulated analog outputs utilizing PWM (available on the Arduino Uno). Ladder logic was introduced with i-TRiLOGI ladder logic simulators. Relay ladder logic was presented with a focus on the similarities to the graphical, 'wiring' approach to programming found in LabVIEW. The Arduino skills of addressing inputs and outputs and documenting code were also reemphasized as was a focus on program/logic flow. Allen Bradley PLCs programmed with RSLogix 5000 software were the final platform introduced to the students, applying their acquired knowledge of ladder logic from i-TRiLOGI to industry grade hardware and software. Throughout Arduino, i-TRiLOGI, and RS Logix 5000, a common exercise was used to highlight the similarities, differences, and capabilities of each platform. © American Society for Engineering Education, 2013.