Arduino Opta Trainer Wiring: A DigiKey Lab

Education
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Introduction

This hands-on lab serves as a wiring guide for the Arduino Opta Programmable Logic Controller (PLC) using a variety of DigiKey field devices as shown in Figure 1. This includes an industrial 22 mm switch, pushbuttons, a capacitive proximity sensor, a red-green panel indicator, a control relay, and a 24 VDC fan. The lab concludes with a troubleshooting session where a More Knowledgeable Other (MKO) inserts a variety of wiring flaws into the circuit. Students will gain independence and a greater understanding of the circuit by troubleshooting and then restoring the trainer to full operation.

Figure 1: Image of the complete PLC trainer showcasing the Arduino Opta PLC and supporting field devices.
Figure 1: Image of the complete PLC trainer showcasing the Arduino Opta PLC and supporting field devices.975×731 99.1 KB

Figure 1: Image of the complete PLC trainer showcasing the Arduino Opta PLC and supporting field devices.

The completed trainer may then be used to explore PLC programming using the IEC61131 languages of ladder logic, function block, structured text, sequential function block, and instruction list as well as the classic C++ language supported by the Arduino IDE. Programming is simplified as the trainer and associated wiring are a constant throughout the programming lessons.

Tech Tip: We can’t overemphasize the importance of wiring. Most real-world problems involve broken or loose wires. Technicians must quickly repair these problems. Engineers need to design robust systems that are easy to troubleshoot.

Prerequisites

The student must have some familiarity with industrial switches and relays. These DigiKey labs are considered prerequisites:

Tech Tip: The designation of More Knowledgeable Other (MKO) is used throughout this lab to indicate the collaborative relationship between the learner and others who act as instructor, mentor, supervisor, coach, or even the advanced student familiar with the material. A good MKO knows when to provide assistance, when to let the student struggle with independent learning, and anchors the topics into a greater framework of learning.

Learning Objectives

The lab objectives include:

  • to use hand tools to construct a physical assembly
  • to wire a PLC trainer that serves as the base for a variety of programming exercises
  • to wire a PLC-based systems using space-saving terminal blocks
  • to troubleshoot a PLC-based system leading to greater understanding of industrial control panel wiring

Tech Tip: Physically wiring a PLC system is an essential part of the learning process. It helps develop muscle memory so that you intuitively understand how and why things are connected the way they are. This is essential for troubleshooting as well as your ability to specify and design PLC-based systems.

At the same time, we recognize that learning to program a PLC is facilitated by a stable hardware platform. Consequently, this lab is a compromise, it provides a stable learning platform allowing you to focus on the IEC61131 programming languages.

Don’t skip the troubleshooting section! The MKO will challenge you, leading to a better understanding of the PLC wiring.

Measurable Assessment

Students will demonstrate mastery of the lab via these measurable assessments:

  • Assessment 1: The trainer is wired in accordance with the Figure 3 wire diagram and associated pictures.
  • Assessment 2: The trainer is disassembled. The individual student must rewire the trainer in accordance with the wire diagram within 15 minutes, with zero errors.
  • Assessment 3: The student can troubleshoot at least three increasingly complex wire problems inserted into the circuit by the MKO. This critical task can be done independently without assistance.

Required Materials

The required materials are shown in Figure 3. A complete description of each component may be found in the Guide to Selecting Components for Industrial Education. The parts checklist for this portion of the project includes:

  • DigiKey trainer with DC power distribution configured as described in this earlier lab.
  • Common hand tools such as a screwdriver, nut driver, wire cutter
  • Variety of pre-cut and ferruled wires
  • DC power supply capable of 24 VDC at up to 2 A with ability to automatically shift between constant voltage and constant current mode
  • 1 ea 22 mm on-off selector switch
  • 1 ea 22 mm industrial switch body with red pushbutton assembly
  • 1 ea 22 mm industrial switch body with green pushbutton assembly
  • 1 ea normally closed switch block
  • 2 ea normally open switch blocks
  • 1 ea NPN capacitive proximity sensor
  • 1 set of 3-tier terminal blocks for sensor connection
  • 1 ea 22 mm dual color Red/Green indicator
  • 1 ea DPDT control relay
  • 1 ea 60 MM 24 VDC fan

Figure 2: Image of the components as used in the experiment including the external DC power supply.
Figure 2: Image of the components as used in the experiment including the external DC power supply.975×731 82.7 KB

Figure 2: Image of the components as used in the experiment including the external DC power supply.

Tailgate / Toolbox Safety Brief

Before starting this lab, the student and More Knowledgeable Other (MKO) should conduct a tailgate briefing to review lab safety, objectives, and procedures. Recommend following this checklist:

  • Ensure that the experiment is conducted using an isolated 24 VDC current limiting bench power supply. While this is generally considered safe, always turn off the power supply when making adjustments to the circuit.
  • Review the PLC connections including power, input block and output block.
  • Review the concepts of sinking and sourcing as applied to PLC loads.
  • Review the Arduino Opta PLC IDE focus on establishing a connection between the PC and PLC.
  • Introduce the demo program including advanced program to view I/O status as described in this post.
  • Review troubleshooting procedures for industrial control systems

Tech Tip: Construct the PLC trainer in small steps. Take the time to test each section as you go. This can save considerable time and lead to a better understanding of the process.

Procedure

  1. Wire the PLC power, two green pushbuttons, dual indicator, and associated connections. Use blue wire for 24 VDC distribution and any wire that could potentially carry 24 VDC e.g., the switch to Arduino interconnection. Use white with blue stripe wire for any connections directly associated with the 24 VDC return line. As a rule, white with blue stripe wires are connected directly to the return section of the power distribution block.

Tech Tip: Wire color is a form of communication between the designer and all future personnel who will work on the panel. Wire color carries information about voltage levels and the intended purpose of the signal. In this example, blue is associated with a DC control signal. By contrast, a black wire would indicate a potentially dangerous AC signal – not to be used with this trainer.

  1. Work with the MKO to download and install this ladder logic program into the Arduino PLC. Note that this is a relatively advanced Arduino Opta program allowing the LEDs to display the status of the I/O as described here. While this program is effective for use in this wiring lab, we do not recommend it as a starting point.

InitialWire.plcprj (246.8 KB)

  1. Work with the MKO to verify that the red and green indicator lights operate when the selector switch is on, and the red pushbutton and green pushbutton are respectively pressed.

  2. Wire the remainder of the circuitry.

  3. Work with the MKO to verify:

  • Switch on and red pushbutton activates both the red indicator lamp and the control relay.
  • Switch on and green pushbutton activates the green indicator lamp.
  • Switch on and inductive proximity sensor activates the fan.
  1. Work with the MKO to complete the measurable assessments.

Figure 3: Simplified wire diagram for the PLC trainer.
Figure 3: Simplified wire diagram for the PLC trainer.872×633 64.7 KB

Figure 3: Simplified wire diagram for the PLC trainer.

Related Information

Please follow these links to related and useful information:

Follow up

Please reply using the button below if you have any questions about this DigiKey lab or the components used in this lab.

Questions

The following questions will help reinforce the content of the article.

  1. True / False: The Arduino Opta features solid state outputs.

  2. True / False: The Arduino Opta outputs are independent of each other.

  3. True / False: A Daisy chain may be used to provide 24 VDC to the panel mounted selector switch and pushbuttons. Any break in the daisy chain will result in the loss of all controls.

  4. True / False: The Arduino Opta outputs are compatible with 120 VAC systems.

  5. Research and then describe the Arduino Opta in terms of number of inputs, number of outputs, and number of points.

  6. Research and then describe when a normally closed pushbutton is preferred to a normally open pushbutton. Hint: Fail safe start vs stop.

  7. Review this guide to troubleshooting. Describe two steps that you found intuitive. Also describe two steps that you found challenging.

  8. Research the Arduino Opta power supply specifications as well as the specifications for the capacitive proximity sensor and the dual color indicator lamps. What are the combined system power supply voltage requirements?

Critical Thinking Questions

These critical thinking questions expand the article’s content allowing you to develop a big picture understanding of the material and its relationship to adjacent topics. They are often open ended, require research, and are best answered in essay form.

  1. What is the resistance of the featured control relay’s coil?

  2. This trainer is designed using a relatively safe 24 VDC system. What hardware changes would be necessary to operate the trainer on a line-powered 120 or 208 VAC system? Hint: Focus on the safety ground.

  3. Reflect on your learning by describing your learning journey starting with helpful assistance from the MKO leading to independence.

  4. Reflect on your learning and identify at least three troubleshooting errors that you will insert into the trainer. Hint: What could you do with clear tape to insulate the contact(s)?

  5. How will you present this lab assuming you will one day assume the role of MKO?

About this author

Aaron Dahlen, LCDR USCG (Ret.), is an application engineer at DigiKey. He has a unique electronics and automation foundation built over a 27-year military career as a technician and engineer further enhanced by 12 years of interwoven teaching experience. With an MSEE degree from Minnesota State University, Mankato, Dahlen has taught in an ABET-accredited EE program, served as the program coordinator for an EET program, and instructed military technicians in the art of component-level equipment repair. Dahlen has returned to his Northern Minnesota home and thoroughly enjoys bridging the gap between application and theory.