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Figure5.Theauthor’sactualprototypeArduinoUnoPLCwiringdiagram You will place your digital voltmeter across R1 of the actual PLC prototype shown in Figure 5 and press the PB1 tactile switch. An approximate reading of +5V should be displayed on the electrical measurement instrument’s LCD. If the voltage reading is not approximately +5V, check your wiring and repeat
  The tactile pushbutton switch PB1 and PB2 are wired as digital logic switches. When pressing PB1 or PB2, approximately +5VDC is applied to pins 3 and 2, respectively. To illustrate the method of testing the wired digital switches, Figure 6 is presented. You will notice in the Tinkercad circuit model the digital voltmeter is attached across resistor R1. One end of the USB cable is inserted into the Arduino Uno. The other end of the cable is inserted into your PLC development machine’s USB port. A power-on LED will be visible on the Arduino Uno printed circuit board (PCB); this indicator signifies the ATMEGA328 microcontroller and the supporting electronic circuits on the printed circuit board (PCB) are active or powered.
Figure 6. Testing a digital logic switch
the measurement. You will perform the same test measurement on the PB2 tactile switch. Press the PB2 tactile switch to read approximately +5V on the digital voltmeter. Congratulations, you have functional digital logic switches for your Arduino PLC. You
You will now wire and test the output LED indicator on a solderless breadboard. Figure 7 shows the Tinkercad circuits model of the wired and powered output LED indicator on the solderless breadboard. You will use this circuit model as a reference when testing the output LED indicator on the actual solderless breadboard prototype. If your output LED indicator is turned on, job well done!
Figure 7. A functional output LED indicator
Your output LED indicator is working properly. Remove the USB cable from your PLC development machine’s USB port. Replace the red wire attached to the 560-ohm (Ω) resistor with a long jumper wire. You will take the end of the jumper wire attached to the 560Ω resistor and insert it into cavity 7 (D7) of the female header connector mounted to the Arduino Uno’s PCB. Congratulations, you have wired and tested digital logic switches and an output LED indicator of your prototype Arduino Uno PLC. The final stage of the PLC project is to build and upload the OpenPLC Hello World LD program to the Arduino Uno PLC. We will discuss this in the next issue.
Dr. Don Wilcher,
an Electrical Engineer, Technical Education Researcher, Instructor, Maker, Embedded Systems-Mechatronics Lecturer, and Book Author. He is the Director of Manufacturing and Technology at Jefferson State Community College.
     highTECH NEWS | JANUARY/FEBRUARY 2023 | 17
  Dr. Don Wilcher

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