I’ll be blinking the built-in leds and screen of different embedded architectures…

So, we first need to cover what a PLC (Programmable Logic Controller) is… A PLC has a MCU inside but it was developed for a more hostile environment (industrial). PLC tend to be extremely expensive (around 10K USD Dollars) and the needed software to program them is not free nor opensource like its counterpart (Arduino Boards). Do to this normally to see interact with one you would have needed to work in a place that could afford this hardware and software. SIEMENS changed the game by developing a small PLC that is in a more accessible cost range and named it LOGO!.

LOGO! 8 Structure (Download User Manual to See this Picture)

For this segment I’ll be experimenting with WOKWI to simulate the code I plan on using for my final project.

WOKWI is an inline simulator that lets you test code and hardware in a virtual space. Being able to test a specific developer board with a list of hardware can greatly impacted the process of jumping to designing your own PCB. Quick disclaimer… I’ll be using the 5V pin of the MEGA because WOKWI doesn’t have a DC power supply. When dealing with servo motors it’s better to give them a separate power source because they add a lot of noise to the circuit. Just remember to have a common GROUND. Otherwise, the circuited won’t work properly.

WOKWI Simulation

1. Developer Board: Arduino MEGA

2. Components:

• 3 Servo Motors: WOKWI only has 180° servos but the once I’ll be using have 270° rotation

• Breadboard: Helps to make multiple connections on the same node.

3. Code: In essence, this code

• Initializes 3 servo motors and sets them to their starting positions.

• Blinks the built-in LED.

• Waits for characters to be received through the serial port.

• Based on the received character, it moves the servo motors to different positions.

• To use this code, you need to connect the servo motors to pins 9, 10, and 11 of your Arduino MEGA, open the serial monitor (9,600) in the Arduino IDE, and send the characters '1', '2', 'C', or '8' to control the servos.

• Remember to add the libaries that are declared in the WOKWI Library Manager. Skipping this step will result in an error.

Getting Started with WOKWI

When you go to the WOKWI website you’ll be greeted with the main page that lets you select the development board you want to work with. I use an Arduino MEGA to simulate the code ill be using with part of my final project. Pleas watch the following video before you keep reading.

In the video you’ll see that I added in the hardware section 3 servo motors and a breadboard. My final project is a box with 3 compartments. Each compartment will have a door that will be opened with the servo motors (1 servo per door). The breadboard come into play when I need to connect wires in the same Arduino pins. In this particular case the servos need to share the seme 5V and GND (ground) pin. The PWM (Pulse Width Modulation) pin needs to be different because the servos are moving at different times and coordinates. If the 3 servers move at the same time and coordinate then they can share the same PWM pin.

WOKWI Hardware Schematic

Now we need to understand a little of the wiring of the servo motor… Servos have 3 wires (V+, GND and PWM). Please check the following pictures to identify the location of the wires. Servos share 2 wires and if you observe the pint of the Arduino MEGA there is only one V+, three GND’s and multiply PWM. Smaller developer boards tend to only have one GND. Now the breadboard comes into play. If you put the breadboard like in the picture It would be easier to understand how they work. Each row is what we call a node and in simple words it’s a pin that you can access in 5 different positions (Ex. A1, A2, A3, A4 and A5). Jumping to a different row takes us to a different node.

Please observe the following picture before reading what comes next. If you observe the hardware schematic you can see 3 colored wires (RED= V+, BLACK= GND and GREEN= PWM) that represent V+, GND and PWM. As mentioned before V+ and GND will need more space to connect multiple wires in the same pin or node. Please observe that the final step to officially merge every wire to the same node you need to connect the 5V and the GND pins of the Arduino to the V+ node and the GND node on the breadboard. The PWM wires go directly to the corresponding pins (PWM).

Coding in WOKWI

If you have any kind of experience coding in the Arduino IDE then you’ll defiantly feel at home. There is only one extra step that is related to the libraries you declare in the code. There is one extra step that you need to do. Please see the following video .

If you saw the video then you’ll noticed that WOKWI has a tab named “Library Manager”. In this tab you must upload or select the libraries that are declared in the code. In my case it’s the Arduino Servo library. Now lets talk about the code... The following code will drive my Final Project.

Arduino Code (Final Project)

  
//Walter Lenigan - Fab Academy 2025

#include <Servo.h>

Servo S_1;  // create servo object to control a servo
Servo S_2;
Servo S_3;


char Accessories =0;


void setup() {
  Serial.begin(9600);
  pinMode(LED_BUILTIN, OUTPUT);

  S_1.attach(11); 
    S_1.write(0);
//    delay(1000);


  S_2.attach(10); 
    S_2.write(0);
//    delay(1000);


  S_3.attach(9); 
    S_3.write(0);
//    delay(1000);

    Serial.println("Hola Lenigan");


}

void loop() {

  digitalWrite(LED_BUILTIN, HIGH);   // turn the LED on (HIGH is the voltage level)
      delay(1000);             // wait for a second
      digitalWrite(LED_BUILTIN, LOW);    // turn the LED off by making the voltage LOW
      delay(1000);             // wait for a second

  if (Serial.available() > 0) {     // It will only send data when the received data is greater than 0. 
    Accessories = Serial.read();
switch (Accessories) {
    case '1': 
      S_1.write(63);
      S_2.write(0);
      S_3.write(0);
      Serial.println("Servo #1 Open");
        break;

    case '2': 
      S_2.write(59);
      S_1.write(0);
      S_3.write(0);
      Serial.println("Servo #2 Open");
        break;

    case 'C': 
      S_3.write(65);
      S_1.write(0);
      S_2.write(0);
      Serial.println("Servo #3 Open");
        break;

    case '8': 
      S_1.write(0);
      S_2.write(0);
      S_3.write(0);
      Serial.println("Servos to ORIGIN");
        break;        }


  }
}
  

The code uses 3 objects (S_1, S_2 and S_3) that will be used to control three separate servo motor in specific moments. Through the serial port the code is in stan-by waiting to receive characters '1' (moves Servo_1), '2' (moves Servo_2), 'C' (moves Servo_3), or '8' (moves all servos to initial position). Only 1 servo will be active at a time so if you send the characters in sequence one servo will move to the defined position and the previous one will move back to initial position. After sending the character the code will send a response message with a serial print indicating the servo that moved and the built-in led will be blinking for no specific reason hehe. Now please see the following video