Application Code

Here is the entire code put together.

/*
Title: Control Relays with Nextion HMI
Written By: (put your name here)
Date: 03/11/2023
Description:
This code can read messages from the Nextion HMI over serial. 
The code will then turn these messages into commands for the Arduino
Nano Every to perfrom. Thus turning on or off the 2 relays based on
the state of the switch widgets on the HMI.
*/
const int relay1 = 7; // relay 1 is on digital pin 7
const int relay2 = 8; // relay 2 is on digital pin 8

String cmd =""; // string variable to store messages in

void setup() {
  // open serial port with computer; use for debugging  
  //Serial.begin(9600); 
  
  // open serial port between HMI and Arduino Nano Every; recieve and send messages
  Serial1.begin(9600); 

  pinMode(relay1, OUTPUT); // configure relay 1 pin as an output
  pinMode(relay2, OUTPUT); // configure relay 2 pin as an output
}

void loop() {
  if(Serial1.available()){ // is there any bytes on the serial 1 port buffer
    cmd = "";
    delay(5);
    serial_input(); // custom function to handle the messages over serial 
  }
}

void serial_input() {
  while (Serial1.available()) {
    cmd += char(Serial1.read()); // read avaialbe bytes into dfd string
  }
  if (cmd.substring(0, 3) == "R1:") { // does the substring = R1:
    String relay1_cmd = cmd.substring(3, cmd.length()); // read the cmd into relay1_cmd string variable
    if (relay1_cmd == "ON") { // if true then turn on relay 1
      digitalWrite(relay1, HIGH); // set the digital pin high
    } else { // if false then run this statement and set the digital pin low
      digitalWrite(relay1, LOW);
    }
  }
  if (cmd.substring(0, 3) == "R2:") { // does the substring = R2:
    String relay2_cmd = cmd.substring(3, cmd.length()); // read the cmd into relay2_cmd string variable
    if (relay2_cmd == "ON") { // if true then turn on relay 2
      digitalWrite(relay2, HIGH); // set the digital pin high
    } else { // if false then run this statement and set the digital pin low
      digitalWrite(relay2, LOW);
    }
  }
}