Cpp
#include <HardwareSerial.h>

// Define the UART pins
#define RX_PIN 13 // Replace with the correct RX pin of your ESP32
#define TX_PIN 17 // Replace with the correct TX pin of your ESP32

// Initialize the UART connection
HardwareSerial CO2_Serial(1);

void setup() {
  Serial.begin(115200); // Initialize the serial monitor for debugging
  CO2_Serial.begin(9600, SERIAL_8N1, RX_PIN, TX_PIN); // Initialize the UART for the CO2 sensor

  Serial.println("Starting CO2 sensor reading...");
}

void loop() {
  int co2_ppm = readCO2();

  if (co2_ppm >= 0) {
    Serial.print("CO2 concentration: ");
    Serial.print(co2_ppm);
    Serial.println(" ppm");
  } else {
    Serial.println("Error reading CO2 sensor");
  }

  delay(5000);
}

int readCO2() {
  // MH-Z19B request data command
  byte requestCmd[9] = { 0xFF, 0x01, 0x86, 0x00, 0x00, 0x00, 0x00, 0x00, 0x79 };

  // Send the request to the sensor
  CO2_Serial.write(requestCmd, 9);

  // Wait for the sensor response
  delay(10);

  // Read the sensor response
  byte response[9];
  CO2_Serial.readBytes(response, 9);

  // Verify the checksum
  byte checksum = 0;
  for (int i = 1; i < 8; i++) {
    checksum += response[i];
  }
  checksum = 0xFF - checksum + 1;

  if (response[0] == 0xFF && response[1] == 0x86 && response[8] == checksum) {
    int co2 = (response[2] << 8) | response[3];
    return co2;
  }

  // Return -1 if the reading failed
  return -1;
}

1. Pin 1: Connected to the I2C clock line $Net \ IO22/ESP32/I2C_SCL$ used for communication with I2C devices.
2. Pin 2: Connected to the I2C data line $Net \ ESP32/I2C_SDA$ used for communication with I2C devices.
3. Pin 3: Connected to the 3.3V power net, providing power for connected peripherals.
4. Pin 4: Connected to the ground (GND), which acts as a reference point or return path for current.