CO2 measurement module MH-Z14A for ESP32 arduino core. use library https://github.com/squix78/esp8266-oled-ssd1306

MH-Z14A_ESP32_OLED.ino

#include "SSD1306.h" 

HardwareSerial Serial1(0);

SSD1306  display(0x3c, 5, 4);
uint8_t cmd[9] = {0xFF,0x01,0x86,0x00,0x00,0x00,0x00,0x00,0x79};
uint8_t reset[9] = {0xFF,0x01,0x87,0x00,0x00,0x00,0x00,0x00,0x78};
uint8_t res[9] = {};
uint8_t idx = 0;
bool flag = false;
uint16_t co2=0;

void setup() {
  display.init();
  display.flipScreenVertically();
  display.setContrast(255);

 
  Serial.begin(9600);
  Serial1.begin(9600);
  delay(100);

  display.setTextAlignment(TEXT_ALIGN_CENTER_BOTH);
  display.setFont(ArialMT_Plain_24);
  display.clear();
  display.drawString(DISPLAY_WIDTH/2, 30, "preheating...");
  display.display();
  delay(3*60*1000);
  display.setFont(ArialMT_Plain_16);
}

void loop() {
  Serial1.write(cmd,9);
  while(Serial1.available()>0)
  {
    res[idx++]=Serial1.read();
    flag=true;
  }
  idx = 0;
  if(flag)
  {
    flag=false;
    co2 = 0;
    co2 += (uint16_t)res[2] <<8;
    co2 += res[3];
  }
  Serial.println(co2);
  display.clear();
  display.drawString(DISPLAY_WIDTH/2, 30, "co2 : " + String(co2)+" ppm");
  display.display();
  delay(60*1000);
}