MH-Z19 NDIR CO₂ Sensor

#include <stdio.h>
#include "driver/uart.h"
#include "driver/gpio.h"
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"

#define UART_NUM UART_NUM_1
#define TXD_PIN (GPIO_NUM_17)
#define RXD_PIN (GPIO_NUM_16)

void app_main(void) {
    const uart_config_t uart_config = {
        .baud_rate = 9600,
        .data_bits = UART_DATA_8_BITS,
        .parity = UART_PARITY_DISABLE,
        .stop_bits = UART_STOP_BITS_1,
        .flow_ctrl = UART_HW_FLOWCTRL_DISABLE
    };
    uart_param_config(UART_NUM, &uart_config);
    uart_set_pin(UART_NUM, TXD_PIN, RXD_PIN, UART_PIN_NO_CHANGE, UART_PIN_NO_CHANGE);
    uart_driver_install(UART_NUM, 256, 0, 0, NULL, 0);

    uint8_t cmd[9] = {0xFF, 0x01, 0x86, 0x00, 0x00, 0x00, 0x00, 0x00, 0x79};
    uint8_t response[9];

    while (1) {
        uart_write_bytes(UART_NUM, (const char *)cmd, 9);
        vTaskDelay(pdMS_TO_TICKS(500));

        int len = uart_read_bytes(UART_NUM, response, 9, pdMS_TO_TICKS(1000));
        if (len == 9 && response[0] == 0xFF && response[1] == 0x86) {
            int CO2 = (response[2] << 8) | response[3];
            printf("CO2 Concentration: %d ppm\n", CO2);
        }
        vTaskDelay(pdMS_TO_TICKS(2000));
    }
}

uart:
  tx_pin: GPIO17
  rx_pin: GPIO16
  baud_rate: 9600

sensor:
  - platform: mhz19
    co2:
      name: "MH-Z19 CO2"
    temperature:
      name: "MH-Z19 Temperature"
    update_interval: 60s

[env:esp32dev]
platform = espressif32
board = esp32dev
framework = arduino
monitor_speed = 115200

#include <Arduino.h>
HardwareSerial co2Serial(2); // UART2: sensor TX -> GPIO16 (RX2), RX -> GPIO17 (TX2)

void setup() {
    Serial.begin(115200);
    co2Serial.begin(9600, SERIAL_8N1, 16, 17);
}

void loop() {
    // "Read CO2 concentration" command from the MH-Z19 datasheet
    byte cmd[9] = {0xFF, 0x01, 0x86, 0x00, 0x00, 0x00, 0x00, 0x00, 0x79};
    co2Serial.write(cmd, 9);
    delay(500);

    if (co2Serial.available() >= 9) {
        byte response[9];
        co2Serial.readBytes(response, 9);

        // Validate the reply: header plus 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];
            Serial.print("CO2 Concentration: ");
            Serial.print(CO2);
            Serial.println(" ppm");
        } else {
            Serial.println("Invalid response from sensor");
        }
    }
    delay(2000);
}

from machine import UART, Pin
import time

uart = UART(2, baudrate=9600, tx=Pin(17), rx=Pin(16))

cmd = bytearray([0xFF, 0x01, 0x86, 0x00, 0x00, 0x00, 0x00, 0x00, 0x79])

def read_co2():
    uart.write(cmd)
    time.sleep(0.1)
    if uart.any():
        response = uart.read(9)
        if len(response) == 9 and response[0] == 0xFF and response[1] == 0x86:
            co2 = (response[2] << 8) | response[3]
            return co2
    return None

while True:
    co2 = read_co2()
    if co2 is not None:
        print(f"CO2 Concentration: {co2} ppm")
    else:
        print("Error reading CO2 concentration")
    time.sleep(2)