ESP32 MH-Z19B: Building a DIY CO₂ Monitor for Smarter Air Quality Projects

Introduction

Indoor air quality has become a significant concern, especially in the wake of increased awareness about health and environmental factors. Monitoring CO₂ levels is crucial for ensuring a healthy living and working environment. The MH-Z19B CO₂ sensor, when paired with the versatile ESP32 microcontroller, offers a cost-effective solution for real-time air quality monitoring. This guide will walk you through the process of setting up the MH-Z19B sensor with the ESP32, enabling you to create a smart, Wi-Fi-enabled CO₂ monitoring system.

Understanding the MH-Z19B CO₂ Sensor

The MH-Z19B is a compact, non-dispersive infrared (NDIR) CO₂ sensor known for its accuracy and reliability. It measures CO₂ concentrations ranging from 0 to 5000 ppm, making it suitable for various indoor applications. Key features include:

• High Accuracy: ±50 ppm + 5% of reading.
• Dual Output Modes: UART (serial) and PWM.
• Operating Voltage: 4.5V to 5.5V DC.
• Preheat Time: Approximately 3 minutes.
• Long Lifespan: Over 5 years of continuous operation.YouTube+1Python in Plain English+1

The sensor’s UART interface operates at 3.3V logic levels, making it compatible with the ESP32 without the need for level shifters.

Why Choose the ESP32?

The ESP32 is a powerful microcontroller with integrated Wi-Fi and Bluetooth capabilities. Its dual-core processor and ample GPIO pins make it ideal for IoT applications. When combined with the MH-Z19B sensor, the ESP32 can:

• Collect real-time CO₂ data.
• Transmit data over Wi-Fi to cloud services or local servers.
• Trigger alerts or control ventilation systems based on CO₂ levels.
• Display data on web interfaces or mobile apps.

This combination allows for the creation of smart air quality monitors that can be integrated into home automation systems.

Wiring the MH-Z19B to the ESP32

Proper wiring is crucial for accurate data transmission between the MH-Z19B sensor and the ESP32. Here’s how to connect them:

Note: Ensure that the sensor’s TXD connects to the ESP32’s RX pin and vice versa. Also, provide a stable 5V power supply to the sensor, as the ESP32’s 3.3V output is insufficient.

Programming the ESP32

To read data from the MH-Z19B sensor, you’ll need to program the ESP32 using the Arduino IDE. Here’s a basic example:

cppCopyEdit#include <SoftwareSerial.h>

#define RX_PIN 16 // ESP32 RX
#define TX_PIN 17 // ESP32 TX

SoftwareSerial mySerial(RX_PIN, TX_PIN);

void setup() {
  Serial.begin(115200);
  mySerial.begin(9600);
}

void loop() {
  byte cmd[9] = {0xFF, 0x01, 0x86, 0, 0, 0, 0, 0, 0x79};
  mySerial.write(cmd, 9);
  delay(1000);

  if (mySerial.available()) {
    byte response[9];
    mySerial.readBytes(response, 9);

    if (response[0] == 0xFF && response[1] == 0x86) {
      int co2 = (response[2] << 8) + response[3];
      Serial.print("CO2 Concentration: ");
      Serial.print(co2);
      Serial.println(" ppm");
    }
  }

  delay(2000);
}

Important Tips:

• Wait for the sensor’s preheat time (~3 minutes) before taking readings.
• Ensure the baud rate matches the sensor’s default (9600 bps).
• Use a stable power supply to prevent voltage fluctuations.

Integrating Wi-Fi and Cloud Services

One of the ESP32’s strengths is its Wi-Fi capability. You can enhance your CO₂ monitor by:

• Sending Data to Cloud Platforms: Use services like ThingSpeak or Blynk to visualize data remotely.
• Creating a Web Server: Host a local web page on the ESP32 to display real-time CO₂ levels.
• Implementing MQTT Protocol: Integrate with home automation systems like Home Assistant for automated responses.

These integrations allow for real-time monitoring and control, making your CO₂ monitor a smart device.

Calibration and Maintenance

For accurate readings, periodic calibration of the MH-Z19B sensor is recommended. The sensor supports:

• Automatic Baseline Correction (ABC): Enabled by default, it calibrates the sensor to 400 ppm over a 24-hour period.
• Manual Calibration: Expose the sensor to fresh air (approximately 400 ppm CO₂) and send the calibration command via UART.

Maintenance Tips:

• Avoid exposing the sensor to high concentrations of volatile organic compounds (VOCs).
• Keep the sensor away from dust and moisture.
• Ensure proper ventilation around the sensor for accurate measurements.

Conclusion

Combining the MH-Z19B CO₂ sensor with the ESP32 microcontroller provides a powerful platform for monitoring indoor air quality. This setup is not only cost-effective but also offers flexibility for integration into various smart home systems. By following this guide, you can build a reliable CO₂ monitoring system that contributes to a healthier living environment.