M5Stack CO2 Sensor

M5Stack Core2 based CO2 sensor using a SenseAir S8 with MQTT support.

Overview

This project implements a CO2 monitoring system using an M5Stack Core2 and a SenseAir S8 CO2 sensor. The device continuously measures CO2 levels, displays them on the built-in screen with color-coded warnings, and publishes readings to an MQTT broker for remote monitoring.

Hardware Requirements

• M5Stack Core2: ESP32-based device with 320x240 touchscreen display
• SenseAir S8 CO2 Sensor: NDIR CO2 sensor (0-10,000 ppm range)
• Wiring:
  • S8 RX → M5Stack GPIO 13
  • S8 TX → M5Stack GPIO 14
  • S8 VCC → 5V
  • S8 GND → GND

Software Dependencies

Install these libraries via Arduino Library Manager:

1. M5Core2 (by M5Stack)
2. Adafruit MQTT Library (by Adafruit)
3. SoftwareSerial (built-in to Arduino/ESP32)

Configuration

Before uploading, modify these values in s8_m5.ino:

const char* mqtt_server = "192.168.1.100";  // Your MQTT broker IP
const int mqtt_port = 1883;                  // Your MQTT broker port
const char* ssid = "YourWiFiName";           // Your WiFi SSID
const char* password = "YourWiFiPassword";   // Your WiFi password

Optional configuration:

int valMultiplier = 1;  // Set to different value for alternate S8 models
#define FEED "esp32/co2"  // MQTT topic to publish to

Installation

Using Arduino IDE

1. Install Arduino IDE 2.0 or later
2. Add M5Stack board support:
   • Go to File → Preferences
   • Add to "Additional Board Manager URLs": https://m5stack.oss-cn-shenzhen.aliyuncs.com/resource/arduino/package_m5stack_index.json
3. Install board: Tools → Board Manager → Search "M5Stack" → Install
4. Install required libraries (see Software Dependencies)
5. Select board: Tools → Board → M5Stack Arduino → M5Stack-Core2
6. Select port: Tools → Port → (your device port)
7. Upload the sketch

Using Arduino CLI

# Configure board support
arduino-cli config init
arduino-cli core update-index
arduino-cli core install m5stack:esp32

# Install libraries
arduino-cli lib install "M5Core2"
arduino-cli lib install "Adafruit MQTT Library"

# Compile
arduino-cli compile --fqbn m5stack:esp32:m5stack-core2 s8_m5.ino

# Upload (replace /dev/ttyUSB0 with your port)
arduino-cli upload -p /dev/ttyUSB0 --fqbn m5stack:esp32:m5stack-core2 s8_m5.ino

# Monitor serial output
arduino-cli monitor -p /dev/ttyUSB0 -c baudrate=9600

Operation

Startup Sequence

1. Device initializes M5Stack hardware and display
2. Connects to WiFi (displays connection progress on serial)
3. Begins main loop: reading CO2, updating display, publishing to MQTT

Display

The CO2 reading is shown in large text with color coding:

• Green (< 500 ppm): Good air quality
• Yellow (500-700 ppm): Moderate air quality
• Red (≥ 700 ppm): Poor air quality, ventilation recommended

MQTT Publishing

• Topic: esp32/co2 (configurable)
• Format: Integer value (CO2 ppm)
• Frequency: Every 5 seconds
• Connection: Automatic reconnection with 3 retries

Serial Output

Connect at 9600 baud to see:

• WiFi connection status and IP address
• CO2 readings every 5 seconds
• MQTT connection status and publish results

SenseAir S8 Protocol

The S8 uses a proprietary serial protocol:

Command Packet (Read CO2)

0xFE 0x44 0x00 0x08 0x02 0x9F 0x25

Response Packet (7 bytes)

Byte 0: 0xFE (Header)
Byte 1: 0x44 (Command)
Byte 2: 0x00
Byte 3: CO2 High Byte
Byte 4: CO2 Low Byte
Byte 5: Checksum High
Byte 6: Checksum Low

CO2 value calculation: (Byte3 × 256) + Byte4

Troubleshooting

WiFi Connection Issues

• Verify SSID and password are correct
• Check WiFi signal strength
• Ensure WiFi is 2.4GHz (ESP32 doesn't support 5GHz)

Sensor Not Reading

• Check wiring connections
• Verify S8 has power (LED should be on)
• Check GPIO pins 13 and 14 are not used by other hardware
• Allow 30 seconds for sensor warm-up

MQTT Connection Failures

• Verify MQTT broker is running and accessible
• Check broker IP address and port
• Ensure no firewall blocking port 1883
• Check broker logs for connection attempts

Display Issues

• If text size is wrong, check setTextSize() value
• Color thresholds can be adjusted in the display logic

Maintenance

Sensor Calibration

The S8 sensor has automatic baseline calibration (ABC) enabled by default. For accurate readings:

• Expose sensor to fresh outdoor air (≈400 ppm) regularly
• ABC assumes sensor sees 400 ppm at least once every 7 days
• For manual calibration, refer to S8 datasheet

Performance

• Update rate: 5 seconds (adjustable via delay in loop)
• S8 measurement time: ~2 seconds per reading
• WiFi reconnection: Automatic if connection drops
• MQTT reconnection: Automatic with 3 retry attempts

Advanced Modifications

Changing Update Frequency

Modify the delay at the end of loop():

delay(5000);  // Change to desired milliseconds

Adding Data Logging

The MQTT feed can be subscribed to by:

• Home Assistant
• Node-RED
• InfluxDB + Grafana
• Any MQTT-compatible system

Multiple Sensors

To publish multiple sensors to MQTT, add additional feed definitions:

Adafruit_MQTT_Publish temperature = Adafruit_MQTT_Publish(&mqtt, "esp32/temperature");

References

• SenseAir S8 Datasheet
• M5Stack Core2 Documentation
• Adafruit MQTT Library

License

See repository LICENSE file for details.