LamaPLC: CJMCU-6814 combined gas sensor module for CO, NO₂, NH₃

The CJMCU-6814 is a specialized gas sensor module designed for air quality monitoring, primarily built around the MiCS-6814 sensor. It is a “3-in-1” device capable of detecting carbon monoxide (CO), nitrogen dioxide (NO₂), and ammonia (NH₃) simultaneously through three independent analog channels.

Key Technical Specifications

• Target Gases & Range:
  
• Carbon Monoxide (CO): 1 – 1000 ppm.
• Nitrogen Dioxide (NO₂): 0.05 – 10 ppm.
• Ammonia (NH₃): 1 – 500 ppm.
• Secondary detection: Detects Ethanol, Hydrogen, Methane, and Propane.
• Operating Voltage: 4.9V – 5.1V.
• Output: Three analog output pins (Red, Ox, NH3) corresponding to the internal sensing elements.

Important Usage Notes

• Warm-up Period: The sensor requires a significant warm-up time to reach a stable operating temperature. The datasheet indicates that it can take more than 120 minutes for the internal heater to stabilize.
• Calibration: It is designed for relative measurement, not absolute precision. You must calibrate it in your specific environment (e.g., “clean air” as a baseline) to convert analog voltage changes into meaningful ppm estimates.
• No I²C: Unlike some other MiCS-6814 breakout boards, the purple CJMCU version typically does not support I²C. You must use the Arduino analog pins (e.g., A0, A1, A2) to read data.
• External Resistors: For optimal results and to prevent sensor damage, it is often recommended to use external pull-up resistors (e.g., 47 kΩ) or a combination with a 10kΩ potentiometer to tune the output range.

To interface the CJMCU-6814 with an Arduino, you read the three analog output channels (CO, NH₃, NO₂) using analogRead(). This sensor typically does not use I²C, so you must connect the pins directly to the Arduino's analog inputs.

This sketch reads the raw voltage from each sensor channel every 5 seconds.

// CJMCU-6814 Basic Reading Example
const int pinCO  = A0; // Carbon Monoxide (RED channel)
const int pinNH3 = A1; // Ammonia (NH3 channel)
const int pinNO2 = A2; // Nitrogen Dioxide (OX channel)
 
void setup() {
  Serial.begin(9600);
  Serial.println("CJMCU-6814 Gas Sensor Initializing...");
  // Sensor requires a long warm-up (up to 30-120 mins) for stability
}
 
void loop() {
  // Read raw values (0-1023)
  int rawCO  = analogRead(pinCO);
  int rawNH3 = analogRead(pinNH3);
  int rawNO2 = analogRead(pinNO2);
 
  // Convert to voltage (assuming 5V Arduino)
  float voltCO  = rawCO  * (5.0 / 1023.0);
  float voltNH3 = rawNH3 * (5.0 / 1023.0);
  float voltNO2 = rawNO2 * (5.0 / 1023.0);
 
  // Print results
  Serial.print("CO: ");  Serial.print(voltCO);  Serial.print("V | ");
  Serial.print("NH3: "); Serial.print(voltNH3); Serial.print("V | ");
  Serial.print("NO2: "); Serial.print(volt8); Serial.println("V");
 
  delay(5000); 
}

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