Introduction

The Gravity: Laser CH4(methane) sensor is based on Tunable Diode Laser Absorption Spectroscopy (TDLAS) technology for methane gas detection. It adopts a dual-pass optical path structure, offering excellent gas selectivity, no oxygen dependence, and long service life. An integrated temperature sensor allows direct output of methane gas data (%LEL, Lower Explosive Limit) with temperature compensation. Compared with catalytic bead methane sensors, the laser detection principle ensures higher safety.
The onboard Gravity interface supports I2C/UART data output, and the standoff mounting design makes it easy to fix the sensor onto any flat surface.

Product Feature

• High measurement accuracy with pre-delivery factory calibration
• Low cross-sensitivity, exclusively sensitive to methane
• Extended service life (>10 years)

Product Specification

• Supply Voltage: 3.3–5 V
• Operating Temperature: -13 to 58 °C
• Operating Humidity: 0–95% R.H. (non-condensing)
• Operating Current: <300 mA
• Warm-up Time: 15 s
• Response Time: T90 <15 s

Pinout

Toturial

Prepare

Hardware

• DFRduino UNO+IO Expansion board (SKU:DFR0216-2) * 1
• Gravity: Laser CH4 Sensor（SKU:SEN0654) * 1
• Gravity I2C Sensor Cable(Come with Gravity: Laser CH4 Sensor)

Software

• Download Arduino IDE： Click to download Arduino IDE
• Download DFRobot_MHZ9041A library and install .zip library manully：DFRobot MHZ9041A Github
• Or Search and install "DFRobot_MHZ9041A" library in the library manager

Hookup diagram

Sample code

• Ensure the dip switch on CH4 sensor is on the I2C side
• Upload following code and check the serial monitor

 /*!
  * @file  get conncentration.ino
  * @brief get ch4 conncentration
  * @copyright Copyright (c) 2025 DFRobot Co.Ltd (http://www.dfrobot.com)
  * @license The MIT License (MIT)
  * @author ZhixinLiu([email protected])
  * @version V1.0.0
  * @date 2025-04-24
  * @url https://github.com/DFRobot/DFRobot_MHZ9041A
  */

#include "DFRobot_MHZ9041A.h"

#define I2C_COMMUNICATION  //use I2C for communication, but use the serial port for communication if the line of codes were masked

#ifdef  I2C_COMMUNICATION
  DFRobot_MHZ9041A_I2C ch4(&Wire ,0x34);
#else
/* -----------------------------------------------------------------------------------------------------
 * |  Sensor  | Connect line | Leonardo/Mega2560/M0 |    UNO    | ESP8266 | ESP32 |  microbit  |   m0  |
 * |   VCC    |=============>|        VCC           |    VCC    |   VCC   |  VCC  |     X      |  vcc  |
 * |   GND    |=============>|        GND           |    GND    |   GND   |  GND  |     X      |  gnd  |
 * |   RX     |=============>|     Serial1 TX1      |     5     |   5/D6  |  D2   |     X      |  tx1  |
 * |   TX     |=============>|     Serial1 RX1      |     4     |   4/D7  |  D3   |     X      |  rx1  |
 * ----------------------------------------------------------------------------------------------------*/
/* Baud rate cannot be changed */
  #if defined(ARDUINO_AVR_UNO) || defined(ESP8266)
    SoftwareSerial mySerial(4, 5);
    DFRobot_MHZ9041A_UART ch4(&mySerial, 115200);
  #elif defined(ESP32)
    DFRobot_MHZ9041A_UART ch4(&Serial1, 115200 ,/*rx*/D2 ,/*tx*/D3);
  #else
    DFRobot_MHZ9041A_UART ch4(&Serial1, 115200);
  #endif
#endif

void setup()
{
  Serial.begin(115200);
  while(!ch4.begin()){
    Serial.println("NO Deivces !");
    delay(1000);
  } Serial.println("Device connected !");

  //ch4.reset();
  ch4.setMode(ePassivityMode); // set Passivity mode
}

void loop()
{
  float ch4Concentration = ch4.getCH4Concentration(); // get CH4 concentration
  float temperature = ch4.getTemperature(); // get temperature
  eFaultCode_t errorCode = ch4.getErrorMsg(); // get error code
  String sourceData = ch4.getSourceData(); // get source data
  Serial.print("CH4 Concentration: ");
  Serial.print(ch4Concentration, 2); // print CH4 concentration
  Serial.println("%LEL");
  Serial.print("Temperature: ");
  Serial.print(temperature, 2); // print temperature
  Serial.println("C");
  Serial.print("Error Code: ");
  Serial.println(errorCode); // print error code
  Serial.print("Source Data: ");
  Serial.println(sourceData); // print source data
  Serial.println("===================================");
  delay(20);
}

Result

Open the serial monitor, methane concentration, module temperature, and related data would show up.

Toturial with Gravity SCI DAQ

The Gravity SCI DAQ offers a code-free solution for sensor monitoring and data logging. It allows users to view real-time sensor data directly or record time-stamped measurements into a .csv file without any programming effort.

Hardware

• Gravity: SCI DAQ (SKU:DFR0999) * 1
• Gravity: Laser CH4 Sensor (SKU: SEN0654) * 1
• Double-headed PH2.0-4P Cable(Come with Gravity: SCI DAQ) * 1

Tutorial

According to this Firmware update tutorial, upgrade the Gravity: SCI module firmware to version V1.0.5 or above. Once upgraded, the Gravity: Laser Methane Sensor can be directly connected to the SCI module to view methane concentration, enabling programming-free scientific experiments and exploration.

Result

API list

/**
 * @enum eFaultCode_t
 * @brief Types of sensor fault codes
 */
typedef enum {
  eSensorNormal = 0x00,                   // 00 Sensor operating normally
  eTempControlError = 0x01,               // 01 Temperature control error
  eAmbientTempError = 0x02,               // 02 Ambient temperature error
  eAmbientAndTempControlError = 0x03,     // 03 Ambient temperature error & temperature control error
  eLaserSignalWeak = 0x04,                // 04 Weak laser signal
  eAmbientAndSignalWeakError = 0x06,      // 06 Ambient temperature error & weak laser signal
  eLaserSignalError = 0x10,               // 16 Laser signal error
  eAmbientAndSignalError = 0x12,          // 18 Ambient temperature error & laser signal error
} eFaultCode_t;

/**
 * @enum eModuleMode_t
 * @brief sensor work mode
 */
typedef enum {
  ePassivityMode = 0x00,
  eActiveMode = 0x01,
} eWorkMode_t;

/**
 * @fn setMode
 * @brief Set the working mode
 * @param mode Working mode
 * @note 0x00: Active mode, 0x01: Passive mode
 * @return null
 */
void setMode(eWorkMode_t mode);

/**
 * @fn getSourceData
 * @brief Get raw sensor data
 * @return Raw data string, up to 43 bytes in length
 */
String getSourceData(void);

/**
 * @fn getCH4Concentration
 * @brief Get methane (CH4) concentration
 * @return CH4 concentration value, two decimal places, the second digit is always 0, unit: %LEL
 */
float getCH4Concentration(void);

/**
 * @fn getTemperature
 * @brief Get ambient temperature
 * @return Temperature in degrees Celsius
 */
float getTemperature(void);

/**
 * @fn getErrorMsg
 * @brief Get error code information
 * @return Error code
 */
eFaultCode_t getErrorMsg(void);

/**
 * @fn getActiveData
 * @brief Get raw data in active reporting mode
 * @return Raw data string in active mode
 */
String getActiveData(void);

/**
 * @fn reset
 * @brief Reset the onboard methane sensor; hold the reset pin low for 2 seconds to complete the reset
 * @return null
 */
void reset(void);

/**
 * @fn setDeviceID
 * @brief Set the module address,range 0x03~0x7F
 * @return Returns 1 if successful, otherwise returns 0
 */
bool setDeviceID(uint8_t id);

/**
 * @fn getDeviceID
 * @brief Get the module address
 * @return Module address
 */
uint8_t getDeviceID(void);

UART protocol

UART config: 115200bps 8-N-1
Note: The UART output is an ACSII string that is uploaded every 1S, totaling 44 bytes.

Output String Parsing Guide:
Example: A+000.00 +24.0 0665.38 +16.1 B+066.0 00
A: Frame header
+000.00: Methane concentration value, with two decimal places; the second decimal digit is always 0. Unit: %LEL
+24.0: Ambient temperature. Unit: °C
0665.38: Reserved
+16.1: Reserved
B+066.0: Reserved
00: Error code value — 0: normal; 1: abnormal

More

• Schematic
• Layout
• Dimensional drawing
• Github repo

WIKI modify history

Product modify histroy

Get one sensor in DFRobot store