Methane Gas Sensor MQ-4 Module

Detects the presence of of methane gas in the air as is found in natural gas (CNG).

Description

The Methane Gas Sensor MQ-4 Module detects the presence of of methane gas in the air as is found in natural gas (CNG).

PACKAGE INCLUDES:

• Methane Gas Sensor MQ-4 Module

KEY FEATURES OF METHANE GAS SENSOR MQ-4 MODULE:

• Sensor type used to detect natural gas leak in home
• Analog sensor output
• Digital sensor output with user adjustable sensitivity and LED indicator
• 5V operation

The module includes the MQ-4 sensor which provides a direct analog output. In addition, the module has an LM393 comparator IC and adjustment potentiometer to provide a digital output with an adjustable set-point, power LED, digital output active LED and a header for easy hookup.

These modules can be used to detect the presence and amount of methane / natural gas present in the air.  This can be used to create an alarm for monitoring the presence of a gas leak or any other source of methane such as flatulence if you should be so inclined.

Heating Element

The sensor contains a small heater, so the power draw is about 150mA.  The sensor will get warm to the touch after it has been operating for awhile.  The module can be powered off a 5V power pin on the uC, but it draws too much power to try to power it off a digital pin.

For accurate measurement, the sensor needs to be fully warmed up.  The sample code below has a 1 minute warm-up, but for maximum accuracy the warm-up time before taking a reading can be extended.

Sensing Element

The sensor uses SnO2 (tin dioxide) for the sensing element which is heated and changes resistance when exposed to methane vapors in the air.  A voltage divider is used to provide an analog output voltage that correlates to the amount of natural gas in the air.   When the sensor is left in storage, the calibration of the device can drift.  When first being put into use, the mfr recommends operating it for 48 hours before relying upon the accuracy of its readings.  For experimenting, running for an hour seems to settle down the readings enough to start working with the device.

Adjusting Digital Output Trip-point

If using the DO (Digital Output), a potentiometer on the module allows for the sensitivity of the trip-point to be adjusted.  When the level of gas exceeds the trip-point, the DO output will go LOW and the DO-LED will light.

Module Connections

There is a header on the module for making connections

1 x 4 Header

• VCC = Connect to 5V
• GND = Connect to ground
• D0 = Digital output of comparator circuit.  Active LOW when gas is detected
• A0 = Analog output of sensor. Voltage increases with the amount of gas detection

OUR EVALUATION RESULTS:

These devices work very well to detect the presence of natural gas / methane gas (CH4) and provide an analog output relative to the amount of gas that is detected as well as a digital output once the gas level exceeds the set-point.

Be aware that temperature and humidity have an effect on the readings.  This can be demonstrated by running the sample program below and blowing on the sensor.  The sensor reading will go up. The sensor has a built-in heater required for correct operation of the sensor, so for best stability it should be given some time to heat up (sensor warm to the touch) which will minimize the effect of temperature.

In our testing using the code below, the sensor analog reading runs at about 30 after it has had a couple of hours to break-in.  When initially used, it is good to let the module idle while running this program and keeping an eye on the reading.  You will see it drift down for a while and then start to stabilize at which point it is ready to use.

To test the basic sensor operation, a gas stove burner was turned on without starting a flame and some natural gas collected in a zip-lock bag that was held over the burner for a few moments (be sure to turn the burner off afterwards).  The sensor was then placed in the bag and a reading of 350 was obtained.  Based on the level of rotten egg smell in the bag after conducting the test a couple of times, an initial alert setting of 250 was deduced.  The digital output was also adjusted to trip at about that same point using the same zip-lock bag trick.  Not a very scientific calibration process by any means, but at least it gives a starting point.

The program below uses pin A0 for the analog input but this can be any analog pin.  The digital output is brought into pin 8 but these can be any digital pin.  The reading is taken every second and reported out to the Serial Monitor window.

Methane Gas Sensor MQ-4 Module Example Program

/*  MOQ-4 Natural Sensor Module Test

   This type of sensor is commonly used for detecting natural gas / methane leaks
   which might include flatulence.
   
   Monitor sensor analog output 'A0' on ADC input A0
   Monitor sensor digital output 'D0' on digital input pin 8
*/
// Define pins used below
#define ADC_PIN A0      // Use any available ADC Pin, connect to A0 sensor pin
#define DIGITAL_PIN 8   // Use any available digital pin, connect to D0 sensor pin
#define WARMUP_TIME 30  // Warmup time in Seconds
#define GAS_ALERT 250   // Level at which to raise alert

//===============================================================================
//  Initialization
//===============================================================================
void setup()
{
  Serial.begin(9600);          // Set Serial Monitor window comm speed
  Serial.println("Warming up the sensor ");  //Wait while we warm up the sensor
  for (int i=0; i<= WARMUP_TIME; i++) {
    Serial.print(". ");
    delay(1000);
  }
  Serial.println(" Warmup Complete");
}
//===============================================================================
//  Main
//===============================================================================
void loop()
{
  int val_ADC = analogRead(ADC_PIN);          // Read analog value from sensor
  int val_Digital = digitalRead(DIGITAL_PIN); // Read  digital value from sensor
  Serial.print("Natural Gas Analog Data = "); // Printout the raw data
  Serial.print(val_ADC);

  Serial.print("tDigital Output = ");      
  Serial.print(val_Digital);          
                                             // Printout our alert level
  if (val_ADC >= GAS_ALERT) Serial.println("tGAS ALERT!");
  else Serial.println("tReading below alert level");

  delay(1000);      // Take a reading every second for test purposes.
}

BEFORE THEY ARE SHIPPED, THESE MODULES ARE:

• Sample tested per shipment

Notes: 

1. None

Technical Specifications