MQ-4 Natural Gas, Methane Gas Sensor Module

Features:

• 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