Using the MQ4 Methane Gas Sensor With Arduino Made Easy

Introduction

In this article, I will show you how to use the MQ4 Methane gas sensor with an Arduino microcontroller. This will enable you to create a cost-effective and efficient methane gas detection system. In the following I will provide you with a step-by-step connection guide, code examples, and a FAQ section.

Let’s grab the sensor and get started!

Components Needed To Build Arduino And MQ4 Sensor Project

Hardware Components

• Arduino UNO x 1
• MQ4 Methane Gas Sensor   x 1
• Dupont wire x 1 set
• USB Cable for Arduino Programming x 1

Software

• Arduino IDE

Fundamentals Of The Methane Gas Sensor Module

Importance Of Methane Gas Sensors

Methane gas, while very useful for cooking and heating, it can also be quite dangerous if not monitored correctly. It’s odorless, invisible, and can lead to catastrophic accidents if it builds up in unventilated spaces. This is where the magic of the MQ4 methane gas sensor comes in.

The MQ4 is a simple, yet powerful sensor that can detect the presence of methane gas in the environment. By integrating this with an Arduino microcontroller, we can develop a system that not only detects the presence of methane but can also alert us or take preventive actions when the gas concentration reaches a dangerous level.

MQ4 Gas Sensors Pinout

A typically available methane gas sensor module is shown in the image below. It usually comes with 4 pins (VCC, A0, D), GND).

Here is the summary of the methane gas sensor module pins.

Pin Names	Pin Description	Remarks
VCC	Power Supply	5 V is the recommended power supply
A0	Analog output	Connect this pin directly to the analog input of the Arduino board
D0	Digital Output	Connect to any GPIO of the Arduino
GND	Ground connections

The methane gas sensor module can be directly connected to an Arduino as it is 5 V compatible. The below table provides you the detailed specifications of the methane gas sensors. If you have further questions, please post them in the comments section.

MQ4 Gas Sensor specifications

Methane gas sensor parameter	Conditions / Specifications
Circuit voltage	5 V +/- 100 mV
Heating voltage	5 V +/- 100 mV
Load resistance	20 kOhms
Heater resistance	33 ohms +/- 5%
Heating consumption	< 750 mW
Operating temperature	-10 ℃ to +50 ℃
Storage temperature	-20 ℃ to +70 ℃
Relative humidity	< 95% RH
Oxygen Concentration	Upto 21%
Sensing resistance	10 kOhms to 60 kOhms
Preheat time	> 24 hours

For more details see the data sheet:

 

Internal Workings of the MQ4 Gas Sensor

The MQ4 is comprised of several key components, each contributing to its ability to detect methane gas effectively.

Firstly, at the heart of the sensor is the gas sensing layer composed of a metal oxide (SnO2). When methane gas comes into contact with this layer, it reacts with the oxygen present on the surface of the SnO2, resulting in a change in the material’s resistance. This change is then measured to detect the presence and concentration of the gas.

Wrapped around the sensing layer is a heater coil. This is a crucial component because the SnO2 layer needs to be heated for the chemical reaction with methane to occur.

Encasing these components is the tubular ceramic. It physically protects the sensing layer and the heater coil. Simultaneously, it helps to maintain a stable temperature within the sensor by providing some thermal insulation.

Finally, we have the electrodes, typically made of gold or platinum. These are attached to the sensing layer. The electrodes measure the changes in the resistance of the sensing layer.

Sensitivity Characteristics of the MQ4 Gas Sensor

The MQ4 gas sensor is primarily designed to detect methane (CH4), but it also has varying levels of sensitivity to a range of other gases including LPG (liquefied petroleum gas), hydrogen (H2), carbon monoxide (CO), alcohol, and smoke. The sensor’s sensitivity refers to the ratio of the sensor resistance in various gases to the sensor resistance in clean air. The following graph shows the sensitivity characteristics for those gases.

For methane, the MQ4 has an excellent sensitivity, which means it can accurately detect and measure changes in methane concentration in the atmosphere. Even small changes in the amount of methane will result in noticeable changes in the sensor resistance, providing an accurate indication of methane presence.

For LPG and hydrogen, the MQ4 sensor also shows a fairly high sensitivity, although not as high as it is for methane. Therefore, while it can detect these gases, the readings might not be as accurate or as responsive as they would be for methane.

On the other hand, the MQ4 sensor has a lower sensitivity to carbon monoxide, alcohol, and smoke. This means that while the sensor will react to these gases, the changes in resistance will be smaller and less noticeable. This can result in a lower accuracy for these gases, and they may only be detected at higher concentrations.

Humidity and Temperature Dependency of the MQ4 Gas Sensor

The performance of the MQ4 gas sensor is influenced not only by the presence of target gases but also by environmental factors such as humidity and temperature. These dependencies can cause alterations in the sensor’s readings, making it important to consider them in certain applications. The following graph shows the change in resistance depending on ambient temperature and humidity:

Humidity can affect the sensor’s performance, mainly because the water vapor can occupy the active sites on the tin dioxide (SnO2) sensing layer where gas detection reactions usually occur. At high humidity levels, the sensor’s sensitivity to methane may decrease, which can lead to less accurate readings.

Temperature dependency is another important factor when using the MQ4 gas sensor. The MQ4 sensor includes a built-in heater to maintain the necessary temperature for the SnO2 sensing layer. However, ambient temperature can still influence the sensor’s performance.

For accurate and stable readings a combination of the MQ4 gas sensor with a temperature and a humidity sensor could be considered. Also note, that the MQ4 needs to warm up (remember the heating element) for at least 20 seconds before its readings become stable and reliable.