How to Use MQ4 Gas Sensor?

The MQ4 methane gas sensor is a MOS (metal oxide semiconductor) type sensor that detects methane gas concentration in the air at home or in the workplace and gives an analog voltage output when read. The concentration range for sensing, in this case, is 300 pm – 10,000 ppm, which is suitable for detecting a leak.

The main component of this gas sensor is a detecting element made of aluminum oxide (Al2O3) ceramic covered with Tin dioxide (SnO2) and organized within a stainless-steel mesh.

The pin configuration of the MQ4 methane gas sensor is shown below. 

MQ4 Pinout

• Good sensitivity to a wide range of combustible gas

• High sensitivity to Natural gas

• Stable and long life

• Small sensitivity to alcohol, smoke

• Fast response Stable and long life

• Power requirements: VCC - 5V±0.1

• DO output: TTL digital 0 and 1 (0.1 and 5V)

• AO output: 0.1-0 .3 V (relative to pollution), the maximum concentration of a voltage of about 4V

• Detection Gas: Natural gas/Methane

• Operating temperature: 14 to 122 °F (-10 to 50°C)

• RH Related humidity less than 95%Rh

• O2 Oxygen concentration is 21% (standard condition) - Oxygen concentration can affect sensitivity

• Load resistance: 20KΩ

• Sensing Resistance Rs: 10KΩ- 60KΩ (1000ppm CH4)

• Preheat time:Over 24 hour

• Detection Concentration: 200-10000ppm (Natural gas / Methane)

• Interface: 1 TTL compatible input (HSW), 1 TTL compatible output (ALR)

• Heater consumption: less than 750mw

The power LED illuminates as soon as the module is turned on. The MQ-4 detects the presence of methane in the atmosphere. The sensor's analog pin then produces an analog signal proportional to the amount of CH4 in the air. An ADC microcontroller can be used to measure a sensor's analog output.

Most microcontrollers nowadays include an ADC peripheral that can be used to read the analog output of sensors like the MQ4. The methane gas sensor's analog output signal is read by the microcontroller, which then performs signal conditioning to transform the observed analog voltage into methane concentration in the air. When methane gas is detected, the digital pin turns HIGH and the built-in LED for the Digital output illuminates. This digital pin can also be used to control other operations using a microcontroller.

When there is methane gas present, the D0 pin creates a high (equal to VCC) signal and a low (equivalent to about 0.1 V) signal. The trimmer pot on the circuit can be used to calibrate this "digital" output.

MQ4 Digital Output Circuit

The D0 pin is connected to the Arduino's digital pin 2. The Arduino sketch below uses an interrupt to ensure that the MQ-4 is always detected first by the microcontroller.

MQ4 Arduino Data

• Determining PPM Equation

  

Sensitivity curve of the MQ-4

This graph, taken from the device datasheet, depicts the MQ-4's sensitivity to gases. It's especially sensitive to CH4, the molecular term for methane, as shown above. Propane and butane gases are not included in the curve, even though they are both known components of LPG (which is second to methane in this curve).

The graph depicts the relationship between RS/R0 and gas concentration in parts-per-million on a log-log scale (PPM). The ratio of sensor resistance at target gas (RS) to sensor resistance in clean air (R0) is RS/R0 (R0). As a result, knowing RS/R0 allows us to calculate the gas concentration in PPM.

To derive a formula, we take two points on this graph. Later on, we'll use this formula in our Arduino sketch.

When RS/R0 = 1 and PPM = 1000, the most evident point appears. When RS/R0 is around 0.58 and PPM = 5000, the second point is reached. The formula begins with:

From the first point, we'll assign Y1 = 1, X1 = 1000, and from the second point, Y2 = 0.58, X2 = 5000. Substituting these values into the previous equation:

Changing Y to RS/R0 and X to PPM and solving for PPM:

• Methane PPM Output Arduino Diagram

In the presence of methane, the sensor resistance is RS, while in clean air, the sensor resistance is R0. R0 would be the simplest to figure out of the two. Using an ohmmeter, we measure the resistance of electrodes 1-6 or 4-3.

MQ4 Arduino Diagram

As can be seen, Aout is connected to one of the electrodes and a resistor RL in parallel. This indicates that the electrode resistance generates a voltage divider with RL, resulting in the following voltage at Aout:

The resistance of our target electrode, RS, fluctuates depending on the amount of methane present.

RL is an SMD resistor with the designation 102, by the way. This is equivalent to a 1k resistance.

So we apply this formula to get RS.

MQ 214, MQ306A, MQ-5, MQ306A & MQ-2

MQ2, 3, 4, 5, 6, 7, 8, 9, 131, 135, 136, 137, 138, 214, 216, 303A, 306A, 307A, 309A

MQ4 Gas Sensor Dimension