How to Detect Concentration of Gas by Using MQ2 Sensor




Introduction: How to Detect Concentration of Gas by Using MQ2 Sensor

MQ-2 Gas sensor is used to detect the gas level around the area. This sensor able to use as home or factory gas leak monitoring, suitable for gas, butane, propane, methane, alcohol, hydrogen, smoke and other monitoring devices.


  • Size: 35mm x 22mm x 23mm (length x width x height)
  • Main chip: LM393, ZYMQ-2 gas sensors
  • Working voltage: DC 5 V
  • Characteristics:
  1. With a signal output instruction.
  2. Dual signal output (analog output, and high/low digital output)
  3. 0 ~ 4.2V analog output voltage, the higher the concentration the higher the voltage.
  4. Better sensitivity for gas, natural gas, city gas.
  5. With a long service life and reliable stability.
  6. Rapid response and recovery characteristics.

Step 1: Gather Materials

Step 2: Understanding Pin Definition of MQ2 Gas Sensor

Step 3: Set Up the Circuit Above

LCD pins

-Pins D7 , D6 , D5 , D4 connect to arduino digital pins 2,3,4,5 respectively.

-Pins A and K connect to 5V and GROUND respectively

-Pins VSS and VDD connect to Ground and 5V respectively.


-Use as a LED indicator for the calibration process of the MQ2 gas sensor

-Connect to digital pin 13 of Arduino Uno

MQ2 Gas Sensor

-Analog output connect to the A0 of arduino


-Center pin connect to the V0 of LCD display

-Other two pins just connect to 5V and GROUND respectively

*Note: All of pins above is configured regarding the circuit figure above. You can configure the connection yourself regarding your favourite.

Step 4: Programming the Arduino Uno

As you can see in the graph above , it shows several gases.

The values are plotted on a semilog paper, as you can see the values indicate 100......1000.....10000 ppm.

These values when plotted on a normal graph would represent a curve like an exponential one.

Formula In the Coding

pow(10,( ((log(rs_ro_ratio)-pcurve[1])/pcurve[2]) + pcurve[0]))

Based on the graph MQ2, the derivation of ppm formula will be:

Y - y1 = m( X - x1)

X= (y-y1)/m + x1

X= (Rs/Ro-y1)/m + x1

log X =(log (Rs/Ro) - y1)/m +x1

X =10^( (log (Rs/Ro) - y1)/m +x1)

*Note: X = ppm on the graph

Y= Rs/Ro

***The derivation formula are same and can be used for other types of MQ gas sensor.

If you have any problem about the coding, you are welcome to ask any question in the comments below or contact us for further details.



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    21 Discussions

    why releasing lpg also changes other valus also...........whether these sensor used to measure accurately concentration of gases?

    In the video, you start up the arduino, it calibrates, and consequently, all readings say 0 ppm. This I understand, but the you open the lighter, releasing flammable gas (probably similar to LPG), and then the readings for CO and Smoke also rise. I think there is a error in reasoning: the values should be read as possible values: either this much ppm LPG, or this much CO, or this much Smoke, or possibly all at the same time. But it is impossible to distinguish between the gases, since any combination of gases, or a rise in the concentration of one, gives the same reading. Maybe this could be clearer, for the code and the readings are very ambiguous otherwise.


    1 year ago

    If i may ask, how did you get these values LPGCurve[3] = {2.3,0.21,-0.47}; //two points are taken from the curve.

    1 reply

    log(200)=2,3 (200 is first point from ppm axe)

    log(1.6)=0.21 (0.21 is first point from Rs/Ro axe)

    log(10000)=4(last point from ppm axe )

    log(0.25)= -0.6 (last point from Rs/R0 axe)

    and with (2.3, 0.21, 4, -0.6) will obtain slope =-0,47

    May I know how to adjust load resistance(RL) which is given to be 5Kohms, do I need to adjust the on board load resistor or what, how should I twist it to get 5kohm


    Question 5 months ago

    How to adjust load resistance(RL) which is given to be 5Kohms in data sheet..and how clean air resistance (Ro) is taken to be 10Kohms?

    Hi, we are not sure for it. Anyway you may refer to the datasheet

    first take 2 points from the graph, find y axis co-ordinate and x-axis co-ordinate, since it is log-log graph, find respective log values of each co-ordinate with base 10,then substitute in (y2-y1)=m(x2-x1), where "m" is slope..

    Hi how do you distinguish the different gases? this is not clear to me

    1 reply

    By comparing with the different slopes give in the data sheet


    Question 6 months ago

    i want to make same projct but for mq7 (i use a Modula like you use but mq7 )
    my quastion
    what is RL for mq7
    and R0 and clean air
    and normal RO
    because i search in data sheet and didn't understand this thing

    hi . please give us an example about how i can detect a gas with mq2 ireallyneed to underestand this because of my project i really need an example....please help me

    hi . please give us an example about how i can detect a gas with mq2 sensor i really need to underestand this because of my project i really need an example....please help me

    Hi! I am trying to integrate your sketch into a room climate station where I also run a DHT22 and a Shinyei PPD42 to measure temperature, air humidity and dust.

    When compiling the sketch I always get the error message that MQCalibration was not declared (line 56 in your sketch)

    Since my setup is quite different I can not run your sketch without rebuilding the whole thing...

    How does smoke concentration measured and sensed by the MQ-2 brief please??