How to detect concentration of gas by using MQ2 sensor

Understanding MQ-2 Gas 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.

Specification:

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

Step 1: What You Need?

1 x Arduino UNO R3
1 x M-2 Gas Sensor

1 x Potentiometer (10k Ohm)
1 x LCD (20x4)
1 x LED (Red)
1 x USB Type-B Cable 
1 x Breadboard
Female-to-Male Jumper Wires (FM)
Male-to-Male Jumper Wires (MM)


Optional 

Arduino Uno R3 Acrylic Transparent Casing

Arduino Compatible UNO Ultimate Starter Kit / Learning Kit

Don't have components? Don't worry. Just click the component's name. 

Step 2: Build Your Circuit.

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.

LED

-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

Potentiometer

-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 3: Upload The Code.

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.

Download:

Arduino IDE
M-2 Gas Sensor Datasheet

Sources:http://www.instructables.com/id/How-to-Detect-Concentration-of-Gas-by-Using-MQ2-Se/?ALLSTEPS

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My Robot Education Sdn. Bhd. (Robotedu.my) was founded in 2015 as the first robotics education centre in Malaysia to provide Arduino-based robotics courses for youths. Our vision is to be able to provide robotics education to every youth in Malaysia.