Gas leakage Alarm using MQ_ Sensor [Diy].

LPG gas is highly inflammable in nature, leakage of such gas at Home, Industry or any other places can be extremely dangerous. This circuit based on MQ2 sensor can be used to detect and raise alarm on leakage of such inflammable gas.

Components Required:-

  1. MQ2 Sensor Module
  2. Transistor:-
  3. IC
  4. Resistor:-
    120 ohm
    470 ohm
  5. Zener Diode
  6. LED -(2)
  7. Speaker – 0.5W, 1W or above.
  8. Power Supply – 5V

Above is an image of MQ2 sensor module, we can see four pins on it marked as Vcc, Gnd, Digital out and Analog out; sometimes Digital out is also marked as Dout or DO and Analog out as Aout or AO.
Vcc pin is used to give +ve power supply to the module and Gnd to give -Ve or Ground supply to the module.

MQ2 Sensor Module:_
MQ2 Sensor Module is designed to detect Combustible Gas(LPG) and Smoke. When gas is detected by the sensor the digital state of the digital output pin is changed. There are two types of modules available in market, first one whose output state changes from HIGH to LOW on the detection and the second one whose output state changes from LOW to HIGH on detection of the gas. The majority of module available in market is of the first type which we are using in this project.

The sensitivity of sensor can be adjusted by rotating(clockwise or counterclockwise) the trimpot mounted on the module.
Analog pin gives analog output according to the amount of gas present in the air, which we are not using in this project.

A simple version of the Circuit


The Gas Leakage alarm circuit can be made using a more simple circuit, as shown above. we can see that a lot of components are eliminated in this simplified version of the circuit.
So what’s the difference between these two circuits??
— In the simplified version of circuit we are using a Buzzer which will make continuous beep sound when inflammable gas is detected while in another circuit( first one) we are using UM3561 based tone generator which will produce Police Siren Sound or Fire Alarm Sound, so it will be more appealing, also Darlington pair of transistor is used to produce a loud alarm.


MQ2 Sensor module runs on 5v, so a 5vdc regulated power supply is required.
The second part of this circuit is a tone generator. IC UM3561 can generate four different types of tones:- 1)Police Siren 2)Fire Force 3)Ambulance 4)Gun Sound. In this circuit, we are using two of them, first and the second one i.e. police siren sound and the Fire Force sound. switch S1 is used to toggle between two sounds.
When Gas is detected, output at digital pin of the ‘sensor module’ goes from high to low which turns on the PNP transistor 2N3906; as a result, UM3561 based tone generator circuit gets ON.

UM3561 works on a voltage range of 2.4V to 3.6V, but we are using 5V power supply for this circuit, so to regulate suitable voltage for IC UM3561 we have added a 3.1V Zener diode.

Two transistors 2N3904 and 2N2222 are connected to the output pin[pin 3] of IC UM3561, these transistors are connected in Darlington configuration which results in a louder output sound.

How to use

After connecting all the components according to the circuit diagram, connect the circuit to a 5V dc power supply, a USB charger or USB power bank can also be used as Power supply, now wait for 30 to 60 seconds this time is required by the sensor to warm up, after this time sensor will be ready to detect inflammable Gas.
A Potentiometer is preinstalled in the Gas Sensor Module which can be used to adjust the Gas sensitivity of the sensor module.
“How to adjust this potentiometer??”” ,, A small screwdriver can be used to rotate the potentiometer in the clockwise or anticlockwise direction which will increase or decrease the sensitivity.

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