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Simple LPG Gas Detector Alarm Circuit

Simple LPG Gas Detector Alarm Circuit

Are you feeling vulnerable or suspecting a possible LPG gas leakage in your house? Then may be this gas leakage alarm circuit might help you.

Written by: Sai Srinivas

The Concept

This circuit is a simple solution for detecting LPG gas leakage in households which causes severe physical and monetary losses if left unattended for a long time!

This circuit uses a MQ-6 gas sensor which is more sensitive to LPG gas than other sensors like MQ-2. The MQ-6 gas sensor consists of a small heater coil and some chemical composition of the compound SnO2(Tin Dioxide).

The heater coil remains heated always as long as the circuit is on and hence, the circuit continues to draw current even when there is no gas leakage.


gas leakage sensor device


First let us understand the pin outs of the sensor MQ-6. This sensor consists of six pins but in this circuit, two pairs of shorted pins are made by shorting two—two pins separately such that two pins together form one pair and another two pins form another pair and the other two left over pins are used normally without any shorting.

Here, we named one pair of shorted pins as XX and other pair as YY so that we could understand the circuit more easily.

Gas Sensor Pin Connections

The pins can be connected either way round, as they does not have polarity.

The heater pins are named as H each. While the pin XX is connected to Vcc, the pin YY is connected to the base of the transistor BC548. The heater pins can also be interchanged. The preset resistor is used to set the sensitivity.


MQ-6 gas sensor pinout details

simple MQ-6 gas sensor circuit

The gas leakage alarm circuit uses a BC548 transistor to turn on the buzzer whenever LPG gas is detected by the sensor.

Initially, when the circuit is turned on, the coil inside the sensor starts heating up and the current flow through the coil is controlled by a 33 ohms resistor while the zener diode makes sure that the voltage flow does not exceed 5.1V.

The XX pin is connected to the +ve of the power supply via a resistor while the YY pin is connected to the base of the transistor BC548. The 100K preset resistor is used to set the sensitivity.

When the gas concentration in the air increases, its output goes high and it makes the transistor to trigger the buzzer and a LED. The buzzer and the LED remain powered until the concentration in the air decreases below the specified level.


Use a general purpose PCB for assembling the circuit and use a ribbon cable to connect the MQ-6 sensor to the circuit. After completion of the making of circuit, take it near the LPG gas stove and switch on the power supply.

Make sure that there are no flames or electrical devices that could cause sparks in the vicinity of the stove and the circuit.

Now, turn on the gas stove without lighting it and adjust the preset using the screwdriver so that the buzzer rings only when there is reasonable gas concentration in air. After the adjustment is over, enclose the circuit in a suitable casing and install the sensor nearer to the gas stove.

Make sure not to include any electro-mechanical devices in the circuit as the sparks that might be produced while they are working could cause fire when there is a gas leakage. 



R1 – 33 ohms,

R2 – 2.2K,

R3 – 100K preset resistor,

R5 – 390K,

R6 – 2.2K,

D1 – 5.1V, 1W zener diode,

L1 – Red LED,

Q1 – BC548,

BUZ1 – 6V buzzer

Power supply – 6V, 800ma(should not exceed this voltage)

Prototype Image

MQ-6 gas sensor circuit prototype on PCB with alarm


While this gas leakage alarm circuit is tested for satisfactory working, it might fail sometimes to give a buzzer indication due to any reason like for example, power failure. So, please don’t depend entirely on this circuit and keep an eye on the stove always.

I am not responsible for any consequences that you might face while and after making this circuit.


About the Author

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials. If you have any circuit related query, you may interact through comments, I'll be most happy to help!

2 thoughts on “Simple LPG Gas Detector Alarm Circuit”

    • connect it where the speaker is connected…but use 12V separately for the relay and make sure to add a 1N4007 diode in parallel to its coil

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