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-8 gas sensor which is more sensitive to LPG gas than other sensors like MQ-2. The MQ-8 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.

WORKING PRINCIPLE OF THE CIRCUIT:

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.

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.