Here is a circuit that can be used to detects the leakage of LPG gas and alerts the user through audio-visual indications. The circuit uses SEN-1327 gas sensor module from RhydoLABZ. Its output goes high when the gas level reaches or exceeds certain point. A preset in the module is used to set the threshold. Interfacing with the Sensor module is connected to circuit through a 4-pin SIP header. The circuit powered by 9V PP3 battery. Zener diode ZD1 is used to convert 9V into 5V DC to drive the gas sensor module.
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An MQ-6 LPG gas sensor is used in the gas sensor module. According to its datasheet, it has high sensitivity to propane, butane, isobutene, LPG and natural gas.
The sensor can also be used to detect combustible gases, especially methane. This circuit has been tested with LPG gas and was found to work satisfactorily.
Whenever there is LPG concentration of 1000ppm (parts per million) in the area, the OUT pin of the sensor module goes high. This signal drives timer IC 555, which is configured as astable multivibrator and works as a tone generator. Output pin 3 of IC 555 is connected to LED1 and speaker-driver transistor SL100 through current-limiting resistors R5 and R4, respectively. LED1 glows and the alarm sounds to alert the user of gas leakage. The pitch of the tone can be changed by varying preset VR1. Use a suitable heat-sink for transistor SL100.