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L41, LPG Gas Leakage Sensor Alarm

This is the schematic diagram of LPG gas leakage sensor alarm. The circuit operates off a 9V battery. Zener diode ZD1 is applied to convert 9V into 5V DC to drive the gas sensor module.

The SEN-1327 gas sensor module from is applied in this circuit. Its output goes higher when the gas amount reaches or exceeds specific point. A preset within the module is utilized to set the threshold. Interfacing with the sensor module is performed by a 4-pin SIP header.


  • IC1 = NE555 Timer

  • Transistor T1 = SL100

  • R1 = 22ohm, R2 = 4.7K, R3 = 10K

  • R4 = 1K, R5 = 50ohm

  • VR1 = 10K

  • C1 = 0.1uf, C2 = 0.1uf

  • Zener diode ZD1 5v

  • LED (Red color)

  • Loud speaker LS1 = 8ohm 0.5watt

  • 4 Pin Gas Sensor GS = MQ-6 (SEN-1327)

  • 9volt Battery

MQ-6 Gas Leakage Sensor Device-

An MQ-6 gas sensor is applied in the gas sensor module. it has great sensitivity to propane, butane, isobutene, LPG and all-natural gas. The sensor can also be implemented to detect combustible gases, especially methane.

This circuit has been tested with LPG gas and was observed to do the job satisfactorily.

Whenever there’s LPG concentration of 1000 ppm (parts per million) in the spot, the OUT pin of the sensor module goes higher. This signal drives timer IC 555, that is wired as an Astable multi-vibrator. The multi-vibrator generally works as a tone generator.

Output pin 3 of IC 555 is hooked up to LED1 and speaker-driver transistor SL100 via current-limiting resistors R5 and R4, respectively. LED1 glows and also the alarm sounds to alert the user of gas leakage. The pitch of the tone could be adjusted by varying preset VR1. An appropriate heat-sink should be used for transistor SL100.

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