Gas Leakage Alarm

gas is supplied in pressurized steel cylinders. As this gas is heavier
than air, when it leaks from a cylinder it flows along floor and tends
to settle in low spots such as a basement. This can cause fire or
suffocation if not dealt with. Here is a circuit that detects the
leakage of LPG gas and alerts the user through
audio-visual indications. Fig. 1 shows the circuit of the gas leakage
alarm. The circuit operates off a 9V PP3 battery. Zener diode ZD1 is
used to convert 9V into 5V DC to drive the gas sensor module. The SEN-1327
gas sensor module from RhydoLABZ is used in this circuit. 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 done through a 4-pin SIP header. Pin details of the gas sensor module are shown in Fig. 2.

An MQ-6 gas sensor is used in the gas sensor module. As per 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 wired as an astable multivibrator. The multivibrator basically
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.

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