hii shital here n i want gas leakage alaram using ic555 pcb layout

The gas leakage alarm circuit operates off a 9V PP3 battery.
Zener diode ZD1 is used to convert 9V into 5V DC to drive the
gas sensor module. A preset in the module is used to set the
threshold. Interfacing with the sensor module is done through a
4-pin SIP header.
Whenever there is LPG concentration of 1000 ppm 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 speakerdriver
transistor SL100 through current-limiting resistors R5 and
R4, respectively. LED1 glows and the alarm sound 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.
Here is a LPG gas leakage sensor circuit that detects the
outflow of LPG gas and alerts the user via audio and visual
indications. The heart of this the simple engineering circuit is a
gas sensor module SEN 1327. QM 6 gas sensor is used in the
SEN 1327 module. The output signal from SEN 1327 gas sensor
module is used to drive a 555 timer based astable multivibrator
circuit. Here 555 timer works as a tone generator, the frequency
of tone can be altered by varying the preset VR1.