Sensors Connections will according to type of Gas sensor Use-
Normally Gas sensor start from MQ2 to MQ15 . According to gas required
For Smoke- MQ2
LPG- MQ5
Alcohol – MQ3
Components Used:
Q3- BC548
Q4-BC558
D&- LED 5mm
R12- 10k variable resistor
R13- 1k
R14+R15- 1k
555 timer
LDR- 5mm- 50 ohm
Soldering wire
Soldering Iron
Multimeter
PCB-