Gas alarm circuit (1)

Circuit working principle: Normally, when there is no gas in the air,
the resistance value between the A and B poles of the gas sensor QM-N5 is large, the potential of the control terminal 7 of the LED bar driver integrated circuit Ic
is almost 0, and its output terminal Pins 2-6 are all low level ,
LED1 to LED5 are all off, the alarm circuit and ventilation control circuit do not work
; when the gas in the air reaches a certain concentration,
the resistance The value becomes smaller, there is a certain voltage at pin 7 of the control terminal of IC1, the corresponding output terminal outputs high level
, and the corresponding LED lights up.