fire smoke control circuit

This circuit is suitable for detecting smoke generated by the combustion of coal gas, liquefied gas, gasoline, oxidation monoxide, alkane volatile gases, and paper, wood, screws, plastic products, etc. ,
    (1) The working principle circuit is as shown in the figure.
    The power supply is 12V from the battery, and the power switch is S, Ri,
Hurricane,,. Qodedu÷ voltage regulator - tube vs group Qi. QM-N5
uses semiconductor gas sensors as sensors to achieve "gas-to-
electricity" conversion. The 555 time base integrated circuit and surrounding components form
the trigger circuit and alarm audio circuit. Since the heating voltage of the gas sensor
is required to be quite stable when working, a 12V power supply is used to stabilize
the voltage of the gas sensor heating filament , so that the alarm can operate stably in the range of 180 to 260V. When the circuit is working, the self-excited multivibrator composed of 555 time base circuit is triggered by its reset terminal. When the gas sensor comes into contact with flammable gases and the above-mentioned smoke, its resistance decreases, causing the voltage at pin ④ of the reset terminal of the 555 time base circuit to rise. When the voltage reaches 1/3 of the power supply voltage V2 of the 555 time base circuit, the output Pin ③ outputs a high level to drive the speaker to emit an alarm sound with high sensitivity.