Exhaust fan automatic control circuit (2)

Working principle of the circuit: Turn off the manual control switch S: of the exhaust fan M, turn on the power
switch S, and pin 2 of the three-terminal integrated voltage regulator Ic2 outputs a stable DC voltage (12 V)
as the power supply of the circuit. IC, and peripheral components form an astable circuit. The high and low transition time of
pin 3 of the output terminal of IC is determined by the charging and discharging time of capacitor C, that is,
C. The charging and discharging times of are respectively the power-on and power-off times of M. Therefore, adjust C.
The charging and discharging time of M can be realized automatically. When the power is first turned on, C.
The voltage at both ends is zero and cannot mutate, so pins 2 and 6 of IC are low level, pin 3
outputs high level , relay K is powered on, and M is powered on.