Exhaust fan automatic control circuit (4)

Circuit working principle: The circuit is
composed of Doppler effect sensor, amplification controller, delay circuit and power supply circuit. IC is a Doppler effect sensor module
. When the human body moves within the effective range of the detector, a frequency shift occurs between the reflected signal and
the original transmitted signal. The weak frequency shift signal is amplified and Doppler detection
After the wave, a DC output level suitable for the displacement signal of people and objects is obtained. The fluctuation signal
output from IC pin 6 is amplified by the transistors VT, VT2. When VT2 is turned on, the relay K is excited and closed. K． Once it is closed, its normally open contact will be closed. Then it is closed, and the power supply charges the capacitor c5 through the resistor. When the terminal voltage of c5 reaches the power supply value, the Darlington tube composed of VT3 and VT4 is turned on, and the relay Kz is excited and closed. After K2 is closed, its normally open contacts K: one, and K2 one: are closed, and the exhaust fan motor will be energized to work. When people move within the effective range of the IC , the exhaust fan will run continuously. Once people or objects leave the effective range of the IC , the exhaust collapse will stop for a period of time. The size of its delay value is determined by the values ​​of Rs and C.