One of the liquid level automatic control circuits using power switch integrated circuit (fill-in type)

Due to the use of power switch integrated circuit A, it has the advantages of simple circuit,
high sensitivity, and reliable operation. It belongs to the filling type liquid level automatic control circuit.
    When the water level is below electrode B, pin 2 of A is low level (ov), A is turned on, pin 4 is low level (Ov),
relay KA is closed, KM is closed, and the water pump starts running and supplies water to the water tank. Water enters; when the water level rises to electrode A,
pin 2 of A is high level (>1.5V), A is cut off, KA and KM are released, and the water pump stops filling.