Simple water level controller circuit (1)

Working principle of the circuit: When the water level is below A, (not in contact with A,), the thyristor
vs conducts due to the voltage drop on Rz, K: works, pulls in K: 1, and the water pump starts
pumping water. When the water level rises with A. When in contact, it is equivalent to adding a bias resistor E to the base of VT
, and the composite tube composed of VT, and VT2 is turned on, K. To work, disconnect K. one. ,
but because the thyristor is turned on and the trigger voltage is turned off, it is still turned on, and the water pump continues to add water. When
the water level rises and contacts A3, K3 is also made to work and K3 is disconnected. Kz
disconnects the water pump due to loss of current (K2 is disconnected), and the water pump stops adding water. When the water level begins to decrease and
Ai is not in contact, VT4 and VT3 are cut off, K does not work, K3 is closed, but vs is still cut off because
there is no trigger voltage . Only when the water level drops to 　4. When K, is closed,
K3 is turned on, K2, is closed, and the water pump adds water. The power supply can be supplied by a 6V transformer, which is
rectified and filtered and then output to the circuit.