Bidirectional thyristor liquid level control circuit

As shown in the circuit in the figure, the controller consists of a water level detector, a trigger controller and a step-down rectifier circuit. Water level detection electrodes a, b, c and W1, R1, R2, R3 form a bias circuit as a liquid level detector. When the water surface is below b, Vp-b≈R3×VDD/(Rw1+R1+R2+R3)<1/3VDD, 555 is set, the SCR is triggered and turned on, and the motor runs to pump water. When the water surface rises to a, Vp-a≈R3×VDD/(Rw1+R3)>2/3VDD, then 555 is reset and pin 3 is low level. The SCR is cut off and the motor stops automatically when there is no power. This cycle continues to keep the water level within a certain range.