Water tower automatic water supply control circuit

Working principle of the circuit: three metal sheets l, 2, and 3 are suspended in the water tank of the water tower using wires with insulators. When the water level in the water tower is below the metal sheet 2, the voltages of pins 2 and 6 of the time base circuit
NE555 are both 0 , it can be seen from the logic state of NE555 (see
attached table) that at this time pin 3 has a high level output, the transistor VT is saturated and turned on, the motor is powered to
pump water, and the water level in the water tank rises. When metal sheet 2 is submerged but has not yet reached metal sheet 3 , this is equivalent to a resistor
being connected between metal sheets 1 and 2. As can be seen from Figure 1-3, this is equivalent to connecting pins 4 and 2 of the power supply. By adding a resistor, if the size of the metal piece is appropriate, the potential of pin 2 of the time base circuit NE555 can be greater than 1/3 Vcc, but the voltage of pin 6 is still 0 at this time. It can be seen from the logic state of the time base circuit that the output state of NE555 remains unchanged at this time, that is, the motor continues to pump water. When the water level touches the metal sheet 3, because the water conducts electricity, it is equivalent to connecting a resistor between pins 4 and 2, pins 4 and 6, and pins 2 and 6 of NE555 , so that pin 2 of NE555 The voltages of pin 6 and pin 6 are all greater than 2/3 Vcc, so pin 3 of the output terminal outputs low level, the transistor is cut off, and the motor stops pumping water.