Simple potted flower water shortage indicator circuit schematic diagram

The circuit schematic diagram of a simple potted flower water shortage indicator is as shown in the figure.
Its working principle is: the circuit consists of two humidity sensors, electrode A and electrode B, buried in the flower pot. When the soil is short of water, the resistivity of the soil increases a lot. At this time, the resistance between the two electrodes is very large, causing the field effect transistor V to cut off and the semiconductor transistor to conduct. The voltage drop generated on R4 makes the oscillator composed of 555 Start vibrating.