Simple pot flower shortage indicator circuit schematic

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The schematic diagram of the simple potted water shortage indicator circuit is shown in the figure.
The working principle is as follows: the circuit is buried in the flower pot by two humidity sensors of electrode A and electrode B. When the soil is dehydrated, the resistivity of the soil increases a lot. At this time, the electrical resistance between the two electrodes is large, causing the FET V to be turned off, the semiconductor transistor to be turned on, and the voltage drop generated on R4 to be an oscillator composed of 555. Start up.