Soil moisture meter circuit diagram

This circuit consists of VT1, VT2, capacitors C2, C3, resistors R1, R2, R3, R4, etc., which together form an oscillation circuit. The oscillation frequency is controlled by R6. One end of R6 is connected to a lead of the probe, and the probe is inserted into the soil. As the soil moisture changes, the resistance value on the probe also changes significantly. When this change is transmitted to R6, it will change the oscillation frequency of the oscillation circuit. The frequency change can be displayed through the swing of the ammeter connected to the collector of VT2, and people can judge the humidity based on the swing scale of this meter needle.