Soil moisture measurement circuit diagram

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Soil moisture measurement circuit diagram [Copy link]

The circuit is composed 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 which 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, the oscillation frequency of the oscillation circuit will change. The frequency change can be displayed by the swing of the ammeter connected to the collector of VT2, and people can judge the humidity based on the swing scale of the needle.

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I want to use a hygroscopic resistor to test the water tightness of our products. Is this circuit feasible? Or can I use a bridge to measure the group value of the hygroscopic resistor?