Soil moisture detection sensor 2

As for the circuit, there is nothing special. The 555 generates a signal of about 400K, and the capacitor C is the sensing area. Pay attention to the distance between the two plates of the capacitor C. C is the particularly long sensing area. Do not let OUT and GND Too close, at least the distance should not be less than the distance between the C plates, so as not to affect the effect. The diode and voltage stabilizing circuit have been removed, which does not affect the use. Therefore, the input voltage must be between 3.3-5V and stable. Most development boards have stable voltage module, so I considered removing the voltage regulator on this sensor. The relationship between OUT output voltage and humidity is inversely proportional and non-linear. Please calibrate it in water first. Data processing is all a matter of program. The size of C5 determines the frequency, and the simulation is different from the actual circuit board! To simulate C5, you only need 680P. In fact, C5 is much smaller. C5 must be about 100P to output a frequency of 340 kilohertz. It is generally believed that the higher the frequency, the more accurate the measurement.