Grain moisture detector circuit

During the grain purchase season, the grain management department has certain requirements for the humidity of grain. At present, many places still use the simplest method of touching and biting the teeth
to judge the moisture content of grains, but its accuracy is poor. Using the grain moisture detector as shown in the figure can quickly, accurately and intuitively give
the humidity of the measured grain. Its working principle is based on the fact that the capacitance of a plate capacitor is related to its dielectric. Two copper plates with the same volume and a fixed distance
form a flat capacitor. When granular grain is placed between the two flat plates of the flat capacitor , the medium changes from air to granular objects,
causing changes in dielectric loss and electric current. Capacity increased.
The oscillation frequency of the multivibrator composed of 555 timer also
changes accordingly. Differences in grain humidity will also cause
changes in the oscillation frequency. The rectified DC voltage also
changes accordingly. In this way, the humidity of the grain is converted into DC
voltage and is indicated by the DC voltage. The capacitance of the flat capacitive sensor should change by 1OFrF, and the DC voltmeter will indicate a change of 2V. As long as the humidity indicator or the qualified red band is engraved on the DC voltmeter, you can easily measure whether the humidity of the grain is qualified . RP is the zero adjustment potentiometer.