|MadSci Network: Agricultural Sciences|
There are many ways a moisture meter can be constructed. Probably the way yours works is the following: (this is the cheapest way)
The two probes have an alternating voltage applied to them. If you have some who has an oscilloscope, you can measure the voltage. Or you can measure the voltage with a Digital Multimeter (DMM) if someone has one of those. The alternating voltage keeps the probes from corroding. If the meter applies voltage to the probes in one direction only, the probes suffer from electrolysis.
Once a voltage is supplied, the meter measures the current that travels from one probe to the other. Moisture in the soil causes the electrical resistance of the soil to drop and more current can flow. The amount of current is used to approximate how moist the soil is.
If you have more questions, e-mail me at firstname.lastname@example.org
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