Calibrating the moisture meter


New Member
OK, I have burried a gypsum sensor in the ground, hooked up the moisture sensor to it, written some software, and have finally got some readings. The onboard thermometer is giving me some sensible readings (actually a bit high but thats probably the voltage regulator keeping the board warm).

The voltage reading seems to be hovering around -0.005 Volts (-0.00559375 a few minutes ago).

What I don't know is if this is a reasonable starting point or not. I could leave it in the ground for a year or so and look for patterns (I expect to do this anyway) but I'm trying to work out if I'm even in the right ballpark at the moment.

What sort of voltage ranges do people get in a range from dry to wet soil?

Thanks a lot.
I don't have any general information on the ranges since each sensor is going to be slightly different. When I make the sensors I try to be as consistent as possible but some things are harding to control like temperature and humidity in the room (I don't have a nice climate controlled factory :rolleyes:. What I normally tell people to do is (before it is buried) to take a dry reading, then place the sensor in a cup of water and take a wet reading. Those will then be your extreme values. It will unlikely that you will ever get all the way to either exteme once the sensor is buried but that will give you a good starting point.

Hope that helped.


This is more or less what I expected. Unfortunately I didn't do it. I understand that every situation will be different because of different chemical makeup of the soil, different ideas of what wet is and so forth. I might at least get a reading "open circuit" which should correspond to completely dry. I did this a few months ago but have since fixed a software bug that made my initial reading meaningless.

Some heavy watering might help me to get some sort of wet reading.

When I get this working I'm looking forward to getting some more bits to hook up and play with!