Soil Moisture Probe

[last updated: 2016-09-02]
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probe block diagram

The probe is made from 3/8" rebar. The rebar itself is the ground connection, with point-of-contact distributed along the length of the rebar.

There are 5 soil contacts, spaced about 5" apart. The deepest is about 1" back from the tip of the probe, and the top one is 3" under the surface.

Since there aren't enough analog inputs available to read each probe contact's resistance on its own input, the Mux is needed. The analog signal is the voltage drop across the soil resistance (in ref to drivePin2). The resistance R is arbitrary and just limits current through the probe. I set mine at 56k.

Probe Construction

eof