Moisture Meter

I think they are actually two dissimilar metals and they are connected to a microammeter. The moisture is the electrolyte in a sort of battery- and the metals are consumed over time.

Best regards, Spehro Pefhany

Yup! Seen them in stores with garden stuff (Home Depot comes to mind). It is an ohm-meter; some look like a single probe that one pokes into the ground - it has two sections insulated from each other.

plants?

I used a commercial IC from National Semiconductors to measure the resistance with AC. Despite using AC, metal electrodes dissolved in a few months. This was soved by using carbon rods from old D size batteries.

It has been discussed before, see:

The standard low-cost way of doing this is with a "Gypsum block" normally a pair of wires cast in a gypsum block. Strip about 20mm of insulation off some wire, then cast them in a plaster of paris mix. A

You must use AC when measuring the probe impedance, otherwise electrolysis gives you very wierd results, although a number of newer commercial systems use short DC pulses of a few mSec with good results.

There's many thousands of these things buried in orchards, etc. They have a typical life of 4-5 years.

There's also a number of other techniques used, all much more complex. See

Barry Lennox>

Succes, Wim Ton

That would be another way to impliment the function. The one i saw was an ohmmeter.