Lawrence Lile wrote:

> Problems I encountered when I built one of these:
> 1.  Soil resistance changes over time.  I would plug my two probes
> into the wet soil, then an hour later it would start beeping.  I made
> a little circuit to plot this on my datalogger, and noticed a dramatic
> change in soil resistance.  Of course I was measuring with an AC
> signal to prevent corrosion.

  Do I take this to mean that the (continuous) measurement current (AC
notwithstanding) is causing "polarization" at the electrodes, drying the
soil locally?

  Surely the advantage of the 12C508 is the ability to sleep most of the
time (and even then, execute the test cycle only every so many
"sleeps",) and apply current and make a measurement only every five
minutes or so?
--
  Cheers,
        Paul B.