|Probe to Contact Closure Schematic
Schematic diagram which shows how
to connect up to 4 soil moisture probes to a set of 4 relays. This
circuit is useful for connecting the probe to sprinkler systems, or
moisture sensing alarms.
The circuit can be used with analog probes
that produce a voltage proportional to soil moisture such as the
vegetronix.com VG400 probe. The circuit uses op-amps as unity gain
buffers to buffer the output of the probes. This buffered
output is then fed to a comparator with hysteresis, which compares
the value to a voltage set by a variable resistor. If the high
threshold is surpassed the relay energizes. Likewise if the
low threshold is surpassed the relay releases.