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The DS2438 is originally a "Smart Battery Monitor".
For use in the home automation, he has four interesting features:

  • A voltmeter, this provides the bus voltage - ideal for monitoring (VDD)
  • A thermometer - can always be useful (Temperature)
  • An AD converter (VAD) - can be used for measuring the moisture or brightness
  • A current input (Xsens) - at leisure
DS2438: Tree

Practical example: moisture measurement

The humidity sensor HIH-4000 from HONEYWELL has an accuracy of 3.5%, ranging from 0 to 100% RH.
Because of its linear output the DS2438 can be read out directly. A temperature compensation can be taken into account because the DS2438 has an internal temperature sensor.

As it goes, illustrates the following script:
$Vad = GetValue(44045);
$Vdd = GetValue(14570);
$temp = GetValue(18691;
$Srh = ($Vad - 0.958062) 30.680;
$Srh = $Srh / ((1.0305 + (0.000044
$temp) - (0.0000011 pow($temp,2))));
echo "Humidity: $Srh %rh Temp.Comp.\n";
SetValue(49935 /
[Humidity %rh]*/, $Srh);

Any questions?