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