DS2438

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

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);