Serial Port Temperature Sensors - Windows Software
This page describes the Windows software required to interface
to the temperature sensors via a PC's serial port.
Overview
On linux, the digitemp application is required to
query the temperature sensor.
There are various software applications that allow DS18S20 temperature sensors
to be queried in Windows, but the easiest is the Windows port of digitemp.
Installing digitemp
Download digitemp for Windows,
and extract digitemp.exe from the zip file.
Note that you'll need the version suitable for the DS9097 serial port adapter (ie, digitemp 1.x),
as the serial port interface circuit
described previously is equivalent to the DS9097U 1-wire serial port adapter.
Configuring digitemp
Initialise digitemp
First we need to configure the interface by telling digitemp the serial port that
the interface is connected to.
By default, digitemp will look for a configuration file (digitemp.cfg)
in the current working directory, so we'll explicitly specify the location of the
configuration file.
Assuming the interface is connected to COM1:
digitemp -i -s1 -q -cc:\temp\digitemp.cfg
You should see output similar to this:
Turning off all DS2409 Couplers
.
Searching the 1-Wire LAN
100486B60008009E : DS1820/DS18S20/DS1920 Temperature Sensor
ROM #0 : 100486B60008009E
This will create a file c:\temp\digitemp.cfg
containing the configuration information for digitemp.
Adjust Read Delay
Note that the DS18S20 temperature sensor has a slightly slower response time
(to convert its reading to a temperature) than the original
DS1820 sensor
The DS18S20 sensor takes approx 750ms to do the temperature conversion,
and digitemp defaults to a 1000ms read delay.
If you are occasionally getting temperature readings of 85 degrees Celsius (which is the sensor's error code),
you'll need to slow down the read delay performed by digitemp from
the default 1000ms.
To set the read delay to 2000ms and store this configuration in
c:\temp\digitemp.cfg, run the following:
digitemp -i -q -r2000 -cc:\temp\digitemp.cfg
With relatively short wire runs between the sensor and the serial interface
circuit, I've found that the default read delay of 1000ms provides reliable
temperature readings.
Reading Temperatures
Query Temperature
The sensor can now be queried for the current temperature (the "-a" tells
digitemp to read all connected sensors):
digitemp -a -q -cc:\temp\digitemp.cfg
and output similar to this should be displayed:
Apr 17 23:09:56 Sensor 0 C: 26.69 F: 80.04
Handling Errors
Note that occasionally the DS18S20 temperature sensor will return an error code,
returning a value of 85 degrees Celsius, instead of a valid temperature reading.
If this occurs, re-reading the temperature will normally return the correct value.
last updated 27 Jul 2012
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