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rtl_868 for Windows : receiving LaCrosse TX29 weather data

This article is a part of a whole global project : build my own weather station, based on Lacrosse weather sensor. For this project, I have to build a software decoder to retreive weather data from the radio sensor. I tested several software, including a program called RTL_868. This program was only for Linux or MacOSX, and I provide in this article a Windows version.

The original version of RTL_868 was made by Git Hub user “sum-sum”, and source code is available on Git Hub.
The source code can not be compiled out-of-the-box for Windows, so thanks to Git and the GPL Licence, I forked the project to create a Windows version of rtl_868.
Now, I can build a Windows version from a Linux box, by doing cross-compilation.

You can download the binary executable of rtl_868.exe here. It is build for Windows 32 bits version, so it works on 64 bits to. I use it on Windows Seven.

To use it, you must have the RTL SDR tool box, for Windows with the FM demodulator (works also with AM).
Download and install the Windows version of rtl_868 in the same directory as the “rtl_fm.exe” binary you installed.

Then you can use the following command line to decode Lacrosse TX29+IT radio sensor (transmission on 868,2Mhz) :

rtl_fm.exe -f 868.26e6 -M fm -s 500k -r 75k -g 42 -A fast - | rtl_868.exe
-f 868.26e6 : frequency (could be adjusted depending of your sensor)
-M fm : modulator
-s 500k : sampling rate
-r 75k : resampling rate (it is the real sample rate of the outputed data)
-g 42 : gain (should be adjusted from 0 to 50)
-A fast : math method used by the RTL dongle

Then, after a few seconds, you will see something like :

Found 1 device(s):
0: Realtek, RTL2838UHIDIR, SN: 00000001
Using device 0: Generic RTL2832U OEM
Found Rafael Micro R820T tuner
Tuner gain set to 42.10 dB.
Tuned to 868635000 Hz.
Oversampling input by: 3x.
Oversampling output by: 1x.
Buffer size: 5.46ms
Exact sample rate is: 1500000.014901 Hz
Sampling at 1500000 S/s.
Output at 500000 Hz.
2016-12-08 21:04:20, 1481227460, 22, 8.90, nan, 0.
2016-12-08 21:04:21, 1481227461, 33, 21.00, nan, 0.
2016-12-08 21:04:24, 1481227464, 60, 3.90, nan, 0.

On each line, you see : the date, the timestamp, the sensor IR, the temperature (in °C), the hygromethry, and a flag (1 if low battery).

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