Different temp sensor: LaCrosse / TFA IT+ on 868Mhz

[mlo818]

Hi, I'm looking for a way to get readings from a different temp sensor type (Lacrosse/TFA IT+ protocol) on the 868MHz band using RTL_SDR. I read it's supposed to be "easier" to decode than the one you implemented (signal uses OOK).
Binary protocol is quite well documented on the net (see http://fredboboss.free.fr/tx29/index.php?lang=en, or here if you like french ;) http://www.jacquet80.eu/blog/post/2011/10/Decodage-capteur-thermo-hygro-TFA ) so I think if I could get the "binary data" I could handle the decoding part.
Unfortunately I'm not familiar with "radio decoding" so I have no idea where to start from using rtl_sdr...
Do you think you could help ? Of course I can provide any info you need (sample output from RTL_SDR or whatever). Thanks for your help !

[merbanan]

Hi, try running with rtl_433 -f 868428000 -a. This should tune to the 868MHz band and if there is an OOK signal there will be a log output that describes the signal, pulse start, pulse length and duration between pulses. You can also add a file name argument after -a then it will save the demodulated data to a file. If you are able to save a pulse file I can help look at it. But first get a log of the signal and pastebin it. The log will tell alot about the signal.

[mlo818]

Thanks for this quick response ! I gave it a try but without any luck... nothing in the output file. The transmitter sends info every 4 seconds so I waited for more than 10 secs., which should have given at least 2 readings.

Just in case you see something wrong about my setup here is my output:

$ ./rtl_433 -f 868428000 -a > demod.txt
Found 1 device(s):
0: NOXON, DAB Stick, SN: 0

Using device 0: Terratec NOXON DAB/DAB+ USB dongle (rev 1)
Found Fitipower FC0013 tuner
Sample rate set to 48000.
Sample rate decimation set to 0. 48000->48000
Bit detection level set to 10000.
Tuned to 868428000 Hz.
Reading samples in async mode...
^CSignal caught, exiting!

User cancel, exiting...

[merbanan]

Use rtl_fm and tune to a frequency and listen. If you hear something beeping every 5 seconds you are on the correct frequency. If not find the correct one somehow. You can lower the bit detection level by setting it to 1000 instead (-l 1000).

[mlo818]

Tried -l 1000 with no luck. I guess the frequency is wrong as you said (I cannot "listen" as i'm not on site) but I don't really know how I'll find it. Anyway two more newbie questions: which mode can I use for RTL_FM (narrow FM ?), and how "precise" has the frequency to be (ie how close do I have to be to hear something). 10000 hz ? 1000 hz ?
Thanks again for your help ;)

[pauldd]

I would like to recommend "multimode.py" if not already known to locate signals ;) just google for it

[merbanan]

Reopen if you still want help to sort out the signal.

[mlo818]

Hi,
After playing a bit with RTL_TCP and SDRSharp, I concluded that my dongle was (kind of) deaf at this frequency. I just got a new cheap one from ebay... and this one looks better. I had to lower the bit detection level (-l 3000 is the maximum) but I now have something using

./rtl_433 -f 868428000 -a -l 3000

Looks coherent: same frequency found by the guy in the 2nd link in my first post, and i got something every 8 seconds, which is the specification of the temp. sensor.

Output can be found here: http://pastebin.com/FhqmGwqm
Now.. I'd love to get that decoded ! Can you help ?

Let me know if you need anything else from my side (more readings maybe ?). And by the way I don't know how to re-open the issue !

[mlo818]

Hi,
I'm still looking for a way to decrypt IT+ transmissions on 868mhz... output is still here: http://pastebin.com/FhqmGwqm

[merbanan]

Update your code to the newest one and send the output of ./rtl_433 -f 868428000 -a

[merbanan]

Use -a -t, this will save the signal it finds.

[mlo818]

Hi,
For whatever reason i had to lower the bit detection level woth the new version. Output can be found here http://pastebin.com/AtgRQg0L and I have the ouput signal saved files available too (but don't know what to do with them).

[merbanan]

The decoding of the signals doesn't work.The logs show only broken data. I think that the lowering of the detection level is messing it up. Can you record the signal with just rtl_sdr ? You can look at it in audacity by loading raw 8bit stereo data.

[mlo818]

Hi. In the end, I nerver managed to get any "meaningful" readings at 868mhz so... I gave up and moved to 433 mhz sensors (which works much much better..;)

[sum-sum]

I have created a receiver for FM modulated temp stations. These include TX29 and other devices which were sold by Aldi in Germany. See sum-sum/rtl_868 on github: https://github.com/sum-sum/rtl_868

[pyrog]

See MMMMobileAlerts ?
It document the protocols of ELV Mobile Alerts sensors (LaCrosse)

[zuckschwerdt]

At a quick glance they don't seem to decode the radio protocol but rather bridge the UDP traffic from a head unit.