quinta-feira, 5 de outubro de 2017

433.92Mhz ASK/OOK Decoding

I have an old 433MHz remote temperature sensor laying around and decide to do some testing. I've used my Hackrf One to probe the frequency and the modulation type using the osmocom_fft and the insepctrum application.
First run on a terminal osmocom_fft -a hackrf -v -f 433e6 -s 8e6 -g 0
If you are using an rlt-sdr use osmocom_fft -a rtl=0 -v -f 433e6 -s 2048e3 -g 0 . Notice that on the right lower corner there is a rec button just record some transitions from the sensor and notice the frequency.
osmocom_fft
 Using the REC button record the sensor activity and use inspectrum to analyse it by open the recorded file.
inspectrum
Now we can clearly see what is append. This is much better than use audacity to look at the demodulated signal. The ASK/OOK signal is clear now, we can demodulate and "time travel" our signal at will, you can even try several types of modulations at the same time and figure which apply.

There is also rtl_433 application that will decode the temperature sensor, or your car tire pressure sensor or many things from an rtl-sdr, on your terminal just use rtl_433 -G
rtl_433 in action using an DXPatrol MK4