How to decode a 433MHZ signal

Question

I've made the classic 433mhz send/receive experiment, using cheap hardware on the same breadboard and same raspberry, I've wired both sender and receiver to VCC 5V, GND to GND and data to GPIO 27 (receiver) and 17 (sender). I used the 433Utils as software and Piscope to check th result. The first thing I've noticed is taht on Picope's channel 27 there is a continuos signal also if i don't use any sender, that's so weired for me (I'm a beginner). Then, I did enter the sendcode command only one time but the receiver console print 4 times the code, it is correct? More: on Piscope I see the sent code is repeated 10 times, why? I think this result is not correct, anyway I see something was sent and received, so I suppose the experiment did well.

The wave on channel 27 seems to be like the sent one, I post here the image, can someone tell me how to decode the signal received? Thanx

Answer 1

These types of radio systems are inherently unreliable, which is the reason the transmitter tends to repeat the signal multiple times. Ten repetitions is not unusual. As an aside consider a TV infrared remote control, it will continually transmit the signal until you take your finger off the button.

The receiver is seeing radio static. The automatic level detection circuitry will kick in once a proper carrier and signal is detected.

If you plan to process the received data I suggest you filter the static as far as possible. pigpio provides a glitch filter which is useful in this case, it rejects all GPIO level changes shorter than a specified number of microseconds in length. I suggest you experiment with values in the 50 µs region.

From the command line try

pigs fg 27 50

See http://abyz.me.uk/rpi/pigpio/pigs.html#FG

Answer 2

Firstly, I've noticed when I launch the Piscope& command, the shell release this message "** (piscope:2283): WARNING **: Error retrieving accessibility bus address: org.freedesktop.DBus.Error.ServiceUnknown: The name org.a11y.Bus was not provided by any .service files (piscope:2283): Gdk-CRITICAL **: gdk_window_create_similar_surface: assertion 'GDK_IS_WINDOW (window)' failed"

but the windows start and piscope is going well.

Then, I've tried to launch pigs fg 27 50 from any shell (I got 3 opened: the one where I've launcehd Piscope, the sender's one and the receiver's one) but nothing happened: the noise on ch 27 is still there. maybe I do wrong where and when sending the filter command?

Anyway when I send the code the ch 27 duplicate the ch 17, so it seems it is correct. My only doubt is that the code is sent via wire and not via radio, but I'm not sure this is possible.

Here another image in detail. the code sent is: 1234. how can i decode it? The main purprose of my project is to decode other signals: I use to test it a garage opener named CAME top 432 (datasheet confirms it works at 433.92 mhz) clicking it very close to the receiver but the receiver console doese'nt print anything, so I don't know if really the raspy receive something to decode (also because the ch 27 is noised)

any other suggestion please?