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I have these remote controlled wall outlets (Brennenstuhl Funkschalt-Set RCS 2044 N Comfort). And I'm trying to make an arduino circuit with an RF transmitter so I can switch them on and off without the remote.

I sniffed the signal from the remote with an RTL-SDR and found out that the signal frequency is 434 MHz. So I went online and ordered an 434 MHz transmitter (from sparkfun).

After I hooked the transmitter to my arduino and wrote the code with the exact same signals as the remote had send out. I tested the circuit and saw that it didn't work.

So to see where it went wrong I also sniffed my signal from the RF transmitter, to see if it's the same as the one from the remote. And I found out that the frequency of my 434 MHz transmitter is actually 433.92 MHz.

But this turned out that it wasn't a mistake. But the chip in the datasheet even says that it is 433.92 MHz. And when I went online to find a real 434 MHz transmitter I couldn't find one, because all the 434 MHz transmitters that I found were also actually 433.92 MHz.

So then I tought how the hell has my remote a 434 MHz transmitter if I can't find one? And I screwed it open and saw in the casing that even the transmitter of the remote is 433.92 MHz. But for some reason it sends out a 434 MHz signal. So it must have some kind of circuit inside that modifies the 433.92 MHz to 434 MHz.

And now my question to you is:

How can I do that? How can I modify a 433.92 MHz signal to a 434 MHz signal?

Thanks in advance!

(I uploaded some pictures of the remote, the wall outlet, the RTL-SDR, the RTL-SDR captures on my laptop, The (simple) arduino circuit and the transmitter module)

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  • \$\begingroup\$ How do you know the signals you're sending are in any way compatible to what the remote expects? The transmitters you've bought look (barely) capable of doing simple "somewhat continuous phase on-off-keying", and that might or might not be the same thing your wall outlet remote expects. \$\endgroup\$
    – Marcus Müller
    Commented Mar 25, 2018 at 16:40
  • \$\begingroup\$ @MarcusMüller has a serious point. The frequencies are half the problem. What if they use a different protocol, bit/byte order? You have an untenable problem we cannot help you with. \$\endgroup\$
    – user105652
    Commented Mar 25, 2018 at 19:50
  • \$\begingroup\$ I sniffed the signal, and analized the bits. That is not the problem. \$\endgroup\$
    – piet_lu
    Commented Mar 26, 2018 at 13:15

1 Answer 1

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"How can I modify a 433.92 MHz signal to a 434 MHz signal?"

Don't. Frequency-wise, what you bought is fine.

The difference is only 0.02%, the electronics would have a very hard time to distinguish between those two frequencies, especially the very cheap electronics found in typical consumer products. So the documentation often rounds the value a little (or just chops off the .92 part and calls it 433). I very much doubt that your oscilloscope would be able to tell the difference, so the 434.000 you measured is probably 433.92 (or at least meant to be).

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  • \$\begingroup\$ I was about to reply stating don't change the freq, change the allowed tolerance and leave it :) \$\endgroup\$
    – user16222
    Commented Mar 25, 2018 at 12:03

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