A few questions about 868.3 mhz RF modules and RF modulation


I'm completely new to arduino and electronics - my skills are close to (if not exactly) zero.

I want to start automating my home as a fun project to learn while also saving money by not buying some finished system.

My ultimate goal is to eventually have a "base" that controls everything that can receive signals through wifi/bt/rf/whatever and send out signals to lights, applications and thermostats.

But I want to start by controlling the lights in my livingroom, which is already working on RF 868.3 mhz frequency from a remote (remote and receiver specs at the bottom).

Now from what research I have been able to do, I've found out that I need a 868.3 mhz transmitter, and somehow to read the signals sent by the existing remote, so a receiver.

I've found this receiver: RFM217-868S1 Module - Data sheet

And from the RFM217 specs it does seem like it should be able to handle 868.3. In the datasheet it says 868.35 spesifically, and here are my questions.

  • Exactly how accurate does these signals have to be? Are 868.35 close enough to 868.3, is 868 close enough to 868.3? etc.

As I understand it from reading up a little bit, the transmitter sends a modulated signal that the receiver interpetes and acts upon, which brings me to the second question.

  • If a transmitter is on the correct frquency and sends the right modulation, is that enough for the receiver to accept the transmission? or are there different types of moulations too within a frequency (which could mean this receiver can't receive the signal from the remote).

I got a little excited and bought this 868 transmitter without thinking about how to get the signal first :stuck_out_tongue:
Transmitter: RFM42-868-D Module - Data sheet

As I'm reading the datasheet in table 2/3 (page 5/6) it has a frequency range from 848 to 888, but! Next question;

  • I wasn't able to figure out how accurately it was able to be, as in, could it be frequency 868.3?

And 2 last question.

  • If the Receiver and Transmitter above are in the correct range and accurate enough and all else I might not know that need to match, do they acually match with my receiver on the lights and the remote?
  • How easy is it to break (burn?) these chips.. Should I order more than 1?

Thanks for helping a beginner out :slight_smile:

And some data on the remote and the receiver if needed:

Couldn't find a data sheet in english, but here it is in norwegian, and I'll try and translate to the best of my abilities below as well.

The receiver module the lights are connected to are: (data translated from Norwegian in the link above)
Moeller Xcomfort CDAU-01/01
( I could only find the CDAU-01/01 in the data sheets I found, but the one installed is 01/02).
Frequency: 868,300 MHz
Transfer method: bidirectional, coded
And the remote control is a:
Moeller Xcomfort CHSZ-00/01 (data belo translated from Norwegian)
(extra pdf in german, don't speak that though, so not sure what is says.)
Current: 3V
Channels: 6 x 2 =12 (24 functions) Status - LED
Frequency: 868,300 MHz
Transfer method: bidirectional, coded

If the frequency is stated to be 868.3 MHz, then all units have to be tuned to that frequency, as accurately as possible.

There is very little useful information in those documents (I speak German), but the "transfer method" is stated to be bidirectional in both.

I believe this means that both the sending unit and receiving unit are actually transceivers, with some sort of data integrity check and a "successful transfer" acknowledge operation.

There are many different types of radio signal modulation, and an unlimited number of data encoding protocols. Generally, each manufacturer designs their own unique protocol.

Until you completely understand this bidirectional data transmission protocol, it will be impossible to duplicate with your own equipment. Data may also be encrypted, which means that simply interpreting the messages transferred could be quite challenging.

Here is an introduction to investigating transmissions by simple weather station remotes: Reverse Engineer Wireless Temperature / Humidity / Rain Sensors — Part 1 « RAYSHOBBY.NET

Ah man! So much for starting out with an easy automation. :stuck_out_tongue:

I was guessing there were probably more to the modulation than a simple "here's the signal, have fun".

Thank you for the link, I'll give that a read a little later today.