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Reverse Engineering central heating wireless thermostat - help needed!

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LaserSteve:
Why in the heck would you want to try to demod the RF when you have access to the SPI on BOTH ends?
Unless a Demod tool is already coded, that is just asking for a huge development project.  You could spend tens of minutes waiting for a single command burst. 

I'd vote for Sniffing the bus.  Even my low end four channel scope has a sniff mode option for SPI. 

Dear OP, if you want to see the burst rate, I'll link what I was going to suggest if the transmitter was on/off keyed.
One diode detector, one scope channel, and a 81 mm length of wire as a quarter wave antenna..

http://www.techlib.com/electronics/detect.htm

On Chuck Wenzel's detector circuit,  linked above, you may need to lower the value of the 0.1 uF cap or the 100K resisitor to see a full envelope.



Steve

picitup:
Hi

I wanted to go the RF route for two reasons;  firstly I wanted to know that I can acquire a transmitter (868.3MHz) that would work with the system otherwise it will never work and secondly, going the RF route, I can play until my heart's content rather than start hacking the transmitter around and killing it as the cold weather approaches then we have no heating.  This may cause local tensions  ;)

Another option is to buy another (cheap) wireless stat and receiver, fit that to the central heating then I'm free to hack this one around.

Both reading the SPI bus and the RF side are interesting to me.  I think there's plenty of scope for me to learn a lot.

I've seen an RTL-SDR stick on eBay for £7.81 item number 161897487881.  Is this the kind of stick I would need?

Ps I don't mind spending the time if I'm learning something new.

Thanks again all for your comments.

Cheers

Steve

picitup:
OK I've done a bit of reading and youtubing and found these 2 videos, that you might find interesting if you're an RF noob like me.  Both show using the RTL2832U stick on Androids using OTG.





So I've put my hand in my pocket and bought a stick which is fleabay item 172017000295 for £7.58.  Despite the main pic, it comes with an aerial and remote control.  It's stocked in the UK supposedly so hopefully it won't take too long to come.

I'll post up when it arrives.

Cheers

Steve

picitup:
Yes when you start digging into devices, it's amazing how scabby the designs are.  It gives me hope for the future!

Well no SDR stick today, so hopefully Monday.  I decided to buy the cheap transceiver from fleabay mentioned above.  It's item 141804081741 and is £2.40 and is apparently a Silicon Labs SI4463 clone which is another SPI->Radio solution.  I asked the seller for the data sheet and he sent me Silicon Labs AN632 EZRadioPro advice note:

https://www.silabs.com/Support%20Documents/TechnicalDocs/AN632.pdf

The SI4463 datasheet is here:

https://www.silabs.com/Support%20Documents/TechnicalDocs/Si4464-63-61-60.pdf

and I'm pretty gobsmacked.  It's a fully featured programmable spi->radio with I/O and configurable frequency and modulation etc.  It has a config program which allows you to change many settings and I think you can code it in C too.

I thought I was buying a simple on/off point-point device but it's the full works.

I'm hoping I can learn how to use it in less than a year lol, but coupled with the SDR stick I think I'm in for some fun.

Cheers

Steve

ataradov:
Well, actually Si446x is a subset of Atmel AT86RF215. IEEE 802.15.4g specifies a lot of modes, so it appears that things are infinitely configurable, but they are not.

And Si446x does not support QPSK modes, so if your RF212-based device is using them, then it will be completely useless.

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