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Salus RT500RF + Arduino + RFM12B

This is 90% a testbed and 10% an intermediate solution for me, the intention is to be able to turn on and off a Salus RT500RF boiler controller using an 868Mhz RFM12B from HopeRF. The RFM12B is essentially discontinued but is still an extremely useful piece of hardware. The replacement the RFM69CW should be easy enough to replace the RFM12B with in the hardware. Using a little of Jeelib's compatibility library.

Salus RT500RF on Ebay

I based this project on top of this one

http://the.cyclingengineer.co.uk/2013/11/23/home-automation-integrating-salus-rt500-rf-in-openhab-using-a-jeelink/

I reduced the decode complexity using GQRX and improved a few minor details along the way. Removing pretty much all jeenode code as I'm not really interested in using Jeelib and Jeenode as those things seem to be hard to get ahold of now.

The wiring method is as described here:

wiring diagram

If you're using a 3.3V board like a mini-pro then remove the resistors and connect directly to the arduino.

I'd suggest that a RTL-SDR dongle is a required piece of hardware to decode your Salus RT500RF's signal with.

Every RFM12B will have slightly different transmission characteristics or even firmware variations which can be accounted for by shifting the frequency center and the frequency shift.

With GQRX

  • Mode WFM (oirt)
  • Squelch/Attenuate the signal appropriately so you can see the transmission clearly
  • Record the audio of the signal
  • Find the pair of transmission peaks in the waterfall around 868.2 Mhz
  • Find the frequency in the center, and the gap in khz between the transmission peaks
  • Open the Wav file in Audacity and zoom to one of the repeated signals Ignore the noise this is usually reflection around your home, look for the distinct up/down usually early in the signal.
  • Decode the signal by aligning the frequency shifts to a grid and reading the bytes
  • Signal is in the form of 0xAA 0xAA 0xAA 0x2D 0xD4 0x?? 0x?? 0x?? 0x5A Where the ?? bytes are the code to YOUR boiler, on and off use transmit different codes
  • Edit the bytes below to your appropriate settings.

You should expect to be able to get a signal that looks something like this:

signal pattern

Sample data

On
A    A    A    A    A    A    2    D    D    4    0    0    0    1    0    1    5    A
1010 1010 1010 1010 1010 1010 0010 1101 1101 0100 0000 0000 0000 0001 0000 0001 0101 1010
Off
A    A    A    A    A    A    2    D    D    4    0    0    0    2    0    2    5    A
1010 1010 1010 1010 1010 1010 0010 1101 1101 0100 0000 0000 0000 0010 0000 0010 0101 1010