I was asked this question a lot of times. Didn’t have a clear answer because in my early attempts to make them talk to each other I didn’t have success. I didn’t spend a lot of time on that since my interest has leaned towards RFM69 transceivers since they are much nicer and feature-rich overall (nicer packet engine, hardware AES encryption, digital RSSI etc).
Forum user timw has forked my RFM12B and RFM69 libraries and modded them to make them compatible, see this forum post for details. Turns out these mods makes communication possible between RFM12B and RFM69 transceivers. This is great news!
I was able to load his version of the libraries in my Arduino/libraries folder (I had to move/remove my original libraries because of conflicts), and using the examples that come with the two libraries (Struct_receive example on the RFM69 side, and Struct_send on the RFM12B side) I was able to see data coming through the RFM69 end. Seems very stable too. The signal strength (RSSI) fluctuates a little more than if I had RFM69 radios on both ends but it’s great to actually see a signal strength for a RFM12B transmitter:
The caveat is that the encryption must be turned off on both ends with the current version of the libraries. That’s because RFM69 uses hardware AES encryption and RFM12B does not support hadware encryption but uses a software XXTEA algorithm instead. The two are not compatible. One workaround would be to port/duplicate the XXTEA encryption on the RFM69 side, probably a little slower but worth it if encryption is important.
So anyway this should help folks that are trying to salvage their RFM12B nodes and make use of them while moving towards RFM69 based nodes. For me personally I will likely just upgrade everything to RFM69 moving forward but still this is a great development. Thanks timw for sharing your work!