We are very charmed by the HopeRF RFM95 module, since it has a relative small form-factor and a high output power compared to -for instance- the RN2483.
However, since it has a minimum of firmware on board, the drawback is that you have to provivide the LoraWAN stack yourself. And in doing this, you have little choice of available software libraries and usualy end up with the LMIC library. And however this library is very neat, it is quite complex and hugely overfeatured for dumb sensor applications.
So, I set it upon myself to derive a more simple stack out of it, so simple in fact, that you should be able to run it off an ATtiny85, the smallest processor we work with.
It took the usual blood, sweat and tears, but I got it working. The compiled software for a basic dumb sensor application (sending data every X timeperiod) is only 3.242 bytes (53%), and 381 bytes out of 512 RAM is used (I had to put some tables for encryption in flash memory). So that leaves plenty of room for some more application software.
It is single frequency and fixed SF, it does not do downstream messages or OTAA, but it suits our purpose!
It took my whole weekend to debug because of a nasty porting-issue and the very limited debugging features of the Attiny, so I’m putting it aside for now If I have some time I will clean up the software and post it on Github. In the mean time if you are interested, send me a message!