RFM12B Linux Kernel Module development

If you’ve read any of my previous posts on the topic I’m trying to get OOK, FSK and potentially PPM (Differential Pulse Position Modulation) working in the Linux kernel with the HopeRF RFM12B adapter. This is mostly for ARM SBC/SoC type situations like the RaspberryPi or beaglebone.RFM12B

The intention here is to allow you to easily intercept, and transmit consumer wireless signals on the 434/868 MHz bands. There are existing ways to do this. However they all appear to depend on the Jeenode or at least an atmega chip running JeeLib.

I want to remove the dependency on the atmega, and yet still exploit the RFM12B to provide OOK/FSK transmission. Right now I’m adapting the existing RFM12B-Linux module to allow sending and receiving OOK signals, I’m also adding in the code to interact with specific defined devices. So far my thoughts are that it shouldn’t be too hard to have drivers for multiple devices in the module.

I thought best to do a link dump of everything that is currently important to this endeavour;

After merging someone else’s OOK sending efforts. I’m not too sure that listening for OOK and FSK is really important. After all an SDR can happily listen across the frequencies and decode the signals.

I unfortunately get very little time to work on this, or other projects on this blog but try to keep it updated with my experiments from time to time. Once I have my Salus under control I plan to release the branch on github. Until then I get a little time here and there to experiment. My latest outcomes have been hampered by insufficient power to my Pi3. There have also been some issues with transmitting on the 868 band.


Kernel hacking for the RFM12B

RFM12BI’ve been busying myself with fixing up and adapting the RFM12B Linux driver. My first thought was simply to give people support for sending and listening for OOK signals as an extension, then taking the device support in the rtl_433 decoder to extend RFM12B driver to include lots of OOK device support for things like weather stations and energy monitors.

JeeLib already does most of this work on Arduino so for the most part this is simply a matter of joining lots and lots of code together from different places and making sure it sits right. I’ve decided that in order to do this it would probably be better to re-write the driver while trying to fix some of the original driver’s TODO list along the way.

The driver will loosely allow :-

  • Compatibility with the original RFM12B driver & original JeeLib compatibility.
  • Send OOK, FSK messages to devices.
  • Listen for OOK, FSK messages from devices.
  • Set tuning to a specific frequency.

Continue reading →

Upgrades… Salus RT500RF 868MHz wireless boiler control

RT500RFI’ve just received a Salus RT500RF in the post. I’m pretty much all prepared to hack this thing, at first I’ll sniff the airwaves with the RTL-SDR and try and get a handle on how it works. There’s been at least one blog article regarding this unit so I’ll also have a dig around them and see what they can tell me too. The idea is to get the Raspberry Pi with the 868MHz RFM12B to send a signal to turn the heating system on/off, and if possible, interrogate the current state of the boiler.

This will be the first stage in smartening up the house. The OWL CM160 and the Salus RT500RF are the first devices that I’m going to mess with as they’re the most useful to me right away. Next I’ll be turning my hand to Oregon Scientific weather sensors, Wireless door bells and other hardware on the 433/868 bands. These bands of course are used in Europe and some other locations, the equivalent is 315/915 for the US. So if you’re following my work then make sure you pick up the right bands for your location. It’s always best to buy radio transmitters and receivers in your own country because the likelihood of anything being on sale which isn’t allowed is reduced.

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