Sunday, December 28, 2014

Amateur Radio information on modern social networking.

I'm slowly starting to get some of the appeal of Reddit.    At first I was drawn there by /r/rtlsdr, as there didn't seem to be much info elsewhere.   There is a bit of a digital divide, for on-line sources many hams go to with it's 1990's design and god awful ads flashing all over the page.  Try as you might, some of the old guys can't remember to try anything but The other big source of info is Yahoo groups which are starting to show their age, but have been made much less useful due to Yahoo trying to figure out how to get more page views.

So two useful places to get answers to amateur radio related info:
  1. Reddit: /r/amateurradio  []
  2. StackExchange: []

Wednesday, December 17, 2014

Decoding 433.92 Mhz devices with RTL_433.

I've been doing a bit of playing with merbanan's rtl_433, which uses the rtl_sdr code to decode signals from 433 Mhz ISM devices that mostly use On-Off-Keying.

So far I've been working on decoding
  • Lacrosse TX-7 temperature and humidity sensors, same protocol as TX-3, TX-6.
  • DSC wireless security contacts (door/windows, smoke and carbon monoxide detectors)
There is a lot I've learned from playing with the devices using rtl_433 and digging into the code.  I need to write it up because there are almost no instructions.

I've posted the LaCrosse code to github and submitted a pull request to merbanan/rtl_433.

I'm successfully decoding the DSC contacts using a separate Python script that parses the debug output from rtl_433.  I need to write a new pulse decoder for rtl_433 in order to handle the DSC protocol as it's a little different than other pulse or distance coded signals. It doesn't send anything for a zero (0) bit, so there can be long periods (up to 8 bit slots) of no signal.

For more info, contact me if I haven't posted here or to github.

Update: 2015-01-11, merbanan processed a whole bunch of pull requests, including mine, so the LaCrosse TX-7 support is now in the main merbanan/rtl_433 github repository.

I haven't pushed any code for the DSC sensors yet. I have to decide how I want to do the decoder and call back yet.  Anything I push will probably be only be in rct/rtl_433 for a while as it is likely to be experimental.

Good tutorial on Serial from Saleae (working with microcontrollers)

Here's a good tutorial on serial communications, particularly if you are working with microcontrollers.
  • Learn Asynchronous Serial -
I want a Saleae Logic 8 for Christmas.  They look pretty neat.