[aprssig] Should I develop an embedded I/F to Davis WX?

scott at opentrac.org scott at opentrac.org
Mon Aug 2 00:01:42 CDT 2004

>I have not dug deep into the Davis protocol yet, Scott, but it looks like
>Davis unit responds to polled queries.  I'd just ask it a bunch of
questions to
>fill a weather packet.  I am not clear at the moment how much of the

I haven't messed with them myself, but so far everyone I've heard from using
one for APRS has been using the Data Logger.  If no one's figured out the
native protocol yet, doing so would certainly help reduce the cost of
deploying one of these units.

>I am hoping for this system to have ears.  As I understand it,
>OpenTracker/TinyTrac3 is transmit only.  I'll look and see if the
>module can support receive too.  If so, it might be a way to avoid
designing new
>hardware.  Learning a new assembler is part of the fun.

What do you need it to receive?  Both the OpenTracker and TinyTrak3 use an
energy detect to see if the channel's busy, but that's about it.  The
OpenTracker has its audio input connected to an A/D channel, so in theory
you might be able to do something more with it, but it hasn't really got the
horsepower or RAM to do AFSK decoding.

I do have two receive-capable projects in the works - the first intended as
a dirt-cheap TX/RX capable unit suitable for things like Anti-Tracker style
operation, based on the OpenTracker modulator and an XR2211 demodulator, and
the second as a full-featured USB KISS TNC / digi / datalogger / HUD built
around a CML CMX860 modem.

I just built the demodulator section of the first design, and will be
testing it when I get a chance.  Thanks to OpenTracker code reuse I might
have some prototype hardware working in the next few weeks - hopefully I'll
have something to show off by DCC.  The second design is still further off
and will probably reuse code from this first project.

Let me know what you find out on the Davis protocol.  If I can get some
usable docs, maybe I'll pick a station up on eBay and start writing some


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