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

scott at opentrac.org scott at opentrac.org
Tue Aug 3 12:27:25 EDT 2004

The OpenTracker has about 8k of Flash, and 192 bytes of RAM.  My next design
has 32k of flash and 512 bytes of RAM, and the big one will have 60k of
flash, 4k of RAM, 32k of slower nonvolatile FRAM, and support for at least
32M of external flash in the form of a SD/MMC card.

Is the raw weather station protocol documented, or just what comes out of
the add-on data logger?

If you want to run a digi, a KPC-3+ should work.  If it doesn't support your
weather station, I guess you're back to either making a data translator or
setting it up to share the radio with the OpenTracker or something.

Really, if you've got a cabin there, I'd suggest using a low-power PC like
the ones Soekris Engineering sells... you could probably get it to run
everything you need under Linux.  When I tried, 10 watts of solar power was
ALMOST enough to keep it going.


-----Original Message-----
From: aprssig-bounces at lists.tapr.org
[mailto:aprssig-bounces at lists.tapr.org]On Behalf Of J. Gary Bender, WS5N
Sent: Tuesday, August 03, 2004 7:01 AM
To: TAPR APRS Mailing List
Subject: RE: [aprssig] Should I develop an embedded I/F to Davis WX?

On that first reply, Scott, I had connected you with being Mr. OpenTracker!
is a pleasure to meet you.

How much ROM/RAM are available on the OpenTracker?  Davis has the protocol,
using their Data Logger module, pretty well documented on their support
Looks like it has not changed much for the Vantage Pro.  Most of the docs
Vantage Pro filenames, but don't mention it internally, just older models.

On being able to receive ...
Maybe I am showing my inexperience with APRS.  It just seems like the right
thing to do.  I am getting a handle on my coverage environment and I should
eventually be at least a RELAY, I would think.  The digi I can hear is 42
away (DVPORT), and I am just lucky that I am going between several peaks and
mesas to see it LOS.  (The "direct profile" of DeLorme's TopoUSA is a cool
tool!)  I have a great location ... 200' AAT to the north and 1000' AAT to
south, so I can probably fill coverage in that part of the state.

I was also thinking that I might want to ask it for more information and
control functions that could be sent to the unit.  Maybe I should get my
wet with a working APRS/WX before getting too fancy.  In practical terms, it
would be adequate if I could make it smart enough to send a message to my
QTH for certain alarm conditions ... smoke detector, cabin door open, kind

My little brag: I picked this location for my future retirement for a
High, remote, rare county/grid, few neighbors (1000' to the closest),
quiet power lines (I hope BPL never happens).  About N34 37.6, W108 31.0
Gary, WS5N

On Sun, 01 Aug 2004 22:01:42 -0700, scott at opentrac.org wrote:
>> I have not dug deep into the Davis protocol yet, Scott, but it looks
>> like
> the
>> 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
> OpenTracker
>> 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
> code.
> Scott
> N1VG

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