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

J. Gary Bender, WS5N WS5N at mindspring.com
Tue Aug 3 13:02:03 EDT 2004

I just ordered a WeatherLink 5.4.  I don't feel like dealing with the serial 
interface hardware problems for now.  This version is supposed to have APRS 
output, so I might be home free (probably with a PC, though).

8K of program space should be plenty, but the 192 bytes of RAM might be a bit 
too tight in your current OpenTracker.  Your next increment, with 512 bytes, 
should be plenty.  Is there a UART available for receive?  Or enough horsepower 
for a bit-banger?

Looks like my embedded device will be more appropriate to replace a KPC3+ in the 
i/o chain.  Allowing me to use an old TNC from the junkbox.  A Davis-to-APRS 
data translator module would be pretty easy as an interim step.  It could make a 
VantagePro+DataLogger look more like a PeetBros, providing an APRS output 
without a PC.

All I have found is the protocol to talk to the Data Logger.  I have not yet 
tried to get more info from Davis directly with email.  I am facing a conflict 
between wanting to get something running quickly, and wanting to create a fun 
little gizmo.

I'll have a 30 watt solar panel on this baby, so a little PC might be an option. 
 I'd be more inclined to use an old Palm, however.
J. Gary Bender
Tijeras, New Mexico USA

On Tue, 03 Aug 2004 09:27:25 -0700, scott at opentrac.org wrote:
> 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.
> Scott
> N1VG
> -----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! It 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 site.
> Looks like it has not changed much for the Vantage Pro.  Most of the
> docs are
> 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 miles
> 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 the
> 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
> some
> control functions that could be sent to the unit.  Maybe I should get my
> feet
> 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 home
> QTH for certain alarm conditions ... smoke detector, cabin door open,
> kind of thing.
> My little brag: I picked this location for my future retirement for a
> reason.
> High, remote, rare county/grid, few neighbors (1000' to the closest),
> totally
> 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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