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

J. Gary Bender, WS5N WS5N at mindspring.com
Sun Aug 1 13:22:12 EDT 2004

I am looking for advice for putting together an APRS standalone weather station. 
 I have real estate (eventually my retirement home) about 200 miles away.  I 
also have way too much time on my hands.  I am thinking about writing my own 
embedded interface to handle the data translation between my weather station and 
APRS/TNC.  I am competent to do the programming, but I am not sure I won't be 
reinventing the wheel.

  Davis VantagePro 6150
  MFJ 8621 Data Radio
  Tasco Telereader 211 TNC (with Japanese documentation!)
  -or- Pac-Comm Tiny-2 TNC
  12 VA sealed battery
  2.9 amp 21 v solar panel.

I remember using the Telereader years ago and it seemed to work with 
conventional commands, so I can probably get by without having English doc.  It 
is a nice small unit with low power consumption.  I don't think either TNC would 
impact my power budget much (200-250 ma).

What I need is a cheap way to fetch and convert Davis data to APRS weather 
packets.  I probably should add some additional APRS intelligence to the MCU.  I 
will include some telemetry; things like battery condition and the state of a 
few switches/alarms.  I have not monitored traffic yet, but nothing shows up 
near the 87315 zip code on FindU.  However, I can hear something every few 
minutes full-quieting, so I probably have a digi I can hit.

I also have two Zilog Development Kits sitting here begging to be applied to 
something useful.  One for the Z8Encore! And another for the Z8Acclaim!  Either 
chip family has plenty of room for a lot of features.  I am guessing that an 
interface can be put together for much less than $50 in small quantities.  We 
are looking at the Z8... MCU, a voltage regulator, a TTL/RS-232 level converter 
or two, plus a few support components.

Basically I want to plug-and-play the Davis to the MFJ as easily as folks say 
the Peet Bros weather stations do.  It turns out there are lots of Davis units 
on eBay, so it is worth a couple hundred bucks to do it.

My questions:
1) Has this already been done for a low power solar environment?
2) Is there a list of TNC attributes that should be implemented at startup?  
Reading the APRSSIG the last couple months, I see there are some parameters that 
a well behaved APRS controller should initialize.
3) Would there be enough interest in this sort of device for me to generalize 
the code so it can adapt to other weather stations and TNCs without too much 
    Gary, WS5N
    Tijeras, NM  USA

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