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

J. Gary Bender, WS5N WS5N at mindspring.com
Mon Aug 2 00:31:07 EDT 2004

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 
poll/response behavior is built-in to the weather monitor console and how much 
comes along with the Data Logger device.  I might have to buy the WeatherLink 
software in order to get the Data Logger.

If I have to spend another $150 to get the Davis to talk to me on a serial link, 
it will put a damper on my enthusiasm.  We'll see.  The weather station will be 
here next week.  I'll poke around a little.  I'll ask Davis if they can tell me 
what the Data Logger really does besides the logging function, which I would not 
be using anyway.

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.
Gary, WS5N
Tijeras, New Mexico USA

On Sun, 01 Aug 2004 11:37:31 -0700, scott at opentrac.org wrote:
> How complicated is the Davis protocol?  Does it require true RS-232
> signal levels?
> You might consider starting with the OpenTracker hardware if you're
> comfortable programming in C or assembly for the HC08.  It already
> supports the Dallas 1-wire weather station (beta code should be
> available this weekend) and having Davis support would probably be nice
> since that's one WXTrak doesn't support yet.
> The OpenTracker will report battery voltage through its on-board voltage
> divider - at the moment it doesn't do that in weather mode, but it'd be
> easy to set up.  It's also got an on-board temperature sensor, but that
> could be excluded and used as another general-purpose I/O line.
> I'll be working today on a demo of the power control function to turn on
> and off the radio during WX mode operation for use in a low-power solar
> setup. My goal is to have the whole thing run off a 5-watt panel with a
> 5-minute transmit interval.  While idle, it draws about 5 ma right now -
> I should be able to reduce that, but I'm having trouble with the MCU's
> STOP mode.
> Anyway, the hardware's pretty cheap ($29/kit), the existing code is open
> source (BSD license), and it'd let you avoid using a TNC entirely since
> it's already got the hardware and code to do AFSK and BPSK.  Its RS-232
> output is 0-5 volts, though, so it may require some extra hardware if
> the weather station demands a true bipolar signal.  Once I get the
> surface mount kit in production, that'll be a more convenient way to
> integrate it with custom hardware.
> Check out the project website at http://n1vg.net/opentracker
> Scott
> N1VG

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