GPS baud rate setting

On Thursday, May 8, 2014 2:42:52 PM UTC-4, Martin Gregorie wrote:
On Thu, 08 May 2014 08:23:01 -0700, Richard wrote:



What is your take on a 4800 baud rate system that also transmits

PowerFlarm and Vario sentences two ways.



I don't have enough information to make any estimate. To do that you need

to know:



- baud rate and character format



- format of the various messages exchanged with the FLARM and vario



- the frequency and order in which the messages are exchanged.



and I don't have any of this stuff.



I am able estimate the spare capacity in a GPS receiver's output stream

because I found the NMEA sentence formats and character format (8N1) on

the 'net [1] and spent some time with a Garmin GPS2+ and a GPS35 hooked

up to the serial port on a PC, watching the data stream and working out

how it changes as the GPS settings are changed, i.e. no active route,

active routes with different numbers of waypoints.



[1] http://aprs.gids.nl/nmea/ gives some NMEA sentence formats: enough

for our purposes and the NMEA 0183 specification gives baud rate and

character encoding. However, this stuff is quite hard to find because it

seems that the standards that define NMEA sentence formats and ordering

are not exactly an open source document. The full spec will set you back

around $2800.



BTW, it seems that 38400 baud is also a standard NMEA transmission rate.

It is used for AIS (Automatic Identification System), an automatic

tracking system used on ships and by vessel traffic services (VTS) for

identifying and locating vessels by electronically exchanging data with

other nearby ships, AIS base stations, and satellites.





--

martin@ | Martin Gregorie

gregorie. | Essex, UK

org |

Typically varios send one sentence a second containing the lift data and some
other stuff. Sentences indicating things that don't change that often (MC,
ballast, bugs, whatever) are sent less frequently, or only when those values
change. FLARM data volume depends on the connection speed. At 19.2K it
sends a pretty large amount of data describing all the targets in view. At
slower speeds you just get the warnings.

Matt

On Thu, 08 May 2014 13:04:39 -0700, mattmckrell wrote:

Typically varios send one sentence a second containing the lift data and
some other stuff.

Some (mainly older ones?) like the SDI C4 don't send anything - they just
receive GPRMB,GPRMC,GPROO,GPWPL - the set needed to calculate wind and
final glide. Presumably 'other stuff' includes IAS.

Sentences indicating things that don't change that
often (MC, ballast, bugs, whatever) are sent less frequently, or only
when those values change.

Makes sense. How big are the sentences? Are their formats generally
available?

FLARM data volume depends on the connection
speed. At 19.2K it sends a pretty large amount of data describing all
the targets in view. At slower speeds you just get the warnings.

I'd heard that, but have seen any documentation of either those messages
or the FLARM additions to their IGC log files. IIRC both message sets are
regarded as proprietary/undocumented.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

On Thursday, May 8, 2014 6:31:58 PM UTC-4, Martin Gregorie wrote:
On Thu, 08 May 2014 13:04:39 -0700, mattmckrell wrote:
FLARM data volume depends on the connection
speed. At 19.2K it sends a pretty large amount of data describing all
the targets in view. At slower speeds you just get the warnings.

I'd heard that, but have seen any documentation of either those messages
or the FLARM additions to their IGC log files. IIRC both message sets are
regarded as proprietary/undocumented.

The FLARM message sets for traffic and collision warnings are very
well documented and used by at least a dozen other manufacturers
and software packages to display FLARM info. See "Data Port Spec":
http://www.flarm.com/support/manual/index.html

See the "Sentence PFLAA" section for explanation that 19200 is
required to receive traffic information.

Hearsay is dangerous (and rampant on RAS)...
Best Regards, Dave "YO electric"

On Thu, 08 May 2014 15:42:42 -0700, Dave Nadler wrote:

The FLARM message sets for traffic and collision warnings are very well
documented and used by at least a dozen other manufacturers and software
packages to display FLARM info. See "Data Port Spec":
http://www.flarm.com/support/manual/index.html

Thanks for the link, Dave. Bookmarked.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |