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