Venus 634 NMEA output time sync'd to second?

GPS/GNSS Development Boards
1

one more question you may be able to help me with. Currently the venus http://www.sparkfun.com/products/9133

outputs NMEA data with timestamps like this:

$GPGGA,193012.133,5023.2654,N,00354.4738,W,1,06,3.9,192.0,M,53.2,M,0000*4E

$GPRMC,193012.133,A,5023.2654,N,00354.4738,W,0002.2,178.2,080411,A*4E

$GPGGA,193012.233,5023.2653,N,00354.4742,W,1,06,3.9,209.0,M,53.2,M,0000*46

$GPRMC,193012.233,A,5023.2653,N,00354.4742,W,0002.0,172.9,080411,A*44

$GPGGA,193012.333,5023.2653,N,00354.4744,W,1,06,3.9,222.7,M,53.2,M,0000*4F

…

$GPGGA,193827.695,5024.1629,N,00351.5961,W,2,09,1.8,153.2,M,53.2,M,0000*43

$GPRMC,193827.695,A,5024.1629,N,00351.5961,W,0055.2,239.3,080411,D*43

$GPGGA,193827.795,5024.1621,N,00351.5981,W,2,09,1.8,153.2,M,53.2,M,0000*44

$GPRMC,193827.795,A,5024.1621,N,00351.5981,W,0054.6,239.2,080411,D*40

$GPGGA,193827.895,5024.1614,N,00351.6002,W,2,09,1.8,153.1,M,53.2,M,0000*4F

as you can see the time stamp milliseconds move from .x33 to .x95

is it possible to sync the nmea output data to the millisecond so it

would look like this example:

$GPGGA,193827.600,5024.1629,N,00351.5961,W,2,09,1.8,153.2,M,53.2,M,0000*43

$GPRMC,193827.600,A,5024.1629,N,00351.5961,W,0055.2,239.3,080411,D*43

$GPGGA,193827.700,5024.1621,N,00351.5981,W,2,09,1.8,153.2,M,53.2,M,0000*44

$GPRMC,193827.700,A,5024.1621,N,00351.5981,W,0054.6,239.2,080411,D*40

$GPGGA,193827.800,5024.1614,N,00351.6002,W,2,09,1.8,153.1,M,53.2,M,0000*4F

$GPRMC,193827.800,A,5024.1614,N,00351.6002,W,0054.8,239.2,080411,D*46

$GPGGA,193827.900,5024.1606,N,00351.6023,W,2,09,1.8,153.1,M,53.2,M,0000*4E

$GPRMC,193827.900,A,5024.1606,N,00351.6023,W,0055.3,239.1,080411,D*4E

so all data would export on the 1/10th of a second exactly?

Thanks again

2

Now it MAY be possible to get the unit to send out at even units of tenths, but that will not mean a whole lot. Will the time stamp be when the fix was calculate, when the first bit of the message was sent, or when the last bit was sent?

Many of the GPS units I have used have a 1PPS, 10PPS, or faster output. The edge of this logic output is for the time that GPS is abount to report with its next message. This solves the issue of what the time refers to.

3

Cheers, so although looking at it, the time only slips by 5 100th/s of a second in total in the example. Each position and time stamp are exact(ish) at the time of output.

Thanks

4

Hi i mailed skytraq and they came back with:

Please use 0x3E 1PPS mode command :

A0 A1 00 03 3E 01 01 3E 0D 0A

This will sync to UTC second when 3D fix

how do i set this option as it does not seem to be listed as a command on the skytraq gui?

Thanks

5

One must write your own application to send over this byte sequence, or call back the manufacturer to see if there is a way to send arbitrary messages with their tool.

6

I think you can just send this byte structure over to the Skytrak. If you are communicating to the unit with a micro using code you have written, just send the bytes. For windows I have used a program called [realterm which allows you to send a hexidecimal format byte string.](http://realterm.sourceforge.net/)

7

Thanks, i have emailed skytraq back with the question, and i have looked at realterm but has to many buttons for me to understand.

8

Reply from skytraq:

Seems we have changed name, use “Configure GPS Measurement Mode” from the skytraq gui.

i have set GPS Measurement Mode to sync to UTC when 3d and now all nmea stamps are 1/10th seconds exact

Thanks