On Tuesday, May 6, 2014 9:16:17 AM UTC+12, Bastoune wrote:
Hi all,



I have a GPS puck that acquires/computes a GPS fix every second (1Hz). This GPS then transmits this data to a Vario (V7) and then PDA.



The default baud rate of the GPS is 4800 baud but I have the ability to increase it to 9600 or 19200 bauds. Is there a benefit of a higher transmission baud rate for the GPS? Does a 4800 baud rate allow the full transmission of a GPS NMEA 0183 sentence every second? I am not sure how much data is contained in a NMEA 0183 sentence, and if it can "all go through" every seconds at 4800 bauds. (Note: The vario and PNA can receive a 19200 bauds). What are the drawbacks of a baud rate set too high? Transmission errors?



Given the GPS limitation (1Hz fix) I understand that, best case, my vario (V7) and PDA cannot get a fix more frequent than one per second. I want to set the baud rate high enough where the GPS 1Hz fix is the limiting factor, not the speed of communication between the GPS and the Vario/PDA.

Thanks all for your inputs.

B.

You've got it right.

GPSs always started with 4800 BPS because there's too much data for 2400. If you run it at 19200 then you'll be sure to get the up to date data with less than 1/4 of a second delay.

The chances of error at 19200 are higher, but still minuscule with a short, well shielded, cable in an electrically quiet environment. You could probably run at 1 Mbps like ancient 3rd party AppleTalk stuff did on RS422 (if your gear supported it) and seldom see errors. And anyway, the NMEA sentences have a checksum which will pick up most errors.

Just run it at the higher speed :-)