Using AEK-COM-GNSST31 board with the Teseo Liv3f GPS on. I have successfully accessed the data from the gps but I want to recieve only $GPGGA, $GPGLL and $GPRMC messages. How do I do this ?

[G. Michael]

Hello,

I tried using the $PSTMNMEAREQUEST command setting only the bits for the 3 messages but I am still getting the periodic messages.

Thanks in Advance!

[Tesla DeLorean]

Is the device responsive to any queries or commands sent to it? Check wiring, UART settings, and if the sentences sent are checksummed and have CR,LF line termination.​

[G. Michael]

Yes, the device is definitely responsive because it prints my requests and other data as seen in the photos below. Wiring, UART and checksumm are I suppose and CR,LF also present.

• For checksumm I am using an online NMEA checksumm calculator.
• Commands in my code are like this - for the GPGLL msg "$PSTMNMEAREQUEST,0x100000,0x0*7D\r\n"

Here is the output of my code

As you can see it is responsive and the GPGLL is printed upon request, but every period it gives a lot of other data like in the next photo.

 

Is there a way/command to stop any other message except the requested ones ?

Thanks !

[Tesla DeLorean]

>>but every period it gives a lot of other data like in the next photo.

Your buffering of the USART data appears borked.

Shouldn't be missing characters and lines randomly.

Perhaps implement an IRQ based buffering scheme, rather than polled, and have a deep enough buffer.

Copy the data out of the live buffer (changing under IRQ) if you're storing a line at a time.

[G. Michael]

Thank you for your help,

I adjusted the buffer and the messages are not being Cut randomly.

I solved the issue with the specific messages using the $PSTMCFGMSGL instead of $PSTMNMEAREQUEST.

I have a question though. I want to extract the vertical distance made by the GPS (at time 0 distance is 0 and then for example moving upwards 1m) but, the altitude I extract from the GPGGA message is measured from mean sea level and it is varying on a wide range when the gps is on for a while.

Is there a way to have that altitude ?

Thanks !

[Tesla DeLorean]

HAE would be the sum of the alt/msl values. Might reasonably expect a 4-5m variation in that for a CEP 3.0m device, in optimal conditions.

I'd expect the MSL to come from a relatively course EGM96 grid table. Your ST FAE might be able to provide exact specifics.

The quality of the fix is going to be driven by placement of the antenna, the effectiveness of it's implementation and the cost of the solution. Data sheet numbers likely being developed over a 24 hour static test with a well placed $2K antenna.