RTK Postcard - Interface GNSS data to microcontroller

GPS/GNSS
1

I wish to monitor the GNSS messages from a RTK Postcard with Portability shield in real-time so I can react to velocity changes. Are these messages available on the USB output or can the USC port be used for this function?

Also, Is there any access via SPI or I2C to this data?

Jeff.

2

Hi Jeff (@JeffNickel ),

Welcome!

With Postcard running our RTK Everywhere Firmware, you have multiple options:

  • LG290P UART1 is connected to the CH342 USB interface chip on its channel B. Install the CH342 drivers, connect USB, select the CH342 B COM port, open a terminal at 460800 baud to see the messages
  • LG290P UART3 is connected to the 4-pin JST connector. You can connect an external 3.3V “FTDI” USB-UART cable or converter to access the messages. Again, at a default of 460800 baud
  • CH342 channel A is connected to the ESP32, and the ESP32 is connected to LG290P UART2. You can configure the RTK Everywhere Firmware to passthrough the UART data from the LG290P to the CH342 channel A

The LG290P is connected to the Qwiic bus, but its firmware does not currently support I2C. Quectel may add support in a future update. SPI is not supported.

I hope this helps,
Paul

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3

Hi Paul,
​​

Your response is extremely useful as my Postcard and Portability Shield arrived today.

Do I have to do any configuration to pass the GPS messages to the LG290P Uart3 JST connector? Also, can I configure what data is included in this message or is that standardized?

Thanks,

4

Do you have any references to the header pins, male/female, I’d need to attch the Portability Shield to the Passport?

Thanks,

Jeff

5

Hi Jeff (@JeffNickel ),

UART3 (JST connector) will output the standard set of NMEA messages: at 10Hz, at 460800 baud. It’s a lot of data… You can lower the rate to 1Hz and enable / disable individual messages. The Postcard Resources docs page has a lot of helpful links. The Protocol Specification is the key document to get to know. If you search this forum for $PQTM, you’ll find a lot of helpful posts. There is a little AI-generated garbage in that list, but not much. You can trust any post by Marco @bamarcant .

You can find links to the headers in the required-materials. I’ll include them below too. This page has a close-up photo of the assembly.

Welcome to the party!
Paul

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