Writing NMEA messages to L76 GPS chip

  • Hi All

    Could anyone provide assistance on writing NMEA messages to the L76 chip aboard my Pytrack 2.0 using L76GNSS.write()? The Pycom documentation for this command is very sparse and I am struggling to interpret the GPS datasheet containing the MTK NMEA commands from Quectel.

    Specifically, I'm trying to issue a command to cold restart the chip so that it gets a GPS fix with no prior almanac or ephemeris data. Then I'd like to ask it to warm restart so I can see the time difference between the TTFF's. From what I've tried so far, it's not clear whether the chip is obeying the commands, or if the TTFF variations I'm seeing are just natural variation.

    For example, the following command should cause a cold restart.
    Screenshot 2020-08-13 at 13.29.36.png

    However, I know from the documentation that no acknowledgment of this message should be sent by the chip, so I've tried other commands such as to ask for the version number of the chip, but I still get no response. Perhaps there is a command to configure the chip to give responses?

    Could anyone lend a hand?

  • Hi @jcaron

    Ok, thanks very much! I've tried that new format but I'm not sure what to expect from the chip by means of response. The specific command PMTK103 shouldn't warrant an acknowledgment, so I'm sending PMTK605 which is a command to query the firmware release info and see if I get a response to confirm this whole thing is working.

    L76GNSS.dump_nmea() isn't showing the response message I'd expect (PMTK705) after writing PMTK605 to the L76 chip. Is there a better way to see responses from the L76? Or do I first have to configure it to send acknowledgments?


  • @WilkinsSq A quick glance at the source of the L76GNSS module tells me the write method will automatically add the $, the *, the checksum, and the CR+LF.

    So l76.write("PMTK103") should be enough. Can you confirm?

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