Use AT commands over UART on mDot

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  • March 29, 2019 at 11:01 pm #27574
    David Sun
    Participant

    Hi, so I’m trying to use the mDot as a LoRA module for another microcontroller through the use of AT commands.

    I’ve hooked up my UART pins to pins 2 and 3 of the mDot for communication and try sending “AT” among other failed attempts, and I get no response from the mDot.

    I can tell that the mDot is on, as I am measuring a current draw through a multimeter, so I’m lost at what the issue might be.

    It is possible to use the mDot like a separate module and send packets over LoRA using just the AT commands sent over the UART pins on the default firmware, right?

    I don’t have a development board, so I can’t simply plug the mDot to USB.

    April 1, 2019 at 8:06 am #27577
    Leon Lindenfelser
    Moderator

    Hi David,

    Are you sending commands at 115200bps? Did you connect ground?

    Leon

    April 1, 2019 at 1:29 pm #27579
    David Sun
    Participant

    Hi Leon,

    Yes, my baud is 115k and I connected ground. I can verify that it is not an issue with UART on my main microcontroller, as I can communicate with a different microcontroller just fine over UART using the same baud.

    So I recently looked under an oscilloscope on the Tx pin of the Mdot and there wasn’t anything coming out, despite it being powered on and receiving a UART signal from my main one.

    Maybe I have to reflash the firmware?

    April 1, 2019 at 2:17 pm #27580
    Leon Lindenfelser
    Moderator

    Hi David,

    If the AT application is not loaded, that could be the issue.

    The reset line has a weak pull up on it. So that should be fine.

    Leon

    April 1, 2019 at 5:10 pm #27582
    David Sun
    Participant

    Hi Leon,

    So I reset it and checked under an oscilloscope again.

    It seems that I am getting a response, but it is a very low voltage: not high enough for my main microcontroller to identify as a UART signal.

    Any ideas on why that might be? I am just sending “AT” to see “OK” from the Mdot. See picture attached.

    oscilloscope output from Mdot

    April 2, 2019 at 1:20 pm #27590
    Leon Lindenfelser
    Moderator

    Hi David,

    Please measure the voltage you are providing to the mdot. VDD is pin 1. The voltage needs to be in the range of 3.3v-5v.

    What voltage is your host board expecting? Is it a direct connection to the UART… no transceiver or level shifters?

    Kind regards,
    Leon

    April 2, 2019 at 1:34 pm #27591
    David Sun
    Participant

    Hi Leon,

    VDD is 5V, which I confirmed to be the case on the scope.

    It is indeed a direct connection to UART.

    Also, I used another mDot in the meantime with the same microcontroller and connections, which sent back the “OK” correctly.

    So I’m convinced this is definitely an issue with this particular mDot.

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