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I have this HAT i bought for a pi project I am working on. I get the device to power on, I can connect via USB from PC, and can connect from pi too.

However, the NET LED just blinks every second, meaning it cannot connect to cellular network.

I have confirmed that the SIMs can connect to the network by putting them in iphone and ipad.

What do I need to do to debug this connectivity issue? Is there a specific plan the SIM needs to have? I am lost.

Barry Chapman
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1 Answers1

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I have this same HAT and I've just gotten it working. Here's an overview that may help.

  • Ensure both jumpers are set to setting 'A' for USB operation
  • Test connection to the device by connecting a serial console and trying a command like ATI (most devices will tell you something about themselves)

If you're using Linux and have screen installed on the Pi, you can probably execute screen /dev/ttyUSB0 115200 to open a serial console with this device. (It could be ttyUSB1 or some other number). If you're connected properly the "TX" LED on the device should flash green whenever you press a key on the keyboard.

Once connected to the modem you can do some debugging:

  • ATI Should return general info about the device (not required, just good to know things might work)
  • AT+COPS? Gets information about current operator. Some example responses:
    • +COPS: 0 No carrier/operator
    • +COPS: 0,0,"T-Mobile",7 Registered on T-Mobile
    • +CME ERROR: 10 No SIM
  • AT+COPS=? Scans for networks. Notice the =. This usually takes a few seconds and spits out a list of operators
  • AT+CGREG? Check registration status (You probably want +CGREG: 0,1 -- see details here)

If the modem shows possible networks, you may need to configure and/or start the data connection

  • AT+CGDCONT=1,"IP","<your apn here>" Sets up the PDP context
    • For example,AT+CGDCONT=1,"IP","fast.tmobile.net" might be used for T-Mobile US
  • ATD*99***1# Establishes a PPP session (using PDP context 1 from above)
    • If this command is successful and you're using screen, your session with either appear to freeze and/or show garbage. (Exit with CTRL+A, k, y)

Another quick check is to try dialing a number. To dial a (US) number like +1(888)000-0000 you'd enter ATD+18880000000;.

isaacparrot
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