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.

  • You can connect to the HAT by USB? Does the HAT has an usb port? What RasPi model do you use? The HAT is attached to the 40 pin connector of the RasPi so you can connect from the pi too?
    – Ingo
    Nov 1, 2018 at 20:12
  • Have you disabled the PIN-code on your sim-card?
    – Denys
    Mar 5 at 23:20

1 Answer 1


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;.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.