I'm currently battling with a LinkSprite GPRS shield (it's based on the SIMCom SIM900 chip) and seem to have absolutely no luck trying to connect to the network. I've got two SIMs, both of which should be active, but I cannot get the connection light on.

I've got a serial connection going and it's responding to various AT commands, but I can't connect:


is working, and giving me a list of networks, so I think my antenna is good, but


immediately gives me +CREG: 3.

I'm now wondering whether there's a fault with my board, and that it's not seeing the SIM cards. A few commands that I thought would work aren't, for example:


just returns ERROR

Similarly, when trying to read SMS data:


returns ERROR.

Have I proved that the board isn't seeing the SIM, or is there something definitive I can try?

Thanks in advance!


Having exchanged the board for another one (that works!) I can now confirm that the calls above (e.g. AT+CMGL) should work if there is a working SIM connection.

  • Are the boards identical? Or are they of different versions/manufacturers?
    – Paul
    Apr 22 '16 at 7:13
  • They were identical. Apr 22 '16 at 11:52

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