The SM5100B was chosen for debugging our UART/serial code with AT commands. There are various evaluation boards available for the SM5100B, and we purchased both the module and eval board from Sparkfun. We also purchased an antenna from Sparkfun to be attached to the board.


SM5100B module with evaluation board from Sparkfun. Also shown: AT&T activated SIM card and Sparkfun duck antenna.

SM5100B GSM Module:

SM5100B Evaluation Board:


Duck antenna purchased from Sparkfun.


Quad-band Cellular Duck Antenna:

One thing to note about this module and the evaluation board is that the documentation available for it is lacking. The schematic is incomplete and the datasheet doesn’t have any application notes. Luckily we found some hints and tips via the comments section on the Sparkfun product pages and were able to get it up and running.

To all sparkfun users, we would like to offer our experience. We were using a AT&T “go-phone” (pay as you go) sim card purchased in Arizona, USA. We too had a lot of trouble learning how to interface with the device. This is what worked for us:

  • Use minicom terminal in Linux, Putty in Windows
    • setup your desired serial port for 9600 baud, 8N1 (eight data bits, no parity, one stop bit)
    • be sure to turn off software flow control
    • If in linux be sure that you are a member of the dialout group and have access rights to the device ie “dev/ttyXXX”
  • As a previous sparkfun user suggested, plugin the device while powered off and open serial port, and then flip power on
  • You will see 5 bytes of garbage
  • Next you will see +SIND messages
  • +SIND messages indicate the status of your connection
  • If you are using AT&T in the US the issue the command “AT+SBAND=7”, this sets the operating frequency of your chip to the proper settings for AT&T service
  • You will need to first insert your sim in a normal cellphone and make a call in order for the sim to become fully registered on the network. You can check your carrier settings with AT+CGREG?

The back of the eval board.

The current top comment on Sparkfun’s eval board page was extremely helpful to get us started:

1. Start with the power switch off.
2. Plug in the USB cable and make sure windows recognizes it as a com port.
3. Plug in a separate power source to the barrel jack that can handle the 2 amps that might be drawn.
4. Using a terminal program connect to the new COM port using a BAUD rate of 115200… 8 data bits – no parity – 1 stop bit.
5. Turn the power switch on.
At this point I get 5 groups of garbage and then it starts speaking intelligently with SIND messages updating me on it’s progress in connecting to the network.
SIND 11 is the one to watch for that typically says it’s connected and ready to go.”

– Patrick, aka Carnagio


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