TCP connection over GPRS with SM5100B module

After having no success sending GET requests to HTTP servers I finally decided to set up my own tcp server by directing a port on my router to my PC and setting up a simple tcpserver listener in cygwin like this:

~ > tcpserver -t1000 -v -Bare_we_receiving 0 9876 bash -c "sleep 1000"
tcpserver: status: 0/40

Then I sent the following commands to the modem


For some reason the MY_ROUTER_ADDRESS had to be the text host name instead of the IP address, which was something like for me as per my router.

Immediately I saw a connection appear in the tcpserver log:

tcpserver: status: 1/40
tcpserver: pid 5232 from
tcpserver: ok 5232 :::ffff: :::ffff:
tcpserver: end 5232 status 256
tcpserver: status: 0/40

And then some data was received on the GPRS modem side:

> +STCPD:1

Which I read back promptly:

> +SOCKSTATUS: 1,1,0102,54,0,16
> OK
> +SSTR:1,are_we_receiving
> OK

And it exactly matched the banner text. So atleast I can establish TCP connections. The AT command interface though is a real pain.


Basic testing the SM5100B

SM5100B GSM GPRS modem setup

The parts for the first phase have arrived and basic functionality of the GSM modem was tested and found to be operational. Here is a log of the modem receiving a phone call:

+SIND: 1
+SIND: 10,"SM",1,"FD",1,"LD",1,"MC",1,"RC",1,"ME",1
+SIND: 11
+SIND: 3
+SIND: 4

Here is a list of what I’m using:

  1. From SparkFun
    1. SM5100B Evaluation Board
    2. GSM/GPRS Module – SM5100B
    3. Quad-band Cellular Antenna SMA
  2. From EvilMadScience
    1. 5V, 3A Regulated Power Supply
  3. From BG Micro
    1. 2.5mm Jack To 2.1mm Plug

I also tested receiving SMS text messages but it seems that, they aren’t pushed over the UART. Instead I had to poll to check if I had received any new SMS messages.

+CMGL: 1,0,"REC READ","1511","12/09/09,00:29:11+00"
Welcome to T-Mobile! Dial #BAL# to check your balances. Your T-Mobile number is 1***412****
+CMGL: 2,0,"REC READ","+1***721****","12/09/09,01:14:02+00"
Hello, world
+CMGL: 3,0,"REC READ","+1***721****","12/09/09,01:16:33+00"
Hello, world 2

I am currently using this with a T-Mobile pay-by-the-day plan which gives me unlimited voice, text, and 2G data for $2 per day.

Next I am going to spend some time thinking about how I want to proceed.