SMS Gateway

During a conversation with the Order of Prayer it became apparent that being able to send and receive texts. I have an arduino with an old GSM Playground from Hardware Kitchen so thought that’d do.

I got the arduino working with the GSM Playground and an ethernet shield, and made a web tool to queue and receive texts via the arduino. Worked fine, but texts were limited to about 100 characters instead of the whole thing, and I couldn’t figure out why.

I saw on AliExpress that there were GSM kits available for a couple of quid. So I ordered one.

The first challenge was soldering SMD components, which I’d not done before. As it happens the only error was soldering up a through-hole and not being able to clear it, but it was a redundant ground connection so it didn’t matter. The spaces on the PCB didn’t match the component count though, so I had to guess at what to miss out. There’s what looks like a LED in the pictures on aliexpress, and the kit didn’t come with a LED so I left it off.

I’d read about problems with it not having enough power, so I used an old PC power supply to check it was working ok, teamed with an FTDI bridge (USB-Serial). I hooked it up and fired up PUTTY and, with a bit of learning around AT commands, got it working!

It needs BOTH the 5v and 3.3v lines powered. I had thought it’d be one or the other but no, it’s both.
I tied the mystery pin (labelled in Chinese on the picture on AliExpress) to ground and it works.

The AT commands are as follows:

TO SEND AN SMS

At+cscs=”GSM”
At+cmgf=1
At+cmgs=”phone number”
Message [terminating in ctrl+z]

TO READ UNDREAD SMS

At+cmgl=”REC UNDREAD”

DELETE READ and SENT SMS

At+cmgd=1,2

The next step is to pair it with an ESP-12.

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