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
Message [terminating in ctrl+z]
TO READ UNDREAD SMS
DELETE READ and SENT SMS
The next step is to pair it with an ESP-12.