Connecting up my GM862 — the first step towards my DIY vehicle tracker

At last, all the parts have arrived (or so I thought) for connecting up my GM862 via a breakout board, and so I plugged the module in to the board, and found that the antennae had a different type of connector from those on the module, so I couldn’t do any actual GSM/GPRS or GPS operations with it yet; yet another thing to order by post. Anyway, they’re not needed to try out communication with the module by serial port, so I connected it to my main home machine and powered it up.

It didn’t work with the suggested settings; I had to use “flow control off” instead of “hardware flow control”. This will probably matter later, so I’ll need to investigate.

To my relief, when I sent it an empty “AT” command, it replied “OK”, and I started to try commands from the documentation. Some bits of the documentation weren’t quite clear, but on the whole it was easy enough. There’s a lot of stuff in there that I don’t know about — stuff from deep within the internals of the GSM world, in particular. Also, I have over 770 pages of documentation, mostly as PDF although I’ve printed some of it out.

The next stages will be to get the right antennae connectors, and to try uploading Python programs into it.

I will probably get new antennae too, rather than adaptors for the present ones, and set up an eBay account (I’m moving into this millenium at last!) at last to sell off the ones I first bought, as they have very long wires and I want the antennae in the completed project to be in the same enclosure as the module itself. This is because if they were outside the enclosure, the tracker could be defeated by cutting the wires so it couldn’t text me to say that something was going on. I’ll put a tamper switch in the casing, so that if opened it will immediately send me a message, hopefully before the attacker works out what needs to be cut.

When you issue the command to start uploading a Python script, the module changes the baud rate to the fastest one, and switches on hardware flow control. I’ll try to find, or probably throw together, a program to handle this at the computer end. OTOH I used gtkterm to interact with the module; as the source for that is open, I may just extend it to handle this.

A note about a design decision: I got the RS232 breakout board rather than the USB one because I expect to add an Arduino-based project to the vehicle (or possibly one based on an ARM board) and I wanted to be sure I could easily enough talk to it from that.


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