After writing back in April about my ideas of using an off-the-shelf mobile phone module as a ComGSM I’ve not made much progress since. I did order a suitable unit from ebay direct from China, and after a few weeks it arrived.
I eventually got one of these:
I took a few photos myself but the light is a bit odd and it looks exactly the same. Predictably, there are no useful instructions with it at all, so I’ve had to make a few guesses.
It has a standard pin header on the side, which is labelled on the board from left to right as VCC, Tx, Rx and GND. There is also a power supply connector block with two screw terminals labelld + and -. This is on the left of the picture. I did find reference in the brief information I could find to its standard settings being 9600baud, 8 bits, no parity and one stop bit. This is a pretty standard configuration and the same as I used for my tests described in earlier posts.
So in the end I thought the best thing to do was take the plunge and connect it up, and see what happened. I made a link cable up out of another old motherboard cable, and wired the power into the Aux 12v supply available on the main board. This isn’t a great picture but shows everything lashed up. The antenna is out of shot but just dangling on the antenna wire at the moment.
Here I learned some more important lessons which unfortunately cost me some time. After wiring it in I tried to connect using Wintex but I couldn’t make it work. I was really worried that I’d blown something up by connecting the GSM unit and after a lot of fiddling around I finally realised that I had simply got Wintex configured for the wrong type of panel (Premier 48 rather than Elite 48)!
Once I’d got this working, I then found that all of my sensors were dead and thus I once again worried that I’d broken something. Looking closely at the board I saw a new red light beneath one of the PCB fuses for the Aux 12v supply. I had obviously shorted out the supply when wiring the GSM board at some point. I was quite impressed with the attention to detail in the design, as having a red light under the fuse immediately showed me what was wrong. After replacing the fuse all was well again. There are several very bright red lights on the GSM board itself as well.
I’ve not been able to do much more testing as I’ve not yet put a SIM with credit into it. However, I did configure COM2 for the GSM module and on running Wintex saw the following:
So it does appear that the unit is recognising the GSM unit – hence GSM status ‘Online’ in the bottom right. The signal strength is effectively non-existent but that’s not surprising given that there is no working SIM in it. Also I’m not getting any errors that the COM port won’t initialise, which you do you get if you try to configure the module with nothing actually present.
So this all looks good… next thing is to get some credit on the SIM and try sending some messages!