I am really facing a big problem with the Telit GM862 Module. I bought my module from mikroelektronika with the EASY GSM/GPRS board, and I connected the whole thing to the breadboard.
The thing is, the module does start up, but after the STATUS_LED flashes for 7 times, the whole module shuts down.
A lot of people told me that the problem is with the power supply as it can’t give a 2A current, so I made a power supply that is suppose to do this, but still.
I went to my University Lab, and I found there a power supply ranging from 0-30v (3A) and I tested the board, but still the STATUS_LED flashes and then the whole module turns off.
Does anybody know what is wrong here?? As it seems from the internet that his module is very easy to work with.
Make sure you have filter caps near the power pins of the module and that the wires between the power supply and module are as short as possible. Even if your power supply can provide the required current you may be getting a voltage drop at the module. If you can, look at the power pin of the module with an oscilliscope.
Some people told me it is the 100uF Tantalum Capacitor(with low ESR) that I must connect to the board. I didn’t put this Tantalum Capacitor at all, and all the people are saying the problem is with this CAP. My question now, is this the right capacitor or not:
The important thing is that your entire power system can handle the big current spikes. The power supply must not droop under load and the module must not see any voltage drops below its minimum voltage.
I’d recommend a much larger capacitor than that. I typically use a 2,200uF electrolytic in parallel with a 0.1uF ceramic. Place both of these as close to the power pins as possible. Also, make sure all of your power traces, from input connector to module, are wide (0.100"). Finally, make sure you have adequate grounds. A ground plane is best.
many guys say there should be no voltage drop,but actually no one can guarantee for their power system.the key is how long does it drop will make GM862 dead?
Some negative pulse is obversed on my system,the voltage is even down to 0V.but the period is about 10us or 100us,NOTHING happens.GM862 works normally.
So does anyone can provide this “dead period”?i guess is 100ms.
I own one of these modules and I can confirm that you probably need the low ESR tantalum cap in there for it to work properly. Mine cuts out too without it.
The Telit has two blinking patterns. When searching for the network, it does a fast blink. When attached, it drops back to a slow blink. Are you ever seeing the slow blink?
As for next steps, have you hooked up the serial port yet? That will let you access the AT commands, giving you a better set of tools to diagnose the issue.
Am presently in the process of trying Khaled’s method using a MAX232 just to establish comm’s and then using a 74HC4050 to allow communication from an arduino mini pro 5V to the gm862.
I’ve only used the Telit in a 3.3V system - initially I didn’t have any level conversion, but added a simple 3.3/2.8V buffer in the 2nd rev of the board. Didn’t have any issues with either. Since you’re at 5V you definitely need the resistors at a minimum.
But yes, start with the MAX232 (or even better SparkFun’s simple USB-FTDI breakout board - trust me, you’ll end up using it on every project) - get basic comms working there first, then switch to the Arduino. If you can’t get HyperTerminal or CRT to work, it’s not going to be any easier from a uP where you have limited debug capability!
