GSM/GPRS modem hang problem

[wanchope]

at+csq

Hi, all,
I am testing the siemens GSM/GPRS modem module MC35i.
Everything works fine until one day the modem just hang there although it is still responding to my AT command. But it can not dial any more. When i try to send a message, it returns a error message saying ' sim not inserted'. Then i measured the vCC of the sim card. 0 volt!
The modem engine has already stop powering the sim card as it thought the sim card is not there (already removed). But my sim is still safely sitting in. Just confused why the engine said so. Of course after i restart the power, it is working again. But this problem is still not resolved. Every now and then it will just hand at the 'sim not inserted' state, and a hardware reset is required to restart it.
Any body encounter similar problem, not necessary the same part. Can give a hint?
Thanks.
Wanchope

 

[kuldeep]

at csq

This problem happens when the SIM card is not connected properly or because of lowsignal strength.

U should follow follow check sequence:
1. Check if the module is connected to home network, using AT+CREG<CR> command. If the module is not connected to network it will return 0,2 or 0,3 in response.

2. Check the signal strength . If the response with and without module inserted is same then the problemis with antenna.

Follow the procedure under these conditions:
1. Both SIM and Antenna Connected.
2. SIM connected but Antenna not connected.
3. Antenna connected but SIM removed.

All the best!

 

[pisoiu]

reset gsm modem

This could be an antenna related problem or power supply related problem, or both. If the antenna is mismatched and/or it has high VSWR, will cause high currents being consumed from the power supply, during TX pulses. If your power supply is not powerfull enough, this pulses will cause voltage drops below minimum operating value, and this can dazzle the logic part, causing strange behaviour. The power supply connection is also important (this is valid for almost all GSM modems). You should place decoupling capacitors nearby the module. The caps must have the value as indicated in the module's datasheet. The traces between the caps and power pins must be as short and as thick as possible. Use the maximum width you can afford, and avoid stub connection between the caps and power nets. Use low ESR capacitors. If the power supply is not ok, the same phenomena will happen, during transmission (when the module can surge usually up to 2A in low signal strenght conditions), the main voltage can temporarely drop below minimum operating voltage and can cause strange behaviour.

/pisoiu

 

[kuldeep]

gm862 low esr

I strongly suggest this test:

Connect the Antenna but dont insert the SIM. Check the Signal Strength using AT+CSQ<CR>, the response should be other than 99. Check it number of times.

Now insert the SIM with Antenna connected. Again check the Signal Strength using AT+CSQ<CR>, if the command response code is 99, then clearly the problem is with SIM connection or as stated by other member the problem can be caused because of the supply design issue.

 

[pisoiu]

at +csq

I seriously doubt that the modem will reply this information without the sim card. The reported signal strength is a parameter of the network you are logged on. In the same location you can have diffrent signal strengths, depends on which network you are connected. Usually, the reply at AT+CSQ without sim card is error (or 4<CR> for numerical codes).

/pisoiu

 

[kuldeep]

modem csq

No it doesnt give error.

When I tried this thing I got full strength response. Try the AT+CSQ<CR> cmd more than once.

 

[pisoiu]

gprs hang

Then perhaps it depends on the modem. I get an error each time for telit gm862. I have another question for you. I assume you have several GSM networks in your area, on both 900 and 1800MHz. Let's say that for one of them the BTS is on the top of your buiding and for another the BTS is 3 km away. For which one is the signal strength indication when you place AT+CSQ without the sim card?

/pisoiu

 

[kuldeep]

reset gprs modem

Then perhaps it depends on the modem. I get an error each time for telit gm862. I have another question for you. I assume you have several GSM networks in your area, on both 900 and 1800MHz. Let's say that for one of them the BTS is on the top of your buiding and for another the BTS is 3 km away. For which one is the signal strength indication when you place AT+CSQ without the sim card?

/pisoiu

I get full strength indication, on a wild guess there are 2 possibilities:

> The module indicates strength of the default band (say low frequency) signal.
> Strongest signal.


When I remove both sim and antenn then I get signal strength below -56dB on connecting antenna i get above -56dB strength.

 

[cesare]

gsm modem hang

How is connected the SIM presence pin ?

Is it connected to SIMVCC ?

 

[plr]

reset gprs modem

Peoples!

after some hours GPRS-connect Siemens MC35i hangs and don't respond to any windows-ras-initial script (commands) and I lost any control to Siemens MC35i, I cannot send any AT-command, modem is hang. how can I automaticaly reset it?

Thank you!

 

[abi26]

at+csq signal strength

It happen on almost all GSM modem, better add microcontroller to reset automatic, ie every 5 hours. The best reset is by dsiconnect the power.

 

[mitesh]

how to check kms 8 gprs

It even depands on SMPS power supply, its best first check with battery.

 

[planet69]

gsm modem +csq

It doesn't make any sense why the gsm module did not respond. BTW, is the problem due to insufficient power supplied? What does the manufacturer has to say?

 

[mitesh]

gsm gprs low signal

Its is due to lack of cuurent as gsm need more then 1.5amps current when it starts .

 

[ali sadek]

plllllllllllllllllllllllllease help me ,its part of my graduation project ..... i have this Siemens GSM/GPRS modem and it never respond to AT command !!! when i type AT it doesn't respond !!!!!!! _i use hyperterminal_(9600_8_1_hardware and none )