Sim900a gsm module,simcard is loosing registration after working for few days

[shivakumar.r]

Dear friends,

I am using SIM900A gsm module for my product.
My product will be installed in a place where the signal quality is less than 10( checked from AT+CSQ command) , and is fixed very near to noisy environment (next to 3 phase starter).
I am using GSM module for both voice and SMS.

My problem is - after i install the box it will be working fine for 4 to 5 days, but suddenly sim card will loose the registration and when i call to it response from it will be either "not reachable" or "switched off".I have confirmed that sim card is loosing registration by observing the netlight LED which will be blinking very fast(for every 1 seconds it blinks).when module is proper netlight LED will be blinking every 4 seconds.

Some times GSM module is not giving any response to the AT commands,it is in a hanging kind of state

when i reboot the GSM module by removing the power suppy and re connecting it every thing will work fine for some days and again same thing repeates.

This same problem i am getting in 5 to 6 gsm modules.

I am using SMPS power suppy and battery.SMPS is rated for 1.5 amps current and battery is 1800 mah.

please suggest me some solution either in hardware or software.

 

[FvM]

This same problem i am getting in 5 to 6 gsm modules.

Same brand?

 

[shivakumar.r]

same gsm module SIM900A.
i have made nearly 50 boards and installed in different places,in many places i am getting th problem.

 

[FvM]

I'm not using SIMCOM products, thus I can't determine if it's possibly a SIM900 software problem. You should contact manufacturer support in any case. I imagine, that the behaviour may be caused by specific network properties as well.

I apresume, that the problem can be overcome by monitoring registration state in your application firmware and forcing a re-registration if necessary.

 

[shivakumar.r]

Thanks for the feed back..

As you said registration can be checked using AT+CREG and if registration fails i can reboot the gsm module.
But what should i need to do if the GSM module is in hang state,How can i bring back to normal state.

 

[FvM]

The GSM module should definitely not hang. The issue should be reported to SIMCOM. Of course you can restart the module by asserting NRESET or dropping the power supply, if either option is provided in your hardware.

 

[GSM Man]

I've seen a lot of problems with GSM modules, especially on this forum. Most problems are caused by poor power supply designs & poor PCB layout. Problem similar to yours can also be caused by software - not handling communications with the module properly is the main issue. If you are using delays in your code to control messaging your asking for trouble.

Without more info on your design it's impossible to give you specific recommendations, however, if you search the forum for my posts you'll see a lot related to GSM problems that may help you.

 

[shivakumar.r]

The GSM module should definitely not hang. The issue should be reported to SIMCOM. Of course you can restart the module by asserting NRESET or dropping the power supply, if either option is provided in your hardware.

In the present design i have not provided this facility,But for my future design i will provide it.

connection to NRESET can be made as per the datasheet ,but what about "dropping the power supply".
How can i controll the power supply of GSM module from microcontrolle?,please suggest me.....

 

[FvM]

How can i controll the power supply of GSM module from microcontrolle?,please suggest me.....

Using a switch transistor?

 

[shivakumar.r]

I've seen a lot of problems with GSM modules, especially on this forum. Most problems are caused by poor power supply designs & poor PCB layout. Problem similar to yours can also be caused by software - not handling communications with the module properly is the main issue. If you are using delays in your code to control messaging your asking for trouble.

Without more info on your design it's impossible to give you specific recommendations, however, if you search the forum for my posts you'll see a lot related to GSM problems that may help you.

Thanks for the feed back......
Most problems are caused by poor power supply designs & poor PCB layout.
---> I am using SMPS which is capable of delivering 5V, 1.5Amps current.I am using LDO-LD39300 to step down the 5v to 4.2v.
Please tell me what are the informations required from me ,i can provide it.

Problem similar to yours can also be caused by software - not handling communications with the module properly is the main issue. .
---> not handling communications with the module properly is the main issue - please provide me more details on this .
Is there any document which gives the information on how to handle communication with GSM,If available please share it.

If you are using delays in your code to control messaging your asking for trouble
---> After sending the SMS i am using 1 second delay,is this delay is cousing the problem?
Do i need to include 2 to 3 second delay between every AT command?....Please help me ..

- - - Updated - - -

Using a switch transistor?

Any recomended transistor(part number),
Is it BJT transitor or Mosfet.Which is good?

- - - Updated - - -

Any recomended transistor?
Is it BJT transistor or MOSFET

 

[GSM Man]

delivering 5V, 1.5Amps current.I am using LDO-LD39300 to step down the 5v to 4.2v.

Two Words - Transient Response - Look at my other posts

Is there any document which gives the information on how to handle communication with GSM,If available please share it.

It's all in the SIM900 manual

Do i need to include 2 to 3 second delay between every AT command?....Please help me .

Let me say it again - using delays will get you in trouble! Read the response from the module and have your code act accordingly. If you don't read the response you have no idea what the module is doing or what the problem may be.

I have over 500 posts on this forum related to the issues you are seeing. Please, just do a little work and search them: - It will be the best education you can get.

 

[mailgsurya]

hi,
I also had the same problem. Some of the suggestions the i can tell is ,,,,
=> use a capacitor filter (around 1000uF) in the power supply of the gsm modem.
=> avoid AC power lines passing near the controller and GSM modem
=> the distance between the controller and the gsm modem should be less for effective communication

check this out......
8-O

 

[shivakumar.r]

Thanks for all of your help.....

I have added 2sec delay between each AT command and given 1 minutes of delay when GSM module is powered up.
In software for every 2 hours i have made GSM to reboot.
I have increased the track width of VCC of GSM module by adding a thick wire.

Now my system is working quite good...I am still doing the field testing ....Hope the issue will be completely solved......

Thanks for your valuable suggestions......