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[SOLVED] SIM 900A modem is getting reset...

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Mahesh Kumar Arumugam

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Can anyone know wat are the reasons for GSM modem getting reset. How to over come this issue...
 

Sir, Thank you for your replies...the power supply is good even though the module is getting reset...
 

What is the current rating of your power supply?
 

Sir, am using 2A power supply, what happens is when i use 2A power supply there is no prob, but when i use 3A power supply am getting this issue.
 

So you showed that the problem is related to power supply.

Without seeing power supply waveforms we can just guess, probably the 3 A supply isn't prepared for the current pulses of a GSM transceiver, or the voltage is beyond specified range. GSM modems usually need supply filter capacitors to absorb the current pulses, at least several 100 µF.
 
SIM900 throws an unsolicited text "UNDERVOLTAGE" or something like that, you can check this in the technical documents provided by SIMCOM. There is a big possibility not to get this text, if the voltage sink is very quick. So, you can adjust your software to perform an action if this text is received (light a LED or something). Or you can connect GSM to the PC and obseve communication history, via a terminal software.

Sir, am using 2A power supply, what happens is when i use 2A power supply there is no prob, but when i use 3A power supply am getting this issue.
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I can't imagine how could this happen... What is the power supply in each case, 2A and 3A?
 

Both(2A and 3A) are 12V supply...the voltage remains same as 4.00V when measured while module gets reset...
 

What about your antenna connection, perhaps there is a matching problem and a high VSWR might be the cause of your problem.
 

Thank you all for the replies....

The problem has been fixed...the reason is the non mounting of higher value capacitor near the modem and capacitor in the output of the voltage regulator.

2A power supply - Is stable - So no reset of the modem
3A power supply - Is not stable - So the modem getting reset

Note: All these tests were done under low signal condition.
When the signal high is there no such issues being faced.

Thanks All.
 

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