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139 posts

Master Geek
+1 received by user: 1

# 171727 29-Apr-2015 11:02
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I have a EFCOM gsm shield connected up to Arduino Mega 2560 Via Hardware rx and tx on the gsm shield to the pins 18 and 19 on the Arduino mega.

Sketch used on mega
void setup()

void loop()
if (Serial1.available())
if (Serial.available())

I can seen the GSM shield trying to connect to the network but then it looks like it restarts and prints some strange characters (see video here of net and sta lights on shield and serial output and continues the process over again.

if I enter the following AT+COPS=? I get :

+COPS: (1,"2degrees","2degrees","53024"),(1,"vodafone NZ","voda NZ","53001"),,(0,1,4),(0,1,2)

So it is in some way communicating with gsm networks.

- I have tried using a different carriers sim card.
- Have tired using different power supplys.
- Have checked the IMEI is not black listed here in New Zealand.
- Have re-flashed firmware onto sim900.
- Have tried changing the AT+COPS from Auto mode to manual mode and entered the information for the carrier of the sim card.

I am not sure what else to do, any help would be appreciated :)



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3885 posts

Uber Geek
+1 received by user: 1757


  # 1293715 29-Apr-2015 16:19

Which networks sim card are you using? Since it is 2G only it won't work with spark or skinny. But should work with 2 degrees and Vodafone.

139 posts

Master Geek
+1 received by user: 1

  # 1293998 30-Apr-2015 08:12
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I have tried both vodafone and 2d.



139 posts

Master Geek
+1 received by user: 1

  # 1297468 4-May-2015 10:10
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I Got it working !!laughing

Tried shield on another arduino, got the same result as before.

Powered the GSM sheild directly to the Vin and gound pins from an external power source and vola it works beautifully.

I assume the sheild was drawing to much from the Adruinos powersupply and tripping some type of fuse.

Now to figure out how to post data to my webserver from the arduino.undecided

3267 posts

Uber Geek
+1 received by user: 77


  # 1297779 4-May-2015 17:13
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GSM modules can easily draw peak currents of around 2A, it should be externally powered.  They are designed to run directly off batteries (which has a low impedance).

You can never have enough Volvos!

22264 posts

Uber Geek
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  # 1297784 4-May-2015 17:22
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I had no end of issues with mine losing the network when I was trying one on 2degrees. Never tried vodafone sim in it at that time. But the LED would go back to the looking for network pattern. There is about half bars on a phone inside where I was using it on 2G so should have been fine.

Also getting into some state where AT commands were having no effect. That was on a leonardo so I had it on the inbuilt hardware serial, but when I connected a USB to the computer to have a look at the debug output the leonardo reset and that also seemed to unstick the GSM shield, even tho I didnt see anything different going over the serial connection between the 2 depending on the initial start up and when the sketch was trying to send the SMS's


3267 posts

Uber Geek
+1 received by user: 77


  # 1297995 5-May-2015 06:41
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The USB connection either gave you more power for the peak current or it provided a good GND reference.  Electronics can by tricky, but it is even worse when you add RF.  Add to that the fact that finished products have to pass thorough compliance testing but development boards need virtually no testing so it does not have to meet emissions or immunity standards.

You can never have enough Volvos!

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