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Topic: ICOMSat Sim900 / Mega2560 (Read 16500 times) previous topic - next topic


Funny thing is that both Arduino MEGA and GSM_Shield library are "supported" by the IComSat.(At least it's said in its website :p)

Not IcomSat - they only make the SIM900 chip, IteadStudio is responsible for the library and the shield it is mounted on. FWIW, I found the minimal libraries to be OK for SMS and like functionality but totally inadequate for GPRS operation. For that, I ended up writing my own series of commands to make the SIM900 module do exactly what I wanted it to (i.e. transmit to Cosm).

I use iTeadstudio quite a bit for PCB manufacturing but "support" in general for their goods is less than optimal. For example, not all devices they offer come with drawings or libraries, making it difficult to incorporate them into your designs. You get a nice apology note if you point it out to them, but I have yet to notice changes to their web site in response to customer inquiries.

Seeed Studio seems related to itead but separate enough to offer better support. If you want really good support, buy from Adafruit Industries. They publish great tutorials for almost all the stuff they sell, are responsive to tech support inquiries, and offer helpful forums also. You pay extra for that support but them's the rules...


I guess it's finally solved.


Do you have any photos how to connect 18 and 19 pins to TX and RX? Thank you for informations, i am a beginner.


I'm very busy right now.... but I'll answer this when I get home ok


I have also read this with big interest after struggling with a Mega 2560. I followed the outlined instuctions and changed to serial1 and removed the include but still having problems with sending a SMS. I am sure it must be a pin-connecting problem - somehow I must have misunderstood the pin configuration ?. So -like kamillo1888 - I would love to see a clear picture/description of how to patch pin 18 + 19.



I hope you guys are talking about the same module, I am planning to buy one.

One question, I couldn't find how to power the module, does it take power from Arduino as it looks like a shield?
Just wanted to confirm before I place the order.

I will be using it with Arduino Duemilanove (which is almost like Uno).





It uses power from arduino.
I recommend you check if the library is compatible with your arduino and with other components you're going to use.
My project became much more complicated because after I done what I mentioned above, the receiving script stopped working properly,
so I had to reprogram it. And I turned into a slow script, that took around 3 seconds to verify if a message arrived... it was a problem
because the user was going to press a button just to verify if the message arrived.
If you can afford to buy a more expensive but compatible shield, do it.



I am hoping to get some help. I am working with the uno and icomsat v1.1. I used the icomsat as a shield to the uno and connected directly to my laptop. I used the libraries from competefornothing.

When I ran the serial monitor, it says :

GSM Shield testing.
ERROR: SIM900 doesn't answer. Check power and serial pins in GSM.cpp


Could I get some advice on this please?

Thank you...


Well, check if you're connecting RX and TX to their correspondent in the shield. Also check if the baudrate of your script is the same used by the shield. (if you don't know what is that, google it )

I ran into this problem very early in my project, but I don't really remember how I got it solved... Just try the above and gimme feedback ok? :)


works great, thanks for all!

my config:
ARDUINO UNO R3 + ICOMSAT 1.1 + ARDUINO IDE 1.X + LIBRARY FROM https://github.com/jgarland79/GSM_Shield
*OPTIONS FROM GSM_Shield.cpp by Default (2,3)
*Turn on pressing the first button (SIM900-POWER) after connect the arduino.

and works!!

my big question is: how i can put in "auto power-on"

thanks again.


and the last thing folks:

Icomsat and other gsm modems needs an external power plugged into the Arduino because it uses about 1 amp to boot up.

(thanks to warren from http://www.competefornothing.com/)


Apr 14, 2013, 06:24 pm Last Edit: Apr 14, 2013, 06:28 pm by Constantin Reason: 1
IIRC, the Seeeedstudio shield is as beefy as it is re: capacitors (470uF vs. OEM recommended 100uF) for precisely that reason, i.e. to allow the shield to function even if it's 'just' using USB power. The maximum power draw is around 2A, though only in very short bursts. Hence, the big capacitors.

The Seeedstudio shield has worked fine for me in a GPRS application, using a PC as well as a Mac USB port as a power source, though I realize that not all USB ports are created equal (i.e. some allow more than 500mA to be drawn). Similarly, a GPRS / Arduino board I built is happy with just USB power. Both the Seeeedstudio as well as my board use the Simcom 900 chipset.


Hey, GOOD news!
I had the amazing idea of opening the GSM_Shield.cpp and change all the "mySerial" for "Serial1", and deleting all the #include NewSoftSerial
By doing this, I just changed the comunication to Serial1 (pins 18 and 19) of MEGA, so I jumped the RX to the TX to these pins aaaaaand... the results are the following:

system startup
no call
no call
no call

...And when I called the shield from my cellphone:

incoming voice call from xxxxxxxxx (my number)

YES, it's working!! I'm so happy!! :) That's it my friends!

Hi there,

I had the same issues but I finally managed to solve most of them, including receiving calls. Yet, there is one remaining issue I cannot solve: so far, I am not receiving any SMS on the SIM. If I connect it to a normal mobile phone, I start receiving SMS. If I connect it to the shield, no SMS is received. Do you have any idea why this is happening?

Best regards,

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