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I'm in a situation and need some advice.

Scenario 1: Arduino Uno/Genuino + ICOMSAT SIM900 Module(http://www.itead.cc/icomsat.html) (placed the jumpers such that Digital Pin 2 is rx and 3 is TX on the shield) Code Used: The send receive SMS example code in the arduino website.( (https://www.arduino.cc/en/Tutorial/GSMExamplesReceiveSMS) Everything Works fine without a glitch.

Scenario 2: Arduino Uno/genuino + GSM breakout board(https://www.google.co.in/search?q=sim900A&espv=2&biw=1600&bih=717&source=lnms&tbm=isch&sa=X&ved=0CAYQ_AUoAWoVChMIqd748qb8yAIVYXumCh2s2Aaq#tbm=isch&q=sim900a+gsm+module&imgdii=9zJcFQBaoLAKzM%3A%3B9zJcFQBaoLAKzM%3A%3B7eDw6qGc3qZjMM%3A&imgrc=9zJcFQBaoLAKzM%3A)

Had loads of issues with softwareSeial.h library and ended up cross connecting the default on board rx/tx with GSM board's RX/TX and everything worked fine. (though I didn't liked the fact that everytime during programming I had to change connections to upload a sketch) code used is from here (http://www.theengineeringprojects.com/2014/06/send-sms-with-arduino-uno-and-sim900d-using-at-commands.html)

Now my Problem: Since the shields are very costly, I decided to settle on the cheaper boards for my project. But the Code used for the GSM shield was so easy to understand (since the library was doing all the heavy lifting) I tried to use that. I connected Rx of GSM board to pin 3 and TX to pin 2 of arduino and uploaded the same code I used for the GSM shield scenario. But the code won'r work, I tried to tinker a few blocking things like the enable pin code where the shield is brought up etc. but no luck. Can anyone put some light on it, has this been tried before, is it not supposed to work the was i want it to ? Thanks a lot in advance.

abhishek chattopadhyay
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  • can you show how exactly are you connecting the two , also if you can elaborate what steps you took to debug.. You must have done some testing .... check step by step... – dmSherazi Nov 07 '15 at 08:59
  • @dm: I cross connected RX/TX of the GSM board to TX/RX of arduino. Made the ground common. Powered UNO and GSM separately. Used the code as shown in here https://www.arduino.cc/en/Tutorial/GSMExamplesReceiveSMS Now nothing works. No activity in serial console. Seems like the library is not meant to be used this way. Or there definitely is a need for a hack which can fake a breakout board and present it as a shield. – abhishek chattopadhyay Dec 30 '15 at 07:46
  • most of the libraries use `softserial` instead of `RX TX pins`. usually pin 3 and pin4 – dmSherazi Dec 30 '15 at 11:38

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