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Topic: About the SIM900A module (Read 6237 times) previous topic - next topic


Greetings and salutations, fellow Arduinoers ;). I am close to loosing my mind over this stupid GSM module I bought off ebay. Its the Sim900A 5V one.
So, here's the deal. I cannot get it to respond to anything, it sometimes gives me some backwards ? in return, sporadically. I have hooked it up to a separate powersupply, and combined the gnd's. Everything lights up, but I am not getting any response when sending AT commands through to it.

Has anyone been successful in using this module? My project depends on a mobile internet connection for my remote sensor to work.

So, my module powers on, and the status led flashes... I am not able to tell how many ms the led is lit and how many ms it is dark, but it just flashes constantly. It is off longer than it is on...

If anyone has a better idea or a better module I can use, I am happy to hear it.
My goal for the project is small size and low power consumption.

Anyone? before I become a raving lunatic...


Have you tried resetting it and looking at the output at different baud rates? Perhaps it is using some rate that is unusual.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.


May 23, 2017, 09:19 pm Last Edit: May 23, 2017, 09:43 pm by luddiluddludde
I have reset it, and tried all the baud rates... It just doesn't seem to want to speak to me...
I have connected three pins. RX to 10 and TX to 9, and then the GND to the common GND.

Any ideas for something that can make my life easier with something that just works?


I used a SIM800 from DFRobot, there was some pin input sequence that had to be applied during setup, wonder if SIM900A needs the same.

No links to libraries at the place you bought it?
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.


I have contacted the ebay user I purchased it from to see if he has any clue.
Looking around the internet a bit yesterday, I think I have made a huge mistake with the SIM900A as it appears not to support Europe... So, what should I get instead?
I have a mini SIM800, but that is a very pesky circuit that is really fixed on getting the exact voltage, which is not 5V... So not wanting to use that...

As mentioned, I need a simple circuit with not too much stuff to get things to work. My goals is simple, some circuit running off an Arduino Nano that is capable of doing POST to a webserver at my house over the mobile internet.

Any other SIM modules I can use that will just work?


Officially giving up on my Sim800L module. Noticed there is another one with built in voltage regulator that will work on 5V. Behold: http://www.ebay.com/itm/262575441445

If I am lucky, this new module will help me accomplish my goal ;). Anyways, now I have time to make the rest of the code while waiting for the module to arrive.


Hi luddiluddludde,

Did you have any luck with the replacement GSM module? I am just starting out with a GSM project and getting hardware together.

However from what I have understand these modules should always reply to a (valid?) AT command with OK  even if not on a network.

The SIM900 series seem to run on around 3.5v - 4v. The card I am looking at has on an board reg and level shifters. As it can draw a peak current of 2A it will not run form the Arduino card's regulator.

I am proposing to power both from a 9v psu. One "got-ya" is the GSM still needs an external 5v for the level shifter to work. This seems to be low current so can be fed from the Arduino


Sorry about not getting back to you earlier. I am still in the dark when it comes to getting the GSM module to work. I seriously need to look into the level shifter and signal stuff, but it will take some time. I wish it was as simple as just adding a small module and running it off the 5V in the Arduino.


Beginners guide to using the Seeedstudio SIM900 GPRS/GSM Shield


You have many suggestions receiver. One is RESETTING the SIM900 modem, but no instruction for that. Guess I experienced the same problem as you firstly explained, namely that the AT command you put in the command window of the serial monitor did not respond with OK.
1. Make sure setting the correct baud rate (ie. 9600 or 19200) according to your sketch.
2. Rest by typing   ATZ.
3. Check for working by typing  AT. The monitor should now answer with OK. Hereafter you can type any AT-commands.


I want to see phone number from gsm 900A shield sim card in 20*4 LCD display.. & with the help of 4*4 keypad i want to change the sim number location address.. When m press a key the location address increase & automatically the number will be changed & when m press other key the location address decrease & number will be changed automatically.. Plzz help me out..  I dont know how to solve this problem  :( .. Plzz help me if possible.. Code plzz...

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