I'm using a SIM900A mini v3.8.2 GSM/GPRS board to make a phone call on certain conditions. I have connected the module through a CH340 USB to TTL converter to a PC (Windows 10) for testing. All connections are OK. I'm using a 5V 2A power supply so no power issues. The connection LED blinks after every 3 seconds, which means the network is connected. The power LED is on without any blinking.

enter image description here

I'm using the AT Command Tester software to test the SIM900A functionality.


  1. When I call a number it simply says NO CARRIER or NO Carrier: Call dis-connected.
  2. It does not send or receive any SMS/voice calls.

Note: I have sufficient tariff/balance for SMS and voice calling, and the SIM is unlocked.

Different AT commands responses are as follows:

enter image description here

When I try to make a phone call its response is this:

enter image description here

When I send an SMS, the SIM900A response is as follows:

enter image description here

Now where is the problem? I also tested AT commands for voice calling in Arduino terminal manually but problem is same. Is there any 1st time settings or configuration that has to be set for successful communication, like APN, SIM provider settings, etc.?

  • \$\begingroup\$ Do you have credit on the sim card? \$\endgroup\$
    – MaNyYaCk
    Commented Jul 4, 2018 at 9:19
  • \$\begingroup\$ absolutely Yes... \$\endgroup\$
    – Tehseen
    Commented Jul 5, 2018 at 11:07
  • \$\begingroup\$ Seems ok. Can you check the current and voltage when it tries to send SMS or call? When I had one back it would spike upto 1.8A when calling \$\endgroup\$
    – MaNyYaCk
    Commented Jul 6, 2018 at 11:43
  • \$\begingroup\$ Have you checked the SIM with a regular phone? electronics.stackexchange.com/questions/364045/… \$\endgroup\$
    – filo
    Commented Nov 3, 2018 at 15:12
  • \$\begingroup\$ To anyone wondering if it absolutely does not work: It works with a SIM only if you register it with PTA (Pakistan Telecommunication Authority). Otherwise after 2 months, they block it. Registration is very easy. Follow these steps for all such devices: youtu.be/1ZZjip5MlRQ I have registered, paid their fee and works just fine. \$\endgroup\$ Commented Dec 13, 2022 at 6:48

1 Answer 1


I understand the problem after all... I guess that this SIM900A module does not working due to our country regulations about IMEI number registration.... This module is imported from China from online shopping website so It is not registered by PTA (Pakistan Telecommunication Authority) that is why I believe they blocked this module and no sim carrier is providing service to this module... So I threw this module in trash after all...


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.