I have Simcom SIM900a GSM (SIM900a Mini DEV Board v3.9.2) and I am interfacing it with Arduino UNO. I have no idea how to connect SIM900a to Arduino UNO.

What I did now is: SIM900a; My reference image

I connect the following Pin from above Image to:

5 to: GND (Digital GND near Pin 13)

6 to: 5V of Arduio

2 to: GND of Arduino near 5V

3 to: Digital Pin 0 of Arduino (RX)

4 to: Digital Pin 1 of Arduino (TX)

1 to: (No idea)

From Picture option 7, 8, 9 are not connected to anything.

Can you please guide me am I doing right?

I am getting hard time to find out what is TX and RX in my SIM900a module as it is not written there.

My SIM900a looks like this, this(Schematics given) and this.

When I upload sketch of:

Example > GSM > TestModem:

to Arduino, I got this output from Serial Monitor:

Starting modem test...ERROR, no modem answer.

Checking IMEI...Modem's IMEI: 0

Reseting Modem... Modem is functioning properly: IMEI: 0

  • \$\begingroup\$ Hint: Am I suppose to provode external power supply of 5v 2A OR Do I need Some TTL to RS232 converter \$\endgroup\$
    – fWd82
    Sep 9, 2017 at 19:27
  • \$\begingroup\$ The links you give clearly show that the black power wire is positive, and red is negative, contrary to customary practice. If you've connected Red to positive, you've likely killed the module. \$\endgroup\$ Sep 9, 2017 at 19:35
  • \$\begingroup\$ Hi @PeterBennett You are right. But the image of module they have there is wrong placement of wires, and the one I am using is correct sequence of wires attached. My module is good and running as well led is blinking. \$\endgroup\$
    – fWd82
    Sep 9, 2017 at 19:57

1 Answer 1


Seems like you have a wrong connection, look this image:

enter image description here

Follow this instructable for more details

  • \$\begingroup\$ Hello @GEPD Thank You for your reply. I have updated my question HERE, Can you please have a look. I will be glad if you find out what I am missing. As I am wiring it Okay. \$\endgroup\$
    – fWd82
    Sep 19, 2017 at 21:14

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