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SIM900A Arduino Tutorial

Using the SIM900A GSM Module with the Arduino

The SIM900A is that other module from SIMCOM popularly used as a GSM shield for sending and receiving SMS. I’ve already covered the SIM800L, now let’s look at the SIM900A breakout board.

The SIM900A Breakout Board

Similar to the SIM800L module, the SIM900A breakout board has eight pinouts. They don’t have labels so allow me to provide them for you:

SIM900A Breakout Board with Annotations
The primary difference between the SIM900A and the SIM800L is that this board doesn’t have Bluetooth and FM support. But the AT command set for both are identical which means we can use the same library!

The SIM900A breakout board has a 5V and a 4.2V version. Mine is the 5V version with the “V5.1” print near the VCC pin. This version can be powered by a 4.5 V to 5.5V source. There’s no information on what the 4.2V version looks like. I will update this post once the information is found.

Arduino Connection

The module has 3.3V TTL levels which means connecting its Rx pin directly to an Arduino’s Tx pin is a no-no. Here’s a diagram you can use to connect the breakout board to an Arduino UNO:

SIM900A to Arduino wiring diagram


We can then use the same sketches we used in the SIM800L tutorial.

Sending SMS

For the sketch explanation, refer to the SIM800L article.

Reading SMS

For making and receiving a call, attach the positive terminal of a speaker on the SPEAKER pin and the negative terminal to the GND pin. You can then use the same sketch used with the SIM800L.

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3 comments

  1. How come no external power source is required? What's the current draw of the SIM900A module?

  2. mehboob ur rehman

    what will be the value of resistors?

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