I just bought a SIM900 Arduino shield from AZDelivery. I only have a Mega 2560 board, thus I am trying to use this although most examples (like the tutorial from AZDelivery) are with the Uno board. I am using the SIM card from my mobile phone, not having any PIN. This is the Arduino library I am using.

  1. I didn't flash anything on the SIM900 board prior to testing, because in the instructions from AZDelivery Ebook this was not mentioned.

  2. My NetLight LED is blinking constantly (1 blink per second) I guess it is not finding the mobile network.

  3. At the momemt, I only have a 1A supply, though I've already ordered a new one with 2A. Could this be the reason for point 2? Does the board need 2A to log into the network?

  4. Asuming it would log into the network, the AZDelivery Instruction Sketch/Example is using "SoftwareSerial.h" due to its compatibility to the Uno board. Since I am using a Mega board, can I just use D30 and D31 and set them as Rx and Tx using the SoftwareSerial library?

  5. Can you give me a link to an up-to-date library and/or example for SIM900 working with the Mega 2560 Rev3 and Arduino 1.8.4?

I hope you can help me getting started with the SIM900 module.

1 Answer 1


I was just able to send an SMS (even with the 1A supply). Here the answers to my questions.

  1. No, it is not necessary to flash the SIM900 board
  2. I was not connected, because I didn't insert the SIM card properly on the shield.
  3. No it does not necessarily need 2A for logging into network and obviously not for sending SMS though there might be reasons for the board consuming 2A during SMS sending, e.g. bad network connection.
  4. If you want to use Sotware Serial, you need certain digital lines allowing software interrupts. In the case of the MEGA board, e.g. D10, D11 or for the UNO D7,D8.
  5. I was using this tutorial to get communication via SoftwareSerial working. Afterwards I added the code for sending SMS.

I hope I can help some others who are looking for a low level description of how to get started with MEGA and SIM900.

  • the mega board has 4 hardware serial ports; why use software?
    – esoterik
    Jul 30, 2018 at 19:17

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