hi sir how to interfacing gsm module with atmega 328, i use MAX232 between atmega 328 and gsm module SIM900A but not working.
help me if you have any solution i need it on my projet 2016

We'll need a lot more information about what and how you've connected stuff together.
First your hardware configuration, and the type of GSM shield you're using.

The SIM900 doesn't require RS232 levels unless it's in a module specifically designed for RS232 connections. All piggyback style shields are intended to use TTL/3.3V interfaces.

  • also worth noting that RS232 transceivers will invert the data on the link segment of the connection.

When you eventually post your code (not necessary at this point), please use [code tags /]