Electrical – SIM900 not getting powered on

In your code the following function call is wrong:

serial_Tx(data1[i]);

Because data1[i] has a type of char but void serial_Tx(char *str) expects a char*, this function is for sending strings, not single characters. This way it causes runtime error, hence you won't get the expected output.

Though, it won't generate a compilation error, but the compiler will give a warning like this:

It is recommended to check and fix these warnings, because as you could see they could cause troubles in runtime.

So, replace the function above with the void uart_put(char data) function, like:

uart_put(data[i]);

and it will work.

1. LM317 is not a good candidate for this project,use LM2576 & LM2596 adjustable voltage regulators
2. check UART level between your host controller(MCU or ...) & Module,if they operate in the different level you need a level shifter buffer.
3. PWR KEY used for turning module ON/OFF,for doing this you must pulled it down for a moment(less than 500 ms or around)
4. Read simcom's app notes and reference manual & datasheet,all above described there in detail.