B4R Question Help with schematics (Arduino-SIM900)

I have successfully used a different GSM shield with ESP8266 and I remember it was tricky.
First lesson learned, don't power the GSM module from the Uno, it draws too much current and you may fry the Uno.
The Comms are simple TX-Rx but there the CS pin that need to be pulled up during initialization.

It's all I remember, and I no longer have code to share...

If I remember correctly the only important pins are the power and ground pins and the two software serial pins: http://wiki.seeedstudio.com/GPRS_Shield_V2.0/

Erel said:

If I remember correctly the only important pins are the power and ground pins and the two software serial pins: http://wiki.seeedstudio.com/GPRS_Shield_V2.0/

Click to expand...

Thanks Erel
A little more than that.. The button, LED and resistors connection not so clear to me.
Best.
We need a volunteer to draw the sch

Both Ground are comman...means connected with each other

Transmitter of GSM....Receiver of Arduino
Receiver of GSM.....Transmitter of Arduino

Both having separate power supply....in this scenario