The Engineering Projects

I have a problem. I bought a SIM900 board, but I can not connect there with the Arduino. To send AT commands on the serial the SIM900 doesn't respond, but the LED indicating that the network is on. I've tried to change the baud rate of 9600 to 19200 in the firmware of the Arduino, but it still fails. I think I'm having a problem with the connections of the SIM900, since this board strikes me as obscure (could not find the schematic on the Internet)

I'm 90% sure that I am connecting to the wrong pins. But I tried to reverse the jumpers and even some soldered pins on UART.

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