my teacher want that i shoul design gsm kit, that contains gsm module , some rs232 or usb interfaces , i m searching but didnt got any thing on the circuit diagram of this gsm kit can any one help me
Given the large amount of information that may be found using Google, I can't really see exactly what help you would need.
"my teacher want that i shoul design..."
He said that you should design.
"design" is a verb; that is, a "doing" word - it is something that you need to do.
Your teacher didn't say that you should just expect to find a ready-made design to your precise requirements!
See:
http://www.keil.com/forum/docs/thread9113.asp
http://www.keil.com/forum/docs/thread10238.asp
http://www.keil.com/forum/docs/thread9379.asp
etc, etc...
How would the RS232 interface circuit to a GSM modem differ from the RS232 interface circuit to any other sort of modem?
How would the RS232 interface circuit to an 8051 differ from the RS232 interface circuit to any other sort of microcontroller?
One thing to note: In RS232 terminology, a modem - any modem - is called a DCE, and anything else is a DTE.
Many internet sites get this wrong, in particulr thinking that a computer is the DTE and anything else is a DCE!
Many device manufacturers also get this wrong (deliberately or otherwise), and wire their serial ports as if they were DCEs.
The point of the RS232 spec is that it defines the interface betwen a DCE and a DTE; ie, between a modem and anything else.
The RS232 spec defines "interchange circuits" between the DCE and the DTE; eg,
* The Transmit Data "interchange circuit" (TxD) carries the data from the DTE that is to be transmitted by the DCE;
* The Receive Data "interchange circuit" (RxD) carries the data to the DTE that has been received by the DCE.
Thus TxD is an output from the DTE, and an input to the DCE; Similarly RxD is an input to the DTE, and an output from the DCE.
Thus, when connecting a DTE to a DCE, you connect the TxD pins together, and the RxD pins together;
But, when connecting two DTEs together, you connect the TxD of one to the RxD of the other - this is known as a "crossover" connection, or "Null modem".
See: www.8052.com/.../read.phtml