Microcontroller interfacing with SIM900 A

[ashutosh9989]

I am trying to use SIM900A chip. I made the circuit for this chip and I am able to get the call but AT commands are not working always. Sometimes it works but sometime its serial port does not respond.

 

[kgshankar1980]

@Ashutosh9989,

SIM900A Chip??? This is not a chip and it is a GSM module..

What circuit you made??

Are you trying to connect the GSM module directly to a PC or via MCU??

Share your schematic...

What you mean by sometime its serial port respond and some times does not??

 

[ashutosh9989]

@Ashutosh9989,

SIM900A Chip??? This is not a chip and it is a GSM module..

What circuit you made??

Are you trying to connect the GSM module directly to a PC or via MCU??

Share your schematic...

What you mean by sometime its serial port respond and some times does not??

https://www.open-electronics.org/small-breakout-for-sim900-gsm-module/ ...schematic is available over this webpage...i m connecting this rx and tx to the pc through max233cpp ic( voltage level shifter rs232 and TTL)....

 

[ashutosh9989]

https://www.open-electronics.org/small-breakout-for-sim900-gsm-module/...schematic n m trying to connect to pc via max233 level shifter

 

[kgshankar1980]

@ashutosh9989

Can you pls share the schematic of Tx & Rx with the MAx233 IC?

 

[ashutosh9989]

that is direct connnection...nthng else...

 

[kgshankar1980]

@ashutosh,

You said that the Tx and Rx of the gsm module is connected using max 233 ic..pls share that schematic??

Now you are saying that is direct connection...what does it means?

 

[ashutosh9989]

you asked for connection of Tx and Rx with max233....so that connection is direct...and that part is working...there is no problem with that part..since I am using that from a long time...

 

[kgshankar1980]

@ashutosh,

The hyperterminal should be set to 115200,8,N,1,NONE Baud Rate.

And by default the module will be in Echo mode off. To turn it On type ATE1<Enter> and check the AT commands.

 

[ashutosh9989]

no default it is 9600 with same settings as u hav told...and default i guess echo was off but if was off then why it was sending echo sometimes? now it is working thnk you buddy...

 

[toorajtoosi]

hi
I connect sim900 to microcontroller and sen AT command with usart.
everything is ok and sim900 response correctly.
but after send AT command sim900 resend that AT command for me again.
how I