am trying to connect the atmega 328 standalone with the gsm sim 900 but no ommunication is going through.....
I have the crystals and 22pf capacitors but the problem is connection of TX and Rx pins to sim 900.
#what could be wrong....?
1st: "what could be going wrong" is a very large results-set. Most of us prefer not to guess when answering questions that are too broad.
2nd: make your project work with the Arduino UNO.
3rd: build a barebones 328P-PU and test it beyond just blinking a LED. Make certain all the inputs and outputs work. I have a sketch you can butcher to get that right. ... just remove the USB stuff.
4th: remove the Arduino from #2 and attach/program your board-duino. Everything should work correctly.
Here are a couple of naked-builds I have done in the past.
As Ray suggested, test your code with Uno and Sim900.
Before connecting sim900 to your standalone one, test the serial communication using a USB to FTDI cable. Using CoolTerm or any Serial communication software, you can send Serial data and see whether your Standalone Arduino is responding to your commands. Here you are simulating Sim900 commands.
If the serial communication works then you can connect your Sim900.
I havent used any GSM module yet, but used Bluetooth with a standalone one. To debug the communication and sketch uploading. I kept my Hardware serial connected to USB FTDI cable. For bluetooth communication I used Software Serial.
Also to understand whether i am receiving the right data from bluetooth, I just write the received data from software serial to Hardware serial. This way i can monitor the data received from bluetooth via coolterm.
my GSM works well with arduino uno but fails when am using atmega 328 standalone.
when connected,it breaks the connectivity of GSM Shield.