Am I gonna need a bigger Arduino?

Projects General Guidance
1

Here's my project scope, please let me know if the Uno will cover it, or if I'll need something like the Mega with more Serial Ports:

--This unit will read RFID tags and communicate the data to a website via a GSM module.
--It will simultaneously communicate via Xbee with another Arduino with an LCD screen.

So that's an RFID module, GSM module, and Xbee module all at once.

2

Just my opinion, but go with the Mega!
A "genuine" or the VERY excellent SeeedStudio Mega Clone!

The SeeedStudio Mega is cheaper, has a JST connector, which makes for a better connection in a fixed project.

And it's sexy red!

3

--This unit will read RFID tags and communicate the data to a website via a GSM module.
--It will simultaneously communicate via Xbee with another Arduino with an LCD screen.

There are different types of RFID reader out there some even dn't need power to operate and some need.
You have to be clear about what type of LCD you would be using because there HD44780 driver based character LCD's and there are Graphic LCD's which will eat all the pin's on your arduino and there are also sparkfun nokia 6610 breakout module which will use less of arduino pin's and there are some printer LCD's that use ONLY 3 PINS to driver the LCD.

i would suggest use a mega for the one with which a LCD would be used and use UNO for other stuff

4

I have Duemilanove with a motor driver (2pins) an RFID reader/writer (3pins software serial +1 ) and a 16x2 LCD screen (6pins). I still have 2 digital pins free (not using digital pins 0 1) and all the Analog pins are free.

So you should be able to get away with a UNO, but if you want to have better serial them a Mega may be better and Having a Mega to play work with is also fun useful.

5

cyberteque:
Just my opinion, but go with the Mega!
A "genuine" or the VERY excellent SeeedStudio Mega Clone!

The SeeedStudio Mega is cheaper, has a JST connector, which makes for a better connection in a fixed project.

And it's sexy red!

Also has a nice auto-reset on/off switch and a useful manual voltage selection switch. The Seeeduino mega board is a sweet value added arduino compatible design. Even has a voltage level switch to allow the board to run as a 3.3volt platform or the standard 5 volt platform, even though running @16Mhz @ 3.3vdc is 'pushing' the AVR specs.

Lefty