Arduino Uno or Arduino Mega

Hi,

I'm trying to decide weither i can use a Arduino Uno for my project or i need a Arduino Mega.

i need to power 4x http://www.seeedstudio.com/wiki/13.56Mhz_RFID_module_-_IOS/IEC_14443_type_a and read and write data over its TTL interface.

Now i do know that the Arduino Mega has 4 Rx and Tx ports but i am not sure if these are needed since in http://www.seeedstudio.com/wiki/File:Rdm880_bb.png they are connecting the Rx and Tx of the module to I/O pin 2 and 3 of the Arduino. (this could mean an Uno could connect 4 modules too? )

Anyone could tell me if i could power them with either one(maybe even an other Arduino?) and which one would be the best choice?

Also Serial ( 0 ,1 ) does communicate via USB right? So connecting a module to this port will make all data sent go to PC too?

Thanks in advance

At a baud rate of 9600 it's often convenient to use SoftwareSerial, a software emulation of the hardware serial found on pins 0 and 1, to communicate to not so picky devices. But you can have only one instance of SoftwareSerial receiving at a time so if you want to connect four modules you must go for the Mega2560 with it's four hardware (USART) serial interfaces.

pylon: At a baud rate of 9600 it's often convenient to use SoftwareSerial, a software emulation of the hardware serial found on pins 0 and 1, to communicate to not so picky devices. But you can have only one instance of SoftwareSerial receiving at a time so if you want to connect four modules you must go for the Mega2560 with it's four hardware (USART) serial interfaces.

Thank you, so it is possible to connect 4 modules to the Arduino Uno, but can only receive from one Serial input at a time (might be able to multiplex this?). Would this cause things like missing data?

The Mega2560 gives the possibility to receive from 4 Serials in parallel? I read that the Serial ports 0 and 1 are connected to the Serial over USB, wouldn't this cause all data that is sent to the module connected to 0 and 1 to be sent over USB to my PC too?

The last question that remains is if it is possible to power the 4 modules with one arduino

Thank you, so it is possible to connect 4 modules to the Arduino Uno, but can only receive from one Serial input at a time (might be able to multiplex this?). Would this cause things like missing data?

Yes, it is possible to connect them but you would have to control, when they send something to the UNO. If you cannot control that (like with the RFID modules you mentioned) you have a very high potential of data loss.

The Mega2560 gives the possibility to receive from 4 Serials in parallel? I read that the Serial ports 0 and 1 are connected to the Serial over USB, wouldn't this cause all data that is sent to the module connected to 0 and 1 to be sent over USB to my PC too?

Yes, everything you send to the module on serial port 0 (pins 0 and 1) is sent to the PC too if it's connected by USB. If you need that connection to the PC (over the USB) and can connect one of the modules by SoftwareSerial.

The last question that remains is if it is possible to power the 4 modules with one arduino

Yes, the four modules consume a 280mA max. which should be no problem if they are the only devices connected to the Arduino.

Thanks :) this is all i needed to know