Good afternoon! I have a project for this semester of college and, 
necessarily, have to use the FPGA. So, I had the following idea: 
Stopwatch FPGA controlled by Android phone (via Arduino): The project 
aims to implement a timer in Amendment DE2 development board, available 
in the laboratory of digital systems, controlling it via a cell that has 
Android operating system. For this, we will have to perform a 
communication (serial, for example) with a microcontroller - where was 
chosen the Arduino - easy programming and module with integrated 
bluetooth, sending commands to the phone. These commands would be 
equivalent to buttons Pause, Stop and Reset. Stopwatch counts up to 10 
minutes after the burst count, an LED indicator light. But still can not 
find a way to make communication between the Arduino and the FPGA, 
someone already tried something similar or know somehow? Thankful!

> But still can not find a way to make communication between the Arduino
> and the FPGA, someone already tried something similar or know somehow?
As you already said: use a RS232 port or use a SPI interface. Both of 
them are fairly easy to implement on a FPGA. A few lines of VHDL (or 
Verilog) and its done...
Try this (its German, but maybe Babelfish or Google translate can help 
out):
http://www.lothar-miller.de/s9y/categories/42-RS232
http://www.lothar-miller.de/s9y/categories/26-SPI-Slave