Raspberry Pi shield for the Arduino

I want to be able to communicate with my newly built Arduino board from my Raspberry Pi using the serial port on RPi´s GPIO.
The problem is that my Arduino works with 5.0V and the Raspberry Pi pins only work with 3.3V.

The motivation for this is to:

USB to serial

• Use the processing power of the PI for the robot mapping project.
• Free up my USB to serial by being able to program the
  Arduino from the PI
• Start using GPIO on the Pi and learn about level conversion

So the plan is to build a shield for the Arduino with a 26 pin connector on it so I can connect it to the RPi using a flat cable. Eventually some other components (radio or Bluetooth) should be placed on the same shield.

The new Arduino with not functional RPi headers...

I did a similar thing on the newly built Arduino board, but could not get it to work, so Im kind of curious on how to solve it.

I have converted between 5 and 3.3 V before using a AND-gate when communicating with a enc28j60 ethernet chip.

First step is to put something up on a breadboard...

• Level conversion 
• perhaps I can use the AND gate I have. 
• transistors?
• voltage dividors?
• LED lights for RX, TX

This guy has done it before but found some issues so he used a level converter instead.

This also shows it working with a voltage divider

http://7h0ma5.org/2012/07/raspberry-pi-arduino-serial/

And another one http://www.andremiller.net/content/raspberry-pi-and-arduino-via-gpio-uart

And this is really what I want...

http://www.electrokit.com/nivaomvandlare-3-3v-5v-logik.45725