using a cmos cd4050 buffer chip to convert 3.3v to 5v.
the raspberry pi has its UART run at 3.3v and the arduino needs 5v. so, this little DIY perfboard 'shield' is needed.
note, how the chip is specifically (yes, very much on purpose) resting on the unused white riser connector. there is no other support (or screw mounts!) on this version-1 raspberry pi board.