Arduino - Raspberry Pi serial communication I need to connect a Raspberry Pi and an Arduino Uno through serial communication and decided to follow this guide, which mentions the use of a voltage divider. 

I understand the connection to the Raspberry Pi GPIO requires 3.3V but I also plan to power the Raspberry Pi from the Ardunio's 5v output pin.

What's the safest approach to achieve this and the recommended current? Thanks.
You CAN NOT reliably power any model Pi from the Arduino 5V output.
You can interconnect the Arduino serial to the Pi using a voltage divider or (preferably) a level converter, as suggested in the linked article. (I might add that the linked article contains a number of errors which will not work on recent Pi models).


Better still you can use a USB connection, to provide serial communication to the Arduino, AND you can power the Arduino from the Pi (I often do this).