While Raspberry Pi and Arduino are very different boards, you can use them together for powerful projects.
How to Use Raspberry Pi and Arduino Together : Read more
How to Use Raspberry Pi and Arduino Together : Read more
Because its fun and after learning that way knowing will be fun as wellWhy not just use an A/D converter? There's less hardware, much less complicated, you only need to program the R-Pi, don't need to also write code for Arduino. This article shows you the way (except the software bits are outdated): https://learn.adafruit.com/raspberry-pi-analog-to-digital-converters