Using The Nexus 7 As A DVD Deck In My Car

So my plan is to use my nexus 7 as a dvd deck in my car. I have everything i need except im just trying to find a way to use the old fashioned rotary knob for my volume. I would like it exactly as the picture, but if i just have the knob then thats fine. if anyone could help that would be soo amazing thank you!
00.i.aliimg.com/wsphoto/v0/740610502_1/Digital-TV-ISDB-T-6-2-HD-Android-Double-Din-Car-DVD-Player-Stereo-Radio-head.jpg_350x350 (dot) jpg