In this article, I'll go step by step on how to build a wireless in-car entertainment system using the Raspberry Pi and a Chromecast.

Requirements

• - An in-car entertainment system that has accessible HDMI and a powered USB port (preferrably very close to each other) **Note: this will work with your home TV, with very few changes**
• - Raspberry Pi (Model B recommended)
• - A 2GB+ SD card (Raspberry Pi's hard drive.)
• - A power cable for the Raspberry Pi (preferrably a Micro USB cable +USB-car adapter with sufficient juice for the Raspberry Pi)
• - An HDMI cable (for configuring the Raspberry Pi only)
• - A Raspberry-Pi-compatible wifi USB dongle
• - A Google Chromecast
• - A USB external hard drive (I used a USB 3.0-powered sleeve and an SSD, to reduce cables and power)
• - A smart phone that supports wireless tethering
• - A DLNA/UPnP player of choice on a secondary smart device (phone or tablet)
• - Videos or Movies or whatever (preferrably in Google Chromecast's preferred format unless your DLNA/UPnP player supports transcoding)

Instructions

Note: More detail and screenshots will come later. For now, you might have to google to fill in the blanks.

USB External Hard Drive Setup:

1. Format the drive to NTFS
2. Put videos/movies/whatever on the drive
3. (Optional, depending on your DLNA/UPnP player of choice) Format the video files to Google Chromecast's preferred format using an encoding software of choice.

Raspberry Pi Setup:

1. If you didn't buy an SD card pre-installed with NOOBS, you will need to prepare your SD card to boot OpenELEC (I recommended this option because you get the latest version of OpenELEC)
2. Connect the Raspberry Pi to your SD card, USB external hard drive, wifi dongle, HDMI (to any TV for the moment)
3. Boot your Raspberry Pi by plugging in the power cable
4. Install OpenELEC (which is a version of XBMC that works well on the Raspberry Pi)
5. Go to System -> OpenELEC settings -> Connections and configure it to connect to your smart phone via tethering
6. Go to System -> Settings and configure the Pi to be controllable by other devices (this step turns it into a server as well as a media center)
7. On a secondary smart device, download your favorite DLNA/UPnP player (I used MCPlayer for iOS, others will work as long as they have Chromecast support)
8. Connect the secondary device to your smart phone via tethering
9. Open up your DLNA/UPnP player of choice and verify that you can connect to and control the Raspberry Pi running OpenELEC
10. Disconnect the HDMI cable, and then move the Pi and such into your car

Chromecast Setup:

1. Using your phone and another wireless smart device, configure the Chromecast to connect to the phone via tethering
2. Connect the Chromecast to your car (ideally, your entertainment device will have an HDMI and a powered USB port next to each other)

How to use it:

1. Turn on wireless tethering on your phone
2. Turn the power on to all the devices in the car
3. Connect your secondary smart device to the phone via tethering
4. Open your DLNA/UPnP player of choice on your secondary smart device and connect to the Raspberry Pi running OpenELEC
5. Pick a movie, and use the DLNA/UPnP player's chromecast integration to make the movie play on the screen that the Chromecast is connected to
6. ?
7. Profit.