Car Mounted Nexus7 (2012) – Intro

It’s been well over a year since I came across a post on hackaday.com where someone had mounted a 7-inch tablet in their car, in place of the radio. After some consideration and thought, I decided to take this on as a project myself! All of my ideas are a culmination of many other tablet installations along with brainstorming with a good techie friend (Griffin Hooper fb/g+).

Part of the reason I did this project was because I had gotten tired of the Clarion Max675VD that had been in my car for years. The unit always had a low SNR, and the iPod integration was no longer amazing after a few generations of iDevices (and I was now using an Android phone and tablet). Enter the realization that a Nexus7 is practically the exact size to fill a double-din opening, along with the endless possibilities that can be achieved with a tablet for FAR less than a new head-unit.

Requirements:

  • Fixed installation (securely)
  • Easy to use (storing and accessing music)

Issues to resolve before I could install a tablet in my car:

  • Power (cars are 12v, tablets want 5v)
  • Signal Processing (EQ, balance, fade, … the tablet will not be sufficient alone)
  • How was the usability going to work? Since this is in a car.

After a little Googling, I came across Timur’s USB Rom, which was specifically intended for in car applications as it enables USB Host mode, sends the tablet to a deep sleep when there is no external power, plus many other benefits that would be convenient for a car installation. The only requirement of this ROM is that it only runs on a Nexus7 (2012), which I already had. The down side of this tablet happens to be the analog headphone port. Internally, the analog signal connects to the same circuit board and ribbon cable as the USB data connection, this allows the analog lines to pick up interference and create a very dirty audio signal. The upside of this ROM is the USB Host mode and a built in USB audio driver. This meant I could get a USB DAC and entirely avoid using the headphone output of the tablet, and also giving me a pure digital signal. I downloaded the ROM, checked it out for awhile, and tested a few things. Things were definitely moving in the right direction for this project! My remaining item to address was how would I do any signal processing? I never was satisfied with the limited EQ of my prior head-unit and had always wanted a full 32-band EQ (the prior sales guy talked me out of it somehow). Since I was going to have a digital signal coming out of the tablet, why not finally get a DSP like I had wanted before? Enter the Rockford Fosgate 3sixty.3 (do not pay MSRP listed on their site!!). With the right DAC, I would be able to send my digital signal optically from the console of the car, to the DSP, leaving me with only a couple feet of analog signal from the DSP to the amps (which I already had from the prior setup). At this point, my initial plan was sufficient enough to start putting pieces together.

…more details coming!

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