I personally (and I'm sure others) would be interested to see a full build thread on this somewhere. If this is truly possible to have all this functionality with "hardware", it would be an intriguing concept - so please share it in detail!! I'm not a fan of these "teasers"..
Sorry about the "teasers." I really do not have time to post/maintain a thread with all the details (and I certainly do not want to hijack this thread). My hope is that either someone else (with the time) will take the ideas and take off with it; and/or that some of these Ideas would be helpful in conjunction with Timur's mods. I sent you, and several others the PM I copied below. Only two people asked more detailed questions, which I answered. One plans is to use a 2013 N7, the other is working on the 4.3 ROM/kernel compatibility.
If what I am describing is well within your (or anyone's) 'knowledge base' then it is pretty simple to implement and figure out. However, if 'electronics is not your thing' then a fully detailed description is never going to be as "plug and play" as Timur's work is. I love math and solving all things electronic, writing code is not my thing. I am impressed by those that like code, but I choose a different route, and when I saw Timur pull out (and lots of people wondering about the 2013 N7) I decided to offer some encouragement to anyone with the knowledge/skill to take advantage of the work I had done. My apologies to anyone (especially Timur) if this is not the place for offering my input. Again, if anyone wants to open a public thread, please do (and let me know how I can help).
Previously PM'd to to those interested:
I am using an external PS (instead of the N7's PS). I tried it without the battery (simulating its existence), but experienced some issues occasionally when cranking the engine (I also tried an external charger with some custom isolation circuitry, but it was unnecessarily complicated). I am very happy with a simple DC-DC converter (always on) connected directly to the N7's battery. I am using 4.00v (this is the best compromise I have found, but if you know a LOT about the electrochemistry of lithium batteries then you can choose your own voltage, for your own reasons (just make sure you really know what you are doing).
As far as the wake/sleep issue: I am taking advantage of the N7's built in "proximity" sensor (think old school reed switch); this activated using a magnet. It was designed for a cover with a hinged lid (and a sewn in magnet). I was able to get this to work in two ways. The first is with a constant duty solenoid moving a magnet when the car accessories were on, and returning it when the accessories where off. The second is with a homemade electromagnet that is active (using less than 25ma) when the accessories are off, and is off when the accessories are active. Both work flawlessly and both take very little real estate behind the tablet. (Another option would be to connect directly to the internal sensor your choice). No matter how anyone chooses to use this method you CAN use apps to sleep the tablet, but it is not strictly necessary if they use the external PS for the battery.
For sound, I was not satisfied with the quality of either the bluetooth or the headphone jack; I was also not a big fan of the external DAC's I tried, however I am more than satisfied with pogo (internal DAC) output. Using the pogo created a need/opportunity for another interface. This works out well for me. I use the proximity sensor to wake/sleep the tablet with the insertion of the key; and I use the pogo 5v (input sent from the activation of my head unit) to activate the "fixed install" home screen and related apps (this allows me to effortlessly use the tablet in two modes, if I want). I can also use the tablet independent of the head unit with a cheap separate amp and speakers (the options here are endless and VERY useful).
I am using the OTG for and external drive, a back-up camera, DVB-T SDR, etc. I am using a powered hub, but tried it with an un-powered and had no issues.
Need an external microphone? Ever use a stethoscope? Are you old enough to remember when airplane headsets where just hollow tubes you stuck in your ears? Or maybe you have seen or used an old school pilot's microphone? I ask all that because, while the "technology" is OLD, it DOES work. And that is the principle I used for my external microphone; I enlarged one of the mic holes (inserted a flared fitting from the inside - which keeps everything in place nicely) and attached a 1/4" tube to the outside of the tablet. I ran the other side of the tube to an existing opening in the dash. I was not sure how well it would work, but it works BETTER than an unmodified N7 does just sitting in font of me.
I choose to go with this mod for my own reasons, but I have all this working on a UNrooted N7 running 4.3, and fully ready for 4.4 the day it is pushed. However, any, or all, these things will work with rooted tablets (any) and with custom ROM's/kernels; to me the beauty of using hardware solutions to work around a software problem (that was my goal/challenge)."