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Old 02-04-2014, 10:30 PM   #1
July57
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Default Yet another Nexus 7 in dash install (2012 WRX)

I was inspired by the likes of zedix and metajames to try and install my nexus 7 in my car. My project was slightly different. I wanted to keep my steering wheel controls as well as the ability to listen to over the air radio. Here are the parts I used:
  • Asus Nexus 7 (2013):
    • Elemetalx Kernel for OTG/chariging functionality
    • Android 4.3 AOKP
  • Alpine KTP-445U
  • D-link 4 port USB hub
  • Custom OTG cable (more on this later)
  • Keedox RTL SDR
  • DROK DC-DC voltage converter
  • RCJoyConn steering wheel adapter (more on this later)
  • Metra harness, double DIN adapter
  • Bluetooth OBD2 adapter
  • Misc parts, cables, connectors I had lying around
I'll put up the results before diving into the whole process:
I'm very satisfied with the results. Everything works well and looks pretty good!



Well, that's the result. Now for the interesting part. The first hurdle i found was that OTG functionality was very limited with Android 4.4. I downgraded to 4.3... Not much worked . Secondly, while in USB host mode and connected to my powered USB hub, it would not charge. Even after I hooked it up using a USB Y cable. After doing some research I found Flar2's ElementalX Kernel on XDA-developers (http://forum.xda-developers.com/show....php?t=2249774). This guy enables OTG USB host mode and charging at once... It also allows for overclocking!
With that out of the way, OTG and charging was enabled (It's also running at +250MHz clock and can underclock to about 500MHz)



With the chraging while in USB host mode sorted out, I tested out the Keedox SDR (Software Defined Radio). It allows the tablet to recieve FM radio. I used SDR Touch to control the FM receiver (https://play.google.com/store/apps/d...ndrosdr2&hl=en)



Second Issue: The tablet is expecting the otg cable to be unplugged with each use. Therefore if I powered down the USB hub (simulating turning off the car), and powered it back up (turning on the car), the tablet would charge, but no USB recognized. I found out the USB OTG cable is a Male USB micro B to female USB A with the 4th pin grounded. The OTG cable diagram is courtesy of a google search.





I used a 12V relay SPDT with the coil powered by the accessory switch on the metra harness to toggle the ground. The Sense pin is grounded when the car is on.

Now the tablet "thinks" the cable is removed when the car is turned off and plugged in when it turns on.

Everything was working quite well. I busted out the 12V/5A supply for more testing! I had first used a LM7805 regulator that can handle 1.5 amps. It did not last, after about 1 minute it burned up. I used the the DC-DC converter to bring the 12V down to 5V without any real heat generated. The device is rated for 100W at 12A, I'm pulling about 7W (5V at 1.25A).



Now I have 5V power, FM radio, OTG with charging. For the steering wheel control I used a device from a gentleman (or lady) in Korea. It reads the resistive controls from the car and translates them to customizable keys. I used volume up, down, next track, prev track on the default steering wheel buttons. I'm using the 'Mode' button for pause and the 'hang up' for screen off. Here is a link to the module's website http://www.rcjoycon.com/base_3/menu_...m_board_idx=14

I used Tasker to wake the tablet when power is applied (car is turned on) and to shut down the GPS, bluetooth, and lock the device when it is removed (car is turned off).

I used a piece of aluminum and some 3M VHB tape to secure the Alpine amp to the car, the wiring harness, USB hub, DC-DC voltage converter and the radio module were taped to a piece of acrylic.





The tablet is pressed against the double DIM adapter, the adapter is taped to the car's trim piece (Using the 3M tape as well)

I used the Bluetooth OBD 2 adapter for the Torque app. Best 30$ spent on this project!



Still to do/fix:
  • There is an screech comming from the tablet whenever the tablet's audio driver is turned off (e.g. music is paused/stopped for more than 30 or seconds) .
  • The USB hub does not always come on. I have to restart the car in order for it to be detected.
  • Breaking out the power and volume rocker for the passengers or so that i don't need to pull the car's trim off to power up the tablet.
  • Adding a signal splitter to the amp so I can use the Aux jack in the center console if I want.
  • Adding the center console USB connection to the hub.
  • The steering wheel control module behaves like a keyboard. The tablet removes the on-screen keyboard. I have to go into the settings and disable the hardware keyboard (steering wheel controls still work though) in order to get the on-screen keyboard to show up.

This is longest post I've ever written. Let me know what you guys think.
Thanks for reading.

PS: Sorry for the terrible pictures. I took them while working things out, troubleshooting, I ended up just using my phone.

PPS: I also appologize for any forum faux pas. While I am not new to reading forums, I am new to posting.
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Old 02-04-2014, 11:56 PM   #2
Siress
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How does the KTP445U sound?

I've been planning an install myself for quite some time. The Alpine KTP-445U was a very tempting piece of gear, but powering 4x40W,4ohm drivers and 2xTweeters via, I'm assuming, passive crossovers hidden somewhere in the car, makes me worry that trying to power them with the little 445U would exacerbate the 1% THD rating when trying to drown out the engine (for the few songs worth drowning out the engine with......you're right, there are none...I'm sorry.)
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Old 02-05-2014, 12:48 AM   #3
socalwrxx
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Looks really good! I'm planning to do my own install very soon..

How was fitment with the nexus 7 and metro double din kit? any modifications or fabrication? how is the nexus attached? thanks
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Old 02-05-2014, 09:38 AM   #4
July57
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For my purposes, the power pack sounds great. Much better than the stock head head unit. It doesn't seem to be having any issues powering the speakers and tweeters. I assume the car has passive crossovers, the factory harness only has 4 pairs of wires for the speakers.

I had to cut notches into the double din bezel for the usb cable and the 3.5 mm jack. I also had to cut the right middle tab on the trim piece and the car dash to fit the usb cable. I also removed 2 plastic nubs near the screw holes where the amp is held.

The bracket that holds the amp in place has 2 pieces of acrylic that press the tablet to the double din bezel. It fits almost perfectly into it. The car's trim piece and the bezel hold it in place from the sides and the bracket holds in from the back.
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Old 02-05-2014, 09:40 AM   #5
July57
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What is 1% TDH? I tried searching but I couldn't find anything related to audio.
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Old 02-05-2014, 10:48 AM   #6
Siress
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From Crutchfield's website:
"The amount of change in harmonic content of the signal as it is amplified. A lower figure indicates less change and a more accurate amp. THD below 0.10% is inaudible."

Since the OEM speakers will push the upper limits of the KTP445U's abilities, I worried it would be a very noticeable distortion. However, I've just been reading about this stuff. It could all be marketing gimicks for all I know. Enjoy your setup, dude!

Are you going to try a USB/Wifi webcam? I've read on the Joycon website that you can wire a reverse light powerline to the C or D channels to signal the N7 to switch to rearview camera mode (though I think Joycon has a dedicated app in windows for this, whereas we'd need to use it to trigger an android event via keyboard hotkey)
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Old 02-12-2014, 09:38 AM   #7
July57
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I was toying with the idea of a USB rear view camera. But whenever I plugged my Web cam into the usb hub, the tablet would start using usb sound (as opposed to the 3.5 mm jack). I would also have to figure out a way to launch an app with the a keyboard shortcut (probably not hard). And finally figure out a way to mirror the camera's image. I may eventually get to it. I'm happy with the current set-up though.
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Old 02-12-2014, 10:06 AM   #8
S1000RR
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Quote:
Originally Posted by July57 View Post
I was toying with the idea of a USB rear view camera. But whenever I plugged my Web cam into the usb hub, the tablet would start using usb sound (as opposed to the 3.5 mm jack). I would also have to figure out a way to launch an app with the a keyboard shortcut (probably not hard). And finally figure out a way to mirror the camera's image. I may eventually get to it. I'm happy with the current set-up though.
Apparently using an Easycap (with a STK1160 chipset) and any type of non-USB backup cam will work with the Nexus. You just need to install this kernel module.

The FEBON100 looks like it may also work.

XDA thread: http://forum.xda-developers.com/show...ghlight=backup

Last edited by S1000RR; 02-12-2014 at 10:17 AM.
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Old 02-12-2014, 11:23 AM   #9
CorEnFa
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Nice looking install.

With all the Nexus 7 in-dash installs going on lately, I've decided to do my own. Once I have my post count where it needs to be, I'll post pics, etc.

Very nice work over all. What have you considered to be your biggest head-scratcher?

Cheers-
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Old 02-12-2014, 11:44 AM   #10
sumone
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wow that is awesome! I'm very tempted to do this now..
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Old 02-12-2014, 04:55 PM   #11
July57
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Quote:
Originally Posted by CorEnFa View Post
Nice looking install.

With all the Nexus 7 in-dash installs going on lately, I've decided to do my own. Once I have my post count where it needs to be, I'll post pics, etc.

Very nice work over all. What have you considered to be your biggest head-scratcher?

Cheers-
Thanks!
I'd say the biggest issue I had were with the nexus 7 firmware and os. In hindsight I think I should have gone with a samsung tablet or with the 2012 version of the nexus. Everything worked real well on my stock Galaxy s4. No need for rooting or flashing anything.
Secondly was getting the otg cable recognized when the car was turned off.
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Old 02-12-2014, 06:17 PM   #12
Siress
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Agreed about firmware and software being the most difficult problem.

I'm still in progress, but I wasn't going to pull the trigger on this without solving the 'head scratchers' first.

My solution for this is...
MultiROM manger running the following, will probably add ubuntu after it's installed.
  • CM11 M2 (M3 is out, so use that instead)
    • Native 16bit USB Audio support
    • USB OTG + Power support (IIRC, not to sure I've checked)
    • Just needs better customization, stability and DoubleTap2Wake for me to delete the following ROM...
  • ElementalX kernel with ASOP 4.4 ROM
    • USB Media Player Pro
      • HD USB audio for local files ONLY.
    • No need for access to hardware buttons (except on/off)
    • GravityBox Xposed module
      • Great UI customization
      • USB OTG+Charging
    • Requires several apps to support other features like StickMount for USB storage... Feels like you're getting two-dollared to death in the app store.

Last edited by Siress; 02-12-2014 at 06:22 PM.
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Old 02-21-2014, 03:08 PM   #13
July57
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I know what you mean with the app store!
By the way, I have not been able to get the factory pancake "sub" to work. It was my understanding it only took power, ground and front/left speaker inputs. It is getting power and the speaker signal from the harness.
Thanks.
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Old 02-21-2014, 03:40 PM   #14
Siress
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There needs to be a remote line as well. This tells the amp in there when to turn on.
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Old 05-05-2014, 07:25 PM   #15
flyboy1100
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How did you wire the joycon?
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