Nexus 7 Tablet Install for Dummies (Guide)

[Infosecdad]

Just curious - any advantage to getting the LTE Nexus? Can it be added to an AT&T prepaid plan where we never use all the data, to do things like nav? Or surf the web when NOT DRIVING?

 

That would be useful for sure, I couldn't find one for a reasonable price when I was looking, so I tether to my iPhone for Nav and streaming on trips.

[xt2005bonbon]

Also, does the OTG cable/hub work to attach extra storage? SSD attached to USB adapter? If so, getting the 16GB version shouldn't be that bad, right?

 

I have a usb hub where four devices are connected to it: a 128 GB usb stick, a usb dac, a vagcom cable, and a USB VC grabber. All of that stuff is connected to a 16GB nexus 7.

[utc_pyro]

Is there a good way to go about this WITHOUT using Timur's rom? I'm trying to build a mini version with a phone, and have been using iOS so long I dont know where to even start over in Android land.

[funkycharms]

Is there a good way to go about this WITHOUT using Timur's rom? I'm trying to build a mini version with a phone, and have been using iOS so long I dont know where to even start over in Android land.

 

What features specifically are you looking for? If you plan to use a phone, i'm assuming this won't be in the dash?

 

What is good about timur's rom is that it powers on and off with the car because the power button is not accessible and has a few battery tweaks. Besides that, it's just a regular android OS. I don't see why you can't run an OTG cable to your smart phone, purchase BTSSM software, etc...

[utc_pyro]

What features specifically are you looking for? If you plan to use a phone, i'm assuming this won't be in the dash?

 

What is good about timur's rom is that it powers on and off with the car because the power button is not accessible and has a few battery tweaks. Besides that, it's just a regular android OS. I don't see why you can't run an OTG cable to your smart phone, purchase BTSSM software, etc...

 

It will be in the dash, built into the cubby door actually. I have another mount for my iPhone that I'll keep using for music, calls, or whatever.

 

I want to auto on-off functionality with it in a super deep sleep mode when off. When it turns on I'd like it to go to some launcher that would have BTSSM, waze, and android auto quickly accessable. I remember seeing apps that did the latter back when I was using android, so it's more the startup/super sleep automation that I need help with.

[solidxsnake]

It will be in the dash, built into the cubby door actually. I have another mount for my iPhone that I'll keep using for music, calls, or whatever.

 

I want to auto on-off functionality with it in a super deep sleep mode when off. When it turns on I'd like it to go to some launcher that would have BTSSM, waze, and android auto quickly accessable. I remember seeing apps that did the latter back when I was using android, so it's more the startup/super sleep automation that I need help with.

 

I use a custom-modified version of the ElementalX kernel (version 4.05) with SlimLP 5.1.1. Pretty much, I took the EX-4.15 kernel and merged Timur's USBHost hack into it.

 

In general, you can use any ROM you want (in fact, I don't particularly like Timur's since it's not particularly configurable, and the way he handled putting a pay-wall on his kernel, which derives from the AOSP project really irks me, to boot), the only thing you need a modified kernel for is for the USB OTG + charging hack.

 

I use Tasker to handle all the automation on my Nexus 7 install. When the tablet gets power, it will turn the screen on, mount my SD card reader (which has all my music on it), open my music app and start playing it, enable wifi and bluetooth, and then return back to the home screen. When it loses power, it will pause and close the music app, unmount the SD card reader, close any other open apps, disable wifi/BT, and enter battery saver mode. This effectively forces the tablet into deep-sleep mode.

 

Here's a quick overview of my setup:

 

Finally finished (well, mostly) my in-dash Nexus 7 install:

 

 

Showing some of the basic features (music, BtSsm, Waze/Google Maps). SlimLP gives me some extra buttons in the nav bar that I use for previous/next track. Also gives long-press options for all of the nav buttons. I use a long-press on the recents button to shut off the screen, and a long press on the home button to open up the power menu (like I hit the power button). Running SlimLP 5.1.1 and my modded version of the ElementalX-4.05 kernel (details in my previous post).

[utc_pyro]

USB OTG+charging isn't a huge deal for me as I was planning on using the Qi charging port for power. Currently I have Cyanogenmod/LineageOS 14.1 on it, but cell data is being glitchy so I may need to change to something Android 6.0.1 based.

 

I do need to ether find a way to kill OTG power with IG/ACC is off though. Is this best accomplished by powering the USB 5V separately, so doing something in tasker?

Edited May 16, 2017 by utc_pyro

[solidxsnake]

USB OTG+charging isn't a huge deal for me as I was planning on using the Qi charging port for power. Currently I have Cyanogenmod/LineageOS 14.1 on it, but cell data is being glitchy so I may need to change to something Android 6.0.1 based.

 

I do need to ether find a way to kill OTG power with IG/ACC is off though. Is this best accomplished by powering the USB 5V separately, so doing something in tasker?

 

If you're doing a fixed-install, you won't be able to rely on Qi charging to power and keep the tablet charged, the rate of charging is just too low (unless you keep the tablet display off the whole time).

 

Without one of the USB OTG + charging hacks, you won't be able to kill OTG power. Regular OTG functionality (by the USB spec) means the tablet will power the devices plugged into it. You could, I suppose, make a custom USB cable where the ID pin is connected to COM through a NO relay. When there's IG/ACC power, the relay will close and connect the ID pin to COM (enabling OTG mode). That involves some custom wiring though.

[utc_pyro]

It will be a fixed install, but the Qi charging wont be Qi, it'll be straight into the power ports under the back cover: https://forum.xda-developers.com/showthread.php?t=2722657

Testing this with my bench supply works fine, haven't checked the charge rate though.

 

I'm fine with building any sort of custom cabling as needed. My question on the power is more, what happens if I DON'T used the 5V+ from the USB OTG and instead power the USB devices by an external regulator that's switched? With the phone freak out or is this allowed by the USB specs?

 

The idea of messing with the ID pin is a good idea though, I need to find an angled USB pigtail with the ID pin broken out.

[solidxsnake]

It will be a fixed install, but the Qi charging wont be Qi, it'll be straight into the power ports under the back cover: https://forum.xda-developers.com/showthread.php?t=2722657

Testing this with my bench supply works fine, haven't checked the charge rate though.

 

I'm fine with building any sort of custom cabling as needed. My question on the power is more, what happens if I DON'T used the 5V+ from the USB OTG and instead power the USB devices by an external regulator that's switched? With the phone freak out or is this allowed by the USB specs?

 

The idea of messing with the ID pin is a good idea though, I need to find an angled USB pigtail with the ID pin broken out.

 

You should be fine with that, just make sure you have no connection to the tablet's internal +V USB pin (eliminate that from the USB connector). On second thought, that should work just fine, even without separating the ID pin. Once your external devices lose power, they should just disconnect from the tablet cleanly. Surely shouldn't hurt anything to try. Just make sure the COMs are connected from your external +5V supply and the tablet.

[utc_pyro]

Are you saying I should backfired 5V into the USB port even if running on external power?

 

Also you may be right on the Qi not cutting it deal. I'm measuring 800ma with 4.65v input, but the charge rate with the screen on is close to nill. I'm not seeing an easy way to turn ACA (USB host + charging) on in the kernel source code, but people have done it on the similar S5 mini so it may be possible.

Edited May 17, 2017 by utc_pyro

[SubOperator]

to slightly divert this : is nexus 7 tablet the only choice we have for this project? the newest one discussed is from 2013 and is 4 years old at this point.

 

hardware went a long way since then.

[solidxsnake]

Are you saying I should backfired 5V into the USB port even if running on external power?

 

Also you may be right on the Qi not cutting it deal. I'm measuring 800ma with 4.65v input, but the charge rate with the screen on is close to nill. I'm not seeing an easy way to turn ACA (USB host + charging) on in the kernel source code, but people have done it on the similar S5 mini so it may be possible.

 

No, I'm saying the exact opposite. Of the 5 USB pins on the tablet's port, you should completely float the +V pin, but connect the D+, D-, COM pins (with the ID shorted to COM) to your USB hub/devices. The +V pin on your USB hub should only be connected to your external 5V source, and the negative terminal from this source should connect to the COM pin from the tablet.

 

As for the OTG + charging hack, take a look at the diffs of the code for my modified version of the ElementalX kernel at my GitHub account. I pretty much just took Timur's USBROM code and merged it with a fork of the ElementalX code. Works wonderfully for me. You can configure the USBHOST settings through sysfs (/sys/kernel/usbhost if I remember correctly). Essentially you need to modify the USB handshake/connection state machine in the kernel USB driver code to change how it handles power management when in USB host mode.

 

to slightly divert this : is nexus 7 tablet the only choice we have for this project? the newest one discussed is from 2013 and is 4 years old at this point.

 

hardware went a long way since then.

 

No reason not to use any other device. The N7 2013 is just a very nice size, very cheap, and all of the software work has pretty much already been done, so it's a popular choice.

Edited May 17, 2017 by solidxsnake

[SubOperator]

 

No reason not to use any other device. The N7 2013 is just a very nice size, very cheap, and all of the software work has pretty much already been done, so it's a popular choice.

 

Got it, makes sense.

 

Is there any link I can read that describes process of converting N7 2013 from plain vanilla stock to unit ready to go in the dash? Instead of asking million questions here...

 

Also, how to handle the JDM navi bezel coming without air duct adapter for most sets sold here? did you guys mock something up, or just left central vents non-operational?

[solidxsnake]

Got it, makes sense.

 

Is there any link I can read that describes process of converting N7 2013 from plain vanilla stock to unit ready to go in the dash? Instead of asking million questions here...

 

Also, how to handle the JDM navi bezel coming without air duct adapter for most sets sold here? did you guys mock something up, or just left central vents non-operational?

 

Pretty much it's as simple as flashing a kernel/ROM that supports USB OTG + charging. That's an Android-specific problem, not anything car related, so that's something to look up over at xda-developers or similar. If you haven't already seen the original "Tablet PC as Carputer?" thread, read through that to see various other setups. The rest of the software choices are up to you (what apps you like to use for music, navigation, etc.).

 

I'm not 100% certain about the vents, but I believe for a regular LGT (with a cubby and not the factory satnav system), the JDM ducts are more-or-less interchangeable with the USDM ones. However, in my spec.B, which came with the factory nav, the original vents were almost double the length of the JDM ones. To make it work, I just took a spare set of USDM ducts (from a regular cubby bezel) and just shoved them over the end of the JDM vents to extend them into the ducting in the dash, with a little bit of masking tape around the seams to seal it... it's not pretty but it gets the job done.

 

Check out the pictures in this FS thread for what I mean about sliding the regular vents over the JDM ones.

Edited May 17, 2017 by solidxsnake

[utc_pyro]

As for the OTG + charging hack, take a look at the diffs of the code for my modified version of the ElementalX kernel at my GitHub account. I pretty much just took Timur's USBROM code and merged it with a fork of the ElementalX code. Works wonderfully for me. You can configure the USBHOST settings through sysfs (/sys/kernel/usbhost if I remember correctly). Essentially you need to modify the USB handshake/connection state machine in the kernel USB driver code to change how it handles power management when in USB host mode.

 

Well this is going down a path I was never expecting to attempt in life: building a custom Android image. The stuff I was reading over lunch they were just modifying some configuration files in the charging settings.

 

So if I'm reading this right, you ripped out the USB fast charging function and replaced it with a new USB Host mode that supported fast charging?

[solidxsnake]

Well this is going down a path I was never expecting to attempt in life: building a custom Android image. The stuff I was reading over lunch they were just modifying some configuration files in the charging settings.

 

So if I'm reading this right, you ripped out the USB fast charging function and replaced it with a new USB Host mode that supported fast charging?

 

Pretty much. ElementalX already had USB OTG + charging, but it was extremely buggy (if you lost USB power on your devices, the only way to get them to re-connect was to reboot the tablet or physically disconnect/reconnect the hub).

 

Let me know what ROM you want to use. I already have the work done for the ElementalX modifications, so I can just re-compile the kernel for your ROM and save you the trouble.

 

FWIW, any AOSP ROM should work just fine. I'm using SlimLP (Android 5.1.1 AOSP-based ROM).

[FunkyDragon]

Thanks to this thread, and MANY youtube clips, I've nearly completed my build.

 

 

It's a 2nd Gen Nexus 7 (2013) with Timur's ROM, and Nova Launcher.

 

I've got a USB-DAC, and a JoyCon EXR module to tie into the steering wheel controls. I also modified the stock NAV buttons to act as a hard button for power and for Volume Down (so i can navigate the boot loader, and take screenshots if I need to), and will program the JoyCon to activate the home button and the task button.

 

 

I'm hoping to tie the DAC output into the onboard NAV's audio input so that the sound from the tablet plays over whichever input I'm listening to - so that i can get turn-by-turn while listening to the radio. - if anyone has a wiring diagram for that, i'd greatly appreciate it!

 

next steps are to rip apart my dash, and center console so that i can install this bad boy!

[Infosecdad]

That's awesome!

I had a similar mounting strategy with the brackets in the back of the tablet.

I choose to mount the USB hub under the shifter trim so that I could add/remove devices as needed without removing the tablet.

I love that you figured out ways to invoke the buttons, that will be very useful over time.

[xt2005bonbon]

mmmh. You are inspiring me now. Cause I just got a joycon exr as well so that I can use my steering wheel buttons. And just as you, I am using the oem nav bezel but without the oem buttons. But now, I might as well get these buttons and do the same thing you are doing. I may pm you

[FunkyDragon]

mmmh. You are inspiring me now. Cause I just got a joycon exr as well so that I can use my steering wheel buttons. And just as you, I am using the oem nav bezel but without the oem buttons. But now, I might as well get these buttons and do the same thing you are doing. I may pm you

 

I ended up cutting a micro USB cable in half, and soldering half to the nav buttons, and the other half to the ribbon cable that controls the power/volume buttons. that part was hard, as it was difficult to get the solder to rest in one spot. the Mini USB cable has 5 pins/cables, so i was only able to connect 2 buttons (Positive and ground) and cut the 5th wire. I also tried using a Cat-6 ethernet cable, but the solid copper core would not take the solder at all, and kept coming loose. once all connections on the tablet were in place, i ran a thin line of hot glue to kind of keep it all in place. i had to cut off the bottom part of the tablet's casing in order to snap it closed, but I'm happy with how it turned out.

 

for the electronics board in the NAV buttons, that took a little deciphering to figure out where to solder the other cables. here's a pic. Red circle is the positive, blue circles are the ground. i've included pics of both sides of the board. I recommend using a thin gague wire (like the USB cable, or the included JoyCon EXR cables) and applying a little bit of solder, then thread THROUGH the pin-holes highlighted. then top it off with some solder on the bottom of the board to keep the wires in place.

 

[xt2005bonbon]

As you know, in order to get the steering wheel buttons to work with the joycon exr, you had to find the two wires hidden under the steering wheel column and connect them to the joycon exr.

So I am guessing you can't just find the 'magic' two wires out of that white connector found on that circuit board you're showing here?

[FunkyDragon]

As you know, in order to get the steering wheel buttons to work with the joycon exr, you had to find the two wires hidden under the steering wheel column and connect them to the joycon exr.

So I am guessing you can't just find the 'magic' two wires out of that white connector found on that circuit board you're showing here?

 

I honestly didn't have the patience to try it. but if i had to GUESS, bottom picture, just under the connector - the pins all the way to the left.

[xt2005bonbon]

It's true that there are a lot of pins on that connector, which would require a lot of testing with a multimeter.

 

Ok, I think I want to do this now cause it looks super clean. Now onto sourcing this board .

[utc_pyro]

Let me know what ROM you want to use. I already have the work done for the ElementalX modifications, so I can just re-compile the kernel for your ROM and save you the trouble.

 

FWIW, any AOSP ROM should work just fine. I'm using SlimLP (Android 5.1.1 AOSP-based ROM).

 

Wow, thanks for the help solidxsnake! Truth be told I haven't researched the optimal rom to run for this, but was leaning toward CyanogenMod 13 or AOKP MM (6.0.1) just from past experience. Unfortunately ElementalX and SlimLP arent supported on my devices (Galaxy S5, kltespr) so the modified USB host will need to be transplanted into a different rom series.