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Android Head unit install/write up


NAXJA Forum User
boston, ma

I had wanted an android auto head unit for a while, but they are pricey and most are double din which won’t fit in the cherokees 1.5 din radio slot. The single din adroid auto head units have motorized screens and are ugly. I recently switched to Google’s Project Fi for my wireless service, and was aware that they offer free data only sim cards that can provide wireless data for any device with a sim card slot. As it happened I had a couple year old nexus phone lying around that was available to use, so I set to work thinking through the whole install process.

Bezel design

Firstly I needed to find a way to mount it in the existing radio spot. I had not previously used a 3d printer, but have had a passing interest in them for a while, and decided that would be a good way to go to get a nice clean look for the mount.
I started by removing the aftermarket bezel that had been housing my pioneer head unit and used this as a reference for the outer tolerances of my design. I used calipers to very precisely measure the length, width, and depth of the bezel, and the size and location of the mounting tabs. I also used the calipers to get precise measurements on the phones outer dimensions, the screen dimensions, and the offset of the screen from the phones outer edge.
Measurements in hand I turned to Sketchup to start my design. Sketchup is a free design program with various applications. It’s not the most popular 3d print design program, but it’s free, user friendly and can convert the files to .stl format (via an extension) which is needed to output to the 3d printer. This was also my first time using Sketchup, but I found the learning curve to be fairly shallow and was quickly designing and navigating confidently.
If you are intimidated by sketchup, there are a number of tutorials online that will get you on your way quickly.
In the end my design ended up being in two pieces (for reasons I will explain below). There is the main front facing bezel piece which frames the phone and supports the phone, and has a space for the volume knob, and a rear piece which helps to hold the back of the phone in place so that it doesn’t move when the screen is being interacted with.
There are various types of 3d printers out there, and they have different strengths and shortcomings. The printer at my library is a makerbot replicator 2. It’s a beginner machine for sure, and one of its shortcomings is that it can’t print overhanging structures, i.e everything that is printed has to have material below it. The other is that the finish that comes out isnt very pretty to look at. With these in mind I decided to use the library printer only for the back piece. It has no unsupported structures and will be out of sight, so I figured the library would be a good match for this part, and the price (free) was certainly right.
There ARE ways to get a nicer finish from these units with some post production work, but since my design was easiest to implement with unsupported structures, I turned to an online company called Shapeways for the main bezel piece. The printer they use can print unsupported structures, and they post process the piece to provide a much nicer cleaner finish.
Using shapeways was painless. You upload your design, and it runs it through a program to ensure that your design is 3d printable. Once it does that, you choose your material and color, and then they get to work. Mine did take a little longer than was first estimated, but it sounds like this was because the piece got broken in the finishing phase and they had to go back to square one. All in all I’m glad they took the time to do it right and send me a good piece.
This should go without saying, but be sure your measurements and design are complete and correct before submitting it. The piece cost me about 50 bucks and took about ten days to get to me. If you submit an incorrect spec and they build it to your spec you’re out of a chunk of change and a fair bit of time.

Sound design

There are a couple ways to approach the design of the system after we get the phone mount set up and we get sound coming down the wire.
I decided early on that I wanted a volume knob. It would be possible to just use a volume slider on the phones screen, but I like the tactile act of turning the knob and want to be fiddling around on the screen as little as possible. In addition to that, I think it adds a nice look to the finished product, and as you can see in my design, the knob actually provides a clever way of securing the phone in place.
Past the volume knob I have a noise isolator, an EQ, and a small 4 channel amp to power the door speakers and the rear speakers in my jeep. You could do this without the EQ and just the small amp, or you could even reuse your aftermarket head unit as an EQ and amp if you really want to keep the cost down. You’d have to be clever about finding a place to bury it, and it’s not really ideal, but it is possible.
As far as signal path goes, it leaves the phone via the hadphone jack, goes into the ground isolator, then into the knob. Out of the knob it goes back to the eq which it mounted under my back seat next to the sub amp. From the EQ it goes back up front via 4 RCA cables to the Alpine KTP-445U amp which drives the door speakers and rear speaker. I have this amp tucked in the factory radio area behind the phone.

Usb power

Obviously the phone needs to get power from somewhere, and this proved to be a bit more of a challenge than I had expected. I will write about my experience, though I imagine it could be different for different phones.
My phone that I used for this project was a Nexus 6P. This phone charges via USB-C. My initial plan was to use a 12v female USB-A adapter wired from the cigarette lighter power wire to pass power through a USB-A to USB-C charging cable. Unfortunately this setup wasn’t able to provide enough power to actually charge the phone, so I went back to the drawing board. I decided to take apart a fast charging USB-C cigarette light power plug and solder wires to its contacts to wire up to a switched ignition source. It’s very important to use a switched power source and not a constant source. There are two reasons for this, the first being that if you use a constant source, your phone will drain your car battery and you’ll have a dead battery. That’s not fun! The second is that we use the charging current to tell the phone to turn on/wake up.

Phone alterations

There were some light changes to the phones software/UI that need to be made to make this all come off smoothly. Depending on your comfort level with this, you may choose to do it differently than I, but personally I’m quite happy with my setup, and if the first sentence here struck fear in your heart, fear not, it’s actually pretty easy.
First off you need to install a launcher that will allow your phones home screen to operate in landscape orientation. I chose Lawnchair as my launcher. It closely replicates stock android with some added options that let you use the home screen in landscape orientation, and change the icon size so they are easier to hit on the phone. You can use whatever you like, but the landscape option is a must.
Secondly you need to enable developer options on the phone. This is really easy to do (just google it) and once you do that, you can enable a setting that keeps the screen awake when it is receiving charge. This way the screen is always on, and will turn on as soon as you turn the key to the on position.
Lastly, and this is the hardest part, you need to use ADB to change a line of code on the phone. This is supposed to be fairly easy, but I had a hard time installing the tools on my Mac, so I enlisted the help of a more computer savvy friend with a PC to help with this. This doesn’t have to be done for all phones, so you may be able to skip this step. What we are doing here is telling the phone to turn on from a powered down state when it gets a charge. Some phones are programmed like this, but unfortunately mine was not. It took my friend and I about 15 minutes to do this. This is pretty important because if your car sits for a few days the phones battery will run down and you won’t be able to power it back on without removing it, which would be a pain in the butt.

Finished product

The end result is really clean. The phone has a data connection when it needs it, can run navigation and control my music. It wakes with the cars ignition, and will power on from a powered down state when it gets a charge. The bezel fits perfectly and looks almost like a stock setup, save for the fact that the tech wasn’t available at the time of the jeeps production.