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Thread: Another Nexus 7 Subaru Install, but this will be a bit different.

  1. #1
    Constant Bitrate zapwizard's Avatar
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    Another Nexus 7 Subaru Install, but this will be a bit different.

    I have been posting this in the Subaru forums, but forgot to start a thread here too.

    When I bought my 2010 Forester, I started a Car PC project the first week I had it. (I have had a Car PC in every car I owned previously.)
    However, I never really finished it, because the software and control systems just never really worked well enough for daily use.

    Fast forward a few years, and now there is lots of ways to make a good car PC from a Tablet. The Nexus 7 just went for $130 a few weeks back, and so I thought what the heck. Dozens of people have done it.

    I have a very long commute, and so far have been using a iPhone for audio books, podcasts and music. However it is a pain (and mess) to always have to connect up the cables, launch my audio, and then launch waze. Not to mention having to switch between apps all the time.

    For the past week I have been living with the Nexus in the car, and I have to say I like it. The screen size is perfect, and with Tasker and Timur's Kernel it is easy to customize and configure.

    So here is the start of my project log. I will reserve my first few posts to keep sections on my plan, hardware, and software.

    Here is the teaser:




  2. #2
    Constant Bitrate zapwizard's Avatar
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    If you put a Nexus 7 in front of the Bezel, it almost fits perfectly width-wise. It is a bit too tall, but I plan on using that to my advantage.

    What I plan on doing is constructing my own docking station. The docking station will have five pogo pins. These are a USB-on-the-go connection and will provide data connection.
    I don't want to use the Pogo pins for primary power (or USB for that matter). Instead I will install the Google Nexus wireless charger into the dock. I may install it completely hidden behind the dock, or I may leave it exposed since it has a slick glass surface and Nexus logo.

    Th wireless charger has four magnets, if they can hold the tablet well enough then great. Otherwise I can always add more magnets and thin metal plates to the inside of the case.

    --------------




    Here is a CAD rendering of the Charger, pogo pins, and four extra magnets to help hold the tablet. (I am a mechanical engineer, so CAD comes first for me)

    --------------

    Here is a rendering showing how I plan on arranging the dock, super-imposed over a shot from my previous build.




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    (THIS IS NOT A PHOTO OF THE INSTALL!)

    Here is a rendering showing what the tablet might look like while docked.
    I still haven't decided if I will cut away any of the existing bezel to make the tablet more angled or not.

    I have an extra bezel, and I may end up heavily modifying it to make the end result more slick. Until then I will make a basic mount which works without cutting the bezel.

    --------------



    The pogo pins will make contact with five small pads inside the Nexus 7. These pads are not part of the original design of course.
    What I will do is remove the back, and drill five small holes.

    There is plenty of space between the battery and rear of the case for some thin contacts, there is also nothing electrical on the inside in this area. I will make the contacts from thin copper tape adhered to double sided tape. The five contacts will then be soldered to pins on the USB connector. (Wired internally)

    The end result will be a tablet that looks stock, other then five small holes on the back. It will still be perfectly usable as a portable tablet.

  3. #3
    Constant Bitrate zapwizard's Avatar
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    Today's progress was making a wireless charging mini-keyboard.

    I want to use my Logitech Dinovo Mini keyboard in my car PC. However the keyboard was designed long before USB micro was a standard power source, and certainly before cheap wireless power.

    The existing power adapter uses a tiny hard to find barrel plug, and who wants another loose cord inside the car?

    Parts:
    Logitech Dinovo Mini Keyboard (original Bluetooth version)
    Qi Wireless charger pad
    Qi Wireless Charger USB receiver.

    ----------------



    First I removed the battery and battery cover.

    ----------------



    Logitech is famous for hiding screws behind their labels. Time to void the warranty (which expired many years ago).

    ----------------



    I then removed the two hinge covers which are just snapped in place, under them are two screws holding the keyboard cover in place.

    ----------------



    To completely remove the cover you have to tilt the lid forward a bit, but it comes off easily once all the screws are off.
    The mouse-pad is connected using a thin ribbon cable, I loosened the connector and pulled the cable.

    ----------------



    I remove the keypad, revealing the raw PCB. In the top-left corner is the power input. It takes 5 volts.

    ----------------



    I soldered two wires to the Qi compatible wireless module. The output of the module is a two-pin USB mini connector, it was easy to figure out the pinout and to solder to the terminals.

    I tested the output with a multimeter and get exactly 5V.

    ----------------



    I soldered the Wireless receiver into the two spots where the power input goes to.

    ----------------



    I trimmed away a small cutout for the cable to travel to the battery compartment.

    ----------------



    I tested that the circuit works and the Dinovo Mini charges.

    ----------------



    The receiver is simply stashed in the battery compartment.

    ----------------



    It works!

    The keyboard charges on the Qi pad, no issues.

  4. #4
    Constant Bitrate zapwizard's Avatar
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    Okay, time for the hard part.

    Adding a DIY flex-PCB to the inside of the Nexus 7.

    The PCB will connect to the USB connector internally, and have one extra contact for me to sense when the Nexus is docked, and enable power to the whole system.

    -------------------------------------



    First I took apart the Nexus 7, there are plenty of guides on how do this. I prefer the ones at iFixit.com

    -------------------------------------



    The Nexus is even still functional with the back removed. I did however disconnect the battery during these mods, just to be safe.

    There is a nice large flat area at the top of the battery. It is empty, and perfect for this modification.

    -------------------------------------



    I then used a large sticky note to layout the plan for the PCB shape and location. I took care to stay clear of the Wireless charger area, and any exposed traces.

    The pads are on 10mm centers, and 38mm from the middle of the tablet.


    -------------------------------------



    I used double sided tape to transfer the sticky note to the back of the case without any alignment error.

    I double checked that the holes were properly centered and level from the edge.

    -------------------------------------



    I drilled pilot holes from the inside, then drilled the outside holes using a stepped bit which cuts plastic much cleaner then a traditional drill bit.

    -------------------------------------



    Then using the back as a template, I marked the location of the landing pads for the pogo pins. The flexible PCB material is a single sided copper layer over flexible plastic. I bought it at Adafuit.com. The material is Pyralux, and it can be chemically etched just like any PCB.

    -------------------------------------



    I am not going the pretty route here, functional is key. That means a quick and dirty PCB trace job using the tried and true method of drawing a mask with a sharpie. You can see the test piece also which I etched first as a test.

    -------------------------------------



    Etching took about half an hour. In the mean time I tested soldering on the test piece, and it takes solder very well without curling up.

    -------------------------------------



    After etching. I wasn't as careful about keeping off finger prints as I should have been, but with just a little bit of clean-up, and one repair from a tear, the flexible PCB is done. Each contact checks out okay, no shorts, and everything is properly connected.

    -------------------------------------



    Using thin double sided tape, I adhered the PCB in place over the battery.

    -------------------------------------



    I soldered the PCB to the connections on the USB connector. I doubled up the wires on the ground and +5V signals.

    I then double checked each contact, again no shorts and good contact from the USB connector to the pads.

    I tinned the pads with some solder, as silver solder won't tarnish quite as fast as raw copper.

    As a precaution I used some clear tape as a crude solder mask. There really isn't anything on the inside of the back panel which would contact the PCB.

    -------------------------------------



    Here it is with the back of the tablet in position. (Not fully assembled until I build a prototype of the other half for testing.
    Once its fully assembled I will have a dock-able tablet.

  5. #5
    Constant Bitrate zapwizard's Avatar
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    I decided to prototype to actual dock using some wood. It just a few minutes to mock it up with the pogo pins and magnets in the right spots.

    The prototype showed that the magnets work well to align the tablet, however there isn't enough pressure near the pogo pins to reliably keep a connection. The solder pads also weren't reliable enough, they required constant pressure to keep contact. It wouldn't work while driving on a bumpy road for example.

    ---------------------------------------



    What I needed was a small reliable target for the pogo pins to make contact with, I also need it gold plated to help keep it working over time.

    The solution was to use the ends of a PC power supply contact. I had some which were already cut, scavenged from a old power supply. They are the perfect diameter, but of course way too long.

    ---------------------------------------



    To get small rings I can solder down to my flex PCB, I used a dremel tool and carefully cut 6 rings of equal length from the end of each molex contact. (Okay I ended up cutting eight, since two of them ran away and hid somewhere in the garage)

    ---------------------------------------



    I carefully aligned and soldered each ring to the flex PCB. Again checking for conductivity and shorts afterwards.

    ---------------------------------------



    Next I needed a solution to keep more pressure near the pogo pins. Such that they remain compressed while docked, and their 90mil travel distance can be used to eat up any bumps in the road.

    The solution was to mount a pair of magnets next to the pogo pins.
    I super glued each magnet to a thin steel washer to act as a anchor inside the case, I trimmed off part of the washer to keep it away from the solder contacts. I also applied some electrical tape over them after taking this photo as extra insurance.

    ---------------------------------------



    Here is a close-up of the contact rings and magnets. Any misalignment you may see was due to my drilling holes the actual contacts are all 10mm spaced apart to match the pogo pins.

    ---------------------------------------



    I modified my dock with a corresponding set of magnets.

    ---------------------------------------



    I threw the tablet onto the dock with a USB DAC connected and it works! The connection is now very solid, it takes quite a bit of force to dis-lodge the tablet, and no amount of shaking caused the USB to disconnect.

  6. #6
    Constant Bitrate zapwizard's Avatar
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    Here is a rendering showing the current design.

    ---------------------------------------



    Behind the tablet is a SD card reader. The SD card connects to a USB reader mounted behind the face.

    ---------------------------------------



    The mount is the key to this design. I am having it 3D Printed by a guy here in Austin. I found him on Makexyz.com, and the part costs about half of what I would have paid for an online printer. Since I plan on sanding and painting the final part, the actual layer look of a 3D Printed part shouldn't be an issue.

    The mount will screw directly to the bezel, allowing the design to be removed and serviced.

    ---------------------------------------



    By using a 3D Printed part I am able to custom design the mount to work the way I want.

    The pogo pins are inserted at the top. The magnets will insert into holes in the front, with small ejecting holes at the back in case I have to remove them. I plan on using pressure fit at first, then gluing them once everything is working.

    The PCBs are all removed from their original housing to save space. Each PCB will have its USB connector removed, and a shielded cable soldered in its place.

    The blue PCB is a 7 port USB HUB. I bought it for literally $3 while on a trip to China. It is the smallest hub I have and it shares a single +5 rail, which will making powering everything easier.

    Below it is the Joycon Ex steering wheel controller. It also will trigger the reverse camera. The green PCB is a USB video capture card, it will connect to the yellow RCA for the rear camera video feed. The orange PCB is a SDR Radio receiver, it will connect to the cars antenna jack. You can also see the SD card reader installed behind the RCA connector.

    Finally two more USB ports will allow me to connect to the USB DAC, which will be installed directly onto my amplifier. And I have one extra USB port which I can use for a more accurate GPS receiver.

  7. #7
    FLAC SNOtwistR's Avatar
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    Nice detailed thread. Great for people doing similar mods. Keep up the great work! SNO

  8. #8
    Maximum Bitrate RAWPWR's Avatar
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    I'm impressed, excellent work indeed. :-)

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