Wednesday, June 20, 2012

Android Tablet as Car PC

Android Tablet as Car PC
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An android tablet ia a logical choice for a car PC. The device offers additional features beyond regular car stereos. While many car stereos have GPS, the android device offers a more intelligent GPS. It has all of your google contacts addresses already in the GPS, it has your calendar with events and their locations, Chrome to phone can automatically send directions from your computer to your car. The device can store music, use internet radio, or play music using a cloud player such as Amazon cloud. These are features not available on even the most high end luxury cars.

I recommend choosing a tablet that already has a car dock. This dock can be easily modified to be permanently installed where a double din CD player would normally go. Also, with a car dock, the device will be easily removable so you can prevent theft and use the tablet elsewhere.

Wire Strippers/Crimpers
Soldering Iron (Recommended)
Screw Drivers
Dremel with Cutting Blades

Tablet with Car Dock ( I chose Samsung Galaxy Tab 7+)
1/4" Sheet Lexan (Approx 10"x6")
1-1/4" Hole Saw
3/8" Drill Bit
Car Audio Adapter
Spade Plugs
Wire - Heavy Gauge to Power Amp
Wire - Medium Gauge for Speaker Signals
Electrical Tape
Scotch Tape

Step 1The Audio

Replacing the stock stereo unit with a android tablet requires an external amplifier for the sound to play through the speakers. I choose a 4 channel amplifier. Four channel because my car has four speakers. I have the amplifier mounted under my passengers side seat, but the amp could be mounted just about anywhere.  I chose just about the cheapest amp I could find.  I don't listen to much music, mostly audio books and podcasts, so I was not too concerned with sound quality.  I do listen to music using this amp and it sounds good enough for my ears.

Step 2Wiring the Amplifier

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The amplifier will be powered directly by the battery.  This will involve running heavy gauge wires from you car battery to the amplifier.  Read the instruction manual of the amplifier to determine the necessary wire gauge for powering the amplifier.  There are kits online that have pre-packaged wire for amplifiers or you can save yourself some money and go to the local hardware store and get them to cut a few feet of wire for you.

Step 3Amplifier Location

The amplifier is out of the way in the truck of a car, but it is also a long way away from the battery.  I chose to mount the amplifier underneath the passengers seat to limit my cable run lengths.  The seat had to be removed but this is actually quite easy.  Only four bolts hold the seat in along with the wires for the occupancy detector for the airbags which has to be unclipped.

Step 4Amplifier Tools and Accessories

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You will need a crimper to crimp spade plugs onto the end of each wire.  I have some spade plugs that have heat shrink around them which I think is really cool and looks very professional.  You will also want loom to cover the wire inside the engine compartment.  High temperature loom is highly recommended.  The loom may be hard to find at local stores but is available at McMaster Carr.  You can tell the difference because high temperature loom will have a gray stripe on it.  This loom is specifically designed for high temperatures locations like that of an engine compartment.

Step 5Amplifier Power Warning

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Also, you have to put a fuse in the power cable of the amplifier.  Radio shack sells small waterproof inline fuse holders that can be used for this.  Very Important: Remember to put a fuse into the power cable for the amp as close to the battery as possible.  Without this fuse, a short can set your car on fire.  Yes really.

Step 6Running Wire Through Holes in Metal

Also, to get the power from your battery to the amplifier you will probably have to drill a hole in your firewall of your car.  You may be able to poke the wire through a hole already there, but it is quite easy to drill a hole in the firewall.  Here or anywhere you run wire through a hole in metal use a rubber grommet.  This will prevent the jacket of the wire from being worn down from rubbing on the metal.  I have a small hole in the passengers side footwell.  The power cable for the amplifier runs through the hole, directly under the carpet, up through a hole in the carpet underneath the seat to the amplifier.

Step 7Amplifier Sound - Vehicle Harness Adapter

For attaching the amplifier to the speakers, I recommend you buy the adapter for connecting an aftermarket stereo to you stock system. This will prevent you from needing to cut any of the wires in the car.  If you go to Crutchfield's website and look to buy an aftermarket stereo there will be two adapters.  One for you car and one for the stereo.  These adapters are labeled and have short stripped wires on each end.  Simply order the one that is for the car and attach it to the plug that was originally in the back of your stock stereo system.

Step 8Amplifier to Car Adapter

You will need to run 2 cables per channel and a signal cable from the amplifier to the car adapter.  This connection can be either butt-connected with crimp style connectors or (better) use soldered connections with heat-shrink.  I recommend a piece of scotch tape wrapped around a sheet of paper to label the ends of the wires.  The other option instead of scotch tape is clear heat shrink.  This really leaves a really nice looking label.

To connect the source, in this case the android tablet, a stereo mini to rca (red and white) is needed. If you plan on having the device charge while it is being used, a ground loop isolator will needed to be added to this audio circuit. If powering the device and also using it as an audio source without this isolator you will hear a lot of static.

Step 9Charging the Tablet - Adding a Circuit

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Using the GPS in the tablet will eat the battery pretty quickly.  So it is nice to have the battery of the tablet charging as you drive down the road.  Probably the best way to do this is to create a separate fused circuit in your car.  If you look in the fuse box under the hood there will be some auxiliary fuse holders that are empty.  The labeling of the fuse box is usually on the bottom of the lid for the fuse box which will reference your car's manual.  To add you own circuit you can buy an add-a-fuse.  This is a device that has a fuse and a short power wire.  To this power wire you will want to add a female 12 VDC power socket (a cigarette lighter style socket).  These can be found in auto parts stores or online.  The red wire goes to power this socket and the other end must be ground.  I found plenty of room where the CD player used to be to install the power socket.

Step 10Charging the Tablet

Some of these auxiliary fuses draw current if the car is on or off and some only draw current when the vehicle is turned on.  The quickest way to tell which is which is just to plug the add-a-fuse in to different fuse spots with something connected.  Important - By connected I mean with a power socket and the unmodified car power adapter for your tablet.  Turn the car on and off and see what happens.  I chose a fuse that did not draw any current when the car is off as to not drain the battery.

Step 11Taking Out the Old CD Player

I first had to remove the portion of my dashboard that contained the stock CD player.  If you are unfamiliar with doing this for you particular car, I recommend a Haynes manual.  This manual will help you find every screw and clip holding that dash in place.  With the dash out, I measured and cut a piece of 1/4" lexan slightly larger than the hole where the stock radio was.  Lexan can be found in your local hardware store in the glass cutting section.  Just about anything can cut it although I still have problems getting a really clean edge.  Luckily in the application all of the edges will be behind the dash so it won't matter.  The dash is probably curved and you may notice small gaps in the side because the lexan is flat.  You can ignore these because when the tablet is in place, they won't be visible.

Step 12Mounting the Lexan

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To keep the lexan in place, I attached it along the back using one of my favorite inventions.  A two part epoxy putty.  This stuff is great for attaching weirdly shaped items.  Just mix it together and stick it on.  When it dries it will be rock hard and solid.

Step 13Installing the Mount

I used a 1.25" hole saw to drill a hole in the middle of this piece of lexan. After cutting off the suction cup portion of the mount for the tab, I epoxied it into the hole in the lexan. I also drilled a 3/8" hole next to the mount to run the power and audio cables through.

Step 14Paint

The lexan is fairly easy to paint.  I roughed up the surface with 220 grit sandpaper.  I then applied a layer of spray primer and then a layer of flat black.  The paint does not have to be perfect as the mount will cover most of the paint job.

Step 15The Finished Product

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The final product has a clean and professional looks but not quite stock. The only thing left is to upload some apps to enhance the experience. I recommend Google Navigation, Pandora, Amazon Cloud Player, tuneFM, Audible, doggCatcher, ChromeToPhone.

Remember to always drive safely and obey all traffic laws. This is not a device to watch movies or read emails when you are driving. It should be used in a safe and intelligent manner.

Step 16Mistakes I Made for You to Learn From

I did not like the idea of having to plug the headphone cord into the top of the tablet.  I knew that the dock connector had pin outs for analog audio.  I bought a cable that allowed me to charge the tablet as well as to play audio through the same cord.  However when testing this in the car, I was unable to get rid of the noise when charging the dock and powering the amplifier at the same time.  There may be an electrical hobbyist on here who could tell me why or help figure out a solution, but I was unable to figure out a solution.

After this didn't work I bought a bluetooth audio receiver that I plugged into the amplifier.  This device worked and I was able to use the audio without attaching a second cable.  However, I the sound isn't as clear as with an audio cable.  I also run it to issues where the bluetooth has trouble connecting.  For the time and effort, I would highly reccomend just using the headphone cable.  It is the best option I was able to come up with at this time.

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