Hack32.Connect a Car PC to Your Factory Screen


Hack 32. Connect a Car PC to Your Factory Screen

Almost any factory screen can be connected to your in-car computer with the right adapter.

Usually, in the U.S. market at least, auto manufacturers are too cautious to enable DVD features on a dash-mounted monitor, even if the car is not in motion. Thus, one of the most popular aftermarket hacks is to connect DVD players and video games to these screens with a video AUX-input adapter. Some of the vendors listed in "Get Computer Audio into Your Head Unit" [Hack #14] also make adapters for factory screens, but as new vehicles and screen configurations are coming out all the time, it's difficult for the manufacturers of these adapters to keep up.

The factory rear-seat entertainment screens in most vehicles are easier to hook up to play DVDs. There are fewer product-liability concerns with these screens, and because they don't have to integrate with a navigation computer, they use the more conventional composite video signaling and readily connect to DVD players, video games, and car computers.

The navigation and control screen in the front-seat area is designed to work with its own special embedded car computer via an RGB connection. Outside of the U.S., where liability lawsuits are less prevalent, the manufacturer usually includes DVD playback and navigation capabilities, as well as auxiliary input for video game or other devices. In the U.S., there are laws that prohibit most front-seat video except for navigation, and the NAV systems even have a "click-through license" that drivers have to agree to in order to indemnify the manufacturer before they can use the system. Of course, since you're putting your own computer in your car, you're the manufacturer, so be nice and don't sue yourself when your in-car computer makes you spill hot coffee on your lap.

Seriously, though, there are several main strategies for getting your computer to display on a screen in the front-seat area of your car.

3.11.1. European A/V Entertainment Systems

If your car has a less-crippled version overseas, as is the case with Mercedes, you can find an importer or car stereo shop that can transplant that "adult" European version of your entertainment system, which has a DVD player and auxiliary audio and video inputs. Then, you simply connect your computer's composite video output and stereo audio outputs to this system. Your upgraded system will have a method of switching between the primary display or navigation system, the integrated DVD player, and whatever auxiliary video you connect.

3.11.2. Rearview Mirror Systems

Although many U.S. laws exist prohibiting front-seat DVD video, a legitimate reason to get AUX input for your factory screen is to connect it to a rearview mirror camera for safer reversing. The fortunate byproduct of such an install is that the center screen can now accept any video signal, from a camera, DVD player, or computer.

Several vendors make rearview mirror devices. For example, Pacific Accessory Corporation makes a product called VCI-X (http://pac-audio.com/products/video.htm) that works with almost any RGB screen out there. The only problem is that they don't provide plug-and-play connectors for most carsyou have to locate the R, G, B, ground, and sync wires and splice into them to install the product, which is not permitted under most car leasing agreements (but if you're hacking your car, you're probably not leasing it…right?).

There are actually several standards for RGB. Fortunately, most vehicles use the same standard, with red, green, blue, and ground wires, and a synchronization signal on a separate wireRGBS. Another standard is to have only three wires (plus ground), with the synchronization signal in the green wireRGSB. And outside of the car realm there's yet another wiring standard (more commonly found in older computer monitors and video systems), with RGB and two synchronization signals. Pacific Accessory Corporation provides detailed documentation for all the vehicles they support, showing the exact pinout (a document containing a description of what each wire is for) for each vehicle's NAV system.

Another manufacturer of video AUX-in adapters is AVElectronic, Inc. (http://www.avelectronic.com/NavigationVid-Switcher.htm). Their device has several benefits. It integrates both a video switcher, allowing selection between three different inputs, and an FM modulator (in case your stereo doesn't have an audio AUX-in). Most interestingly, it has an S-Video port. S-Video really improves the sharpness and clarity of the input signal from the computer, making text more readable and colors brighter. Although it would be best to get RGB directly out of the computer, the S-Video option definitely improves things.

AVElectronic provides plug-and-play adapters for a handful of cars and are trying to make more. They provide instructions minimizing the amount of wire cutting needed for popular cars such as the Hummer H2, Mini, and Lincoln Navigator. Another in-car computer company, G-Net (http://www.gnetcanada.com/factoryintegration-products.htm) also provides adapter solutions for a wide variety of cars.

Figure 3-14 shows an example of a so-called "plug-and-play" adapter. To install this in a car, it is only necessary to find the connection between the NAV system and the screen, unplug it, and plug in the converter box in line. Powering the box (+12V to the red wire, ground to the black wire) and providing a video signal to the RCA connector is simple compared to locating and cutting the R, G, and B wires.

3.11.3. Installing an RGB Screen Adapter

All the systems described in this hack for RGB screen integration use essentially the same approachthey insert an adapter box in line between the navigation computer and the screen. When a video signal is detected (or when a switch is toggled), the adapter box turns off the video signal from the navigation computer, converts the input video signal from composite to RGB, and sends it to the factory screen.

Figure 3-14. AVElectronic navigation audio/video switcher


If you go to http://pac-audio.com/vcix/vcix.asp, you will find general installation instructions for the VCI-X, as well as specific instructions for locating the RGBS and ground wires for many popular vehicles. The basic procedure for installation is to use the vehicle guide to locate the wires, then courageously snip them and splice in the Molex connectors indicated in the diagram. (Molex is a manufacturer of plastic plug interfaces for various electronics applications, including those in vehicles and computers.) Make sure you follow the instructions to connect the male Molex plug (with solid-colored wires) to the NAV unit and run the female Molex plug (with striped wires) to the display.

Because the Molex connectors provided with the VCI-X mate together, you should be able to verify that the NAV screen still works before you install the VCI-X. Simply connect the Molex plugs directly together and power up the vehicle. If all is well, inserting the VCI-X and giving it power and a video signal is all that is left to do. The common problem at this point is that the colors will look wrong if they've been swappedthe green, red, and blue wires will need to be correctly matched in this case.

Since the VCI-X is designed to enable a reversing camera function, it has a switch that enables display of the video input when the car is backing up. Whenever the car is shifted into reverse, a pair of white lights activate on the rear of the car. The VCI-X has a pair of wires that need to be connected (through a switch) when the AUX video input is supposed to be connected. The reversing lights go on when 12V is applied to them. To use the 12V "on" reversing light power to close a switch, it is necessary to use a relay. A relay is designed to allow one system to turn a switch on another system while isolating the two systems electrically (you don't want to send the 12V of the reversing lights into the VCI-X).

A little relay trivia is helpful here. SPDT relay means single pole, double throw. The number of poles is the number of different things for which the relay can act as a switch. If you had double poles, you could have two separate devices switched at the same time. The single pole means that the relay is intended to switch one device. Double throw means the switch has two outputs. Instead of just on and off, there are three posts to connect wires to. When the switch is off, posts 1 and 2 are connected; when the switch is on, posts 2 and 3 are connected. The manufacturers could just as easily have used an SPST (single pole, single throwi.e., only one connection) switch, because the goal is simply to close (connect) the two wires on the VCI-X.

Your application may not need a relay, though. If the VCI-X is being used for an in-car computer rather than a reversing camera, the two wires can simply be run to a front panel switch. You can purchase a single pole, single throw switch that you can install in your dashboard at any Radio Shack (go to http://www.radioshack.com and search for "SPST").

3.11.4. Finding Your RGB, Sync, and Ground Wires

If you have a vehicle that has a built-in RGB screen but is not listed in the help sections of any of the vendors' web sites mentioned previously, you should still be able to find the RGB wires and use one of these adapters. What you need to do is find and isolate the wires carrying red, green, and blue to the screen.

The best sources of information about hacking video into the NAV screens of U.S. automobiles are vendors such as those described earlier in this hack. Each of these companies will likely continue to get phone calls for decades to come, with questions such as "Do you work with my 2015 Hummer H3?" Since they can sell more units if they adapt their products for the hottest new cars, they compete to be the first to market with an adapter for the new Cadillac, the new Lexus, or the new Mercedes. In fact, as soon as their friends at the dealerships loan them cars, they reverse-engineer them and make new adapters.

But what if you have a brand new car that no one has yet made the hardware for? Or what if you have a vehicle that the vendors won't make an adapter for, because they're worried they'll disable the OnStar, or because it would take too much modification and they can't make a plug-and-play kit? And what if you want to move your adapter from your other car into your new car? Well, you can do the same thing the adapter makers do: open up the dash and take a look.

The best starting source of information on your car is the manufacturer's manual, which is an invaluable reference if you are taking apart your navigation system. Also, if your car is popular, you can find a lot of additional information with Google. If you can find someone who has done a take-apart of your car, analyzed the pieces, and made a web page describing the process, you're golden.

But even without a manual, you can do the investigation yourselfand if you don't totally understand what you see, you'll at least have gathered more clues for further searching online. In fact, even if all you find out is that you'd rather just throw in the towel and install a replacement screen, you'll still have moved the project along. So get your screwdriver and start carefully taking apart that dash.

If you can get into your car and identify the manufacturer part numbers of the screen and navigation unit, you may find that the same model is also used in a different car. Try Googling for that NAV unit (instead of your make/model of vehicle), and if it's used in any other vehicle, you can see if there's an adapter for that vehicle that will work for you. Even if it's a one-of-a-kind NAV unit not used in any other cars, once you've identified the actual manufacturer of your screen and accessories, you can contact them and ask for the wiring and video format information. It may be publicly available, or just an email away.

Alternatively, if you truly crave adventure, you can get a pair of wire snips, some electrical tape, and a multimeter and just jump in. Like disabling a bomb in a spy movie, you want to find good candidates for the R, G, B, and sync wires, and then carefully turn off the vehicle, snip one of them, turn on the vehicle, and see if you've disabled one of the colors. If you snip the sync wire, you should have a wavy picture. The ground wire is usually black. If you snip a wire that doesn't seem to be one of the ones you're after, you'll need to connect the wires back together [Hack #4] and verify that things still work.

This procedure of snipping wires is for the courageousas with any device, if you power it up with some of the wrong wires disconnected, you could damage something. Unless you possess the right skills and equipment (i.e., an oscilloscope), or the same reckless overconfidence that I possess, you should stick to what others can discover for you.


3.11.5. VGA to RGB Conversion

The adapters listed earlier work for most applications, such as DVDs and video games, and if you're using your computer to play MP3s or movies they should work acceptably. However, you will notice that with any of these adapters, your image is not as sharp and clean as the factory video. The reason is that converting from composite or S-Video up to RGB is much cheaper (for the manufacturer) than converting from VGA down to RGB.

If you need the same sharp, readable text that your NAV system produces from your computer, and the S-Video input is still too fuzzy, you're going to have to get your computer to output the right RGB signal. Although a full explanation is outside the scope of this hack, there are two paths you can pursue: find a video card that outputs RGB (like the video output of the NAV unit itself), or find a scan converter, a small device that can translate the VGA signals down to the RGB the screen expects.

3.11.6. Composite Video Screens

Now, if your screen does have a factory DVD option that connects to a rear-seat entertainment fold-down screen, or even the front screen in European setups, you should be able to connect your computer to it as well.

DVD players almost always use composite video outputs, so finding where to plug in your computer is as easy as removing the DVD player itself and finding where the wires lead. If you're very fortunate it will even use conventional RCA cables, but in any event you should be able to figure out which cables are power, which are audio, and which are video.

The basic approach is the same with all this investigative worktrace the source of your video, follow it to the screen or to the video source, and find out where you can splice into it. Then, insert a switcher so that you can pipe multiple sources into it, including the original.

As a parting reminder, use high-quality (thick, well-shielded) video cables for this workwhen video is run long distances through a car in unshielded cables, its signal weakens and the quality suffers.



    Car PC Hacks
    Car PC Hacks
    ISBN: 0596008716
    EAN: 2147483647
    Year: 2005
    Pages: 131

    flylib.com © 2008-2017.
    If you may any questions please contact us: flylib@qtcs.net