Hack23.Understand Video Connectors


Hack 23. Understand Video Connectors

If you can connect a VCR or game console to your television, you can connect a video screen in your car.

Televisions have been finding their way into cars since the early 1980s, when miniature 12V-powered TV sets appeared on the market. Picture tubes were long and unwieldy, though, and the small space available in a car made them impractical for rear-seat entertainment. Tiny LCD flat-screen TVs were initially installed in airplanes for in-flight entertainment, but once they started coming down in price they began migrating from the airplane to the car.

While larger LCD screens are designed to connect to computers, most small LCD screens are configured to connect to VCRs and DVD players, and thus have the same kinds of inputs as a television. The screens used for factory navigation systems use yet another method of connection.

Figure 3-1 shows the four basic connectors you will be dealing with when you connect screens in your car:


Composite

These are the ubiquitous yellow RCA-type plugs and jacks that you see on VCRs and video game consoles. They are the most widely used video connector and work pretty well at carrying standard television and video signals. However, they were not originally intended to carry high-resolution computer signals, and their color is a bit washed-out. You often find composite cables bundled with two other RCA cables, where yellow is the video and the red and white cables carry the stereo audio. Most flat monitors for cars have a composite video input.


S-Video

These are your basic upgrade from composite. They look sort of like PC keyboard plugs but have only four pins. Because they have four wires instead of two, they are able to separate the brightness and color signals and send them separately. This results in a brighter and sharper picture. S-Video cables should be used whenever possible. S-Video can be down-graded to composite with a simple, cheap adapter. Some higher-end in-car screens have S-Video inputs.


RGB

These connectors provide a sharper and higher-quality image than composite and S-Video television connectors but do not provide the high resolutions that computer connectors provide. RGB has separate wires for red, green, and blue (hence RGB), as well as one or two synchronization wires. The factory screens in most vehicles that have built-in navigation systems use RGB connections, making the text more readable than with composite or S-Video connectors.


VGA

These are the traditional 15-pin connectors found on the back of any computer. These connectors separately transmit red, green, and blue signals along with several other signals to synchronize the monitor to the many resolutions that a computer can produce. Flat-screen computer monitors and touchscreens for both indoor and automotive use have VGA connectors.

Figure 3-1. From left to right, composite, S-Video, RGB, and VGA connectors


3.2.1. Choosing Your Connector

Every modern PC has a VGA output, and any computer designed to connect to a television has a composite or S-Video output. The choice of how to connect a screen to your in-car computer depends on how you intend to use the screen (for video or text) and your budget.

The cheapest screens are composite, and you can get headrest screens of this type for less than $150 at your local Wal-Mart. These screens usually have a much lower resolution than conventional TVsperhaps only around 400 x 200 pixelsbut they're still perfectly adequate for watching movies.

Most of the screens you see in retail stores have composite video connectors and are designed to connect to in-car DVD players, not computers. Thus, they have bright screens and are ideal for viewing films or playing video games. If you want to do actual work on your computer, such as running an office application, you'll need a VGA connector and a high-resolution display. Otherwise, the text may be blurry and illegible.

Small flat-screen monitors with VGA connectors can multisync, meaning they can adjust to whatever resolution you send to them. However, unlike conventional monitors, they have a native resolution, a precise number of horizontal and vertical dots that they can actually display. These screens look their sharpest only when the computer's output matches the native resolution.

3.2.2. Powering and Feeding Your Screen

The screens described in this chapter have several things in common. Almost all the screens have multiple inputsthey can switch between several composite video sources, or even VGA. Many of them have built-in speakers, and some have headphone jacks or even wireless headphone connections. And all of them run on 12V. The screens with built-in speakers that face away from the viewer are essentially useless for most audio applications, but they can be used for the speech on a navigation system. Built-in headphone jacks are a convenient solution for private listening.

Whatever screen you choose to install, you need to run at least two wires to it: one to feed it power and another to feed it a video signal. You can snake these wires to the video and the power source, be it in the trunk, under a seat, or behind the dashboard. Running these connections under the carpeting is a great way to keep them concealed. Depending on your vehicle, you may have to unscrew floorboards or other items to loosen and lift up the carpeting. If you have multiple audio and video sources [Hack #35], you'll need to run wires from each source to the screen, which usually has two or three inputs.

You'll also need to run a wire to a source of 12V power. Screens usually take less than 1 amp of power (for instance, the Lilliput 7" touchscreen takes about 550 mA), so they can run off any available accessory-switched 12V line. It's a good idea to power the screens only when the car key is in the accessory or on positions [Hack #4], or they could slowly kill the battery when your car is off (the Lilliput draws 16 mA in standby).

Cables that carry video can be susceptible to RF interference. If you are going to spend a little extra on something, make it the cables. Shielded video cables will help eliminate cross-talk interference (wire-to-wire electrical interference), engine whine, or interference from strong wireless antennas. It's best to run your audio/video and power cables on opposite sides of the car, if possible. Flexible, shielded conduit can be used to protect wires against moisture, friction, and interference. Avoid putting cables in places where they may be pinched by a door, crushed by feet, or submerged. It's good to do the same for power connections, as 12V car power does not play well with water.

The following hacks describe the unique installation steps and features of particular screens. Once you get the wire down to the floor, you'll know what to do if you read "Connect Your Wires" [Hack #4].



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

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