Hack33.Install a Rearview Mirror Screen and Camera

Hack 33. Install a Rearview Mirror Screen and Camera

Rearview monitor and camera combinations can double as a convenient display for your car PC.

With the progressive miniaturization of LCD display technology comes the option of putting screens everywhere. Rearview mirrors can now be purchased with embedded 35" screens, and coupled with tiny video surveillance cameras, they've become a great option for improving rear visibility in large vehicles.

Trucks and buses without rearview mirrors were the first to really benefit from rearview monitors and cameras. But now, tall SUVs with tinted windows are just as likely to crush small obstacles when backing up, unless they are enhanced with video surveillance technology.

However, hindsight is not the only use for these rearview mirror screens. For in-car computer applications, the rearview mirror is ideally located to provide information to the driver while minimizing eye movement away from the road. Rearview screens are necessarily small, perhaps only 45" diagonally, but that's enough space to show a few lines of large-point text, such as the title of the currently playing MP3 or album, just as you would get on a modern digital radio receiver (see Figure 3-15).

Figure 3-15. A rearview mirror screen in action

One of the nice things about the way screens are integrated into rearview mirrors is that the screens are reflective, so the entire length of the mirror still serves as a rear view, and by simply changing the focus of your eyes you can read the text on the screen.

3.12.1. Installing the Screen

Rearview screens install in a similar way to sun visor screens [Hack #27], except that the video cables need to travel under the headliner [Hack #29] before they make their trip down a pillar.

Another difference is that rearview screens have another wire that detects when the car is in reverse and automatically switches the video to the rear camera. The installation of this backing-up activation feature is discussed in the section "Installing an RGB Screen Adapter" in "Connect a Car PC to Your Factory Screen" [Hack #32].

3.12.2. Installing the Camera

There are several options for installing a rearview camera.

The easiest to install are the units that are integrated into the license plate holder. Since there are usually already wires running power to a rear plate light, you can pass the camera wires through the hole that they use. Another popular unit is a cylindrical camera that replaces the trunk or rear door lock fixture. Since most cars can unlock the trunk using a keyless entry remote, and lifting the trunk gate or back hatch does not require the key, this is a good place to install a camera. These units have a longer lens and thus a better picture, and they install very seamlessly.

The more conventional rear cameras require a hole to be drilled, either on the back hatch or in the roof of the vehicle. These come in a variety of configurations, and it is probably best to have them professionally installed unless you feel comfortable drilling a hole in the exterior of your vehicle. Figure 3-16 shows a rearview camera.

All of these cameras terminate with a video cable somewhere in the back of the car, in either the trunk or the back hatch area. In the case of a trunk install, the wire can be snaked around the edge of the trunk and clips can be used to mount the wire until it enters the body of the car, where it can be fed under the carpet to the rearview screen. Find a place to pass through the wire that won't encourage water to come in and spoil the party. Any gap in the door or hatch seals will leak to some degree. Finding a spot between the seal and the outer skin and drilling a small hold to gain access to the interior is one way to keep the seals sealed. If possible, remove the connector head, or the hole will have to be bigger than the wire diameter to let it pass through. Then, once it's all in place, use silicone sealant (available in any hardware store) to plug up the hole.

In a back-hatch install (i.e., in SUVs or vans) you have to remove the paneling on the hatch, and in the process figure out how to get the wire up around the hatch window and through the watertight wire pipe that connects the hatch and the body of the vehicle (as in Figure 3-17). Depending on how close this wiring is to the inside framing, you should be able to run the video cable either above the rear headliner, or to one of the rear pillars and down to the floor of the vehicle.

Figure 3-16. A rearview camera

Figure 3-17. The watertight wire pipe, an important part of the wiring of your camera

3.12.3. Hacking the Hack

There are some interesting hacking possibilities with the rearview screen and camera combination.

In terms of the user interface, some of the very popular in-car computer motherboards have dual-video-output capabilities. You can connect one screen to your PC as your primary, and connect the rearview mirror screen as a second monitor. You can then display a skinned media player such as Winamp on the small screen (in a big font) to get track and album information while you're playing tunes. Better yet, you can run any application that gives you useful informationthe time, compass directions, a GPS map, WiFi signal strength while wardrivingand have that information available at a glance.

Another interesting hack is to record the rearview video. Since you have a full-fledged PC in the car, you can use a capture card, or a USB 2.0 video-capture device, to pipe the rearview video into your car PC. If you install a program that automatically starts recording the video to disk when the computer is turned on (webcam software with an archiving feature is good for this), you will have a built-in surveillance camera for behind your vehicle. Then if you need the license plate of that hit-and-run or the guy who was tailgating you, you're in luck, because your vehicle is recording it all.