There are many ways to build an in-car PC. The "right" way depends on what you want to use the PC for, and whether you are building from scratch or using parts you have on hand.
If you are an IT guy with too many spare computers to count, you probably want to see if you can put your existing parts together to make a PC for your car. Or perhaps you just upgraded your laptop and you figure that the older one, which can play DVDs and still has 10 minutes of battery life, could be adapted to power your in-car entertainment system. Maybe you're a gamer with a top-of-the-line Alienware (http://www.alienware.com) machine, and you expect to get in some extra time on your massive multiplayer online role-playing game over your new broadband wireless cell phone connection while someone else drives. Or maybe you're a hacker who wants the computer to run all the time, so you can remotely control your car windows and an in-car camera through your computer's wireless Internet connection.
Let's look over the major considerations that go into selecting a car PC hardware platform.
If you have a top-of-the-line PC on your desk, your first impulse may be to build the same sort of system for your car. Certainly, if you are doing seriously demanding work, such as playing 3D, 2D, or online games, or running platform game emulation (i.e., emulating a PlayStation, Xbox, Nintendo 64, or older console), you need the fastest computer money can buy.
Extremely fast computers have the drawbacks of being expensive, noisy, power-hungry, and bulky. If you mount the computer in your trunk and don't mind the space it takes up, that solves the size and noise issues. But if you have an SUV, you may not have a sonic barrier between your rear area and the cabin of the car. In this case, you will want to reduce the noise your PC makes.
Another consideration is temperature. Keeping your PC cool enough requires there to be adequate airflow, and the trunk of a vehicle tends to be fairly leaky, allowing some of this hot air to get out. For in-trunk high-end PCs, though, you'd do well to make sure you have fans that are heat-controlled, so that their speed increases (and the computer is possibly even shut down) in response to high-temperature conditions.
If you have an SUV, minivan, or luxury car that has air-conditioning vents in the rear of the vehicle, you can run a ventilating pipe from an A/C vent to the intake fan of your PC. With SUVs, using the A/C can help reduce the effort required by PC fans to keep the computer cool, and tinting the rear windows keeps the sun off the PC and helps it to stay cool.
If your main consideration is cost, you can build a car PC out of whatever you have lying around. Depending on what you want to use it for, you can get away with an old or low-powered computer. Older computers tend to run cooler and make less noise than anything you purchase today.
If you only want to play MP3s and run Winamp visualizations on a screen, anything over a 90-MHz Pentium is sufficient. Computers below 200 MHz might even have an old AT power supply (with an on/off toggle switch on the front of the case), which are much easier to get working in a car. (For more on startup and shutdown, see "Start Up and Shut Down Your Car PC" [Hack #43] .)
If you need to play DVDs, you can supplement a slow processor with a circa-1999 DVD decoder board from your junk pile. Software DVD decoding requires a 450-MHz Pentium III at a minimum, but with a DVD decoder board or a video card with onboard DVD decoding capabilities (such as some ATI Rage 128s), any PC can do it.
Even if you can't play current PC video games on a low-end system, many older video games from the 1980s and 1990s can be run with emulation software. And because these types of games have simple keypad controls (most don't require a full PC keyboard), they are well suited for in-car passenger entertainment.
If you want to operate the computer when the car is off, its power usage is a primary consideration. You might only want to use the PC for brief moments while the car is stopped, or you might try to design a system where the computer is always powered so that it can "phone home" for telemetry functionality (remote measurement and control, such as downloading music, video, and emails; tracking your car's location; or even viewing a live security webcam installed in your car).
When both space and power are considerations, the best solution is to use small motherboards that are designed for compact, low-power environments. Over the last few years, computers have been shrinking—and not in the traditional sense. Instead of packing more functionality into the same ATX form factor, there has been a trend to make smaller, cube-or pizza-box-shaped PCs that can fit in the space of a VCR or a DVD player.
One manufacturer of cube-sized PCs is Shuttle (http://www.shuttle.com). While quiet and high-performance, Shuttle PCs are almost as power-hungry as traditional desktop computers.
VIA Technologies (http://www.via.com.tw), a major motherboard manufacturer, has developed and standardized entirely new PC form factors that they have dubbed Mini-ITX (pictured in Figure 4-1) and Nano-ITX. On their embedded web site (http://www.viaembedded.com), you can find links to their wide selection of feature-packed EPIA series motherboards.
VIA's EPIA boards use their own low-power, Intel-compatible processor, running at speeds of around 1 GHz. The boards are only 17 cm square, have every connector and port you could want, and consume only 20–30W of power. Their newest board, the Nano-ITX, is only 12 cm square—about the size of a CD case. The community surrounding these boards is quite extensive, as people have begun using them to hack computers into any conceivable device or object. Mini-ITX.com (http://www.mini-itx.com) has a long list of creative projects for which these boards have been used, as well as links to the many small cases in which you can install these boards.
If you are building a car PC from scratch, your best starting point is an EPIA board such as the EPIAM2, which has a PCMCIAslot (essential for the many wireless Internet connectivity options) and a CompactFlash slot (great for shock-resistant nonmechanical flash file storage), and can run at speeds as fast as 1.3 GHz.
If you're looking for a computer that's already all put together, you should also take a look at the Mac Mini as a hardware solution [Hack #54] . Capable of running both OS X and Linux, the Mac Mini is almost exactly the size of a single-DIN car radio and has a slot-loading CD drive. Buying one of these can be even cheaper than building an EPIA-based PC (Mac Minis start at about $500); what's more, they're more powerful, more compact, and already assembled.
Using a laptop with an automobile power adapter is a quick, easy way to get a computer into your car. You can even leave the laptop plugged into the cigarette lighter adapter when the car is off for several hours without any harm, but if you leave your laptop charging overnight it could discharge your car battery. If you want to permanently install a laptop in your car, you still need to use a startup/shutdown controller [Hack #43] , as you would with a regular PC.
Laptops are great if you simply want to play MP3s and surf the Web in the car on an occasional basis, but it's difficult for the driver to safely operate a laptop that's just sitting on the passenger seat, and it can go flying in an accident. The excellent thing about laptops is that they are compact and power efficient; also, many used laptops available on eBay include DVD players, making any laptop over around 600 MHz suitable for in-car audio/video entertainment.
The drawback of laptops is that you can't disconnect the screen on them and put the laptop in the trunk and the screen in the ceiling, so the screen becomes a wasted resource. Out-of-warranty laptops with cracked screens or many dead pixels are great candidates for in-car computers ("Hey boss, can I take your broken Dell off your hands?"). But if your laptop is slim and stylish enough, you may find you can get the screen and the computer in your car if you mount it on the ceiling [Hack #31] .
Your in-car computer does not have to be a "computer" at all. All the most recent game consoles, such as the Xbox, PlayStation 2, and GameCube, have interfaces for hard drives, networking, and keyboards. Each of these platforms can even run Linux, with easily available modification chips.
The benefits of using a game console as an in-car computer are obvious. For one, consoles are far cheaper than PCs, as well as smaller and quieter. You can install one console for each passenger if you really need to. Although the consoles can't play ordinary console games when booted to Linux, they can run thousands of other applications, including MP3 players and Linux-based games and game emulators.
The latest Palm (http://www.palmone.com) and PocketPC (http://www.microsoft.com/pocketpc/) devices are multimedia-capable, with processor speeds exceeding 600 MHz. Their portability ensures that their power consumption will be low, making them viable in-car computers. In fact, there are a variety of PocketPC and PalmOS GPS/navigation solutions, where the GPS unit plugs into the top of the handheld device and the handheld is mounted on the dashboard, facing the driver. The only problem is that there aren't any good docking stations (yet) that enable you to plug this type of portable multimedia device into the dash without having wires everywhere.
Another diminutive option is the recently released OQO (http://www.oqo.com) computer, which uses a low-power Intel-compatible chip to squeeze a 1-GHz processor into a handheld computer. With a simple docking adapter, this device connects to a VGA monitor and a standard keyboard. It has an integrated 800 x 480 touchscreen and a 20-GB hard drive, and it can power itself for a long time when connected to a car battery. You could simply Velcro the OQO to your dashboard and drill a small hole to pass through the USB and power cables.
As more powerful, pint-sized devices like this come on the market, the task of getting computing into the car becomes easier and easier.
Though a variety of companies make cases for Mini-ITX form factor boards, only a few companies have created motherboard enclosures designed for in-car use. You can see a sampling of car PC cases in Figure 4-2.
Morex (http://www.morex.com.tw) cases are some of the cheapest. They adapt easily to in-car use but don't have any car-specific power connectors, so power wires will have to pass through some hole into the case.
Opus Solutions (http://www.opussolutions.com), makers of some of the best power supplies [Hack #42] , also make several in-car computer enclosures that are solid, expandable (they add an additional PCI slot for the VIA motherboards), and have optional shock-absorbing rubber spacers for industrial vehicle (or sports car) installations.
In-Dash PC (http://www.indashpc.org) makes an inexpensive single-DIN enclosure for car PCs. Their approach is unique in that they've managed to squeeze a VIA motherboard, a slot-loading optical drive, and bootable flash memory into a box that can fit in your dashboard. This is excellent if you really don't have room in the trunk, and it saves you the trouble and expense of running wires to a computer in the trunk.
CarBot (http://www.carbotpc.com), my own company, has been selling a very pretty (but expensive) brushed aluminum enclosure for Mini-ITX boards. One of the features of the CarBot case is that it has all the PC-related ports on one side and all the car-related ports (such as 12V, ground, ignition, and RCA audio input and output) on the other side. This makes it possible to take a CarBot case into an install shop and say "hook it up" without getting blank stares from the installers, as you do with many other car PC enclosures.
There are dozens of other cases on the market. The following links will help you find some other options that may fit your needs.