Car PC Hacks | O'Reilly Media

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Home electronics and car electronics are quite different. Homes are designed to power dozens of large appliances; cars are designed to power a handful of small electronic devices. Homes run on high voltages that could give you a heart attack; most of the electricity in a car won't even give you a shock.

This chapter is going to give you a rapid-fire, metaphor-rich tutorial on electronics, and automotive electronics in particular. It will go over key terms, such as voltage, amperage, and wattage, and give you a basic understanding of how to do arithmetic with these numbers. The goal is to get you up to speed quickly on car electronics, and show you the essential system upgrades that will help you hook up and power your in-car computers and accessories.

Different electronic systems, such as those for houses, cars, and computers, use very different connectors, voltages, and power levels.

If you are familiar with only home or computer electronics, you will need a little bit of background before you start playing with the wires in your car. This hack will introduce you to automobile power. Because you will probably want to "bench test" your in-car computers in the house before installing them in your car, it will also show you how you can hack a computer power supply to power your in-car accessories indoors.

The first term you need to learn about is voltage, which is simply the amount of potential (work, force, energy, change) in an electrical flow. Different devices are designed around a certain level of electrical potential, which can be thought of as the amount of pressure propelling the electricity. The analogy most often used to explain voltage is water flow, where the pressure of the water coming out of a hose is like the voltage, which can be turned up and down by a valve or spigot. The same hose can release high-pressure water to clean a driveway, or a low-pressure flow to fill a water balloon.

Electricity, however, doesn't flow readily through the air like water does. Electricity travels well only through

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Home electronics and car electronics are quite different. Homes are designed to power dozens of large appliances; cars are designed to power a handful of small electronic devices. Homes run on high voltages that could give you a heart attack; most of the electricity in a car won't even give you a shock.

This chapter is going to give you a rapid-fire, metaphor-rich tutorial on electronics, and automotive electronics in particular. It will go over key terms, such as voltage, amperage, and wattage, and give you a basic understanding of how to do arithmetic with these numbers. The goal is to get you up to speed quickly on car electronics, and show you the essential system upgrades that will help you hook up and power your in-car computers and accessories.

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Different electronic systems, such as those for houses, cars, and computers, use very different connectors, voltages, and power levels.

If you are familiar with only home or computer electronics, you will need a little bit of background before you start playing with the wires in your car. This hack will introduce you to automobile power. Because you will probably want to "bench test" your in-car computers in the house before installing them in your car, it will also show you how you can hack a computer power supply to power your in-car accessories indoors.

The first term you need to learn about is voltage, which is simply the amount of potential (work, force, energy, change) in an electrical flow. Different devices are designed around a certain level of electrical potential, which can be thought of as the amount of pressure propelling the electricity. The analogy most often used to explain voltage is water flow, where the pressure of the water coming out of a hose is like the voltage, which can be turned up and down by a valve or spigot. The same hose can release high-pressure water to clean a driveway, or a low-pressure flow to fill a water balloon.

Electricity, however, doesn't flow readily through the air like water does. Electricity travels well only through conductors, such as metal wires, and in order to flow it requires a return path (usually called the ground) going back to the source of the voltage. In our water metaphor, the ground would be represented by a drainpipe. (Of course, water conveniently doesn't require a returning drainpipe to flow.)

Another, slightly more accurate analogy for electricity is that of water pouring over a cliff. The cliff represents the positive (or +) end of a battery, and the electricity flows from the high cliff down to the ground (negative, or–). The higher the cliff, the higher the voltage. However, I'll continue to use the hose-pressure metaphor because of the corresponding analogy between wires and hoses.

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Only you can prevent electrical fires (as the paraphrased saying goes), and fuses are an essential form of prevention.

In any electrical system, it's important to protect against miswiring that can result in device damage or even fires. This hack explains voltage, amperage, and power levels, and points out several of the safety features (i.e., fuses) of your automobile's electrical distribution system.

"Understand Car Electrical Systems" [Hack #1] defined voltage as the amount of potential or pressure behind electrical flow, and gave the analogy of a high- or low-pressure hose. To explain current in terms of water, we would be considering how many gallons of water went through the hose per hour. A very unscientific conceptual definition of electrical current (measured in Amperes, or amps —not to be confused with sound amplifiers!) is simply how many gallons of electrons pass through the wire per hour.

It's pretty simple: if you're trying to power a small device, such as a light in your car, you only have to give it a few teaspoons ( milliamps, or mA) of electrons every hour. If you're trying to power your car radio, you need a cup of electrons every hour (amps, or A). If you're tooling around town in your electric car, that's where the gallons of electrons ( kiloamps, or KA) come in.

To continue our simplified analogy here, the more amps you need for your device, the bigger your "hose" or wire should be. "Gauge Your Wires" [Hack #3] discusses the different sizes of wire and how thick they should be for a given application.

Fuses are protective devices placed along the path of an electrical circuit. To fuse means, basically, to melt. Fuses melt to protect the circuit, wires, and devices when you put too much current (electrons per second, or amps) through them. You usually get too much current going through a wire because of a

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The general rule in car wiring is that the thicker the wire is, the better. However, thick wire is expensive, and financially it's worth learning how thick a wire you really need to bring power to all the devices you add to your car.

The width of wires is usually given in a unit called gauge. As with shotguns, a smaller number represents a bigger diameter. Continuing our electricity-as-water analogy, the wider your wire is, the wider a "pipe" the electricity has to go through. Thus, if you are trying to carry a lot of power to your trunk to power a small studio of TV screens, computers, and audio amplifiers, you will want to use a thick wire. But how thick?

Using a wire that is too thin can be a fire hazard: too much amperage will overheat the wire, potentially melting the insulation and lighting the carpet on fire. However, using a wire that is too thick can be a financial hazard: you will spend hundreds of dollars on wires alone and have no money left for gadgets.

Wire comes in several types, including solid core, which is just thick, bendable copper, and stranded, which consists of many smaller wires braided together. For automotive applications, stranded wire is more desirable than solid because it's more flexible, especially at colder temperatures.

The maximum amps a wire can carry safely depends on the gauge and length of the wire. You probably won't be running wire longer than about 6 meters (20 feet) in a vehicle, but it's good to know that the longer you run the wire, the thicker it should be, because some of the electricity gets lost along the way as heat.

Wire gauge differs in the U.S. and Europe. In the U.S. you will see the term AWG, for American Wire Gauge, which I will be using here. As mentioned before, gauge is a bit odd in that the larger the wire is, the lower its number is. (Europe uses a more sensible metric-system-based wire gauge scheme. I won't cover it here, but I will give you the metric equivalents of the AWG numbers so you can visualize how thick the wires are.)

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There are several ways to do in-car wiring: quick-and-dirty, functional, or professional, depending on who's going to see it and how long you want it to last.

In the process of hacking computers and other devices into your car, you have to connect lots of wires. Unlike the inside of a computer, where all the wires are keyed and standardized, each car has its own set of connectors, and most of these are already in use. Except for cigarette lighter power outlets, which are really more for temporary connections, there is no standard "outlet" in the trunk of your car where you can seamlessly plug in your gadgets.

What happens instead is that new wires are run to the locations where devices are installed. They are usually run under the floor carpet, or inside the plastic baseboards or framing at the edges of the seats and carpets. When the wires poke out, professional audio shops usually surround them with plastic sheathing and zip-tie them down, as shown in Figure 1-11.

There are several ways to connect all your wires. Which method you choose depends on how permanent a solution you want, your budget and tools, and how important appearances are to you.

Figure 1-11: Tidy professional wiring

Section 1.5.1.1: Twist and tape.

The cheapest way to connect your wires is to twist them together and wrap electrical tape around them so they don't short out. This is the hallmark of an amateur, but it's my favored method when I am doing temporary installations or fixing or installing a radio while driving (er, not that I would do that).

The minimal tools required for this approach are:

Hard fingernails (or sharp teeth) to strip wire insulation
Electrical tape to insulate and protect the wires you twist together

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To make sure you don't kill your car battery, learn how to do quick-and-dirty estimates of power drain for in-car devices.

There are a number of ways to compare battery characteristics. One of the main measurements of power storage capacity is amp-hours, which roughly means the number of hours for which your battery can put out a certain number of amps. However, interpreting exactly what this number means is tricky.

If you've ever seen the movie Apollo 13, you may remember the scene where the scientists and astronauts are calculating how much power they have left, and trying to come up with an escape plan that doesn't use too much of the spacecraft's limited power. Automotive electronics is often like that. Everything is fine while the engine is on and you're still generating electricity. But once your car is off and you're running on batteries, you have to count every electron, or you'll find yourself in the parking lot holding out jumper cables and begging for a jump start.

The reason you want to know how many watts a device is using is so you can determine how long you can run it in your car, with the engine off, without killing the battery.

You will need several tools and supplies while hacking your car PC. This is just a quick list that should cover a wide variety of needs:

Cordless drill, drill bits, and assorted driver heads: A cordless drill is a must-have for a professional installation. A powerful drill with strong torque will make quick work of pilot holes, fasteners, screws, and long bolts. Drill bits are good for pilot holes, which keep plastic from distorting and weakening and let you fasten large-diameter grounding screws to interior body panels. Most hardware stores carry assorted driver kits that include Phillips, Torx, flathead, hex, and a few other types of driver. When one wears out, replace it. Old driver heads strip fasteners.

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If you want to add a lot of electrical devices to your vehicle and still be able to start it up and drive it, you may need to upgrade your car battery.

There are two primary competing purposes for the battery in a vehicle:

To provide a very high-amperage output for several seconds to start the car, then allow the engine to generate any further needed electricity.
To provide a medium- to low-amperage output for many hours when the vehicle is off, to power devices such as car alarms or the station preset memory in car radios.

To meet these two different needs, two types of batteries are used in automotive applications: conventional lead-acid and deep-cycle.

If you are familiar with laptop or mobile phone batteries using nickel cadmium, nickel-metal hydride, or lithium ion, you know that they are designed to be completely discharged and recharged many times. Conventional automobile batteries use lead-acid and are designed to put out a large current (to start the car) for a short time, and then be recharged after only a shallow discharge. If you completely discharge your automobile battery (say, by leaving all the lights on for several weeks) you are likely to severely limit the life of the battery.

Recreational vehicles (RVs) often have two batteries—one starting battery with its good starting characteristics, and one deep-cycle battery designed to put out a lower amperage for a long time and to survive deep discharge.

In addition to the starting and deep-cycle qualifiers, a few other measurements are used to compare batteries:

Cranking amps (CAs): This is the maximum output amperage the battery can sustain for 30 seconds (i.e., to start the car). A good battery can put out 1 kiloamp (1000A) for about 30 seconds before the voltage starts to sag. Since cold weather makes batteries very tired, another necessary comparison is

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Modern devices such as laptops, cell phones, and video cameras often have 12V power adapters so they can be used, or charged, from a car's cigarette lighter outlet. If you have more devices than outlets, you can easily add more power connectors.

Some modern vehicles come with switched and unswitched 12V outlets throughout the car. If your vehicle is not so equipped, you can easily and cleanly install 12V power outlets wherever you have a plastic panel.

Let's say you're going on a trip. You and your friend/spouse both have cell phones, but they're from different manufacturers, so you have different car chargers. You've also brought along your laptop, so the kids/passengers can watch DVDs on the way, and your iPod adapter, so you can recharge it while you're playing tunes. You have a cold box that stays cool when it's plugged into the cigarette lighter adapter, and to top it all off, you've got your video camera plugged into a power inverter [Hack #11] (you were scatter-brained and forgot to charge it, and you're hoping to recharge it on the way so you can use it tonight).

How can you make it possible to use all of these devices simultaneously? Well, the first approach is to get one of those triple-decker one-outlet-to-three splitters, which look strange and take up a good deal of dashboard space. But if your car only has the cigarette lighter power socket that really holds a cigarette lighter, and points awkwardly up from an open ashtray (as in older Mercedes), then what you really need to do is install more outlets.

Your friends/family surely won't mind while you implement this hack in just a few hours. You'll be on the road in no time, and all your devices will have the power they need, where they need it.

The first step is simply to draw a quick sketch of where you want the outlets. The cleanest installation will be where you can find a nice flat plastic, vinyl, or other panel with a few inches of depth behind it.

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A large capacitor is often used to maintain bass amplifier response, and can address other problems as well—including voltage sags when the car is started.

One of the many goals of aftermarket car audio systems is to create a reverberation that exceeds the boundary of the car, shaking other nearby cars and buildings. Car audio enthusiasts have been using 1-farad capacitors for years to make sure their cars go Boom! Boom! without brownouts or voltage sags.

Bass response is the ability of the subwoofer to reproduce the low-frequency bass sounds in music with fidelity. One of the problems with subwoofers is that they need a lot of electrical energy to move the large speaker to reproduce the low-frequency bass sound waves. When the bass beat kicks hard, the speaker should instantly slam in response—but often, the car's battery and electrical system can't put out enough power to ensure an instant response.

I can explain this with another water analogy. Sometimes in houses with old plumbing, you lose water pressure in the shower whenever someone flushes the toilet or turns on the washing machine. Plenty of water is coming to the house via the mains; that's not the problem. The problem is that the plumbing can't maintain the pressure when too many demands are made on it.

Capacitors are one of the solutions to the problem of sagging voltage (electrical pressure). Capacitors are devices that store up electricity, like a temporary battery (think "capacity"). One of the uses of a capacitor is to help keep voltage at a constant level.

Returning to the water pressure problem, imagine you had an extra device hooked to your plumbing, which I'll totally randomly call a capacitor. This extra device consists of a reservoir that holds perhaps 30 gallons of water. Whenever someone makes too many demands on the water system, the capacitor steps in and supplies the extra water.

So, if you're taking a shower, and then somebody flushes the toilet and washes their hands, the capacitor has enough water to keep the pipes full for a little while and keep the pressure up. If, however, someone turns on the washing machine and someone else starts watering the lawn, the reservoir will probably run dry after a while, and the capacitor won't be able to maintain a comfortable shower pressure for the duration.

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It's possible to install so many electronic devices in your car that the battery continues to discharge even when the engine is running. Upgrading to a high-output alternator ensures that there's enough power to feed all the devices while keeping the battery charged.

An alternator is a device in modern automobiles that acts as the voltage generator for the engine (Figure 1-19). While the battery does the job of getting the engine started, once the car is running off fuel it technically doesn't need a battery anymore. You could even disconnect the battery while a car was running, and it would probably continue to run (this applies to older cars without a lot of electronics; newer cars would throw a fit because the battery keeps the voltage levels stable). If you've ever gotten a jump start and then driven around with a "dead" battery, you understand this feature.

Figure 1-19: An alternator in a car

Once the engine is started, it's actually the alternator's job to supply the electrical power for the whole car. As an electrical generator the alternator is very efficient, but its voltage tends to fluctuate. The car's battery acts to smooth out the voltage and keep it at around 13–14V. In the process, the car's battery gets recharged.

A normal alternator might be designed to put out 100A. This might seem like a lot, but once you start adding high-power devices with hungry CPUs, you could easily exceed this level. Once that happens, the car will act as if the alternator has stopped working—the battery will have to make up the difference between what the alternator is putting out and what the car's entertainment system is demanding. The battery can thus become completely discharged, and for conventional batteries, this essentially makes them "dead." If you don't realize that the real problem is that you've exceeded your alternator's capacity, you might think that your battery is dead and upgrade it to a new top-of-the line battery, only to kill that one, too.

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Adding a second car battery is a great way to get lots of standby power when the vehicle is off. You can upgrade your car so that it has the same power setup as a recreational vehicle, with one battery for starting and running the engine and another for powering devices.

Adding a second battery doesn't really increase the number of devices you can power while the car is on—for that you need to upgrade your alternator [Hack #9] . What a second battery does do is more than double your power storage capacity, increasing the time for which your devices can run when the engine is off and ensuring that your primary battery always has the power to start your car.

To illustrate the information in this hack, I'm going to appeal to your intuitive understanding of batteries. If you look at the label on AAA, AA, C, and D batteries, you'll discover that they all supply 1.5 volts. But you would expect that a D is better than a AAA somehow, if only because it's bigger. What you may not know is that the main difference between the two types of batteries is the length of time each battery can put out 1.5V, and how many amps they can sustain. That's why devices that need to put out power for a long time, such as flashlights or boomboxes, use D batteries, while remote controls and pagers only need AA or AAA batteries.

You may or may not also know that you can wire a pair of batteries in parallel. The combination will output the same voltage, but for longer. For example, if you take 4 AA batteries and wire them in parallel (tops to tops and bottoms to bottoms, with wires daisy chained between them), they'll probably be able to put out more sustained power than a single D battery, but only at the same 1.5V that a single battery delivers.

What you wouldn't want to do is put a D battery in parallel with a AAA battery. After the AAA battery was discharged, the D battery would still be putting out voltage, and the AAA battery would be sucking it up—not the desired effect. The general rule is that you put batteries in parallel only when they are the same kind and age. Even then, if one of the batteries goes bad it can take the other ones down with it, so don't leave a dead battery mixed in with good ones.

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If you need to power a device that doesn't come with a car adapter, or if you want to run a top-of-the-line PC that consumes 300 watts, you will need to use a device called an inverter to convert your vehicle's 12V to the 120V or 220V found indoors.

"Understand Car Electrical Systems" [Hack #1] showed how you can convert the high-voltage power from a wall outlet into the 12V and other voltages needed by computers. If you need to power an in-home device in the car, however, the reverse can be done, using a device called an inverter.

American household voltages have been standardized at around 120V, and power in Europe generally runs at 220V. While vehicles and batteries use something called direct current, indoor voltages are alternating current. Direct current (DC) is simple: 12V on one wire, 0V on the other, and the current goes around in a loop from the 12V wire through the device and back to the 0V ground wire. Alternating current (AC) has a wavy pattern: the main two wires in AC trade off being at ±60V (in North America), back and forth, 60 times per second. (In Europe, the voltage waves ±110V, 50 times per second). The third "ground" wire in AC voltage usually connects to a metal pole sticking into the ground, and it actually acts as a failsafe return path for current if there should be a power surge, short circuit, or lightning strike. So, inverters have to do two things: they have to increase the 12V 10 to 20 times, and then they have to convert the simple DC voltage to the more complex back-and-forth AC current.

Inverters use a certain amount of the power coming into them just to convert the voltage—about 20% of the wattage is lost in translation. Thus, if your computer needs 100W to run, the inverter will draw 125W from the battery/alternator in order to supply it. In practice, you should probably have an inverter rated for twice what your devices demand. In my experience, when you first turn on devices (such as computers or power supplies for laptops) they create a big power surge, which can flip the circuit breaker built into your inverter. Then, even though the device settles down to its rated power draw, well within the inverter's rating, the inverter will have freaked out and shut down everything. The only caveat is that too powerful an inverter will waste power (on fans and heat) and give you less running time when the car is off—but you shouldn't be using an inverter if you're trying to maximize battery time.

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Audio entertainment has long been the steadfast companion of the driver. Since the first tube radios were introduced, the latest audio technologies have always found their way into vehicles—and the recent success of subscription satellite radio and portable music players shows that people will adopt almost any new technology that satisfies their need for audio choices.

This chapter focuses on ways to get the latest audio-entertainment technologies into your car, whether it was originally equipped for them or not. While auto manufacturers are slowly seeing the light on satellite radio and MP3, it may be a while longer before they begin equipping vehicles for general purpose computers, MP3 players, and portable hard drives. Still, with some basic understanding of your car's audio system and a few simple tools, you can hack the latest audio technology into your vehicle's sound system.

The centerpiece of your car's entertainment system is the car radio. You should know how it interacts with your car's speakers and other electronics before you yank it out.

Almost every car ships with a radio. Most car radios also include a tape deck or a CD player, and some current vehicles still come equipped with both. Many new car radios are also capable of controlling a multi-disc CD changer or connecting to a satellite radio. Because the car radio is really a master control for all sorts of electronic entertainment devices, it is often called a head unit.

General Motors, BMW, Honda, Saab, Ford, and car company you can think of, all manufacture different head units for their vehicles, and they often use different units depending upon the year and vehicle model. Each car company has its own proprietary interface for CD changers, and there are no real standards. Figure 2-1 shows a simple OEM (original equipment manufacturer) head unit.

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Audio entertainment has long been the steadfast companion of the driver. Since the first tube radios were introduced, the latest audio technologies have always found their way into vehicles—and the recent success of subscription satellite radio and portable music players shows that people will adopt almost any new technology that satisfies their need for audio choices.

This chapter focuses on ways to get the latest audio-entertainment technologies into your car, whether it was originally equipped for them or not. While auto manufacturers are slowly seeing the light on satellite radio and MP3, it may be a while longer before they begin equipping vehicles for general purpose computers, MP3 players, and portable hard drives. Still, with some basic understanding of your car's audio system and a few simple tools, you can hack the latest audio technology into your vehicle's sound system.

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The centerpiece of your car's entertainment system is the car radio. You should know how it interacts with your car's speakers and other electronics before you yank it out.

Almost every car ships with a radio. Most car radios also include a tape deck or a CD player, and some current vehicles still come equipped with both. Many new car radios are also capable of controlling a multi-disc CD changer or connecting to a satellite radio. Because the car radio is really a master control for all sorts of electronic entertainment devices, it is often called a head unit.

General Motors, BMW, Honda, Saab, Ford, and car company you can think of, all manufacture different head units for their vehicles, and they often use different units depending upon the year and vehicle model. Each car company has its own proprietary interface for CD changers, and there are no real standards. Figure 2-1 shows a simple OEM (original equipment manufacturer) head unit.

Figure 2-1: A CD and tape player head unit

There's rarely an opportunity to upgrade the head unit for a better one from the dealer who sold you the car, but the vast majority of cars can accept aftermarket head units. These range in price from under $50 for a simple model to upwards of $2000 for a fold-out touchscreen that can interface with DVD players, CD changers, and satellite radios, and that includes navigation capabilities.

Although many new cars are starting to make aftermarket stereo installation more difficult by "featuring" swooping dashboards that require nonrectangular head units sold only by the car's manufacturer, there actually are some size standards for car stereos.

Single-height stereos, which are used by most car manufacturers, correspond to a size called DIN (which stands for Deutsches Institut für Nor-mung, a.k.a. the German Institute for Standards, who established the standard). DIN is about 2" high and 7" wide. Chrysler and a few other manufacturers produce radios that are twice that height and fit a size called

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After you've pulled out your head unit, you may want a few tips on putting in a new one.

Most technophiles' needs will exceed the capabilities of their factory car stereos very quickly. First, they'll want to play some computer-based audio format, such as MP3, and they'll have to use a tape adapter to get it into the stereo. Then they'll start wanting to load up MP3s on a CD, and they'll be frustrated that the built-in stereo won't play them. Even if it does, they'll expect the works—intuitive navigation, album art display, and track names. They may also want to install satellite radio in addition to the CD changer. With a three-to-five-year development cycle for new products, auto manufacturers usually can't keep up. That's where the aftermarket comes in.

If you're looking to hook up an in-car computer to your factory stereo, there are definitely ways to do it, but it's often easier to just upgrade to an aftermarket stereo with auxiliary inputs, or even a fold-out video screen. And as you may want to upgrade your sound in the process, adding an external amplifier [Hack #15] is a very standard and beneficial upgrade. But if you're just replacing the head unit, in many cases it is simply a matter of splicing together the correct wires.

A bundle of wires grouped together in a car is called a harness. All radios with built-in amplifiers have pretty much the same wires going from their specific harness to the car, with a different plastic end connector.

Your conventional factory and aftermarket head units usually have the following wires (see Figure 2-4):

Front left speaker (two wires, + and–)
Front right speaker (two wires, + and–)
Rear left speaker (two wires, + and–)
Rear right speaker (two wires, + and–)

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Aftermarket CD changers and DVD players have become very popular of late, as have MiniDisk players, MP3 players, and legions of other small audio devices. To use these devices in a car, however, you'll need to smuggle the audio into your (usually closed) head unit.

The concept of getting audio into the car stereo is almost completely foreign to automobile manufacturers, who tend to run years behind state of the art when it comes to audio technology. And the concept is familiar but threatening to aftermarket manufacturers, who want to lock you into buying their CD changers and their navigation units, not allow easy use of your own laptop or MP3 player.

Fortunately, there are several ways that you can get audio into your head unit.

A tape adapter (Figure 2-5) looks like a cassette tape with a wire coming out of it and a mini headphone plug (2.5 mm) on the end. The headphone jack plugs into your external audio device. Tape adapters have a magnetic output device that converts the sound coming in the wire into magnetic signals like those on a normal cassette tape.

Figure 2-5: A tape deck adapter

Tape adapters are the cheapest solution for audio input; they can be purchased for $10–20 and they plug in and work right away. They are the quickest way to get your computer or MP3 player's audio into the car's head unit, and they work quite reliably.

However, from an audio perspective, tape adapters are a pretty low-fidelity solution. For one thing, the audio signal goes through multiple translations—from the source, through a wire, through a magnetic head, read back by a tape head, then amplified—and it loses a bit of quality in each step. Additionally, the spindles that move the tape are rotating for no reason, and these scraping rotors and their motors generate both electrical and audible noise. ("Reduce Your Audio System's Noise"

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Connect your PC or other audio device directly to an amplifier, bypassing the head unit altogether.

If you have an external amplifier in your vehicle, you may not have to adapt your head unit to get audio from external devices to play through your vehicle's speakers. Although the head unit/auxiliary-in approach in "Get Computer Audio into Your Head Unit" [Hack #14] gives you the ability to control the volume of all devices from the head unit, you can connect computers and portable devices with their own volume controls directly to the RCA inputs of your amplifier, bypassing the head unit altogether.

Amplifiers come in two-channel (stereo) and four-channel varieties, with a corresponding number of RCA inputs. You can see an amp and these inputs in Figure 2-8. Some amplifiers also have a set of "high inputs" that can take the output of a cheap head unit's built-in amplifier, convert it down to a lower level, and then reamplify it with the strength and audio fidelity of the amplifier. There are also separate line-level converters that can achieve the same function, for when your head unit doesn't have RCA outputs.

If you install a separate amplifier for all your speakers, as in Figure 2-9, you can improve the sound quality and add additional options for inputting audio from sources other than the head unit.

Figure 2-8: An amp and its RCA inputs

Figure 2-9: Adding an amp to the sound path

One of the features of a head unit is a front-to-back audio balancing feature called fade. If you use the pair of RCA outputs of many lower-end head units, such as with a twochannel amplifier, you will have to split this stereo signal into four channels for the front and rear lefthand and righthand speakers, and you will lose the fade feature.

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If your budget is highly constrained or you're out in the wilderness, there's still a way to install an auxiliary input to your tape deck.

Let's say you're preparing for a long drive home from your grandparents' ranch in the country. Your car is old—it runs well and has surprisingly good A/C for its age, but the cassette player just started eating tapes and you don't want to drive a thousand miles without music.

You brought your laptop, and with amazing foresight you also brought your car power adapter for the laptop. You want to listen to the music stored on your laptop, but road noise makes its tinny speakers inaudible while you're driving. You'd like to output the audio through your car speakers, but how? The obvious solution, to use a tape adapter, isn't an option, because your grandparents live in a small town that stopped growing in the 1970s—there isn't a store where you can buy the tape adapter you need.

Still, if you're enterprising, and lucky, you may be able to hack your way out of this technological void. Here's how the hack might go.

First, you have to yank the deck out of your car to take it apart. You improvise some pliers, and pull the head unit out of your vehicle. Using a steak knife as a makeshift screwdriver, you open the unit, pulling off the top cover. You notice that there are two spots inside the tape deck where you see wires that might let in some audio. The actual wires running from the magnetic head that reads the tapes look like they could be spliced, and you have a pair of cheap headphones at hand, so you decide to sacrifice your headphones and connect them to the tape deck, using the twist-and-tape method of connection [Hack #4] .

You cut the earpieces off your headphones to expose the wires. You then splice the red (right channel), white (left channel), and black or copper ground wires from your cheap headphones to the corresponding colors in the tape deck, as illustrated in Figure 2-13. You can usually identify the ground wire, even if it's not black, as a braided wire that surrounds the white and red headphone wires.

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There are ways to reduce or eliminate the buzzing and high-frequency noise that the engine adds to your in-car audio.

Despite the fact that we spend so much of our time listening to music in our cars, the automobile is a fairly hostile environment for someone seeking audio perfection. The alternator of the car and the electrical pulses from the spark plugs both create oscillating electronic currents in the audio signal. Really, any moving electrical part can create magnetic waves that show up in electrical wires as audible noise. This is why cables are shielded.

The power from the 12V car battery that powers your car computer fluctuates from 12–14V and includes many other little electrical oscillations from the car. While the battery can still successfully power your computer, the little fluctuations pass through the computer and show up in the analog audio signal that it puts out. At other times, the car's electrical noise is picked up directly by audio wires that act as a sort of antenna. This line noise can mess up the audio on its way from the computer to the head unit or the speakers.

Just as there are many potential causes for line noise, there are a number of ways to reduce the noise in a car computer setup. We'll look at those now.

You can spend hundreds of dollars on high-quality speaker wire and RCA cables alone. However, the importance of using quality wires is not to be underestimated. Cheap, thin, long RCA cables are like antennas that can pick up noise all along the path they travel through the car. Upgrading to thick, shielded cabling can reduce unwanted noise in the audio signal.

Monster Cable (http://www.monstercable.com) is one of the leading manufacturers of well-shielded cable. They're expensive, but if you use cheap cables the labor of re-running wires and diagnosing hums and buzzes will work out to be more costly in the long run. Just as with computers, using high-quality cables will save you a lot of head-scratching time in the end.

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Apple's iPod can now integrate directly with a number of factory and aftermarket head units.

Apple's iPod portable audio player is quickly becoming the de facto jukebox standard for cars. Until just recently, however, the state of the art for iPod/vehicle integration was cigarette lighter power and a tape adapter. Give some points for style, though—the plastic and wires of these adapters were white.

This situation improved dramatically when Apple released the first interface that allowed iPods to be controlled by the CD changer controls of several BMW models, as well as the Mini (the car, not the iPod). With the iPod BMW adapter, the iPod emulates a CD changer when you plug it into a special adapter stealthily hidden away in the glove compartment. You can create five playlists in iTunes that can be selected by the CD changer buttons 1–5; button 6 selects additional playlists in sequence. (Visit http://www.apple.com/ipod/bmw/ for more information.)

On the heels of Apple's announcement, everybody got into the game. Pacific Accessory Corporation (http://www.pac-audio.com) released the Swiss Army knife of iPod adapters, the AUX-POD. This device can interface with the factory head units of dozens of different car makes and models. The first generation of adapters are relatively simple in operation; they allow you to click "next song" and possibly to select playlists with the factory controls, and they terminate in a simple wire that you connect to the bottom of your iPod. PAC's newer adapters are designed to use the full text-display capabilities of modern satellite-radio-ready head units.

The major aftermarket vendors have responded and added more features to take advantage of their high-tech head units. Alpine's KCA-420i (http://www.alpine.com) upped the ante by displaying the full song title and album name and adding search features, and Pioneer has announced a unit with comparable features. In fact, just about every major stereo manufacturer is adding iPod integration into some part of their product line.

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With the right receiver, your PC can take over the radio function of a car's head unit.

Receiving radio broadcasts via home PCs has always been somewhat of a novelty option. Every generation of PC has had its tuner cards or external USB receivers. But as radios already do a great job of receiving broadcasts, it's only the added features—such as remote control and timed recording—that make PC radios valuable. Now you can take advantage of these features with your car PC, too.

There are two basic kinds of PC radios: external radios connecting to USB or serial ports, and PCI cards with FM tuners on board. Almost all of these cards output analog audio via a pair of cables and use the USB or PCI connection only for tuning the station. There's no real point in sending audio over a digital connection, because the broadcasts are analog to begin with. Instead, the audio goes into the CD-in, line-in, or microphone input of the computer's sound card.

Every computer radio comes with software that allows you to control the tuner, select different channels, and display which channel you are on. None of these applications, however, are designed for in-car use; they are generally quickly-thrown-together Windows programs that do a rudimentary job of tuning and may or may not offer extra features such as timed recording, pause, and so on.

Radio is one of the most difficult responsibilities for the PC to take over. For one thing, head unit radios are very mature and sophisticated, and they are designed to clearly receive broadcasts while moving at highway speeds. PC radio cards and USB receivers, on the other hand, usually use the cheapest radio chip available and are designed to sit still on a desk or in a window. This means that the signal quality of these devices is not as high as it could be.

Another problem with PC radios is that they do not adhere to a standardized programming interface. Each new unit from a different manufacturer has its own method of changing stations, and these aren't usually part of a published API. Luckily, the interfaces usually get reverse-engineered by the Linux community to produce open source drivers and documentation, but this does mean that in-car GUI software has to be re-coded to control each different FM receiver.

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A variety of software programs enable your computer to make scheduled recordings of radio programs.

TiVo has grown in popularity over the past few years, and personal video recorders (PVRs) are proliferating as a must-have feature for set-top boxes. Naturally, consumers of audio content want the same features, and many PC programs have been developed to meet this demand.

The real key to a functional personal media recorder (PMR) is the database. It's quite easy to plug a radio into a sound card, tune it to a station, and record, but what makes the process more user friendly is to have the computer tune the channel automatically and provide the end user with a menu of choices. Also, as the success of TV Guide tells us, the information on what is playing is as valuable as the recording itself.

While there are a bunch of programs that find and record online radio stations, few of them control the radio to change the station, and almost none of them offer any sort of radio program listing. However, one subscription service, Radio Time (http://www.radiotime.com), does it all, and will provide you with an inexpensive radio tuner that looks conspicuously like the D-Link DSB-R100.

As Radio Time has to pay licensing fees for their database of program listings, they pass that cost on to the consumer in the form of a subscription service. For around $40 a year, you get access to their database of the programs in your area, and they will sell you the FM receiver hardware as well.

To use their system, you simply enter a Zip Code, and you get a list of radio stations in that area. The stations are displayed in a web interface and include many of the program search features you'd expect (by station, category, genre, etc.).

To use this interface on the road you must have mobile Internet access (discussed in Chapter 6), but programs you record, once set, record at their scheduled times regardless of connectivity. The service recommends broadband Internet access, because it can record a wide variety of Internet radio stations as well.

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Have your email, blogs, and RSS feeds read to you using computer text-to-speech voice synthesis. It's safer than reading while driving.

Computers have had primitive speech synthesis capabilities since the early 1980s (you may remember the awkward computer voice of the Speak & Spell), but only recently have computers gotten powerful enough to produce speech that sounds, well, natural. While the alt-rock band Radiohead pioneered the use of speech synthesis in a song on their album OK Computer, this hack shows off some products that you can use to have your email read back to you or keep up with blogs while you're on the road.

To get the email messages into your car PC to begin with, you need to either carry them to your computer via a portable storage device or follow the hacks in Chapter 6 to enable your computer for Internet access.

One option for reading your mail is to use a product such as ByteCool's CoolSpeech (http://www.bytecool.com), which fetches email from a POP3 email account and reads it to you. The program relies on the built-in voices available on your computer, and you can purchase additional, higher-quality voices from their web site that work with Microsoft's Speech API (SAPI). You don't have to worry that the emails will get deleted from the mail server; the email feature in CoolSpeech is read-only and leaves the messages in place so that you can download them later with your regular email client.

Another approach is to simply convert the emails or text documents to MP3 on your desktop computer, and then carry the MP3s to your car computer via a portable drive. You can Google "email TTS MP3" (or similar keywords) to find a variety of programs to do this, such as Visual Text To Speech MP3 ( http://www.visual-mp3.com/text-to-speech/).

In fact, most text-to-speech programs (http://www.microsoft.com/speech) come with some sort of helper application you can use to quickly convert text to speech and save it to a WAV file, which can then be easily ripped to an MP3 by another program. For more on this approach, check out

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If you know what time you were listening to the radio, you can find out what song you were listening to using a web service.

"Record Radio Shows" [Hack #20] highlighted a subscription-based web application that provides a program guide for upcoming terrestrial (and Internet) radio. However, with a different web service you can answer the question "What was that song?" for a day after the program ran.

Table of Contents

Section 1.5.1.1: Twist and tape.