The FAQ (Work In Progress)

This section attempts to answer some of the questions generally asked by people wanting to build their own systems. The way I have built mine is just one of many ways to build such a system.

What motherboard and processor should I use?

Pretty much anything you like. The requirements are that you can power it, you have an input mechanism (keypad or IR, eg), an output mechanism (a sound card and video output), sufficient processing power to achieve what you want to do and software to do it. A conventional AT or ATX motherboard would be just fine. A popular choice is the Via Epia series of motherboards. Something to keep in mind is that more powerful systems require a more powerful power supply solution. If you don't need the power of a 3GHz P4, you might be better off opting for a lower power solution and save yourself some headaches when trying to sort out the power supply.

What power supply should I use?

A good choice is one of the Opus series of power supplies. They are currently available as a 90w or a 150w vesion, and can be purchased from a number of resellers. The Opus supplies usually include a shutdown controller, allowing the system to be started automatically when you turn on the ignition, and shut down cleanly when you turn it off again. They provide full regulation on all supply lines, and can cope with powering the PC whilst the voltage drops during cranking.

An alternative for lower power systems is something similar to the popular ITuner style power supplies that plug directly into the ATX connector on motherboards. These are oftem used for the Epia motherboards. Be aware that the 12v line often not regulated (check the specs) and that you may need a pre-regulator and shutdown controller as separate units. Two such units are the Carnetix and the ITPS. The ITPS uses a linear regulator and so suffers from voltage dropout if you are putting less than 13.5v into it.

A third choice is to use a conventional mains power supply and use a power inverter to generate the mains voltage to power it.

Yet another option is to design and/or build your own. There are a couple of designs available on the web (search for Sproggy or Mastero).

What screen should I use?

Character based screen. These are usually connected to a parallel port, a serial port or sometimes a USB port. They require special plugins for the player you are using to display the information. The wiring diagrams for the displays will depend on the particular plugin you use. Most are suitable for an HD44780 based LCD/VFD and will use an 8 bit parallel interface. VFDs are brighter, but require slightly more power and tend to be more expensive.

Composite monitor connected to a TV-out output. Use of a TV-out output and a composite LCD screen will allow graphical output to be displayed. Although this option is relatively cheap, the quality acheivable is not great - the modulation of luminance and chroma onto a single signal, the relatively low horizontal scan rate and the interlaced screen will mean that you will see flickering, very low resolution, and cross talk between edges and colour.

VGA LCD monitor. A better option is to use a VGA LCD monitor. These take 31kHz horizontal sync signals with separate RGB signals to provide high quality output. Examples are the Gain, Lilliput and Xenarc screens.

Direct digital connection (LVDS or DVI for example). The highest quality option is to connect an LCD monitor over a digital interface such as LVDS or DVI to the system. This kind of system can be prone to noise when extending the signal cables over any kind of distance (don't expect to have your screen up front and your system in the trunk with this one).

Can I use a laptop screen?

It is generally not economically viable to use a laptop screen unless you are connecting directly to a digital LCD port that some motherboards have (a DVI port doesn't count). Even then it can be an intricate process to figure out the connections. To use a laptop screen in other cases, you will need a LCD panel controller card suited to the LCD panel, and these tend to be very expensive when compared with alternative options (a VGA LCD for example).

What should I do for software?

You have a lot of options here. It would be pointless of me to try and summarise them here, since list is always changing. Most require Windows to run. See MP3Car for more info.

Your options for DOS include mpxplay which is the generally accepted DOS player. Or you could write your own using some of the freely available codecs on the web (mpg123, libvorbis).

How do I get sound from the computer to the speakers?

You have several options here:

Method	Advantages	Disadvantages
FM modulator.	Easy, inexpensive.	Modulation/demodulation loses quality. Can interfere with radio reception.
Cassette adapter.	Easy, inexpensive.	Inductive coupling loses high frequencies. Dangling wires are ugly.
CD changer aux adapter.	High quality sound, nicely integrated.	Can be expensive. Availability of adapter for your headunit may be a problem.
Direct to amp.	High quality sound, headunit DIN slot can be used for other purposes such as a screen.	Alternative volume control method is needed, either via PC or an inline volume control.
Hacked headunit.	High quality sound, nicely integrated.	Can be difficult to achieve. Requires electronics knowledge.

How can I solve noise problems?

The first thing to understand is where noise come from. Common causes are a noisy power supply, induced noise, or noise caused by ground loops. Noisy power supplys can be caused by invertors and badly regulated/smoothed supplies. Induced noise can be caused by running signal wires near to power wires or speaker wires. Ground loops are caused by different parts of the audio path having different ground points. This causes small variations in the signal which are then amplified and fed to the speakers.

Noisy power supplies will cause noise even without the engine running. To test this, run the system without the engine running. The addition of filters to power lines can help. If you can hear hard disk noise, this may be a sign that the supply to your sound card is not isolated well enough from the logic circuitary on your motherboard. Replacing the sound card or using a USB sound card may help this.

Induced noise from power cables can come from power wires, speaker cables or noisy contact breakers (old cars only). Try routing signal wires away from the power cables or using higher quality shielded cable.

Ground loop noise will generally vary with revs. To determine if this is the case, start the car with music playing, and rev the engine. If the pitch of the noise changes, then a ground loop may be your problem. Either ground all your audio components at the same point, use a ground loop isolator, or use digital audio paths to isolate the grounds (optical is best, since there is no electrical conection, and they are not susceptible to induced noise).

Where should I mount the computer?

Several options:

Location	Advantages	Disadvantages
Trunk / boot	Lots of space available. Out of sight from prospective thieves.	Long cable runs for optical drives, screens, power, audio signals.
Under passenger seat.	Short cable runs to headunit and screen. Accesible optical drive from the cabin.	Not much space available.
In dashboard.	Very short cable runs to headunit, screen and drives. Easily accessible drives can be integrated into dash.	Very small amount of space.

How should I control the computer?

Several options:

Method	Advantages	Disadvantages
Infra red remote via an IRMan or a UIR. Receiver software is generally programmable, so any remote can be used, or a specialist steering wheel mounted remote.	Receiver can be concealed. Easy to do. Any one in the car can control the system.	Losable remote. Need to buy batteries. Some remote systems feel laggy.
Hardwired buttons to parallel port or serial port.	Buttons can be integrated into dash. Very responsive input system (no IR code to decode).	Takes some effort to integrate tidily. Limited number of buttons.
Standard keyboard or mouse (either cabled or wireless).	Easy to do.	Large, awkward to use whilst driving.
Touchscreen.	Very intuitive interface. Easy to program for (looks like mouse clicks).	Expensive. Some touchscreens have problems with heat and degrade over time.

What should I use for a case?

A regular case would suffice. You may want to use something smaller though. Commercial cases can be bought that will fit into a DIN slot (eg, the C134), be beware of the depth of the case (10") and that they may require some clever internal arrangement to get everything in.

If you choose to fabricate your own case, you again have several options. Some like to show off their installs with a plexiglass case with neons. Others (like me) prefer to have the smallest possible case and hide it away from would be thieves. You can either build your own case from sheet metal, plexiglass, wood, etc, or start with a project box and modify it to suit your own needs.

How can I watch movies?

You'll need a motherboard with a fair amount of grunt to decode the movie. A better option might be to get a motherboard with specialised hardware to assist the decoding (some video chipsets have this).

Movies are big, so you'll need some fairly major storage capability.

What are the legal issues?

Many regions do not allow a video screen in the view of the driver whilst the vehicle is moving. This is why a lot of in dash screens have a lockout wire that should be connected to the handbrake. There are some exceptions (and you should check the specifics with your local authorities), the most notable being a system that displays information relating to an entertainment system (eg, radio receiver or a CD player), and displays of navigation information (satnav systems). It is important that you verify with your local area the rules concerning in vehicle displays to avoiding breaking the law. If you are found to have an illegal system it could mean fines, points on your license, or adversely affect any insurance claims in the case of an accident.

DISCLAIMER: I am not a lawyer, I do not claim that the above is true in your region. I am alerting you to the existance of such regulations, and it is up to you to investigate further. I take no responsibility for anything you install in your vehicle and the conformance with local requirements.