Electronic Design

Car PC, Part 2: The Mini-ITX PC

This is the second article in a multipart Car PC project. The first part addressed the installation of the Car2PC interface module that links a USB-based system to the audio head unit that is typically a radio/CD player combination. The initial testing was done using a laptop PC. This next step will use a Mini-ITX-based PC with a motherboard supplied by ITOX.

Building a PC for the automotive environment is not as simple as it sounds. The environment is significantly more rugged than an office environment. Power is not as clean and wiring can be a royal pain.

Being relatively new to this type of design I took advantage of the expertise of one of our suppliers, Logic Supply. My interview with Scott Hayden, Sales Director for Logic Supply, covers some of the areas that Logic Supply addresses as well as the kinds of support they can provide designers.

Logic Supply's support was very helpful. I made the usual mistakes, like wanting to use a conventional power supply, which does not work in an automotive environment. Logic Supply was able to help in this area, describing their M2-ATX power supply, which I used in the project. It meshes perfectly with the CarTFT VoomPC case also provided by Logic Supply.

Logic Supply can handle all your Mini-ITX needs, including motherboards, but we turned to ITOX, an industrial motherboard company, who suggested their G4M100-MS12 motherboard for the project. ITOX can provide technical support for embedded designs like this project as well, although their case selections do not target the automotive space. The Celeron-based G4M100-MS12 is comparable to the Intel-based Mini-ITX boards available from Logic Supply. Likewise, ITOX has a wide range of motherboards that can provide cooler systems with less performance or systems with higher performance processors.

This system does not include lots of hardware. The two other main components are Seagate's 160-Gbyte Momentus 5400.3 SATA drive. It gets its capacity courtesy of perpendicular recording. The other component is a pair of 400-MHz DDR PC3200 SDRAM modules from Crucial Technology.

Each of the products used in this project have individual reviews so you can check out the details in those articles. The rest of this article addresses the construction of the system. The next article in this series will add a GPS receiver and a complete Windows-based automotive navigation system.

Building the Mini-ITX Car PC

Building the Car PC is comparable to building a regular PC-based system, but you need to pay attention to details because otherwise they will come back to haunt you. Power, heat dissipation and vibration are more important on a Car PC versus a regular PC, as is the case with most embedded systems.

The first thing is to make sure that the heat sink is sufficient for the job. The ITOX motherboard comes bundled with this Celeron processor and heat sink (Fig. 1) so the choice is not an issue for this project. It was important that there be enough headroom above the heat sink fan for proper air flow. Still, the space above the fan to the top of the VoomPC case was minimal.

The first step was installing the Celeron processor in the ZIF (zero force insertion) socket (Fig. 2). This and the installation of the heat sink/fan combination must be done before the motherboard is mounted on the VoomPC's bottom plate (Fig. 3). The bottom plate has risers for the motherboard and the power supply board. There are holes for the hard disk. Air flow under the board goes across the hard disk.

The motherboard is mounted on the bottom plate using four screws (Fig. 4). The next step is to install the Seagate hard disk behind the motherboard (Fig. 5). Unlike the 2.5-in. IDE drives used in previous projects, this SATA drive uses the same connectors as other SATA drives, so it does not require an adapter.

The Seagate hard disk is mounted using four screws from the bottom. The drive sits on four foam washers that provide additional vibration protection. It keeps the drive about an 1/8 in. above the bottom plate to allow air flow under the drive.

Next install the power cable and SATA drive cable to the Seagate hard disk. The other end of the SATA cable is plugged into the motherboard. The two Crucial Technology PC3200 DIMMs can be installed as well.

It is now possible to install the M2-ATX power supply above the hard disk. It is held on using just two screws. This is enough to keep the power supply from moving around, but be careful when plugging in the power supply cables since the board is only supported in two places. It is possible to install all the cables before mounting the board. Don't forget to check out the power cycling jumper settings. The default is no jumpers and the system then works as it would with a normal power supply. This is fine for testing but not what you want for final installation. Setting 1 is recommended and seems to work well for this application.

The power supply has a number of cables connected to it including the external power cables (Fig. 6) and the cables that connect the power supply to the motherboard (Fig. 7). The latter includes the 4-pin 12-V power cable. Once you are all done it looks something like Figure 8.

Next it is time to add the extra fans to the VoomPC. The case comes with one already installed, and adding one or two more is simply a matter of four screws per fan. Just make sure the fan cable is long enough to connect it to the motherboard before it slides into the case. In some instances it might be easier to connect the cable to the motherboard, slide the motherboard part-way into the case, and then screw in the fan using a small screwdriver.

There are two spots where the bottom plate will slide into the case. For this motherboard, the bottom slot must be used to provide enough headroom for the processor's cooling fan (Fig. 9). It is then time to button up the system and screw in the back plate (Fig. 10).

Testing the Mini-ITX Car PC

It is possible to connect the system to the car's power system and then fire up the board. That is not recommended. Actually, I tested the system in increments as the pieces were put together. First I used a conventional power supply to power the motherboard and test out the hard disk. I also took the liberty of attaching a DVD drive via the IDE port. This allowed me to install Windows XP on the hard disk so it did not have to be done later when a USB CD or DVD drive would have to be used.

Of course, this approach made it easier to install since I also attached a standard VGA monitor and USB keyboard and mouse to the system. One thing that needed to be done was to configure the BIOS so the board would boot automatically and ignore any errors — such as no keyboard.

I also ran an extension cord out to the car where the Car2PC adapter was installed so I could check the system out using the external power supply. I had installed the Car2PC software as noted in the first article and made sure the system was working.

The other part of the job was to wire up a cable for providing power from the car's battery to the system. This is specific to each type of car and it pays to check things out thoroughly. Shorting out the battery or power supply is no fun. The M2-ATX power supply has a 15-A fuse, and it doesn't hurt to connect the power cable from the Car PC through another fuse. Just make sure there is sufficient power available or you may be popping fuses.

Don't just plug in the custom power cable once you have it ready. Use a voltmeter to check the polarity. The fuses should protect everything but it can get expensive if you get it wrong.

For test purposes, it is possible to build a power cable that plugs into the power outlets on most cars. These are the round sockets that used to house cigarette lighters and now power portable games, MP3 players and the like in most late model cars.

The actual testing and operation of the system with a direct connection to the car's power should be the same as using the regular PC power supply. Of course, you can always plug a monitor into the system to see what is supposed to be going on but if you can play the MP3s then you are all set.

The second most difficult job after building and testing the custom power cable is actually routing the cables to where the Car PC will finally reside. This may be under the dash, under the car seat or in the trunk depending upon the car and what you want to do with the Car PC.

I'll forego the details for mine at this time since the next article in this series adds a touch screen LCD for the navigation system.

If you just plan on using the system for audio support then it is possible to use a much smaller hard disk and a lighter-weight motherboard, since the audio application barely taxes the system. It is possible to keep the system headless and still update the MP3 files using USB memory sticks and some creative scripts that are automatically run when the memory stick is installed. I'll leave that as an exercise for the reader.

A more preferable approach for many is to use Windows XP's remote console support and the Ethernet connection in conjunction with a laptop PC. A reversing Ethernet patch cable will allow direction connection between the Car PC and the laptop. It is easiest to use fixed IP addresses for this process, although the more adept may want to setup a DHCP server on the Car PC.

Till the next article in the series, enjoy the music.

Related Links




ITOX Applied Computing

Logic Supply



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