Getting my USB gamepad working under DOS was the major show-stopper with this project. Once that problem was solved I finally got the chance to order some hardware and start building my new system.
Choosing a computer case:
I was looking for a case that was small and compact, but large enough to accept a PCI card. One case that immediately caught my attention was the Voom PC case. I liked everything about it except for the fact that it's too small to allow you to use a PCI card. I went over to the Mp3car.com forums and searched around, looking for other ideas. I noticed that a couple of people were using a similar case, made by Mobile Computing Solutions. Their case is about 1/2" taller than the Voom case, allowing just enough room for a PCI card.
Choosing a motherboard:
Since I'm not playing video, I don't need a fast CPU. Instead, I wanted a motherboard and processor that are energy efficient. This makes it easier to keep the system cool, and allows me avoid using a super-expensive power supply. DC-DC power supplies are expensive enough, already. I picked the Jetway NF76-N1GL-LF motherboard. It uses the 1.0 GHz fanless version of the Via Nano processor. I liked the fact that it doesn't need a CPU fan. It's one less thing to go wrong. The processor doesn't draw much power. The motherboard has 4 serial ports (that ought to be enough). It has two SATA ports (I need at least one). Last, but not least, it has onboard video and networking. This allows me to use a sound card in the PCI slot.
For a car-computer, solid-state storage is ideal because there's no moving parts and it isn't temperature-sensitive. The only problem is the cost. Large solid-state drives are extremely expensive. The next best thing is a laptop hard drive. They take up less room than a desktop drive and draw less power. Since the year is 2009, not 2001, laptop drives are dirt cheap. As a compromise, I used a 4 gigabyte Transcend IDE Flash Module as the boot drive, and a 250 GB Hitachi 5K500.B laptop hard drive for the music.
I picked the DIAMOND XtremeSound XS71. It's cheap, and it's based the MPXPlay-compatible CMI8768 sound chip. It also has a coaxial SPDIF output jack, which would come in handy if I can find a way to get it to work in MPXPlay.
After the basic components had arrived, I hooked up a standard desktop power supply, hacked up some extension cables, and measured the amount of power draw on the 3.3v, 5v, and 12v rails. Without that information, it's impossible to know how big of a power supply you need. The system draws 0.33-0.35a from the 3.3v line, 0.55a from the 12v line, and 1.23-1.75a from the 5v line. This meant that I could use a low-wattage power supply and still have plenty of room to spare. The Mo-Co-So case was designed to use the Minibox M2-ATX power supply, but after reading mixed reviews I decided to look elsewhere. The Opus 150w power supply gets a lot of good reviews, but it's 7" long, which would make it difficult to fit in the Mo-Co-So case. Finally I took a look at some of the industrial power supplies and found one that I liked: the Magic Power MPD-807H. It's a 70w DC-DC ATX power supply with a wide input range (9-32v). The primary and secondary sections are isolated, which should make it less noisy as well as avoiding potential ground-loop issues. Last but not least, it looks like it's built to last. After taking some measurements I determined that while there isn't much room to spare, it will fit in my case. It doesn't have a shutdown controller, so I'll need to hook it up to a relay. I'll also need to make my own mounting plate.
Last Update: 9-13-2009
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