Headless solution / carputer as head unit?

**roothorick** · 08-25-2005, 08:10 PM

I recently promised to set up a carputer in a friend's Jeep Cherokee (late 1980s). He buys the parts, I do the labor for free. Catch is, I've never done this before, and have only worked with desktop computers and the occasional laptop before.

This project began earlier today when he conveyed that the faceplate for his Sony Xplod head unit had been stolen and the unit is now useless. I made the suggestion he replace the HU with something a bit more homebrew, and after some persuasion, we (well, mostly I) started making plans. The system will consist of a computer running Linux mounted behind the rear seat, and a custom-made interface filling the HU socket in the dashboard, consisting of an LCD display, some buttons, and a slot-load CD-ROM in a homebrew enclosure, possibly built from the casing of his old HU. (VERY custom job, in other words.)

I still have a few kinks in my design:

As far as I've seen, nobody's actually tried to use a computer as a HU before, only connected it to their HUs which then manage the speakers and handle volume control. Has anyone ever replaced their HU with a computer? What extra steps/equipment was necessary?

I'm not sure how the buttons will interface with the computer. Is there a nice USB package to do this perchance? What have people used for buttons in their setups?

For controlling the CD-ROM, I'm leaning towards gutting a USB enclosure and using the electronics from it. I'm not sure how to power the CD-ROM though. It needs a 12v line, which the USB connection can't provide. (There's a 200mA limit anyway, not enough to power a CD-ROM drive by any stretch.) Should I run power wires from inside the computer across the truck to the dashboard, or hack up the enclosure's amp to run off the car battery (if possible)? Will the chipset misbehave if it's not receiving power except via USB?

As for the dashboard unit itself, I intend on building the unit by hand, but I don't know exactly how to do this. I've heard talk about fiberglass and something called "bondo", but don't really know what it means or how to use it / where to get it. Being a desktop computer technician by trade with no taste in aesthetics, I've never done as much as case modding before. How should I approach making this dash unit?

I was looking at using the Opus 150W power supply; however it's a tad expensive and driving up the unit price in a big way. I'm running on a tight budget ($500 for parts for dash interface, computer, and everything else) so $160+ hurts. Is there anything else that's reliable but still car-safe that I can fit in a Micro ATX case?

He's had numerous problems with theft before (in fact, that's how this whole project started), so is there any way I could mount the computer into the truck so it can't easily be removed? Same for the dash unit.

**Jcarere** · 08-25-2005, 08:56 PM

For cheap power I would suggest a desktop power supply (200 -300 watts) and an inverter. Inverters cost about $20 for a 225 watt and $30 for a 400 watt. You will also need to setup a startup and shut down controler to allow the computer to start when the car is started and to allow it to safly shut down when the car is off so it does not drain the battery. (http://www.mp3car.com/vbulletin/show...3&postcount=21)

I would suggest running the cd rom and lcd off of the regulated 12v and 5v lines of the power supply, that way they start with the computer and provides regulated current for longer life.

For audio you will need a 4 ch amp and possibly a subwoofer amp. You will need a front and rear output on the motherboards onboard sound or a 5.1 sound card. You can in a pinch use the single speaker out on a motherboard if you split the jack into two and use two headphone jack to rca converters which would plug into the 4ch amp. The amps remote turn on would require you to run a +12v line from the computers power supplie to the remote lead on the amp. So it will turn on with the computer.

You may also need a fm tunner card if your friend would like to be able to listen to the radio.( since he will no longer have a head unit.)

As for the lcd a 7 or 8 inch touch screen monitor would be ideal and that could be run off his computer 12volt line on his power supply.

You many also want to consider installing a usb hub in the front of the car to allow for usb devices like a keyboard and mouse. If you are planning on running a usb hard drive or cd rom you should use a powered usb hub. This requires you to run a 5 volt line from the power supply to power that and allow it to support usb powered devices.

Hope this helps.

**Jcarere** · 08-25-2005, 09:02 PM

As for the thieft issue if he has a rear spare tire well you can possibly make a floor out of mdf and create a trap door in it to access the computer. This would allow you to put a latch and a lock if you desired. Or you can bolt the computer case to the floor of the jeep or to the seat brackets. Just a few opinions

**roothorick** · 08-25-2005, 09:44 PM

FWIW: He just informed me his Cherokee is a 1989.