After finally collecting all the main bits of the setup I've been planning, I finally got everything in the car for a rough fit Tuesday, and after some frustration with a ground loop, resolved that on Wednesday just in time for a nice 400 mile road trip.
My car is an '06 Nissan Sentra SE-R Spec V, Carputer is a 1st generation MacBook Pro, and a Lilliput screen. Long term plan is for the brains to be mounted in the trunk, with VGA, Audio, and USB cabling running to the dash, display will flip up from the storage compartment on top of the dash, an Apple Keyboard (the new smaller one) on the back side of the driver's visor, and a control pad on the steering wheel. My main goal will simply be for the system to play music, my old click-wheel iPod is just too tiresome in the car. The built in Front Row software suited my needs almost exactly, except for the annoyance of it not working with mouse or touchscreen input.
So, my rough install is far simpler, the Lilliput screen wedged into the storage bin, cabling running to the laptop under the driver's seat, a non-powered USB hub connecting the display and keyboard to the Mac. A TrippLite power inverter provides AC for the Mac, and finally a Logitech gamepad in the glove compartment for controlling Front Row.
I'm using the USB Overdrive software to map the controls from the gamepad to the desired keys for Front Row, the up/down d-pad buttons are up/down arrows, left dpad is Esc, right dpad is return. This actually seemed workable at first, until I needed to skip a song, so I mapped the right arrow to another button.
The Mac is set to not sleep while on AC power, and to sleep after 1 minute (minimum setting) when on battery, and to automatically wake when AC power is present, so I should never had to worry about having to manually powering it on.
The last major piece is a script that I'm still tweaking to sync my iTunes library from the living room Mac to the carputer via my home wifi network. Other than the speed being a bit slow because of a weak signal, it's working fairly well, I run the script manually from the dock.
So, I wanted to write briefly about the ground loop issue I had, now that I've got all that background info out of the way.
In the past, I've experienced issues when connecting laptops to some AV equipment at the office, video by itself would work great, but as soon as the audio cable was plugged in, a noticable hum could be heard. So, when I had a hum, I assumed ground loop and tried to fix that on the audio side, but was unsuccessful. Troubleshooting further, I found that the issue existed even when the Mac was on battery power with no AC adapter, but the issue went away when the power inverter was powered off. At this point, both the laptop and the Lilliput were powered via the inverter. Everything going to the inverter seemed to be well grounded, the lighter socket had a good connection, etc, but obviously some difference existed between there and the radio where my audio was being fed in via the Aux jack.
Running low on time before I had to get on the road, I dug out the car power adapter for the Lilliput, and plugged this into the front socket, and instantly the buzzing noise went away. I'm still planning to power the screen via the AC adapter when I do a more permanent install, but will need to be sure that I ground the screen at the dash to keep this issue in check.
The road trip was a great success, 6 hours in the car with plenty of tunes, and most importantly, it passed the wife test.
She even liked using the gamepad to control the tunes, which should make it much easier to justify any future time and expenses in this project...
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