Skipjacks

I'm sure this has been discussed before but my search came up empty. Unfortunately I have no idea what the problem is so it makes it very hard to search for.

Here's the deal...(And I'll try to include as much information as I can so you know what I'm dealing with)

I finally switched over from using an FM modulator to using an auxiliary input to my head unit for my audio.

As soon as I did though I had some kind of electrical interference that I don't understand. Hopefully I just need to switch something around for a quick fix, but I don't know where to start.

To get the problem ALL of the following have to be true...

1) The car has to be running.

2) The monitor has to be turned on (meaning the power light is green, NOT that it just has power supplied to it)

3) The audio cable from the computer to the head unit has to be connected.

The computer does NOT have to be turned on. If any of the above three things doesn't occur I don't get the noise. I know the computer isn't outputting that noise because it doesn't broadcast it through the FM modulator and I get the noise with the computer turned off. I also know the head unit isn't the problem because it goes away if I just turn the monitor off.

The monitor is a 7" Lilliput and I do have the voltage regulator egg connected.

The monitor is powered off the circuit that powers the cigarette lighter. I THINK that's the same circuit that provides the constant voltage to the head unit.

I don't get the problem unless the head unit is set to AUXILLARY. So it doesn't mess with the output of regular radio or CDs.

A woman at my local electronics store, who admittedly had no experience with carputers, suggested it could be a grounding problem with the computer or a mismatched impeadence between the computer and the head unit. But she wasn't sure.

The grounding issue seems to be the most likely but I'd think with the computer powered off the grounding would be an issue. Am I off base there?

It's the fact that the computer doesn't have to be on that totally throws me. And that I can fix the problem by turning off either the car engine or the monitor and get crystal clear audio.

Does anyone have any thoughts on this?

Thanks in advance.

__________________
Here it is! My carputer install! 1997 BMW M3

MP3Car.com

 

Skipjacks

Update:

So I tried out the grounding scenario and it seemed to help when I was just holding a grounding wire in place. I think if I had a solid connection to a good ground it would be even better.

Where should the system be grounded FROM and what TO? The set up I had simply had the power inverter grounded to the car body. Obviously that wasn't doing much.

Where should the ground wire attatch on the computer and what should I ground it to in the car to get the best ground?

__________________
Here it is! My carputer install! 1997 BMW M3

durwood

Well you could try to ground it to the chassis of the head unit. In the back of it there is usually a screw point directly in the middle somewhere. That could help. Or go with the point you found. That seemed to work right?

FYI: Also, monitor cables can create noise on any audio cable if they are routed too close to them.

__________________

Skipjacks

I thought of that but they aren't routed near each other. Plus that would give me the problem with the car off too I figure.

I'll try grounding to the back to the head unit screw. That's worth a shot.

__________________
Here it is! My carputer install! 1997 BMW M3

Skipjacks

Okay I somewhat fixed the problem, thanks to the help from this board. (As always!)

There was a grounding issue with the computer. Solved that!

But I realized after I got that hissing out that I had another hiss. This time it's definitely interference from the car engine. When I rev out the engine the whine picks up in pitch and volume.

Again it's only in the head unit's auxiliary mode. The head unit is properly grounded. (I think)

Is there some kind of isolator I can put on something that would filter out the engine noise?

__________________
Here it is! My carputer install! 1997 BMW M3

MP3Car.com