Jantsa

Just installed Carpc, and touchscreen. I found out that when engine is on, whining comes along from the speakers. Did some research and found that touchscreen LCD is the one making the noise. Whining gets louder when RPM gets bigger, so my question is, how can I ground my touchscreen? Power for the screen comes from the cigarette adapter plugin, and screen is connected to the computer with USB and VGA.
Any ideas?

EDIT:
Oh, sorry about the bad explanation.. laptops audiocable is connected to connect2box, which is connected to my cars head unit (cd charger). It makes AUX-IN connection possible.
So the sound is coming from the car speakers. Screens speakers are not connected at all. More ideas?

JimmyFitz

Turn the volume all the way down on the screen. Or disconnect its speaker.

__________________
2002 T-Bird, Via SP13000, Travla C158, M1-ATX, 1GB RAM, 120GB 2.5" drive, SlimSlot DVD-RW, XP, RR, Winamp, Xenarc 700TSV, HTC Touch PPC/Phone, BU-353 GPS/iG3, Elmscan OBDII, Griffin PowerMate, 2 Blaupunkt amps, Polk spkrs, 5 sec startup/STR
~Jimmy

Jantsa

Oh, sorry about the bad explanation.. laptops audiocable is connected to connect2box, which is connected to my cars head unit (cd charger). It makes AUX-IN connection possible.
So the sound is coming from the car speakers. Screens speakers are not connected at all. More ideas?

Jantsa

I was still thinking about what I tested today..and..

Laptop was on, touchscreen was on, and they were both powered by cig lighter.
There was loud whining.

I unplugged the audiocable from the laptop, to another laptop without no
touchscreen, and sound was clear, no interference.

So...

It's not screen, it's not screens power, it's not AUX IN connects2box, it's not head unit, problem has to be something between laptop and touchscreen..

Could it be VGA, or USB cables..

Tomorrow I'm going to test unplug those cables and see what happens. I'm preparing myself allready, that problem is there. Well what can be done if it's VGA or USB interference...?

JimmyFitz

You have the right idea about isolating the source of the noise. Once you determine which device is the culprit, try re-routing the offending cables away from the others, etc. Also, keep your RCA audio cables as short as possible.

__________________
2002 T-Bird, Via SP13000, Travla C158, M1-ATX, 1GB RAM, 120GB 2.5" drive, SlimSlot DVD-RW, XP, RR, Winamp, Xenarc 700TSV, HTC Touch PPC/Phone, BU-353 GPS/iG3, Elmscan OBDII, Griffin PowerMate, 2 Blaupunkt amps, Polk spkrs, 5 sec startup/STR
~Jimmy

wywywywy

Or try a ground loop isolator.

Jantsa

I got rid off that annoying sound.

I tested it today, and I found out that it doesn't matter which laptop was connected. Yesterday I was probably so tired, that most of the sound was coming from my head..

I moved laptops place from under the passengers seat to different place and interference wasn't that loud anymore. Then I went to car-audio store, and bought ground-loop isolator.
That was the final cure. Interference is finally gone, and I'm happy.

I can imagine what it would be like if isolator wouldn't help. There would be huge job trying to seek the cause of the interference..

wywywywy

And now you just need to figure out how the interference is affecting your GPS/WiFi/Bluetooth/Radio...

Jantsa

Radio, bluetooth and wifi seems to work fine, no interference there. I can't yet test gps, because I'm using Tomtom navigator before I found laptop navi-solution suitable for me.

Is it how likely that there will be problems with some of those things (bt, wifi, gps, radio)?

numbers

Not very likely. Probably in 9 out of 10 cases where someone thinks they have an "interference" problem, it's not interference at all but rather a case of mismatched grounds.

Commonly called alternator whine, your noise was actually caused by an internal connection between your laptop's power ground and audio signal ground. Current flow over the audio ground wire through your head unit caused a voltage difference between the laptop end of the audio cable and the head unit end of the audio cable. With the engine off, this static difference is pretty harmless, but once the alternator begins sending a very dirty waveform of voltage to the electrical system at high frequency, that voltage difference between the two ends of the wire oscillates with the alternator and since the left and right channel wires don't oscillate along with the ground, the voltage difference ends up making it to the speakers.

The end result of all that is: the frequency being output by your alternator winds up coming out your speakers. When you added a ground loop isolator, the current travel over the ground wire stopped, and so did your noise. The ground loop isolator is nothing but a 1:1 transformer, which means that a/c (sound waves) get through and d/c (power consumption) doesn't.

Jantsa

Thank you for the great information. I didn't quite understand what component(s) causes my problem and how dp they cause it. I also didn't know what ground-loop isolator does that interference stops. That was great piece of information. Hopefully isolator keeps interference away.