unwanted noise when connecting wince tablet to car stereo using aux in

Thread Starter

tonyjms2005

Joined Jul 23, 2014
21
hello
I have a wince tablet sat nav, I have the nav unit connected to my car stereo via 3.5mm aux in. I get unwanted noise in the form of an intermittent sound the almost sounds like data being sent like the old fax machines.
The power supply and ground for the nav unit uses the same earth point as the stereo, there is no alternator interference.

Would I set of capacitors remove this unwanted noise?

Thanks

Antony
 

JoeJester

Joined Apr 26, 2005
4,319
Does the "noise" increase and decrease with you adjusting the volume on the tablet?

You might be over driving the aux input ....
 

Thread Starter

tonyjms2005

Joined Jul 23, 2014
21
Hi
Thank you for the swift reply.
I will try to reduce the volume on the nav unit when I drive the car later on, I will let you know how it goes.

Thanks

Antony
 

BR-549

Joined Sep 22, 2013
4,938
How long is the "data being sent like the old fax machines." sound, it's duration?

Is this when you are driving? or is this when you're sitting at a light or driving thru intersections?
 

Thread Starter

tonyjms2005

Joined Jul 23, 2014
21
Hello
I have tried reducing the volume but it has no impact on the sound.
The sound happens every time the nav unit is switched on and periodically when driving. I think perhaps its when the unit is perhaps refreshing the Bluetooth connection or perhaps talking to the gps saterlites?

Thanks

Antony
 

BR-549

Joined Sep 22, 2013
4,938
Ok, I'm confused. Doesn't take much. Is the audio connection, so that it (sat nav) can tell you when to turn left and when to turn right?

What's the bluetooth for?
 

Sensacell

Joined Jun 19, 2012
2,587
Is your cellular phone located near the whole setup?

You can hear the transmissions from cellphones quite easily when low level audio signals are involved.
Every time they ping home...
 

Thread Starter

tonyjms2005

Joined Jul 23, 2014
21
Hi
My phone is kept away from the setup, I have also tried switching my phone off.
The unit is basically a wince touch screen unit with gps and Bluetooth. I replaced the factory fit sat nav in my car as the system was outdated.
I use the aux in on my car oem car stereo so that sat nav instructions can be broadcast through the cars speakers and the same goes for telephone calls via the Bluetooth option.

The gps unit I bought is not an expensive unit, it is actually unbranded but it was the one I could find that would perfectly interface with the car, ie the screen fits the motorized housing inside the car perfectly, and the unit can be made to easily switch on and off with the car ignition.

The only issue I get through the aux line is unwanted background noise, the noise does not change with the engine rpm, in fact the noise is present even when the engine is not running.

I was hoping maybe I can modify or construct my own aux in lead with a noise filter, or perhaps if anyone knows an "off the shelf solution"?

Thanks

Antony
 

BR-549

Joined Sep 22, 2013
4,938
Thanks for the set-up. Let's figure out the problem, before applying a solution.

Can you play music audio from your tablet (like mp3 files), to your car radio? Analog audio, not digital signal. And if so, do you get noise?

You said that nav instructions and phone calls were noisy. Is audio music noisy?

Nav and phone signals come from a radio, music audio does not.
 

Thread Starter

tonyjms2005

Joined Jul 23, 2014
21
I have only played music via bluetooth using my mobile phone, the noise is present. The music does contain the unwanted noise, also just a pointer the noise is present through the car stereo when aux in is selected on the stereo, the volume on the tablet turned up but not loud and with the tablet not outputting any audio. Ie in between navigation instructions.

Thanks
Antony
 

BR-549

Joined Sep 22, 2013
4,938
PICK ONE ONLY.

A. Your car radio makes noise when you use your tablet satnet bluetooth and aux audio connection.

B. Your car radio makes noise when you use ANY bluetooth, and/or ANY aux audio connection?


Which one is it?

That pointer needed to be said in first post.

Any other pointers?
 
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Thread Starter

tonyjms2005

Joined Jul 23, 2014
21
My personal belief is that the noise is being created by the actual sat nav unit as it wasn't an expensive unit. I am thinking that the only solution is to use some kind of noise cancelling on the auxiliary in cable?

Thanks again

Antony
 

Thread Starter

tonyjms2005

Joined Jul 23, 2014
21
Just saw your last post, basically only this nav unit that I keep permanently plugged into my stereo generates the noise, the stereo is fine otherwise, its actually a bose system.
Thanks

Antony
 

JoeJester

Joined Apr 26, 2005
4,319
Using your phone only and the navsat de-energized.

Play audio via Bluetooth. Noisy or not?
Play audio via aux input. Noisy or not?

Use your WinCE only and de-energize the phone.

Repeat those two tests.
 

Thread Starter

tonyjms2005

Joined Jul 23, 2014
21
Hi

I just did some tests with the wince unit unplugged from the stereo:

Audio via Bluetooth is not noisy
Audio in general not noisy

With wince plugged in :

Audio via wince unit (sd card and this also has Bluetooth) is noisy

All audio coming from wince unit is noisy

With phone switched off is also noisy

The wince unit itself is definitely the source of the noise

Thanks

Antony
 

JoeJester

Joined Apr 26, 2005
4,319
Nice job, the preliminary troubleshooting is done. The major source has been identified.

Once a link to the WinCE tablet (model number) and if a user manual can be located, more progress can be made.

The problem with reducing the "noise", especially if it sounded like a fax machine, is it lies in the audio spectrum. Reducing it will reduce a portion of the spectrum and words might not be pronounced "correctly".

On a side note, can you return the WinCE because of the noise to get a replacement? Why dig into more troubleshooting if they will replace it.

Do you have access to an oscilloscope and other test equipment?

Can you open the tablet and post a picture of the inside?

You probably will get requests to get closer on certain area's once a picture of the printed circuit board is circulated here.
 
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