charging ipod while playing causes interferance

[buttdart]

i was excited about the aux/power outlet that came in the arm rest of the ms3.

i just have one small issue - i can't charge the ipod while it's playing on the aux input!

i bought a usb charger and plugged my ipod into both the dash charger and the arm rest charger. both cause a nasty static.

i decided to pull my old car up along side the ms3 and plug the charger into the old car. the static interference was gone!

i thought it might be the usb charger, so i returned it and bought an actual ipod car charger. same thing!

i guess i should take the car to the dealer and have them figure out the issue. my guess is a bad ground or a unshielded wire somewhere.

 

[Rotus8]

This is a standard Mazda misfeature. You need a line out isolator. They are available from Crutchfield or Radio Shack. The crutchfield one is better because the connectors match.
http://www.crutchfield.com/App/Product/Item/Main.aspx?g=181150&i=127SNI135&search=isolator&tp=2653

 

[ehidle]

It's not a "standard Mazda misfeature." It's just a ground loop and is to be expected whenever you have equipment connected to ground in more than one place.

In this case, the ground of the Ipod is connected to the stereo through the sleeve of the aux cable, and also to the chassis of the car through the charging cable. This creates a big galvanic loop in the ground, causing it to behave as an antenna, picking up lots of electromagnetic noise.

The isolator is just a 1:1 transformer in the audio cable, which degrades the audio somewhat, but breaks the galvanic ground loop.

If i designed an isolated power supply for the Ipod and built it, would anyone buy it?

 

[buttdart]

If i designed an isolated power supply for the Ipod and built it, would anyone buy it?

i don't really want to wait, but if it's something you can 'make' within a week or so, i'd buy one asap! heck, i'll be the test dummy.

 

[icspots]

+1 to what everyone else said.

ehidle couldn't you just rewire one of the power points to tap the power/ground off the HU and avoid differing ground potential?

 

[buttdart]

if i purchase an isolator, will the interferance be completely gone?

 

[montrealms3]

It's not a "standard Mazda misfeature." It's just a ground loop and is to be expected whenever you have equipment connected to ground in more than one place.

In this case, the ground of the Ipod is connected to the stereo through the sleeve of the aux cable, and also to the chassis of the car through the charging cable. This creates a big galvanic loop in the ground, causing it to behave as an antenna, picking up lots of electromagnetic noise.

The isolator is just a 1:1 transformer in the audio cable, which degrades the audio somewhat, but breaks the galvanic ground loop.

If i designed an isolated power supply for the Ipod and built it, would anyone buy it?

Sure . . . depending on price

 

[ehidle]

icspots: if you do it that way, you'd be pushing all the current that the ipod needs through the signal cable, and I don't know if it will handle that kind of current. It probably will, but it is also not the best practice to have power and signal grounds in common.

buttdart: The best you could hope for would be a few weeks. It takes time to do the circuit design, analysis, and lay out the board and do the signal routing, and procure the components and have someone build it. Then, there has to be testing, testing, and more testing, especially if I'm selling them. It's not exactly a quick process. I don't want to sell you guys something and have it catch fire in your cars and get sued But yes, breaking the ground loop and providing a QUIET power supply to your iPod should get rid of any ground loop noise issues.

I actually don't have an iPod, so could someone tell me what the current requirements are? What I am thinking is that I will simply provide a USB jack with an isolated 5V supply with tons and tons of output filtering to prevent any noise getting into the iPod. I suppose that since a high current USB port has 500mA available, that would be a good number to design with.

Probable features:

Input voltage detection and over/undervoltage lockout (will turn off if input voltage is too low or too high)
2kV ESD protection across the Isolation Barrier
Ultra low-noise, low-ripple output
Regulated 5V output, up to 500mA with output over-current protection

I can tell you guys now this won't be one of those cheap $10 chinese dealies you can find on ebay. I design stuff that goes into oil refineries and other stuff that can explode violently if it fails, so this will likely be along those lines.

 

[buttdart]

does this help with the power specs?

http://docs.info.apple.com/article.html?artnum=60939

what kind of price point would we be looking at off the top of your head?

 

[ehidle]

does this help with the power specs?

http://docs.info.apple.com/article.html?artnum=60939

what kind of price point would we be looking at off the top of your head?

That's odd. That site says it uses 12V, which is not to USB spec. Does your iPod indeed charge itself when it is plugged into the USB port? Does the USB cable for the iPod go directly from the USB adapter on the computer to the iPod itself, or does the iPod have to plug into a cradle which is plugged into both the computer and the wall?

Just trying to get an idea of what has to be done...

As far as price, it will depend completely on how many units I have to build. If I am only building one or two, the boards alone will cost a fortune. If I can get orders for 100 or so together, that will make them MUCH cheaper. The most expensive parts will be a) the printed circuit boards and b) the labor to build them. The more I do in a run, the less the unit cost will be.

I don't even want to guess right now, because I still don't know what the requirements are. But, I will look at some components tonight and see if I can come up with a reasonable estimate.

If the iPod really has to have 12V, that changes things somewhat.

 

[buttdart]

the ipod does plug directly into a USB port via PC to charge, or even a wall outlet. no craddle needed.

 

[ehidle]

the ipod does plug directly into a USB port via PC to charge, or even a wall outlet. no craddle needed.

Ok that is good news. I'm thinking I should have a second USB jack on this power supply to charge another device, such as a cell phone or camera or whatever.

Let the feature-creep begin

 

[Mid_Life_Crisis]

Ok that is good news. I'm thinking I should have a second USB jack on this power supply to charge another device, such as a cell phone or camera or whatever.

Let the feature-creep begin

What you need to remember is that this is something that could be used in just about any car. With proper marketing, you could sell a ton of these. Make an adapter available so it can be more or less permanently mounted behind the dash with just the port showing and it could really take off.

 

[nytmar3]

charge your ipod at home.......listen in the car.....problem solved ;-)

j/k

 

[buttdart]

charge your ipod at home.......listen in the car.....problem solved ;-)

j/k

thats what i've been doing. in fact, i CAN charge the ipod as long as i'm not on the AUX input, i get no hum.

 

[iredremix]

hahaha yea i have the same problem.. i just get over it and charge the ipod when i'm not listening to it

 

[camrycev6]

charge your ipod at home.......listen in the car.....problem solved ;-)

j/k

Or spend a little quid for the iPod adapter. No noise issues, no charging issues, not wires hanging out to the arm rest, and best of all...control it all through the exisiting controls on your steering wheel. I have tried both methods. If fact, I still think I have my Crutchfield ground isolator loop... I could give it to you. (You just pay the shipping.)

 

[nytmar3]

Or spend a little quid for the iPod adapter. No noise issues, no charging issues, not wires hanging out to the arm rest, and best of all...control it all through the exisiting controls on your steering wheel. I have tried both methods. If fact, I still think I have my Crutchfield ground isolator loop... I could give it to you. (You just pay the shipping.)

Does somebody actually make one that shows the text on our radio?

 

[camrycev6]

Not that I am aware of... Still, it is 168.445% better than using the aux jack.