webby makes a ground loop isolator

This is a follow on from my previous post in which I made a vague effort to stop my mp3 player/phone making noise when it was connected to my car radio while charging.

While the linear regulator helped reduce the noise, it was still audible.
Time for a ground loop isolator!

For the uninitiated, a ground loop is where the ground/shielding/0v connections form a loop (hence the name). In theory this wouldn't be a problem, except that devices within a ground loop usually want to be at different potentials and throw tantrums if they can't have it their way. Or something like that... See wikipedia for a real explanation.
In my case the phone, radio and charger form a loop and I end up with lots of whiney noise coming from the speakers.


To the workshop shed basement desk that I use for everything!
Step 1: order parts
2x 1:1 audio transformers
1x box (optional, but only if you like police bomb squads)
1x shielded audio cable (I used the leftovers from the previous phone bodgery)

Step 2: Tea
Tea is the most important part of engineering, closely followed by hotglue and shiny things.

Step 3: Draw really easy to interpret diagrams
This should really be the first step, but it's a really basic project.

Normal audio cable:

From carphone2

Ground loop isolator cable:

See! dead simple! From carphone2

Step 4 make it happen:

note: 2 of the 4 cores on the 4 core cable are connected to  ground. From carphone2

Should have made the wires longer...  From carphone2

From carphone2

No more noise!

I think I'll order some longer wire for it so I can hide it under the dash a bit more at some point. There's no degradation in audio quality (none that you'd notice over the MP3 compression and weedy speakers anyway...)

All in all, I'm quite pleased with the result

car notphone

(Rant)
Have you heard the radio recently?
Does anyone actually listen to that rubbish?
...
What do you mean "Yes"?

Fine, be like that then, but I find the content broadcast from payola land to be poor at best and one can only take so much radio four before the need to kill a politician takes hold.
(/Rant)

Solution:
Old mobile phone to in car mp3 player conversion!
"But that's easy" I hear you say. Well yes, it is easy, but it's a Sunday and my soldering iron needs some exercise.

So we take one of these:

From carphone

Do this to it:

mmmm.... hot glue...  From carphone

And this:
(so I can find the buttons without looking)

more hotglue!!  From carphone

then do this:

yet more hotglue! xD From carphone

To keep it running forever I threw together a charger:

12V through a USB port backwards.. nice one guys.. From carphone

no such thing at too much hotglue From carphone

Hopefully this one wont put an annoying buzz onto the audio output like the switch mode ones do. Either that or next week will be "webby makes a ground loop isolator"

In addition to the hardware, I've put sypftp on the phone so I can upload music to wirelessly and light control to keep the backlight lit while the phone is unlocked.

I'll give it a test on the way to work tomorrow. :)