[Robotgroup] car audio stuff

[mlists at resistive.net]

Hey Andre' -

Thanks, I'll give that a shot.  Oddly enough, the noise on the radio input
seems to be minimized when the charge line is plugged in, but the noise on
the ipod input seems to be minimized when the charge line is unplugged.  I
had a 100uF cap across the chip power and the audio output sounded pretty
muffled.  I'll have to play with it.

-Nick


> Nick,
>
> Sounds like you have a ground loop. But, tell me do you hear the noise
> WITHOUT the power lines connected to the iPod? The first step is to
> simplify
> the circuit, so you can focus on each piece. If there is still noise with
> the power disconnected to the iPod, then the things to try are
>
> 1. Put a .1, 1uF, 10uF cap in parallel across your chip first off.
> 2. Try putting an audio isolation 1:1 transformer in front of the signal
> to
> the iPod, really cheap, and will remove the ground from the iPod.
>
> Andre'
>
>
> ----- Original Message -----
> From: <mlists at resistive.net>
> To: <robotgroup at puremagic.com>
> Sent: Tuesday, March 18, 2008 11:06 PM
> Subject: [Robotgroup] car audio stuff
>
>
> Hey Robotgroup -
>
> Any audio or auto electronics folks out there?  I didn't have an aux input
> to my radio in my car, so I cut the leads where the tuner goes into the
> circuit board on my radio and put in a switch for my ipod
>
> http://www.resistive.net/schematic.jpg
>
> I also added a power line so that I could charge it too (bought a cable
> with an ipod interface) The only problem is that there's a faint noise
> when the car's running (a whirring from the spark plugs and alternator
> noise - automobiles are notoriously noisy to work in power-wise)  I get a
> little bit of a difference when the ipod charger is plugged in too, so
> that bit of capacitance across the power and ground seems to affect it as
> well.  I tried to add a cap between the power and ground but it seemed to
> make the problem worse.  Anyone have any suggestions on how I can clean up
> my signal, I've done a lot of reading on ground loops but not quite sure
> if I have some sort of loop or if the power to my audio switching chip is
> just not clean enough (or both)
>
> I'm pretty close to giving up on the chip and sticking a relay in there, I
> think I tried to get too fancy with the IC.
>
> Any suggestions would be much appreciated
>
> -Nick
>
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