[Robotgroup] car audio stuff

[Andre Lamothe]

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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