Car audio source selector

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Thread Starter


Joined Nov 14, 2011
Hi y'all!
This is my first post in allaboutcircuit so I want to introduce me before anything:
I'm a system engineer from Spain who loves arduino and mountain biking ;).

I want to modify a car audio installation like this:

The car is a 2003 Peugeot 406 coupe. It's from a friend of mine.
We want to install a Parrok MKi9100 and listen it on every car speaker (because it plays also MP3s from USBs, iPod and BT Phones).

So I started to search about simple audio switch and based it on various on the net (like

This is my monster:

The circuit works more or less well with the engine off, but when the engine is working add noises to the sound (to both sources).
It is a problem with ground loop?

Don't hesitate to show me all the errors in the circuit I'm a totally newbie with electronics.

Thanks so much in advance.


Joined Jul 9, 2011
Discussion about automobile modifications are prohibited on AAC. I don't know if this applies also to audio installations. The moderators will decide this.

Since you already installed it I see no harm in giving you some advice.

You should try to filter your 5V power supply better. Where did you take the ground from? Directly from the battery or from the radio connector?

Did you use shielded cable for the audio sources?

Can you post a complete schematic with ground connections? Just take your "After" block schematic and add the ground wires.

Noise from a running engine usually comes from spark plugs/ignition system. Or is it a diesel motor?


Joined Nov 25, 2009
Unfortunately, the All About Circuits forum Administrative Team has elected not to host discussions of automotive electrical system modifications/enhancements due to safety concerns, the potential of legal ramifications and the possible circumvention of vehicle regulations at the state and federal level.

This thread is against the AAC forum rules, Chapter 6, as seen here:
Namely, automotive modifications of any kind are strictly forbidden.
Therefore, this thread will be closed.

Please understand the reasons behind this action and bear no grudge.
Feel free to tread on the rest of the forums.

You might find answers to your questions in one of these forums:
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