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Audio Selector


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I am an electronics n00b.  Even more than that.  I only know what I learn from school.  I have a problem.  And to that problem I made a solution.  But I have no freaking idea how to implement the solution. 

Basically here is the source of my problem.  I am running both linux and windows at the same time.  I recently purchased a new sound card.  However, though it has windows drivers, linux does not yet support the sound card.  So I am thinking about using my soundcard that is built in to the motherboard.  So the actual problem is, I have two soundcards and one speaker output.  I need something that can detect an audio input and select which one is active and use that signal and send it to the speakers.  That part I knew how to do.  I learned it in class.  I built up a truth table and did all this fancy smancy DeMorgan's stuff and built a circuit like I was taught.  I have a circuit but I have basically no freaking clue on how to actually build it using real world stuff. 

Included is an image of what I have so far.  Basically I have two inputs A and B.  A is my preferred sound card and B is my onboard crap sound card.  X is the desired output.  1 signifies an active signal and 0 signifies no signal.  Here is a truth table and image.


A    B    |    X
0      0    |    A
0      1    |    B
1      0    |    A
1      1    |    A

I built a truth expression of A or NotB.  The output of this expression is to be feeded into a multiplexer that can select which to output.  A and B are both inputs for the multiplexer as well.  Tell me if you see any flaw in my work so far. 

But basically, what does a real multiplexer look like?  Is it just a chip?  I am guessing so.  But I want my device to be a small box.  So would I have to have 3 chips?  One for the Not gate, One for the Multiplexer, and One for the Or gate?  I guess I have to buy the inputs and outputs of the audio plug things.  I am guessing I need a plastic box that this would all fit in.  Would I need to build my own or is there some sort of universal box that can hold stuff?  Also I need a power source, I am guessing this takes a small amount of power so how long would a bios type battery or AAA battery last?  Basically, what would I have to buy?  Thanks for your help.

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I assume that the cards' outputs drive an external amplifier, and do not directly drive speakers. If so, then since there is no output from the inactive sound card, why don't you simply mix the outputs of the two cards together with a summing amplifier? A single opamp would do.


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  • 1 month later...

Are you sure the system is not de-activating the on-board sound card since you are using the address for the new sound card?  You might have a conflict even after you make the hardware.
Not being a fan of Linux, my suggestion would be to uninstall Linux and....problem solved.


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