Wow this forum looks really promising, and if so then this should be a sinch for all you guys. What im looking to build is a way to switch between two audio sources, automatically. One output is an iPod and the other is a walky-talkie, now the tricky part. I need the iPod to play straight through to a headset, but when the radio chimes in I need the iPod to be bypassed and for the radios signal to play through to the headset. Its a single ear piece so i dont need stereo capabilities. Thanks much.

 

Usually a walky will have a COR light that comes on when it recieves a signal. You could wire the signal from this light to a small relay via a transistor.
If you don't want to MOD the walky, then you'll need a VOX circuit to trip the relay. Google for a VOX circuit.

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Ha never thought about using vox, that would provide me with enough power to switch a relay, but my next question is, is a relay the best way to switch the audio sources or is there something else i could use, i want the device to be pretty small. Maybe using another comparator to actually switch the b/w the two sources.

 

I recall a simple squelch design that was simply a capacitor connected to the audio output of a weather radio. The no-signal noise output from the capacitor was sufficiently different from signal-present output to trigger or not trigger a mute circuit. You might employ a capacitor and LM339 or similar comparator to drive a relay.

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stevez

 

A relay is probably the best solution. Trying to use an IC or something could lead to distortion etc. Whereas a relay phsically changes the connection.
They make some pretty small relays that would be able to handle this low power application.

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Use a DG409 analog switch. Has high fidelity, and is used in data aquisition systems with high resolution with no problems.

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Aight so if i combine the vox circuit with the DG409 i should be set to go then right? Ill draw up a visio schematic and post it to make sure im 100% sure on whats being described, Thanks for all the help...

Ok heres the schematic i ended up with in visio, only a few questions. For VCC that could be a 9v battery correct? And all the ground would be the negative terminal on the battery right? And on the DG408(which i chose for its single output) the V+ and V- could be just the battery + and - too correct?



The bottom half is a vox circuit i got from http://www.rason.org/Projects/basicvox/basicvox.htm i left out the resistance and such just for ease of looking at but everything is there.

 

For the 408 or 409, a bipolar supply is necessary if you have a signal that is bipolar. So if your audio source goes both neg. and positive, then you must have a +9, -9 on the chip, or whatever voltage you pick within its range.

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"Everything that is done in the world is done by hope." -Martin Luther
"There are two ways to live your life. One is as though nothing is a miracle. The other is as though everything is a miracle."-Albert Einstein

 

How would i be able to generate the negative voltage, ive never dealt with it before, i quit EET after 1 term, kinda wish i woulda stuck around now.

 

The on-resistance of the DG408 is far too high to drive a speaker.
You would need a separate power amplifier to drive the speaker then any Cmos analog gate can switch the line-level signals to the amplifier.

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Uncle $crooge

 

Yes, I was assuming the OP was using line level signals.

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"Everything that is done in the world is done by hope." -Martin Luther
"There are two ways to live your life. One is as though nothing is a miracle. The other is as though everything is a miracle."-Albert Einstein