Need help with design of automatic audio input switching

[Firebird!]

Hello guys. I wanna know if you can help me with the design.

Here is what I wanna do:
I have a GPS system and XM radio connected to a single simple amplifier. I am using a toggle switch to change inputs GPS or XM.

I wanna know if it is possible to built something simple to make an automatic switching from XM to GPS when the sound comes from GPS (like spoken directions) and then if GPS stays quiet goes back to XM in like 30sec.

Thanks

 

[audioguru]

Look in Google for a VOX circuit. It switches inputs when a sound is played.

 

[mneary]

Try searching for 'audio ducker schematic', which is an automatic preemption for Public Address systems.

 

[Firebird!]

Okay - I'll look for that - Thank You

 

[Firebird!]

Finally found some time to get this done. I think it works pretty good. C3/R5 and R7/R8 gives me a delay of an about 30sec - just what I wanted. Used 4558 Op-Amp I found in my old modem (anyone should work).

 

[MikeMl]

Are you using the "***** in the (GPS) Box" to mute the XM radio?

 

[Firebird!]

Yeah - I drive a big rig and sometimes it helps to keep the eyes on the road and listen to the text to speech directions when I am going to the new places

 

[MikeMl]

I have a Garmin 496 aircraft GPS with XM radio built-in and it does this automatically. Your circuit is close to what I have done previously.

 

[Firebird!]

WOW $1500 unit - well mine is only $130 Mio s501 (got it on sale) - so no built in XM here . I put iGo in it - so now it kicks butt