Inject sound into stereo channel

[jkomets]

I'm interested in electronics, but a complete newbie, so please bear with me. My area of expertise is computers, but I'm always willing to learn new things. I can use a soldering iron well enough to solder a modchip in a Wii, if that's a good gauge of skill. I can also program in several high-level languages, if a digital circuit is recommended.

Anyway, I have an O2 XDA Orbit (navi/phone), and I wanted to build a device that would "inject" the sound into my two front speakers in my car. It would have a stereo input and a stereo output for the actual speaker channel. It would also have a 3.5mm jack for navi input. When the circuit detects input from the navi channel, it redirects the stereo input through another channel, on which I would put a "volume-reducer" (forgive, but all I know is that you can buy at electronics stores 3.5mm to 3.5mm cables that can regulate volume). It then directs both the navi instructions from the phone and the reduced-volume music from the head unit to the front speaker channel. When the navi is finished, I would like the system to wait for a settable amount of time before resuming normal playback, to avoid the navi pausing in its instructions and having the music play again in the middle of the instructions.

Is this feasible? Would a digital or analogue circuit be best suited? How much should this project cost?

Is there a better way to do what I want? I basically want music from my head-unit that gets muted or paused when my navi has something to say.

Is there perhaps anything I should know that I might not know to ask? Any mistakes I made in my naivete?

I appreciate your help very much. I know it can be hard to help newbies.

 

[flat5]

I don't understand what a NAVI device is but I think you want to mute your car stereo when the NAVI is sending you a message.

You might use a relay to disconnect the speakers from the stereo player during this period. This won't require tearing apart the stereo.

You will also need an amplifier & speaker for the NAVI and a control circuit to drive the relay, probably audio derived.

Any of this make sense - work for you?

 

[jkomets]

I don't understand what a NAVI device is but I think you want to mute your car stereo when the NAVI is sending you a message.

You might use a relay to disconnect the speakers from the stereo player during this period. This won't require tearing apart the stereo.

You will also need an amplifier & speaker for the NAVI and a control circuit to drive the relay, probably audio derived.

Any of this make sense - work for you?

I've spent a few days researching.

A navi is short for navigation device. Kind of like a TomTom-brand product, but in the form of a PDA and phone. It has its own output, "headphones," that I was planning on using. I also actually wanted to have this audio channel play over the two front speakers instead of the head unit when it had something to say. The music can keep playing in the back, I just need the directions up front.

I'm not sure what a control circuit is. I'm going to put the device, if possible, between the head unit and amp because the audio coming from a head unit and from an MP3 player, for example, is the same, right? (This assumption, which I'm questioning now, might require a redesign.)

I looked up what a relay is, and it seems good for this project. Would an electromechanical relay or a solid state relay be better suited?

How about a PNP transistor? Since I want to disconnect the HU from the output upon detection of a signal, wouldn't a PNP transistor do that fine? Also, that voltage controller could be a potentiometer. If the potentiometer and normal channel are both connected, wouldn't the flow go around the potentiometer, eliminating the need to add an NPN transistor?

 

[flat5]

I think you are saying you have a car stereo (head unit) and a power amp. You could connect both sources to the power amp but should provide some kind of isolation between the sources. You don't want the stereo to feed power into the Navi.

In the old days I'd say tap into the stereo's volume control.
This may still work if it's not voltage controlled.
This also will require power supply isolation (most likely).

Me, I'd forget the whole idea and use a seperate amp and speaker for the Naiv if one is really required. Sorry.

 

[jkomets]

I think you are saying you have a car stereo (head unit) and a power amp. You could connect both sources to the power amp but should provide some kind of isolation between the sources. You don't want the stereo to feed power into the Navi.

In the old days I'd say tap into the stereo's volume control.
This may still work if it's not voltage controlled.
This also will require power supply isolation (most likely).

Me, I'd forget the whole idea and use a seperate amp and speaker for the Naiv if one is really required. Sorry.

How would isolation work? Simply diodes before the junctions? Or would I need more than diodes, or a different solution entirely?

 

[chilinski]

Would something like this be adaptable to your needs?

**broken link removed**

 

[jkomets]

Would something like this be adaptable to your needs?

**broken link removed**

It's very complicated, and not exactly what I need. If it was really only about switching, I could use a relay. Plus, it costs much too much.

 

[jkomets]

How would isolation work, exactly?

 

[flat5]

"This also will require power supply isolation (most likely)."

Capacitors and maybe resistors (to not load the stereo) and transformers to pass the audio and isolate the DC supplies.

Lousy sentence but ...