Trying to make a circuit

[BigB9k]

Noob here, trying to make a circuit (or find one)

I'm trying to take a radio, and add in an auxiliary port.
This is easy by tapping into the FM tuner's L & R audio output. But, I want to leave the FM functioning, still easy to do with a standard 3.5mm stereo jack, that switches when something is inserted.

But I don't want to use a headphone jack, I want to use RCA's
Any ides on an automatic (stereo) audio switching circuit?
That will switch over to the secondary input once it detects audio?

It's a 12v radio, and the am/fm tuner is pre-amp, so when I connect my mp3 player to it, it'll be a stronger signal of course, but I'll worry about limiting that later.

So, any ideas?

 

[BigB9k]

Turns out this is called a 'ducking' circuit, which seem to be slightly complicated.
Couldn't some form of Voltage detector and relay be used to simply accomplish this?

 

[MrDEB]

kinda lost??
you have an FM radio that has a speaker as output
you want to connect an mp3 player to the radio outputs so the radio speakers still output sound AND your mp3 player has the same audio coming from the headphones?

 

[BigB9k]

well, here is an example:

He added a port to the front of the radio, by tapping into this harness:

**broken link removed**

Which is fine and all, if you want to drill a hole in the front of your radio.
(I do not) Im after rear RCA inputs.

So when whatever is activated, and sound/signal is delivered to the RCA's it'll switch over to use the RCA's for sound. Thus, cutting off the FM/CD signal.

 

[RMMM]

What about a stereo FM transmitter that the RCA(phono) plugs into? It could be set to an un-used station, and you could just use a preset button to recall that station.

That would allow work, and could be done with few components.

There are already products like this available. Most have stereo 3.5mm plugs, but you could easily use a 2-RCA(phono) to stereo 3.5mm Y-adapter.

Just an idea.

 

[4pyros]

I would use a switch, Can you drill some whare elseon the dash? Just how are you going to use this new input? Andy

 

[BigB9k]

The FM tuners are pretty crappy.

I would use a switch, Can you drill some whare elseon the dash? Just how are you going to use this new input? Andy

Trying to avoid the toggle switch option.
New input could be anything. DvD player, Mp3 player, GPS, anything really.


One option I have heard about is an audio level detector and a solid circuit relay.

Thoughts on that?

 

[4pyros]

OK how would you hook it up without making holes. Let the wires hang out from under the dash?

 

[ronv]

When do you want it to be switched back to the radio? When the player is unplugged or??

 

[BigB9k]

OK how would you hook it up without making holes. Let the wires hang out from under the dash?

Run the wires behind the dash, under the carpet, and had them exit within the center console.

When do you want it to be switched back to the radio? When the player is unplugged or??

When it stops detecting sound.
I was thinking of this circuit:
https://www.electro-tech-online.com/custompdfs/2011/01/AUDIODETECT1.pdf

Combined with a DPDT relay

 

[RMMM]

What about a lull in audio between songs? That would shut off the circuit until the next song started.

You would have a "blast" of whatever radio station you were last listening to, between every song unless you put in a timer to "hold the line" live for x seconds after the signal is lost.

 

[4pyros]

Run the wires behind the dash, under the carpet, and had them exit within the center console.

If you ran both input and output wires to the center console than you could disconect the radio from the amp and plug in you MP3 without any extra circuts. Andy

 

[ronv]

Your circuit should work. You just need to set the time constant long enough to avoid the problem posed by RMMM.

 

[BigB9k]

What about a lull in audio between songs? That would shut off the circuit until the next song started.


You would have a "blast" of whatever radio station you were last listening to, between every song unless you put in a timer to "hold the line" live for x seconds after the signal is lost.

So a time delay circuit combined with a solid state? DPDT relay, and something to convert the 12v to 2-8v (what the LMC7125 is designed for)

No problem huh?

Your circuit should work. You just need to set the time constant long enough to avoid the problem posed by RMMM.

 

[4pyros]

This is what you need........

**broken link removed**

Andy

 

[RMMM]

A delay-on-break type of timer. As soon as the comparator drops to 0, the timer starts that will keep the circuit live. I think the average time between songs is 4 to 5 seconds. It is likely googleable

I know many CD burning and itunes downloaded songs have a 2 second "gap" between songs. So 4 seconds seems ok.

 

[BigB9k]

This is what you need........

**broken link removed**

That is exactly what I need. Only small enough to fit into a radio.
Andy

A delay-on-break type of timer. As soon as the comparator drops to 0, the timer starts that will keep the circuit live. I think the average time between songs is 4 to 5 seconds. It is likely googleable

I know many CD burning and itunes downloaded songs have a 2 second "gap" between songs. So 4 seconds seems ok.

Agreed.

I whipped this up:

**broken link removed**

Whatcha think?

Questions are, the circuit is made to run off 3v, the radio is 12-14v, and the mp3/In is .03(?)v
Is it ok for everything to share the same ground?

Is it possible to convert the supplied circuit to 12v? the LMC7215 says 2v-8v, is there a 12v option?
Also, looks like the LMC is only surface mount. That is pretty small for me to try and solder down. Think there is a larger version? (with pins)

 

[4pyros]

BigB9K; I you are going to have fun making this gofor it. Other wise buy the one I showed you and put it in your dash not your radio. Just cut the lines inside the radio and run RCA cables out the back or the radio to the switcher in the dash and one pair of RCAs to the center console. Its already 12VDC so just use a fused supply, and your radio will stay almost stock. In the end all you would have to do the reverse the mod to the radio would be to hook the 2 RCA pairs together.

 

[ronv]

Vox

Try this one. It has about a 6 second delay before it switches back and runs off of 12 volts.

 

[BigB9k]

Thanks for posting that!
Thanks a lot for everyones input too

Ok, my expertise is quite limited. Really limited. I got the workings of a relay down, and that is about it.
The data sheet from mouser says the LM339 is a 16pin?

the IRF530 looks like this?

**broken link removed**

Surface mount hmmm? I guess I should tackle how I'm going to get that all squared away.
How does one connect that middle pin?