Audio switching feeding one headset from 2 different inputs

[bob Myers]

Audio switching

I am in need of a circuit to feed one headset from 2 different inputs.
My goal is to have a standard input operating all the time and when a signal is received from a secondary device have it mute the first and become priority until signal stops.
It actually sounds easier than it has proven to be, listen to stereo on my bike, when either the CB or the ham radio(one or the other, never both) breaks squelch and sends a signal to an external speaker have it commandeer the headset until it quiets again.

 

[E-design]

Re: Audio switching

Can be done, but I can't think of a simple solution. Should be possible with 2 op-amps, some MOS switches and a small speaker driver. It will help if the stereo signal can be treated as mono otherwise it gets a bit more complicated switching between the CB, HAM and stereo audio.

 

[strennor]

Audio switching

interesting application...

I guess you may use the switches here:
https://www.fairchildsemi.com/sites...q&attr1=Function&attr2=Analog+or+Audio+Switch

but you need another audio signal sensing device to controll the switch

 

[bob Myers]

Audio switching

More on this, the bike already has a stereo and CB/intercom. When the CB or intercom is active it mutes the stereo. For whatever reason they chose to do this the signal coming to the headset is mono, so that eases that problem. My want is to add the ham radio and have a harness to plug into the existing harness(easy part, this I already have) and mute the stereo when ham radio is active. I have found an audio "switch" IC in Mouser "NJM 2520D" , it is a 2 input and 1 output IC but I cnnot find a pinout on it yet.

Edit; Pinout found, IC is obsolete, no stock in USA!

 

[E-design]

Audio switching

Just make sure the audio switch can handle large signals. My idea was to use 2 gain adjustable peak detectors with a RC charging constant on the CB and ham incoming audio. Use this to switch the MOS audio switches in some lockout configuration. So when say the CB audio comes in, the O/P of that detector switches this audio through while muting the stereo & ham audio. Also a lockout signal prevents the Ham audio from interfering while CB is active. The RC constant allows for some delay before the active audio switch will reset. Another similar circuit is used to sense the ham audio line.

 

[bob Myers]

Re: Audio switching

Yes, your design idea makes perfect sense, it would control all 3 items and have 1 priority. What I may have failed to say is the stereo/cb already has this setup internal to it, with the intercom overriding all the aforementioned. I would like to build a simple circuit that would override this, at my headset for my ham radio. I do not expect it to be terribly active but the wife and I both are ham ops and she will be on her bike with ham radio. You can only imagine the pain and suffering I would endure if I failed to anser her because I was listening to the stereo!

 

[E-design]

Re: Audio switching

**broken link removed**

Datasheet for your audio switch. Looks like a low level audio switch that can't handle high speaker level audio. This is the reason I thought that an additional audio driver will be needed. Something simple like a LM386

 

[bob Myers]

Re: Audio switching

Ok, I see what you meant. I am in your hands at this point! I have no more novice ideas worthy of trying.
I have found in the interim that the cb sends a 5.7 volt signal to the stereo to quiet it during receive, the intercom sends similar but smaller value signal to the same pin of the PA. Possibly I could pick off a signal of the ham unit, rectify it and use that to clunk a relay, sending signal to the power amp? I will try to get a schematic of what they did to accomplish this. It may end up easier than originally presented?

 

[E-design]

Re: Audio switching

Yes it might be easier once you know how the existing interface works.