FB to control audio switching?

**Curiosity** · 05-24-2009, 01:40 AM

Originally Posted by rodweb

That link may not be right. sort of took me nowhere. Which Chip are you suggesting?

Oops. Links fixed. It put 2 into 1

Relays are fine. I've seen them used before. They actually make shielded signal relays for high frequency switching, but you know, it clicks on and off every time you use it, contacts get dirty, and cost per relay gets up there quick.
http://electronics.dantimax.dk/Kits/...ors/index.html

**rodweb** · 05-24-2009, 02:06 AM

Curiosity. This has been very interesting and has helped me validate some ideas I have had. Almost moving off topic now but I also found this circuit

Here http://www.discovercircuits.com/DJ-C...diodetect1.htm

So a circuit like this could be used to trigger the A-B switch instead of the HU remote Amp on signal. eg. A phone kit or CB radio could grab the audio output with no PIC involved when the speaker cackled to life! You would need to use a speaker to line out adapter. Ive already got one of these and it has attenuation controls built in. No longer using it since I put a car PC in.

This could be used to route both phone and my CB (using one channel each and splitting it).

**colin** · 05-24-2009, 03:03 AM

Typically you'd want to avoid the audio-activated switches due to the simple fact that most devices don't stop their audio. If you use a radio, it's always outputting. Computer is often outputting. What if your phone rings just as you start a song? It gets messy.

**2k1Toaster** · 05-24-2009, 03:12 AM

Also it seems everyone keeps thinking relay as in standard automotive relay. You can get solid state relays, or just build a transistor level circuit. A transistor is a switch after all, and so is a relay.

If high quality parts are used you can get it to be of audiophile purity. I would say for simplicity juse use a solid state relay.

**rodweb** · 05-24-2009, 03:35 AM

Originally Posted by 2k1Toaster

Also it seems everyone keeps thinking relay as in standard automotive relay. You can get solid state relays, or just build a transistor level circuit. A transistor is a switch after all, and so is a relay.

If high quality parts are used you can get it to be of audiophile purity. I would say for simplicity juse use a solid state relay.

Sounds like it would be a good accessory for FB, want to add an Audio A-B switch to your product range?

**Curiosity** · 05-24-2009, 07:15 AM

Yeah, the auto switching can get annoying. When both are are, the priority device will always be on. So you have to turn one off or disconnect it to hear to other one. A head unit is pretty easy to turn off though. That's why I suggested a mux/mixer. Why not, if it's cheap enough?

Transistors and MOSFETs are DC, so they can't pass the analog signal. A bilateral switch is basically AC. I think internally it's 2 MOSFETs in parallel to make a bi-directional path. That's probably what a SSR is, but those are pricey aren't they?

**colin** · 05-24-2009, 12:29 PM

Yes they are. With some electronics knowledge and parts and time, you could potentially use op amps to create your switcher.

**rodweb** · 06-22-2009, 11:02 PM

Hi guys, I thought I'd raise this thread again. I have just about got to the stage this is my next project on my car pc and I can see two ways forward and wanted to get some advice as I am not really an electronics guy.

Option 1 - Simple A-B selector
Follow through on the original idea I suggested here of having the head unit amp on signal to switch inputs using the 4066B Bilateral switch (which is a newer version of the 4016 I posted earlier, see http://docs-asia.electrocomponents.c...6b800271e1.pdf ) and a 14069 inverter (see http://docs-asia.electrocomponents.c...6b805fb985.pdf ) to switch it. Both of these components handle up to 18 volts so it looks like they could be be directly connected to the car 12 volt lines which makes this really easy. I think I need to add one capacitor.

Would it be safe to run this off unregulated 12 volts in the car?

Option 2 - Four way (A-B-C-D) input selector
Use the MC14052B Analog multiplexer (see http://docs-asia.electrocomponents.c...6b805fb5ba.pdf )
which will allow switching between 4 inputs using 2 outputs from a controller like the Fusion Brain. It also handles up to 18 volts.

This chip takes four pairs of inputs (eg. Left and right channel inputs) and switches them to one pair of outputs (eg. Left and Right hand channel outputs). These are selected by connecting two output ports on the controller to the A and B pins and outputting high and low binary values of 0, 1, 2 and 3 to the pair of ports (see the truth table in the link).

I think I could also use option 2 to make an A-B switch simply by tying pin B to ground and attaching the radio remote on signal to A and ignoring the other two input pairs.

Could somebody confirm where VDD, VSS and VEE should be connected? I think it is :
Vdd = positive voltage
Vss = Ground
Vee = Ground

Anyway, I think both approaches have their advantages. I like the simplicity of the A-B switch being triggered when you turn on the head unit. This will work with the PC turned off.

I also like the processor controlled 4 way switch idea which could provide identical functionality to Mitch's input select box via a USB interface.

Any, any feed beck on the merits of these ideas would be appreciated.

**Iamthehor** · 06-23-2009, 02:34 PM

I exchanged a few PMs with the OP, I think he's abandoned the original idea. The 6.1ch + 2ch & the portability requirements caused too many problems. He already has solid equipment to work with anyway, just not ideal for his original idea. there's always tradeoffs in audio, especially car audio.

I'm not an electronics expert by any stretch of the imagination but I've seen some ideas thrown around that would work. Normally I'll DIY if it works as well as a commercial product & is cheaper, but not in this case. I want as few devices as possible molesting my audio. I don't have golden ears like some, but I am picky about the sound & I can see all kinds of problems that you couldn't anticipate from these ideas. Your situation(s) are probably different & I'm sure you could make it work, but I don's see the benefit vs the possible problems & cost.

**malcom2073** · 06-23-2009, 04:42 PM

I am actually thinking about doing this using an analog multiplexer similar to the one mentioned earlier in this thread. It's difficult to design it right to provide as little interference as possible, but putting gain amps on both the input and output is an easy low-component fairly simple solution to improving the quality of such a device. At least that's what I'm planning on doing