Has anyone created or found a circuit/product that would do this….

Say you have a second head unit, iPod or navigation device (whatever) and you want to be able to activate this second unit and have the empeg automatically switch to AUX when audio from this second device is present. Then (optionally) switch back to the empeg once the audio is no longer present. The second device does NOT have a mute out line.


I’m thinking this could be done as follows…


AUX Audio Source ---- Device?----------------- AUX Audio In --------
......................................... | .............................................. EMPEG
............................................. -------------------- Mute Line --------


The empeg mute line could be toggled high or low by the device which through Hijack’s extmute_on=xxxxxxxx option could then turn on or off the AUX source on the empeg.

The only connection needed to the AUX source would be to hook up to the Audio out.


I’ve been looking at mic. audio switches that do this sort of thing but have not found one that would do the job 100%. I’ve also thought of designing a circuit using perhaps an op amp and a 555 timer.

Anyone have any ideas or suggestions?

thanks

I don't think there's any way to do it "100 percent" from detecting an audio signal on the RCA cables. It might "false" once in a while due to noise or such. Although I know it's do-able because I've got a subwoofer at home which automatically powers on when it gets an audio signal. But mostly I'm not worried about that "falsing" because there's no drawback to having it switch on unexpectedly, other than a little power gets wasted. With the empeg, on the other hand, it would be very irritating to be listening to MP3s and have it "false" and switch to the Aux line in the middle of a song.

Most devices that you'd want to do this would have some other way of indicating power-on status, something more reliable to test against. And probably simpler, so that the most you'd need is a relay.

How about you tell us what device you intend to do this with and we can think of a simpler solution?

My use would be for a Gramin IQue (GPS/PDA) that gives turn by turn instructions. It has a car cradle with a built in speaker but when I’m “Jamin Out” to the empeg there is no way I can hear the instruction from the tiny and sad car cradle speaker. The iQue does put out good, if not great, sounding audio so it would be nice it I could, plug into the iQue headphone jack, and then when a trun instruction comes up the sound would come over the car speakers through the AUX empeg input. The iQue puts out a pre-announcement warning beep so that would help in the cutover timing.

I tried hacking the car cradle to find a “high” or “low” signal but it appears the cradle amp is always on and it get no such signal.

That’s a good suggestion about the sub amp switch. Mine does the same thing. I don’t think noise would be too much of an issue because I could just turn down the input if that happens (so it would be lower than the music) and I don’t get any noise through the car cradle now. However I imagine sub amps have a frequency “awareness” and only turn on at or around the crossover. So ripping apart a sub amp might require some additional hacking.

Okay, that does sound like a good application for an audio-sensitive relay. I don't know how to make one but I'm sure it's relatively simple. Have you tried googling for a schematic of one?

Yea, I did search Google but I guess I'll need to be more creative in my searches.

I did find some microphone auto-sensing switch schematic that might be useful and one for a telephone recording device. I was kind of hoping someone already did this for an iPod or something. Seems like someone in the world would have already marketed something that would send a “mute out” signal for devices that don’t have a “mute out.” Maybe they do but I don’t know what to look for.

The perfect device (IMO) would send a pulse a mute signal when auto appears so empeg will turn on the AUX and then pulse a signal when the auto shuts off to turn off AUX. That will probably be hard to find out of the box. My second best solution would be to pulse the mute, then wait for a timed duration, then pulse the mute again. The third solution would send a high or a low on the mute line while audio is present and then I would have to manually turn it back to empeg. Manual = “Bad Word”

Thanks for your help.

This is interesting:

http://home.att.net/~hotdog321/discovery.htm

You might be able to modify that or at least use his idea (basically, use a rectifier to convert the pseudo-AC of an audio signal to DC).

Something to consider is that switching to aux for voice prompts is probably going to be pretty jarring. I suspect it'd work better if you could get the "mute line" created and just use it to trigger the hush function. This is how OEM nav systems work, and it's a much more pleasant experience.

I use the mute line to switch to aux for the phone, and it works for that great, but I can't imagine having it pause the music and say something every thirty secconds as I approach a turn.

Matthew

Thanks Bitt.

I never would have thought of an audio rectifier. The only issue I see is that a rocket is a constant source of sound, and a lot of it, voice on the other hand has pauses that would recult in zero voltage. I could use something like this to initially set a trigger and the untrigger after the voice voltage is not present for a time.

Hopefully this will not “Thump” the speakers. I believe the transition will be smooth is because of the timing. The audio will trigger the AUX. If the AUX was switched on before the audio there might be a thump. I can also adjust the volume from the iQue so that Bitching Betty (it nickname) does not yell at me.

Yes, interrupting my empeg listening experience will be disturbing. However I’d rather be interrupted than be lost. If I am in the city and have a turn every 30 seconds I probably won’t be “Jamin out” and will have the empeg at a reasonable volume. Highway cursing is where I can really get into the music and lose track of my exits.

Yeah, I was thinking that you could use a rectifier, plus a capacitor to even it out and help with the gaps in sound. Disclaimer: IANAEE.

Here’s some leading contenders…. in the I make it catagory

I like the idea of modifying the old lady’s clapper…

http://home.maine.rr.com/randylinscott/dec97.htm


Now this one looks pretty simple and might work…..

http://www.reconnsworld.com/audio_electretamp.html


The op amp stuff gives me ideas…

http://www.redcircuits.com//Page28.htm


Seems like a cool chip but would probably never figure out how to set it up…

http://www.rohm.com/products/databook/audio/pdf/ba3430s.pdf


The Schmitt trigger looks like it might work. Maybe hooked to a LM555 timer …..

http://www.swarthmore.edu/NatSci/echeeve1/Class/e72/E72L2/Lab2(OpAmp).html

The audio detector you want is what is called vox. There are a lot available on the net (search for "vox circuit" in google).
That vox circuit basically keeps its output HI as long as there's audio at its input. There is an adjustement (by varying a capacitor value at design time) that tells how long a silence must be before resetting the output. This prevent pauses in voice to be interpreted as end of audio signal.

Then, you could use something called an edge detector (search for edge detector in that pdf file).
What that does it create a pulse (user definable length, also by changing a cap value during design) at both beginning and end of a input signal. You could then feed that to the empeg input. I'd suggest to use an optocoupler to electrically isolate both the circuit and the empeg, just to be sure no harmful voltage is sent to the empeg, or ground loops.

Code:

---

Audio Signal:
--/|/\/\/|--/|/|/|\/\/\/\--------------
Vox output:
__--------------------------________
Edge detector output:
__-_________________________-_____ 

---

Hope this helps

Thanks Patrick that's exactly what I need.

Ording parts and warming up my iron now....

Thanks to everyone's help I did it! The empeg is now politely letting my GPS tell me where to turn.

I used a voice activated switch kit (only $7, cool) I found here -> http://www.rainbowkits.com/kits/vox-1p.html and with a few minor modifications it works great. I used it to find my way to work this morning (need all the help I can get in the mornings). One of the modifications I did was to replace a resistor (R2) with a potentiometer so I could adjust sensitivity. Once I tweaked the pot a few times the VOX switched great. One thing that helps out on the timing is that the GPS has an alert tone that beeps right before it starts talking. The VOX switch activates on this beep so it doesn't cut off any of the voice prompts. I also noticed that the mute line on the empeg is way more 0 volt sensitive than 12v. Instead of trying to drive the mute line to 12v I used the vox to drive it to 0v.

The Hijack mute/button hack to switch AUX on and off worked great. So for a grand total of about $15 (and a few evenings) I've got an integrated empeg to GPS solution, I'm pumped.

Very very cool!

agreed this is way cool...

where did you mount the circuit board?

i am a soldering novice. is it simple to solder?

I used the below project box from Radio Shack ($4, cool) to mount the kit. I keep it in the glove box for so I can unplug it if desired. I connected to the empeg via an RCA wire connected to the AUX input with the other end being a head phone male plug. I have a female headphone jack on the box (got it from Mouser, like $1) so I can unplug the AUX from the VOX box if I wish. So if I want I can then plug in an iPod or something directly to AUX and not go through the VOX. I know I didn't explain this very well but hopefully you can picture this. I'm heading out of town on vacation to the woods for 3 weeks or I'd get you some pictures now. Maybe when I get back if you are interested

http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&product%5Fid=270-283

pics would be cool

btw, i have a gps as well.

Hi.

Anyone else done this?

of have a pic of the completed board as that company won't sell to the uk.

Thanks

C.

Here's some pics.

This one is of the two boards. The bread board is just for the extra transister that grounds the mute line instead of taking it high.

Audio in plug...

One problem I’m having is with engine noise activating the mute line. I put an inline filter on the output but that didn't help. Going to try the input as well. If anyone has any suggestion like a good notch filter or something I'm all ears.

Having just had my empeg installed in my new car, I've got some interest in something like this. A few questions...

1. You mentioned you were having problems with engine noise inducing a false start, is that still the case?
2. If I understand right, it switches over as soon as it senses audio, and then waits for a period of silence before switching back. How variable is this time period between switching back?
3. Is it possible to tell it never to switch back? i.e. always switch when it gets sound, but wait for the user to manually switch back to Aux.
4. Once you have something reasonably finalized, would you consider building them and selling them? It doesn't look *too* complicated, but I'm not sure I'd want it to be my first electronics project, either.

Nice one!

When the mute line is activated, does it just mute the signal completely or just hush it to a certain level?

I've been looking at doing something similar, well actually it would probably fade the signal down quickly and then fade slowly back up, it would be completely separate to the empeg, in fact the empeg would be completely oblivious to what was going on.

I'll probably just build a ducker which is basically an audio compressor which works on the output chain but is keyed by a separate audio input (the sat nav). I can then tweak the attack and decay to suit.