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  • Converting an Audio Signal to a Voltage

    I'm sure the title sounds a little obtuse, let me try to explain. My head unit supports a connection for a phone kit, phone mode is activated by applyting 12v (or ground, can't remember which) to a cable, this then takes the audio feed and plays it through the left speaker.

    Now, what I want to do is take the audio output from my iPaq which I use for GPS and hook it in via this kit so that when it gives me directions it will mute the head unit an play through the speaker. To do so I suspect I need some way of detecting the audio signal and using it to cause some for of switching (a relay?) to activate the phone setup.

    Do any of you know if this is viable or how it might be done? My concerns are how fast it would switch and what would happen in dead spots or pauses between words, would it be switching on and off etc.

    Any thoughts welcome..!

    Chris.

  • #2
    First of all, on all the mute inputs I've seen, they have all been negative. Consult your install manual on this one.

    As for getting a low voltage AC audio signal converted to a switched ground, I may have an idea.

    If you are comfotable with relays then this could be a snap! I've never done exactly what you are trying to do, but my idea is very similar to what I've done to create a viable amp turn-on signal by using speaker outputs from a head unit.

    Anyways, get a hold of a LVT (low voltage trigger). Try to find one that is adjustable if at all possible. Tag this to the audio output of your nav device. Then the LVT should have a positive output that is 12v. If you find one that has a negative output as well then your set. If not then just use the relay to switch to a negative output witch you can connect to the mute wire! If you need any further help, such as how to wire up the relay or LVT, I can help.

    Let me know how it turns out!

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    • #3
      Oh, btw...... these parts should not run more that $20, so have a ball!

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      • #4
        I've been looking at this http://www.aaroncake.net/circuits/vidswitch.htm my concern is when it will reset, it has to stay active through pauses but disengage when the speech is done, would a LVT do that do you think?

        I'd have a go at this circuit if I could translate the parts list in to part numbers at Digikey or Mouser or somewhere!

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        • #5
          david navone sells a relay that is triggered by an audio signal. should be what you need in a nice neet package
          New System in progress:
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          • #6
            http://www.autosound2000.com/pulsestretchers.htm
            This new device was designed to supply +12 volts to activate aftermarket components with OEM decks that do not have electric antenna control leads. The N-902 works by sensing speaker voltage from terminals of a readily available speaker. When the speaker voltage is present, the circuitry activates and +12 volts DC IS produced on the green wire.
            New System in progress:
            M10k
            Phaze TD1500 ~> Dynaudio MD130
            Phaze TD1500 ~> Seas g18rnx/p
            Zapco Ref 500.1 ~ 12" tc-9
            Behringer DCX2496 ~ Envision Electronics psu
            Transflective Xenarc

            My Car Pc Install
            My Boat Pc worklog

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            • #7
              Excellent!! Thank you!

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              • #8
                Yup, this is a LVT that you speak of. But again, that mute wire is probably negative! Its not that difficult to do with a relay.

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                • #9
                  David Navone just replied to my email, unfortunately the unit as it stands would not disable until there was a 16 second delay in the audio signal, this is a little long for my needs. I've emailed him to see if it could be "tuned" at all, meanwhile I might build the other VOX circuit as a test.

                  Chris.

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                  • #10
                    UKChris,

                    Have you built this circuit yet? I want to do the same thing to fix an issue with my TomTom Mobile and Nokia handsfree.

                    Thanks in advance.

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                    • #11
                      No, I tried and failed. A guy I know who is a real electronics guy is working on it now.

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                      • #12
                        Originally posted by ukchris View Post
                        No, I tried and failed. A guy I know who is a real electronics guy is working on it now.
                        You can try something called a VOX (or voice activated switch). I have a schematic at home, it just needs a little modification to make it work as you suggest. Can be built for much less than the David Navone piece. I just haven't had time to sit down, build, and test the thing, but in theory, it should work.

                        Michael
                        ...I love the French language...especially to curse with...Nom de Dieu de putain de bordel de merde de saloperies de connards d'enculés de ta mère. You see, it's like wiping your *** with silk, I love it.

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                        • #13
                          I have a couple of schematics for VOX circuits, even tried soldering one up but it didn't work for me. I don't know enough about the electronics to determine why. I'm not bad at sticking the bits together if someone can tell me what bits work, the ones in the circuit I followed didn't.

                          Chris.

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                          • #14
                            Originally posted by ukchris View Post
                            I have a couple of schematics for VOX circuits, even tried soldering one up but it didn't work for me. I don't know enough about the electronics to determine why. I'm not bad at sticking the bits together if someone can tell me what bits work, the ones in the circuit I followed didn't.

                            Chris.
                            What happened/what didn't work about it? DId you modify the circuit at all?

                            Michael
                            ...I love the French language...especially to curse with...Nom de Dieu de putain de bordel de merde de saloperies de connards d'enculés de ta mère. You see, it's like wiping your *** with silk, I love it.

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                            • #15
                              PAC Audio makes a TR4 or a TR7 that MIGHT work. Maybe your audio signal voltage level might be too low though. Have you measured what the output AC voltage is of your audio signal with a multimeter? What is the minimum voltage level your VOX will work at?
                              System always under construction


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