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  • audio signal to ground or power signal

    I was wondering if there is any way to take a signal coming from rca wires and change it into a power or ground singnal that you would run into a relay, then off of that relay you could send a signal to the mute wire on your headunit. That way you could hook up an scanner and each time a transmission would come thru it would be heard over your speakers. Thanks, Drew
    1998 Camaro Worklog Starting over, New setup for 2010

  • #2
    I thought of a way to do this a while ago... I'll see if I can find the post. Had to do with using a 4 diodes in a diamond configuration (to take AC to DC) and then sending it through a few capacitors to smooth it out, then through a transistor to make it 12v for regular relays as well as a big inductor just to store more charge. That should produce a somewhat level signal but it has never been tested.
    Fusion Brain Version 6 Released!
    1.9in x 2.9in -- 47mm x 73mm
    30 Digital Outputs -- Directly drive a relay
    15 Analogue Inputs -- Read sensors like temperature, light, distance, acceleration, and more
    Buy now in the MP3Car.com Store

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    • #3
      i would love to see a diagram of this or at least a parts list. I'm will to try anything i the chance that it'll work. Thanks
      1998 Camaro Worklog Starting over, New setup for 2010

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      • #4
        What 2k1Toaster said is a rectifier -> envelop detector -> amplifier - the problem with the design is that a transistor is an inverting amplifier - so you would end up turning the relay off when you had signal instead of on. You can fix this by adding a second transistor. Of course you only need one transistor if you're making a ground instead of a power wire - but u could have some strange side effects.

        You should be able to form your own circuit diagram by searching for the individual components in google. Search for Common Emitter instead of amplifier.

        Spuzzdawg

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        • #5
          common collectors dont invert inversion is not a function of the transistor, it's a function of the resultant 'voltage divider'.
          It's been a while...

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          • #6
            Assuming the MUTE input is a rather high-impedance input, it might suffice if you just take the peakdetector (diode+capacitor) between the speaker output and the mute input. Would save you all the transistor hassle.

            BTW inversion is a function of amplifier configuration.

            white bream
            working on a trilogy: CARGO - UNIGO - MERGO
            CARGO = the Car Computer
            Intel Celeron M, [P]SDC, uBlox GPS, GPRS, WLAN, Silabs FM, RDS, TMC,
            Dual-audio, Onecable TFT, Microsize: 45 x 108 x 168mm (1.8 x 4.3 x 6.6")

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            • #7
              common collectors also have a voltage gain close to one therefore negating the reason for using a transistor

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              • #8
                wow i seem to be getting more confused with each reply...
                1998 Camaro Worklog Starting over, New setup for 2010

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                • #9
                  Originally posted by spuzzdawg View Post
                  What 2k1Toaster said is a rectifier -> envelop detector -> amplifier


                  Just do that. I have no idea what the others are babbling about. There are 2 types of transistors, one "inverts" and one does not. The only reason I suggested one is to take whatever weak signal is coming out of the circuit and amplifying to 12v so you can trip your amps turn on. Think of it as a really small relay. You could in theory use a relay, but the problem is there are not many relays that could be driven off the weird weak signal that is going to be put out because there wont be enough to physically create a huge magnetic field and move metal contacts. There is enough however to work some magic in some silicon.

                  What the rectifier does:



                  Common way of drawing in a circuit:
                  Fusion Brain Version 6 Released!
                  1.9in x 2.9in -- 47mm x 73mm
                  30 Digital Outputs -- Directly drive a relay
                  15 Analogue Inputs -- Read sensors like temperature, light, distance, acceleration, and more
                  Buy now in the MP3Car.com Store

                  Comment


                  • #10
                    The MUTE signal wire on a headunit will mute the headunit when the wire sees a ground, not 12V. At least that is how it usually works. The MUTE wire is usually used to mute the audio so you can hear an incoming phone call and that is how it works with handsfree phone car kits. .
                    System always under construction


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                    • #11
                      Originally posted by durwood View Post
                      The MUTE signal wire on a headunit will mute the headunit when the wire sees a ground, not 12V. At least that is how it usually works. The MUTE wire is usually used to mute the audio so you can hear an incoming phone call and that is how it works with handsfree phone car kits. .
                      doh!

                      I completely missed the "for a transmission" part.

                      In that case, then just invert it either with a transistor or use the other pins on the relay for NC instead of NO.

                      Not too bad.

                      Again, I have never done this, or know how well it would work. It might induce quite a bit of noise to the system, or stare WWIII, I dunno.
                      Fusion Brain Version 6 Released!
                      1.9in x 2.9in -- 47mm x 73mm
                      30 Digital Outputs -- Directly drive a relay
                      15 Analogue Inputs -- Read sensors like temperature, light, distance, acceleration, and more
                      Buy now in the MP3Car.com Store

                      Comment


                      • #12
                        the only thing he didn't say was if he has his audio running through amps or the HU? If he has aux in or the amps, then he would have to build some relays to switch the RCA audio signal back and forth. If there is no aux in or no amps, I don't know what his "transmission" will play over. I don't think it would start WWIII but maybe send signasl into space like Contact
                        System always under construction


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                        • #13
                          Guess something like this should do the job...


                          white bream
                          working on a trilogy: CARGO - UNIGO - MERGO
                          CARGO = the Car Computer
                          Intel Celeron M, [P]SDC, uBlox GPS, GPRS, WLAN, Silabs FM, RDS, TMC,
                          Dual-audio, Onecable TFT, Microsize: 45 x 108 x 168mm (1.8 x 4.3 x 6.6")

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                          • #14
                            the signal sent over the rca cables is not AC. AC by definition passes through zero. This is more of a fluctuating DC, like an AC signal already riding a DC bias. A rectifier does no good there, as the signal doesn't pass through zero. What about an inverting, comparator op amp. This would give high input impedance, as seen by the scanner, could bump up the signal to a desired level to keep the mute off when wanted. Filter it's output for noise and to keep the opamp from turning on the mute function erroneously.
                            It's been a while...

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                            • #15
                              Originally posted by h3rk View Post
                              the signal sent over the rca cables is not AC. AC by definition passes through zero. This is more of a fluctuating DC, like an AC signal already riding a DC bias. A rectifier does no good there, as the signal doesn't pass through zero. What about an inverting, comparator op amp. This would give high input impedance, as seen by the scanner, could bump up the signal to a desired level to keep the mute off when wanted. Filter it's output for noise and to keep the opamp from turning on the mute function erroneously.
                              Well the rectifier will make sure that the signal is going the right way. Without the rectifier, if you connect the wires backwards, it will not work. So for like $0.04 in diodes, you get the lazy man's circuit.
                              Fusion Brain Version 6 Released!
                              1.9in x 2.9in -- 47mm x 73mm
                              30 Digital Outputs -- Directly drive a relay
                              15 Analogue Inputs -- Read sensors like temperature, light, distance, acceleration, and more
                              Buy now in the MP3Car.com Store

                              Comment

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