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  • Need help from electronic gurus

    Check out the link in my sig for the basics behind my setup.

    I currently have this:
    http://www.antec.com/us/productDetails.php?ProdID=77102

    The little LEDs up front in the A/C vents light up whenever the subwoofer hits (because the sound part is in the trunk next to the woofers. I had to extend the wires, but that wasn't hard.)

    What I want to get is this:
    http://www.sonicelectronix.com/item_148.html#
    http://www.hifisoundconnection.com/S...id/0/SFV/30046

    I would LOVE to make it so that the LEDs inside the woofer grill ran the same as the LEDs from the first thing. But here's the problem, the first thing runs on a 5v source (USB-powered), the woofer grill says it should be plugged into any 12v source.

    Anyone have any ideas whether I can make that work?
    A car without turbo is a car with perpetual lag.

    My Ride
    My New Page

  • #2
    Use a transistor to switch the 12V load based on the 5V signal. You could also take apart the grill to use different value resistors for it (LEDs themselves are generally 1.5 - 3V devices), but the transistor's probably the easier way to go.

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    • #3
      *edit: looks like mushin and I think alike, but I take too long to type here it is anyway...*

      there's 2 options.

      1) you can try to hack into the grille and see if there is a current-limiting resistor in there. if you can find one, then you can replace it with a lower value so it's bright enough on 5v. however, there might not be one (the LEDs could be designed for direct 12v operation)

      2) you can use a transistor to switch the grille LEDs on and off with the others. grill LED + wire to +12v, grill LED - wire to NPN transistor collector terminal, transistor emitter terminal to ground, and the pulsed 5v output from the antec thing through a resistor (say, 1k ohms, if that's a little weak, put another one in parallel with it to get 500) to the transistor base terminal. that should hopefully be enough to get you started, based on the transistor pin diagram on the package if you get one at radio shack... you can pick up a suitable transistor (TIP120) and resistor for a couple dollars there.
      But don't take it from me! here's a quote from a real, live newbie:
      Originally posted by Viscouse
      I am learning buttloads just by searching on this forum. I've learned 2 big things so far: 1-it's been done before, and 2-if it hasn't, there is a way to do it.
      eegeek.net

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      • #4
        I like the idea of using an NPN transistor. As my limited electronics understanding goes, by using a transistor, the grill LEDs would then be using their own power, rather than using the power supplied by the 5v device. This seems good because I still want them to be bright enough.

        I even think I understand the NPN thing. It means that you connect it on the negative side of things, as evandude discussed in option 2. But I'm not 100% on the connection from the 5v thing to the transistor base terminal. Could you elaborate more... especially on the need for a resistor? Also, how do I determine which specific transistor would suit my purposes? I understand the basics of electronics, but not enough to do this without help.

        Thanks!
        A car without turbo is a car with perpetual lag.

        My Ride
        My New Page

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        • #5
          evandude, you may take long to type, but I'm just too lazy in my responses

          maxxel, the resistor is so that too much current doesn't pass through the transistor. The base/emitter resistance of a bipolar junction transistor (BJT) is pretty low, so you need the resistor so you won't fry it. On the other hand, the resistance can't be too high or the transistor won't allow much current through, and the LEDs will be dim (or dark).

          Basically a BJT switches the collector-emitter current based on the base-emitter current. For an NPN, that means current will flow from the collector to the emitter based on how much current is flowing from the base to emitter. Beyond some threshold (the saturation current) the transistor is "completely on", which is what you want when the 5V signal goes high.

          I hope that made sense . You don't need to worry too much about transistor specs, since your voltage and current reqs are easily within the range of just about every discrete transistor you'll find. Just check the rated C-E and B-E voltage/current ranges, and the C-B breakdown voltage to assure yourself.

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          • #6
            In other words, go to radioshack and explain the whole situation to them and ask which transistor to buy and which resistor I would need to use in order to have the transistor's saturation current be reached when the LEDs light up. Then hook it up as discussed above and hope nothing melts.

            Should I use a voltimeter to see how much current is passing through the LEDs when they light in order to determine the proper resistor?
            A car without turbo is a car with perpetual lag.

            My Ride
            My New Page

            Comment


            • #7
              Haha, have fun with the radioshack thing, im sure you will walk out with a cell phone instead.
              I think radioshack only has like 2-3 choices for an npn.
              I would say for the the resistor you are looking in the 400-500 range, but i didnt do any cal, so thats a guessament. Buy the assortment-pack, like the 1ohm - 1k ohm pack and you should be fine, since you will end up using resistors on some other project down the line.
              Core duo
              1tb harddrive
              256 ddr
              8 lilliput
              bu-353

              still installing...

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              • #8
                Originally posted by maxxell
                In other words, go to radioshack and explain the whole situation to them and ask which transistor to buy and which resistor I would need to use in order to have the transistor's saturation current be reached when the LEDs light up. Then hook it up as discussed above and hope nothing melts.
                Well... you'll be lucky if they know what a transistor is, let alone how one works Here, I'll make it easy: get this one

                Originally posted by maxxell
                Should I use a voltimeter to see how much current is passing through the LEDs when they light in order to determine the proper resistor?
                No, if you go the transistor route you don't need to do that - you'll be giving the grill 12V, just as if you wired it up straight. The resistor is to limit the swithcing current through the transistor. The previously suggested 500ohm - 1Kohm resistor will probably work fine.

                I'll attempt an ASCII schematic for you (unfortunately whitespace is stripped out, so I can't do "real" ASCII art):

                12V -- (+)[grill](-) -- NPN collector
                pulsing 5V from gizmo -- [.5K - 1K resistor] -- NPN base
                GND -- NPN emitter

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                • #9
                  Sweet, thanks!
                  I think I want to take it one step further. I want a switch in there so I can make the sub lights constant. That shouldn't be hard, though. I'll build the thing as described above and put a DPDT (is that the right terminology?) switch just upstream (closer to the grill). Put the neg from the grill to the middle prong, one prong to the above device, and the third have a normal wire which gets bound to the wire coming out the back of the above device, and they both go to the neg on my 12v source (Opus).

                  That would do it, right? Do I have to worry about choosing a switch that can handle the power, or will any of the ones I have in my electronics pile do?
                  A car without turbo is a car with perpetual lag.

                  My Ride
                  My New Page

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                  • #10
                    just powering an LED grille, I wouldn't guess it would be very high current at all, so nearly any switch should be fine (even small switches are often rated to 0.5 - 1 amp or so)
                    But don't take it from me! here's a quote from a real, live newbie:
                    Originally posted by Viscouse
                    I am learning buttloads just by searching on this forum. I've learned 2 big things so far: 1-it's been done before, and 2-if it hasn't, there is a way to do it.
                    eegeek.net

                    Comment


                    • #11
                      Interestingly, my friend's girl wanted something similar so I got to use her system as a guinnea pig for my own. I was able to get everything wired up correctly, but I was surprised how accurately I had to tune the resistor in order to get the transistor to turn on/off accurately. Too high a resistor and nothing happens, too low a resistor and the transistor's neons turns on full and the LEDs stopped working completely.
                      A car without turbo is a car with perpetual lag.

                      My Ride
                      My New Page

                      Comment


                      • #12
                        Okay, I FINALLY got the parts for this and I'm making the thing right now. I have a few more questions...

                        12V -- (+)[grill](-) -- NPN collector
                        5v -- (+)pulsing 5V from gizmo (-) -- [.5K - 1K resistor] -- NPN base
                        GND -- NPN emitter

                        Right?
                        A car without turbo is a car with perpetual lag.

                        My Ride
                        My New Page

                        Comment


                        • #13
                          Alright, I thought I got this stuff. But when I wired everything up, it didn't work. WTF.

                          Here's what I've got:



                          At this point, neither the sound-activated LEDs nor the subwoofer grills are lighting. What am I doing wrong???
                          A car without turbo is a car with perpetual lag.

                          My Ride
                          My New Page

                          Comment


                          • #14
                            I suspect what is going on is that because LED1 and LED2 are in series with the resistors, insufficient current is flowing to turn on the LED or saturate the transistors. You should leave the sound LEDs connected on to the negative terminals of the sound device, and wire the resistors to the positive terminals of the sound device, in parallel to the LEDs.

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                            • #15
                              ...
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