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Audio/LED Circuit Help

Discussion in 'Audio' started by dannylee, Mar 31, 2013.

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  1. dannylee


    Mar 31, 2013
    Hi guys,

    I'm looking for some help, suggestions etc. for a basic circuit i'm currently working on. I've reached my knowledge limit and theres only so much Googling and reading I can do before my head hurts.

    I currently have 2 LEDs in my car that I want to 'dance' with the music coming from my car radio, basically increase in luminance with the bass, and stay on a low luminance when there's no or quiet audio. I've attached my current diagram (please excuse the quality, i know it's poor!). I've tried a prototype, and it works but i'm not happy with the design for several reasons, and am hoping someone could give me some help.

    1. The audio output of the car radio seems to be at 5v even when there's no audio, so I am assuming that it swings from -5v to +5v to produce the waveform for the speaker. How can I measure the peak output so I know what resistor to use to prevent any high volume audio from causing damage?

    2. Do I need a resistor and a diode between the audio output and the base/emitter to prevent negative voltages from damaging the TIP31? If so, what type of diode?

    3. Is TIP31C my best option?

    4. Any other suggestions, I have a big hunch this circuit is completely wrong even though it does seem to work.

    5. Also, i'd like to make a version that switches the LEDs OFF when there is presence of bass audio, and stay on a low luminance when theres little bass or no audio, can anyone point me in the right direction here, are we talking a PNP transistor?

    Thanking you in advance for any help you can give, it will be much appreciated!

    Last edited: Apr 2, 2013
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    This might work.

    Your circuit is not a good one.
  3. sheldonstv


    Jul 17, 2007
    heres one i built earlier......use hi brightness leds and away you go

    Attached Files:

  4. Electrobrains


    Jan 2, 2012
    Hi Sheldon
    I hesitate to mix into other people's working circuits, but I think you could simplify it a bit.
    I guess you could do the task with 1/3 of the components.

    CDRIVE Hauling 10' pipe on a Trek Shift3

    May 8, 2012
    I think this thing is being over complicated far beyond what's required to light common LEDs from the speaker outputs of an auto stereo. There's more than enough power available across the speaker lines to employ something like this. The no signal LED current is about 575uA and is set by the value of R1. I sim'd this with VG1 having an internal impedance of 8 Ohms. While this circuit will need tweaking to protect against very high audio levels it certainly provides the basic concept.


    Attached Files:

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