*Noob* Sound reactive leds question

Discussion in 'The Projects Forum' started by colben22, Oct 26, 2011.

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  1. colben22

    Thread Starter New Member

    Oct 26, 2011
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    Hey guys, this is about the first thing I have tried to create any help would be great.


    [​IMG]


    I am trying to have the first set of leds always be on with the first switch, and the second set to switch between always solid like the first set and sound reactive by the transistor (TIP31 or TIP120 I really have no idea in the difference)

    I have tried to search around, but in this context of what I am trying to do and want to expand to do it doesnt help me much.
     
  2. Audioguru

    New Member

    Dec 20, 2007
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    You connected the base-emitter diode of the transistor directly to the speaker without a series resistor to limit the current. Then the signal will cause an extremely high current which will probably blow up the amplifier and the transistor.

    When the signal reverses at the base-emitter (it is an AC signal) then it will probably exceed the maximum allowed emitter-base reverse voltage of usually 5V which will cause a very high current that will also blow up the amplifier and the transistor.

    If the circuit is fixed to limit the base-emitter current and to prevent reverse voltage with a diode then the LEDs will average only 10mA when the music is at full blast because the signal is AC and the transistor will rectify the signal and light the LEDs only half the total time.
     
  3. colben22

    Thread Starter New Member

    Oct 26, 2011
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    All the diagrams I have seen have had the speaker wired liked that, do I need to move the transistor and switch?

    Im starting to think this wont work out the way I am wanting.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    Well, you're trying to power the LEDs by the output of the amplifier.

    "Light organs" as they were called back in the 60's and 70's would get the line-level audio input, which is the signal level between the preamp and the amplifier. If you try to drive them directly from the output of the amplifier, you will introduce a great deal of distortion.

    Velleman sells kits for sound-activated LED lights. The kit has a built-in microphone so that it will pick up ambient sound in the room, and blink the LEDs on the circuit board. You might wish to start with a kit like that, instead of trying to build something from scratch.
     
  5. Audioguru

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    They were Instructables designed by a 13 years old kid who knows NOTHING about electronics.

    No, they will be fine.

    It is a disaster. But it will work fine if you add a series resistor to the base of the transistor to limit the base-emitter current and add a diode in reverse to the base-emitter to clamp the reverse voltage.
     
    Last edited: Oct 27, 2011
  6. colben22

    Thread Starter New Member

    Oct 26, 2011
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    This is going to sound bad since I am trying to wire this but I have NO idea what that means.


    I wouldnt mind using a kid but I dont think its going to be as easy as installing a mic to a board to use inside my car and expect the results I wanting through out.
     
  7. Audioguru

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    No.
    Look at his schematic. The LEDs are powered by the 12V supply and turned on by the collector of the transistor. But the base-emitter diode is shorting the output of the amplifier without any current-limiting resistor.
    When the speaker signal is higher than 5V peak then the reverse-biased emitter-base has avalanche breakdown with another very high current.
    It is a SMOKE MACHINE.
     
  8. colben22

    Thread Starter New Member

    Oct 26, 2011
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    so if I am understanding what youre trying to say is I just need to add a resistor between the speaker positive and the transistor B input?
     
  9. Wendy

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    Mar 24, 2008
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  10. Audioguru

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    Dec 20, 2007
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    Yes.
    The value (ohms) of the resistor must be calculated from the maximum RMS power from the amplifier.

    Also, a 1N914 or 1N4148 diode must be connected between the base and emitter of the transistor with the cathode at the base.

    The amplifier might be bridged and drive both wires of a speaker then a 0.33uF capacitor also must be connected in series with the resistor and the base of the transistor.
     
  11. iONic

    AAC Fanatic!

    Nov 16, 2007
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    So, if the Velman kit is not doing what you want, what exactly do you want do accomplish with this or any circuit. Unfortunately your experience level suggests that a kit would be the best place to start.
     
  12. colben22

    Thread Starter New Member

    Oct 26, 2011
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    I looked a little more into velleman circuit but not enough to figure out it it would be able to work with the number of leds I am interested in doing.

    Another concern of mine was the sectioning I was WANTING to do. I wanted multiple sections wired to different sections of speakers. I really dont want to spend 70$ on kits if I can rig something together that will work.

    Vague idea on how I want to do it.

    [​IMG]

    Audioguru - When you mention amplifier are you speaking of the amplifier that drives the speakers them self?

    EX - My front speakers are 110watt rms and will be running very close to that number, how would I calculate the size of resister I need between my speaker positive and the transistor?

    And I guess I dont really understand where the diode would go :/


    Thanks again for all your guys help, I know this a ridiculous project for someone of my knowledge but I am hoping I can get it working!


    Bill_Marsden - Ill take a look through it tonight when I get a chance.
     
    Last edited: Oct 27, 2011
  13. Audioguru

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    Dec 20, 2007
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    The Velleman kit can drive only the few LEDs that it has and no more.

    It is easy if each group of speakers has its own filter and amplifier.

    Yes as you showed in your first post.

    If your LEDs are ordinary 20mA 5mm ones and each group has 3 strings then the output of a transistor has a current of 60mA and then the input must have at least 6mA. The max allowed base current is about 50mA.
    110W into 8 ohms is a voltage swing of 42V peak. Use a 6.8k/0.5W series base resistor.
    110W into 4 ohms is 30V peak. Then the series base resistor is 4.7k/0.5W.

    Like I said before, "a 1N914 or 1N4148 diode must be connected between the base and emitter of the transistor with the cathode at the base."
     
  14. iONic

    AAC Fanatic!

    Nov 16, 2007
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    There is also this kit, but it will cost you some bucks as well.

    led-color-organ
     
  15. Audioguru

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    It has a number of errors, read the comments about it.
     
  16. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    As you intend to use the circuit in a car as stated in post # 6:
    I am closing this thread as it violates AAC policy and/or safety issues.

    Quote:
    6. Restricted topics. The following topics are regularly raised however are considered “off-topic” at all times and will results in Your thread being closed without question:

    • Any kind of over-unity devices and systems
    • Automotive modifications
    • Devices designed to electrocute or shock another person
    • LEDs to mains
    • Phone jammers
    • Rail guns and high-energy projectile devices
    • Transformer-less power supplies
    This comes from our Tos:
    Terms of Service
    There will be enough sites where automotive questions can be discussed :
    Member selected automotive forums

    bertus
     
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