30 leds blinking with music (not vumeter)

Discussion in 'General Electronics Chat' started by Johan Valderiba, Jul 17, 2016.

  1. Johan Valderiba

    Thread Starter New Member

    Jul 17, 2016
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    Nice forum, I am new here, i hope somebody here (an angel) can help me.

    - I am making a subwoofer box for my room, which its specs are 8" 4ohm subwoofer feeding by about 100w.
    - I put about 30 leds that lets say, they are directly connected to the power source 24V DC of course with their resistors, they are always OFF because I still have to work in a switch that switch them at the rhythm of the music.
    - I initially thought using a tip31, with the base connected at the output of the "pre" amp, so now this tip31 will switch the leds that I mentioned. I am doubting about this idea (some people use it as a basic vumeter of single led) and yes, I need all my leds on/off at same time, not like those classic vumeters, I said that I although this is a good and basic idea, I think that this will low the quality and strenght that pre amp delivers to the line in of the amplifier, is not it?

    - Then I thought that what if I take some signal from the ouput of the amplifier, there are lots of watts (100watts) can I simply connect there a solid state relay (3-30V) that will switch my led circuits? maybe I cannot connect the relay directly to the speaker terminals, but what about adding a resistor, or a ic7805, or I DONT KNOW, and thats the reason I am posting here.

    - I also thought making a simple vumeter that triggers with an electrec micrphone, the idea is good enough I think, but theres a risk that leds turn on with external noises in the street or my room, which is undesired.

    - I also thought adding a pre amp which has high output, so it can feed amplifier and trigger the tip31 without any effort, so the signal will be strong even with these components, I really dont want to do this, because the bluetooth amplifier board I am buying, already come with its pre amp, so its not convenient working in another pre amp, what I pointing is to take some signal from amplifier output, please tell me there is a way, I have seen passive vumeters where the leds are being turned on just by the amplifier output, I don want to feed all my leds from that energy, I simple want to use a little of that energy to simple trigger a switch, so the leds that are directly connected to the main power supply, can blink with the sound.

    What would you recommend me ?
     
  2. Johan Valderiba

    Thread Starter New Member

    Jul 17, 2016
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  3. Externet

    AAC Fanatic!

    Nov 29, 2005
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    And do you want all the LEDs flashing simultaneously at the same beats of audio; or do you want the quantity of LEDs flashing to increase or decrease by the audio level; or do you want the light intensity of all LEDs to vary according to audio ?

    To start, check if the application note for 3 pieces of LM3914 in cascade mode please you.
     
  4. Johan Valderiba

    Thread Starter New Member

    Jul 17, 2016
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    All leds should blink at same time and with same brightness level, no matter if sound is low or high. Please can you explain me about the LM3914? is not more easy taking signal from amplifier output? Thanks so much.
     
  5. Externet

    AAC Fanatic!

    Nov 29, 2005
    758
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    Then you need a circuit that triggers a mosfet or proper solid state relay on peaks only. The peak level can be adjustable.

    A complete LM3914 based circuit is then, not what you would be pleased with. Unless you pick the output of a single higher level pin of the LM3914 to trigger the driver for all your leds.
    Example : use pin 10 or pin 11 only ----> http://www.zen22142.zen.co.uk/Circuits/Audio/audiobargraph.png
    (Nothing connected to other output pins)
     
  6. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,515
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    Getting LEDs to follow the beat of music without getting confused by the actual notes is a bit more tricky that you might think. Even though the audio to a sub-woofer already has been lowpass filtered, It still has a frequency range that might extend down to 20 Hz. In contrast, the frequency of the beat ("beat frequency" has a specific meaning in electronics) probably is 1 to 5 Hz. What is needed is maybe a lower frequency lowpass filter followed by an envelope detector, something that produces a voltage equal to the overall loudness of the audio, followed by a level detector. Anything above the level is considered a beat (lights on) and anything below the level is the space between beats (lights off). This circuit is not as complicated as this might sound, and at the end there can be your TIP transistor driving the lights.

    What is your skill set for things like assembling an opamp circuit on perf board?

    Another thought - to get started you can go a much more simple route. Amp output > rectifier diode > capacitor and resistor > output transistor or solid state relay > LEDs. If this works but the lights don't look quite right, then move on to the opamp circuits.

    ak
     
  7. dannyf

    Well-Known Member

    Sep 13, 2015
    1,767
    357
    I think someone recently asked the exact same question, with the exact same transistor, the exact same number of LEDs, drawing rhe exact same style of schematics, trying to do the exact same thing.

    So a little searching may help you.

    Long story short, the answer depends critically on your definition of "switching" the LEDs.
     
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