12v RGB led pulsing to sub - Choosing transistor/designing circuit layout

Discussion in 'The Projects Forum' started by logan74k, Nov 24, 2015.

  1. logan74k

    Thread Starter New Member

    Oct 30, 2010
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    Hey everybody,
    I'm trying to build a subwoofer with integrated LEDs which will pulse to the beat. I've seen some projects for this around the internet, but everybody seems to be 'winging it' and not necessarily creating a circuit that will last.

    So, if it's possible I'd like to do this the 'right' way. The extra twist I've got going on is I'm using RGB strip lights with a controller.

    The most helpful project I've found is here: http://www.instructables.com/id/How-to-make-LED-Lights-flash-to-music-in-a-car/ So I've been using this as a jumping off point, using a transistor to govern the power going to the LEDs off a separate source.

    This is the controller I plan to use: https://www.superbrightleds.com/mor...patible-rgb-multi-zone-controller-/1800/4374/

    And these are the LEDs: https://www.superbrightleds.com/mor...gb-smd-led-5050-with-lc4-connector/1468/4696/

    What I hope to achieve is a design where the controller can do all of its functions properly (dim/change colors) while the LEDs are only lit when getting power as controlled by the audio amplifier/transistor. For the controller to work 100% I assume it has to be powered full-time, and the transistor/speaker cable hookup must be between the controller and the LEDs themselves.

    I sketched a layout based on my extremely limited understanding of how transistors work and where they need to be in a circuit, but hopefully somebody can set me straight and let me know how the wiring could/must be changed in order to work. Also hopefully point me towards a suitable transistor!

    Thanks very much for any help. v1 wiring.jpg
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    That rgb controller is for wifi only, you cant use a transistor on it.
     
  3. logan74k

    Thread Starter New Member

    Oct 30, 2010
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    Thanks for the input - but, sadly for me, I'm not understanding why it can't take a transistor. It has the 4 wire screwdowns to run directly to the LEDs and the wifi antenna unit is a separate component which, I think, acts similar to the remote in controlling the functions of this piece. Please let me know where I'm mistaken! Thanks again.

    rgb controller.jpg ?
     
    Last edited: Nov 25, 2015
  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    You are correct, the wifi controls the function of the leds, and therefore you cant fit a sound to light transistor mod, as there is no input for audio.
     
  5. logan74k

    Thread Starter New Member

    Oct 30, 2010
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    Ok... no input for audio, got that.

    The controller I'm assuming changes colors by applying PWM to each channel, if that's correct, the leds are always getting ~12v, just in bursts.

    I may be a bit naive, but you're saying there's nothing that can be put in that path that will interrupt the voltage, and only let it through when a current is applied from another source?

    Thanks for putting up with me!
     
  6. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    The only way i can see you modifying it, is to interrupt the common supply of the leds, with a mosfet transistor, like what you have drawn, but it will just flash when the music is loud. It wont alter the colours of the leds!
     
  7. logan74k

    Thread Starter New Member

    Oct 30, 2010
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    That's pretty much all I'm looking for, to flash with the beat, hopefully with some variation in brightness based on the intensity of the applied signal.

    I was thinking the controller could be doing its thing in regards to color and brightness of the 3 channels, and the transistor/amp would take that from 0-100% based on its own signal. How exactly that would work math-wise is beyond me. Totally new to transistors, and my LED experience otherwise is based on simple basic circuits.

    If the controller was giving 100% to the LED strip (all colors, so, white) , would the transistor/amp allow the brightness to ramp in relation to the amount of voltage it was getting from the audio amplifier?

    Thanks.
     
  8. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    no it wont ramp up, just puts leds on or off to the beats of the music, try this circuit,,,
    Note there is no isolation from the speaker ground to your led box


    fet.png
     
  9. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    You should add a 1M resistor from gate to source. Otherwise the Mosfet will latch after some time with no current path to ground and capacitor coupling.
     
  10. logan74k

    Thread Starter New Member

    Oct 30, 2010
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    Thanks for the sketch and the information!

    I hope you'll forgive my thickness on this - to clarify for those of us who don't work with electrical schematics all day long - we have now a 100uf capacitor followed by a 1k (fuse?) going to the gate on the mosfet from the positive speaker lead, and GopherT would put in a 1M resistor ... soldered to the source lead on the mosfet?

    Can I possibly get a laymans description of how each of the new components improve the circuit as it relates to the application? (except the fuse, if it's a fuse, I can wrap my brain around its function pretty well) I'd like to understand better exactly what I'm building. And, what are the limitations which won't allow the circuit to ramp the brightness with the varying power from the amp?

    Lastly, I don't follow the sentence :"there is no isolation from the speaker ground to your led box" I interpret it as "the black speaker cable is connected directly to the RGB controller" Should there be isolation? Is having the two directly connected as weird as it sounds?

    Thanks a lot for your help guys, and Happy turkey day.
     
  11. logan74k

    Thread Starter New Member

    Oct 30, 2010
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    ...too many questions?

    I realize I'm a mere mortal toying in a world of mathematics I don't fully comprehend, but I'm trying to learn and would appreciate anyone's assistance. Thanks again.
     
  12. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    1k is a resistor also..
    gopher is saying to also add a 1Meg resistor with one side soldered to the gate and the other side to the source of the mosfet
     
  13. ScottWang

    Moderator

    Aug 23, 2012
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    I don't think the symbol is a good demo, because the symbol you drew almost used in jfet as 2sk30A, etc...
    IRF640 datasheet.
     
  14. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    image.jpg
     
  15. logan74k

    Thread Starter New Member

    Oct 30, 2010
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    Thanks for the clarifications on how the circuit is intended to be built. I'll try to keep it to one question per post as this forum seems all about brevity!

    Can anybody comment on the finer points of how the capacitor and resistors improve the circuit for this application vs. a bare mosfet? I don't doubt that they do, I just don't comprehend exactly how.
     
  16. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    The resistor and capacitor prevent the dc voltage from speaker keeping the transistor on,so only ac signal (music) can pass through.
     
  17. logan74k

    Thread Starter New Member

    Oct 30, 2010
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    Thanks Dodgydave!

    I don't follow the sentence :"there is no isolation from the speaker ground to your led box" I interpret it as "the black speaker cable is connected directly to the RGB controller" Should there be isolation? Is having the two directly connected as weird as it sounds?

    The audio amp is putting out 0-18v AC, is there a concern having the negative spliced to the DC controller's + wire?
     
  18. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    You're correct, the two grounds are connected together,
     
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