Color organs

Discussion in 'General Electronics Chat' started by GFTMC, Jan 21, 2008.

  1. GFTMC

    Thread Starter Member

    Jan 20, 2008
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    This ttopic is about color organs. Very simple ones. I only found 2 topics about this when I searched for them, and both haven't answered my question.

    This is it: What is the simplest color organ that can be made? I speak of one that only references overall volume and doesn't refer to each frequency volume. I thought that something such as A single power source that leads to a very simple AMP, then five resistor, each of bigger Ohm connected parallely, with each resistor ending with a LED.

    Will such a thing work? If no, how can it be made to work?

    Also, the entire thing should operate using a 12V battery, or using a 230V to 12V transformer.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Your idea is more like a VU meter that indicates the magnitude of the audio signal. Look up the data sheet for an LM3814 to see how it works. The LED's can't be driven off a common voltage divider.

    Color organs normally use filters to have outputs for bass, midrange and treble frequencies. here is a link to a modern "classic" design - http://www3.telus.net/chemelec/Projects/Color-Organ/Color-Organ.htm.
     
  3. GFTMC

    Thread Starter Member

    Jan 20, 2008
    18
    0
    Thanks for your reply.

    What do you mean by "indicates the magnitude of the audio signal"?

    Can I create a similar circuit to indicate the volume of the sound?
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
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    Get the data sheet for the LM3914 - http://www.national.com/mpf/LM/LM3914.html. You might want to use the signal driving the amp rather than the amplifier output, but you could always pad that down resistively. The outputs can be applied to external transistors which can then drive more LED's if you want a big display.
     
  5. GFTMC

    Thread Starter Member

    Jan 20, 2008
    18
    0
    thanks for your time. I will begin working on it soon.
     
  6. Audioguru

    New Member

    Dec 20, 2007
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    896
    An LM3914 is a linear voltmeter. The bottom LEDs will have huge spaces in volume while the top LEDs will have very small spaces in volume. The total range is 20dB.

    An LM3915 is a logarithmic sound level meter. The LEDs are spaced with equal volume steps. Each step is half or double the power. The total range is 30dB.

    Your hearing responds logarithmically to loudness so you can hear a pin drop and hear a jet airplane nearby.
     
  7. nomurphy

    AAC Fanatic!

    Aug 8, 2005
    567
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    However, if you want a much better approach using a quad IC, see the attached. This is also a great circuit for driving a 3914/15 for a VU/level meter.

    Attach a LED (or LED's) with properly sized ballast resistor at the output near the bottom right side.
     
  8. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    You haven't tested that have you? The output peak rectifier/filter rectifies only positive peaks, and has no discharge path for the caps - worse than that, the LM324 has PNP inputs, which means it will charge the caps. The active rectifier in front of that puts out positive peaks that are at the positive saturation limit of that op amp, and are not related to the signal amplitude. The negative peaks go a diode drop below Vref.:confused:
    EDIT: If you reverse D402, and then take its cathode from the other end of D401 (the op amp's inverting input), you might be getting something close to what you are after.
     
  9. nomurphy

    AAC Fanatic!

    Aug 8, 2005
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    Good catch, there's a resistor missing (see attached).

    Yes, this circuit has been built and works great.
     
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