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Amp driving LED project issue

Discussion in 'LEDs and Optoelectronics' started by Pharaday, Jan 28, 2020.

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  1. Pharaday

    Pharaday

    137
    4
    Jan 18, 2016
    Okay so I have worked up to this point with yall's help and this is the closest I've ever come to completing a project LOL. I've been working on this for quite some time. For me this is a rather large project. I'm taking an amp but instead of speakers giving LEDs to light. I want to make two of them for an electric guitar and violin so that any sound they produce will cause this led to light. So easy a caveman could do it right? 2 f***in months later..... Here I am.... Anyways here's the setup I'm using. I will either splice into the existing or add a little Piezo pickup. Those both work. And they will lead to this TDA7231A amp:
    Screenshot_20191210-151426.png
    And just instead of speakers I put one LED. I should also let you guys know that one of those capacitors seems to be without polarity. I did not have that value so I created one bye connecting two capacitors of double the value in series. I was told that this would create a capacitor of half the value of the two combined but with no poles. It's the best amp I've ever built anyways, with the most gain and least noise. This works great for one or two notes. Then it just seems like there's a capacitor that giving this LED power and it starts out strong but slowly Fades. Then if you leave it alone for a long time and give it a chance to charge, it works again. It takes a long long time to charge. I've even tried connecting the speaker output as the triggering current for a transistor that should allow a good 3 or 4 volts to flow no. But it doesn't it behaves the same way. I'm pretty sure I'm connecting the transistor correctly, maybe not. Here's what it looks like fully connected with a transistor that seems to do nothing but working, if for only the first few notes:
    20200128_155802.jpg
    I thought about using a relay instead but I don't have any with an activation voltage low enough. It would be nice if it was a dim light for quiet noises and a bright light for loud noises oh, but I would settle for just light at 1 brightness for any sound. I just can't get this for more than a few notes and then it needs to recharge. What can you guys suggest? Perhaps changing one of the capacitors? I've fiddled with this so long it would be a shame not to get it working. I appreciate y'all's help.

    Edit: oh and I did try adding another amplifier between the LED and the first amplifier. Oddly, the same thing happens. There is no amplification. The LED works for the first few notes then quits. I don't get this, amps amplify.

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    Last edited: Jan 28, 2020
  2. Pharaday

    Pharaday

    137
    4
    Jan 18, 2016
    someone else suggested this and says it will solve the problem but I'm skeptical. He changed that odd cap without polarity to a 0.1uF
    amplifier blinks LED.png

    I have another TDA7231 so I'll try it tomorrow
     
  3. Pharaday

    Pharaday

    137
    4
    Jan 18, 2016
    I just want y'all to know what info others have given so we can all pool our brain power *puts on floaties*. I have been in contact with some of my old circuits classmates (who now have kids and I'm still gathering broken electronics LOL), my professor and others. One of them told me that instead of that transistor I could use a VU meter type circuit or possibly just a comparator for the whole thing. I've got to study these options before I can comment on them.
     
  4. Audioguru

    Audioguru

    3,257
    702
    Sep 24, 2016
    You are too late. The LM3915 was an IC with 10 comparators in a logarithmic arrangement of level detectors. It made a simple but useful VU meter. it could make a bar of light or a dot of light move up and down with the level. It ain't made anymore.

    I have one in my living room with a microphone as its input. It has been working nonstop for 14 years.
     

    Attached Files:

  5. Pharaday

    Pharaday

    137
    4
    Jan 18, 2016
    Dude 90% of my supplies aren't made anymore. You guys buy components? Whenever I need something, I go wading through a spare bedroom full of circuit boards. Harvesting and recycling is the main part of this Hobby. 3915, you say? But would I really need more than one comparator for this? I'm aware of comparators but I've never done any work with them. Also, uh oh, you know I'm double-dipping forums. Could you stay on one forum please?
     
  6. Pharaday

    Pharaday

    137
    4
    Jan 18, 2016
    Ah man those things are cool! You made that with 3915, huh? Those would work perfectly for this thing I'm trying to do. Guess I'm adding sound level indicators into my "to research" list. What happened to our lives, fellas, when research is our Recreation? Fun is now my boring!
     
  7. bertus

    bertus Moderator

    1,762
    677
    Nov 8, 2019
    Hello,

    The LM3915, that audioguru showed, has 3 dB steps.

    LM3915_typical_schematic.png
    The LM3916, has a VU meter arangement.

    LM3916_typical_schematic.png

    Bertus
     

    Attached Files:

  8. Audioguru

    Audioguru

    3,257
    702
    Sep 24, 2016
    3dB is double or half the power that sounds only a little louder or a little less loud.
    The first comparator in an LM3915 turns on its LED at a certain loudness that you set then the second turns on at a loudness a little more, then the third at a little more..... all the way up to the tenth that turns on to a little louder than the ninth.

    The first time I used an LM3915 I connected two of them in series to show a 60dB range.
     
  9. Pharaday

    Pharaday

    137
    4
    Jan 18, 2016
    Well don't that beat all
     
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