I know there are tons of examples of music driven LED circuits out there, but they mainly control just one LED or one string of them. I want to make a circuit that will control quite a few LEDs, with each LED at a different range of frequencies.

To do this, I am planning on making an array of band pass filters. Each filter would drive a different LED (or string, or something else)... through a BJT perhaps? Here is a quick sketch of what I am thinking.enter image description here

I might add in a high and low pass filter in the end, but I'll decide that later.

Anyway, would this work? I am wondering if you have advice for me, or maybe some different tricks that could reduce the complexity of this project. Are there certain things to watch out for, such as my source not being able to supply enough power to my filters, ect?

Thanks in advance! I really appreciate any help!

  • \$\begingroup\$ You have recreated the wheel. Er color organ. Same exact circuitry. \$\endgroup\$ – Passerby Dec 13 '15 at 3:09
  • \$\begingroup\$ You could simplify it by replacing the op amps with transistors. \$\endgroup\$ – Passerby Dec 13 '15 at 3:13
  • \$\begingroup\$ If you really want to reduce complexity, look at MSGEQ7 and add a micro. \$\endgroup\$ – Roger Rowland Dec 13 '15 at 5:41

You're on the right track but there are a couple of problems.

  • You'll find your bandpass filters are too wide because the 'Q' is low. This would, for example, cause a loud note of any frequency to get through all the filters and trigger all the comparitors.
  • Speaking of comparitors, you have the non-inverting input connected to common. What do you think will happen if the inverting input goes even 0.1 mV below the non-inverting input?

You may get a better result if you improve the filters, rectify the signal and, somehow, vary the intensity of the LEDs to match the intensity of the sound.


A completely different approach is to do a fast fourier transform (FFT) of the signal with a micro and get the intensity of each band with the transform. I've never done it but there's a good animation of how FFT works on https://en.wikipedia.org/wiki/Fourier_transform.

Your original idea is worth pursuing to gain experience with analog electronics - very hands on and no code. The FFT approach is great if you want to work in software and minimise the hardware design.

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  • \$\begingroup\$ Thanks for the info! How would you go about improving the quality of the filter? And varying the intensity of the LED was phase 2 of this plan haha, so if you know of a good way to do that, please let me know! As far as the comparators, I didn't really know what I was putting there yet, but I knew I had to have some sort of amplifier. So I just put them there for examples sake. If you know how to correctly add them, it would be very helpful! \$\endgroup\$ – Gigaxalus Dec 13 '15 at 1:46
  • \$\begingroup\$ What you're designing is a 1970's sound-to-light controller - very popular in the discos and often built in the form of traffic lights. You should find plenty of sample circuits on the web. You can pick the best bits of each to fashion your own. In the 1970s it was all triacs and mains lamps so you'll need to replace these with suitable LED drivers. \$\endgroup\$ – Transistor Dec 13 '15 at 1:53
  • \$\begingroup\$ I've added a digital approach to my original answer. \$\endgroup\$ – Transistor Dec 13 '15 at 2:01
  • \$\begingroup\$ Thanks! I figured there must have been a digital way to do this too, but I much prefer the analog approach. To me, it is more satisfying to build it than to code it. Also now I know what to look for. I was googling "LED music drivers" ect, but google "light organ/ sound to light controller" gives me much better results. \$\endgroup\$ – Gigaxalus Dec 13 '15 at 2:05
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    \$\begingroup\$ @user2951303 You could half or full wave rectify the output of the BPF and send it to a resistor and capacitor with another resistor draining said capacitor. Basically the output of the BPF would feed a leaky bucket, then you send the leaky bucket output to an op-amp or led driver. \$\endgroup\$ – horta Dec 13 '15 at 2:51

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