LED Spectrum Analyzer schematics

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Discussion Overview

The discussion revolves around building a basic LED spectrum analyzer for a car stereo, focusing on the design of circuits that can visually represent audio frequency bands. Participants explore various approaches, including analog filters and digital signal processing (DSP), while seeking schematics and component recommendations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant seeks advice on components and schematics for an LED spectrum analyzer that would use bandpass filters for different frequency bands.
  • Another participant shares links to existing projects that resemble the desired design, expressing a need for a more complete circuit.
  • There is a suggestion to consider using DSP and a microcontroller to process audio signals, although some participants express uncertainty about their ability to implement this approach.
  • Concerns are raised about the complexity and cost of building a DSP-based circuit compared to a simpler analog solution.
  • One participant mentions finding a Velleman kit that may serve as a building block but notes that one of the integrated circuits (ICs) is no longer available.
  • Another participant questions the viability of a simpler audio analyzer design they found, expressing skepticism about its effectiveness.
  • Some participants emphasize a preference for analog solutions, specifically requesting simple filter designs that do not involve DSP.
  • It is noted that older stereo systems used high-pass and low-pass filters, and that a modular design could be implemented with standard components.
  • There is a mention that all filters in a proposed circuit are identical except for component values, indicating a potential approach for constructing multiple filters.

Areas of Agreement / Disagreement

Participants express differing opinions on the use of DSP versus analog solutions, with some advocating for a simple filter design without DSP. There is no consensus on the best approach, and multiple competing views remain regarding circuit complexity and component selection.

Contextual Notes

Participants highlight limitations in their knowledge of circuit design and DSP, indicating varying levels of experience and comfort with different approaches. The discussion reflects a range of assumptions about the feasibility and accessibility of proposed solutions.

Who May Find This Useful

This discussion may be useful for hobbyists and enthusiasts interested in building audio visualizers, particularly those exploring both analog and digital approaches to circuit design.

SilentBob
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Hi,
I am looking to build a basic spectrum analyzer (if that is what you would call it) out of some LED lights for a car stereo.

Basically, I want about 8 - 10 bars (for different frequency bands), and I want them to jump up and down to the music, giving it a direct feed off of the car stereo head unit.

Looking for advice on components, any schematics that I may be able to use for the various parts (I figure I will need to build several cheap bandpass filters for each of the frequency bands, or use some sort of multi-band filter that I might find in a basic cheap equilizer circuit or something like that.

Still trying to get some ideas.
 
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I googled stereo led bargraph, and got lots of great hits. Here's the 2nd one on the list:

http://www.talkingelectronics.com/Projects/StereoVUmeter/StereoVU.html

Welcome to PF, Bob.
 
Last edited by a moderator:
Thanks for the info (and the welcome)

I have already been doing a bit of searching...

These two most closely match the basis of what I am trying to accomplish:
http://sound.westhost.com/project60.htm
and most specifically this:
http://www.rose-hulman.edu/~sharpjm/led/led.html

The second link, is almost exactly what I am trying to accomplish, however, I am relatively new to circuit design, and I was hoping to find something that was a bit more complete, but I don't think I'm going to .

The best I can tell, I am going to end up building 8-10 of the circuits that are described in the second link, and then I will need to build 6-8 bandpass filters , plus a high-pass filter and a low-pass filter and then feed my audio input into that whole mess.

Does anyone know of a circuit design that would give me multiple band bandpass filters all in one project, that I could use as a basis to feed into the LED circuits?
 
Last edited by a moderator:
One alternative is to use Digital Signal Processing (DSP) and a fast microcontroller (uC) to process the audio and calculate the running filter output values. Have you explored the DSP approach at all?
 
No, I haven't. I'm not sure if such a circuit would be beyond my capabilities or not...I guess it would depend on how much I had to start with...

How expensive or complex would it be to build such a circuit? Would I still be able to use the same basic LED VU meter design for the outputs?
 
If you haven't programmed a uC before, and haven't had an introduction to DSP yet, then it probably is not a good match for your current project. If you were going to use the DSP option, then you would probably buy a medium-end uC evaluation board (like for a PIC18F4455 or Atmel AT91SAM7S64 or similar), and build an audio ADC circuit and an interface circuit to your LED drive board from the uC evaluation board. Then you'd program the DSP algorithm (mostly in assembly with a C wrapper) and test it out using the appropriate debugger.
 
Yeah, probably true. I am more of a programmer than I am a circuit designer, but this might be a more abitious project than I would want to take on as a first time uC program.

I found this Velleman kit that I think is what I was looking for:
http://www.animeguru.com/images/velleman/k4300.html

However, from what I understand, one of the ICs is no longer available.

Still trying to figure out if there is a way around that, or to at least use this as a building block...
 
I just found this page...
http://users.otenet.gr/~athsam/mini_audio_analyzer.htm

It seems too simple, would it actually work?

It looks like all I would need to do would be to add some additional LEDs coming off of the LM3914 or LM3915

Is there something I'm missing?
 
Have you made any progress on this project?

I've been beating my head against the wall, trying to find a practical solution to the same issues you faced. Please let me know. I'm very interested!

Thanks a bunch.
 
  • #10
SilentBob said:
Yeah, probably true. I am more of a programmer than I am a circuit designer, but this might be a more abitious project than I would want to take on as a first time uC program.

I found this Velleman kit that I think is what I was looking for:
http://www.animeguru.com/images/velleman/k4300.html

However, from what I understand, one of the ICs is no longer available.

Still trying to figure out if there is a way around that, or to at least use this as a building block...
The key element to the Velleman circuit is the Filter Sections A and B which pick out the frequency bands for the display.
A DSP solution would implement these as a FFT in software.

With some minor modifications, you should be able to substitute the LM3914 for the obsolete IC
Or you could use the first circuit Berkeman posted as a substitute.
 
  • #11
No DSPs...

Hi...

Thanks for the reply. I am looking for a clean, simple elegant solution to the filter design for the different LED bars. The LM3914 is not scarce... I just bought a dozen off ebay for about $30. Using a DSP is not an option for me... and I know absolutely nothing about them. I'm not into saving pennies on transistors either. I'm just looking for suggestions on a simple filter design, maybe a modular design using standard/basic components that I can replicate and adjust the component values to filter the different frequency bands.

Does anyone have a simple solution that does NOT involve a DSP? I know there is one, because the old stereos had this before DSPs were availlable.

Many thanks
 
  • #12
Old stereos used high pass and low pass fillters.
Using this approach a 3 channel display can be done with only a few passive components.

For more channels you need active bandpass filters like the ones in the Velleman circuit.
All 10 filters are identical except for the component values.
They do not use DSP.
 

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