Audio Controlled LED Chaser using Bandpass Filters and RGB LEDs

Thread Starter

Cody Johnson

Joined Feb 18, 2016
11
Well, I have decided to take on a rather ambitious project to start out my 2016, but I am at a loss on where to start. I know what I want the project to do, and have a decent understanding of what needs to be done, but could use a little guidance in what circuit layouts would work best.

I want to make a circuit/combination of circuits that will drive a series of RGB LEDs in sequence, based on the target audio range (treble, mid, bass). I will be using a car stereo pre-amp outputs for my audio signal so I am working with a line-level audio input.

Essentially, I want to separate my audio in to three channels (treble, mid, bass) and have each channel run it's own sequencer circuit that will run a single leg of the RGB LED. The idea is that all 3 sequencer circuits will be running at different timing intervals, producing a completely random display of colors in the LEDs depending on when 2 or 3 sequences align with eachother. Ideally I would like the LEDs to fade out as it advances to the next one in sequence, that way I have a better variance of color as the sequences will align more often and at varied intensities at each leg of the LED.

Any guidance would be greatly appreciated. I have no problem messing around with different layouts and combining different circuits to get the desired effects, I just don't know what types of circuits I need to be looking at to produce each step efficiently.

I have an engineering background and do have a fair amount of experience building circuits, but need some advanced thought on this one.
 

AnalogKid

Joined Aug 1, 2013
8,259
What you are describing is called a color organ, and there are a LOT of schematics and projects on the innergoogle. Basic operation is that audio comes in, is buffered, and drives three filters: lowpass to pick off the bass, highpass to pick off the treble, and bandpass to get the midrange. The filter outputs still are audio. these are amplitude detected like an AM radio to produce a varying voltage where up = brighter and down = dimmer. These three control voltages drive whatever the output is, 110 Vac lamps through TRIAC dimmers, LEDs through PWM drivers, or whatever. With this modular approach, each section can be tuned for your pleasure.

ak
 

dannyf

Joined Sep 13, 2015
2,197
If you can describe the sequences I am sure it is quite doable.

In the simplest form, produce a mcu based solution where the sequence of lights changes with input.

Feed the audio signal through three filters plus three sequencers and you are done.
 

Thread Starter

Cody Johnson

Joined Feb 18, 2016
11
Circuit layout.jpgThis is what I envision needing to do, but do not necessarily know what circuits I need to do this. I will be using a 12V input.
 

Thread Starter

Cody Johnson

Joined Feb 18, 2016
11
What you are describing is called a color organ, and there are a LOT of schematics and projects on the innergoogle. Basic operation is that audio comes in, is buffered, and drives three filters: lowpass to pick off the bass, highpass to pick off the treble, and bandpass to get the midrange. The filter outputs still are audio. these are amplitude detected like an AM radio to produce a varying voltage where up = brighter and down = dimmer. These three control voltages drive whatever the output is, 110 Vac lamps through TRIAC dimmers, LEDs through PWM drivers, or whatever. With this modular approach, each section can be tuned for your pleasure.

ak
I have built a number of color organs; however, that is not what I am looking to do for this project. I do not need something that has varied light intensity according to audio amplitude. I posted a general layout of what I see as needing to be done. That may help clear up what I am wanting to do a little better.

I want something very similar to this :
but I want to use RBG LEDs with each of the 3 frequencies controlling one leg of the LED and I want the LEDs to fade when it goes forward in the sequence. The fading will allow a much broader color spectrum as the 3 sequences cross paths with varying intensities due to the delay circuit.
 

Thread Starter

Cody Johnson

Joined Feb 18, 2016
11

AnalogKid

Joined Aug 1, 2013
8,259
No problem, that's what I guessed it was. Looking at the schematics, there is a third option that will give a more even range of brightness. In both of the schematics on the site, the LED current changes from off to full on over a relatively small range of base voltages. Since you have plenty of headroom with a 12 V rail, the circuit can be modified to give a wider range of brightness with better control, probably with a smaller capacitor for less group delay. By the way, what you are calling a delay circuit actually is a ramp generator.

Moving on, what does the 555 do? My guess is that it is a free running astable, and the audio modulates the frequency through the Control pin. If so, we can come up with something with more gain - a greater change in oscillator frequency per volt of control signal change.

ak
 

Thread Starter

Cody Johnson

Joined Feb 18, 2016
11
I was hoping to get away from the 555 and 1470 by using a 3914, but I do not know the implications that would arise from running that. I know it essentially does the job of the 555 and 1470 as an all-in-one unit, but I do not know how the 3915 works other than it can be used in dot and bar mode, with dot being what I am looking for in this application.

I am a few years out of my college electronics courses, so I will be relying on other people and google to help me modify circuits I find online; both to set up the correct capacitor and resistor setups, and to help choose appropriate circuits to combine inline to achieve the desired effects.

Once I have all the circuits designed and theoretically working, i will get them put together on a breadboard, and once tested I will print out a PCB design and etch the board to alleviate a mess of wires.

If you know of any schematics for the different stages of this deal, it would be greatly appreciated if you could provide some links.
 

Thread Starter

Cody Johnson

Joined Feb 18, 2016
11
Due to input from a couple of forums, I have some edits to the flow of my circuits. In lieu of using 3 555s, I want to try to use a single CD4584; in lieu of a CD4017, I want to try to use CD74HC4017s; and finally, in lieu of 30 different fader circuits, I would like to use a single fader circuit on the common ground of each color group of LEDs.

I have no experience in the use of a CD4584 or the CD74HC4017. If it is not too much to ask, even a simple hand drawn schematic would be great. I can figure a lot of it out, but a quick drawing of the connection between the CD4584 and the 3 CD74HC4017s would help a lot. And including the layout of the fader circuit with the common ground would be amazing too.

In summary, if I can get a schematic starting at the output of the audio filters and terminating at the lights, that would be great. I think I can conjure up the filter circuit and the LED driver circuits, but the timer and decade counter circuits I have trouble with.
 

Thread Starter

Cody Johnson

Joined Feb 18, 2016
11
Well I think I have a fair amount of this figured out now. But I do have some specific questions on a few components. I have created a layout that shows each individual component of the series. Does this look about right? Any glaring errors?

To power the whole thing, I will be using a computer power supply, so the 12V and 5V connections will be simplified.

If anyone can provide some additional input on this, that would be great, as I am a bit stumped at this point.Driver Circuit.png
 

Dodgydave

Joined Jun 22, 2012
8,686
Looks to me you want to make a 3 channel light chaser, split into Bass, Middle, Treble using cd4017 counters???

If you want to use the lm3914/5 chips then it will be like a VU meter, in dot or bar mode.
 

bertus

Joined Apr 5, 2008
20,240
Hello,

In the purple block, the inverters can not be connected to the +12 and - 12 Volts.
The maximum allowed voltage for CMOS chips is usualy 15 Volts and now they would have 24 Volts accross them.
When connected between +12 Volts and ground, the inputs may not go below 0 Volts.

Bertus
 

dannyf

Joined Sep 13, 2015
2,197
Well I think I have a fair amount of this figured out now.
I would suspect no.

You have to figure out what you are trying to do, and why the set-up you have will get it done. For example, why do you think a hc4017 will work here?

Conceptually, what you are trying to do is simple: separate the signal into three bands and display each band. Looking at your design, which does which?
 

AnalogKid

Joined Aug 1, 2013
8,259
Small - the audio filter outputs need pull up resistors.
Small - two-pole active filters will give better separation among the three frequency bands, so one loud note does not cause activity in two output sections.
Medium - If the "decade counter input signal" section is supposed to be three oscillators, you are missing a few parts.

Large - I'm still not clear on the relationship between a frequency band, its amplitude envelope, the 555, and the desired output. Clearly the desired output will be a visual ring counter, a single light that progresses through a string of locations, returning eventually to the first location and repeating. But what causes the counter to increment one count? Does it increment whenever the average amplitude of the audio for its frequency band dips below a threshold value and then rises above it to create a clock pulse? Or is the counter driven by an oscillator so it is always moving at a minimum speed, and the speed of the chase pattern changes with the audio band volume? Or something else...

ak
 

Thread Starter

Cody Johnson

Joined Feb 18, 2016
11
I would suspect no.

You have to figure out what you are trying to do, and why the set-up you have will get it done. For example, why do you think a hc4017 will work here?

Conceptually, what you are trying to do is simple: separate the signal into three bands and display each band. Looking at your design, which does which?

The idea that i am trying to work through is: The audio is separated in to high, mid and low. The filtered audio signals will go through the peak voltage detector which is fed in to the CD4584 ( in lieu of using 3 555s) to provide the input signal to the HC4017. The HC4017 was chosen at the suggestion of a member of another forum as it provides more output current than the CD4017. The Decade counter will them be used to provide a signal to the legs of the RGB LEDs, one color through each 4017. Theoretically, each band will produce a different sequence on the 4017s, advancing the individual colors of the LEDs at different intervals.

Essentially what I want this to do is use low frequencies to power the blue leg, mid frequencies to power the green leg and high frequencies to power the red leg. These 3 different frequencies would advance through the individual legs at different rates and would make different colors as the sequences cross eachothers paths.

Hope that helps to make sense of what I am trying to achieve.
 

dannyf

Joined Sep 13, 2015
2,197
The Decade counter will them be used to provide a signal to the legs of the RGB LEDs, ...

Essentially what I want this to do is use low frequencies to power the blue leg, mid frequencies to power the green leg and high frequencies to power the red leg.
If I were you, I would ask myself

1) what output will the counter generate? does that math your desired output?
2) to generate that output, what input will need to be fed to the counter? are you feeding that kind of input to the counter?

Unless you are looking for something really weird, I can say with 100% confidence that your design here doesn't fly.

I am happy to tell you why but you will learn a lot more if you go through the datasheet of the 4017.
 

Thread Starter

Cody Johnson

Joined Feb 18, 2016
11
Small - the audio filter outputs need pull up resistors.
Small - two-pole active filters will give better separation among the three frequency bands, so one loud note does not cause activity in two output sections.
Medium - If the "decade counter input signal" section is supposed to be three oscillators, you are missing a few parts.

Large - I'm still not clear on the relationship between a frequency band, its amplitude envelope, the 555, and the desired output. Clearly the desired output will be a visual ring counter, a single light that progresses through a string of locations, returning eventually to the first location and repeating. But what causes the counter to increment one count? Does it increment whenever the average amplitude of the audio for its frequency band dips below a threshold value and then rises above it to create a clock pulse? Or is the counter driven by an oscillator so it is always moving at a minimum speed, and the speed of the chase pattern changes with the audio band volume? Or something else...

ak

I would like to have it set up so the average amplitude of the audio for its frequency band dips below a threshold value and then rises above it to create a clock pulse?

I believe that is what the video I posted above is essentially doing. The difference being that instead of a microphone, I want to use the filtered audio input to drive the advances.
 

Thread Starter

Cody Johnson

Joined Feb 18, 2016
11
And I have no issue at all scrapping my entire approach if someone has a better idea of how to accomplish what I am looking to do.
 

AnalogKid

Joined Aug 1, 2013
8,259
in lieu of 30 different fader circuits, I would like to use a single fader circuit on the common ground of each color group of LEDs.
That will save a large number of cheap parts, but it also will change the dynamics of the display. with individual ram generators, LED6 ramps up to full brightness while LED5 is ramping down to darkness. With perfectly symmetrical ramps the two would pass each other at 50% brightness, and the light would look more like it is sliding from one location to the next rather than turning off, moving, and turning on. With a single fader for all LEDs of one color, something has to tell the fader to leap into action. For example, the 4017 clock signal can trigger a monostable that is shaped into a down and up ramp signal for the fader, but there always will be a moment of complete darkness (for that color) between every location change. No right or wrong answer here, just two conditions to chose from.

And a 2-3 second fade time will be overrun by the clock pulses.

ak
 
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