Giant cylindrical color organ/VU meter for a nightclub

[mjkelly93]

Guru ill take a look at it tomorrow. I actually bought a pack of LM3915s but decided to go this route instead.

So the advantage would be that the peak level would be fully lit? That sounds like it would be neat. I'll try and put one together tomorrow and test it out.

 

[audioguru]

So the advantage would be that the peak level would be fully lit?

Yes, because if an LED lights for a duration of less than 30ms which peaks of music frequently do, then the brightness is seen as a dim blur. A peak detector holds the level of each peak for 30ms then all lighted LEDs will appear bright.

If LEDs light for 30ms then are turned off for 30ms then on then off over and over like a machine gun then our vision sees the very fast flashing at full brightness so do not worry that a peak detector will make repetitive peaks look too slowed.
An opamp circuit makes a good peak detector. The very high open loop gain of the opamp cancels the voltage drop of the rectifier diode.

 

[mjkelly93]

Guru, correct me if im wrong here, but, if i had 3 LM3915, one for each color, and they all took the same audio signal and divided it up, wouldn't the lights always be white?

Just for example, wouldn't the 3915 put out the same exact amount of voltage for each color?

I was under the assumption that the 3915 only took an audio signal and divided it up into multiple outputs, each one less than the previous one. The MSGEQ7 takes the audio signal and splits up into frequency bands, then the arduino assigns each band a color, THEN im taking the signal and dividing it up into multiple outputs.

Is there a way i can send my blue, green, and red output digital signal from my arduino to the LM3915 and use the LM3915 to chop that signal up into different outputs, each one less powerful that the previous one? I was under the assumption that the LM3915 needed an audio signal input and wouldn't function with a signal from the arduino?

Perhaps im totally wrong here though.

 

[audioguru]

An LM3915 measures the level of an audio signal and turns on one output (it has a total of 10 outputs) when the input level reaches and exceeds each comparator threshold voltage. It can be set for one output turned on (DOT mode) or set for all lower outputs also turned on (BAR mode).

An MSGEQ7 is an audio filter IC (not an opamp) that has seven bandpass frequencies. Since you have only 3 colors then many audio frequencies will not properly light your LEDs. It has only one output with all its frequency bands multiplexed in sequence.
Its multiplexing causes one of its bandpass frequency levels to be at its output for only a very short time (then it produces the output level of the next frequency band, then the next, then the next etc.) which complicates your circuit. I do not see wires on your wiring layout (the schematic is missing) that shows that the multiplexing is converted to 3 outputs.

Your circuit would be much simpler and work better if you replaced the arduino and MSGEQ7 with a lowpass, a midrange bandpass and a highpass analog filters. Each of these filters will have outputs working all the time. Then three LM3915 ICs.

 

[mjkelly93]

The diagram i posted is only showing i did the color blue. You would just replicate that for red and green.

OK im going to try that. Do you think radio shack would carry those filters?

 

[audioguru]

Radio Shack went bankrupt and its new owners now sell cell phones. Radio Shack left Canada 11 years ago. I do not know if a three filters IC you need is available. You would need to find or design the circuit for it.

 

[mjkelly93]

Huh theres a radio shack right down the road from here. I bought a bunch of resistors there yesterday.

Ill look into it.

 

[audioguru]

Some Radio Shack stores in Canada were bought by Circuit City who also went bankrupt then Bell Telephone Company of Canada bought them and operate them called The Source. They sell mostly cell phones.

 

[mjkelly93]

Huh no kidding. I guess some radio shacks are still radio shacks here in the states. I know they are going through bankruptcy though.

The local store is like 75% cell phones too then one small section in the back for resistors and headphones and stuff like that.

Im in the middle of building the lm3915 circuit now. Gonna stop for lunch and go back at it.

Im thinking for the low pass filter doing a 10k resistor and 10nf capacitor then for the high one 10k resistor with a ~550pf capacitor based on this guys two videos:

 

[audioguru]

A filter made with one resistor and one capacitor has a very gradual cutoff slope. You need second-order Butterworth filters made with an opamp instead.

 

[mjkelly93]

Well thats not good.

These butterworth filters are separate chips? I can just buy them and hook them up? Or can i run multiple resistors or capacitors and test out my own circuit here first?

 

[mjkelly93]

Guru im comparing what i have built here to LM3915s online and i think im gonna stick with the way this is built here.

In fact, im actually playing what i have built here using youtube videos displaying an lm3915 tower. The lm3915 towers are cool but they aren't as high energy as what i built here. I want that strobing and blinking and up and down really fast. The towers im watching are cool because its actually showing the peaks and stuff but they are too slow for the club, i think.

This is the video im watching here:

Mine is way better than that. Maybe not as scientifically accurate as that but im not teaching a class on audio frequency. It just needs to be high energy and a huge wow factor.

 

[audioguru]

Nobody makes a 3-bands audio spectrum analyser IC so it must be made with opamps, resistors and capacitors. The middle frequencies must use a fairly wideband bandpass filter with 2nd-order slopes and the lows can use a lowpass second-order Butterworth filter and the highs can use a highpass second-order Butterworth filter.
One RC lowpass filter has a gradual slope of attenuation to higher frequencies. Two RC lowpass filters in series affect each other and produce a drooping slope that begins attenuation very slowly. A Butterworth second-order filter uses an opamp to boost the response at the cutoff frequency so that its response is flat to the cutoff frequency then it attenuates higher frequencies quickly and twice as much as a single RC. A Butterworth second-order highpass filter is the same except it attenuates lower frequencies.

I used my Sound Level Indicator circuit to display the VU of the music in the video "LM3915 IC VU Meter Tower" that you posted and its peak detector activates much faster than the one in the video.
For its peak detector I used a fairly fast opamp driving an emitter-follower transistor instead of a diode and the transistor charges the 330nF storage capacitor quickly in about 36us. The circuit in the video charges its storage capacitor fairly slowly, maybe it is an "average detector" instead of a peak detector.

 

[mjkelly93]

Guru do you have a video of your project? Id love to see it in action.

 

[audioguru]

Sorry, no video. My LEDs light very quickly and their fall time depends on the value of the storage capacitor.
Your video had the LEDs blinking to the basic beat but my LEDs brightly showed each very fast pulse of the triplets. "Boom, boom, boom, triplet. Boom, boom boom, triplet."

 

[ClydeCrashKop]

mjkelly93 , Did you finish this project?

How did it turn out?