Author Topic: Audio LED VU meter  (Read 1307 times)

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Offline Sizigi

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Audio LED VU meter
« on: January 03, 2018, 10:55:13 am »
When I was a kid, I saw my friends dad open up his audio cabinet for the first time to put on a movie for us and there I saw a huge array of LEDs come to life as the 20th century fox tune blasted through the speakers, I was mesmerized as the bars danced in time to the audio. That was my first love of VU meters, and now that I'm 20years older and earning a bit more then a paperboy in the 90's. I to want to have my own multi channel UV meter display.

On aliexpress I found a "VU Meter Level Indicator Amplifier Board Dual Channel 32 LED MCU Adjustable Display Pattern LED"

https://www.aliexpress.com/item/VU-Meter-Level-Indicator-Amplifier-Board-Dual-Channel-32-LED-MCU-Adjustable-Display-Pattern-LED/32810039688.html?spm=2114.10010108.1000014.5.30ed99cdJyHugN&traffic_analysisId=recommend_3035_null_null_null&scm=1007.13338.80878.000000000000000&pvid=58acd4ca-23ca-437d-adb1-aa9d46953612&tpp=1


I'm wondering if anyone knows of a board or circuit that will take an audio feed from a stereo jack, and out put a feed suitable for one of these modules. It would need a tune-able upper and lower cut off threshold, so that one board and module can control one frequency band of of the audio spectrum. This way one module can be set for a certain band by playing a tone and tuning that board and my hope is that it can be scaled so you can have as many bands in the VU meter that you want 4,8,16,32 and my hope eventually, 64 band.
If it was something I could solder up on a thin strip of perf board, or maybe get a simple pcb made for it about the same width as the module that would be great I'd like to say clear of microprocessors and coding as I see it more as a plug in and tune module some thing that could be installed  in a euro rack synth or a 19" rack unit if you made a front panel for it I don't want it to control the volume or effect the audio it is only to display,

Ive made a rough block diagram of how i think it might work

if it was possible to have one board capable of doing all the bands with only changing the values of the trim pots that would be good. But as you probably can tell my actual circuit design and component selection knowledge is non existent but I'd like to think this idea could be made in to a "solder your own" style of kit for common folk and diy synth or just any one that wants a cool LED UV meter

Any help ,designs or guidance would be appreciated in the far brained plan

-Sizigi
 

Offline Audioguru

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Re: Audio LED VU meter
« Reply #1 on: January 03, 2018, 04:06:48 pm »
The Ali Chinese VU meter has no spec's. Its dB's per segment are unknown. Are the 8 highest LEDs all red?
It is unbelievable that its maximum input is 101W to 130W. Then with a normal much lower input level it won't show anything.

Why do you want to see the levels of many bands of frequencies? Many bands will show nothing most of the time. My VU meter has only one bar of LEDs that show the level of all frequencies and it has a microphone to show all sounds. Then my hearing tells me if the frequency of a sound is high pitched or is low pitched. You certainly do not need 64 bands, 7 bands of frequencies are plenty. Each frequency selecting circuit needs an opamp plus some resistors and capacitors.
 

Offline Sizigi

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Re: Audio LED VU meter
« Reply #2 on: January 04, 2018, 09:18:53 am »
yes there are 3 green bar LED blocks and one red one.
I'm not worried about having an accurate value for the DB in each band it is only meant as a rough visualization.

You were right the 101W input seamed off to me as well , I found another seller of the same and he states it operates between 7-12V and 20W per channel 
https://www.aliexpress.com/item/Singel-32-Level-indicator-VU-Meter-Stereo-Amplifiers-Board-Adjustable-light-Speed-Board-With-AGC-Mode/32813452531.html?spm=2114.10010108.1000014.23.8d534c34teKTV&traffic_analysisId=recommend_3035_null_null_null&scm=1007.13338.80878.000000000000000&pvid=2a4e9998-523e-4a9e-b519-eb6117c1abd5&tpp=1

As for why so many bands personally I just think it would be cool to have a large display of flashy lights
kinda like https://www.aliexpress.com/item/Full-color-music-spectrum-display-AGC-automatic-control-Any-combination-of-64-kinds-of-various-sizes/32274536861.html
The bands wouldn't have to be all different for each module, you could only have 32 bands but have 2 modules for each, that I think is the cool part of having them tune-able, and they whole concept scale-able for how ever many bands or modules you want to have.
I'd like it to run of a direct feed so you don't pick up any other sounds in the room

Is what I'm looking for basically an adjustable RCL band pass filter?
 

Offline DrGeoff

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Re: Audio LED VU meter
« Reply #3 on: January 04, 2018, 09:34:39 am »
Check out the data sheet for the LM3915/6 devices. That should give you a clue.
I think there is a basic spectrum analyser display in the NatSemi data sheet, which appears to be what you are after.

Was it really supposed to do that?
 

Offline Sizigi

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Re: Audio LED VU meter
« Reply #4 on: January 04, 2018, 10:37:56 am »
the modules I'm looking at already have a controller on the board for the LED's so I don't have to drive the LED's my self I just have to provide them an isolated audio signal
if I'm not mistaken I think I need a circuit that I can swap out a resistor and/or capacitor value to get the rough band,
then I can tune the upper and lower cutoff points with a variable resistor and/or capacitor to filter a specific frequency
and then control the amplification of that frequency to feed into the LED module which should only light up when that frequency plays in the audio.
 

Offline mikerj

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Re: Audio LED VU meter
« Reply #5 on: January 04, 2018, 12:53:03 pm »
Seems like you are simply trying to make a crude spectrum analyser with an LED display?  If so there are easier ways to do this than by building and tuning dozens of bandpass filters e.g. using a microcontroller to digitize the signal and perform an FFT.

There are dozens of projects like this on the web if you have a search, and there are several kits to build your own from China e.g. 11x12 LED, 32x32 LED.
 


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