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Author Topic: VU Leds on speakers, no arduino involved?  (Read 464 times)
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Hi everyone,

I am trying to figure out how to connect VU meter leds on speakers to give visibility to the audio signal that they will play.

This is as part of an installation and, because of its location and design, it could be a little complicated. The set up is out side, so everything needs to be waterproof, while the amps (that will power all the speakers) will be in another place covered.. so there will be long wires going all the way to the speakers, and I would like to avoid adding other cables running from the amp to the speakers, so I was hoping to use just the power running on the speakers cable. We found this kits: http://store.qkits.com/moreinfo.cfm/FA102, but they are pretty expensive and would be good to find something in europe..

Any solutions or ideas would be much appreciated! Thanks a lot..
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You could use a LM3914 or even better a LM3915. Do a google search and you will get a lot of examples how to use it.



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Hi Erni, thanks a lot for your reply! the LM3915 IC looks really good but I am not sure it's what I really need. I did a quick search but it looks like it requires external power... at least 3volts (that is not so bad cause i could use a battery pack). I really want to understand how that kit (http://store.qkits.com/moreinfo.cfm/FK102) can work just by using the power running on speaker cable..

Any clues?
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can work just by using the power running on speaker cable
Wow what a piece of crap is that!
It will distort the signal like mad, it will only work on systems that produce 9V for full power and it is linear indication where as the ear responds to the log of the intensity, so it won't look very good.

It works simply by having the LEDs in series and feeding the audio in to each node through a resistor. Therefore with a 2V peak input only the first LED will light. With 4V there is enough voltage for the bottom two to light and so on.
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I am not really worried about the signal quality. as I will have more then 30 speakers it is not needed to be precise, it's not an audiophile application if you know what I mean.
I also found another one here: http://www.quasarelectronics.com/velleman/k4307-audio-power-meter-kit.htm but it's really expensive. I was wondering if anyone would have made something similar himself?

Thanks

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it's not an audiophile application if you know what I mean.
Yes I know what you mean and I am by no means a fan of audiophiles. However an audiophile would consider an LM3915 a poor circuit which is a million time better that what you are looking at.

There is nothing very clever about that latest circuit, The main difference is that it uses transistors to turn on the LEDs and so you can bias more of them for any given input voltage range.
The circuit is very similar to the bottom half of this circuit:-
http://www.circuit-projects.com/audio/audio-volume-unit-meter.html
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There is a schematic on the bottom of this page for the one that needs no external power.

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as I will have more then 30 speakers it is not needed to be precise, it's not an audiophile application if you know what I mean.
That's probably a "constant voltage" (typically 70.7V) system, with transformers on each speaker to determine their power setting.  You'll probably need to put the LED meter on the speaker-side of the transfomer.
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The branches past the 1st LED have zener diodes to prevent those leds from lighting until the signal voltage threshold is met. Is this a must DIY? There are loads of 70V line meters on the market. Power calculation does not require a power meter as the voice coil transformer taps are marked in RMS power @ the specified load impedance with the line at a nominal 70.7VRms.
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