# VU meter

H

#### [email protected]

Jan 1, 1970
0
I have found an audio level meter in this website as follows

http://www.4qdtec.com/avu.html

I need some help to understand. What does it mean 5 stage
feedback circuit. What are the A and B markings on the
diagram, is this some kind of switch?

Any ideas?

E

#### Eeyore

Jan 1, 1970
0
I have found an audio level meter in this website as follows

http://www.4qdtec.com/avu.html

I need some help to understand. What does it mean 5 stage
feedback circuit. What are the A and B markings on the
diagram, is this some kind of switch?

Can I suggest that if you want to do something like that there are much much
better and easier ways to do it ?

Graham

B

#### BobG

Jan 1, 1970
0
The text explains it... its a log amp... piecewise linear approx of
log... dBs are 20*log(vout/vin). Use a $1 tiny avr E #### Eeyore Jan 1, 1970 0 BobG said: The text explains it... its a log amp... piecewise linear approx of log... dBs are 20*log(vout/vin). Use a$1 tiny avr

When that method originated there were no AVRs of course.

Graham

L

#### Lord Garth

Jan 1, 1970
0
I have found an audio level meter in this website as follows

http://www.4qdtec.com/avu.html

I need some help to understand. What does it mean 5 stage
feedback circuit. What are the A and B markings on the
diagram, is this some kind of switch?

Points A & B connect to points A & B in the LED chain.

H

#### [email protected]

Jan 1, 1970
0
Points A & B connect to points A & B in the LED chain.

Is it switch though? what is so special about the 6th and 7th leds,
if it is a switch, is A always one led under B or can they move up and
down independently? Where are the five stages? we have 10 leds so
does this mean every stage has two leds.

P

#### Phil Allison

Jan 1, 1970
0
Is it switch though? what is so special about the 6th and 7th leds,
if it is a switch, is A always one led under B or can they move up and
down independently? Where are the five stages? we have 10 leds so
does this mean every stage has two leds.

** You are utterly clueless about circuit analysis.

Build the damn thing and maybe you will SEE how it works.

Somehow, I doubt even seeing it will make you one bit wiser.

........ Phil

A

#### Anthony Fremont

Jan 1, 1970
0
Phil said:
** You are utterly clueless about circuit analysis.

You're in SEB Phil, please try to be nice.
Build the damn thing and maybe you will SEE how it works.

Somehow, I doubt even seeing it will make you one bit wiser.

Is that your professional analysis of the circuit?

W

#### Wim Lewis

Jan 1, 1970
0
I have found an audio level meter in this website as follows

http://www.4qdtec.com/avu.html

I need some help to understand. What does it mean 5 stage
feedback circuit. What are the A and B markings on the
diagram, is this some kind of switch?

No, the A and B are just indications that the arrows marked A and B
should be connected to the points A and B on the right --- this makes
the schematic diagram a little less cluttered.

As for the "5-stage feedback": I think BobG has the right interpretation.
A VU meter is supposed to have a logarithmic response, but all the
amplifiers in this circuit have constant gain (linear response).
As the diodes in the diode string light up, they switch some extra
resistors into the third opamp's input, which changes the circuit's
overall gain, and presumably this ends up approximating a logarithmic
response. I don't see why it's described as "5-stage" though. It
looks like it only has 3 or 4 different gain settings.

These days, you can buy VU-meter chips with a logarithmic amplifier and
a bunch of diode drivers. Or you can do it in firmware in a cheap
microcontroller.

C

#### circuithelp

Jan 1, 1970
0
When that method originated there were no AVRs of course.

Graham

I am not consered with the logaritmic scale. I wanted to ask about
the leds and th driver transistors, how this works, and if A and B
signal switch, as otherwise, I see no reason why someone would
start using A B C etc to denote nets.

Ok, hope that's clear
Thanks

M

#### Michael Black

Jan 1, 1970
0
circuithelp" ([email protected]) said:
I am not consered with the logaritmic scale. I wanted to ask about
the leds and th driver transistors, how this works, and if A and B
signal switch, as otherwise, I see no reason why someone would
start using A B C etc to denote nets.
Believe me, it's far better to do that than have traces going from
one side of the schematic to the other merely to connect those
points (as opposed to a line that is being used throughout the circuit,
such as the power supply line). You either have to have those long
connections riding over all kinds of things, or have them go far out
of the way just to keep it clear of the rest of the schematic.

It's really clear, once you know this is happening (and I admit that
in this case, it wasn't so clear because of the way the schematic
wsa drawn). The way I saw it when I was a kid was to have a triangle
on it's side (so the point faces left or right) and then the other point
has a similar triangle pointing towards the first one. It was then pretty
obvious that they were two points to connect together, because they
were special symbols for the purpose.

You can even do it so there is one source, and multiple "receivers",
which can be useful for showing where the power supply line goes, again
so you don't have long traces all over the schematic. In essence, that's
just a variant on the ground symbol. You know those all connect together.

The thing about schematics is that they should be drawn so you can
easily interpret them by looking. THis is not the same thing as circuit
layout. If you drew them the way you'd wire a circuit, it would usually
be a real mess to follow, yet the schematic properly drawn spreads
the circuit out so two points that might on a circuit board be next
to each other are at opposite ends of the schematic.

MIchael

E

#### Eeyore

Jan 1, 1970
0
Anthony said:
You're in SEB Phil, please try to be nice.

Is that your professional analysis of the circuit?

Graham

C

#### circuithelp

Jan 1, 1970
0

Graham

All BEWARE

Phil Allison and Eeyore are well known intelectual property
theives actively targetting this newsgroup.

The way they operate is this:

first they would give you some sort of irrelevant answer
and say that you should do it their way (but not
revealing their way)

The next step they will start becoming dismissive of you
and try to lead you to believe that you are an idiot and
that they are the oracle of knowledge

After that, they will slide into insults and mud throwing

D

#### Don Bowey

Jan 1, 1970
0
All BEWARE

Phil Allison and Eeyore are well known intelectual property
theives actively targetting this newsgroup.

The way they operate is this:

first they would give you some sort of irrelevant answer
and say that you should do it their way (but not
revealing their way)

The next step they will start becoming dismissive of you
and try to lead you to believe that you are an idiot and
that they are the oracle of knowledge

After that, they will slide into insults and mud throwing

Just what the board needs........ Another idiot troll.

J

#### [email protected]

Jan 1, 1970
0
All BEWARE

Phil Allison and Eeyore are well known intelectual property
theives actively targetting this newsgroup.

The way they operate is this:

first they would give you some sort of irrelevant answer
and say that you should do it their way (but not
revealing their way)

The next step they will start becoming dismissive of you
and try to lead you to believe that you are an idiot and
that they are the oracle of knowledge

After that, they will slide into insults and mud throwing- Hide quoted text -

- Show quoted text -

When they do slip up and post something with apparent technical
content, they are often wrong, thereby displaying their profound
ignorance.

D

#### Don Bowey

Jan 1, 1970
0
When they do slip up and post something with apparent technical
content, they are often wrong, thereby displaying their profound
ignorance.

It is more likely that the basic/beginner poster does not understand the
answers they are given, and will not ask for clarification. I noted several
recent posters who received valid replies, but became belligerent over them.

L

#### Lord Garth

Jan 1, 1970
0
Is it switch though? what is so special about the 6th and 7th leds,
if it is a switch, is A always one led under B or can they move up and
down independently? Where are the five stages? we have 10 leds so
does this mean every stage has two leds.

I don't think you can trust the descriptive text. He begins with the
statement that the audio amp runs on 0v-18v power rails but the
schematic clearly shows +18v and -18v from the amp.

You should probably look for a better circuit such as one based
on this chip: http://www.national.com/pf/LM/LM3914.html

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