Go Down

### Topic: Building an Audio Analyzer with Matrices and Mega2560 / Uno and FFT and Op amps (Read 5754 times)previous topic - next topic

#### Aaron_dyer

Does anyone have any good code or schematic using LM386 / LM358 op amps to interface the Arduino Uno or Mega2560 and then to display a nice output on a matrix or matrices for an audio analyzer...I know FFT will need to be calculated....

#### Magician

FYI: LM386 isn't an op amp.
Here is a project build with NE5532, UNO and 74HC595+ULN2008:
http://coolarduino.wordpress.com/2012/06/21/tears-of-rainbow/
http://coolarduino.blogspot.ca

#### dhenry

Quote
LM386 isn't an op amp.

It depends on your definition of opamp. LM386 certainly has the same building blocks as an opamp (linn 3-stage topology) and can be used as one.

#### Aaron_dyer

My bad, a low power audio amp......still has an inverting and non inverting input....just doesn't run off of - V like a 741 does.......same thing if you ask me.....

#### Magician

There is  a definition from wiki:
Quote
An operational amplifier (op-amp) is a DC-coupled high-gain electronic voltage amplifier with a differential input and, usually, a single-ended output.[1]

http://en.wikipedia.org/wiki/Operational_amplifier
Having gain 200 LM386 can't be called op-amp, most regular BJT has more gain.
There is obvious similarity between them, but following this logic we should see no difference between a tiger and a cat, both have a lot in common, four legs, tail etc.
http://coolarduino.blogspot.ca

#### dhenry

Quote
Having gain 200 LM386 can't be called op-amp

google "open loop gain" vs. "closed loop gain".

Also, pick your favorite opamp and I can tell you that its (open loop) gain can be less than 1x. Are you surprised?

#### Magician

Quote
Are you surprised?
Not at all, show me LM386 with open loop configuration.
http://coolarduino.blogspot.ca

#### dhenry

Quote
Not at all,

Does that mean your favorite opamp isn't an opamp by your own definition?

Quote
show me LM386 with open loop configuration.

Not possible.

#### Magician

Quote
Not possible.
If there is no LM386 with open loop configuration, than you shouldn't bring this argument (open/ close loop ) in discussion. It's not related. I don't know what is the definition for infinity:
Quote
An ideal op-amp is usually considered to have the following properties, and they are considered to hold for all input voltages:
Infinite open-loop gain (when doing theoretical analysis, a limit may be taken as open loop gain AOL goes to infinity).
IMHO, infinity is starting from 10^5.
http://coolarduino.blogspot.ca

#### dhenry

Quote
If there is no LM386 with open loop configuration, than you shouldn't bring this argument (open/ close loop ) in discussion. It's not related.

It was to show you that the 200x gain for lm386 is closed loop gain. Comparing that to an opamp in open loop, or a transistor in open loop, makes no sense.

A 800x (hFE) transistor can have a (closed loop) gain < 1x, for example.

apples vs. oranges.

#### Magician

Quote
It was to show you that the 200x gain for lm386 is closed loop gain.
Again, not related. We don't care why it's only 200, if it made and sealed, and there is no way to unrolled it back. What is "operational" means, that you can design a feedback (negative/positive) in a variety ways,  to create any math "operation" - differential, integral or proportional.  The higher gain, the easier it could be done. Device with low gain is not "operational".  Just amplifier.
http://coolarduino.blogspot.ca

#### dhenry

Quote
What is "operational" means, that you can design a feedback (negative/positive) in a variety ways,  to create any math "operation" - differential, integral or proportional.

That definition is valid as long as you get other people to accept it.

Quote
The higher gain, the easier it could be done.

google "open loop gain" and "closed loop gain".

Quote
Device with low gain is not "operational".  Just amplifier.

Every opamp has gain < 1.0x, and by your definition, they shouldn't be called opamp.

Take some good EE101 will help.

#### Magician

Quote
Every opamp has gain < 1.0x
Which one?
Part number, plz, data sheet and reference link. Have you read a wiki?
Quote
Take some good EE101 will help.
I'm an Electronics Engineer. You?
http://coolarduino.blogspot.ca

#### dhenry

Quote
Which one?

Any opamp.

Name your favorite opamp and I will show you how to get it to <1x (open or closed loop) gain.

As an "electronics engineer", you should have known something that basic.

#### Magician

Quote
Name your favorite opamp and I will show you how to get it to <1x (open or closed loop) gain.
I know how to get a gain lower, using negative feedback. Besides, why would I need an amplifier <1x? I wish you show me how you can design two basic blocks :
log amplifier
http://en.wikipedia.org/wiki/Log_amplifier
or any useful filter
http://en.wikipedia.org/wiki/Active_filter
with LM386?

http://coolarduino.blogspot.ca

Go Up

Please enter a valid email to subscribe