Simple 1 LED audio display

Hello, I'm very glad to finally find a good forum about electronics!

I would like to build a simple circuit, that lets 2 LEDs flash when there is an audio signal comming from a source. I'm speaking about a stereo line signal here, so 2 channels and 1 LED per channel only (1 for left, 1 for right). The LEDs should then flash after the audio signal reaches a certain amplitude and this point should be adjustable with a potentiometer.

So very simple actually. I was thinking about realising this with an opamp comparator circuit first, but maybe even a transistor is enough to do this proper!? As I'm not an engineer, I would like to hear some opinions, hints here, from people with more experience than me.

Here's some more info about the situation,
the circuit should meet the following criteria:

- whole thing is 6V Battery powered
- circuit should not draw much current
- the audio signal should not be influenced by the circuit (disturbances etc.)
- circuit should be as simple and small as possible (i'm going to implement this into a very small device)

That's probably it. I'm looking forward to some feedback, thanks in advance.

Audio is AC. A comparator senses DC. You need to rectify and smooth the resulting DC from the signal to feed a comparator.

Maybe it's not necessary to use an opamp.
To keep it simple, I made a small schematics with a transistor.
Wouldn't that work?

OK, too simple maybe.
I just recognized that there of course should be something between the potentiometer and the line out, so that there is no influence on the audio.

Use a coupling electrolytic capacitor between speaker out and the pot. (100 to 220µF) should do.

Boncuk

P.S. If you are anglo saxon you'd better not use "Hanswurst" for your login name. A "Hanswurst" is called a "full idiot" in English.

hanswurst said:

Maybe it's not necessary to use an opamp.
To keep it simple, I made a small schematics with a transistor.
Wouldn't that work?

Click to expand...

Your POT is backwards. How much audio level are we talking here? Speaker level, line level, etc? What is the minimum level you need to trigger the LED? The Max?

kchriste said:

Your POT is backwards. How much audio level are we talking here? Speaker level, line level, etc? What is the minimum level you need to trigger the LED? The Max?

Click to expand...

Thanks. No speakers, the signal is line level. It should be triggered around 1V.

If you reverse the POT as I stated, then your circuit will flash the LED on voice/music peaks. It will load the audio circuit slightly and could introduce distortion due to non-symmetrical loading. What is the ultimate goal of this project?

Yes I got that, the potentiometer is connected the wrong way sorry.
So how can I prevent that the circuit loads the audio?

I actually already mentioned everything in my first post.
The aim of this project is that the LED lights up synchron with the music.
So the music will influence the LED, but the circuit should have no influence at all to the music.

Use another transistor in-between as a buffer.