Amplifier audio signal detecting LED

Thread Starter

alan1975

Joined Jan 1, 2012
42
Hello,

Some time ago i build simple small (<3W) amplifier based on TDA7056A.
I use this for speaker test purpose.

Now i would like to enhance it's capabilities with 2 led detectors.

I'm looking for something what will be connected in series with input and will show me "on / off" is mp3 player is connected and sending signal.
Not need any blinking ect, just information "is something comming in wire".

Same thing with output, led what will show me am i connected correctly to speaker, or wires are in the air connected to nothing.
If wires are not connected to anything, led should stay dark, but when i connect them to speaker and something will be player it should light.

Just to get me idea "its connected succesfully".


Do You have any idea ?

I DO search forum and find some examples, but they are complicated, involved many parts, cutting some frequencies. In my opinion there are to complicated to do the job what i need.


If anyone came up with something.
Please share.
 

nomurphy

Joined Aug 8, 2005
567
If you use a dual comparator, you can easily make two audio detectors. You can run this from between +5V and +12V -- You will need to size R1 based on the supply voltage to set a divider value (+VREF) that works for you (say 0.5V). Also, choose R5 based on supply +V voltage for about 10mA.

When audio input APEAK (-) is greater than the +VREF voltage at (+), then the ouput will go low and the LED will light.
 

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Thread Starter

alan1975

Joined Jan 1, 2012
42
Hello,

Thank You for reply.
It's looks quite decent.

Tomorrow i will give it a try on breadboard and share result.

Regards
 

Thread Starter

alan1975

Joined Jan 1, 2012
42
Hello,
I'm after first test.

I build circuit above, using BA10393 comparator.
I don't have diode BAT54, so i skipped them ^^.

Without it still working quite well.
I do a test using my mp3 player, and discman.



What about speaker output of TDA7056A.
I tried connect set up above, but without any success.
Led is bright, even if i don't play anything.

I don't have oscilloscope to see what's going inside that output...
 

nomurphy

Joined Aug 8, 2005
567
D1 is necessary to rectify the audio input, use a 1n4001 or 1n914 or 1n4148 or something that you do have. I specified a Schottky to minimize the voltage drop. But for whichever diode you use, you may need to adjust the reference voltage (you could put in a pot in place of one of the reference voltage divider resistors). You may need to adjust the reference for a speaker output with a larger signal level.

D2 would remove any negative audio excursion and protect the input to the single-ended comparator instead of D1, but D2 doesn't have to be there.
 
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