Amplifier audio signal detecting LED

Discussion in 'General Electronics Chat' started by alan1975, May 4, 2012.

  1. alan1975

    Thread Starter Member

    Jan 1, 2012
    42
    0
    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.
     
  2. nomurphy

    AAC Fanatic!

    Aug 8, 2005
    567
    12
    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.
     
    Last edited: May 4, 2012
  3. alan1975

    Thread Starter Member

    Jan 1, 2012
    42
    0
    Hello,

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

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

    Regards
     
  4. alan1975

    Thread Starter Member

    Jan 1, 2012
    42
    0
    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...
     
  5. nomurphy

    AAC Fanatic!

    Aug 8, 2005
    567
    12
    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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