circuit to listen to microphone signal

Discussion in 'General Electronics Chat' started by craftindo, Jan 25, 2015.

  1. craftindo

    Thread Starter New Member

    Jan 25, 2015
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    hi anyone,
    I am a newbie in electronics.
    I have several questions:

    1. i bought this microphone circuit from ebay. And, how can i listen to the voice / sound?
    http://www.ebay.com/itm/New-Electro...crophone-Mic-Module-for-Arduino-/200964723455

    2. I use MC34072, and try several circuits: differential amplifier, and non-inverting amplifier, with several different gains, with and without capacitor in input & output, i also try LM 386, but i can't hear any sound. However, if i blow hard to the microphone, i can then hear the sound but not sentences / voice, why?

    3. does it matter which op-amp i use?
    4. does it have to go through pre-amp followed by amp?
    5. is that ok, if i feed that microphone signal directly into amplifier circuit as sold in ebay?
    http://www.ebay.com/itm/291337551133
    6. does it make a difference of the amplifier circuit based on electret microphone or condensor microphone?
     
  2. ronv

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    Nov 12, 2008
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  3. craftindo

    Thread Starter New Member

    Jan 25, 2015
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    Ronv,
    Thanks for the advice. That's what i am looking for actually.

    But, what I bought before is just a pure microphone with resistor & capacitor. So, that's why I have to solve my own amplifier in order to listen to the sound from an headphone.
    I am also interested to design my own amplifier / pre-amp for the headphone if you have any advice. (what's wrong with my circuit? why i can't make it work with my own pre-amp circuit)

    thanks
     
  4. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    It looks like it is wired up as a sound sensor rather than a microphone to actually understand anything. It is intended to be connected to an Arduino or Lego brick and will send a high output when sound is sensed.
     
  5. craftindo

    Thread Starter New Member

    Jan 25, 2015
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    Gopher,
    I understand that. But, i add a (non inverting) amplifier after the microphone signal output. I should be able to hear sound with a headphone right?
    isnt 20x gain is sufficient to hear sound on a headphone?

    or it needs to be much higher?
     
  6. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Not necessarily. If the output is connected to a sample-and-hold circuit to keep the output 'high' until the noise stops. In that case, the signal is filtered and is only outputting the peak value of the sound into the microphone as, essentially, a DC voltage. So, when you amplify a 1.3 volt flat-line DC signal, you just get a higher flat line DC voltage. Likely equal to your supply voltage (20x input voltage).
     
  7. craftindo

    Thread Starter New Member

    Jan 25, 2015
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    In this case, i actually dont' use any ADC yet (I don't connect it to arduino or any ADC).
    mic kit --> capacitor (104) --> amplifier / pre amp LM 386 or MC34072 ---> capacitor (104) ---> headphone.

    But, i can't hear anything yet. Yes, i check with the scope there is a DC bias voltage about 3VDC ( i don't know from where) but i have used the capacitor. It helps reduce the DC bias voltage but only a little.
    I am not sure perhaps i need to use a larger capacitor so that the DC voltage drops to 0VDC to make the headphone working.
     
  8. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    No, you are not understanding. This microphone and THE CHIPS ATTACHED TO IT are set up in such a way that the ONLY OUTPUT IS DC.

    I don't care if you have an arduino or not, this board will only put out DC! It will put out a DC signal that is an average of the DC volume for the past 1/10 second or so. It will SLOWLY adjust the DC signal over time. Way slower than any audible frequencies. You will not hear anything even if your amplifier had 1 million x gain.
     
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  9. craftindo

    Thread Starter New Member

    Jan 25, 2015
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    hi Gopher,
    Can you explain to me a little bit more? You're talking about item 1 that i bought on ebay right? It contains microphone, resistor and capacitor.
    Is it due to the microphone type or the schematic?

    if it is due to the schematic, and if I take out that microphone and use it as a standard microphone , can it produce any sound? (any suggestion :)about biasing microphone circuit?)
    if it is due to the microphone type, can you refer me to a standard microphone?

    thanks a lot

    (i think your answer gives me a light at the end of a tunnel) :)
     
  10. GopherT

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    Nov 23, 2012
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    Ok, it looked at the picture this time instead of the description. We had the Sound Sensor module - I assumed this was the same. Can you check the back of the module, is there any chip or transistor on the back?
     
  11. ronv

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    Maybe it is a microphone. Do you have a schematic of it?
    Anyway if it is here is a preamp. You will still need something like the 386 to hear it.
     
  12. craftindo

    Thread Starter New Member

    Jan 25, 2015
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    hi Gopher,
    Nothing other than those 3 components.
    Any other idea?
     
  13. craftindo

    Thread Starter New Member

    Jan 25, 2015
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    hi Ronv,
    I just got a microphone and will impelemt your non-inverting amp.
    However, i really have difficulties in getting the right capacitor value such as those in your schematic.
    I will use any capacitor that i have and try to use the value as close as possible.
    Do you think it will have huge impact on why i don't get the sound?
    Will inform you after i build the circuit.
     
  14. MrChips

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    Oct 2, 2009
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    Try it and discover.
     
  15. craftindo

    Thread Starter New Member

    Jan 25, 2015
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    Btw Ronv,
    Are you saying this pre amp can't produce an audible sound? Therefore, i will need lm 386 in order to be able to hear the sound?
    isn't preamp enought to produce audible sound on a headphone?

    thanks
     
  16. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    You MUST use a capacitor on the output 300 uF or more. Connect One leg to op amp output the other end to the tip of your headphone jack. A 600 ohm resistor in series will also help limit current and prevent the 081 op amp from going into current limiting protection mode.

    You must also use a cap on the input. Between mike and resistor that connects to the inverting input (inverting amplifier design).

    Also, connect your headphones as follows. You have the tip of headphone connected to the capacitor, you can connect the middle ring on the headphone to ground. Don't connect anything to the ring closest to the headphone's cable.

    Once you plug it in, it will take a few seconds to charge up the output capacitor depending how big the cap is.

    Also, make sure the non-inverting (+) input is biased at 50% of supply voltage with two equal resistors when you use an inverting amp design.

    Good luck.
     
  17. ronv

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    You will probably be able to hear it. Add a big capacitor (100 ufd. or so) from the output in series with your ear phone.
     
  18. craftindo

    Thread Starter New Member

    Jan 25, 2015
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    thanks for the advices, i will give it a try and let you guys know.
     
  19. craftindo

    Thread Starter New Member

    Jan 25, 2015
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    hi guys,
    Finally, i can hear the sound although it is not that loud and clear as i want to.
    The reason is that (this is my own analysis, please correct me if i am wrong).
    I didn't use C2 as shown in "eamp.png". Therefore, the half DC voltage to bias the microphone gets into its amplification which saturates the opamp.
    That's why i couldn't hear anything.

    I guess C2 functions as a DC block so that the DC voltage doesn't get amplified and only the AC, which is the voice from the microphone, gets amplified.
    So, what is the function of C6? (i didn't use c6 and i still can hear my own sound)?

    And, if i want to use differntial amplifier (which i guess will be able to reduce the noise level) where should i put the DC capacitor? All differntial amplifier circuit shown in examples doesnt show it for audio application?

    thanks
     
  20. #12

    Expert

    Nov 30, 2010
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    C6 sets a high frequency limit on the gain of the op-amp. Some op-amp circuits will oscillate at a frequency so high you can't hear it without this capacitor. You find out when you see the smoke.
     
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