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I need to amplify an electret microphone for use with an Arduino Uno. I have a few capacitors and resistors and several transistors one of which is an N-channel. Any ideas? Can you please also provide me with a scheme?

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I don't understand. We cannot use resistors, capacitors, other transistors, or ICs? –  Telaclavo Apr 25 '12 at 15:16
    
We also have resistors 10 kiloOhms and 220 Ohms –  Itay Grudev Apr 25 '12 at 15:18
    
The Arduino Uno isn't a PIC! Question cannot be answered and should be closed. –  Leon Heller Apr 25 '12 at 15:18
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@LeonHeller: it seems that more and more people think PIC is another word for microcontroller. "The PIC is an Atmel AVR." –  Federico Russo Apr 25 '12 at 15:21
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This is most easily done with a opamp. It's not too hard to do it with a few transistors either, but some other components like a few resistors and capacitors will be needed either way. Restricting the problem to what you happen to have on hand is silly because it's easy to get these other parts. –  Olin Lathrop Apr 25 '12 at 15:21
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1 Answer

up vote 1 down vote accepted

Ok this will be quick and hopefully painless.

microphone amplifier

I am not well versed in the microphones themselves, sometimes they are biased sometimes they are not.

So the way this is designed:

Remove DC bias from microphone output

Bias the transistor so that it can maximize the usable range

(For simplicity make R1= R2 10k resistors or less should do it)

Rg (plus the beta of the amplifier) control the gain of the circuit. The higher Rg the higher the gain. HOWEVER, the larger Rg gets the more power it dissipates. this is for low current systems.

the transistor is an NPN (always open, apply voltage to close)

This is also an INVERTING amplifier. For audio applications you will not hear the difference; however, if you use it for anything else it applies a negative gain.

(Vout= -Gain*vin)

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That transistor looks like an IGBT... –  stevenvh Apr 27 '12 at 6:13
    
you can use almost any transistor, but if you want the signal to remain linear with minimal harmonic distortion, i advise using an npn. –  CyberMen Apr 27 '12 at 12:52
    
Yes, I already guessed it's supposed to be an NPN. You definitely don't want an IGBT for this! :-) –  stevenvh Apr 27 '12 at 12:54
    
also i wrote above it was an NPN >_<; –  CyberMen Apr 27 '12 at 12:55
    
No problem, I only meant to say that the symbol you drew looks like having an insulated gate. –  stevenvh Apr 27 '12 at 12:58
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