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I have an arduino schematic from here

http://www.arduino-hacks.com/arduino-vu-meter-lm386electret-microphone-condenser/

I have a problem, the output of the circuit (the pin which is going to connect to the analog pin of the Arduino), from what I have measured has 4.5 V (I think it is a bit high). If I print on the serial it gives me something like 827, 826. However when I clap my hands near the microphone or put music on, the data that I get doesn't change a lot (like 1 -2 units). Should I worry about the schematic or about my microphone?

EDIT: After I rebuilt the circuit and when playing a song at a medium volume, I get values like this: 419-670. I think it is working, though I would like more opinions about these values (the output voltage is now around 3.20 V).

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  • Have you tweaked the potentiometer?
    – Gerben
    Sep 6, 2015 at 13:14
  • yes I have tweaked the potentiometer.Now after I rebuilt the circuit(correctly hopefully) it shows an output of aprox .3 20 V and the values I get on the Serial monitor varies like this (when playing a song on a medium volume): 419 -656 .I think I got it working though I would like more opinions regarding these values.Thank you for your reply I will edit the post.
    – Diana Lc
    Sep 6, 2015 at 13:18

1 Answer 1

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The schematic seems to have both inputs of the opamp at 0V (the one connected to the microphone would actually swing a small amount ±). The opamp also seems to be running open loop, with no feedback and would have a very high gain.

This is poor circuit design, ideally the inputs should be biassed at Vcc/2. At best the output would be severely distorted.

I suggest you search for a more suitable circuit.

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    Actually, the LM386 is an audio amplifier, not an op-amp. It doesn't behave the same way. It is perfectly valid to wire it as shown in the link above - indeed, that is pretty much identical to some of the example circuits in the datasheet from TI. With minimum parts like that you get a gain of 20.
    – Majenko
    Sep 6, 2015 at 20:15
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    What I would be more concerned about is the lack of any current limiting resistors on the LEDs... Those poor IO pins...
    – Majenko
    Sep 6, 2015 at 20:16

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