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I'm using this preamp circuit for my electret microphone and then feeding the output to A0 analog pin of an arduino uno board. For some reason my serial monitor in the arduino ide shows the output at a constant 130 no matter how much sound I make in front of the microphone.

enter image description here preamp circuit^

enter image description here serial monitor^

This is the circuit I'm implementing. https://www.instructables.com/How-to-Deal-with-Noisy-Neighbors/ my connections for the pre-amp part:- orange wire for output, connected to A0 pin of arduino uno. brown wire is the ground pin from uno, red wire is 5v pin from uno. electret mic green wire is +ve, white wire is -ve. Thing is, I've implemented the same pre-amp circuit as the dude above, but for some reason the sound doesn't get picked up. My preamp ckt below. enter image description here

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  • \$\begingroup\$ It's impossible to see if the bias resistor is connected or not and it's impossible to tell if you have not inadvertently connected the microphone up with the wrong polarity. \$\endgroup\$ – Andy aka Nov 17 '20 at 12:35
  • \$\begingroup\$ by biasing resistors you mean r1, r2, r3? The mic (+)red is green wire and (-)black is white wire. \$\endgroup\$ – Ayush Sinha Nov 17 '20 at 12:40
  • \$\begingroup\$ Also note that the output of the circuit is AC and will go negative which could damage the microcontroller's ADC. \$\endgroup\$ – Transistor Nov 17 '20 at 12:41
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    \$\begingroup\$ @AyushSinha that might be pure luck. Instructables.com isn't exactly known for being a source of high-quality circuit approaches. \$\endgroup\$ – Marcus Müller Nov 17 '20 at 12:45
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    \$\begingroup\$ i'll check and let you know. edit: that was the problem, My resistor had a slightly orangish color which I mistook for yellow. \$\endgroup\$ – Ayush Sinha Nov 17 '20 at 12:57
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Measure R2 to check that it is 100 kohm.

that was the problem, My resistor had a slightly orangish color which I mistook for yellow.

and from another comment...

Really thankful, Just wanna ask one more question. I know that it is common-emitter amplification model which has positive current and voltage gains. Question is, what does the mic output actually give to the arduino (the signal), is it voltage or current?

The voltage gain is negative because the circuit is inverting the AC input signal.

The amplifier amplifies voltage AND current but, what is given to the arduino, is a voltage signal mainly.

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  • \$\begingroup\$ Why is output voltage signal negative? \$\endgroup\$ – Ayush Sinha Nov 17 '20 at 13:51
  • \$\begingroup\$ I said the voltage gain is negative. When the input peak is positive the output is at its lowest level and, when the input peak is negative the output is most positive; it inverts the signal. \$\endgroup\$ – Andy aka Nov 17 '20 at 13:53

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