noise detector

Thread Starter

fafty

Joined Jan 26, 2012
7
i am trying to build a circuit that will have a different voltage output depending on how loud i speak in to the electret mic, ive been trying different circuits but none work, please helpp!!
 

crutschow

Joined Mar 14, 2008
23,500
So what have you tried?

All you need is an amplifier for the mic with sufficient gain to give the AC voltage you want and a diode to rectify the AC voltage to give a DC voltage level. For best linearity you could use an op amp connected as an precision rectifier.
 

holnis

Joined Nov 25, 2011
49
You may use a condenser microphone to pick up sounds from the environment. This is a powered microphone, which makes it more sensitive than ordinary microphones.

Then the microphone will transform the sound waves into an electronic signal that is fed to the op amp (i.e 741) .

The op amp in this circuit will be configured as a single-supply inverting amplifier. Then you can adjust the resistance of the reaction R to maximize the sensitivity of your circuit.

then use a capacitor to block the DC component of the signals, so that only the AC component carrying the sound information reaches the output of a transistor.
 

Audioguru

Joined Dec 20, 2007
11,251
You may use a condenser microphone to pick up sounds from the environment. This is a powered microphone, which makes it more sensitive than ordinary microphones.
No.
An electret nicrophone is an inexpensive condenser mic with the high voltage built into its electret material. It has a built-in Jfet as an impedance converter and needs a few volts at 0.5mA to power it. Its sensitivity is the same as an old condenser microphone.

Then the microphone will transform the sound waves into an electronic signal that is fed to the op amp (i.e 741).
A lousy old 741 opamp is 44 years old. It is designed for a 30V supply (some do not work if the supply is less than 10V), it is too noisy (hiss) to be a mic preamp and its poor slew rate eliminates half the frequencies we can hear.

The op amp in this circuit will be configured as a single-supply inverting amplifier.
No.
The opamp should be a non-inverting amplifier that has an input impedance high enough (about 50k ohms) so it doesn't load down the mic.
 

Thread Starter

fafty

Joined Jan 26, 2012
7
thanks guy, i made the circuit and used two BC337 to amplify it and den i put it into an arduino to make a VU meter, it works fine but my teacher told me to put a small signal diode between the output of my amplifier and the input of arduino :/ this reduced my gain, why is the diode needed?
 

Thread Starter

fafty

Joined Jan 26, 2012
7
cool, also my gain from the amplifier circuit is around a 1000 but wen i put the diode in the gain drops to around 12. why is there such a big drop, ino the diode take around 0.7V but my Vout from the amplifier is 1.8V... why such a big drop in the gain?
 

Audioguru

Joined Dec 20, 2007
11,251
Since you did not attach your schematic then we don't know what your circuit is doing.
Maybe your diode is shorting the output of the amplifier to ground instead of rectifying the signal.
 
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