Electret mic / Arduino configuration

Discussion in 'General Electronics Chat' started by frusciante89, Feb 18, 2013.

  1. frusciante89

    Thread Starter New Member

    Nov 13, 2012
    10
    0
    Hi everybody, I have a problem with an electret mic. I searched the forum but i wasn't able to find an answer. I'm pretty new in this field so I hope you can understand my low level... :)
    I am design a sound following robot, and I decided to use two electret mics. First problem is how to amplify the signal going to the Arduino. I saw several boards on sparkfun but I want to build my own. I tried to build this one:
    http://www.inexglobal.com/downloads/ZX-sound_e.pdf
    however, I had to make some modifications due to the available material I had in the lab:
    - I used a MC33078 op amp instead of the TLC272
    - I used a 10 ohm resistor instead of the 12 ohms (I had none)
    - I used only electrolytic caps


    This is the arduino code I'm using for the analog signal reading:

    /*
    AnalogReadSerial
    Reads an analog input on pin 0, prints the result to the serial monitor.
    Attach the center pin of a potentiometer to pin A0, and the outside pins to +5V and ground.

    This example code is in the public domain.
    */

    // the setup routine runs once when you press reset:
    void setup() {
    // initialize serial communication at 9600 bits per second:
    Serial.begin(9600);
    }

    // the loop routine runs over and over again forever:
    void loop() {
    // read the input on analog pin 0:
    int sensorValue = analogRead(A0);
    // print out the value you read:
    Serial.println(sensorValue);
    delay(200); // delay in between reads for stability
    }


    I tried the circuit and it's not working (gives a reading of 910 no matter how loud I speak into the mic), could it be because of the modifications I made?
    I have also a couple of more questions:
    what is the best way to process the signal coming from the two mics in order to tell the direction? should I use a volume based detection or a delay based detection?

    Thanks for your help,
    Andrea
     
  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Be aware that the comparator stage is mislabeled. Pin 5 of the TLC272 is the positive input and pin 6 is the negative input to the second stage which is being used as a comparator. A quick check of its datasheet will confirm my comment.

    hgmjr
     
  3. #12

    Expert

    Nov 30, 2010
    16,278
    6,790
    The 10 ohm resistor is not a problem but the 22uf capacitor on the output of the second op-amp seems like a design error. Most op-amps do not like to drive a capacitor directly and in this case, what purpose does it serve to drive a capacitor?

    In addition, the 272 chip allows the input signal to go below zero volts without objection but the 33078 doesn't like that. So, yes, I think substituting the chip produced a fail.

    The output of the sound detector will be square waves tracking any frequency from 16 Hz. up.

    and finally, "gives a reading of 910" whats? millivolts?
     
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