Audio sound detector for Funduino

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*Disclaimer: The images are merely illustrative.

The electret microphone is a type of condenser microphone. Condensers are essentially capacitors and condenser microphones are formed by a thin diaphragm mounted in front of a plate. Recall that a capacitor is formed by two conductors with an insulator, or dielectric, between them. Both the diaphragm and the plate are conductors. The smaller the distance between these two conductors, the higher the capacitance, given that the surface area of the conductors are unchanged.

When sound reaches the condenser, the diaphragm vibrates thereby changing the distance between the conductors and effectively changes the capacitance between the diaphragm and the plate. This capacitance is converted to voltage with the application of a sufficient charge on the condenser. The voltage is boosted through a built-in transistor inside the microphone as shown in the picture above.

Now condenser microphones needs high voltages to maintain that charge. An electret microphone doesn’t need high voltages because the diaphragm is made out of a special material that stores a high enough charge. This material, which is the electret, is like a permanent magnet but stores a permanent charge.

The voltage changes that are produced by sound should be enough to be detected by an Arduino. This is why sound sensors often always have an operational amplifier IC included. For my Grove Sound Sensor board, the LM358 is the op-amp.

Using an Arduino Microphone

Since the sound sensor board produces a changing voltage, we’ll need the Arduino’s analog-to-digital converter to process that voltage. Here’s a sketch that reads the voltage from the sound sensor connected to A0 which is then displayed on the Arduino IDE’s serial plotter.

int soundPin = A0;
 
void setup()
{
  Serial.begin(115200);
}
 
void loop()
{
    long sum = 0;
    for(int i=0; i<100; i++)
    {
        sum += analogRead(soundPin);
    }
 
    sum = sum/100;
 
    Serial.println(sum);
 
    delay(10);
}

The sound sensor board outputs a noisy voltage so we need to take the average of a hundred samples to be more definitive. Then again, it is still noisy as shown by the serial plotter:

int soundPin = A0;
int LED = 13;
 
void setup()
{
  Serial.begin(9600);
  pinMode(LED, OUTPUT);
}
 
void loop()
{
    long sum = 0;
    for(int i=0; i<100; i++)
    {
       sum += analogRead(soundPin);
    }
 
    sum = sum/100;
 
    if(sum > 600){
      digitalWrite(LED, HIGH);
    }else{
      digitalWrite(LED, LOW);
    }
 
    Serial.println(sum);
    delay(10);
}