Hi. I am trying to build my own (very basic) microphone + amplifier circuit. I bought these electret microphones, numbered CZN-15E for which I found the product sheet and it provides a schematic:
which being relatively simple, I tried to replicate on a board (R = 2.2k, C = 4.7uF) :
I wrote some basic code to read the analog voltage (yellow wire going off-frame in the picture above):
#define VCC 5.0
#define GND 0.0
#define ADC 1023.0
const int sensorPin = A0;
float voltage;
void setup() {
Serial.begin(9600);
}
void loop() {
voltage = GND + VCC*analogRead(sensorPin)/ADC;
Serial.println(voltage);
}
I get the following output:
As you can see there are little spikes whenever I tap my fingers close to the mic, which I am guessing is the output from the mic (could also be electrical noise though, I can't say for sure): what I am aiming to do is amplify these bursts using a CE stage. But what I don't understand is why there is a constant DC level. The schematic shown uses what I am assuming is an AC coupling capacitor right? so shouldn't the DC levels be removed. Speaking of which, the value of C was not given in the schematic so I experimented with a few values (1u,F 4.7uF, 10 uF and 470 uF specifically)---this is also something I am unsure about. Any help is appreciated. Thank you!