VMA309 sensibility

I just bought a vma309 sound sensor.
I connected it to my raspberry pi zero and every thing went well except for his sensibility.
After adjusting the capacitor, his sensibility just “goes off” after a few minutes. I have to scream to make the led turns on. I adjust it again, and again, and after a few minutes I’m at the same starting point.
What am I missing?
Thank you for your time.

Hello Pisensor,

First try the demo code with Arduino to check the sensor board.
Follow manual §5 & 6 pages 3, 4. => https://www.velleman.eu/downloads/29/vma309_a4v02.pdf

If this works well, normally it should work for RPi.

This code is used for testing the sensor.
Turn the variable resistor (blue trimmer on sensor board) until LED12 turns off.
Now, you can make a sound and you will see LED12 turn on

int Led = 12;      //define LED Interface
int buttonpin = 7; // define D0 Sensor Interface
int val = 0;       // define numeric variables val

void setup() {
  pinMode (Led, OUTPUT);       //define LED as output interface.
  pinMode (buttonpin, INPUT);  //output interface D7 is defined sensor.

void loop() {
  val = digitalRead(buttonpin);
  if(val == HIGH){
   digitalWrite (Led, HIGH);
    digitalWrite(Led, LOW);

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