#include "pitches.h"
const float GAMMA = 0.7;
const float RL10 = 50;
int BuzPin = 4;

void setup() {
  pinMode(BuzPin, OUTPUT);
}

void loop() {
  int analogValue = analogRead(A3);
  float voltage = analogValue / 1024. * 5;
  float resistance = 2000 * voltage / (1 - voltage / 5);
  float lightOpacity = pow(RL10 * 1e3 * pow(10, GAMMA) / resistance, (1 / GAMMA));
  
  if (lightOpacity > 99) {
    tone(BuzPin, NOTE_A2,50);
  }else{
    noTone(BuzPin);
  }
}