Projeto de sensor de proximidade utilizando infravermelho

// Fonte do codigo http://labdegaragem.com/
#include <Tone.h> //Include the library

int IRpin= A0; //IR's pin
int IRval=0; //The value of IR
int threshold=100; //The threshold to activate the IR
int error = 10; //The error of IR
int temp[20]={0}; //Store the samples
int x=0; //Counter to temp
int y=0; //Counter to approaching
int z=0; //Counter to go away
int last = 0; //The last sample
int derivative = 0; //The derivative of samples
Tone player; //To play different tones
int note[]={NOTE_A3,NOTE_G4}; //The notes to play

void setup()

{
    Serial.begin(9600);
    pinMode(2, OUTPUT);
    pinMode(3, OUTPUT);
    player.begin(11);
}

void loop()
{
    x=0;
    y=0;
    z=0;
    if(analogRead(IRpin)>=threshold){
        do{
                IRval=analogRead(IRpin);
                derivative = IRval - last;
                last = IRval;
                temp[x]=derivative;
                Serial.println(temp[x]);
                //Serial.println(IRval);
                x++;
                delay(75);
            }while(x<20);
        x=0;
        for(x=0;x<20;x++){
                if(temp[x]>=error)
            {
        y=y+1;
            }
                if(temp[x]<-error){
                z=z+1;
            }
            }
                Serial.print("approaching y=");
                Serial.println(y);
                Serial.print("go away z=");
                Serial.println(z);
                if(y>z && y>3){
        Serial.println("Approaching");
        digitalWrite(2, HIGH);
        player.play(note[0]);
        delay(200);
        player.play(note[1]);
        delay(200);
        player.stop();
        }
        else if(z>y && z>3){
            Serial.println("Go away");
            digitalWrite(3, HIGH);
            player.play(note[1]);
            delay(200);
            player.play(note[0]);
            delay(200);
            player.stop();
        }
    delay(200);
    digitalWrite(2, LOW);
    digitalWrite(3, LOW);
    }
}