adapting am radio metal detector to arduino board

I have seen on the net simple metal detector circuit which you can build yourself in 20 mint. See link www.talkingelectronics.com/html/MetalDetector.html to make clear to my last post, I used this ciruit and adapt it to arduino board to make arduino metal detector see vedio  https://www.youtube.com/watch?v=1Vw4EAmZyls  use the same sketch as befor-

// Arduino based metal detector

// (C)Dzl july 2013

// http://dzlsevilgeniuslair.blogspot.dk/

// Connect search coil oscillator (20-200kHz) to pin 5

// Connect piezo between pin 13 and GND

// Connect NULL button between pin 12 anf GND

// REMEMBER TO PRESS NULL BUTTON AFTER POWER UP!!

#define SET(x,y) (x |=(1<<y))                 //-Bit set/clear macros

#define CLR(x,y) (x &= (~(1<<y)))             // |

#define CHK(x,y) (x & (1<<y))                 // |

#define TOG(x,y) (x^=(1<<y))                  //-+

unsigned long t0=0;         //-Last time

int t=0;                    //-time between ints

unsigned char tflag=0;      //-Measurement ready flag

float SENSITIVITY= 1000.0;  //-Guess what

//-Generate interrupt every 1000 oscillations of the search coil

SIGNAL(TIMER1_COMPA_vect)

{

  OCR1A+=1000;

  t=micros()-t0;

  t0+=t;

  tflag=1;

}

void setup()

{

  pinMode(13,OUTPUT);    //-piezo pin

  digitalWrite(12,HIGH); //-NULL SW. pull up

  //-Set up counter1 to count at pin 5

  TCCR1A=0;

  TCCR1B=0x07;

  SET(TIMSK1,OCF1A);

}

//-Float ABS

float absf(float f)

{

  if(f<0.0)

    return -f;

  else

    return f;

}

int   v0=0;  //-NULL value

float f=0;   //-Measurement value

unsigned int FTW=0;    //-Click generator rate

unsigned int PCW=0;    //-Click generator phase

unsigned long timer=0; //-Click timer

void loop()

{

  if(tflag)

  {

    if(digitalRead(12)==LOW)  //-Check NULL SW.

      v0=t;                   //-Sample new null value

    f=f*0.9+absf(t-v0)*0.1;   //-Running average over 10 samples

    tflag=0;                  //-Reset flag

    float clf=f*SENSITIVITY;  //-Convert measurement to click frequency

    if(clf>10000)           

      clf=10000;

    FTW=clf;

  }

 

  //-Click generator

  if(millis()>timer)

  {

    timer+=10;

    PCW+=FTW;

    if(PCW&0x8000)

    {

      digitalWrite(13,HIGH);

      PCW&=0x7fff;

    }

    else

      digitalWrite(13,LOW);

  }

}

It does not detect gold, only metals.