Metal Detector

// 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<

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

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

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

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()

{

Serial.begin(9600);

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;

Serial.println(f);

}

//-Click generator

if(millis()>timer)

{

timer+=10;

PCW+=FTW;

if(PCW&0x8000)

{

digitalWrite(13,HIGH);

PCW&=0x7fff;

}

else

digitalWrite(13,LOW);

}

}