Arduino Metal Detector

Arduino

BySaddam 27

Metal Detector using Arduino

Metal Detector is a security device which is used for detecting metals which can be harmful, at various places like Airports, shopping malls, cinemas etc. Previously we have made a very simple Metal detector without a microcontroller, now we are building the Metal Detector using Arduino. In this project, we are going to use a coil and capacitor which will be responsible for the detection of metals. Here we have used an Arduino Nano to build this metal detector project. This is very interesting projects for all electronics lovers. Wherever this detector detects any metal near it, the buzzer starts beeping very rapidly.

 

Required Components:

  1. Arduino (any)
  2. Coil
  3. 10nF capacitor
  4. Buzzer
  5. The 1k resistor
  6. 330-ohm resistor
  7. LED
  8. 1N4148 diode
  9. Breadboard or PCB
  10. Connecting jumper wire
  11. 9v Battery

 

Working Concept:

Whenever some current passes through the coil, it generates a magnetic field around it. And the change in the magnetic field generates an electric field. Now according to Faraday's law, because of this Electric field, a voltage develops across the coil which opposes the change in magnetic field and that’s how Coil develops the Inductance, means the generated voltage opposes the increase in the current. The unit of Inductance is Henry and formula to measure the Inductance is:

L = (μο * N2 * A) / l

Where,
L- Inductance in Henries
μο- Permeability, its 4π*10-7 for Air
N- Number of turns
A- Inner Core Area (πr2) in m2
l- Length of the Coil in meters

 

When any metal comes near to the coil then coil changes its inductance. This change in inductance depends upon the metal type. It's decreases for non-magnetic metal and increases for ferromagnetic materials like iron.

Depending on the core of the coil, inductance value changes drastically. In the figure below you can see the air-cored inductors, in these inductors, there will be no solid core. They are basically coils left in the air. The medium of flow of magnetic field generated by the inductor is nothing or air. These inductors have inductances of very less value.

Air Cored Inductors

 

These inductors are used when the need for values of few microHenry. For values greater than few milliHenry these are not a suitable one. In below figure you can see an inductor with ferrite core. These Ferrite Core inductor has very large inductance value.

Ferrite Core Inductors

 

Remember the coil wound here is a air cored one, so when a metal piece is brought near the coil, the metal piece acts as a core for the air cored inductor. By this metal acting as a core, the inductance of the coil changes or increases considerably. With this sudden increase in inductance of coil the overall reactance or impedance of the LC circuit changes by a considerable amount when compared without the metal piece.  

 

So here in this Arduino Metal Detector Project, we have to find inductance of the coil to detect metals. So to do this we have used LR circuit (Resistor-Inductor Circuit) that we already mentioned. Here in this circuit, we have used a coil having around 20 turns or winding with a 10cm diameter. We have used an empty tape roll and wind the wire around it to make the coil.

Coil of Metal Detector

 

Circuit Diagram:

We have used an Arduino Nano for controlling whole this Metal Detector Project. A LED and Buzzer are used as metal detection indicator. A Coil and capacitor is used for detection of metals. A signal diode is also used for reduce the voltage. And a resistor for limiting the current to the Arduino pin.

Arduino Metal Detector Circuit Diagram

Metal Detector using Arduino hardware implementation

 

Working Explanation:

Working of this Arduino Metal Detector is bit tricky. Here we provide the block wave or pulse, generated by Arduino, to the LR high pass filter. Due to this, short spikes will be generated by the coil in every transition. The pulse length of the generated spikes is proportional to the inductance of the coil. So with the help of these Spike pulses we can measure the inductance of Coil. But here it is difficult to measure inductance precisely with that spikes because that spikes are of very short duration (approx. 0.5 microseconds) and that is very difficult to be measured by Arduino.

Metal Detector using Arduino in action

So instead of this, we used a capacitor which is charged by the rising pulse or spike. And it required few pulses to charge the capacitor to the point where its voltage can be read by Arduino analog pin A5. Then Arduino read the voltage of this capacitor by using ADC. After reading voltage, capacitor quickly discharged by making capPin pin as output and setting it to low. This whole process takes around 200 microseconds to complete. For better result, we repeat measurement and took an average of the results. That’s how we can measure the approximate inductance of Coil. After getting the result we transfer the results to the LED and buzzer to detect the presence of metal. Check the Complete code given at the end of this Article to understand the working.

 

Complete Arduino code is given at the end of this Article. In programming part of this project, we have used two Arduino pins, one for generating block waves to be fed in Coil and second analog pin to read capacitor voltage. Other than these two pins, we have used two more Arduino pins for connecting LED and buzzer.

You can check the complete code and Demonstration Video of Arduino Metal Detector below. You can see that whenever it detects some metal the LED and Buzzer starts to blink very fastly.

Code

#define capPin A5
#define buz 9
#define pulsePin A4

#define led 10

long sumExpect=0; //running sum of 64 sums 
long ignor=0;   //number of ignored sums
long diff=0;        //difference between sum and avgsum
long pTime=0;
long buzPeriod=0; 

void setup() 
{
  Serial.begin(9600);
  pinMode(pulsePin, OUTPUT); 
  digitalWrite(pulsePin, LOW);
  pinMode(capPin, INPUT);  
  pinMode(buz, OUTPUT);
  digitalWrite(buz, LOW);
  pinMode(led, OUTPUT);
}

void loop() 
{
  int minval=1023;
  int maxval=0;
  long unsigned int sum=0;
  for (int i=0; i<256; i++)
  {
    //reset the capacitor
    pinMode(capPin,OUTPUT);
    digitalWrite(capPin,LOW);
    delayMicroseconds(20);
    pinMode(capPin,INPUT);
    applyPulses();
    
    //read the charge of capacitor
    int val = analogRead(capPin); //takes 13x8=104 microseconds
    minval = min(val,minval);
    maxval = max(val,maxval);
    sum+=val;
    
    long unsigned int cTime=millis();
    char buzState=0;
    if (cTime<pTime+10)
    {
      if (diff>0)
        buzState=1;
      else if(diff<0)
        buzState=2;
    }
    if (cTime>pTime+buzPeriod)
    {
      if (diff>0)
      buzState=1;
      else if (diff<0)
      buzState=2;
      pTime=cTime;   
    }
    if (buzPeriod>300)
    buzState=0;

    if (buzState==0)
    {
      digitalWrite(led, LOW);
      noTone(buz);
    }  
    else if (buzState==1)
    {
      tone(buz,2000);
      digitalWrite(led, HIGH);
    }
    
    else if (buzState==2)
    {
      tone(buz,500);
      digitalWrite(led, HIGH);
    }
  }

  //subtract minimum and maximum value to remove spikes
  sum-=minval; 
  sum-=maxval;
  
  if (sumExpect==0) 
  sumExpect=sum<<6; //set sumExpect to expected value
  long int avgsum=(sumExpect+32)>>6; 
  diff=sum-avgsum;
  if (abs(diff)<avgsum>>10)
  {
    sumExpect=sumExpect+sum-avgsum;
    ignor=0;
  } 
  else 
    ignor++;
  if (ignor>64)
  { 
    sumExpect=sum<<6;
    ignor=0;
  }
  if (diff==0) 
    buzPeriod=1000000;
  else 
  buzPeriod=avgsum/(2*abs(diff));    
}

void applyPulses()
{
    for (int i=0;i<3;i++) 
    {
      digitalWrite(pulsePin,HIGH); //take 3.5 uS
      delayMicroseconds(3);
      digitalWrite(pulsePin,LOW);  //take 3.5 uS
      delayMicroseconds(3);
    }
}

Video

Comments

  • Kiran k v's picture
    Kiran k v
    Feb 13, 2018

    Please send me the synopsis and full details of the project sir..

  • Ghanim Radi khudear's picture
    Ghanim Radi khudear
    Feb 28, 2018

    what the type of wire used in project ? diameter of wire

  • Ghanim Radi khudear's picture
    Ghanim Radi khudear
    Mar 01, 2018

    but ? i need the think of wire used just that
    plz

  • asd's picture
    asd
    Mar 08, 2018

    what is the thickness of the wire to do the Coil???
    plz

  • WhoIs's picture
    WhoIs
    Mar 28, 2018

    Very nice project , I have successfully made it using arduino uno r3, but the only problem I have experienced is it can't detect small objects like small leds, alligator clips, .. Is it okay that I used the built in USB-B Port of arduino connected to 5k Mah power bank as power supply?

  • Mahesh's picture
    Mahesh
    Mar 29, 2018

    I have a UNO R3 too, is there any difference in circuit and code..Please can you help me through if there is any difference.

  • Kiran k v's picture
    Kiran k v
    Apr 07, 2018

    Bro how u build the electric wire coil

  • kiran's picture
    kiran
    Apr 10, 2018

    please send me the correct code
    i have check the above program but it shows some error. so please mail the code sir.

  • Lokeshwar's picture
    Lokeshwar
    Apr 13, 2018

    I could not able to able get the exact output. My LED and buzzer are blinking as such in a some random manner. I suspect my output is not right coz, even if i keep the metal very close to it, it is not working. Please help me .....
    Thanks in advance.

  • ella's picture
    ella
    May 20, 2018

    Can you pls help me? Can you send me the picture of the breadboard, wires and other components in it?

  • Amit pratap's picture
    Amit pratap
    Apr 04, 2018

    I m using coil , not wire it help me or not...if it can't help me which wire I used breadboard wire...
    Plz tell me ...plz

  • Aswinth Raj's picture
    Aswinth Raj
    Apr 06, 2018

    Coil should have also worked, just make sure if it is enameled!! The wire used here is normal breadboard wire 

  • melvin poulose's picture
    melvin poulose
    Apr 06, 2018

    high qaulity
    capacity

  • akif's picture
    akif
    Apr 17, 2018

    hi.
    can i use different diameter of tape to measure the sensitivity of the search coil? or it will effect the faulty of circuit?

  • MANOJ KUMAR's picture
    MANOJ KUMAR
    Apr 25, 2018

    please send me the correct coad for this project but its shows some errors.

  • youcef's picture
    youcef
    Apr 27, 2018

    i made the circuit, but the buzzer always makes noise and when a metal is here, nothing happens. So it doesn't work. Help please !

  • Nathan's picture
    Nathan
    May 04, 2018

    I was going to do this for a school project and was wondering if the size of the tape thing that you wrap the wire around could effect the ability to detect metals?

  • akshata oak's picture
    akshata oak
    May 09, 2018

    hey guys !pls reply
    I am unable to find a 10nf capacitor and somebody told me to use 10pf capacitor.so,tell me will that go with the metal detector ?will it work?pls...reply fast..
    circuit digest has helped me a lot with my project ..
    just need one more help .. pls reply..

  • Charles's picture
    Charles
    May 16, 2018

    @akshata oak

    There are many ways of defining capacitors. They are usually defined as nanofarads, picofarads, and microfarads. Essentially it's the same thing, with the decimal place in a different location.

    The idea is to end up with a number that makes sense (i.e., that isn't too large or too small).

    For example; these are actually all the same value:

    10nf (nanofarads)
    10000pF (picofarads)
    0.01uF (microfarads)

    You should be able to find an inexpensive ceramic capacitor with that value.

    The capacitor may also be labelled with a three number code. In your case you would want a capacitor labelled 103.

    In such a case the capacitor is measured in picofarads. The first two digits represent the first two values for the capacitor, and the 3 represents the number of extra zeros.

    103 becomes 10 + 000 (3 zeroes) = 10 nF = 10000 pF = 0.01uF

    I hope this helps.

  • shanmugaraman's picture
    shanmugaraman
    Jun 29, 2018

    WE ARE DOING A METAL DETECTOR PROJECT FOR MY M.SC COURSE
    BUT YOUR CODE DOES NOT SUPPORT FOR THIS PROJECT SO I REQUEST YOU TO PLEASE SEND US CORRECT CODE. THANKING YOU

  • Sanarthanan Thirunavukkarasu's picture
    Sanarthanan Thi...
    Aug 03, 2018

    why is this circuit not working all instructions are followed but not work so how can we follow you?

  • Gabriel Idenyi's picture
    Gabriel Idenyi
    Aug 03, 2018

    Please what's the thickness of the the coil used in the project

  • sachin's picture
    sachin
    Sep 03, 2018

    how can the range of it can be increased such that it can be used for searching the metal objects buried inside soil of about 1 m range..?
    thanks in advance

  • Wareyai Emmanuel's picture
    Wareyai Emmanuel
    Sep 04, 2018

    Please can I have the full work on this project. Thank you

  • bhupathiraju vinay chandra varma's picture
    bhupathiraju vi...
    Sep 12, 2018

    can i wound the copper wire as a coil around the tape roll and if i disconnected the arduino from pc how it works can you explain me

  • giorgio's picture
    giorgio
    Oct 18, 2018

    Great job, code worked at first, schematic very clear.

    After an initial mistake (wrong capacitator, realized reading comments...I am a Pharmacist after all ) works perfectly.

     

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