Simple Metal Detector Circuit


ByDilip Raja 65

Simple Metal Detector Project using 555 Timer IC

You can find a metal detector at airports, theaters and various other public places. They are used for the safety of people to detect anyone carrying a metal (Arms etc). In this project we are going to design a simple metal detector circuit. There are so many metal detector designs but most of them are complex in design so here we are going to design a simple metal detector circuit using 555 Timer IC.

Before going further we need to understand concept of inductor and RLC circuits. Let us first talk about inductors. Inductors are nothing but coils of enameled copper wire comes in different shapes and sizes. Based on various parameters the inductance of an inductor is calculated. In all of those parameters we are basically interested in core on the inductor as depending on the core, 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 air. The medium of flow of magnetic field generated by 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 micro Henry. For values greater than few milli these are not a suitable one. In below figure you can see a inductors of ferrite core ,

Ferrite Core Inductors

When inductor coil is wound on a core may be ferrite or an iron core, the inductance of the coil increases enormously. This value is much more than the air cored one of the same size and shape.

Now for a RLC circuit as shown in figure, the reactance or impedance between terminals “a” and “c” depends on the values of L and C if the applied signal frequency is constant.

RLC Circuit

So if the inductance value changes the value of reactance or impedance changes. How these two concepts are used together for a metal detector circuit, is explained in working section of this project.


Metal Detector Circuit Components

  • +9 supply voltage
  • 555 IC
  • 47KΩ resistor
  • 2.2µF capacitor (2 pieces)
  • Speaker (8Ω)
  • 170Turns of 10cm diameter coil (any gauge would work)


Metal Detector Circuit Diagram and Working

Simple Metal Detector Circuit Diagram

The figure shows the circuit diagram of metal detector. The 555 IC timer here acts as a square wave generator and it generate pulses with frequencies audible to human. The capacitor between pin2 and pin1 should not be changed as it is need to generate audible frequencies. 

In the circuit there is an RLC circuit formed by 47K resistor, 2.2µF capacitor, and 150turn inductor. This RLC circuit is the metal detection part. Now as mentioned earlier in previous section, a metal core inductor has a high inductance value over a air cored one.

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 RLC circuit changes by a considerable amount when compared without the metal piece.                  

At first when there is no metal piece the signal fed to speaker causes some audible sound. Now with the reactance change around the RLC circuit the signal sent to speaker will no longer be the same as before, because of this the sound produced by the speaker will be of different to the first one.                                

So whenever a metal is brought near the coil, the impedance of RLC changes making the signal to change resulting in variation to sound generated in speaker. You can also check this Arduino based metal detector.


Common Tips:

  • Enamel should be removed at the tips of coil for soldering connections.
  • With different gauge we will have different RLC impedance, so one should experiment with resistance in RLC circuit for sensitive metal detection.
  • The speaker can be of any type. But with resistance less than 8Ω, the timer might get heated.
  • Use supply voltage higher than 5V.


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  • sunilkumar's picture
    Jan 08, 2016

    can weuse 10 mf capacitor instead of 2.2 mf capacitor

  • Abhishek's picture
    Jan 14, 2016

    Its not 2.2mf, its 2.2uF. Its micro (u) not milli (m). And yes the value shouldn't be changed.

  • arun's picture
    Feb 20, 2016

    i need this circuit

  • M DILIP RAJA's picture
    Feb 21, 2016

    The circuit is present in the description.

  • Eduardo Gomez's picture
    Eduardo Gomez
    Jun 26, 2017

    i neded circuit board the detector and
    the real value of capacitors 2,2 mf o 2,2 nano? thanks very

  • Sumon Mondal's picture
    Sumon Mondal
    Feb 22, 2016

    It really works because i have made this circui & it works perfectly.
    What to do to increase it's sencitivity so that it can be used in various industries?

  • zohaib's picture
    May 04, 2016

    Would you plz help me to make it..

  • jenny's picture
    Mar 06, 2016

    Can I change the speaker to motor or solenoid?

  • Hasan's picture
    Mar 12, 2016

    It's nice but the speaker turns always on.
    It will be fine if the speaker turns off when there are no metal near inductor (coil)
    and the speaker Turns on when a metal brought near inductor .
    how can I do that?

  • Ahmed's picture
    Apr 02, 2016

    can you tell me the reason and explain the jop of every component of the circuit please ??

  • santosh's picture
    Apr 04, 2016

    How to increase its range ?

  • Saisuma's picture
    Apr 15, 2016

    Can u help me out with design Steps? How to choose the values of R, L, C and inductance?

  • wynncoruna's picture
    Apr 25, 2016

    I now understand the concept behind metal detectors.

    Thank you.

  • satish's picture
    Apr 28, 2016

    i want to make door frame metal detector. Can anyone help me?

  • limo's picture
    May 07, 2016

    its works better on alominom
    its awsooome to make

  • umesh's picture
    May 10, 2016

    i need help to design turn off speaker when they is no metal found.. please help me to design..

  • kinley namgay's picture
    kinley namgay
    May 21, 2016

    plz lets us know about theoritical design about this project

  • harish's picture
    May 28, 2016

    29 gauge wire is work or not

  • Hussein's picture
    Jun 15, 2016

    I didn't connect this circuit, although I have question: does the voltage across the buzzer changes if a metal is brought near the coil?

  • Abhishek's picture
    Jul 09, 2016

    Output Frequency of 555 changes, when we bring Metal near to the coil, so sound of Speaker changes according to the frequency.

    Jun 17, 2016

    i have 2 cd player and 1 9volt battery and headphone...can you help me make a metal detector

  • Shoaib Amin's picture
    Shoaib Amin
    Jul 15, 2016

    What transformer should be used so that it connects directly in the power source?

  • Abhishek's picture
    Aug 22, 2016

    You can try having 9v or 5v of regulated DC power supply form the 9-0-9 1A transformer

  • souvenir boris's picture
    souvenir boris
    Aug 02, 2016

    nice mister anyway can u give us the video of how it works

  • Abhishek's picture
    Aug 22, 2016

    Video is already given, please check at the end of the Article.

  • jenita's picture
    Aug 14, 2016

    can i use the coil of 5 cm diameter

  • Abhishek's picture
    Aug 22, 2016

    No of Turns and diameter are important in the coil, so use it as suggested in the article.

  • josh's picture
    Sep 05, 2016

    please can you explain to what causes the continous noise or sound in the speaker.. need the answer as this a likely question in my project defense

  • bharat sahani's picture
    bharat sahani
    Sep 12, 2016

    i need detail about this project

  • Ibrahim Mostafa's picture
    Ibrahim Mostafa
    Sep 29, 2016

    what is the Detecting distance ?
    and if i want to increase it , what I can do.

  • abhijith's picture
    Oct 05, 2016

    the speaker doesnt make any sound what wud be the problem pls help urgent

  • vaishakhee's picture
    Oct 15, 2016

    is it 150 turns or 170? wat xactly?

  • paidamoyo's picture
    Nov 01, 2016

    made circuit using 2.2uf50v 10uf50v capacitors 47k resistor ne555 ic 8ohm speaker on coil i used 0.1mm enameled wire 150turns of120mm diameter . the detactor produces a high pitch sound which does not change even when coil is swept over a metal object. pliz help with specific voltages of capacitors and specific resistance of search coil

  • VARIN's picture
    Nov 01, 2016


  • srk's picture
    Nov 28, 2016

    What is the function of 10 micro farad capacitor here...??

  • sid's picture
    Dec 03, 2016

    I m doing this project in my collage

  • hossameddeen zaher's picture
    hossameddeen zaher
    Dec 21, 2016

    the 555 timer either sourcing or sinking a fixed amount of current from its pin 3,
    so I see as the output is a fixed squarawave tone so the increasing of L coil will increase voltage on it that increasing current draining from pin 3 hence reducing tone....very simple ! I will build the circuit and examine it under oscilloscope and if there is time I will publish results here ...god willing...

  • Abhishek's picture
    Dec 31, 2016

    Yes @hossameddeen, please share the results of you findings when you are done :)

  • Aqsa's picture
    Jan 05, 2017

    I used all the above components but the circuit is not working.

  • MILIND's picture
    Jan 17, 2017

    can it detect all types of metal or only iron metal?? plz tell...

  • Prasanna's picture
    Feb 07, 2017

    Why there is a continuous sound occuring.can i know the reason

  • Maddy's picture
    Feb 27, 2017

    Because 555 timer is generating a square wave which is causing the sound and bringing metal near to it will change the frequency of that square wave hence the sound will also change.

  • Tapendra BC's picture
    Tapendra BC
    Feb 08, 2017

    How can we find the frequency generated by IC in this circuit? Please inform me because I'm in great need of it.

  • Maddy's picture
    Feb 26, 2017

    Can anyone tell me how much does each components cost?

  • sourav shome's picture
    sourav shome
    Apr 25, 2017

    Whats are the voltage of capacitor

  • Rana's picture
    May 21, 2017

    I can't find inductance in my country
    My country stops import it
    What should I do?

  • Maddy's picture
    Jul 07, 2017

    You can build it easily using copper wire.

  • Aderito Magno's picture
    Aderito Magno
    Jul 26, 2017

    Hallo friend i like to learn this metal please send me all project until final thanks

  • Mike's picture
    Sep 26, 2017

    Could we replace the speaker with and LED instead?

  • AKHIL's picture
    Oct 06, 2017

    an we just use the normal copper wire..?

  • ankur's picture
    Nov 22, 2017

    in this circuit diagram pin 2 and pin 6 are connected.I think its only astable multivibrator. am i right sir ??can we design a metal detector using monostable multivibrator configuration where pin 6and pin7 are connected???

  • jhh's picture
    Dec 08, 2017

    What is the use of the 10 micro farad capacitor?

  • Zack's picture
    Dec 11, 2017

    what is the purpose of the 10uF capacitor in the circuit

  • Aswinth Raj's picture
    Aswinth Raj
    Dec 11, 2017

    Its a smoothing capacitor to filter noise. It is optional and hence you can ignore it if you cannot find a 10u cap

  • Tikkupayeng's picture
    Dec 17, 2017

    Thank you....bro
    it has done

  • Divyu Jain's picture
    Divyu Jain
    Mar 21, 2018

    I made the exact same circuit. The coil of 170 turns, 22 gauge copper wire, 10 cm diameter and all the other components were kept the same as mentioned, but it did not work. I've tried it multiple times but not even the slightest of change in noise occurs.
    Help me out. What could be the probable mistake?

  • Lokeshwar's picture
    Jun 19, 2018

    Hey, did you figure out the same mistake because the same issue i'm also having.
    Even i couldn't get the output.
    I have coil of 500 turns remaining all specs are same.

  • Umesha's picture
    Apr 05, 2018

    How thick should be the copper wire

  • Krishnakanth's picture
    Jun 27, 2018

    I want advantages of this project

  • jurgen's picture
    Jun 12, 2020

    Thanks for sharing this project. I was able to make a working copy with the specified components. I'm wondering if it would be possible to filter out the constant tone when no metal is near the coil by simply adding a basic RLC band stop filter between the output and the speaker. It would probably need to be a sufficiently high order one to retain the sensitivity, and band stop because both higher and lower frequencies should be able to pass (to detect both ferromagnetic e.g. iron and non-ferromagnetic e.g. aluminium). Please comment if you have tried something like this :) Also would be interested if someone had experimented with differently shaped coils (for example '8'-shaped) to improve the detection range.

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