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.

 

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)

 

Circuit Diagram and Working

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.
Video: 

Comments (61)

  • sunilkumar's picture
    sunilkumar

    can weuse 10 mf capacitor instead of 2.2 mf capacitor

    Jan 08, 2016
  • Abhishek's picture
    Abhishek

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

    Jan 14, 2016
  • md sajjad's picture
    md sajjad

    Nice

    Feb 08, 2016
  • arun's picture
    arun

    i need this circuit

    Feb 20, 2016
  • M DILIP RAJA's picture
    M DILIP RAJA

    The circuit is present in the description.

    Feb 21, 2016
  • Eduardo Gomez's picture
    Eduardo Gomez

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

    Jun 26, 2017
  • Sumon Mondal's picture
    Sumon Mondal

    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?

    Feb 22, 2016
  • zohaib's picture
    zohaib

    Would you plz help me to make it..
    Urgent

    May 04, 2016
  • jenny's picture
    jenny

    Can I change the speaker to motor or solenoid?

    Mar 06, 2016
  • Hasan's picture
    Hasan

    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?

    Mar 12, 2016
  • Ahmed's picture
    Ahmed

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

    Apr 02, 2016
  • santosh's picture
    santosh

    How to increase its range ?

    Apr 04, 2016
  • Saisuma's picture
    Saisuma

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

    Apr 15, 2016
  • wynncoruna's picture
    wynncoruna

    I now understand the concept behind metal detectors.

    Thank you.

    Apr 25, 2016
  • satish's picture
    satish

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

    Apr 28, 2016
  • limo's picture
    limo

    its works better on alominom
    its awsooome to make

    May 07, 2016
  • umesh's picture
    umesh

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

    May 10, 2016
  • kinley namgay's picture
    kinley namgay

    plz lets us know about theoritical design about this project

    May 21, 2016
  • harish's picture
    harish

    29 gauge wire is work or not

    May 28, 2016
  • Hussein's picture
    Hussein

    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?

    Jun 15, 2016
  • Abhishek's picture
    Abhishek

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

    Jul 09, 2016
  • PRINCE ALBERT PADILLA's picture
    PRINCE ALBERT P...

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

    Jun 17, 2016
  • Shoaib Amin's picture
    Shoaib Amin

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

    Jul 15, 2016
  • Abhishek's picture
    Abhishek

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

    Aug 22, 2016
  • souvenir boris's picture
    souvenir boris

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

    Aug 02, 2016
  • Abhishek's picture
    Abhishek

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

    Aug 22, 2016
  • jenita's picture
    jenita

    can i use the coil of 5 cm diameter

    Aug 14, 2016
  • Abhishek's picture
    Abhishek

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

    Aug 22, 2016
  • josh's picture
    josh

    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

    Sep 05, 2016
  • bharat sahani's picture
    bharat sahani

    i need detail about this project

    Sep 12, 2016
  • Ibrahim Mostafa's picture
    Ibrahim Mostafa

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

    Sep 29, 2016
  • abhijith's picture
    abhijith

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

    Oct 05, 2016
  • vaishakhee's picture
    vaishakhee

    is it 150 turns or 170? wat xactly?

    Oct 15, 2016
  • paidamoyo's picture
    paidamoyo

    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

    Nov 01, 2016
  • VARIN's picture
    VARIN

    I WANT TO MAKE METAL DETECTOR WHICH DETECT METAL FOR 10 FEET DOWN THE EARTH PLZ HELP ME

    Nov 01, 2016
  • Arpit's picture
    Arpit

    Thanks

    Nov 16, 2016
  • srk's picture
    srk

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

    Nov 28, 2016
  • sid's picture
    sid

    I m doing this project in my collage

    Dec 03, 2016
  • hossameddeen zaher's picture
    hossameddeen zaher

    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...

    Dec 21, 2016
  • Abhishek's picture
    Abhishek

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

    Dec 31, 2016
  • Aqsa's picture
    Aqsa

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

    Jan 05, 2017
  • MILIND's picture
    MILIND

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

    Jan 17, 2017
  • Prasanna's picture
    Prasanna

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

    Feb 07, 2017
  • Maddy's picture
    Maddy

    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.

    Feb 27, 2017
  • Tapendra BC's picture
    Tapendra BC

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

    Feb 08, 2017
  • Maddy's picture
    Maddy

    Can anyone tell me how much does each components cost?

    Feb 26, 2017
  • sourav shome's picture
    sourav shome

    Whats are the voltage of capacitor

    Apr 25, 2017
  • Rana's picture
    Rana

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

    May 21, 2017
  • Maddy's picture
    Maddy

    You can build it easily using copper wire.

    Jul 07, 2017
  • Aderito Magno's picture
    Aderito Magno

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

    Jul 26, 2017
  • Mike's picture
    Mike

    Could we replace the speaker with and LED instead?

    Sep 26, 2017
  • AKHIL's picture
    AKHIL

    C
    an we just use the normal copper wire..?

    Oct 06, 2017
  • ankur's picture
    ankur

    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???

    Nov 22, 2017
  • jhh's picture
    jhh

    What is the use of the 10 micro farad capacitor?

    Dec 08, 2017
  • Zack's picture
    Zack

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

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

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

    Dec 11, 2017
  • Tikkupayeng's picture
    Tikkupayeng

    Thank you....bro
    it has done

    Dec 17, 2017
  • Divyu Jain's picture
    Divyu Jain

    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?

    Mar 21, 2018
  • Umesha's picture
    Umesha

    How thick should be the copper wire

    Apr 05, 2018

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