# Simple Metal Detector Circuit

Published  May 14, 2015   65

Author

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.

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 ,

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.

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

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

Submitted by sunilkumar on Fri, 01/08/2016 - 18:50

### can weuse 10 mf capacitor

can weuse 10 mf capacitor instead of 2.2 mf capacitor

### Its not 2.2mf, its 2.2uF. Its

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

Submitted by md sajjad on Mon, 02/08/2016 - 22:08

### electronics mobile

Nice

Submitted by arun on Sat, 02/20/2016 - 16:04

### i need this circuit

i need this circuit

### The circuit is present in the

The circuit is present in the description.

### detector metal

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

Submitted by Sumon Mondal on Mon, 02/22/2016 - 20:48

### feed back

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?

Submitted by zohaib on Wed, 05/04/2016 - 23:15

In reply to by Sumon Mondal

### help

Would you plz help me to make it..
Urgent

Submitted by jenny on Sun, 03/06/2016 - 22:16

### motor

Can I change the speaker to motor or solenoid?

Submitted by Hasan on Sat, 03/12/2016 - 23:32

### Nothing

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?

Submitted by Ahmed on Sat, 04/02/2016 - 21:35

### explain

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

Submitted by santosh on Mon, 04/04/2016 - 22:13

### enquiry

How to increase its range ?

Submitted by Saisuma on Fri, 04/15/2016 - 11:23

### Metal detector

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

Submitted by wynncoruna on Mon, 04/25/2016 - 12:06

### Metal detector

I now understand the concept behind metal detectors.

Thank you.

Submitted by satish on Thu, 04/28/2016 - 18:30

### door frame metal detector

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

Submitted by limo on Sat, 05/07/2016 - 14:46

### explanation

its works better on alominom
its awsooome to make

Submitted by umesh on Tue, 05/10/2016 - 12:49

### design

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

Submitted by kinley namgay on Sat, 05/21/2016 - 14:42

### metal detector

Submitted by harish on Sat, 05/28/2016 - 08:49

### 29 gauge wire is work or not

29 gauge wire is work or not

Submitted by Hussein on Wed, 06/15/2016 - 17:37

### I didn't connect this circuit

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?

### Output Frequency of 555

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

Submitted by PRINCE ALBERT … on Fri, 06/17/2016 - 07:50

### i have 2 cd player,headphone,9volt battery,gluo,scrach tape....

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

Submitted by Shoaib Amin on Fri, 07/15/2016 - 15:34

### What transformer should be

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

### You can try having 9v or 5v

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

Submitted by souvenir boris on Tue, 08/02/2016 - 22:42

### nice mister anyway can u give

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

Submitted by jenita on Sun, 08/14/2016 - 15:21

### can i use the coil of 5 cm diameter

can i use the coil of 5 cm diameter

Submitted by josh on Mon, 09/05/2016 - 06:44

### please can you explain to

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

Submitted by bharat sahani on Mon, 09/12/2016 - 11:29

Submitted by Ibrahim Mostafa on Thu, 09/29/2016 - 18:43

### detecting Distance

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

Submitted by abhijith on Wed, 10/05/2016 - 18:40

### my speaker doesnt turn on

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

Submitted by vaishakhee on Sat, 10/15/2016 - 23:32

### is it 150 turns or 170? wat

is it 150 turns or 170? wat xactly?

Submitted by paidamoyo on Tue, 11/01/2016 - 02:58

### help with parts specs

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

Submitted by VARIN on Tue, 11/01/2016 - 20:27

### HELP TO MAKE 10FEET DISTANCE METAL DETECTOR

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

Submitted by Arpit on Wed, 11/16/2016 - 01:59

### Thanks

Thanks

Submitted by srk on Mon, 11/28/2016 - 14:34

### What is the function of 10

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

Submitted by sid on Sat, 12/03/2016 - 00:49

### no

I m doing this project in my collage

Submitted by hossameddeen zaher on Wed, 12/21/2016 - 22:44

### how circuit work

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...

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

Submitted by Aqsa on Thu, 01/05/2017 - 21:46

### Circuit

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

Submitted by MILIND on Tue, 01/17/2017 - 16:05

### can it detect all types of

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

Submitted by Prasanna on Tue, 02/07/2017 - 19:26

### I want clarification

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

### Because 555 timer is

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.

Submitted by Tapendra BC on Wed, 02/08/2017 - 18:00

### Query

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

Submitted by Maddy on Sun, 02/26/2017 - 18:54

### Price

Can anyone tell me how much does each components cost?

Submitted by sourav shome on Tue, 04/25/2017 - 21:33

### Whats are the voltage of

Whats are the voltage of capacitor

Submitted by Rana on Sun, 05/21/2017 - 14:49

### I can't find inductance in my

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

Submitted by iene on Wed, 05/24/2017 - 11:21

### I am a hobbyist of metal

I am a hobbyist of metal detecting.
Can this metal detector circuit detect all kinds of metal?
There might be large functional difference.

Submitted by Aderito Magno on Wed, 07/26/2017 - 09:59

### please send this l projec for me becouse I want to know it well

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

Submitted by Mike on Tue, 09/26/2017 - 16:12

### replace indicator

Could we replace the speaker with and LED instead?

Submitted by AKHIL on Fri, 10/06/2017 - 21:02

### dought

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

Submitted by ankur on Wed, 11/22/2017 - 21:07

### in this circuit diagram pin 2

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???

Submitted by jhh on Fri, 12/08/2017 - 06:50

### Capacitor

What is the use of the 10 micro farad capacitor?

Submitted by Zack on Mon, 12/11/2017 - 05:19

### capacitor

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

### Its a smoothing capacitor to

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

Submitted by Tikkupayeng on Sun, 12/17/2017 - 09:30

### Thank you....bro it has done

Thank you....bro
it has done

Submitted by Divyu Jain on Wed, 03/21/2018 - 19:02

### Circuit did not work.

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?

### Hey, did you figure out the

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.

Submitted by Umesha on Thu, 04/05/2018 - 16:51

### How thick should be the

How thick should be the copper wire

Submitted by Krishnakanth on Wed, 06/27/2018 - 20:08