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.
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
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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Comments
Jan 08, 2016
can weuse 10 mf capacitor instead of 2.2 mf capacitor
Jan 14, 2016
Its not 2.2mf, its 2.2uF. Its micro (u) not milli (m). And yes the value shouldn't be changed.
Feb 08, 2016
Nice
Feb 20, 2016
i need this circuit
Feb 21, 2016
The circuit is present in the description.
Jun 26, 2017
i neded circuit board the detector and
the real value of capacitors 2,2 mf o 2,2 nano? thanks very
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?
May 04, 2016
Would you plz help me to make it..
Urgent
Mar 06, 2016
Can I change the speaker to motor or solenoid?
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?
Apr 02, 2016
can you tell me the reason and explain the jop of every component of the circuit please ??
Apr 04, 2016
How to increase its range ?
Apr 15, 2016
Can u help me out with design Steps? How to choose the values of R, L, C and inductance?
Apr 25, 2016
I now understand the concept behind metal detectors.
Thank you.
Apr 28, 2016
i want to make door frame metal detector. Can anyone help me?
May 07, 2016
its works better on alominom
its awsooome to make
May 10, 2016
i need help to design turn off speaker when they is no metal found.. please help me to design..
May 21, 2016
plz lets us know about theoritical design about this project
May 28, 2016
29 gauge wire is work or not
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?
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
Jul 15, 2016
What transformer should be used so that it connects directly in the power source?
Aug 22, 2016
You can try having 9v or 5v of regulated DC power supply form the 9-0-9 1A transformer
Aug 02, 2016
nice mister anyway can u give us the video of how it works
thanks
Aug 22, 2016
Video is already given, please check at the end of the Article.
Aug 14, 2016
can i use the coil of 5 cm diameter
Aug 22, 2016
No of Turns and diameter are important in the coil, so use it as suggested in the article.
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
Sep 12, 2016
i need detail about this project
Sep 29, 2016
what is the Detecting distance ?
and if i want to increase it , what I can do.
Oct 05, 2016
the speaker doesnt make any sound what wud be the problem pls help urgent
Oct 06, 2016
Use the coil as mentioned.
Oct 15, 2016
is it 150 turns or 170? wat xactly?
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
Nov 01, 2016
I WANT TO MAKE METAL DETECTOR WHICH DETECT METAL FOR 10 FEET DOWN THE EARTH PLZ HELP ME
Nov 16, 2016
Thanks
Nov 28, 2016
What is the function of 10 micro farad capacitor here...??
Dec 03, 2016
I m doing this project in my collage
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...
Dec 31, 2016
Yes @hossameddeen, please share the results of you findings when you are done :)
Jan 05, 2017
I used all the above components but the circuit is not working.
Jan 17, 2017
can it detect all types of metal or only iron metal?? plz tell...
Feb 07, 2017
Why there is a continuous sound occuring.can i know the reason
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.
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.
Feb 26, 2017
Can anyone tell me how much does each components cost?
Apr 25, 2017
Whats are the voltage of capacitor
May 21, 2017
I can't find inductance in my country
My country stops import it
What should I do?
Jul 07, 2017
You can build it easily using copper wire.
May 24, 2017
I am a hobbyist of metal detecting.
Can this metal detector circuit detect all kinds of metal?
There might be large functional difference.
http://www.kingdetector.com/md6200-professional-underground-gold-searching-metal-detector-p-73.html
Jul 26, 2017
Hallo friend i like to learn this metal please send me all project until final thanks
Sep 26, 2017
Could we replace the speaker with and LED instead?
Oct 06, 2017
C
an we just use the normal copper wire..?
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???
Dec 08, 2017
What is the use of the 10 micro farad capacitor?
Dec 11, 2017
what is the purpose of the 10uF capacitor in the circuit
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
Dec 17, 2017
Thank you....bro
it has done
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?
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.
Apr 05, 2018
How thick should be the copper wire
Jun 27, 2018
I want advantages of this project