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Simple metal detector

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The other day when I was searching instructables I come across on interesting and simple circuit for metal detector. It is build with 555 coil and few other components. Instructable that inspire me to do this project was this one. Main debate was: does it really work? After quick research I found this video that proof it works. That was the time when I decided to make my own metal detector.

I do believe, that before you start working on metal detector you should read more about metal detectors and how they work.

I am not hold responsible for any damage that occurred during reproduction.
 
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Step 1: Parts and materials

Picture of Parts and materials
Parts:
- 555
- 47 kΩ resistor
- two 2μ2 F capacitor
- PCB
- 9 V battery, switch, battery cable and some wires
- buzzer
- 100 m of copper wire, 0,2 mm in diameter
- gaffer tape and wood glue

Instead of buzzer you can use 10 μF capacitor and speaker (8 Ω impendence).

Tools:
- breadboard and wires
- pliers, tweezers, pliers for making holes
- soldering iron and soldering wire
- sharp knife, ruler, pencil and pair of compasses
- hot glue

Step 2: Schematics

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The idea is not mine. I found schematic on this page (there is also other 499 projects with 555). I only added switch beetwen battery and circuit and instead of speaker I am using a buzzer.

Step 3: Coil

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The most difficult part is making coil. In great help was web calculators for air coils. With them, I calculated that with coil 90 mm width I need about 250 windings and with diameter 70 mm 290 windings that inductance can be 10 mH. You can also buy already made coils online.

I made coils core from cardboard. Coil is made from lacquered copper wire which is 0,2 mm in diameter. I did 260 turns. Before soldering, you must clean up both ends of coil. You can do that with help of sandpaper.

Step 4: Testing

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I made circuit on breadboard because I didn’t want when PCB would be finished it wouldn’t work. You can see test in video bellow.
vidhya_rvkmr2 months ago

thnk u it was vry useful for us as v r doing this project.i have 2 questions.will the buzzer be continuously giving sound or only wen it is brought near the metal???can u list the things which this metal detector works???reply me fast!!!!

vonPongrac (author)  vidhya_rvkmr2 days ago

It will buzz all the time. Sound frequency should change when coil will be near metal object.
I tested it with nails, some tools that where on my bench, bike frame, on some metal shelfs. In terms of materials, it works best with steel.

ashnernovilla2 months ago

Sir can I ask why is the buzzer continuously giving sound even if the metal is away from it? I just want to confirm it thank you

vonPongrac (author)  ashnernovilla2 days ago

It should buzz. When coil is near metal (or even strong magnetic field) sound should change.

hii sir... i used a 10mH inductor instead of the coil...i am getting a continuous buzzer sound as soon as giving a supply of 9v...why is it happening?plz can you reply me fast...i need it for my school project?

vonPongrac (author)  sri charitha2 days ago

It should give continuous sound. When coil is near metal object, sound frequency changes.

jahanzeb2001 month ago

sir, what type of gauge wire you used in this metal detector project?

vonPongrac (author)  jahanzeb2002 days ago

I belive it is 23 or 24 (0,25 mm^2). You can use anyone you like or have. Just be sure to use online calculator since number of turns will change.

jhunix031 month ago

can it detect gold?how man inches it could detect something pls anwer fast thanks!

vonPongrac (author)  jhunix032 days ago

It does not go deep, maybe inch (2 cm). I did not tested it for gold but in theory in best case it should detect gold very porly, since gold is very good conductor. But I doubt it (performance is so bad)!

Steph J1 month ago

Hi Mr vonPongrac . I like your project. Can u tell me how to do the coil in details pls? sorry I can't understand. and if we buy the 10mH inductor, is it need to put underneath the two cardboard? thank u so much.

vonPongrac (author)  Steph J2 days ago

In my case cardboard is only a bracket to mount coil on it. And it looks good. You can use 10 mH inductor as it is.

lorgenson7 days ago

i realy like it

vonPongrac (author)  lorgenson2 days ago

Thanks!

I like this project very much. I have to try it in my home next week. Thanks for sharing. Earlier, I have already done this project using another circuit diagram. If anybody interested, try Metal Detector Project Circuit.

Prabhu93 months ago

I like the way it's made, but where did you connect the wires from the coil to?

vonPongrac (author)  Prabhu93 months ago

In Step 3 (Coil) you can see that there are some scrap wires connected to the copper wires. Then in Step 5 you can see that those scrap wires are connected to the circuit. In Step 2 you can see where you connect coil into circuit (uper left element).

rimar20006 months ago
Thanks for sharing.

I have a question maybe you can answer: what impact does the captor coil diameter on detector performance? More sensitivity? More insight? None?
vonPongrac (author)  rimar20006 months ago
Capacitor and coil creates oscilator. Both values (capacitance and inductance) impact to the frequency. So if those coils have different diameter and the same inductance, I do belive that there will be no difference in performance. But you must know that with certain diameter coil's magnetic field will be very week and it won't work propperly. You can make difference with magnetic core. I do belive that coil with magnetic core can be smaller for same results and detector can even perform better. The only thing that you get from smaller diameter is more insight, but it is not very significant.

Let me remind you that this circuit is not for any serious work. It is good for finding nails and other metal object if you drop them. But for nothing else.
What about,detecting No ferrous metals, as cupper
vonPongrac (author)  Dardaro3 months ago
I tried it out, but it doesnt seem to work.
Thanks for your reponse, I will take it in account.
YipAvenger3 months ago
How do you arrange the wires?
sonkaraman5 months ago
can u please provide a simplified circuit diagram the ones available on the internet does not work
vonPongrac (author)  sonkaraman5 months ago
There is no other schematic. The one I posted in Step 2 work just fine.
ok so do we have to connect pin 5 to anything?? and what about pin 7??
vonPongrac (author)  sonkaraman5 months ago
Pin 5 is NC (not connected). Pin 7 also is NC. As in schematic. You can also try circuit from two comments above. I did try it but it did not work. Try it and please let me know if it works.
mohitey0075 months ago
Can u check this circuit on link http://www.555-timer-circuits.com/metal-detector.html
vonPongrac (author)  mohitey0075 months ago
I actually test that one out. Frequency did not change a bit... Maybe I did something wrong. You can test it by yourself and then report to me with the results.
jwoo20235 months ago
is the width 9 cm? it doesnt look like it in the photo.
vonPongrac (author)  jwoo20235 months ago
Whole inductor is 10 cm width (0.5 cm edge so coil do not fall down from core). Why do you think it is not 10 cm in diameter?
flex75 months ago
I don't have no shop to buy the parts from.Is it possible to get them from old computer parts?
vonPongrac (author)  flex75 months ago
I doubt it you'll find 555 in there. Maybe in old TV's or media equiptment.
mohitey0076 months ago
Mr. vonProngrac, i really appreciate your work, my issue is 10mh inductor and m not getting it. Though i got a coil of about 100m and wounded on a circular cardboard having diameter about 8 & a half centimeter. Will it work? When i searched for the 10mh inductor in my near by electronics store, i got a green resistor type inductor, i doubt it wont work coz it may not be an air cored inductor! Please help on this issue Mr. vonPongrac!
vonPongrac (author)  mohitey0075 months ago
I think inductor that you bought in local shop will work just fine, as long as it is 10 mH (mili, not micro). As your air coil, I think it inductance is to big, but will also perform well (indctance of my coil is around 12 mH and it got around 60 m of wire). Let me remaind you that number of turns is important when calculating inductance and not the lenght of wire you used to make coil. Try using air coil calculator from Step 3.
alright then will do as u say, but what if the inductance is not exactly same as 10mh? Will it work even?
vonPongrac (author)  mohitey0075 months ago
As I said in one of the previous comment, inductor and capacitor forms oscillator. If you change one of the values, frequency of oscillator will change. If there is a big change of one of the values, oscillators frequency can go beyond or bellow frequency that you can hear. Read more here.

In my case, inductance is around 12 mH and it still works fine. From this I can tell, that it would work fine, as long inductance is +/- 2 mH. If you were counting number of turns, you can calculate inductance of your air coil.

I did some calculations. With 100 m of wire and coil 8,5 cm in diameter, you get around 375 turns and 28 mH. But I can be wrong.
alyanelc6 months ago
how much sensation is it
vonPongrac (author)  alyanelc6 months ago
I belive you are asking about sensitivity. It is not great. It does not detect object like nails, nuts, washer... You should use inductor with magnetic core and not air coil for greatter sensitivity (like one in the video shown in Intro). This thing is a toy, nothing more.
diamondmine6 months ago
Where do I get copper wire that small? Any suggestions ?
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