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Metal detector circuit help.

Shyamal796

Mar 19, 2012
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I am trying to make metal detector circuit. Here used 555 timer ic which diagram i found one website. as circuit diagram i connect all component but raise alarm all time. But why without metal, inductance is produced frequency?
 

shrtrnd

Jan 15, 2010
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Is your sensing coil near something metal while you're testing this?
 

shrtrnd

Jan 15, 2010
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I know you probably already did, but recheck your wiring. Do not assume something
is right, seriously look at the circuit again one more time. Often I find I made a simple
wiring mistake and then ignored it while troubleshooting because I dismissed it from
my mind. Do you have the correct capacitance for your capacitors ufd and not pfd,
Is is possible you damaged your LM555, and are now just assuming it is ok when it might not be.
Try not to get frustrated, and take some time to recheck everything carefully one more time.
 

twister

Feb 12, 2012
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Feb 12, 2012
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That circuit is supposed to make noise all the time. When you move the coil close to metal you should hear a change in frequency. A larger diameter coil should be more sensitive.
 

Raven Luni

Oct 15, 2011
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I was actually going to experiment with making one of those tonight. It's been years since I read this stuff but a friend has use for one so I'll need to quickly brush up but if I remember what you're actually picking up is a disturbance in the electric field (not the magnetic field) of an inductor caused by motion relative to a piece of metal which can be either ferromagnetic (iron etc) or paramagnetic (copper, aluminium etc).

Anyway, you'd probably start with an AC voltage at an audible frequency giving you a continuous tone which wobbles when you pass over something that disturbs the field (this is what you listen for, not the tone itself).

So when you say 'raising the alarm' do you mean the continuous tone?
 

twister

Feb 12, 2012
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I have heard of people making a huge coil, and then they tow it behind a ATV, and they use it to find meteors. I guess they are worth a lot of money.
 

davenn

Moderator
Sep 5, 2009
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That circuit is supposed to make noise all the time. When you move the coil close to metal you should hear a change in frequency. A larger diameter coil should be more sensitive.

Yup, exactly

So to the OP, Were you hearing a continuous tone from the speaker, that changed in frequency (pitch) when some metal was brought near the coil ??

Dave
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
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A larger diameter coil should be more sensitive.

It depends what you mean by sensitive.

From memory, a larger coil will detect larger pieces of metal at longer distances, but may be less affected by small pieces of metal close to it. Conversely, a smaller coil will be sensitive to small pieces of metal close up, but insensitive to relatively large pieces further away.

Most people are after sensitivity to small items further away
 
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