Building a Simple metal detector circuit

In summary, the author suggests building a circuit with a coil and a m/meter to measure the voltage drop when a steel pendulum is nearby. He also suggests building an RLC circuit in resonance and using the same logic only that the drop should change dramatically (what he needs!) with a slight change in impedance. Neither of these suggestions yielded a clear enough result. He also recommends using optical detection instead.
  • #1
pashnoy
2
0
Hi guys, I am new at this so sorry if i get the format wrong.

Im trying to build a basic metal detector that will respond when a steel pendulum passes nearby. A simple response is all that is needed right now.

I thought of this:
Building a RL circuit with a copper coil air core. placing a m/meter over the resistor and reading that its (the resistors) voltage drop should lower as the inductance of the coil changes with the pendulum passing near to it. (and the flux having a low impedance to pass through )

this didnt work well enough as the change over the resistor drop was minimal!
(the source was set at 10Vp-p and a high frequency)

I then thought to make an RLC circuit in resonance and using the same logic only that the drop should change dramatically (what i need!) with a slight change in impedance.
this too did not yield a clear enough result.

any tips for improving this design or a new simple design all together?
thanx
 
Engineering news on Phys.org
  • #2
A pretty sensitive metal detector topology is having two oscillators at around 250KHz. One oscillator is a reference oscillator and it's shielded. The other one is an LC oscillator like the Colpitts with the inductor being the main pick up coil used to detect metal.

When a metal is brought close, the LC oscillator will slightly change frequency. Then subtract the reference oscillator frequency from the LC oscillator frequency using a mixer. The difference will be in audio range which can be heard as a pitch or tone.
 
  • #3
I (sorta) invented a little metal detector -- more likely I stole most of it from some unspecified online source -- for my robots using a 5" diameter 40 turn coil that calcs out to being about 50uH. The coil makes an oscillator osculate and that is feed into a 4046 phase lock loop which tracks the slight changes in frequency caused by nearby metal thingies and puts out a voltage that changes with frequency:

http://www.etantdonnes.com/ROBOCAR/doc/hardware/RoboOther_sch.png" [Broken]

YMMV on sensitivity and such, but it's a place to start. I found that the 4046 is _extremely_ sensitive to supply voltage, so add a good regulator to the power -- the built-in Zener diode is just not up to the task when the supply is near the cutoff.
 
Last edited by a moderator:
  • #4
pashnoy said:
Hi guys, I am new at this so sorry if i get the format wrong.

Im trying to build a basic metal detector that will respond when a steel pendulum passes nearby. A simple response is all that is needed right now.

I thought of this:
Building a RL circuit with a copper coil air core. placing a m/meter over the resistor and reading that its (the resistors) voltage drop should lower as the inductance of the coil changes with the pendulum passing near to it. (and the flux having a low impedance to pass through )

this didnt work well enough as the change over the resistor drop was minimal!
(the source was set at 10Vp-p and a high frequency)

I then thought to make an RLC circuit in resonance and using the same logic only that the drop should change dramatically (what i need!) with a slight change in impedance.
this too did not yield a clear enough result.

any tips for improving this design or a new simple design all together?
thanx

Can you use optical detection instead?
 
  • #5
I am restained to using a copper wire coil in the detection of the metal
 
  • #6
if you're willing to use 1970-ish technology, try the circuit on page 68-69 of this old book (PDF page 70).
Back before microcomputers I built one and it worked as well as store bought detectors of the day.
http://bitsavers.trailing-edge.com/pdf/signetics/_dataBooks/1972_Signetics_PLL_Applications.pdf

the book is an excellent introduction to phase locked loops. I'd recommend you download and print a copy.

old jim
 

1. What materials do I need to build a simple metal detector circuit?

To build a simple metal detector circuit, you will need a breadboard, a 9-volt battery, a 555 timer IC, a resistor, a capacitor, a potentiometer, a buzzer, and a coil of wire.

2. How does a metal detector circuit work?

A metal detector circuit works by using an oscillator to generate an alternating current that passes through the coil of wire. When the current comes into contact with a metal object, it creates an electromagnetic field that is detected by the coil, causing the buzzer to sound.

3. Can I adjust the sensitivity of my metal detector circuit?

Yes, you can adjust the sensitivity of your metal detector circuit by using the potentiometer. Turning the potentiometer will change the resistance in the circuit, which affects the frequency of the oscillator and the sensitivity of the detector.

4. What types of metal can be detected with a simple metal detector circuit?

A simple metal detector circuit can detect a wide range of metals, including iron, copper, aluminum, gold, and silver. However, the sensitivity may vary depending on the size, shape, and composition of the metal object.

5. Are there any safety precautions I should take when building a metal detector circuit?

Yes, it is important to handle all electronic components with care and to disconnect the battery when not in use. Additionally, avoid using the metal detector near electronic devices or power lines, as this may interfere with the circuit's functionality.

Similar threads

Replies
7
Views
2K
Replies
16
Views
4K
Replies
10
Views
5K
  • Electrical Engineering
Replies
14
Views
740
Replies
2
Views
1K
  • Electrical Engineering
Replies
6
Views
1K
  • Electrical Engineering
Replies
33
Views
4K
  • Electrical Engineering
Replies
5
Views
1K
  • Electrical Engineering
Replies
20
Views
2K
Replies
1
Views
6K
Back
Top