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Topic: Keeping silverware out of the trash- metal detection style. sensors? EMF? WHAT? (Read 7666 times) previous topic - next topic


For the circuit above, can anyone tell me what my sketch is going to look like? I don't have much experience with programming the arduino, so i'm not sure how to write it. But I think that silverware passing through would create it's own "signature" of code. I need a way for arduino to recognize that signature, so I can tell it to flash lights and sound a buzzer when it does recognize it. I think this one is probably best suited for my application, and easier to do for how much I know.

But I like the challenge of figuring out how to make this one work too:

I want to mess around with all the variables, to see what I can come up with. The battery voltage, size of the batteries in relation to current, a variable capacitor, and different sizes and configurations of coils. To me that just seems like a whole barrel of fun and learning! haha

Also, is it possible to do some kind of fancy PWM coding to generate a sine wave directly from the arduino??


Aha! I found another piece of information that will help with this:
The industry standard for flatware is: It has to contain at least 13% chromium, which is the coating material to protect against corrosion and pitting. Since eddy currents skim along the surface, i'm not looking for iron or stainless steel. I'm looking for a reaction with chromium. So I need to figure out what frequency is best to detect chromium....uhhhhh :~


Beside the chromium, there is about 50% iron.
And sometimes also nickel.
So you want to detect the iron.

Only cheap flatware is with a layer on the outside. But many flatware is a solid alloy of metals.
I think if iron is inside, it will be detected, no matter what is on the outside.

The first circuit requires an analog input. If the analog value changes, something passed the coil.
The Arduino uses a function to read the value of an analog input,


Using that second circuit, C1, IC1a, and the coil are forming an oscillator. When metal is brought near the oscillating coil, the amplitude will drop. That looks like a Pulse-Induction type which would not be able to distinguish between different types of materials.

Based on what I read here: http://www.hobby-hour.com/electronics/metal_detectors.php

What you want is the two-coil VLF type. Though it is more complex, it allows one to distinguish between different types of metals.


I know this is an old post, but I have a similar problem.

I wish to detect a metal (iron / steel) rod about 2 feet long by 2 inches in diameter. Dimensions are not exact but close here.

I wish to get some sort of gizmo, Arduino or not, to make this happen and at the greatest possible distance. The rod will be in the air, not buried.

I have looked into various high end metal detectors but they are very expensive.

Any help  is appreciated.


What is the application, how close will the bar be to the sensor, an inductive sensor may be what you need rather than a metal detector.


Tom... :)
Everything runs on smoke, let the smoke out, it stops running....



Thanks for getting back to me:

It needs to sense at a range of about 6 - 8 feet


It needs to sense at a range of about 6 - 8 feet
At the present state of the art you're being unrealistic, IMHO. Even hobbyist metal detectors only sense coins several inches away.  How would you discriminate between the target metal and the machine frame?

There are commercial sorters which use electromagnets but...$$$.



My question is a bit different than the OP: I am talking about a simple bar of steel, say hanging by a rope from a tree branch with no metal near by (just for argument's sake).  To be able to detect its presence / lack of presence is my goal. That is different from what the OP wrote but still has some basics in common I believe: Thus I asked my question on this thread.

Coding Badly

To be able to detect its presence / lack of presence is my goal.
Attach IR emitter(s) to metal bar.  Place IR receiver in the detection area.



What is the application, why do you need to detect if a bar is hanging 6 to 8 feet away.

A metal detector works by producing a magnetic field and sensing its distortion due to outside influences, it takes a lot of power to produce a mag field, and up to 2m away would require a huge coil and transmission current , plus sensitive detection circuitry.

Thanks.. Tom... :)
Everything runs on smoke, let the smoke out, it stops running....



Thank you for the reality check.

I will have to re-think this idea based on feed back here.

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