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[Reply #15 on:]

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??

[Reply #16 on:]

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

[Reply #17 on:]

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,
http://arduino.cc/en/Reference/analogRead

[Reply #18 on:]

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.