Help on new detector design

If you have the equipment or can build one, use a gaussmeter to see how quickly your field collapses on a representative target. You can vary the time based on function. For example, an iron object will keep the eddy currents longer than a silver coin so optimum detection and delay will be determined by how long the magnetic field lasts.

Since silver and gold are not magnetic, they don't keep their field as long as ferrous does. You can build a gaussmeter and use a scope to see the field collapse quite easily. An op amp and a radial coil of almost any rating will help you. By coil, I mean a PCB type coiln, not a detector coil. I use my storage scope when designing and can see when the TX is switched off and monitor the decay. Timing will vary depending on how far your probe is from the target and the orientation. Edge on, flat and etc. This can help in determining the depth of detection.

In summary, the field collapse time along with your RX sensitivity are going to determine your delay time. It has very little to do with the type of material you are detecting, contrary to popular belief. Since every TX/RX relationship is markedly different, your answer is cloudy at best until you do some quantitative testing.

You're on to a good idea with 3 processors. I use two in my "on the drawing board" design. One for control/display and general timing and the other for target analysis. I look forward to hearing or reading about your project as you work through it.

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Thanks guys. Always appreciate info from you. Like your design GD, mine also puts all the human interfacing in one controller, but I have broken out all the pulse generation into a separate controller which is updated by serial info from the main controller. Timing is much more accurate plus I can do it on the fly with instant updates. I also put the processing of the received signal plus the variable multitone audio in to a third processor. By having the arranged this way, the timing is impeccable. It only has to do one thing. I control it with pushbuttons hooked to the main controller.
I do have a 200 mHz 1GSa/s DSO and can look at the  direct signal on the driver, but from what I get from your answer, is to also monitor the rf field. It seems that would reduce any loading and distortion of the signal. Will give it a try. I currently using a drive pulse of 250 uS @ 1kHz rep rate. A value I have used previously, as well as at 160Hz. Looking for more response on copper/silver range, and nickel/gold range, so I have built in a lower response to iron and aluminum in the third controller. Using a TID number system also in helping the op to make the call to dig or not dig. Like I said, a labor of love, and loss if hair. 

Dusty Carl

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A bad day at gold prospecting or metal detecting is better than a good day at work.

Hair today, Gone tomorrow.

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A bad day at gold prospecting or metal detecting is better than a good day at work.

That sounds like a neat project. What are you using for processors?

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wow....interested in metal detector, too.

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