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Offline golddustcarlTopic starter
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« on: July 07, 2017, 02:11:55 am »
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I am working on a PI detector project with a lot of whistles and bells. It uses 3 microcontrollers. There are a couple of ways to transmit the pulse into the ground, but I haven't fully decide which way to go. If I decide to use the standard resistor damped coil mehod, I would like your opinion on what the delay pulse parameters should be. I have coded my pulse generator with a variable width, variable delay positive pulse. The preliminary delay range is 4-50 uS, and the width from 10-100 uS.  Does this sound right, or should I  change it?
All of the circuits are completed, microcontrollers coded. Have some new outside of the box things I want to test, So I have been building it one section at a time, fussing over it until I can't  improve or add another feature. Just a labor love I guess.

Dusty Carl

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Offline GoldDigger1950
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« Reply #1 on: July 07, 2017, 04:57:49 am »
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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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It's all about that moment when metal that hasn't seen the light of day for generations frees itself from the soil and presents itself to me.
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« Reply #2 on: July 07, 2017, 06:12:13 am »
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Cool Beans.  I'll be watching for this one   Another variable you may want to play with is Coil On Time.  Controlling how much energy you have stored in your coil will determine how long your fly back is  going to take to zero.  Some targets like Gold, Silver (Low Magnetic Conductance) respond with Eddy Currents be it short with just a Tickling  or Ping of EMF .  Putting the Target into Saturation is really not required.  One of the few times more power is not all ways a good thing.  LOL

Just a Idle Mine at Work.  LOL



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Offline golddustcarlTopic starter
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« Reply #3 on: July 07, 2017, 09:42:43 am »
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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.  Grin

Dusty Carl

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« Reply #4 on: July 07, 2017, 12:09:00 pm »
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  Hair ?   Gave into that battle long ago.   Cheesy

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Offline golddustcarlTopic starter
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« Reply #5 on: July 07, 2017, 01:18:42 pm »
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Hair today, Gone tomorrow. Cheesy

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« Reply #6 on: July 07, 2017, 05:39:32 pm »
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Congratulations.
i hope you end up with a GOOD detector.
i wish i could help  Sad

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« Reply #7 on: July 07, 2017, 06:08:49 pm »
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That sounds like a neat project. What are you using for processors?

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« Reply #8 on: July 07, 2017, 06:20:24 pm »
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It's Sure not a Arduino !  LOL

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« Reply #9 on: July 07, 2017, 09:02:27 pm »
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wow....interested in metal detector, too. Cheesy

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« Last Edit: July 07, 2017, 09:23:46 pm by nickel_n »
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