Design of BFO metal detectors

[Tepco]

To be bit off-topic here: Not exactly BFO, this one is PLL, from old Signetics data book, circa 1974, 565 chip is now obsolete, interesting just for historical reasons. Version of it was presented earlier, among old forum look MD schematics, this one is original. Just stumbled upon it in archive.

[Qiaozhi]

To be bit off-topic here: Not exactly BFO, this one is PLL, from old Signetics data book, circa 1974, 565 chip is now obsolete, interesting just for historical reasons. Version of it was presented earlier, among old forum look MD schematics, this one is original. Just stumbled upon it in archive.

There have been a number of variations of this idea presented over the years. For example, there is one in the Geotech Projects section by Kamil Kraus ->
http://www.geotech1.com/cgi-bin/page...raus/index.dat
He quotes a detection depth of 75cm, but this is completely wrong. The actual depth is more like 75mm.
The sensitivity using this technique is very poor.

[mikebg]

Can you start to move forward onto the schematics, and leave block diagrams behind?
Otherwise you'll always be getting ready to get ready, and never build anything to prove/disprove the theory.

Unfortunately the CONVOLUTION of target's impulse response with impulse responses of ground is not a theory. The process happens because the target is buried. The energy travels through ground, that means the ground excites target. The target signal travels through ground, that means the ground excites RX coil. I illustrated this with Newton's cradle not for joke. It can be illustrated also with white coin and yellow coin in a glass red wine. When a designer starts to design something called "ground balance", he must know convolution process. No need of knowledge only when he makes patent pending for ground balance; the patent experts are enough incompetent. Fortunately the use of DECONVOLUTION software in metal detectors can not be patented.

The extremely low modulation index of target signal when Monocoil search head is used, also is not a theory to prove/disprove The advantage of induction balance is used in 19th century, 20th century, and even in the second decade of 21st.

What is carrier wave for target signal also is not a theory. The carrier wave exists in the output of preamp when there is no target. However designers of metal detectors don't know this "theory". They connect the RX with a wire to TX and think that the voltage across TX coil is suitable phase reference for synchronous demodulation. This nonwireless RX works at air test, but what happens when the target is buried in "bad" ground?.

Barkhausen's criterium for oscillation also is not a theory for provement. This is a easy rule for design because is created in Frequency Domain. Above is given the block diagram of equipment for "provement and disprovement" of "theory of convolution". This is just a sensitive audio amplifier with tone control (phase shifter). The regenerative principle is used with audio chip LM386 in projects of Leslie Huggard and rev. Thomas Scarborough, but without phase control. I know why phase control is not used, but already promised not to use the word "incompetent" in the forum.

[Qiaozhi]

Unfortunately the CONVOLUTION of target's impulse response with impulse responses of ground is not a theory. The process happens because the target is buried. The energy travels through ground, that means the ground excites target. The target signal travels through ground, that means the ground excites RX coil. I illustrated this with Newton's cradle not for joke. It can be illustrated also with white coin and yellow coin in a glass red wine. When a designer starts to design something called "ground balance", he must know convolution process. No need of knowledge only when he makes patent pending for ground balance; the patent experts are enough incompetent. Fortunately the use of DECONVOLUTION software in metal detectors can not be patented.

The extremely low modulation index of target signal when Monocoil search head is used, also is not a theory to prove/disprove The advantage of induction balance is used in 19th century, 20th century, and even in the second decade of 21st.

By using the word "theory", I was not meaning that the process of convolution and deconvolution needs to be proved in practice. This is already very well defined in the scientific and engineering literature. I was referring to your "theoretical" block diagrams. Unless these block diagrams are translated into real working circuits, they will continue to remain "theoretical".
If your intention is to "teach" metal detector designers how to do their job properly, then you must go the whole hog and actually build something. Otherwise you will eventually become known as Vapourware Mike (or Vaporware Mike, if you live in the U.S.A.).
I'm waiting with antici .......... pation.

The regenerative principle is used with audio chip LM386 in projects of Leslie Huggard and rev. Thomas Scarborough, but without phase control. I know why phase control is not used, but already promised not to use the word "incompetent" in the forum.

As a starting point you could modify one of Thomas Scarborough's simple circuits to prove that your block diagrams have some basis in reality.
At least you've stopped using "that word". However, you cannot continue to claim that metal detector designers have been getting it wrong all these years, without taking the next step.

[Paul99]

Can you start to move forward onto the schematics, and leave block diagrams behind?
Otherwise you'll always be getting ready to get ready, and never build anything to prove/disprove the theory.

Above is given the block diagram of equipment for "provement and disprovement" of "theory of convolution".

Mikebg, do you have the resources where you are to put your theories into practice (build a detector)?

Are the components you need available to you?

[Aziz]

*LOL* Betonköpfe asking for practical schematics? *LOL*

Look at the Laptop project Betonköpfe. You can do the convolution and deconvolution with it. And even the FFT method.
BTW, the FFT method is also a convoluted method. But don't ask me, what is multiplied with the series of samples (maybe the sin and cos(2*pi*f*n)? LOL)

Aziz,
convoluted heavily

[Qiaozhi]

*LOL* Betonköpfe asking for practical schematics? *LOL*

The "concrete heads" are not asking for schematics. We're waiting for practical results from testing in the real world.
Even your laptop-based metal detector design has been going on for several years now without any resolution. Admittedly you've actually built stuff, but it never seems to get beyond the pre-prototype stage.

If you make claims, which imply that metal detector companies have been designing circuits incorrectly and are using the wrong technical terms, etc., then you must be prepared to prove it with real circuits, not just block diagrams, polar charts, SPICE simulations, and lots of rhetoric.

We're all waiting ...

[Davor]

George, please don't fraternise with the well known trolls

Mike's posts do have merit, and you know very well that only a few good ideas ever bear hardware fruits.

The best part of this forum is that people of various walks of life and practice meet here and exchange ideas. All in purpose of our common hobby, and no commercial pressure.

[Qiaozhi]

George, please don't fraternise with the well known trolls

Mike's posts do have merit, and you know very well that only a few good ideas ever bear hardware fruits.

The best part of this forum is that people of various walks of life and practice meet here and exchange ideas. All in purpose of our common hobby, and no commercial pressure.

I'm not trying to discourage either Mike or Aziz from coming up with new ideas (far from it!), but simply prod them into obtaining some real world results to back up their theories. Mike (for example) has been promoting these same ideas for several years now, and the constant repetition is starting to make them sound like a proven fact, which they are not.

In your own case, I am pleased to see that your intention is to actually prove your new ideas with real hardware. Maybe you can encourage these two guys to do the same, as I appear to be failing in my quest.

[kt315]

Mikebg, do you have the resources where you are to put your theories into practice (build a detector)?

Are the components you need available to you?

Mike collects some kinda 'theory on metaldetecting' for his future book. This is why he is here. He will not give you practice schematics, do not wait this. If you can help him with theory - so help.

[Aziz]

I'm not trying to discourage either Mike or Aziz from coming up with new ideas (far from it!), but simply prod them into obtaining some real world results to back up their theories. Mike (for example) has been promoting these same ideas for several years now, and the constant repetition is starting to make them sound like a proven fact, which they are not.

In your own case, I am pleased to see that your intention is to actually prove your new ideas with real hardware. Maybe you can encourage these two guys to do the same, as I appear to be failing in my quest.

I think, I have provided enough interesting ideas and schematics.

(And I have the madman bonus too.)

Ok, I didn't provide the community with the software solutions. (Although I'm a software enginneer.)
Holly ******* hell!, do you want the "total thermo nuclear meltdown" in the metal detecting industry?
Red button?
Red button?
Red button?


Aziz