complete project

[Tinkerer]

Yeah, I know, and I might have something up my sleeve, but it is not nearly ripe yet, and it may end up as complete waste of time.
There is so much energy in there that goes wasted. Actually, prior to your posts I was wandering how come that no one did not notice rising current consumption and concluded that I must be reasoning wrong. Now I know better. Thanks.

We need to give Aziz some credit here. He spent a considerable amount of time trying to get somebody to come up with some numbers on the difference in current consumption caused by aggressive ground.
The problem is, that this information takes some work to get. I just happened to have the circuit hooked up the right way to take the approximate measurement.

Tinkerer

[Tinkerer]

Hi Tinkerer,
Two of my batteries would give a 14Volt supply.
600mAh would make the batteries last almost as long as they do in a Minelab.
The peak switch on i would be much larger than this and I understand the TEM front-end to be only marginally damped and thus oscillatory, is this so? I can see that if it is then we get much more bang from our 8 watts than is first obvious.

I also think a non-motion detector would work extra well in these areas especially when one considers that the whole rim of a mono coil is "hot", not having to keep that in relative motion while poking into and between scrub, would no doubt illuminate targets way off to the side and under the tussocks themselves.

Perhaps, there is a way that both motion an non-motion can be realised in software, it may be as simple as time dependent clearing, or not clearing of some registers?

I need to spend some time searching here and reading up on the development of the TEM TX so that I can understand what is happening.

Regards
Kev.

Hi Kev,

OK for the 14V battery supply. We will work with that. (11 to 14V)

My underwater PI of 25 years ago was a non motion design. I can use that as a reference and improve it.

There is a lot that can be done with software. If somebody would like to contribute the that end, I would be glad to work together on it.

ML detectors use very high gain. This makes them sensitive, but also enhances EF and EMI problems.

The TEM TX method is about 10 times as efficient in power use. So you ask yourself, why does the TINKERERS TEM detector use just as much power?

I make good use of the power by making a very powerful TX pulse. This TX pulse is not damped at all. Rather, I use a capacitor instead of the damping resistor. This capacitor absorbs the Flyback and adds it to the coil pulse current. You could compare it to a voltage doubler, except that it doubles the current instead.

Not only is the current doubled, the current is also re conducted to the battery, or the TX capacitor bank, so the consumption is only the Ohmic loss of the Mosfet and coil.

This can be compared to a resonant circuit, although only the pulse is resonant.

So? How come it does not oscillate?

It is possible to avoid oscillations by bleeding the Flyback power in a damping resistor.

It is also possible to avoid the oscillations by adding more current to the current reversal, just the opposite of the bleeding.

For this purpose I use the current that I send back to the battery.

There is much more to it, I really need to make a full explanation of the TINKERERS TEM DETECTOR METHOD, but I will do that once we have the FULL OPEN SOURCE DESIGN ready to be released.

In the meantime, you might look at Aziz's full TEM TX analysis and explanation, given in scientific engineering terms, some 2 years or so ago.

With this very strong pulse I get a stronger signal response, that needs less amplifying. With less signal amplification, the EF and EMI noise is also less amplified.

Tinkerer

[Kev]

Hi Tinkerer,
This is all sounding very good, and being public, I'd be able to build units for other people such as Rob, whose been looking for such a device for years. I will dig up that thread of Aziz's and study it.

I didn't answer your question about rubbish yesterday. There is a strange situation where you can dig 9 bits of rubbish, mainly rusted iron, to 1 bit of gold, these are areas where the Old Boys have been working the gold, and then patches off to the side that the Old Boys have missed will be 9 pieces of gold to one piece of rubbish, usually more modern such as spent ammunition, i.e. non-ferrous. So the ability to notch out iron would be a boon especially when the target is in water, and so much harder to retrieve.

The iron rubbish can be very small so coil i measurements would be useless as a disc solution I believe, especially with ground variations having similar effects.
In fact much of the gold is small, I attach an image of such, the coin is about 23mm across. 2 of the pieces are 0.07 grams, or 1 grain (480 per ozt). All these were detected with the Minelab GPX-4500 between 2 and 12 inches with a 14 x 9 inch elliptical mono coil.

The ultimate would be a machine having software control of the pulse and sample timings so that either large or small gold could be targeted, in fact my dream has been for a machine that automatically cycles through a couple of sequences tailored for both large and small gold. I've tried this on a std PI before and it sadly generated a lot of noise, noise that I believe SETA was developed by Minelab to overcome. They now have the ability to have a full spectrum of timings cycling, but have perhaps held off releasing it.

How sensitive do you feel the TEM can be made, is it perhaps only effective with coin sized targets and above? Is an earlier sample required to detect small targets as in conventional designs?

I know you're using Paul's UniPI, and I've been playing with a PIC24H DSP which is similar, and he's provided some of the source, so I'm sure we can collaborate sufficiently to get some code working.

The fly in the ointment for me at present is the disorder of my house and equipment, and in a couple of months I'll need to move everything out of my house into a shipping container while some walls and ceilings are rebuild.

Kind regards
Kev.

[Tinkerer]

Hi Tinkerer,
This is all sounding very good, and being public, I'd be able to build units for other people such as Rob, whose been looking for such a device for years. I will dig up that thread of Aziz's and study it.

I didn't answer your question about rubbish yesterday. There is a strange situation where you can dig 9 bits of rubbish, mainly rusted iron, to 1 bit of gold, these are areas where the Old Boys have been working the gold, and then patches off to the side that the Old Boys have missed will be 9 pieces of gold to one piece of rubbish, usually more modern such as spent ammunition, i.e. non-ferrous. So the ability to notch out iron would be a boon especially when the target is in water, and so much harder to retrieve.

The iron rubbish can be very small so coil i measurements would be useless as a disc solution I believe, especially with ground variations having similar effects.
In fact much of the gold is small, I attach an image of such, the coin is about 23mm across. 2 of the pieces are 0.07 grams, or 1 grain (480 per ozt). All these were detected with the Minelab GPX-4500 between 2 and 12 inches with a 14 x 9 inch elliptical mono coil.

The ultimate would be a machine having software control of the pulse and sample timings so that either large or small gold could be targeted, in fact my dream has been for a machine that automatically cycles through a couple of sequences tailored for both large and small gold. I've tried this on a std PI before and it sadly generated a lot of noise, noise that I believe SETA was developed by Minelab to overcome. They now have the ability to have a full spectrum of timings cycling, but have perhaps held off releasing it.

How sensitive do you feel the TEM can be made, is it perhaps only effective with coin sized targets and above? Is an earlier sample required to detect small targets as in conventional designs?

I know you're using Paul's UniPI, and I've been playing with a PIC24H DSP which is similar, and he's provided some of the source, so I'm sure we can collaborate sufficiently to get some code working.

The fly in the ointment for me at present is the disorder of my house and equipment, and in a couple of months I'll need to move everything out of my house into a shipping container while some walls and ceilings are rebuild.

Kind regards
Kev.

Hi Kev,

At present I have no solution for lead, brass or other non magnetic metals. They will show up the same like gold.
These nuggets in your picture are very small nuggets. I have not made any tests for such small targets yet. Rather, I have been working with large coils for deep RELATIVELY small targets. Like 1cm targets with a 1m coil. For this purpose I also use 24 to 30V TX to get sufficient magnetic field density.

I will build a smaller coil and make tests with very small targets, while keeping the TX voltage at 11 to 14V.

I would rather keep the PPS at 5000 to get good S/N. Therefore it is the TX voltage that is the limiting power factor, but we will still get 8 or 9A peak coil current.
Normally I take the first sample at 3 to 5us after switch OFF, when the target response peaks.
The timings for the first and second sample need to very precise for the Iron discrimination.
Software is the key.

Tinkerer

[Kev]

Hi Tinkerer,
The info on the small nuggets was just for reference, many of the small surface stuff like this has already gone, and what is left are targets just out of range, some the size of the coin are detectable up to about 40 cms with a 45cm mono coil, but I know there are many similar pieces much deeper.

I want to keep my cake and eat it also, like Elijah's bottomless oil and flour jars. Being able to detect the smaller stuff helps to locate patches and dabs of nuggets in the first instance. To then be able to clean up the small and deep larger bits is the ideal. Also in searching for float as Rob mentioned you need a pretty sensitive machine, sometimes a number of ounces can be found in one go, incognito, disseminated within large lumps of lode and reef material.

Perhaps for sensitivity when targeting smaller pieces the PRR could be increased above 5000, and pulse width reduced keeping the power output constant but concentrated within the surface zone.

Cheers
Kev.

[Tinkerer]

Hi Tinkerer,
The info on the small nuggets was just for reference, many of the small surface stuff like this has already gone, and what is left are targets just out of range, some the size of the coin are detectable up to about 40 cms with a 45cm mono coil, but I know there are many similar pieces much deeper.

I want to keep my cake and eat it also, like Elijah's bottomless oil and flour jars. Being able to detect the smaller stuff helps to locate patches and dabs of nuggets in the first instance. To then be able to clean up the small and deep larger bits is the ideal. Also in searching for float as Rob mentioned you need a pretty sensitive machine, sometimes a number of ounces can be found in one go, incognito, disseminated within large lumps of lode and reef material.

Perhaps for sensitivity when targeting smaller pieces the PRR could be increased above 5000, and pulse width reduced keeping the power output constant but concentrated within the surface zone.

Cheers
Kev.

Hi Kev,

with an integrator, like we use in the PI detectors, an increase in the pulse repetition rate also produces an increase in signal gain. Increasing the PPR to 10,000 or even 20,000 is no problem at all.

However, with the same coil size, reducing the TX pulse width by half, also reduces the magnetic field density by half. This is not good for small targets. The most important thing for generating a good response from very small targets, is high magnetic field density.

To maintain the same field density, we would need to increase the TX voltage. We could do this by adding a boost battery voltage regulator. This also has the advantage of making the TX power regulated and therefore equal from beginning to end of a battery charge.

There are many things that can be done to increase sensitivity and depth, but every added feature adds to the complexity and cost.

On a different subject: The audio. Could you describe the audio features that you would like?

Tinkerer

[Carl-NC]

However, with the same coil size, reducing the TX pulse width by half, also reduces the magnetic field density by half. This is not good for small targets. The most important thing for generating a good response from very small targets, is high magnetic field density.

Depends on where you are at on the charging curve. Also, lowering the TX peak current can make the recovery faster, allowing you to sample sooner. So there may be a net benefit to pulse width reduction for detecting tiny shallow nuggets. Eric's GoldQuest has a PPR of 10kHz, not sure about the pulse width but it would have to be 50us or less.

- Carl

[Tinkerer]

Depends on where you are at on the charging curve. Also, lowering the TX peak current can make the recovery faster, allowing you to sample sooner. So there may be a net benefit to pulse width reduction for detecting tiny shallow nuggets. Eric's GoldQuest has a PPR of 10kHz, not sure about the pulse width but it would have to be 50us or less.

- Carl

Hi Carl,

very few things have not been tried before. In this case, I believe that Eric Foster experimented with something similar, using SCR's. What may not have working too well, with SCR's, seems to work fine with modern Mosfets.

I am sampling at the peak target response, not the weak remnants of a signal after some delay. However, I totally agree, that there are many factors involved and that it is always a compromise between all of these factors that gives the best result.

Being weak in Mathematics, it seems that I can only find this compromise, or sweet spot by experimenting. Ahh, there are so many possible variations, it just takes a lot of tinkering.

Fixing some of the variables reduces the amount of possible variations. But, which variable should I fix?

Coil diameter? Inductance?

Power? Tx voltage? TX charge time?

PPR?

Sample width?

Pre-amp supply to get good headroom?

To name just a few. Any change in any one of these factors changes the sweet spot to a different place.

I use a near linear charge curve, by the way.

Tinkerer

[Altra]

Tinkerer,

Interesting project you have here. One thing that dawned on me. When considering your PRR, lets say 10khz or 100us. There isn't much time to take a ground sample. For tiny targets, not a problem. But larger targets will start to null. Or maybe I don't understand the TEM ground balancing method? Using conventional gb methods you may have to stay
below 5khz or do some kind of burst mode of short pulses and balance it against a long off period?

Thanks

[Tinkerer]

Tinkerer,

Interesting project you have here. One thing that dawned on me. When considering your PRR, lets say 10khz or 100us. There isn't much time to take a ground sample. For tiny targets, not a problem. But larger targets will start to null. Or maybe I don't understand the TEM ground balancing method? Using conventional gb methods you may have to stay
below 5khz or do some kind of burst mode of short pulses and balance it against a long off period?

Thanks

Hi Altra,

Thanks for the feedback.

In some ways, the TINKERERS TEM method seems not much different from the traditional PI method. However, in fact there are many things very different, some more obvious than others.

For example: The cycle time. With a traditional PI, with 5000 PPS and 50us TX pulse, a 150us target will have decayed about 63% at the time of the beginning of the next cycle.

With the TINKERERS TEM, I use a forced decay (for want of a better name). It makes the target eddy current to decay about 5 times faster.
Therefore, with a 5 times faster cycle repetition rate I have about the same percentage of eddy current decay.

As far as the GB, I am still experimenting with different methods.

Tinkerer

[Altra]

Thanks for the explaination. Is there any technical papers or info on TEM?

Regards

[Tinkerer]

Thanks for the explaination. Is there any technical papers or info on TEM?

Regards

http://www.geotech1.com/forums/showp...&postcount=819

There are several posts there giving ample descriptions.

Attached is a pdf with a description of the TEM method used in Geophysics, with good graphs.

I have posted dozens of LTSpice simulations over the years, but they are scattered all over the forum.

All the best

Tinkerer

[Davor]

It will be nice to see how TEM works with log-weighted PI Rx. So far I simulated it only against Surf PI frontend.

[Kev]

Hi Tinkerer,
Nothing like an image or a schematic to get the theory across. Thank you.

I've been thinking about the audio and believe that the volume and frequency should increase relative to target strength. I don't think the clicking bone type is responsive enough, nor is the simple volume increase, but the two combined creates a strong impression.

I was looking at the raw Rx signal before filtering and was wondering what would happen if this was synchronously demodulated with a precision high speed PLL chip? The result maybe a very interesting decay curve which when sampled at 2 or 3 points could provide some extra information about the target. At least it should provide a consistent almost noise free signal.

I'm ashamed to say I've not built the 12V frontend you posted yet, and it's so simple too....next week I hope. I've got some PLL chips kicking around somewhere among my bits too. Tomorrow I'll have a hunt for some high voltage caps among my junk.

All the very best
Kev.

[Davor]

was wondering what would happen if this was synchronously demodulated with a precision high speed PLL chip?

I'm afraid you'll have a very steep learning curve about the PLL phase noise implications. It should do miracles on IB phase detection though.