Android Phone Based Metal Detector - FCMD

[ivconic]

AI usually hallucinates too much.
I'm afraid that those mathematical dubios will show badly in the real field.
...
Look at those "tax leeches" in Cern; they have been achieving incredible feats for decades...none of which have any useful application in life!
I have the perfect AI task; to create a mathematical model for LRL!

[Aziz]

Hi ivica,

AI usually hallucinates too much.
I'm afraid that those mathematical dubios will show badly in the real field.
...
Look at those "tax leeches" in Cern; they have been achieving incredible feats for decades...none of which have any useful application in life!
I have the perfect AI task; to create a mathematical model for LRL!

well, I don't think so. AI gives us indeed some good tips, which can be checked and peer-reviewed in real world.
I like the idea, where coefficients and parameters become all complex numbers. Or all the GB math doing it in the complex plane.
It's not complex doing complex math. It is even easier do the math in the complex plane.

[ivconic]

[ivconic]

https://www.geotech1.com/forums/foru...-digital-audio

[moodz]

OK its a bit bigger than a box of matches .. the surface mount unit would be smaller.

I added a 20x preamp prior to the ADC and the 10cm x 10cm foil is detecting at just over the meter in air.
The coil current is 1 amp peak to peak true biploar square wave with a fall/rise time of 3 microseconds.
The power consumption for the whole detector is just over 1 watt. ( ie less than 100 ma from 12 volts ).

The code does simultaneous PI and VLF demodulation.

It can be this small because the detector is a true software defined metal detector ( SDMD ) consisting of CPU, bipolar transmitter, preamp and power supply
... there are no switches, demods, integrators or damping resistors.



transmit voltage waveform

[moodz]

Might have nailed it ... found a new method based on very elegant maths that cancels ground (or anything really) whilst simultaneously boosting desired targets.
Below is the output from a python app that shows removal of a ground signal ( nasty ferrites ) whilst simultaneously boosting a wanted signal ( non ferrous ) in the time domain !
The pyhon app is taking a 5 second snap ( 250 samples ) from the STM32 ADC signal chain and doing a parallel execution of the method showing the complete elimination of the ferrite / ground signal but leaving the wanted signal boosted.

[moodz]

Just to prove I am not doing magic tricks like gating or something ... I bring the ferrite near the coil and keep it there ... then wave the target 3 times ... then remove the ferrite from the coil ... you can see this in the top trace. In the bottom trace the method removes the ferrite response leaving the target response ... Magic without tricks

[moodz]

here the ferrite is is held about 10 cm from the coil and the target is waved twice at 80 cm ( 10cm x 10cm foil ). ... very hard to pick the foil without the magic !

[Aziz]

Hi Paul,

Might have nailed it ... found a new method based on very elegant maths that cancels ground (or anything really) whilst simultaneously boosting desired targets.

This sounds good. We would be interested in the elegant math.
What are your K1 and K2 factors?
Aziz

[moodz]

Hi Paul,



This sounds good. We would be interested in the elegant math.
What are your K1 and K2 factors?
Aziz

They are in the patent but the maths is actually something else and hopefully sort of new though in maths nothing is really new. LOL
I will tell you when the patent goes in.

[JoyJo]

Since we've already started talking about «high materials», I'd like to ask how you can make an automatic adjustment of the vdi scale. It's the same as scale calibration using a ferrite target. During the search process, the scale calibration is knocked down due to a change in the residual imbalance of the search coil. This is due to the linear expansion of the epoxy resin and the change in the geometry of the th and px coils.

At the moment, I can imagine this scheme: the use of a calibration resistor. How it can work. At some point in time, a constant resistor is turned on instead of the TX coil. Because the resistor has only active resistance when it is turned on, you can measure the value of the current phase. This phase value is taken as a reference value.

After that, the TX coil is connected and the current phase is measured again, but already in a real circuit: including the actual state of the TX coil, taking into account the change in its geometry, inductance, and other parameters. After that, you can subtract the reference value from the actual value of the phase. Thus, we will find out how much the phase has shifted and will be able to compensate for it mathematically.

Similarly, with the RХ coil: it is possible to make a phase shift of the signal and carry out mathematical compensation.

Thus, it seems to me that it is possible to automatically compensate for the shift of the vdi scale (to carry out ferrite calibration). This is optimal, because the parameters of the TX and Rх coils of homemade sensors may be different.

But in branded metal detectors, I don't know how the calibration of the VDI scale takes place. It's implemented somehow programmatically. After all, branded coils are also influenced by physics and their parameters also change. After all, users of branded metal detectors know nothing about the ferrite calibration procedure and the shift of the VDI scale. They just change the search coils.

[Aziz]

They are in the patent but the maths is actually something else and hopefully sort of new though in maths nothing is really new. LOL
I will tell you when the patent goes in.

Nice. I am looking forward to see your fancy math.

BTW, make your sweep tests with ferrite (or hot rock) and gold together. Just imagine the gold is surrounded in a high mineralized pocket.
Aziz

[moodz]

Since we've already started talking about «high materials», I'd like to ask how you can make an automatic adjustment of the vdi scale. It's the same as scale calibration using a ferrite target. During the search process, the scale calibration is knocked down due to a change in the residual imbalance of the search coil. This is due to the linear expansion of the epoxy resin and the change in the geometry of the th and px coils.

At the moment, I can imagine this scheme: the use of a calibration resistor. How it can work. At some point in time, a constant resistor is turned on instead of the TX coil. Because the resistor has only active resistance when it is turned on, you can measure the value of the current phase. This phase value is taken as a reference value.

After that, the TX coil is connected and the current phase is measured again, but already in a real circuit: including the actual state of the TX coil, taking into account the change in its geometry, inductance, and other parameters. After that, you can subtract the reference value from the actual value of the phase. Thus, we will find out how much the phase has shifted and will be able to compensate for it mathematically.

Similarly, with the RХ coil: it is possible to make a phase shift of the signal and carry out mathematical compensation.

Thus, it seems to me that it is possible to automatically compensate for the shift of the vdi scale (to carry out ferrite calibration). This is optimal, because the parameters of the TX and Rх coils of homemade sensors may be different.

But in branded metal detectors, I don't know how the calibration of the VDI scale takes place. It's implemented somehow programmatically. After all, branded coils are also influenced by physics and their parameters also change. After all, users of branded metal detectors know nothing about the ferrite calibration procedure and the shift of the VDI scale. They just change the search coils.

unfortunately measuring the phase in a resistor wont work .... The coils are manufactured to a certain mechanical and electrical standard so the manufacturer can "preset" or calibrate the characteristics in the code. They could read a resistor to identify the coil but nowadays its more likely to be a chip. I dont think any manufacturer really wants foreign coils on their detector.
In America the detector manufacturers have got together and formed the Induction Coil Enforcement agency ( ICE ) to make sure no-one is using foriegn coils on their detectors. You dont want to mess with those guys.

[moodz]

Nice. I am looking forward to see your fancy math.

BTW, make your sweep tests with ferrite (or hot rock) and gold together. Just imagine the gold is surrounded in a high mineralized pocket.
Aziz

Here is coil sweep across large ferrite then crossing 1 gram gold nugget .. this particular nugget is a weak target and was found by a GPZ7000.
However the nugget signal clearly is extracted from the background signal.

[JoyJo]

unfortunately measuring the phase in a resistor wont work .... The coils are manufactured to a certain mechanical and electrical standard so the manufacturer can "preset" or calibrate the characteristics in the code. They could read a resistor to identify the coil but nowadays its more likely to be a chip. I dont think any manufacturer really wants foreign coils on their detector.
In America the detector manufacturers have got together and formed the Induction Coil Enforcement agency ( ICE ) to make sure no-one is using foriegn coils on their detectors. You dont want to mess with those guys.

I probably didn't describe the situation correctly. The resistor is located in the processing unit. And it sometimes connects instead of the TX coil: for some time necessary to measure the signal phase. It's embedded in the algorithm. And this measurement is a reference, for further calculation. This measurement takes into account only the parameters of the metal detector processing unit. And during the search process, for example, when entering the settings menu, the phase of the TX signal is measured: at the same time, the search coil is connected to the processing unit as usual. This is the advantage: you can measure the phase shift of any coil.