IF YOU HAVE MAKE , TRY THIS .

[sisco]

Thank Carl ,

what this coils is better ?

[Max]

Thank Carl ,

what this coils is better ?

Hi,
depends of what you're trying to do. Seems you want 2TX/RX config.

I assume you wanna use same dimensions for 2 coils.
I assume you wanna use "different" timings for TX1 and TX2 pulses (not overlapping).

Problem of A is that you could just increase magnetization of soil, if some magnetic crystals are there. So, for me, A doesn't improve your S/N.

B will improve S/N cause you'll eliminate net magnetization of soil if use two opposite magnetic pulses, also magnetic viscosity effects would be attenuated... so, ideally, signal would depend "more" of eddy currents in target.

C,D are like in the twinloop old project but DD instead of round... and not overlapped ? could work but I dubt you'll improve S/N e.g. in C version.

D seems better but mainly for pinpointing... easy instead of round coils... other considerations are similar to B in the central, more sensitive, area of coil but you'll lose in D the net magnetization null effect on the whole area of coil, cause coils don't share the same location on the plane.

If you read the old Corbyn's article you'll see that 2 TX coils are used to achive this... but then a separate gradiometer RX config was used to get RX signal.
2 opposite TX share same plane and location... to improve S/N. You can do the same using B config.

So, for me, B is better than others cause you can gain a real S/N improvement.

Kind regards,
Max

[sisco]

Hi Max ,

yes , I want use same dimansion for two coils , but about "different timing"

now I don't decide about this (after making can test this two method with

change program).

so this is best choice for me . yes ?

[sisco]

now ,time of amplifier .

what is your suggest between plan A and plan B ?

(I must complete my information before next project . my next project is

digital PI with real DISC.)

[Max]

now ,time of amplifier .

what is your suggest between plan A and plan B ?

(I must complete my information before next project . my next project is

digital PI with real DISC.)

Hi,
I'll choose A... cause of the cap between...
DC coupling in hi-gain stages is the first cause of "disaster" in metal detectors design.
If you directly connect e.g. 10^6 gain amplifier chain to a dc source... you'll see the UFO.

Any kind of drift on DC signal will make it sound like a jukebox

So use the cap... mind the cap.

Look at the GoldScan4 schematic part... you see the 470nF cap just after 3 op. amps first of the #4.
It's not a case.
Too huge amplification along the chain... to stay without them.

Do not consider 100nF... cause there is a mistake in that older schematic (connection to GND absent) but look just at 470nF.

Signal is preamplified, sampled/integrated then dc chain is broken... just ac passes to next stages.

Kind regards,
Max

[sisco]

Hi Max

see , this is a one part of my new project.

infact this is a one channel of detector .(with timing can tell iron channel or

gold channel).

I want use two or three (maybe four) lines like this with difference timing for

DISC .

what you think ?

[Max]

Hi Max

see , this is a one part of my new project.

infact this is a one channel of detector .(with timing can tell iron channel or

gold channel).

I want use two or three (maybe four) lines like this with difference timing for

DISC .

what you think ?

Hi,
I see. Nice idea having multi-channel : GS4 has 2 one for ground minerals and the main channel for useful signal (usually refered "gold" channel... but it's a bad definition... cause disc doesn't work detecting just gold).

With 2 channels GS4 ignore almost totally ground minerals when their density is constant.

If you use more channels you can integrate signal coming from coils at different times thus giving additional pieces to the mosaic.

I don't know if a true disc could be made that way like is done in some VLFs but it's worth to try and see the results.

Think most important thing is timing and elaboration of result signals by the MCU.

Best regards,
Max

[sisco]

my PCB layout , designed , and ready for making .

I only waiting for OP-AMPs (AD797 and OPA37) , because I can't find in my

city and order. if can't find AD797 and OPA37 must draw new PCB layout for

other OP-AMPs (offset adj pins difference , specially AD797).

what is your suggest for OP-AMPs ?

[Max]

my PCB layout , designed , and ready for making .

I only waiting for OP-AMPs (AD797 and OPA37) , because I can't find in my

city and order. if can't find AD797 and OPA37 must draw new PCB layout for

other OP-AMPs (offset adj pins difference , specially AD797).

what is your suggest for OP-AMPs ?

Hi,
I'll try with OPA211 if can't find AD797 but I don't know if can be replaced as is without modification on pcb/pinouts e.g. for nulling or other external component if required... have to look at datasheet for this.

But specs seems good for OPA221 much like AD797. Problem is that I cannot see the DIP package anywhere... maybe is just smd !

So now you have another to search for.

Best regards,
Max

[sisco]

Hi Max , one hour ago i find this sit , good for search anything.

http://www.datasheetcatalog.net/cgi-...&action=Search

you think this work ? (in this device I use four channel) ???????????????

[Max]

Hi Max , one hour ago i find this sit , good for search anything.

http://www.datasheetcatalog.net/cgi-...&action=Search

you think this work ? (in this device I use four channel) ???????????????

Hi,
if you need datasheets you can find all you want here:

http://www.datasheetarchive.com/

About the circuit I don't understand the use of leds... I mean the only way to get some useful disc is putting resulting signals e.g. into an ADC and then elaborate results with the MCU software.

Led solution is much like some VLFs done with multitone-id... where any channel could be "tuned" to react in a specified phase range, but PI are different. You haven't something like phase-angle to discrimininate and have to investigate e.g. conductivity of target to figure out what metal is.

Your approach is like a MCU-time controlled analog analisys of signal: I think you need DSP inside the MCU.

That way you'll have 4 independent double integrators MCU-driven (you can change by software integration strategy as needed), and 4 signal path to the ADC for DSP.

So the four led are an idea, but you have to drive them by MCU to get they light giving you disc informations and connect output of channels to some e.g. multi-channel ADC, software selecting input... or use e.g. a MUX or something similar you can do by software and MCU data pins.

So I'll add another layer of MCU/ADC/MUX connections at the out of channels.

Best regards,
Max

[sisco]

in this PI for DISC don't need A/D or analys .

see schematic , for example :

adj CH1 timing for ALLMETALL

adj CH2 timing for GOLD

adj CH3 timing for bricks

........

if each these channels can detect his target you hear BEEEEP but can't

understand which channel detect what object so I use LED . for example

if hear BEEP and CH1 LED was ON and CH2 LED was OFF you can

understand your target(object) not gold .

you can with compare these LEDs understand about your object.

I think this is best idea for DISC .if you have better idea I listen.

about use microcontroller : for DISC you must use two microcontroller , if you professional programmer can use two micro but if

you amature programmer like me must use two micro + one A/D converter.

(I have new idea for this , must use ATmega8 + ATmega16 + 64 * 128 grafical LCD but my information not complete , must wait)

for getting analog signal I have a problem , I think best location for this , after third OP-AMP and before capacitor , what you

think?

[Max]

in this PI for DISC don't need A/D or analys .

see schematic , for example :

adj CH1 timing for ALLMETALL

adj CH2 timing for GOLD

adj CH3 timing for bricks

........

if each these channels can detect his target you hear BEEEEP but can't

understand which channel detect what object so I use LED . for example

if hear BEEP and CH1 LED was ON and CH2 LED was OFF you can

understand your target(object) not gold .

you can with compare these LEDs understand about your object.

I think this is best idea for DISC .if you have better idea I listen.

about use microcontroller : for DISC you must use two microcontroller , if you professional programmer can use two micro but if

you amature programmer like me must use two micro + one A/D converter.

(I have new idea for this , must use ATmega8 + ATmega16 + 64 * 128 grafical LCD but my information not complete , must wait)

for getting analog signal I have a problem , I think best location for this , after third OP-AMP and before capacitor , what you

think?

Hi Sisco,
I still think that just channels and different integration timings aren't enough to give a good disc. Maybe it can work somehow on test bench but in real conditions I dubt you can disc that way.

Maybe I'm wrong.

My understanding of PI say me that different metals, with different shape, at different depth could give same effects on the signal curve.

My idea is different. You have always use the ADC/MCU for disc in my view of a possible and reliable disc.
Of course you can avoid at all last part of integrators...just use a preamp and feed directly e.g. an ADC with samples from the preamp.

The use of analog integrators is e.g. an idea if you want avoid doing all the computation by DSP, so numeric integrations. But one can do it.

If you look at Robert Holko project thread you'll see that thing made just by numeric methods inside the MCU.

The real problem is finding a suitable parameter or set of parameters to look at, e.g. conductivity of metal.

Best regards,
Max

[sisco]

Hi Sisco,
I still think that just channels and different integration timings aren't enough to give a good disc. Maybe it can work somehow on test bench but in real conditions I dubt you can disc that way.

Maybe I'm wrong.

My understanding of PI say me that different metals, with different shape, at different depth could give same effects on the signal curve.

My idea is different. You have always use the ADC/MCU for disc in my view of a possible and reliable disc.
Of course you can avoid at all last part of integrators...just use a preamp and feed directly e.g. an ADC with samples from the preamp.

The use of analog integrators is e.g. an idea if you want avoid doing all the computation by DSP, so numeric integrations. But one can do it.

If you look at Robert Holko project thread you'll see that thing made just by numeric methods inside the MCU.

The real problem is finding a suitable parameter or set of parameters to look at, e.g. conductivity of metal.

Best regards,
Max

this object must stay , when i find op-amp , test and tell about this.

now other question ?

maybe think this question is funny but i must know.

in VLF method we use two coil one TX for tranmite and other RX for receive.

RX what do ? detect Reflected signal from target or detect eddy current

from target ?

[Max]

this object must stay , when i find op-amp , test and tell about this.

now other question ?

maybe think this question is funny but i must know.

in VLF method we use two coil one TX for tranmite and other RX for receive.

RX what do ? detect Reflected signal from target or detect eddy current

from target ?

Hi,
VLF is a too generic definition for an MD.

I assume you mean an IB/VLF like e.g. Tesoro's or White's etc are today.

They are IB. Induction Balance type, means they use an arrangement on coils that gives very small (ideally null) signal when there aren't perturbations on field lines.

When a target enter in the field generated by TX coil(s) it give a distortion of them that is due to ferromagnetic (for iron, cobalt, nickel...) or diamagnetic (gold, silver, copper...) properties of material.

Fild lines deflection is an imbalance to the null achieved in coil thus resulting in a useful signal at RX coil.

RX coil detect a voltage that is of same frequency of TX, cause coil is actually an air-core transformer, and intensity proportional to the perturbations of field lines due to the target.

Phase-angle shift between TX and RX is used to disc the object.

So RX detects too , of course, eddy currents flowing in target, cause there is a coupling between magnetic circuit at RX and AC magnetic field due to eddy currents flowing in the target, but this is just a part of RX signal.

In IB you detect both, eddy currents effects (voltage at RX) and TX deflected flux generated voltage in RX coil at the same time, where e.g. in PI you detect just effects of eddy currents cause you look at signal just after TX pulse... so not during tx phase. That way you get just change in voltage at coil when energy is the same (each TX pulse is supposed giving the same energy to the coil).

Best regards,
Max