Let's made a PC-base metal detector with usb interface !!!

[Aziz]

Hi Simonbaker,

Hi Aziz:

Useful findings.

Would you be specific on how you tested the capacitance effect with graphite coating, as much detail as possible (e.g. object causing effect, distance to object, motion of coil, etc.).

Also would be interesting to know how much foil shield changes depth in your air tests.

Thanks,

-SB

AL foil decreases the coil Q. The losses of the coils are increased (producing heat on the AL shielding). The seen parallel coil resistance Rp is lowered. Coil Q affects the sensitivity of the system. The higher the coil Q, the better the sensitivity will be. Remember: Signal drop on the RX coil will be converted to heat due to coil resistances (series coil resistance Rs, parallel coil resistance Rp) and cannot be used for signal processing then.

Graphite shielding is quite good but not good enough for this application. I have observed a high sensitivity for capacitance and ground effects (hand detection, ground detection, etc.) . I will test next time AL shielded coils in the field and expect much lower capacitance and ground effects. Hand detection tests with AL shieldings are passed successfully so far (not detected). But there should not be any unshielded wire or components in the coil anymore. I will also shield the passive electronic components totally to eliminate such problems in the future. The additional balancing winding will be a thin coax cable (RG174).


Aziz

[simonbaker]

Hi all,

I will give you an update of this project:

Last days, I have wound a couple of other coils. They are completely shielded with AL foil now. This eliminates the capacitance problems totally and the ground capacitance to coil will be lowered much. On the other hand, the high mass shielding leads to balancing problems of the coils. In most cases, I cannot null the RX coil and there is much residual voltage (50-100 mV).
The balancing problem can be solved with additional coil winding and a balancing circuit. I will develop a better balancing circuit. (Sick of positioning the coils to 1/1000 mm accuracy).

Graphite shielding is not convenient for this project. It has obviously some advantages, but the disadvantages will be much more. AL foil will decrease the depth performance a bit but it makes the detector more stable.

High Q coils (Q=L/R) both for TX and RX are strongly recommended and will reject noises outside the operating frequency better. Also the sensitivity will be much better. High Q coils have more weight (thicker wire, more windings) and this is the only disadvantage.

Now focusing on a shock resistant coil development.

Aziz

Hi Aziz:

Useful findings.

Would you be specific on how you tested the capacitance effect with graphite coating, as much detail as possible (e.g. object causing effect, distance to object, motion of coil, etc.).

Also would be interesting to know how much foil shield changes depth in your air tests.

Thanks,

-SB

[Aziz]

Hi all,

I will give you an update of this project:

Last days, I have wound a couple of other coils. They are completely shielded with AL foil now. This eliminates the capacitance problems totally and the ground capacitance to coil will be lowered much. On the other hand, the high mass shielding leads to balancing problems of the coils. In most cases, I cannot null the RX coil and there is much residual voltage (50-100 mV).
The balancing problem can be solved with additional coil winding and a balancing circuit. I will develop a better balancing circuit. (Sick of positioning the coils to 1/1000 mm accuracy).

Graphite shielding is not convenient for this project. It has obviously some advantages, but the disadvantages will be much more. AL foil will decrease the depth performance a bit but it makes the detector more stable.

High Q coils (Q=L/R) both for TX and RX are strongly recommended and will reject noises outside the operating frequency better. Also the sensitivity will be much better. High Q coils have more weight (thicker wire, more windings) and this is the only disadvantage.

Now focusing on a shock resistant coil development.

Aziz

[simonbaker]

Hi Simonbaker,



This could be one of the effects. I will make a smaller coil with AL foil shielding to test AL foil vs. graphite shielding. My hand is still be detectable at max. 3-5 cm even there is two different layers of graphite shieldings (coils and coil housing). High Q coils detects very small loss of energy.

I couldn't resist on making some field test. The very wet soil (rainy day) was giving quite high signal level (magnitude). Fortunatelly, the phase shift was small enough to distinguish between real target and ground. This is not really a big problem.

But there is a major coil stability problem. The coils have direct contact with the coil housing and any deformations due to gravitationally force, swing, or mechanical shock is leading to a false signal. The coils have to be buffered via PU foam or polystyrene to decouple them from the coil housing. Also the weight of the coil (+housing) has to be lowered to reduce such effects.

When these effects are lowered, I will have a very sensitive, deep seeking and discriminating VLF MD.

I will start with a new coil as soon as I have tested some ideas.

Aziz

It seems the additional sensivity requires especially well constructed coils, etc. Makes sense.

Most ordinary detectors react to wet sand at the ocean. Human body has similar salinity, pH. The fun part is the signal processing to recognize real targets and reject false. Software gives the most power for that. May take time, but in the long run, has to be the best method.

Keep up the good progress and reports!

Cheers,

-SB

[Aziz]

Hi Simonbaker,

Is it possible the conductivity of your body makes a real target because of exceptional sensitivity of your lock-in?

-SB

This could be one of the effects. I will make a smaller coil with AL foil shielding to test AL foil vs. graphite shielding. My hand is still be detectable at max. 3-5 cm even there is two different layers of graphite shieldings (coils and coil housing). High Q coils detects very small loss of energy.

I couldn't resist on making some field test. The very wet soil (rainy day) was giving quite high signal level (magnitude). Fortunatelly, the phase shift was small enough to distinguish between real target and ground. This is not really a big problem.

But there is a major coil stability problem. The coils have direct contact with the coil housing and any deformations due to gravitationally force, swing, or mechanical shock is leading to a false signal. The coils have to be buffered via PU foam or polystyrene to decouple them from the coil housing. Also the weight of the coil (+housing) has to be lowered to reduce such effects.

When these effects are lowered, I will have a very sensitive, deep seeking and discriminating VLF MD.

I will start with a new coil as soon as I have tested some ideas.

Aziz

[simonbaker]

Going back two steps..

My DD search coil does not meet the required specifications yet. The lock-in amplifier is an ultra sensitive beast and wants to be tamed in right way. So real field testing is delayed a bit.

Main problems:

1. Mechanical stability

Due to it's heavy weight and the tight glued coils to the coil housing, tiny mechanical deformations and shocks will cause false signals.

2. Shielding

The graphite shielding seams not good enough. Still have capacitive effects.

I will make an another coil which reduces such effects. Now a completely different coil production is in the pipeline.. It will be much easier and better this time..

Aziz

Is it possible the conductivity of your body makes a real target because of exceptional sensitivity of your lock-in?

-SB

Graphite polishing advice

Dear Aziz S.A,
As i experienced before about coil graphite covering, kindly i advice you first put the pure coil inside epoxy-polymer mixture; then on top of this mixture (after hardening) it is better you shield the graphite. make sure graphite is being absorbed inside the epoxy-polymer very well by mixing the graphite with soldering wax. then, you measure the ohmage of graphite.
this is my experience about how to decrease having capacitive effects problems.
I hope it works also in your project.

Selamlar, Saygılar

Ronin
<Izmir-Turkey>

[Aziz]

Going back two steps..

My DD search coil does not meet the required specifications yet. The lock-in amplifier is an ultra sensitive beast and wants to be tamed in right way. So real field testing is delayed a bit.

Main problems:

1. Mechanical stability

Due to it's heavy weight and the tight glued coils to the coil housing, tiny mechanical deformations and shocks will cause false signals.

2. Shielding

The graphite shielding seams not good enough. Still have capacitive effects.

I will make an another coil which reduces such effects. Now a completely different coil production is in the pipeline.. It will be much easier and better this time..

Aziz

[Aziz]

Merhaba Ronin,

Dear Aziz S.A,

I m just wondering, if your lasting project will be looking like as linked below?
(Although coils are different, may the same visualizing offered and there is no electronic circuit except UMPC resembling to your project)

link: http://www.accuratelocators.com/PinPointer_Sound.html

If so, do you think UMPC will be enough for such MD visualizing just like they are referring?
I guess such small PCs' audio outputs will make problems, such as you encountered.

my last question is; do you think this linked product is useful for treasure hunting?

Regards From Izmir, i m proud of what you are struggling to achieve....

I am not familiar with this PinPointer MD. BTW, I don't like any MD's with "antenna". GPR's only have real working (micro wave) antenna. I am familiar and experienced with micro wave antennas (developed several types of them 1-2 years ago).

My experiment - yes, it is still an experiment - is using a true VLF type search coils. I have doubts that there is any similarity between my project and the PinPointer. They work very likely completely different.

UMPC's are becoming very attractive devices for small handheld measurement instruments. They provide huge computation power rather than the embedded systems solution (using micro controllers or DSP's). So you can do with UMPC's much more today - there is almost no limit. I don't like graphical visualisations. If there is sunshine, you cannot see anything (except you are searching at night). So just focusing in better audio signalling.

I am using the Asus Eee PC 901 and expect more better devices in the future. So pure software MD's can be realized with minimum of effort. I am trying this at the moment. It is also a general proof of concept. Everybody is welcome to contribute to this project.

I will be faced with huge problems now. Real field testing and ground signals will make my life quite difficult. There is much surprise, which could make this project (experiment) totally obsolete.

Bol selamlar,

Aziz

Dear Aziz S.A,

I m just wondering, if your lasting project will be looking like as linked below?
(Although coils are different, may the same visualizing offered and there is no electronic circuit except UMPC resembling to your project)

link: http://www.accuratelocators.com/PinPointer_Sound.html

If so, do you think UMPC will be enough for such MD visualizing just like they are referring?
I guess such small PCs' audio outputs will make problems, such as you encountered.

my last question is; do you think this linked product is useful for treasure hunting?

Regards From Izmir, i m proud of what you are struggling to achieve....

[Aziz]

It's time again to spend money (1. of month is welfare payday). I have just ordered the Creative X-Fi Xmod USB sound-card.

http://us.creative.com/products/product.asp?category=209&subcategory=668&product=15913

I will test this sound-card for possible suitability and will compare to previously bought USB sound-card.

Aziz

[simonbaker]

Aziz you are a Genius.

I am watching this thread with great interest. it just goes to show that what I predicted was possible back in 1988, you are now proving IS possible.

I feel vindicated now. THANKS!!

It is an important area Aziz is doing great job with.

One of the most useful features I look forward to is programmable response time - turn knob to get different time constant filtering.

Then if you hear a crackle, slow the response and see if a deep target is lurking... I want it!

Keep up good work.

-SB

[Sean_Goddard]

Aziz you are a Genius.

I am watching this thread with great interest. it just goes to show that what I predicted was possible back in 1988, you are now proving IS possible.

I feel vindicated now. THANKS!!

[Aziz]

I can detect a small gold coin at 36 cm (air-test). Even with discrimination. The gold coin (see below) is a standard size turkish gold coin (1/4 of size, called ceyrek altin).

Aziz

[simonbaker]

Hi Simonbaker,



Did you try the following experiment?
Combining the off-resonance and BFO type MD. Well, I didn't yet. Maybe this could give an interesting result.
The coils will be driven in micro-power mode (very low energy on transmitter side). So the sound-card will have enough energy (driving current) for this. The TX coil has its own resonant tank (LC). There is an another RX coil with same diameter, which is operated not in balanced mode (very easy to build). TX and RX coils share the same position (direct coupled) but they are galvanic decoupled (seperate coil). RX coil has also resonant tank (LC) with much more windings to amplify the TX signal to adapt to dynamic range of input signal (ADC). The RX signal level should be at 90 % of dynamic range of ADC. Transmit frequency equals to the receive frequency (matching of two resonant tanks).
Any metal objects nearby the coils will detune the resonant tanks, changing the phase and changing the RX signal level (due to losses). The coils should have much higher Q (Q = L / R) to give more sensitivity. The reference signal is generated internally in the computer.

Just a crazy idea. Well, I will try this experiment soon. If this works good, then the coil are very easy to build. No more balancing necessary.

Aziz

The crazy ideas sometimes not so crazy, or lead to new breakthroughs. That's the fun! If I was a better theorist I probably wouldn't try certain approaches, but one learns either way. I hope you try it. Experiments take lots of time though, I know well!

Regards,

-SB