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

[gwzd]

Can I know who is "the first ten" ?

My neighbors daughter is high on my list!

Regards

[gwzd]

Hi gwzd,

I made some numerical tests with the input data now. The noise is typically on the least 4-6 significant bits of the 24 bit input data.

This makes much more sense, and as you probably understand very well this far from being nanovolts. Incidentally, I got an advertisement the other day to buy a Keithley voltmeter and they proudly claimed 6 and a half digits!
Regards

[gwzd]

... It is quite difficult to synchronize to an external oscillator....

No, it is not

Regards

[gwzd]

So what does all of this tell you? ... that you should be measuring relative, not absolute changes in the signal, and tracking the signal drift over time.

Very true, the easiest and most reliable measurements are the differential ones not the absolute ones. The latest required frequent calibration and very narrow set of conditions.

Regards

[gwzd]

you all will be very surprized, when I am going to show you, that the laptop detector will also work very well with only conntected coil without any electronics.

No electronics! I like that, sounds kind of like dowsing, but then again, those fellows have become "high tech" also.

Regards

[gwzd]

Note: you discovered why all coil covers should be white to keep as cool as possible so less change when you swing in and out of shadows. Tesoro makes a black coil, I think a no-no.

What they have discovered is a lousy temperature compensated oscillator.

Regards

[Aziz]

No, it is not

Regards

Hi gwzd,

nice to hear from you again. By the way, the neighbor's daughter is allways the reason for us, to get
- bankrupted
- totally diseased
- and preventing us to work further.

This was my own bad experience in this case. Be awared!

How you would do the synchronisation to an external oscillator?
With locked injection method?

Regards,
Aziz

[Aziz]

No electronics! I like that, sounds kind of like dowsing, but then again, those fellows have become "high tech" also.

Regards

No external electronics. All the electronics is provided by the laptop itself. And the software will do the rest.

I do not believe in dowsing.

[gwzd]

Hello Aziz,

Hi gwzd,

nice to hear from you again.

Tons of work, we are releasing in august a new GPR with a couple of new antennas and its getting tough with the time schedule.

By the way, the neighbor's daughter is allways the reason for us, to get
- bankrupted
- totally diseased
- and preventing us to work further.

This was my own bad experience in this case. Be awared!

You haven't seen her, so let me tell you, when I finally get her I will not be very worry about bankruptcy or disease, leave alone work!

How you would do the synchronisation to an external oscillator?
With locked injection method?

Regards,
Aziz

Simply, use a PLL or any kind of closed system that allows you to keep track on what's going on.

Regards

[Qiaozhi]

I do not believe in dowsing.

Good - I'm glad to hear it.

[Aziz]

Hi guys,

some experiments with forced resonant mode, where the TX coil is driven with the reference clock from the laptop, has some disadvantages on discrimination possibilities. The phase shift can not be used clearly to distinguish between ferro-magnetic and dia-magnetic materials. In contrast to this, an all metal mode is much better to use with high depth sensitivity. However, this could be used for preferred prospecting mode.

For a better discrimination, an external LC oscillator is much more convenient. The frequency and the phase shift occures in the direction, where a correct discrimination is possible. I will try to lock-on to an external LC oscillator, where some drifts in phase and frequency will be compensated in a defined time constant.

Regards,
Aziz

[TheWizard]

Hi Aziz
I make experiments with phase shifting +/- 0.5 deg at 12500Hz
between Tx / Rx and between Inphase and Quadrature parts
Real, I have two demodulators in one chip - this is only for tests - I looking best solution for MCU/DSP based MD

[simonbaker]

Hi guys,

some experiments with forced resonant mode, where the TX coil is driven with the reference clock from the laptop, has some disadvantages on discrimination possibilities. The phase shift can not be used clearly to distinguish between ferro-magnetic and dia-magnetic materials. In contrast to this, an all metal mode is much better to use with high depth sensitivity. However, this could be used for preferred prospecting mode.

For a better discrimination, an external LC oscillator is much more convenient. The frequency and the phase shift occures in the direction, where a correct discrimination is possible. I will try to lock-on to an external LC oscillator, where some drifts in phase and frequency will be compensated in a defined time constant.

Regards,
Aziz

You raise a question I have had about some metal detector circuits. I often see that the TX coil is part of the oscillator, rather than being driven by a separate oscillator through a buffer amp.

My question is: which is better for measuring phase shift in the RX coil -- 1) TX coil is part of oscillator, or 2) TX coil driven by separate uncoupled oscillator, with the separate oscillator used to as a reference to measure phase shift in the RX coil.

I thought that maybe a target in the ground would shift the phase of both the TX and RX coil in the same direction, so the difference would be less, and harder to measure. But if a separate oscillator were used that is not affected by the target, the phase difference would be larger and easier to measure.

Your experiment seems to indicate that (1) is better.

Would you explain more about what you have found?

-SB

[george boswell]

How many years are you people from making something that will work as good as a real metal detector? Just a guess will work.

[amtech2005]

"Let's make a PC-based metal detector with usb interface!!!

How many years are you people from making something that will work as good as a real metal detector? Just a guess will work.

Hello George ,Welcome to the forum .And the answer to your question is "Closer than Ever" The reason is , In just a few years ,the number of Electronic Technician's and Electronic Engineer's who have joined the "GEOTECH FORUM" has Doubled or Tripled. I do not have the numbers. On the "Design idea" thread, stuff is normally being posted daily,and we are very close to some "breakthrough-designs". Also when there is a Technical Problem or any Metal detector question it usually get's answered within a day....Be patient ,the Forum Members we have here , are "The Best of the Best" from around the world !!!........Take care.......Eugene