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

[amtech2005]

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

AZIZ, YOU KNOW YOU GAVE ME AN IDEA WHEN YOU MENTIONED HEAD-PHONES!!! THE COMPANY CALLED DETECTOR PRO WHO MAKES HEADHUNTER LAND PRO AND ALSO PULSE DETECTOR'S , THEY PUT ALL THE ELECTRONICS IN THE HEAD-PHONES. SOME DETECTOR COMPANIES PUT SOME ELECTRONICS IN THE SEARCH COIL BEFORE IT GOES UP THROUGH THE COAX CABLE TO THE HOUSING. LESS NOISE WILL BE RIGHT AT THE SEARCH-COIL........ AZIZ, HAVE YOU DECIDED WHERE YOUR RX AND TX CIRCUITS WILL BE ???? EUGENE

[TheWizard]

Aziz,
can you measure coils balance dynamic
How how much is TX and RX amplitude
and you say "RX signal from nV to µV"
Where? at RX coil?

[Aziz]

Hi Eugene,

indeed, we can put all the amplifier section electronics in the search coil directly (SMD). Also the resonant capacitors. It makes sense to use a dual low noise op-amp like the NE5532A. I have tested the NE5534 without the driver stage. The power could be big enough to drive the coils directly (delivering up to 35 mA). But I want to test the NE5534 with a driver (BUF634 would be quite good - but my local shop hasn't it). I will test a simple complementary transistor driver stage tomorrow.

There is more potential to lower the total noise. I have to test some op-amps for best performance. The advantage of the laptop MD is, it will work even when the coil is not perfectly balanced.

Another interesting topic is to test the off-resonance detector (off-resonance LC osc). I am sure, this would bring more depth sensitivity with a high Q coil. The advantage of this is, it is much simpler to realize.

So there is much more room for experiments to check. I will do this on the coming weeks.


Hello TheWizard,

I do a standard deviation on my lock-in R (magnitude) and P (phase) output. The standard deviation of this is typical noise rms, which can be seen directly and is quite good to test some amplifiers. So very small changes of the R and P can be seen directly on the output value. It is not relevant how much R and P is. The change of this matters. Even, when there is much signal level on the RX coil due to not balanced perfectly.

Guys, you all are not realizing what I am going to do! The laptop MD is getting to boost out all other VLF MD's!

Regards,
Aziz

[Mojo]

Hey Aziz, Where can we download your software & or source code so we can play too?


Mojo

[amtech2005]

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

AZIZ, CHECK OUT THIS PDF FILE ,ESPECIALY PAGE 3 FIGURE 4. SO THERE IS ALOT ON THE WEB ABOUT PLL-HARTLEY AND ALSO HARTLEY EQUIVELENT CIRCUITS. YOU ARE JUST TOUCHING THE TIP OF THE ICE-BERG HERE !!! THE FINAL OSCILLATOR WILL HAVE PLENTY OF POWER WITH STABILITY.ALSO NOISE CANCELLING WITH NARROW BAND-WIDTH IS POSSIBLE. THE RESEARCH IS BRINGING BACK MEMORIES FOR ME WHEN 33 YEARS AGO I WAS IN MY INDUSTRIAL ELECTRONIC COMMUNICATIONS CLASS!!!! HERE ON THIS FORUM ,WE WILL SUCCEED WITH A LAPTOP DETECTOR ANALYZER AND WE WILL SUCCEED WITH A PI/VLF DUAL DETECTOR. IT WILL TAKE SOME TIME BUT WE ARE ALL MAKING GOOD PROGRESS.HAVE A GOOD DAY ......EUGENE

[Aziz]

Hi Eugene,

thanks for your hint. This could give some improvements probably. I am working to get a very stable LC oscillator at the moment.

And I like the idea of minimized hardware directly placed on the search coil housing:
- simple amplifier
- simple LC oscillator
- using only +5 V from USB port

I want to check, whether this is possible.


Mojo,

I am sorry, my software is only in experimental state. It is more a measuring instrument rather than a metal detector at the moment. I am far from a usable laptop detector. Just investigating at the moment for a good hardware reference platform. The software will then be optimized to the hardware. And there is much to test yet.

Regards,
Aziz

[TheWizard]

Let's made a DSP-base Inductive Balance Metal Detector...

[Aziz]

New detection record with my laptop metal detector:
1 Euro coin at 34-36 cm distance above the coil.
;-)

It is mainly dependend on the following factors:
- stability of the lc oscillator
- stability and noise characteristics of the amplifier
- quality of the sound card

I found on the spectrum some interesting points, that makes the detector very very stable and will allow increasing the detection.

Wizard, you are going on the right direction. A DSP based VLF can be easily implemented.
Aziz

[amtech2005]

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

WIZARD, NICE LITTLE CIRCUIT BOARD YOU POSTED. WITH THE PROPER PROGRAMING OF THE DSP "PIC-CHIP" CAN YOU ANALYZE ALL SIGNALS FROM THE RECIEVE SEARCH COIL . CAN THE DSP ISOLATE DETECTED TARGETS IN THE NANO-VOLTS FROM WITHIN ANY TYPE OF NOISE OR INTERFERENCE ? BESIDES BEING PROGRAMED FOR CONTROL FUNCTIONS, CAN THE DSP BE PROGRAMED FOR SIGNAL ANALYSIS. MAYBE EVEN TELL YOU IF IT'S INTERNAL PCB CIRCUIT BOARD AMPLIFIER NOISE OR NOISE IN THE GROUND OR SEARCH COIL RELATED MAGNETIC FIELD GARBAGE. IS THE CRYSTAL 20 MHZ TO THE RIGHT OF DSP ?? WILL IT TAKE A LOT OF PROGRAMING. I AM VERY INTERESTED SO THANKS FOR YOUR INFORMATIVE POSTINGS............EUGENE

[Aziz]

I worked all the night long. It is interesting, that with higher Q coils, no amplifier for the TX signal is necessary anymore. I can spare the TX amplifier now. TX is driven with ultra small signal level on the sound output (few mW).
Now only the capacitors and the SMD pre-amplifier can be placed directly on the coil housing. It's getting more simply.

Good night!
Aziz

[TheWizard]

amtech2005,

I think - nano Volts (for Metal Detecting) is theory and dreams... in this range the noise is very strong

I don't know(now) the sensibility of this board, Analog part is not ready,
I waiting some OP-AMPs from shop(SMD NE5534 or AD797AN) and I need to make good coil for test for range 5k-15kHz sine
This is experiment board from "sporting malice"...

About DSP and Digital detecting - this way will give more functions from analog design and can be best user friendly

[Aziz]

Hi TheWizard,

don't be so pessimistic! Just work for a good result. If we wouldn't dream on such goals, we can not go through the barriers.

Why you don't make the first software not on the PC? It is fast, cheap and very easy. Later, you can adapt the software to the DSP hardware.

Just try this on the PC for a basic coil connection test:
L-TX, C1 and C2 are the determining frequency of a Colpitts-type resonator. This is coupled through the capacitor C3. Apply a well defined harmonic to the transmit coil.
f = 1/(2*PI*sqrt(LTX*((C1*C2)/(C1+C2))))

The receive coil is a parallel resonator. L-RX and C defining the frequency.
f = 1/(2*PI*sqrt(LRX*C))

Of course, the RX can be amplified before feeding to sound card input. If there is no ampliflier available, one can plug into the microphone input with activated microphone amplification.

Just try out and see the result with Lock-in Amp.
I am not kidding.
Aziz

[Aziz]

PS: Don't forget the protection diodes!

[Aziz]

BTW,

this is my DSP board (current version has 33 MIPS, I have also a 40 MIPS version). Also having a second DSP board for more calculation power. It was made ca. 10 years ago. But I do not want to use it anymore. Just using a laptop PC.

Interesting tip:
Use a cheap DSP starter kit having a codec chip (sound chip). This could make thinks easy and fast.

Aziz

[amtech2005]

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

AZIZ, WILL YOUR SOUND CARD PROVIDE ENOUGH CURRENT TO DRIVE THE TX COIL ???? EVERTHING ELSE LOOK'S GREAT !!! AND ALSO I STILL THINK THE DSP CAN BE PROGRAMMED FOR SIGNAL WAVEFORM ANALYSIS, MULTIPLE NOTCH-FILTER DISCRIMINATION. TX CONTROL PARAMETERS. THE POSSIBILITIES ARE ENDLESS. A DSP SHOULD DO ALL THE WORK FOR YOU , JUST TURN ON AND GO .AND OUT IN THE FIELD "IN THE DIRT " THE DSP WILL AUTO SET EVERYTHING.WITH MY PERSONAL DETECTOR A "BOUNTY HUNTER GARBAGE" I GET TIRED OF SETTING MY GROUND BALANCE CONSTANTLY AND GET WORRIED THAT MY NOTCH SETTING WILL MAKE ME MISS MY OLD NICKEL'S OR EVEN GOLD .MY TARGET ID AND DEPTH ARE DIFFERENT READINGS WHEN I SWEEP FROM RIGHT TO LEFT THAN WHEN I SWEEP FROM LEFT TO RIGHT !!! WHO WANT'S TO SET THEIR DETECTOR IN "ALL METAL MODE" TO DIG DEEP AND FIND GARBAGE, I DON'T !!!WHEN GROUND CONDITIONS ARE SO BAD YOU CANNOT GET ANY STABLE READINGS OF ANY KIND . THE SOUND CARD WILL WORK GREAT BUT WILL YOU NEED THE DSP ALSO ??????? ALSO IT IS A SICK FEELING WHEN SOMEONE ELSE GOES OUT TO YOUR SITE AND DIG'S UP STUFF YOU MISSED. "FINDERS KEEPERS" ............AZIZ AND EVERYONE ,I JUST HOPE WHEN WE ARE ALL DONE WITH THESE "DESIGN PROJECT'S" THAT A VALUABLE DEEP-TARGET IS NEVER MISSED.....TAKE CARE........EUGENE