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

[Aziz]

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

Hi George,

it isn't a matter of years. It would just take 2-3 month of software coding. I am investigating at the moment for better and easy hardware configurations to get a powerful and stable detector. So lots of possible configurations must be tested yet.

I am waiting for a laptop to make real field tests.

Regards,
Aziz

[Unregistered]

How long will it be complete?

Hi Aziz,

I see a lot of ambitions to get to the bottom line result and I hope you will very soon.
Q: If you get a positive result and everything is working great, will it be available for people to buy it from you?
Regards
A.K

[Aziz]

Hi Aziz,

I see a lot of ambitions to get to the bottom line result and I hope you will very soon.
Q: If you get a positive result and everything is working great, will it be available for people to buy it from you?
Regards
A.K

There is some potential to get a well working MD. But lots of questions are not answered till now. I have to implement some new subroutines to get a better synchronisation to an external LC oscillator. I hope, I will solve this soon.

The software will not be for sale. But a simple version will be for free.
Aziz

[amtech2005]

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

Hello Aziz , Everyone, We should move this thread to the top of the page under "Project Ideas" !!! Anyway this Usb ADD-On Device can make some Money !!! A German Company KTS sells a PI-COMBO Unit For $3600.00 Euro !! WOW. And you look at the photo of the pulse detector and again you ask "Discrimination" REALLY" ???? . All I can see on the bottom unit is an intensity meter , no Lcd display . It could be "Equivelent in Power to Delta Pulse" !!. The top unit has a USB port , so it must be just a Deluxe 'Video Card" for a Lap-Top !!!! And I am sure there is some version of software for the Lap-Top....... Aziz , I am sure If you or all of us together designed a " PC Based analyzer with a Video image "COMBO-UNIT" For even $1800.00 Euro ,it would "CONTROL THE MARKET"......... $1800.00 Euro to US DOLLAR is Still good money Today !! .... .......RIGHT ??.......................Eugene

[Aziz]

Hi Eugene,

unfortunately, I was prevented from working further on this project during last week. The damn kraut's (sorry, but they can still go to the hell) won't let me left in peace. So my laptop MD project will be delayed in some month when I will pack my baggage for a big trip (probably emigration to oz).

I was busy with perversity of court, complaint, bailiff, etc..
and with some new very low eddy current causing DD coil shieldings (no graphite).
I hope, I can continue soon.

Aziz

[amtech2005]

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

Aziz, sorry to hear that you will be delayed .... You have had some Great-Ideas so far . We will be waiting for your return ,good luck.....Eugene

[gwzd]

Hi Eugene,

unfortunately, I was prevented from working further on this project during last week. The damn kraut's (sorry, but they can still go to the hell) won't let me left in peace. So my laptop MD project will be delayed in some month when I will pack my baggage for a big trip (probably emigration to oz).

That's very sad to hear, I feel sorry for you Aziz. Let me know if there's something I can do for you, I'll be glad to help you.

My best regards, truly.

[Aziz]

Hi guys,

thank you for taking care of me. Despite of lots of problems here, I will not stop breaking the work.


Yesterday I tried again to synchronize to an external oscillator. Due to very sensitivity of lock-in amplifier for phase and frequency changes, the occured instability (0.1 .. 1 Hz range) of the LC oscillator is not acceptable (for me).

I will try to acquire and process both signals (signal from rx-coil and reference signal from tx-coil) simultaneously to cancel any instability for the lock-in amplifier with an external LC oscillator.

Using an external LC oscillator makes the design very easy and only one sound-card is necessary. The total estimated external hardware cost for the laptop MD will be in range of 10-20 Euro.

Regards,
Aziz

[Aziz]

Update:

Now I made an elegent digital phase shifting algorithym on the time domain signal for the lock-in amplifier. The reference signal of the LC oscillator is fed to the right stereo input. The RX signal is fed to the left channel. The stereo output of the sound card is reserved for audio signal output.

The phase shifting is made on the frequency domain (FFT) and is transformed back to time domain signal. This is much better then shifting the time domain signal in his place because the invers FFT does a numerical resampling of the signal and can be additionally combined with a FFT filter.

It is going forward..

Aziz

[amtech2005]

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

Aziz, Digital Phase Shifting Algorithym and then to a Lock-In amp. circuit is 100 % possible. My idea is of a Band-Pass filter for each type of target on the chart below and then to a Lock-in amp circuit !! But this will not work in Europe where the coins are made different. Gold would work anywhere but not bronze coins .......Just another idea.....Eugene

[Aziz]

Hi Eugene,

the laptop MD is getting now more similar to standard VLF front end. But in digital way and with improved short bandwidth filtering capability (using lock-in amp). The phase output of the lock-in amplifier can then be used directly for the discrimination. It is possible to detect phase changes better than of 1/100 degree. Of course, it depends on the stability of the system. The ground balancing and discrimination will be much easier to implement.

Using stereo signal inputs, we could also use two RX coils for the process. It might be very interesting to check this out.

Well, I will see the result and the stability in the coming days. I hope, the LC instabilty is then cancelled due to direct synchronisation of the LC osc to the lock-in amp. Lots of work is still waiting for me.. lets go on further..

Regards,
Aziz

[amtech2005]

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

Aziz ,Was this your Design ??? IF not I think you may have seen this a couple of months ago , but just in case , here are the photo's from another posting. Anyway my main interest "NOW" is P.I. discrimination . And I think this will become a reality soon with 100% accuracy. But it will take working with D/A conversion and Waveform shaping of the signal , both on the transmit and recieve circuits. And I believe the search coil must have a separate TX winding and a separate RX winding . NO EXCEPTIONS !!! A single coil will not work even with micro-processors.......Take Care........Eugene

[Aziz]

Hi Eugene,

this design is not my own and I saw it month ago and I didn't need it. My laptop MD even worked without amplification of the RX coil side. I just put the sole coil with matched parallel capacitor to match to the operating frequency of the TX side.
On the TX side I tried many external oscillators (difficult to lock in to the frequency) and power amplifiers or just low noise buffers. It will work in any configuration with more or less stability and performance. Using very low noise LC oscillators (+high stability) could bring here the best depth and performance.

I have combined the Lock-in amplifier with a Boxcar integrator and this brings the best performance and stability.

Here are some highlights of my experiments:
- Phase change detection accuracy: 0.001 degree!!!
- Voltage change detection: few µV (within noise level of 1-2 µV)
- 1 Euro coin detected on 40 cm distance (air test) with a DD coil of 20 cm diameter

The experiments showing me, that there is a big potential for implementing the whole laptop MD in hardware. So battery life and portability will not be anymore an issue.

The development is stopped at the moment until I make some comparisons to PI technology. So I have the biggest motivation to implement similar techniques on PI's.

Regards,
Aziz

[simonbaker]

Hi Aziz, can you explain a little more?

I have combined the Lock-in amplifier with a Boxcar integrator and this brings the best performance and stability.

Most Lock-in amplifier descriptions I have seen seem to use a "Boxcar" integrator anyway - a square wave integrated against the received signal.

Did you do something more or different?

Thanks.
-SB

[Aziz]

Hi SB,

usual one channel - in-phase - lock-in amplifiers use following parameters:
- lock-in frequency f (signal frequency / reference frequency)
- phase shift p (of the reference oscillator)
- TC (time constant for the low pass filter for the mixed channel)

The output of the one channel lock-in amp is depended on the phase shift p and at the maximum output value, the phase shift of the signal to reference can be read out directly. So the user has to adjust the phase shift for maximum output value and read then the phase shift and output value. One channel lock-in amps usually used former as analog lock-in amps.

The two channel - or quadrature-phase (I & Q) - lock-in amplifiers do not need the phase shift information from the user. The output of the IQ-lock-in amp represents a unity complex vector (channel I=in-phase, mixed with cos(2*pi*f); channel Q=quadrature-phase, mixed with sin(2*pi*f) ) and the output magnitude R and phase P can be computed directly. Any phase shifts of the reference oscillator will only phase shift the output phase. The magnitude will not be changed on phase shifts. I & Q lock-in amps usually used in digital lock-in amps. My laptop MD is implemented in this way.

The time constant TC is the low pass filter time constant for each channel (I and Q). The -3dB cut-off frequency will be fc = 1 / (2*pi*TC). It defines the filter response and the higher TC is, the higher the signal-to-noise ratio and the lower the response time to changes it will be. So using higher TC will slow down the detection speed. To much TC will slow down the computation time. Taking some reasonable TC's for desired detection speed is necessary.

Now the Boxcar integrator:
The output of the lock-in amplifier (channel magnitude and phase) can be further low-pass filtered using Boxcar integrator. It has some decimation facility to the huge amount of data and will speed up the computation time. Different time constants for the Boxcar can be taken to implement different sweep speeds of the coil. So a higher TC will be used for pin-pointing to get a better sensitivity and stability.

So a two stage of system:
1. Lock-in Amplifier with its own TC
2. Boxcar integrator with its own TC applied to stage 1

If one takes a much higher TC for the lock-in amp, the Boxcar integrator can be neglected. Of course, the laptop has much more computation power to handle this huge of data in real-time! The advantage of implementing more Boxcar integrators is to react to different changes in response time.

Thats all. There is no mystery but a much potential to explore.

Aziz