VLF MD with digital signal processing : Bee-Buzz 1

[moodz]

Any cancelling scheme would also cancel the target because the interferance you need to worry about is inband of your desired signal ..
Amplification only amplifies the wideband noise and the inband signal for no benefit unless you call making the noise bigger a benefit.
When the signal is under the noise then a preamp is more than useless.


So on my WORKING detector that does use a lockin amplifier ( read up on lockin amplifier reserve ) I have a real reserve of 112 dB ... which means it can pull a signal from 112 dB from below the noise level. Commercial lockin amps can pull a signal from 120 dB below the noise level so I am almost on par.
In the picture below I turn on the LED lighting in the lab for about 10 seconds then off again .... you can see the inband interferance coming from the lighting ... dont need a preamp on the ADC. The target signal ( 10 decimal digits in the upper left corner VA corresponds to 180 db of signal range but only the last digit is changing with low noise )

[moodz]

Hi all,

I have done some real measurements with an RX coil. With preamp (gain 100 or +40 dB) and without pre-amp.
So the EMI noise level is approx. -20 dB below the noise floor level (-120 dB) on quiet regions without the pre-amp.
A gain of +20 dB (x10) is minimum required to rise the residual signals above the noise floor level.

You see, I need this fkn pre-amp.
Aziz

LOL ....must be a real special amp that lifts the signal without lifting the noise.

[Aziz]

Hey guys,

I also want to measure the EMI noise in the field. Lets look at the EMI signal level there. I'm sure there is much less noise compared to at home.
I hope the preamp gain of 100 is enough to see the difference.


Aziz

[ArchibaldSTM]

37 pages of empty words, but no result))))

[Aziz]

The ADS1220 is useless for direct sampling. 2 k-SPS vs 192 k-SPS (my sound card) = ADS127L11 400-kSPS, Wide-Bandwidth, 24-Bit, Delta-Sigma ADC datasheet (Rev. C)

My sound card is still better regarding snr, enob and noise specs at 192 kHz SR.


And I don't need any soldering iron and micro controller to operate the chip.

[pito]

The ADS1220 is useless for direct sampling. 2 k-SPS vs 192 k-SPS (my sound card) = ADS127L11 400-kSPS, Wide-Bandwidth, 24-Bit, Delta-Sigma ADC datasheet (Rev. C)

[pito]

Hi all,

I have done some real measurements with an RX coil.
So the EMI noise
You see, I need this fkn pre-amp.
Aziz

EMI mostly is caused by power lines 60Hz/50Hz and harmonic of them, ADS 1220 has filters 60Hz/50Hz


I have done some real measurements with an RX coil. With preamp (gain 100 or +40 dB) = show it on oscilloscope

[Aziz]

Hi all,

I have done some real measurements with an RX coil. With preamp (gain 100 or +40 dB) and without pre-amp.
So the EMI noise level is approx. -20 dB below the noise floor level (-120 dB) on quiet regions without the pre-amp.
A gain of +20 dB (x10) is minimum required to rise the residual signals above the noise floor level.

You see, I need this fkn pre-amp.
Aziz

[Aziz]

Hi all,

now I expect from you all, that the active EMI noise cancelling won't work without an AI RX-coil. So what are your arguments against the novel idea? It hasn't been done yet in the metal detecting field. This is a fnk non-trivial task.
And will it prevent me doing this?

White noise (Johnson noise), 1/f noise (flicker noise), true random events caused noise can't be cancelled. That's a fact.
But the continious EMI noise can be. To some extend. With relative good magnitude and phase prediction.

Aziz

[Aziz]

And here is a ADS detector, what is missing is Arduino Goertzel phase detector code


This is why you dont need amplifier at the front end of the direct sampling ADC metal detector.

The ADS1220 is useless for direct sampling. 2 k-SPS vs 192 k-SPS (my sound card). We would require hw demods for this adc. No go.

[Aziz]

Hi Paul,

I have shown, that there is absolutely no difference between Goertzel, Lock-in Amplifier and FFT demodulation. It's only a matter of decoding bandwidth (bin resolution).

I need the pre-amp with my sound card.
Cheers
Aziz

[Marchel]

Here are projects where these ADCs are used and are made in Arduino.

https://tehnodium.ru/forum-13.html

[pito]

And here is a ADS detector, what is missing is Arduino Goertzel phase detector code


This is why you dont need amplifier at the front end of the direct sampling ADC metal detector.

[pito]

You have to adapt the reference c-code into your arduino system. .

iI am not able to do it

[moodz]

Aziz you have been talking about the wrong solution for the amplifier ....the correct amplifier is a type of lockin amplifier... It pulls the required signal (amplitude and phase) from below the noise floor mainly because 99% of noise is asynchronous which the locking rejects. Synchronous noise is very low if you choose your transmit frequencies carefully. ...eg -140db

the lock-in is implementable in pure software only needs data from ADC. No preamp is required as that would just make the noise worse.

Also FFT is the wrong processing solution ...we already know the TX frequency... It's a phase and time vector discrimination problem.

Allows you to build a detector to that can discriminate targets at 1 meter from the coil with target range better than a PI for same size coil.