VLF MD with digital signal processing : Bee-Buzz 1

[Aziz]

I found post #384, but there I see only theories, or is there an example.
I familiar with arduino programming

You have to adapt the reference c-code into your arduino system. That's all. It's only a programming issue.

[moodz]

Hi Paul,

I didn't know, that there is a market for audiophile friends to pay every price. 40 $ for one discrete op-amp.

Direct sampling with a good sound card with a single ended RX-front end (just the RX coil), works fine up to 19 - 20 bits resolution (or -114 dB - 120 dB noise floor level). But if we use an anti-interference (AI) RX-coil, then we have plenty room to go down the noise floor level (at least 20 dB) to get the faint signals. In this case, a pre-amp is very fine to do the job to rise the signal level above the noise floor level of the ADC. Even if we don't use an AI-coil, the EMI noise at the frequency of interest may be lower than the noise floor level of the ADC system. In this case, a pre-amp is required too to get the faint signals.

BTW, I like EMI noise. It's measureable if active. It's predictable if active. It's cancelable if active. A big software effort should be invested in the active EMI noise cancelling using the FFT.
Cheers,
Aziz

..those discrete opamps can be alot more than $40. Try $200 ...see Burson range ... apparently they are chemically optimised probably to match the $2000 oxygen free single crystalline metal matrix directional copper speaker cables.

[Altra]

Audiophiles are the only group crazier than metal detector builders.

[Aziz]

..those discrete opamps can be alot more than $40. Try $200 ...see Burson range ... apparently they are chemically optimised probably to match the $2000 oxygen free single crystalline metal matrix directional copper speaker cables.

You made my day.

[Aziz]

So the big problem is still there: EMI noise.
White noise is our friend. My ADC system delivers enough of it. Even the preamp delivers a bit.
Any idea about EMI noise problem without an AI RX coil? Filter won't solve any problem here if the frequency of interest is affected by EMI noise source. Reducing bandwidth of the decoder won't solve it either (would slow down the detection rate).

We need some kind of "flux capacitor".
https://en.m.wikipedia.org/wiki/DeLo...Flux_capacitor

Or something equivalent.

[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.

[pito]

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

iI am not able to do it

[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.

[Marchel]

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

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

[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

[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 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]

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

[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

[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)