new MineLab Machine

[Chiv]

just took left and right side of coil on muli all the other pic where centre of coil

[waltr]

agree with taktyk. you see self resonance on your o-scope probe+input.

Does the pickup coil need a damping resistor?

Ahhh yea...pickup coil's self resonance!

[Skippy]

I think Mr. Chiv needs some assistance.
The 5kHz waveform is a square wave, with a period of 1/5000 sec = 200 microsecs. So choose a Timebase setting of 50 microsecs/div, so that one cycle appears as 4 divisions on the screen, and the total screen shows about 2.5 cycles.
Similarly, to best see the 10KHz and 15KHz freqs, choose Timebase = 20 microsecs/div.
The 20KHz and 40KHz would appear best with Timebase = 10 microsecs/div.

Reference Post 30: This is what the 'Multi' waveform looks like. Square in shape, with differing widths to just about every transition. But the waveform does repeat. The lowest frequency component is 5KHz, so the repetition rate is 5KHz. That means the entire complicated waveform cycle takes 1/5000 sec = 200 microsecs. So to see this on a scope screen, you want the Timebase set to 20 microsecs/divn.

Reference Post 74: All the high frequency oscillation ( 450KHz?) DOESN'T exist. It's not produced by the detector. It's entirely generated by your pickup coil, it's inductance and capacitance, and possibly a bit of the scope probe capacitance. A damping resistor across the pickup coil should get rid of the majority of it. A reasonable starting value to try is 200 Ohms, but it may need to be anywhere from 75R up to 500R. The simplest way to find this out is to set the machine in 5KHz mode, and adjust the resistor so on the scope screen the waveform appears 'the most square'.

If you have success, the other outputs we'd like to see would be the gold prospecting mode ones, which may be a mix of 20K and 40K, or maybe 5K/20K and 10K/40K, we don't know.
And do the beach modes produce anything different, compared to land mode?

[Carl-NC]

I keep telling you guys...

LOOK AT THE CURRENT, NOT THE VOLTAGE.

OK, here it is... Drum roll... the Equinox TX waveform:

[Taktyk]

The method is identical as in the Spectra metal detector.
Carl, you have current waveform?

Regards

[Taktyk]

I keep telling you guys...

LOOK AT THE CURRENT, NOT THE VOLTAGE.

OK, here it is... Drum roll... the Equinox TX waveform:

[ATTACH]42979[/ATTACH]

Ok. I also already see... What is the current Ipp?

[Skippy]

Carl: It's not that easy to measure the current, that's why we're avoiding it. Mr. Chiv barely knows how to use a 'scope, he's not going to be using a clamp-on DC current probe; and hacking together a 'break-in' cable so he can put a series resistor inline is not easy. Sure, I could do it, I've access to good lab facilities, have good skills, and I'm confident enough to risk mucking about with 1300 Dollars worth of detector. But I don't have the Nox.
Besides, we're just trying to understand the basic facts, current or voltage will suffice, as up until this point, the only info source has been the manufacturer ..........
We want to know what is different in the different operating modes -
* Are single-freq modes actually that, or are they multi-freq with just one freq processed?
* Prospecting modes are apparently multi-freq... what, though? 5K & 20K, and 10K & 40K perhaps? Or just using 20 &40 ?
* Does Beach mode use all the freqs, or maybe only 5/10/15?

And regarding your scope screen:
The waveform appears to have a period of 380 usec, freq = 2.6kHz. Half what I would expect. Am I missing something?

[kt315]

put a resistor 0.5-1.0R in series and connect o-scope to it. you will see the current.

[Skippy]

It's a bit of bother, though, KT. There's 8 connector pins, probably all of them are used. Unless you know what the connector type is that ML used, you would need some small sockets, like turned-pin IC sockets. Plain wire would be OK to bodge the matching pins. A short break-in cable extension would be best, under 10cm. A bit of DVM / scope probing should tell you what is the TX. The internal pics show some pins have fat tracks to them, these will be the TX and ground connections, I assume:
https://fccid.io/png.php?id=3643401&page=1
Then choose where to fit the resistor, agreed 0.5 Ohm or less should be OK.

[Carl-NC]

Carl: It's not that easy to measure the current, that's why we're avoiding it. Mr. Chiv barely knows how to use a 'scope, he's not going to be using a clamp-on DC current probe; and hacking together a 'break-in' cable so he can put a series resistor inline is not easy. Sure, I could do it, I've access to good lab facilities, have good skills, and I'm confident enough to risk mucking about with 1300 Dollars worth of detector. But I don't have the Nox.
Besides, we're just trying to understand the basic facts, current or voltage will suffice, as up until this point, the only info source has been the manufacturer ..........
We want to know what is different in the different operating modes -
* Are single-freq modes actually that, or are they multi-freq with just one freq processed?
* Prospecting modes are apparently multi-freq... what, though? 5K & 20K, and 10K & 40K perhaps? Or just using 20 &40 ?
* Does Beach mode use all the freqs, or maybe only 5/10/15?

And regarding your scope screen:
The waveform appears to have a period of 380 usec, freq = 2.6kHz. Half what I would expect. Am I missing something?

Fair enough criticism... however, I cheated. I didn't actually measure the coil current, I measured the TX magnetic field. Which happens to have the exact same waveform as the coil current. I used a magnetic field probe which I built...

Ok. I also already see... What is the current Ipp?

...as such I don't know the current Ipp.

BTW, Minelab already published the TX voltage waveform, from which you could construct the TX current waveform. I did this months ago. Today was the first time I actually looked at the real waveform, and it matches exactly what I expected.

[Carl-NC]

And regarding your scope screen:
The waveform appears to have a period of 380 usec, freq = 2.6kHz. Half what I would expect. Am I missing something?

I've started a new thread on this, as a challenge. You guys are pretty smart, let's see what you come up with.

[6666]

something like this ?

[Carl-NC]

Much simpler... just a coil wrapped on small ferrite rod. Actually a surplus pinpointer coil from designing the F-Pulse.

[Skippy]

Mr. Chiv's USB 'scope has spectrum analyser capability, that was going to be my next request once he's got a decent looking trace - what does it make of it all?

I hope your new thread gets a better response than my question on the freq content in Post 27,30.

[Chiv]

I think Mr. Chiv needs some assistance.
The 5kHz waveform is a square wave, with a period of 1/5000 sec = 200 microsecs. So choose a Timebase setting of 50 microsecs/div, so that one cycle appears as 4 divisions on the screen, and the total screen shows about 2.5 cycles.
Similarly, to best see the 10KHz and 15KHz freqs, choose Timebase = 20 microsecs/div.
The 20KHz and 40KHz would appear best with Timebase = 10 microsecs/div.

ok had a crack at this. thanks Skippy for explanation, ended up with680R to give me the best square as I could get.

P1
P1
P1
P1
P1
P1
P1
P1 multi
P1 multi