Ground balance add on board for Mini pulse .

[cristiano.sar]

Is there a finished add-on board to add ground balance to Minipulse Plus beach rev-e? Thanks

[Matt_Rowe]

Heres a pic of what we find in Az, we call these pickers, some call them nuggets but shouldnt, in my mind, a nugget is more than 1oz. This one weighs .3 tenths of a gram.Click on this jpg link.

[Matt_Rowe]

Heres a good read for the Pi about GB and Coil, start at page 2 i guess.
http://chemelec.com/Projects/Metal-1...I-Detector.htm

[green]

and try how I did GB on a HH2:
https://www.geotech1.com/forums/show...ake-on-the-HH2

GB starts in post #14.

May need to increase gain of second sample not sample time before subtracting to GB with MPP https://www.geotech1.com/forums/show...059#post264059

[waltr]

and try how I did GB on a HH2:
https://www.geotech1.com/forums/show...ake-on-the-HH2

GB starts in post #14.

[Qiaozhi]

Hi All,

I am new to this forum, and have just purchased the MPP Beach (RevE) kit, an IP68 instrument case and water proof pots/switches etc .. my intention is to have the complete detector fully waterproof ..

I have a question regarding ground balancing techniques, as I would like to add that too:
Why can you not just increase the sample time for the Earth field effect, so that it takes care of ground as well? Why the extra two samples ... (just trying to do the minimum possible, as long as it works )

Cheers

Try this ->
https://www.geotech1.com/forums/show...769#post201769

or you could lose your mind by reading this ->
https://www.geotech1.com/forums/show...718#post208718
and the 5 posts after it.

[6666]

bump

[SaltyDog]

Hi All,

I am new to this forum, and have just purchased the MPP Beach (RevE) kit, an IP68 instrument case and water proof pots/switches etc .. my intention is to have the complete detector fully waterproof ..

I have a question regarding ground balancing techniques, as I would like to add that too:
Why can you not just increase the sample time for the Earth field effect, so that it takes care of ground as well? Why the extra two samples ... (just trying to do the minimum possible, as long as it works )

Cheers

[Teleno]

Of the two op amp configurations you have designed for the MPP which one would be faster?

This one is faster because the last stage is a current-feedback op amp.

Im going to order the 6181 and is the 2338 critical or will any NPN do ?

The 2N4338 is an N-channel JFET switch. I used it because it's available in LTspice.
The MPP uses J113, you can use it here too.

JFET switches with a lower VGS(off) have lower on-resistance but you need around -10V in order to shut them off properly. On-resistance is not critical in this design, so the optimal type depends on the minimum voltage available to be applied to the gate during tun-off. In the MPP is -12V, so you can go hapily with the lowest on-resistance types such as the J111. If you only have say -5V available then go for the J113.

The characteristics of these types are on page 3 of this data sheet https://www.mouser.com/ds/2/149/J113-889353.pdf

Also should I build the circut above or the one in the spice sim below?

The one in the spice sim below is better, but before using it on the MPP you have to configure U2 as NON INVERTING (it's inverting in the sim), otherwise the output of the preamp will be on the wrong side of GND. It has to be negative going for the MPP.

If you're detecting for nuggets then use the lowest coil current you can afford. it will reduce depth for general targets but since you'll be able to sample earlier, it may actually increase sensitivity to smaller gold. Or just use a DD coil and get the best of both worlds.

[godigit1]

Hi Teleno,
Thanks for sharing your circut.
Of the two op amp configurations you have designed for the MPP which one would be faster?
Also interested in the DEboo configuration you have mentioned. Like I have said I have allot of studying to do.
Im going to order the 6181 and is the 2338 critical or will any NPN do ?

Also should I build the circut above or the one in the spice sim below?

Thanks again

[waltr]

A thing came to my mind... the timing may of course be produced by a PIC. But PIC may also double as a through zero VCO to fix the dual polarity issue. It may as well produce an effect in VCO sound to indicate positive vs. negative response, thus adding a sort of discrimination to it. The existing 555 may still act as an amplifier. A bit radical, but doable.

yes, that is what I did with a PIC (could be done with an arduino as well) on my HH2.
The audio out does high verse low conductor discrimination. Ferrous however can go either way so no Fe discrimination.

[godigit1]

Hi Digger,

Thanks for looking in on this thread. I didnt know if you were still around the forum or not but glad to see you here.
Yes my first question is Find any GOLD???
Second is have you tried different coil types like self shielding versus shielded coils? Does it make any difference in performance?
Thanks for sharing your circut Im just about set back up to finish it. I was going to play with a couple different balance methods if I can but for this add on board Im going to do it your way and just play with the timings so its a plug in add on for the stock MPP.
I may have more quetions along the way but you covered the one I had for now. I was not switching off at the fets instead at ground and -5.
Thanks again.

[Davor]

A thing came to my mind... the timing may of course be produced by a PIC. But PIC may also double as a through zero VCO to fix the dual polarity issue. It may as well produce an effect in VCO sound to indicate positive vs. negative response, thus adding a sort of discrimination to it. The existing 555 may still act as an amplifier. A bit radical, but doable.

[Digger429]

Second attempt at images. This time I'll just link externally to imgur.

The on/off switch for the GB is indeed a two pole switch that just switches to ground. That is, the grey and white wires going to the FETs in this picture here...

...are switched to ground.


Here is a diagram of the timings I've setup, so I can run the machine at about 1000 pulses per second:

[Davor]

That's right. Auto-zeroing the amplifier is simpler than a differential integrator and less tolerance sensitive.

Well, the servo you put to form an auto-zero is also an integrator. But running it separately from a main integrator makes duration of EF largely independent from a main sample duration. It should be possible to use more of the main sample energy for the purpose of ... detecting. Makes sense