Arduino Nano PI Main Discussion

[Qiaozhi]

Hi,Qiaozhi
I'm also concerned the issue that what the best preamp.
What is "Voodoo transmit circuit and PI preamp"? Can you show schematic of it?

See attached files.

[lc516]

In terms of existing [and known working] projects, I would suggest using the Voodoo transmit circuit and PI preamp, as this can be driven from a micro.

Hi,Qiaozhi
I'm also concerned the issue that what the best preamp.
What is "Voodoo transmit circuit and PI preamp"? Can you show schematic of it?

[Qiaozhi]

Perhaps I should be asking what the best TX and pre-amp circuit's are? Wow, that's a loaded question! This rabbit trail might be worthy of a different thread.

In terms of existing [and known working] projects, I would suggest using the Voodoo transmit circuit and PI preamp, as this can be driven from a micro.

[dingbatca]

Qiaozhi (George). UXO is interesting. My end goal is "direct sampling with a much more powerful processor" using a Black Pill. That in combination with some code ported over from the STM32-O-Scope project to allow visualization of any test point on the circuit board in the field, with out the need of a full scope. Basically a PI metal detector that is mostly firmware with minimal electronics. Electronics are scary! My skills are in firmware. :-)

Perhaps I should be asking what the best TX and pre-amp circuit's are? Wow, that's a loaded question! This rabbit trail might be worthy of a different thread.

[Qiaozhi]

As I am genuinely curious; what would it take to tune the Nano Pi to search for gold? I have a little 0.35 gram gold nugget that my Simplex+ can see at 4 inches. But my Nano Pi cant seem to see it at all.

Probably a rework of the RX preamp design and adjusting sample timing and sample delay.
A small piece of natural gold has a very short TC. Therefore one must sample early to detect the very short decay.

You would also need to implement ground balance.
Take a look at this -> UXO Target Detection and Discrimination with Electromagnetic Differential Illumination
There's an Arduino sketch which uses the well-known subtractive method, and it's possible to get the sample delay down to 8us. You could even sample earlier than that by directly accessing the ports and not using digitalWrite(). However this presumes you have a fast coil, have modified the Tx circuit (as shown in the "Investigation of UXO paper.pdf"), and possibly modified the preamp.

[Goaty]

All good Marty. No rush for reply as it looks like you have enough on your hands at the moment!
Cheers
Trev

[MartyJ1963]

Hiya Trev,,,,Hope you and Bridgitte are well! I only saw your email the other day because I've been having trouble lately with my PC and something went wrong with Microsoft Outlook for some reason! When It finally started working and I got logged in I found 1,000's of emails!! It was really overwhelmng and took me hours to read through everything etc,,,! Lol. Thanks for remnding me what 'SS' stands for,,I remember now,,Lol. Say Hi t Bridgitte and I'll be writing to you soon. Take care for now and stay safe, Regards, Marty.

[Goaty]

"SS" is for self shielding as the 'outer' turns effectively shield the main bulk of the coil.

[MartyJ1963]

@Dingbatca, The link you posted of the 'Basket' coil' is the same as the 3DSS coil that it is commonly now called on Geotech. The '3D' refers to the 3-Dimensional finished shape of the coil. I can't remember what the 'SS' stands for now but you can find a really in depth building method on the Chance PI Thread. Regards, Marty.

[waltr]

I know of a basket coil. What is a 3DSS coil? Build instructions?

Search the forum, there are threads about it here.

[dingbatca]

I know of a basket coil. What is a 3DSS coil? Build instructions?

[MartyJ1963]

Hi All. I've only had time to test 2 coils up to present. I thought I'd post some prelimanary results for now before I do my proper tests as I am still bulding other coils that I plan to use with the ANPI.
7" Inch 3DSS:- British 1p/5p/20p coin=10" depth and faintly around 12". British 10p/50p and ?1 coin= 12" depth.
10.5" 3DSS:- British 1p/5p/20p coin really loud at 11-12" and faint at 13-14". British 10p/50p and ?1 coin= 13-14" loud and faint around 15".
I have other coils to try once they're finished. The 7" and 10.5" coils are both exactly 300uh and 1.4 ohms. Both made with 0.5mm/16 strand/PTFE Coated/600v wire. Regards, Marty.

[waltr]

As I am genuinely curious; what would it take to tune the Nano Pi to search for gold? I have a little 0.35 gram gold nugget that my Simplex+ can see at 4 inches. But my Nano Pi cant seem to see it at all.

Probably a rework of the RX preamp design and adjusting sample timing and sample delay.
A small piece of natural gold has a very short TC. Therefore one must sample early to detect the very short decay.

[dingbatca]

As I am genuinely curious; what would it take to tune the Nano Pi to search for gold? I have a little 0.35 gram gold nugget that my Simplex+ can see at 4 inches. But my Nano Pi cant seem to see it at all.

[MartyJ1963]

Hiya Alec,,Hope you're well. I still can't sort my Crossbows though. Even with the new IC's, I swapped everything out, re-checked voltages, re-calibrated all the settings etc and I'm still only getting 4" on a small pair of pliers,,,this is on both Crossbows,,so I really can't figure out what's wrong and how to correct it! Glad I got the ANPI's sorted though,,,really pleased with this little detector! I'd love to have a working Crossbow though too! ,,Lol. Take care Alec,,,Regards, Marty.