Arduino Nano PI Main Discussion

[green]

Charted ground decay(change in integrator out)vs target delay time, 10us target sample. Can detect a 1 to 2mV change at integrator out on the bench.

Looked at chart log-log this morning. Different slope than I expected. Charted ground decay with Excel, amplifier out and integrator out(delay+10us). Looks similar to what I measured this morning. My math skills are lacking, maybe someone could explain why integrator out decay is a lot slower than amplifier out.

[MartyJ1963]

Hiya George, hope you're well. Did you have to shield the ABS plastic enclosure for your Arduino detector? I'm stuck whether to get an Aluminium enclosure or an ABS one,,,which one is best to use please? Regards, Marty.

[Qiaozhi]

Hiya George, hope you're well. Did you have to shield the ABS plastic enclosure for your Arduino detector? I'm stuck whether to get an Aluminium enclosure or an ABS one,,,which one is best to use please? Regards, Marty.

Hi Marty,

I didn't shield the enclosure, and it seems to be fine.
In the past I was convinced that a metal enclosure was almost mandatory to eliminate any external noise, but it doesn't always seem to be necessary in practice. With Crossbow I used an extruded aluminium case, and did notice that it was important to make sure the shield from the coil cable made a good electrical connection to the coil plug casing, otherwise the audio was less stable. The only problem with a metal enclosure is that the detector can become quite heavy.
It would be interesting to get opinions from other members on this subject.

[Qiaozhi]

In a handheld detector the alternative is to make sure the mains frequency aliases outside the target filter bandwidth. This is usually set by the demod and the Nano has a BW = 1.5Hz (which is pretty low). Assuming 50Hz mains, if you set the detector to 1200Hz then the alias is synchronous and becomes a DC offset. But if the mains drifts by 0.1% then the alias is at 1201.2Hz and you hear a 1.2Hz beat frequency. However, if you set the detector to 1225 Hz then the 50Hz alias is at 25Hz which is suppressed by the target filter BW. And any minor mains variation remains suppressed. BTW, the demod is often followed by additional filtering that roughly matches the demod BW to offer better mains suppression. In the Nano, this would be R26-C15... setting them to 1.5Hz will help (they are currently 16Hz).

Interesting ...
The values used by the Nano are the same as those for Surf-PI. I hadn't noticed the difference in cut-off frequency between the two opamp stages, so I'll try changing C15 to 1uF, and setting the detector to 1225pps. Then I'll report back here with the results.

[MartyJ1963]

Thanks George. I'll try an ABS enclosure then for the Arduino project first. Thanks also for the advice on the Crossbow, I was looking for info on that too. I should have my Arduino detector ready to test by the weekend if the 2 components I need arrive. Thanks again, Marty.

[6666]

Thanks George. I'll try an ABS enclosure then for the Arduino project first. Thanks also for the advice on the Crossbow, I was looking for info on that too. I should have my Arduino detector ready to test by the weekend if the 2 components I need arrive. Thanks again, Marty.

Copper tape inside an ABS box works ok.

[6666]

If anybody in Australia is interested I have ordered some nano PCB's and have two spare
if you want to put your name on one pm me,

[Tinkerer]

Charted ground decay(change in integrator out)vs target delay time, 10us target sample. Can detect a 1 to 2mV change at integrator out on the bench.

Does this represent a "viscous ground"? An initial faster, linear decay and then a slower exponential decay? Or in other words, a short TC and a long TC?

[MartyJ1963]

Thanks Bruce. If I shielded it with Copper tape, what would I ground to the tape? And, would I have to leave a gap like you do when copper shielding a monocoil? Is it Battery negative and the coil connector cos' I'm not certain with ever only using Aluminium enclosures? Regards, Marty

[lc516]

I have found the answer to my question.
Please delete this post

[green]

Does this represent a "viscous ground"? An initial faster, linear decay and then a slower exponential decay? Or in other words, a short TC and a long TC?

I think the ground decay is straight line log-log. Including a recording of the California ground I made with my Target Response Tester, amplifier out. Not perfectly straight, probably do to my tester. The quarter starts out straight line log-log and then finally decays straight line linear log. Can't record enough decades at amplifier out to see if ground finally decays straight line linear log. Recording integrator out for targets<10us TC seems to be close to the same as amplifier out(straight line linear log)Thicker targets and ground don't chart the same at amplifier out and integrator out.

[godigit1]

Charted ground decay(change in integrator out)vs target delay time, 10us target sample. Can detect a 1 to 2mV change at integrator out on the bench.

I was wondering where in CA your sample came from?

It sounds like a pretty hot ground sample if it saturates your detector at 3/4 a inch maybe I'm thinking about it wrong, Did you use a magnet to clear out any possibly small iron.
Have you tried detecting your nuggets and foil sandwiched or under the sample?

What % of your soil is magnetic?

If you weigh 20 grams and separate out the magnetic soil it should give you a idea or me of the the diamagnetic properties in your sample.
I could maybe find something close by or even get dirt form the same area.


Can you move your target signal "I" independently of you ground signal "I" or are they synced up.
If so can you find a happy spot where the soil does not react.

I need to get A gb machine up and running on the bench to help me learn and try to recreate your sample timings.
Might be a good idea for me to re fire up the Mpp GB board soon tp help work out timings for the Pro Q.
Allot to do right now I also just restarted my Voodoo as well that I had set aside for troubleshooting and the nano Pi boards should be here the 14th ( Busy Busy) I need a bigger bench.

[green]

I was wondering where in CA your sample came from?It sounds like a pretty hot ground sample if it saturates your detector at 3/4 a inch maybe I'm thinking about it wrong, Did you use a magnet to clear out any possibly small iron. Have you tried detecting your nuggets and foil sandwiched or under the sample? What % of your soil is magnetic? If you weigh 20 grams and separate out the magnetic soil it should give you a idea or me of the the diamagnetic properties in your sample.I could maybe find something close by or even get dirt form the same area. Can you move your target signal "I" independently of you ground signal "I" or are they synced up.If so can you find a happy spot where the soil does not react.I need to get A gb machine up and running on the bench to help me learn and try to recreate your sample timings. Might be a good idea for me to re fire up the Mpp GB board soon tp help work out timings for the Pro Q.Allot to do right now I also just restarted my Voodoo as well that I had set aside for troubleshooting and the nano Pi boards should be here the 14th ( Busy Busy) I need a bigger bench.

https://www.geotech1.com/forums/show...814#post199814 I can adjust target sample time to cancel ground signal from my back yard with GB switched on and the see target as long as it doesn't fall in the hole with my PI. Figure8 Rx coil reduces ground signal and signal from a zip lock bag from back yard is about 1/5 the signal. Figure8 coil can cancel the California bag if positioned between the figure8 Rx coils. Don't know how difficult it would be to keep the signal low enough swinging the coil over the California ground, no problem in the yard with GB on(not usable with GB off). I think 1/5 the signal is still fairly high? Dirt from back yard, almost nothing sticks to magnet.

I see the decay chart reply #46 from above thread states Calif ground 80 times Al ground but chart shows over 3 times. Two many stupid pills? I measured 5 times this morning at integrator out.

[green]

I need to get A gb machine up and running on the bench to help me learn and try to recreate your sample timings.
Might be a good idea for me to re fire up the Mpp GB board soon tp help work out timings for the Pro Q.
Allot to do right now I also just restarted my Voodoo as well that I had set aside for troubleshooting and the nano Pi boards should be here the 14th ( Busy Busy) I need a bigger bench.

MPP integrator doesn't work for GB, use a 1C integrator. https://www.geotech1.com/forums/show...059#post264059

[Qiaozhi]

MPP integrator doesn't work for GB, use a 1C integrator. https://www.geotech1.com/forums/show...059#post264059

If you look at a Goldscan 2 schematic, you will see that it uses the same integrator circuit as the MPP, and the GS2 includes ground balance.