Arduino Nano PI Main Discussion

[green]

I would say, that what you see, is your body field, not the earth field.

I've been thinking a coil has to rotate in a magnetic to develop a voltage. Moving a coil in the Earth field with no NS rotation shouldn't cause a voltage. Maybe I've been thinking wrong?

[Tinkerer]

I've been thinking a coil has to rotate in a magnetic to develop a voltage. Moving a coil in the Earth field with no NS rotation shouldn't cause a voltage. Maybe I've been thinking wrong?

I forgot to ask if the TC is on. Moving the coil in the earth field without the TX on, only the RX, will show the earth magnetic field if it is not compensated by the circuit. If the TX is on, the coil field will induce eddy currents in all conductors for a large distance. The human body is conductive.
We know very little how the eddy currents behave in the human body. Do the eddy currents just circulate in stationary eddies? Or do they discharge to ground? There is so much we don't know.

[lamoiz]

otherwise, the nano with the 32 coil works really well; the guys who are with me at the beach all have ctx3030 eq800 and sovereing minelabs. we did the depth test with the sovereing elite, and the nano. the result is very very close if the nano uses the boost.

[Agme]

Itsy Bitsy display for ANPI

I think I'm about done with this little OLED Display. I Just need to put it on at perf board and print the case.

https://imgur.com/a/aHuq4LO

I decided to give up on trying to make it small enough to go on the ANPI and just used a spare nano to run it. I set up the on board Nano to transmit the delay status and boost status over I2C when requested. Technically you could change the ANPI values through the display, but the knobs are already there.. Maybe next time.

Connections:
ANPI (A5) - Display Nano (A5) - OLED (SCL)
ANPI (A4) - Display Nano (A4) - OLED (SDA)
ANPI (VIN) - Display Nano (VIN) Thru Display power Switch - Voltage Divider
ANPI (GND) - Display Nano (GND) - Voltage Divider - OLED (GND)
ANPI (TP10) - Display Nano (A0)

Voltage Divider (220K/100K) - Display Nano (A1) 5V=16V

Display Switch (1) - Display Nano (D3)
Display Switch (2) - GND

OLED (VCC) - Display Nano (5V)

I am not certain if I need pull-up resistors on the SCL/SDA lines. I think the display already has them so I didn't add them.

Sorry I an lazy and don't want to draw a schematic. I can if someone really wants me too.

I dont really like the case drew.. I will provide models when I'm done with it.
Also I'm not sure how it will work in real world test... I will let you know when I get it mobile.




Revised Code for ANPI and Display Nano attached. I just used the Adafruit OLED Library.. it works for me and I was tired of trying to make the other libraries work on the display that I have.

OLED Test.zip

[green]

I forgot to ask if the TC is on. Moving the coil in the earth field without the TX on, only the RX, will show the earth magnetic field if it is not compensated by the circuit. If the TX is on, the coil field will induce eddy currents in all conductors for a large distance. The human body is conductive.
We know very little how the eddy currents behave in the human body. Do the eddy currents just circulate in stationary eddies? Or do they discharge to ground? There is so much we don't know.

Test was done with Rx coil only(200mm mono coil). Did some more testing, earth field sample connected to common(no earth field correction). Coil was positioned on a board about 2 feet long. Sliding the coil on the board back and forth didn't cause a signal. Positioning the board NS, South end stationary while moving the North end up and down caused a near +-full scale signal. Positioning the board EW, East end stationary while moving the West end up and down had a small signal. Was able to get minimum signal with a small change in EW direction.

[Tinkerer]

Test was done with Rx coil only(200mm mono coil). Did some more testing, earth field sample connected to common(no earth field correction). Coil was positioned on a board about 2 feet long. Sliding the coil on the board back and forth didn't cause a signal. Positioning the board NS, South end stationary while moving the North end up and down caused a near +-full scale signal. Positioning the board EW, East end stationary while moving the West end up and down had a small signal. Was able to get minimum signal with a small change in EW direction.

Just guessing. I would think that you have something in your lab that creates a strong magnetic field.
Inside the house it is common to have all sorts of localized magnetic fields. One usually looks for the place or position in the lab, where the least influences are felt for the coil. If this is not possible, the next best is to use always the same place and position.
Any real tests need to be done outside in a magnetically quite place.

[green]

Just guessing. I would think that you have something in your lab that creates a strong magnetic field.
Inside the house it is common to have all sorts of localized magnetic fields. One usually looks for the place or position in the lab, where the least influences are felt for the coil. If this is not possible, the next best is to use always the same place and position.
Any real tests need to be done outside in a magnetically quite place.

Are you suggesting I will see something different if the tests were done outside? I'm thinking my tests confirm the coil has to rotate thru the magnetic field to to generate a voltage. I would be interested if some would lay their detector on a board with the coil flat and rock the board NS and EW to see if EFE is effected compared to waving the coil side to side. And does waving the coil NS compared to EW make a difference.

[lamoiz]

otherwise, the nano with the 32 coil works really well; the guys who are with me at the beach all have ctx3030 eq800 and sovereing minelabs. we did the depth test with the sovereing elite, and the nano. the result is very very close if the nano uses the boost.

I specify, following my last message here, that the sovereign who was with me on the depth test, had an ULTIMATE 33cm disc and that the discrimination was on, but at zero.

[Carl-NC]

Some comments...

If the Earth field is perfectly homogeneous and you sweep the coil perfectly flat then there should be no EFE. In the field most people slightly tilt the coil at the ends of the sweep, or there can be slight field anomalies due to mineral variation (which might be somewhat deep) which is why EFE still shows up.

I wonder if lamoiz's problem is related to battery level.

In general, PI detectors are notorious for a wet salt "breathing" effect. If you walk parallel to the surf line, as you sweep the coil toward the water the PI picks up a greater concentration of conductive salt and gives a positive response, as you sweep away from the water there is a lower concentration and the response goes negative (quiet, usually). This is exacerbated on heavily sloped beaches and will create a slow response that is exactly in sync with the coil sweep. The best shielding in the world won't stop this. The 2 ways to deal with it are 1) turn the pulse delay up or 2) turn the SAT speed up until it is manageable.

Edit: Third way to deal with it is to hunt perpendicular to the surf; that is, walk straight into the surf, then straight back out of it. Keep the swing arc down to 45 degrees or so.

[lamoiz]

Some comments...

If the Earth field is perfectly homogeneous and you sweep the coil perfectly flat then there should be no EFE. In the field most people slightly tilt the coil at the ends of the sweep, or there can be slight field anomalies due to mineral variation (which might be somewhat deep) which is why EFE still shows up.

I wonder if lamoiz's problem is related to battery level.

In general, PI detectors are notorious for a wet salt "breathing" effect. If you walk parallel to the surf line, as you sweep the coil toward the water the PI picks up a greater concentration of conductive salt and gives a positive response, as you sweep away from the water there is a lower concentration and the response goes negative (quiet, usually). This is exacerbated on heavily sloped beaches and will create a slow response that is exactly in sync with the coil sweep. The best shielding in the world won't stop this. The 2 ways to deal with it are 1) turn the pulse delay up or 2) turn the SAT speed up until it is manageable.

Edit: Third way to deal with it is to hunt perpendicular to the surf; that is, walk straight into the surf, then straight back out of it. Keep the swing arc down to 45 degrees or so.

no, it's not a battery problem, I actually noticed everything that carl has just described. the problem was much less when I was above the water. and more present when on the dry to wet transition. the shielding of my coil is very efficient, so it is after this that I asked myself lots of questions ..
as I am back in the workshop, I was able to control the 12v regulation system ... and there is no problem ...
how to deal with the problem on the nano ..? SAT ..?

[Carl-NC]

Yes, you can speed up the SAT. The default is 470n*220k = 100ms, try a 100k resistor.

[lamoiz]

Yes, you can speed up the SAT. The default is 470n*220k = 100ms, try a 100k resistor.

ok thank you carl, I change r24 with 100k or by a potentiometer on the front to adjust on the ground of the beach. I'm going back to the ocean at the beginning of September and I'm testing this!

[Carl-NC]

I would replace R24 by a 47k resistor in series with a 1M pot, then you can adjust from unreasonably fast to unreasonably slow.

[lamoiz]

I would replace R24 by a 47k resistor in series with a 1M pot, then you can adjust from unreasonably fast to unreasonably slow.

I will do that !

[mermelado]

Some comments...

If the Earth field is perfectly homogeneous and you sweep the coil perfectly flat then there should be no EFE. In the field most people slightly tilt the coil at the ends of the sweep, or there can be slight field anomalies due to mineral variation (which might be somewhat deep) which is why EFE still shows up.

I wonder if lamoiz's problem is related to battery level.

In general, PI detectors are notorious for a wet salt "breathing" effect. If you walk parallel to the surf line, as you sweep the coil toward the water the PI picks up a greater concentration of conductive salt and gives a positive response, as you sweep away from the water there is a lower concentration and the response goes negative (quiet, usually). This is exacerbated on heavily sloped beaches and will create a slow response that is exactly in sync with the coil sweep. The best shielding in the world won't stop this. The 2 ways to deal with it are 1) turn the pulse delay up or 2) turn the SAT speed up until it is manageable.

Edit: Third way to deal with it is to hunt perpendicular to the surf; that is, walk straight into the surf, then straight back out of it. Keep the swing arc down to 45 degrees or so.

Hi Carl: And using it underwater with a waterproof coil, since the salinity is similar everywhere, will that effect occur?