Arduino metal detector?

[useus]

The final firmware version 3.4 is ready - FoxyPIv3_4.ino.eightanaloginputs.hex
What's new:

• MOSFET overheating is excluded
• increased stability
• added auto-tuning interval between ADC samples
• added display of the signal curve after auto-balancing

And here is how the interference from a nearby LCD TV appears:

Congratulations for the project, I would be curious to try an adaptation of your software on the felezjoo pi circuit (same avr of your project, similar but different scheme but I think easily adaptable)

[Vadim18]

FoxyLab make a nice project. At least simple and good as reference for comparsion.
Sory i forget about common mode voltage range limitation, ne5534 will not work here, tl071 will do.

[Vadim18]

OpAmp LM358 too slow for PI-detector

Yes, thats why im wondering to! But in opposite shorter bandwidt will produce a less noise) Of course analog part of this detector is less good than digital, so simply placing ne5534 instead of lm358 will boost sensivity. Also high-pass RC filter with R10k and C 0.1 uf beetwen op amp and atmega will be nice, as it help to reduce low frequency noise. I think at nowedays lm358 is one of the best op amp for flicker noise generator project

[FoxyLab]

Video illustration of metal detector starting procedures:

[FoxyLab]

The final firmware version 3.4 is ready - FoxyPIv3_4.ino.eightanaloginputs.hex
What's new:

• MOSFET overheating is excluded
• increased stability
• added auto-tuning interval between ADC samples
• added display of the signal curve after auto-balancing

And here is how the interference from a nearby LCD TV appears:

[FoxyLab]

OpAmp LM358 too slow for PI-detector

Probably it is.
But he is trying very hard. :-)
All this device is a compromise between extreme simplicity and acceptable sensitivity and stability for me.

[Eddy71]

OpAmp LM358 too slow for PI-detector

[FoxyLab]

I built a model of the entire power part of my metal detector for LTspice XVII:
FoxyPI_v3_tran.asc

You can play with the parameters and watch, for example, the voltage on the search coil (1), on the ADC input (2), the current in the coil (3):

[6666]

I have drawn FoxyPI v3 schematic in KiCad (see attached image for zoom):

Thanks

[FoxyLab]

I have drawn FoxyPI v3 schematic in KiCad (see attached image for zoom):

[FoxyLab]

Finds in the garden with FoxyPI after electrolytic cleaning:

[FoxyLab]

Specified weight: 55 - 60 grams
Density: 3,6 - 4 grams per cubic cm

[FoxyLab]

Hard to tell but looks more like magnatite.
...
Their are shots of color streaks on the web you might be able to see the colors better. But hematite is usually browner than what i see in your picture.

Yes, a strange stone. Still, his streak color is far from the gray-black, which is characteristic of magnetite.

[sinclairuser]

yes a simple stick on pcb, where you can stick the arduino nano direct on with the pin headers, so that there are no loose wire all around

that configuration would be great, as it makes building a pi pinpointer easier.

[godigit1]

Hard to tell but looks more like magnatite.
When you say has magnetic properties. Is it magnetic or attracted to a magnet.
If you had a local goelogist, would not hurt to ask him.
Their are shots of color streaks on the web you might be able to see the colors better. But hematite is usually browner than what i see in your picture.