Arduino Nano PI Main Discussion

[Qiaozhi]

The schematic you have posted is nothing to do with the Arduino Nano PI.
It looks like the sample pulse generator for the old Baracuda PI (not the Geotech version).

[SaltyDog]

Suggest an improved MOSFET FQA9P25 that has half the output capacitance Coss (170pF) of the IRF9640, that together with a fast coil will improve the device for small gold. The above is similar in all other respects.

[Spectrum]

Interesting point George. As you say, the pi pico is nearly 10x faster and has ADC that can reputedly return 10-bit ADC at up to 500k/s at a push. Here's an example of a pi pico doing FFT...
https://www.hackster.io/AlexWulff/ad...pi-pico-f883dd
I'm much stronger on software/firmware than I am on hardware, so I'd be interested to see if I can digitise the interesting bits of the flyback signal and then process it in software. Strongly suspect that this sort of processing might be better done with the help of a dedicated DSP chip ? Also, it's probably unlikely that a pi pico has the grunt to keep up.

Pls can you make a complete pi code for esp32 board

[Nightryder]

Is there an E-book copy of this book?

[ugocapeto]

I have a question about the coil:

Is it ok to use a 8 inch coil from an "old" White's detector (rebranded Sears "GEB/TR Discriminator")?

I have another question about the hardware:

Where do you source the stem, handle, armrest, etc in the US? Do you just buy a cheap one on ebay/amazon and ditch the electronics and possibly the coil?

[Qiaozhi]

Is there an E-book copy of this book?

No.

[Qiaozhi]

I have a question about the coil:

Is it ok to use a 8 inch coil from an "old" White's detector (rebranded Sears "GEB/TR Discriminator")?

It depends on the inductance of the coil and what you want to do with the detector.
It's very easy to make your own mono coil.

I have another question about the hardware:

Where do you source the stem, handle, armrest, etc in the US? Do you just buy a cheap one on ebay/amazon and ditch the electronics and possibly the coil?

Probably the simplest way is to use a donor detector (either one that no longer works and cannot be repaired) or a cheap one from China.
Some metal detector dealers also sell shafts, armrests, etc., as spare parts.

[Solheim22]

Hi, I have a random question and hope not to sound too incompetent. I am currently building the circuit and on step 9 measured the coil flyback voltage to only be -16V with a Vpp of around 17.5V. I am not sure what this means and what I have done wrong. I have measured my coil to have an inductance of 300uH using an LCR meter. I have also checked that the oscillator signal is giving the correct signal as described in the book. Any tips?

[ugocapeto]

It depends on the inductance of the coil and what you want to do with the detector.
It's very easy to make your own mono coil.

Thanks for your reply. Btw, I really appreciate the book splitting the whole circuit into sub-circuits with input/output and explaining what they each do. Really simplifies things. Wish more books were like that.

Assuming the inductance is within the range that you recommend in the book and assuming the MD would be used for the beach, would that coil be good to use?

Is it safe to assume that the coil (old white's GEB/TR discriminator coil) is not shielded? Or are coils in TR or IB detector usually shielded?

[Qiaozhi]

Hi, I have a random question and hope not to sound too incompetent. I am currently building the circuit and on step 9 measured the coil flyback voltage to only be -16V with a Vpp of around 17.5V. I am not sure what this means and what I have done wrong. I have measured my coil to have an inductance of 300uH using an LCR meter. I have also checked that the oscillator signal is giving the correct signal as described in the book. Any tips?

Does the voltage across the damping resistor look anything like the signal in Fig. 4-9, ignoring the actual voltage?

[Qiaozhi]

Thanks for your reply. Btw, I really appreciate the book splitting the whole circuit into sub-circuits with input/output and explaining what they each do. Really simplifies things. Wish more books were like that.

Assuming the inductance is within the range that you recommend in the book and assuming the MD would be used for the beach, would that coil be good to use?

Is it safe to assume that the coil (old white's GEB/TR discriminator coil) is not shielded? Or are coils in TR or IB detector usually shielded?

It's probably unlikely that an old White's coil will have the correct inductance. Have you measured it?
The easiest way to find out would be to try it. Note that the PCB is not designed for IB connections, so you would have to do some modifications,
Building your own mono coil would be a lot easier.

[Solheim22]

Does the voltage across the damping resistor look anything like the signal in Fig. 4-9, ignoring the actual voltage?

Yes, it does (see picture below)
I am using the 10x setting on the scope probe. I have done the 8 <-> 10 pin switch mod and have the moded arduino code by SaltyDog. I haven't connected anything up past step 9 yet.

[Qiaozhi]

Yes, it does (see picture below)
I am using the 10x setting on the scope probe. I have done the 8 <-> 10 pin switch mod and have the moded arduino code by SaltyDog. I haven't connected anything up past step 9 yet.

As you have the scope probe set to x10, then the -16V shown on the scope is actually -160V.

[Solheim22]

As you have the scope probe set to x10, then the -16V shown on the scope is actually -160V.

Oh my goodness. I can't believe i didn't think about that. I also realise now that I had the boost switch connected giving me either -16V or - 20V on the scope (-160V or -200V actually). Thank you so much!

[Qiaozhi]

Oh my goodness. I can't believe i didn't think about that. I also realise now that I had the boost switch connected giving me either -16V or - 20V on the scope (-160V or -200V actually). Thank you so much!

No problem.
Hope the rest of the build goes smoothly.