'WOMBAT' PI Metal Detector

[Teleno]

Hi

Any processors will work if they have an internal analog reference and high speed sample.
eg i think the STM32 is very fast, but the internal analog reference is low (1.1V )?

Also older Arduinos are not quick enough to sample.

To get into the details: the 'megatinycore' attiny has a sample window as quick as 2usec and it can be adjusted. so: 2usec sample + 12uSec to process = 14uSec total. But the 2uSec is important because it is very precise narrow sample width.

The Time of the sample can be adjusted to 1/16 uSec, so it gives a fine control of where the sample occurs.

The internal reference of 4.3 volts is used to get a large analog input range.


Note on noisy signals above: This is the running average of 50 samples. (300 pulses per second average of 50 samples)

Atmega328P, reference 1.1V, preamp gain 14, ADC at 500KHz, IIR filter based on 64 samples...
This is enouh to build a nice PI

[pito]

1. It is look like targets are very close to coil.
2. I see the first PI with VDI ?

[Teleno]

1. It is look like targets are very close to coil.
2. I see the first PI with VDI ?

The coil is 140uH, 18cm diameter spiral wound. The aim is to detect gold nuggets. The result was a 0.5g at 9-10cm distance.

VDI is baed on the ratio of two successive samples. Actually log(s1)-log(s2).

The fun was to do all of this with a simple 8 bit MCU.

Here's the schematic https://www.geotech1.com/forums/foru...260#post313260

I'm developing a second version either based on STM32F030 or on LGT8F328P (Larduino) which runs at 36MHz and has a 12 bit ADC, 8 bit DAC and 2 x 16bit timers.

I'll leave the cable shield floating and see if that way I can do earlier sampling. Currently it's at 6us because of all the added capacitance.

I wonder if EasyEDA can used for collaboratation, then I would open my schematic for contributions and odering populated PCBs from JLCPCB.

[pito]

The aim is to detect gold nuggets =

[Teleno]

The aim is to detect gold nuggets =

My guess is an IB with selective phase.

[pito]

correct

[Op04]

The aim is to detect gold nuggets =

ivconic is this what You're looking for?
Sorry Tec I ask him in your thread.

[ivconic]

Apart from such behavior; it is crucial that it has GEB capability.
That test is not perfect until you bring some "disturbance" to the coil, for example a piece of antique brick, hot rock or something similar.
The best test is with everything from such material.
During my "career" I have seen "miraculous" and "magical" detectors, which do impossible things.
Not one has passed the test on real soil and under real conditions.
At the end of the day, such a video is easy to record, you put a switch behind the camera to turn on/off the detector at the right moment!

[Op04]

Apart from such behavior; it is crucial that it has GEB...
Such a video is easy to record, you put a switch behind the camera to turn on/off the detector at the right moment!

Thanks for your thoughts. All video seem so tease, but unfortunately without schematic or hex provided just another dream project. Dear TEC please continue your updates.thanks

[pito]

@ivconic
At the end of the day, such a video is easy to record, you put a switch behind the camera to turn on/off the detector at the right moment! = You call me a liar out of jealousy because you have no idea how to do it yourself.

I have many projects I have built but I haven't seen your own design.

And this is my latest, just 3 IC and stm32

[ivconic]

[Tec]

Improved Front End (schematic attached)

[Tec]

Signals: Raw vs Averaging.

*The 'Raw samples' is one Raw sample in block of 50 for indication. (Instead of displaying all 50 raw samples)
* The Signal is at the resolution of the AtoD, i.e within one bit of the 10-bit A to D.

[Tec]

Using the UNO R4 'DAC' for audio out;
Making a variable Tone and Volume triangle wave
wombat_dac_audio.zip