Moodz' Awesome Gold Pulse Induction Version 3 - MAGPI V3 Project

[Detectorist#1]

Hi Teleno,

In my project of PI MD I use Two TX coils with bifilar winding and two RX coils in gradiometric connection. The detector works in two modes - "ALL metal" and "Fe only". In "Fe only mode TX coils are not used (no pulses).
The input signal is only from electromagnetic induction in two RX coils. In this mode is very important to use Op Amp with lowest possible noise. Nevertheless, the sensitivity for Fe objects is reduced in comparison with ALL metal mode. The profit is that recognition of Fe objects is 100% reliable.

[Teleno]

Hi Teleno,

In my project of PI MD I use Two TX coils with bifilar winding and two RX coils in gradiometric connection. The detector works in two modes - "ALL metal" and "Fe only". In "Fe only mode TX coils are not used (no pulses).
The input signal is only from electromagnetic induction in two RX coils. In this mode is very important to use Op Amp with lowest possible noise. Nevertheless, the sensitivity for Fe objects is reduced in comparison with ALL metal mode. The profit is that recognition of Fe objects is 100% reliable.

I have trouble encapsulating a spiral mono coil, I can't even imagine how to do it with a gradiometric one, kind of a cilinder I guess.

I'm working on a simpler scheme in which I discharge a cap on the coil for a fixed time (mcu timer) and the residual voltage is proportional to the inductance, so any changes caused by ferrous could in principle be detectable. Will have to verify what the sensitivity is. The residual voltage is also used as the analog ground to simplify the power supply.

[Detectorist#1]

Hi Teleno,

I have not use spiral construction of the coils. The mechanical construction is relatively simple.
Attached is pdf file with explanation of my construction.

[moodz]

Just about to commence laying out a PCB from the breadboard. Maxed out the TX power and speed that will reasonably work with off the shelf mono coils. The final figures for the MAGPI V3x will be something like 10 Khz TX frequency with 1.2 Amps peak current and 1.2 KV flyback. Damped in 650 nanoseconds and two channels ( one for discrim and one for "all targets" ). The waveforms are near perfect damping.
Preamp is 100X - red trace. Flyback and coil current shown.

[pito]

Attached is pdf file with explanation of my construction. = and you have 1600V ?

[talasumo]

Hi Moodz,
Thanks for the feedback.
Are you ok if I go ahead and re-map the GPIO's in your source code..?
I have been trying to simulate your circuit on Multism but I dont think I have the timing right and I note in a previous thread the timing may have changed from 30us to 40us..?
Reffering to your code pasted below the period is 60us and TX is on for half or 30us or 50% duty cycle.
When TX is off the damping loop is still active and will stop 1.7us later then commence again 1.6us after the end of the 1.7us..?
Sample and hold S2 and S3 will start after the 1.6us has expired and sample for 15us each..?
The reason I would like to get the simulation to work is because I am thinking of adding a buffer before the S&H switches.
In my experience when trying to charge up the caps straight from a high gain op-amp there is typically a dip in the signal, I am sure you have seen this also.
So in order to minimise corruption of the signal a buffer should be used to provide the charge to the S&H caps.

How can i see source code not only hex?

[talasumo]

How can i see source code not only hex?

Apologies, found it.

[moodz]

Magpi V3 update ... the original version kind of sucks because you could only ground balance by moving the sample points and ratios very precisely and as soon as you run across ground with lots of ferrite type rocks the GB is useless.

So I have rearranged the scheme a little and now have tracking AGB with ferrite rejection at all times. ( ie response only to conductive targets ). The software V9 will still have adjustable sampling but the boot up will be for optimal ground tracking.
Because there is no subtraction in the scheme there is no "hole" in target response.
The V9 software will add adjustable sensitivity control in addition to volume control.

A hardware bug with the preamp has been fixed and the output is now very stable.

I will be testing and reporting results prior to release

[Detectorist#1]

Hi pito,
Yes, the peek voltage on Tx coils is 1600V. I measure this voltage on the lowest resistor if the 4 resistors TX coil's damping chain. Where is the problem?

[Detectorist#1]

Hi moodz,

Your idea for ZP (zero point active damping) is very spectacular! Thank you for this efforts! Just, I afraid that will be complex to use this idea for the bipolar Tx units. My preference ( as Carl mentioned also) in last time is to use bipolar signals in PI MD. Maybe, using of your idea for ZP damping in bipolar MD is not complex. I need a time to see how to implement this idea.

[moodz]

Hi moodz,

Your idea for ZP (zero point active damping) is very spectacular! Thank you for this efforts! Just, I afraid that will be complex to use this idea for the bipolar Tx units. My preference ( as Carl mentioned also) in last time is to use bipolar signals in PI MD. Maybe, using of your idea for ZP damping in bipolar MD is not complex. I need a time to see how to implement this idea.

Thanks ... however you wont need ZP damping for bipolar ... because bipolar recycles the energy theres no damping required. Additionally there is still a place for monopolar PI as it utilises monocoil and allows ferrous discrim through X and R separation .. this can be done in bipolar also but is more complex and costly.

It can be argued that the simple mono coil system will punch deeper into the ground than a complex bipolar IB coil.

[Carl-NC]

Bipolar PI can be CC or not. With CC you don't need damping, but trad bipolar PI does need damping.

[moodz]

Bipolar PI can be CC or not. With CC you don't need damping, but trad bipolar PI does need damping.

Thats right ... and my understanding is that bipolar is used to negate Earth Field and in military mine detectors. However the ZP damping scheme would become complex and hard to balance out in a bipolar set up.

[moodz]

..heres a video showing the ground tracking rejecting ferrites at the coil.

https://youtu.be/CDZ8Dev_zTU?si=LoqYwRsK8nBgv1gC

[pito]

@Detectorist#1
So it is 5x times more than average detector, and range for coin is ?