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

[moodz]

Are the mods easily transferrable to the through hole version?
I've been holding off building the V3 waiting for a definitive list of changes to bring it up to a final/latest spec. Unfortunately a ready built, surface mount board is the only way I can get something newer in the future as I can't construct anything other than through hole with my myopic vision

You are in luck !
The the holes are already on the V3 thruhole board. The mod is just to remove some components and add some components to the original design. No actual mods ( track cutting etc ) to the PCB.

[Gunghouk]

Are the mods easily transferrable to the through hole version?
I've been holding off building the V3 waiting for a definitive list of changes to bring it up to a final/latest spec. Unfortunately a ready built, surface mount board is the only way I can get something newer in the future as I can't construct anything other than through hole with my myopic vision

[moodz]

So should this be MAGPIV4 thread now?

not yet I only made slight modifications to the V3 and code to achieve ferrite rejection. The iron rejection I may have to leave for V4 but i am testing now.

[Detectorist#1]

Hi pito,
The aim of this construction is to be sensitive for small nugets. The Tx coils are 33uH and only 5tr. The Tx pulse is 12us and peek Tx current is 10A . As a result, the peek voltage on Tx coils is 1600V. The distance for 25c USA is appr. 30cm. This distance is not big - the reason is that the distance between two RX coils is only 12cm. Other advantage of this design is reliable Fe recognition - in "Fe" mode two Rx coils work as magnetometer and Tx pulses are not used.

[Gunghouk]

So should this be MAGPIV4 thread now?

[pito]

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

[moodz]

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

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

[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.

[Carl-NC]

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

[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.

[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.

[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?

[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

[talasumo]

How can i see source code not only hex?

Apologies, found it.

[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?