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

[Dean Sarelius]

Thanks Dean .. dont get me wrong I am not trying to dismiss your ideas for improvement .. I just want to lock down the V3 hardware as there are some built up units already operating by various people and whereas we can change the software because that only involves re-programming those existing units ... if we change the hardware then those existing units and ones being built up might become obsolete and those people would not be happy.

For your info ... I have V4 in simulation already with NMOS and significantly higher power and V5 which is bipolar ... not sure if target sensistivity will increase that much though we hopefully will start to see a discrimination function.

moodz

Hi Moodz,
Yes I uderstand and it is important that there is a baseline project that we work from otherwise it can get very confusing.
My intention it to complete the V3 and to make any changes that would eliminate the shortcomings of my previous designs hence the addition of the buffer.
In the oscilloscope image you provided previously I could see some distortion of the flyback, refer below image, which I have been able to eliminate partially by buffering the high gain stage.
A question regarding the X sample, to my understanding the X sample is taken during the magnetic field cycle and not the back EMF cycle or is my understanding wrong..?
Also I see a lot of advantages with bi-polar front end so was considering to design a detector around that front before you released the completed V3 schematic.
Do you think it will be better to wait for the release of the V4 or would you consider the V3 to be a solid design already..?
I have some hot rocks at the ready for testing the V3 so if it can ignore these then it will be happy days..

[darov922]

Hi Dario ... not big on videos however I will see if I can put something together. This detector will definitely work very well in low mineralized soils ... it will also work well in mineralized .. maybe not extreme ( needs software upgrade ).
It is good for small and big nuggets. There is no target hole ( as far as I know ) as some detectors have. The parts should be easy to come by. I have some boards available.

moodz

Thank you very much for your answer. I'll be waiting for those tables, I'll also wait a little longer until version 5, since I like a version with NMOS transistors better and if it's bipolar even better, I want to start buying the components anyway.

Dario

[moodz]

This project is very interesting and I really want to make this detector... do you have any test video? I am looking for a detector to search for somewhat small gold nuggets in low mineralized soils. Will this detector work?

Dario

Hi Dario ... not big on videos however I will see if I can put something together. This detector will definitely work very well in low mineralized soils ... it will also work well in mineralized .. maybe not extreme ( needs software upgrade ).
It is good for small and big nuggets. There is no target hole ( as far as I know ) as some detectors have. The parts should be easy to come by. I have some boards available.

moodz

[moodz]

Thanks Moodz,
Appreciate all the help.

Thanks Dean .. dont get me wrong I am not trying to dismiss your ideas for improvement .. I just want to lock down the V3 hardware as there are some built up units already operating by various people and whereas we can change the software because that only involves re-programming those existing units ... if we change the hardware then those existing units and ones being built up might become obsolete and those people would not be happy.

For your info ... I have V4 in simulation already with NMOS and significantly higher power and V5 which is bipolar ... not sure if target sensistivity will increase that much though we hopefully will start to see a discrimination function.

moodz

[darov922]

Thanks Ian .. I just took it out for a test swing ... seems to be OK ... I am not sending the shafts .. just illustrating how I mount them.

2 x 20mm conduit clamps - as you can see no expense spared LOL. You will have to open the electronics case ( carefully ) to remount them.

moodz

This project is very interesting and I really want to make this detector... do you have any test video? I am looking for a detector to search for somewhat small gold nuggets in low mineralized soils. Will this detector work?

Dario

[Dean Sarelius]

Thanks Moodz,
Appreciate all the help.

[moodz]

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.

Hi Dean ...

You can remap the GPIOs if you wish as its "open" source code however be aware that the intent of this thread on the forum is to support MAGPI V3 which is a through hole version of the detector and so if you are intending on forking the code and presumably a new board layout it might be
better to release it on a alternate thread or people will become confused if they load it into this hardware version. The reason for the through hole version is that there are lots of folks who would find a SMD version more challenging and are not of an age
where their eyesight or soldering skills are upto SMD. Additionally the components are relatively easy to find and easy to experiment with / probe etc.

The damping loop does not technically "stop" and "start" The reactive "X" error in damping of the coil is sampled and integrated ( stored ) to generate the damping bias on the damping mosfet BSP230 ... the bias is maintained on the BSP230 through the whole cycle.

All timings are referenced to 0 microseconds for each cycle. 0 occurs just after the finish of the preceding TX.
So the X sample begins at 1.6 us and ends at 1.7 us ( not the loop ).
The A target ( first ) sample begins at 0 and ends at 15 us.
The B target ( second ) sample begins at 15 us and ends at 30 us.
The TX cycle starts at 30 us and ends at 60 us.
... as per the code.

The reason for 60 us total cycle time is because longer TX cycles ( eg 40 us on and 40 us off ) are will increase the flyback voltage and TX peak current. This will heat up the linear regulator and risk avalanche of the TX mosfet which will cause it to heat up and the damping time will increase.

A future detector will address these issues. ( MAGPI V4 ? )

The V3 is no slouch ... I have a $10000 commercial detector and the V3 is my goto detector now. ( the V3 is lower noise and lighter but same sensitivity).

You should note we are using integrators here not Sample and Hold. Except in the case of the X sample ( 1K resistor ) .... the other switches are driving integrators with 10K resistor inputs ... the opamp is rated to drive 75 ohms ... so the combined input impedance of the integrators does not
come anywhere near the rated drive capability of the preamp. A buffer will only consume power and potentially add noise.

You are right though ... I did have a earlier version that did use S&H for the loops etc and that did suffer from preamp output distortion due to sudden capactive load on the preamp output.

moodz

[Dean Sarelius]

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.

[moodz]

Hi Moodz,
I just noticed that you made a second revision of the circuit where you used a voltage doubler to assist with the lower battery voltages. I will remove the schottky bridge and replace with discrete schottky diodes.
Regarding the mapping for the encoder have set up as below.

Hi Dean
The revision is so the detector will run OK from 2S Lithium Packs ( 2 x 3.7 volts ).
The schottky diodes dont really matter as the 5 volt linear regulator will run out of volts input before the voltage multiplier does on low battery.
Changing the -9 volt regulator to -8 volts may or may not be problematic as the -9 volt rail is required for the damping control loop.
The op amps are not rail to rail so you have to have enough headroom in that voltage rail to generate adequate bias for the damping loop - I have not tested at -8 volts.
Note that where the rotary encoder attaches is also the programming header on the original schematic.
moodz

[Dean Sarelius]

Hi Moodz,
Thats great that it still works so assume the mapping is A=AN4, B = AN2, C = AN5 and the Switch = AN3...?
Some interupts are good some are bad of course but I guess if you are going to use the encoder to adjust some values you kind of accept that there may be some interuptions to the regular operation.
I wrote an interupt routine in assembler for the AVR with the Alps PEC16 encoder it was only a few lines of code and would exit within a few clock ticks.
By the way have almost completed the schematic.
Having built some model aeroplanes I would like to power with 11.4V lithium packs as I have a charger for these also.
When these battery packs get low they will reach around 9V so am thinking to replace the -9V regulator with a -8V or lower reg also any thoughts..?
Have already replaced D4, D5,D6 and D7 with a schottky bridge rectifier KMB12S or CDBHM120L-G both provide around 0.45 Vdrop at 100mA which should help with the lower supply voltage also.

Hi Moodz,
I just noticed that you made a second revision of the circuit where you used a voltage doubler to assist with the lower battery voltages. I will remove the schottky bridge and replace with discrete schottky diodes.
Regarding the mapping for the encoder have set up as below.

[Dean Sarelius]

Hi Dean ... yes I had a look at the rotary wiring and you are right I have wired the C ( common ) to the B switch Good Pickup !
So I changed the wiring to AB and C to common and its still works OK ... so I guess the code and the wiring is foolproof by accident.

I have never used interrupts for rotary encoders ...if you have some other more critical loop task ( like the TX interrupts ) then if the loop is fast enough to sample you get a rotary encoder or multiple REs with very little code overhead plus free debounce.

The less interrupts the better I always say.

moodz.

Hi Moodz,
Thats great that it still works so assume the mapping is A=AN4, B = AN2, C = AN5 and the Switch = AN3...?
Some interupts are good some are bad of course but I guess if you are going to use the encoder to adjust some values you kind of accept that there may be some interuptions to the regular operation.
I wrote an interupt routine in assembler for the AVR with the Alps PEC16 encoder it was only a few lines of code and would exit within a few clock ticks.
By the way have almost completed the schematic.
Having built some model aeroplanes I would like to power with 11.4V lithium packs as I have a charger for these also.
When these battery packs get low they will reach around 9V so am thinking to replace the -9V regulator with a -8V or lower reg also any thoughts..?
Have already replaced D4, D5,D6 and D7 with a schottky bridge rectifier KMB12S or CDBHM120L-G both provide around 0.45 Vdrop at 100mA which should help with the lower supply voltage also.

[IBGold]

Hi Paul no problems I have my own mounting system all organised cheers will send you pictures when set up.

Regards, Ian.

[moodz]

Paul you again astound me you have taken all the work out of it I have the shaft battery pack Li-Ion ready to go.

Regards, Ian.

Thanks Ian .. I just took it out for a test swing ... seems to be OK ... I am not sending the shafts .. just illustrating how I mount them.

2 x 20mm conduit clamps - as you can see no expense spared LOL. You will have to open the electronics case ( carefully ) to remount them.

moodz

[IBGold]

Paul you again astound me you have taken all the work out of it I have the shaft battery pack Li-Ion ready to go.

Regards, Ian.

[moodz]

... here is the latest build .. that was featured earlier. I have selected cheap but sturdy plastic enclosure and flashed the interior with copper tape.

A ground has been soldered to the tape and check with multimeter < 1 ohm everywhere.

This shields the front end of the detector from stray capacitance that may be to hand ( like your hand for instance ... LOL ).

Any stray capacitance will affect the LC product of the coil and will result in false target / or noisy operation.

You can test a unit on the bench but will notice that the unshielded front end is sensitive in the vicinity.

This unit is yours IBGold ... just wiring in the rotary encoder so you have volume control.

It wont have the LCD fitted .....

moodz