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

[Dean Sarelius]

I havent tried multiple pulses per cycle on the same pin but given that this would be more of an issue for the compiler I dont think it would be impossible.
I have already generated the sampling pulses and can adjust the timing with the encoder and they are extremely fast and clean especially considering the 240MHz clock as you can imagine.
The reason I am interested in using the ESP32 is because of the higher clock rate which allows for a resolution of 4ns per clock.
What this means is that it should be relatively easy to set up a fast comparator or schmidt trigger that is set when the flyback is active and cleared as it falls to a set value say 2.5V.
The idea is to save the time it takes between the start and finish of the flyback and then to compare this with the timing of a detected signal to check the phase.
If the phase is positive then it will likely be ferrous and if the phase is negative it is likely to be non-ferrous.
If you have a particular type of pulse you would like me to try let me know and I will post the video if I can get it working.

[tpet93]

Nice Work
I've been using an SSD1306 OLED screen over I2C with some fiddling in the library to get high frame-rates and a visual indicator.

Ignore the diagonal lines as they are a rolling shutter artifact from the camera.

https://www.dropbox.com/s/38a6u4pwicoqgt5/VID_20230424_152740389~2%281%29.mp4?dl=0

these screens are tiny though! yours would be much easier to read.

how does the ESP32 S3 go with hardware pulse generation?

I was trying to get multiple pulses per cycle on the same pin using the pic32 by DMAing new OCR values after an OCR trigger, however it seems that its only possible to trigger the OC channels once per timer cycle, so i was able to cycle though a series of pulse times, but only one pulse per tx cycle.
I was thinking of using an RP2040 in the future and its PIO modules to allow arbitrary pulse trains to go to the S+ and S- integrators.

[Dean Sarelius]

Hi all,
Been playing around with the Lilygo T-Display module based on the ESP32 S3 (240MHz) processor with 170x320 display.
Using the Arduino IDE and OpenAI to help with the code have produced a menu similar to Moodz PIC with the variables that can be modified with the encoder and are saved to EEPROM when pressing the selection key.
This took me the best part of three nights to get working as the code provided by OpenAI is not perfect and normally requires some editing before it works properly.
Check out the video and remember that this is a processor with built in Wi-Fi and Bluetooth so there is a lot more that can be done like over the air updating.
By the way the reason the TSW value was not saved properly is because I failed to press the selection key again before powercycling.
This module is available from Aliexpress for only AU$32.
My intention is to complete the V3.1 design first with the PIC with the idea of maybe migrating to the ESP32 for a future revision.

https://www.dropbox.com/sh/scrh5edlqo5prlv/AAD71ppCX0ccEX8h0pgeFOSta?dl=0

Cheers

[tpet93]

I've still got the TX loop running at 60us period, just a shorter duty cycle.

[Dean Sarelius]

Just a thought but when you consider that the switching fet in this case the IRF9640 has an Rds of 0.5ohm that in order to ensure maximum power transfer the coil resitance should also approximate to this value also.
If your coil resistance is too low then you should add some series resitance to your coil or alternativley if the coil reistance is too high then you would need to look at how you can make a coil with lower resitance.
Remember also that the frequency of the pulse in your case is approximatley 12us on and 12us off or period of 24us or approximatley 42kHz.
When switching the current through a 300uH coil at 42kHz the AC impedance will be 6.7 ohms compare that to if you would use 30us on and 30us off, f = 17kHz and will have an AC impedance of 4.54 ohms.
Also depending on the parrallel capacitance of the coil the higher the switching frequency the more losses in the coil as the capacitance impedance decreases as the frequency increases.
So for example if the coil capacitance is say 100pF the parralel resitance at 42kHz would be 159 ohms while at 17kHz it would only be 6.3k ohm so a big difference.
In other words the losses at lower switching frequencies are much better than at higher frequencies.
If you wish to reduce the flyback voltage and maintain the original 17kHz frquency then it will probably be better to introduce some resistance in series with the coil to reduce the DC current.

[tpet93]

Yep, adding the 10R resistor in series with the gate of the damping mosfet fixed the ringing.

still getting some warbling and bouncing around in the final output signal, unsure how much is expected during normal operation.
This is my first venture into high performance metal detectors so i don't really have a baseline to compare to for noise and sensitivity.


I was getting some significant dc offset in the output signal coming from the INA125 (capacitor leakage or amplifier input current leakage?) swapping to another INA125 reduced it.
swapping out the LM6171 with a fresh chip seemed to reduce some of the warble/bouncing.

I'm still running quite a short 12us tx pulse until i get some spare bsp230s so perhaps a stronger transmit signal will make the signal more consistent?

As a note for others troubleshooting, when using a speaker and 2*18650s, as the battery's got low, the output started to slowly oscillate at ~0.5hz. I put this down to the speaker drawing more current at low frequency's and causing one of the voltages to drop creating a feedback cycle.
could be tricky to troubleshoot without headphones or a screen attached.

[Dean Sarelius]

I was getting some high frequency ringing on the damping mosfet.
It would appear whenever trying to get close to critical damping. I was using a bench supply to adjust the damping loop voltage for testing.

After a bunch of trial and error (and all but one of my BSP230s) I was able to resolve it by placing a 10R resistor in series with the bsp230 gate.

Running it connected to a de-tech 8" coil. Had to drop the tx time down quite a bit to lower the flyback, will have to wait for more mosfets before trying to increase it again.

Light blue: tx signal Dark blue: bsp source
Pink: flyback/ bsp drain
Yellow: damping voltage/bsp gate

Just checking if you managed to improve on the ringing..?

[tpet93]

I was getting some high frequency ringing on the damping mosfet.
It would appear whenever trying to get close to critical damping. I was using a bench supply to adjust the damping loop voltage for testing.

After a bunch of trial and error (and all but one of my BSP230s) I was able to resolve it by placing a 10R resistor in series with the bsp230 gate.

Running it connected to a de-tech 8" coil. Had to drop the tx time down quite a bit to lower the flyback, will have to wait for more mosfets before trying to increase it again.

Light blue: tx signal Dark blue: bsp source
Pink: flyback/ bsp drain
Yellow: damping voltage/bsp gate

[darov922]

Here are your pdfs ....

[ATTACH]n409752[/ATTACH]
[ATTACH]n409753[/ATTACH]


moodz

Could you provide me with the pdf files of the holes and the top and bottom mask? thanks for your time

[Rick S]

Here is a schematic that makes HEX file down load possible using PicKit 3 with MPLAB IPE. Pickit 3 external power.pdf

[Rick S]

Rick S,

I have used most of the available Litz wires and found that they all work all I can say on the strand thicknesses is most of the after market manufacturers use 32AWG or .2mm and when I was winding my own Litz I found that was what gave me the best outcomes I have even used the the coil wire to make the coax but it is very time consuming and fiddly at 76 my coil building days have come to a close especially as materials are almost impossible to source in Australia now I have used the red 7mm low capacitance Soundlink Microphone coax its not perfect the strands not being enameled and slightly more resistive than the OEM cable but it does work in a pinch I will get the cable designation for you when I go out into the workshop tomorrow.

Regards, Ian.

IBGold,

I am finding no luck in good cable to connect coil to control box without buying in bulk. The PF's are to high. I took a look at WES Electronics and AIC227 and AIC228 are not in the catalog anymore. Also looked at the VIC 206 and 207 and not sure. You mention about making your own cable from scratch using 32awg magnet wire. Question, how did you separate ground, plus and minus? I am guessing that half the wires were plus (+) and the other minus (-). Was there any shielding? Also, what was used to wrap the magnet wire? I have the magnet wire so I am willing to give it a try. The market right now is horrible for buying things. Hardest thing to obtain was the -9v T0-92 reg for this project unless ones buys from China. 6 plus weeks hopefully to get it in hand. This winter record breaking snow fall this past winter. The Game and Fish in the state of Wyoming are saying a 80% kill off of deer, Elk and Prong Horn. At times no way in or no way out where I live. Getting parts has been a challenge.

RickS

[IBGold]

Hi Dario,

Minelab's coil that Moodz is using is Bundel wound and the coil that I am using testing the Magpi V3 is a semi flat wound of my own design and it seems to work fine and I have also tried it with an 8" Minelab mono also and it is fine, I can not tell the parameters of that Amazon cable but one that I have used and does work is as designated on the cable >>> Soundlink USA HIGH GRADE AUDIO INTERCONECT OFC CABLE >>> in Australia sold by WES Electronics part number AIC227 and sold by the metre and you could also try the AIC228 I never got around to trying it their VIC206 or VIC 207 also might be worth a try.

I would start with 26 turns and see how you go you can easily remove a turn until you get the correct inductance some of the aftermarket coils run with inductances from 265 to 320 and resistances from .34 ohms to.55 ohms and the all seem to work there are reasons for the changes but it is to long winded to go into here.

Also with your headphones I have mine wired in parallel with a 36 ohm resister in series to get the threshold quiet enough to suit me.

Regards, Ian.

Hi Dario,

Edit the series resister value to the headphones is 39K ohms the rest I have put on a PM for you.

Regards, Ian.

[darov922]

Rick S,

I have used most of the available Litz wires and found that they all work all I can say on the strand thicknesses is most of the after market manufacturers use 32AWG or .2mm and when I was winding my own Litz I found that was what gave me the best outcomes I have even used the the coil wire to make the coax but it is very time consuming and fiddly at 76 my coil building days have come to a close especially as materials are almost impossible to source in Australia now I have used the red 7mm low capacitance Soundlink Microphone coax its not perfect the strands not being enamelled and slightly more resistive than the OEM cable but it does work in a pinch I will get the cable designation for you when I go out into the workshop tomorrow.

Regards, Ian.

Ian has given me an idea, although I don't know if it would work that well: I could use the 33 strands of litz wire from the coil, wrap it with 1 or 2 layers of teflon tape, then place the taped wire inside a teflon tube of those used for guidance in 3D printers (2mm ID, 4mm OD), to then place a copper tape and mesh of a 75 Ohm coaxial and finally isolate the whole assembly with heat-shrinkable tube... hopefully someone read this can give me an opinion if it will be possible to obtain a low capacitance cable, I hope I am not distorting this post too much... I should place it in the "coils" section... but your words are inspiring... thanks for sharing your knowledge Ian..

Dario

[IBGold]

again, thanks for the info Ian, my calculations had given me about 26 turns of wire, what I'm not sure is what type of winding to face: conventional, basket (flat) or 3DSS, with the intention of lowering the capacitance to the minimum since surely the capacitance of the cable will be high, the idea is to obtain the parameters as close as possible to the coil that Moodz uses (less capacitance in the coil and more capacitance in the cable).

Will this subwoofer cable be of good quality for this application? it has 12pf/ft...
https://www.amazon.ae/Blue-Jeans-Cab.../dp/B005979HBM

Dario

Hi Dario,

Minelab's coil that Moodz is using is Bundel wound and the coil that I am using testing the Magpi V3 is a semi flat wound of my own design and it seems to work fine and I have also tried it with an 8" Minelab mono also and it is fine, I can not tell the parameters of that Amazon cable but one that I have used and does work is as designated on the cable >>> Soundlink USA HIGH GRADE AUDIO INTERCONECT OFC CABLE >>> in Australia sold by WES Electronics part number AIC227 and sold by the metre and you could also try the AIC228 I never got around to trying it their VIC206 or VIC 207 also might be worth a try.

I would start with 26 turns and see how you go you can easily remove a turn until you get the correct inductance some of the aftermarket coils run with inductances from 265 to 320 and resistances from .34 ohms to.55 ohms and the all seem to work there are reasons for the changes but it is to long winded to go into here.

Also with your headphones I have mine wired in parallel with a 36 ohm resister in series to get the threshold quiet enough to suit me.

Regards, Ian.

[darov922]

Hi Dario,

By my calculations you would need around 24turns to achieve around 300 uh and if you are making your own Litz then I would use 33 strands of 32 AWG of solder through enamelled wire I usually wind the the Litz onto the former and add a turn then check with the LCR meter then trim the Litz to achieve the required inductance but remember that when you lace up the coil bundle so that the strands can not move the inductance will rise it is a balancing act.

again, thanks for the info Ian, my calculations had given me about 26 turns of wire, what I'm not sure is what type of winding to face: conventional, basket (flat) or 3DSS, with the intention of lowering the capacitance to the minimum since surely the capacitance of the cable will be high, the idea is to obtain the parameters as close as possible to the coil that Moodz uses (less capacitance in the coil and more capacitance in the cable).

Will this subwoofer cable be of good quality for this application? it has 12pf/ft...

https://www.amazon.ae/Blue-Jeans-Cable-Double-Shielded-Capacitance/dp/B005979HBM

Dario