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

[Rick S]

darov922 or open to forum,

On this forum is a whole bunch of ideas what to use and not use in building a Minelab coils of any size. Plenty info for what type of litz or stranded tin wire and shielding. The big issue is the cable to the box. You loose all that you gain with perfect coil
if the cable has high resistance and capacitance. One says that he had the cable specially made litz 9 type cable. I have use Mogami cables with my PI coils in the past. This will not work with Minelab coils. The cost is one of the problems. Buying a spool litz 9 is cost prohibitive.
I wish I had the answer. Still looking. Anyone on the forum that has good info that can pin point exactly what to use for coil, shielding and cable to box for Minelab required numbers. Going to China is not the best because you have no idea of quality, fraud and time line. I guess
this is the problem in building your own coils. Minelab 10" mono coil starts at $250 and from there as much $1500 for a coil besides the detector $5000 to $8000. Moodz is attacking the box issue I think. Easy build for his MAGPI V3. More to come with V4.

[IBGold]

IAN: really thank you for the information you have given...i plan to make the coil and also the litz wire...although i want to know how many strands of AWG 32 does the 10" ML coil have? i did a quick calculation and to reach the 0.4 Ohms I need 20 wires. Can you guide me a bit, Thank you very much again.

Dario

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.

[IBGold]

darov922 or open to forum,

On this forum is a whole bunch of ideas what to use and not use in building a Minelab coils of any size. Plenty info for what type of litz or stranded tin wire and shielding. The big issue is the cable to the box. You loose all that you gain with perfect coil
if the cable has high resistance and capacitance. One says that he had the cable specially made litz 9 type cable. I have use Mogami cables with my PI coils in the past. This will not work with Minelab coils. The cost is one of the problems. Buying a spool litz 9 is cost prohibitive.
I wish I had the answer. Still looking. Anyone on the forum that has good info that can pin point exactly what to use for coil, shielding and cable to box for Minelab required numbers. Going to China is not the best because you have no idea of quality, fraud and time line. I guess
this is the problem in building your own coils. Minelab 10" mono coil starts at $250 and from there as much $1500 for a coil besides the detector $5000 to $8000. Moodz is attacking the box issue I think. Easy build for his MAGPI V3. More to come with V4.

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.

[IBGold]

Moodz,

All is now up and running encoder in correct orientation and audio as I like it I finally got the required plugs and sockets and now all wired up I have been playing with it in the workshop and find the encoder locks up now and again and the screen also sometime locks up my impressions are the audio is a bit chattery but this is in the workshop when it stops B----- raining here I will take it down to the beach and around one of the salt lakes and see what happens I have had the other device on those areas so know what to expect.

Regards, Ian.

[darov922]

darov922 or open to forum,

On this forum is a whole bunch of ideas what to use and not use in building a Minelab coils of any size. Plenty info for what type of litz or stranded tin wire and shielding. The big issue is the cable to the box. You loose all that you gain with perfect coil
if the cable has high resistance and capacitance. One says that he had the cable specially made litz 9 type cable. I have use Mogami cables with my PI coils in the past. This will not work with Minelab coils. The cost is one of the problems. Buying a spool litz 9 is cost prohibitive.
I wish I had the answer. Still looking. Anyone on the forum that has good info that can pin point exactly what to use for coil, shielding and cable to box for Minelab required numbers. Going to China is not the best because you have no idea of quality, fraud and time line. I guess
this is the problem in building your own coils. Minelab 10" mono coil starts at $250 and from there as much $1500 for a coil besides the detector $5000 to $8000. Moodz is attacking the box issue I think. Easy build for his MAGPI V3. More to come with V4.

Hi Rick, thank you very much for your advice, I am aware of the problem with the cable. I want to get a low capacitance wire and place the box as close to the coil as possible. Now I understand why MOODZ uses a built-in coil: it wants to focus on the V3 circuit and not so much on the coil... The cost information is very useful to me, since I have experience building litz wire and 1 meter of the most expensive wire in my country it will never reach 250 dollars... your PCB board looks great... the impedance of your speaker is 32 Ohm? For my version that will have headphones I will have to adapt the filter for 64 Ohm since I will have to place both speakers of the headphone in series...

Dario

[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-Cab.../dp/B005979HBM

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]

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]

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.

[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

[Rick S]

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

[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

[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

[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]

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.