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

[moodz]

[Tinkerer]

Hi friends,

I've been absent for several years. But this project is really awesum.

Thanks Moodz for sharing your ideas.

Welcome back AZIZ

[kiouijki]

doh ... typo on the damping mosfet ... Here is the FINAL FINAL schematic.

any kikad files
thanks

[Gunghouk]

Not Kikad but here are the gerbers with silk screen and the Diptrace project files..

[kiouijki]

Not Kikad but here are the gerbers with silk screen and the Diptrace project files..

thank you sir

[eduardo1979]

Hello everyone.
First of all, I would like to thank Paul for sharing this wonderful project.
After reading all about this amazing detector, I decided to build one. I don't know if it's supposed to work like this, but in all the videos posted by Paul, his detector seems to work differently than mine. What did I do wrong? I loaded the latest firmware version, 1.5, and I placed the electronic components according to the last schematic posted by Paul. I would like someone to help me, because I really like the concept of this detector. I have several PI detectors and I have experience with them. I have a GPX 4500, a Whites TDI SL and a Surfmaster PI Dual Field.
I recorded a short video of the detector and it is at this link:
https://www.youtube.com/shorts/x3BtCeAp8B0
Thanks in advance.

[Emersonpaz]

I had a detector that warbled alot and another that was rock solid .... even though both had exactly the same components. After about a week of changing components in and out etc ... it turns out that there was stray capacitive coupling from the TX circuit to the linear 7805 regulator. The fix was simply soldering the tab of the 7805 to the shielding ground. This feedback was causing slight variation of the regulated 5 volts hence causing a warble as it would have been modulating the TX current.

This feedback also caused burst oscillation in the TX mosfet on turnoff .... also solved. The heatsink was orginally bolted ... hmm

moodz.

Hello Eduardo, I could be wrong, but in post 208 Moodz connected the 7805 tab to the protection field, I don't know if this is your case. Maybe someone else can help.

[eduardo1979]

Hi Emerson.
Thanks for your feedback.
My PCB is not yet installed inside a metal box. I think I should first install the PCB inside a metal box to avoid interference, and then do with the 7805 what Moodz has done. I'm not sure that this is the solution to my problem. I have a drift problem somewhere and that's why the threshold tone is unstable. The numbers (SIG) are very unstable.
I hope Moodz can help me.

[moodz]

Hi Emerson.
Thanks for your feedback.
My PCB is not yet installed inside a metal box. I think I should first install the PCB inside a metal box to avoid interference, and then do with the 7805 what Moodz has done. I'm not sure that this is the solution to my problem. I have a drift problem somewhere and that's why the threshold tone is unstable. The numbers (SIG) are very unstable.
I hope Moodz can help me.

1. ground the the tab of the 7805 ( no long wires )
2. place 5 to 10 ohm series resistor in the gate of the damping mosfet Q2 ( if step 1 does not improve things )
3. Install the pcb in a shielded case ideally as small capacitive coupling will cause false targeting / drift as any capacitive changes affect the coil reactance.

Note also that the circuit is sensitive to temperature changes such as air blowing on the front end. ( the mosfet bias operating points will change with temp variation ).
In a closed box ... this is not an issue as the air movement is low and any delta Temp is not fast enough to make it through the filters.
It is easy to show this by just blowing on the circuit when it is operating.

Further note. If you are testing the detector in your lab / workshop and you have a switch mode supply such as used in LED lighting ... this may cause interference to the detector ( presume harmonics from the inductor in the switch mode supply. ) In my lab I cannot use the main lighting as it is LED and creates noticeable noise that appears as instability in the detector. Turning off the light restores low noise operation.
Presumably other types ( but not all ) of switch mode supplies may cause this issue also.

m.

[Gunghouk]

Hi Moodz, did the software for the LCD version get past the v1.5 development version with non working volume control ? Thanks

[eduardo1979]

1. ground the the tab of the 7805 ( no long wires )
2. place 5 to 10 ohm series resistor in the gate of the damping mosfet Q2 ( if step 1 does not improve things )
3. Install the pcb in a shielded case ideally as small capacitive coupling will cause false targeting / drift as any capacitive changes affect the coil reactance.

Note also that the circuit is sensitive to temperature changes such as air blowing on the front end. ( the mosfet bias operating points will change with temp variation ).
In a closed box ... this is not an issue as the air movement is low and any delta Temp is not fast enough to make it through the filters.
It is easy to show this by just blowing on the circuit when it is operating.

Further note. If you are testing the detector in your lab / workshop and you have a switch mode supply such as used in LED lighting ... this may cause interference to the detector ( presume harmonics from the inductor in the switch mode supply. ) In my lab I cannot use the main lighting as it is LED and creates noticeable noise that appears as instability in the detector. Turning off the light restores low noise operation.
Presumably other types ( but not all ) of switch mode supplies may cause this issue also.

m.

Hi Moodz.
Thanks for answering my question.
I have done everything you have told me;
I have added a 10 Ohm resistor in series with the gate of the mosfet Q2.
I have put the PCB inside a metal box and connected the tab of the LM7805 regulator to the chassis of the box, as you show in the photos.
I have turned off the LED lights in my lab for a moment to see what happens.
The detector is powered by Lithium Batteries, not by laboratory power supplies.
I have also tried cutting the power supply track on the PCB that you mentioned in a previous post and I have powered the DG411 directly from the Battery as you were explaining in a previous post. All this without success and without noticing any difference. The only thing that works is changing the TON parameter value to 94 or 96 and the SIG parameter value stays oscillating around 400. It is the only way to make the detector work stably.
I have been playing with all the possible parameters, changing all the values and without success, except for the TON parameter, mentioned above.
I have noticed that the detector, working stably, does not reach the depth and sensitivity that your detector in the videos you posted reaches.
I have noticed that the detector rejects ferrite and hot rocks very well, but it does not have any kind of discrimination.
I would have liked it to have at least discrimination for High or Low conductivity like the TDI or the Minelab GPX4500, because here in Europe we also like to search for gold nuggets, but the fields and rivers are full of ferrous trash, etc. In Australia I suppose that in the desert there will not be so much trash and that all the positive signals are gold nuggets.
One last question and I'm done;
Is there any possibility of some kind of discrimination in this detector, since I have now got it working? I have searched all your posts and have not found any firmware available.

Best regards,
Eduardo

[Gunghouk]

Hi Eduardo, I have also been suffering from similar stability problems as you. Installing the 10 ohm gate resistor on Q2 cleared my spurious supply issues and more recently I have reinstated R6, the 10k feedback resistor on the preamp U2. This reduced a lot of the instability albeit for the loss of some signal gain. I am now working on finding working settings for the operating parameters starting from Ton 7.8, Smp 8.0, Xsw 1 and an Xss value of 1.46 us.

Things are looking up and I may try reducing the overall gain further to stop the slow drifting probably by playing with R7 on U3 to something less than the 100k shown in Moodz final circuit (the original was 10k).

I've found that presenting a target will stop/reset the drift temporarily before slowing taking off again.

Best regards

[moodz]

Hi Eduardo, I have also been suffering from similar stability problems as you. Installing the 10 ohm gate resistor on Q2 cleared my spurious supply issues and more recently I have reinstated R6, the 10k feedback resistor on the preamp U2. This reduced a lot of the instability albeit for the loss of some signal gain. I am now working on finding working settings for the operating parameters starting from Ton 7.8, Smp 8.0, Xsw 1 and an Xss value of 1.46 us.

Things are looking up and I may try reducing the overall gain further to stop the slow drifting probably by playing with R7 on U3 to something less than the 100k shown in Moodz final circuit (the original was 10k).

I've found that presenting a target will stop/reset the drift temporarily before slowing taking off again.

Best regards

Slow drift can be a symptom of two things.

The differential amp is overloaded / railed .... the voltage at the oupuf of the differential amplifier U1 should be fairly constant at around 1 to 1.5 volts. If it is closer to 0 or 2.8 volts then the amplifier is seeing an offset current due to ..

1. Leaky input capacitors ... the DC blocking caps must be high quality film caps C6 and C7. Even a very small leakage current will cause an offset DC votage that will rail the output. The integrator caps need to high quality too. Ceramic caps are way too leaky.

2. Overload input ... the samples from the integrators R13, R14, C4, C5 are overloading the input to the amplifier. If the difference between voltage inputs exceeds 150 microvolt approx then the diff amp will overload. Bad sampling windows will do this.

[moodz]

Hi Moodz.
Thanks for answering my question.
I have done everything you have told me;
I have added a 10 Ohm resistor in series with the gate of the mosfet Q2.
I have put the PCB inside a metal box and connected the tab of the LM7805 regulator to the chassis of the box, as you show in the photos.
I have turned off the LED lights in my lab for a moment to see what happens.
The detector is powered by Lithium Batteries, not by laboratory power supplies.
I have also tried cutting the power supply track on the PCB that you mentioned in a previous post and I have powered the DG411 directly from the Battery as you were explaining in a previous post. All this without success and without noticing any difference. The only thing that works is changing the TON parameter value to 94 or 96 and the SIG parameter value stays oscillating around 400. It is the only way to make the detector work stably.
I have been playing with all the possible parameters, changing all the values and without success, except for the TON parameter, mentioned above.
I have noticed that the detector, working stably, does not reach the depth and sensitivity that your detector in the videos you posted reaches.
I have noticed that the detector rejects ferrite and hot rocks very well, but it does not have any kind of discrimination.
I would have liked it to have at least discrimination for High or Low conductivity like the TDI or the Minelab GPX4500, because here in Europe we also like to search for gold nuggets, but the fields and rivers are full of ferrous trash, etc. In Australia I suppose that in the desert there will not be so much trash and that all the positive signals are gold nuggets.
One last question and I'm done;
Is there any possibility of some kind of discrimination in this detector, since I have now got it working? I have searched all your posts and have not found any firmware available.

Best regards,
Eduardo

Hi Eduardo. Not all the signals in Australia are gold nuggets but we do have much less trash than the rest of the world ( except maybe Africa ).

Unfortunately to discriminate there would have to be some changes to the front end and firmware. It really needs an extra channel ... as some targets will disappear with discrim enabled. ( target appears as half ferrous / half non ferrous ).

[Gunghouk]

Hi Moodz, what is the latest version for LCD display ? If there is, any chance of a copy please ? I'm currently using 1.5 with non working volume.
Thanks