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

[Dean Sarelius]

Alps rotary encoder and 2004A generic 4 line LCD with serial / par module ( see ebay or alibaba ).

See the source code for references.

I have not finalised the menus ( keep changing my mind ) but if you attache the rotary you get volume control.

moodz

Hi Moodz,
Just been reviewing your source code it is very neat and easy to read, I am sure you have written code once before right...just kidding.
Have a few questions re main.c
Q1 - PIN 25 = Not Used = 400kHz pwr sync clock << I gather there was no need to use the power sync option on pin25..?
Q2 - OpenTimer3 comments refer to OpenTimer5 but gather that these comments are applicable to Timer3 is that correct..?
Q3 - INT16 initialize() refers to PIC32MX250_setup_pins() but gather that both the 150 and the 250 are identical in their pin out so no problem to leave as is..?

FYI - I am planning to layout a 4 layer SMD version of your design and will make it available to the rest of the forum when completed.

Before I do however would prefer to base it on what you consider to be a final revision so will remain on standby.

Cheers

[moodz]

I really wished you'd picked NMOS like the previous design. This circuit would be awesome if it could be coupled with bipolar designs

Your right ... The V3 is very sensitive but NMOS or SIC will allow more power to the TX without sacrificing damping speed. Working on a plan now.

moodz

[moodz]

Hi Moodz,
Just curiours, which LCD and rotary encoder did you use, or were you considering to use..?

Alps rotary encoder and 2004A generic 4 line LCD with serial / par module ( see ebay or alibaba ).

See the source code for references.

I have not finalised the menus ( keep changing my mind ) but if you attache the rotary you get volume control.

moodz

[eclipse]

I really wished you'd picked NMOS like the previous design. This circuit would be awesome if it could be coupled with bipolar designs

[wtrk]

Hi ... the detector is a pulse induction detector which are generally more resistant to mineralisation. This detector uses some ideas to increase the sensitivity to smaller targets and also to reduce noise.

It is mainly designed for conditions in Australia ( and may suit other places ) where there is a high degree of mineralisation in the ground but relatively little trash ( compared to Europe ).
The main target of interest in Australia is gold nuggets which forces the detector designers to detect smaller nuggets or deeper nuggets.

By using active damping the target sampling can be done earlier and if you are aware of how a pulse induction detector works then you can detect smaller metallic objects.
Noise reduction is also important particularly near power lines. I think this detector will work OK on the beach also .... I didnt find any gold during testing but did find alot of junk in a very short time.

moodz

Brother Im living Türkiye and here there are lot of black mineralization rocks and stones especially near volcanic area. There is no power lines because these areas are far from living area and people left there. But almost all of the pi detectors gets beep beep beep voice. Thats way I have asked about the mineralization.

[Dean Sarelius]

..heres the HEX file for the CPU.

[ATTACH]n409851[/ATTACH]

Hi Moodz,
Just curiours, which LCD and rotary encoder did you use, or were you considering to use..?

[Dean Sarelius]

[lucifer]

The sampled feedback forms a comb filter with the response

H(f) = 2 |sin(π f T_s)|

where T_s is the sample period. The response looks like:



You get a perfect null at DC, plus nulls at every 1/T_s. You can calculate the exact amount of EMI suppression using the equation. For example, at a 5kHz pulse rate the 50 Hz mains is attenuated by

2 |sin(π*50Hz*200us)| = 0.0628 = -24dB

It's not a complete panacea because some EMI frequencies also get boosted; this is where a variable pulse rate is valuable. If the sample is taken after the target signal has decayed to zero then it has no effect on the target response. But for high conductors that have not fully decayed there is some attenuation which depends on the delays of the target sample and the feedback sample.

This technique has exactly the same effect as the classical EFE subtraction sample. The advantage here is that it's applied to the preamp so that you never have to worry about offset headroom problems. The disadvantage is that the nulls are set by the TX pulse rate, and with EFE subtraction they are set by the difference of two sample times which gives you more flexibility in placing the nulls. You could combine the two methods and get the best of both.

Thank you, Carl. That is a great explanation!

[moodz]

..heres the HEX file for the CPU.

MAGPI008.X.production.V3HW.zip

[moodz]

Thanks Jim.

[KingJL]

Thanks Jim .. the circuit is simple enough and could be further trimmed to make a compact PP. I have used a 300 uH ferrite inductor and it works great.

Here is a modified schematic to clarify ... the PCB still works ok. ( ie not modified ). The diodes are rearranged from a inverter to an inverting doubler to cater for lower lithium voltage input ( 8V instead of 12 volts ).

Paul, thank you for your answers... the rearranged diodes a great change. I think I will layout a compact pin pointer. is a great

[moodz]

(2) Is "INSTALL 9 VOLT ZENER AT R19 ANODE TO GROUND" still valid?

The 9.1 volt zener is not strictly necessary ... its a safety net ... if the bias on the gate of the BSP230 mosfet goes too negative or floats the flyback / voltage / current can be conducted into the preamp or blow the 1N1418 or the mosfet itself ... very annoying an usually no warning.

Usually happens when probing around the circuit

So if you feel lucky dont fit it.
moodz

[moodz]

Great work moodz!
After studying the Kicad files, I do have some questions:
(1) Can you provide "BUILD NOTES FOR R19,C18,R1,R20,D8"?
(2) Is "INSTALL 9 VOLT ZENER AT R19 ANODE TO GROUND" still valid?
(3) Is "USE 0.1u FILM for C1" still valid?

Do you think this would make a good pinpointer if implemented in SMD? I personally think it would make a great one.

Thanks Jim .. the circuit is simple enough and could be further trimmed to make a compact PP. I have used a 300 uH ferrite inductor and it works great.

Here is a modified schematic to clarify ... the PCB still works ok. ( ie not modified ). The diodes are rearranged from a inverter to an inverting doubler to cater for lower lithium voltage input ( 8V instead of 12 volts ).

[KingJL]

... here are the kicad files.

Great work moodz!
After studying the Kicad files, I do have some questions:
(1) Can you provide "BUILD NOTES FOR R19,C18,R1,R20,D8"?
(2) Is "INSTALL 9 VOLT ZENER AT R19 ANODE TO GROUND" still valid?
(3) Is "USE 0.1u FILM for C1" still valid?

Do you think this would make a good pinpointer if implemented in SMD? I personally think it would make a great one.

[Carl-NC]

The sampled feedback forms a comb filter with the response

H(f) = 2 |sin(π f T_s)|

where T_s is the sample period. The response looks like:



You get a perfect null at DC, plus nulls at every 1/T_s. You can calculate the exact amount of EMI suppression using the equation. For example, at a 5kHz pulse rate the 50 Hz mains is attenuated by

2 |sin(π*50Hz*200us)| = 0.0628 = -24dB

It's not a complete panacea because some EMI frequencies also get boosted; this is where a variable pulse rate is valuable. If the sample is taken after the target signal has decayed to zero then it has no effect on the target response. But for high conductors that have not fully decayed there is some attenuation which depends on the delays of the target sample and the feedback sample.

This technique has exactly the same effect as the classical EFE subtraction sample. The advantage here is that it's applied to the preamp so that you never have to worry about offset headroom problems. The disadvantage is that the nulls are set by the TX pulse rate, and with EFE subtraction they are set by the difference of two sample times which gives you more flexibility in placing the nulls. You could combine the two methods and get the best of both.