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

[AhmatAhmatov1959]

I think it's 2 microseconds. I'm not sure where to put the oscilloscope or how to understand the data. In the video I had the 2 channels on R12 and on the coil +, both probes connected to battery ground. On my board, I disconnected pin 4 of the INA125P after following an AI suggestion. The signal sits at 121 normally with this change, but with pin 4 connected to 5 and 13, the signal sits at about 433, and the audio pitch is lower. It doesn't seem quite as sensitive when it's reconnected, though the lower frequency is harder to discern

Channel 1 blue is the coil+, and i'm using x10 on the probe. So as far as I can tell, it's around 250v. Channel 2 yellow is about where the diode clipper is, and the damping resistor. Time scale is 1uS / div

My PCB has no metal shield, but my coil does. I'm using a commercial coil made by minelab, which would be screened. I think 4uS is good, but my knowledge is limited

You have disconnected the 4th leg of INA 125. I have read the whole topic but have found nothing. Where can I find out about this? My reaction to a ferrite with a diameter of 15 mm and a length of 40 mm is 15 cm, I don’t know if this is normal. What is yours?

[van0014]

I think it's 2 microseconds. I'm not sure where to put the oscilloscope or how to understand the data. In the video I had the 2 channels on R12 and on the coil +, both probes connected to battery ground. On my board, I disconnected pin 4 of the INA125P after following an AI suggestion. The signal sits at 121 normally with this change, but with pin 4 connected to 5 and 13, the signal sits at about 433, and the audio pitch is lower. It doesn't seem quite as sensitive when it's reconnected, though the lower frequency is harder to discern

Channel 1 blue is the coil+, and i'm using x10 on the probe. So as far as I can tell, it's around 250v. Channel 2 yellow is about where the diode clipper is, and the damping resistor. Time scale is 1uS / div

My PCB has no metal shield, but my coil does. I'm using a commercial coil made by minelab, which would be screened. I think 4uS is good, but my knowledge is limited

[AhmatAhmatov1959]

There's a potential replacement MOSFET for the BSP230. I had trouble getting genuine ones, though BSP225 can be bought from Digikey. But the DMP45H150DHE-13 appears to be similar enough in terms of low input capacitance, 250mA current and 450Vgs. The biggest difference i can find is Rds On, original is 17 Ω, this one is 150 Ω

I've made up a second MAGPi, after my first try failed. I used a -5v reg instead of -9 and it never smoothed out. But now with the new board, it smooths out but doesn't seem sensitive enough. It is working extremely stable, without a metal shield around it. It detects PCB and aluminium ok, but it won't find a big silver coin unless it's about 5cm from the coil. I get about 30 - 40cm maximum distance on PCB or large aluminium, where at max. distance it can change the signal number by 1, which is an audible change. I'm wondering if it's normal or if i've built it wrong somewhere

Hello. I have a reaction to an aluminum square 10 * 10 mm 8-10 centimeters. The coil had a capacity of 40 pF when it was screened with graphite with a resistance of 1000 ohms per 1 cm. The influence of the hand was 20 cm. I applied 2 more layers of graphite to remove the influence of the hand. The resistance of the screen became 150 ohms per 1 cm. The frequency of the coil with cable and screen decreased from 1360 kHz to 860 kHz. I applied graphite on top of the coil. I will screen the next one by turns. Please answer in how many microseconds does it take for your coil to be extinguished. Is it normal for me to do it in 4 µs?

[van0014]

There's a potential replacement MOSFET for the BSP230. I had trouble getting genuine ones, though BSP225 can be bought from Digikey. But the DMP45H150DHE-13 appears to be similar enough in terms of low input capacitance, 250mA current and 450Vgs. The biggest difference i can find is Rds On, original is 17 Ω, this one is 150 Ω

I've made up a second MAGPi, after my first try failed. I used a -5v reg instead of -9 and it never smoothed out. But now with the new board, it smooths out but doesn't seem sensitive enough. It is working extremely stable, without a metal shield around it. It detects PCB and aluminium ok, but it won't find a big silver coin unless it's about 5cm from the coil. I get about 30 - 40cm maximum distance on PCB or large aluminium, where at max. distance it can change the signal number by 1, which is an audible change. I'm wondering if it's normal or if i've built it wrong somewhere

[AhmatAhmatov1959]

Make sure you use a DC blocking low pass filter at the input to the amp. The Magpi puts out PWM but it need DC blocking to remove the DC remainder. ( ie connect speaker via capacitor )

Hello Moodz. Thank you. I installed a 220uF capacitor and the amplifier on the 386 chip worked great. Where I am going to search there are a lot of bears and wolves, so headphones are not suitable for me. I made different coils using the same 21 meter long litz wire. The ideal coil turned out to be a double field. Inductance 300mcg resistance 0.5 ohm and capacitance 10p Также сделал кабель емкостью 40пф. Когда собрал катушку и за экранировал ее графитом емкость собранной катушки не увеличилась, а оказалась 40 пф. Резистор на внутреннюю катушку я не устанавливал. Имульс 240 вольт гасится за 4 микросекунды. Хотел у Вас спросить если установить резистор на внутреннюю катушку возможно ли уменьшения времени импульса. I also made a cable with a capacity of 40 pF. When I assembled the coil and shielded it with graphite, the capacity of the assembled coil did not increase, but turned out to be 40 pF. I did not install a resistor on the internal coil. The 240 volt pulse is extinguished in 4 microseconds. I wanted to ask you if it is possible to reduce the pulse time if I install a resistor on the internal coil.I installed a resistor at the input of the metal detector, the voltage decreased and the pulse time increased. Thanks for the answer. Sorry for my English

[moodz]

Hello. Please advise the sound amplifier circuit for an 8 ohm speaker with volume control. I made it on a 386 chip and didn't like it. Thank you.

Make sure you use a DC blocking low pass filter at the input to the amp. The Magpi puts out PWM but it need DC blocking to remove the DC remainder. ( ie connect speaker via capacitor )

[van0014]

After years of soldering, I have finally realised the importance of using flux. And although solder does have flux in it, it’s not enough to get good results with

These are before and after photos with flux and smaller solder

[van0014]

That's ok. Here's the post: https://www.geotech1.com/forums/foru...007#post410007

[AhmatAhmatov1959]

The original sound circuit is basically a Class-D audio amplifier, and should be sufficient for an 8 ohm speaker. Please try other speakers. Also the volume is low by default, and needs a rotary encoder connected to turn it up, preferably also with a 2004 LCD screen with an I2C backpack..

If you really needed to, the source code can be modified from the most up to date file in these posts, to use a higher default volume. You will then need a pickit 3 if you want to compile the source code. But don't buy the pickit unless you are comfortable with the source code and have compiler software. This is not recommended if you haven't done it before. I highly recommended getting a rotary encoder and screen, and following the photos in these posts to see how to wire them up

Thanks for the reply. I'll have to buy an encoder and a screen.

[van0014]

The original sound circuit is basically a Class-D audio amplifier, and should be sufficient for an 8 ohm speaker. Please try other speakers. Also the volume is low by default, and needs a rotary encoder connected to turn it up, preferably also with a 2004 LCD screen with an I2C backpack..

If you really needed to, the source code can be modified from the most up to date file in these posts, to use a higher default volume. You will then need a pickit 3 if you want to compile the source code. But don't buy the pickit unless you are comfortable with the source code and have compiler software. This is not recommended if you haven't done it before. I highly recommended getting a rotary encoder and screen, and following the photos in these posts to see how to wire them up

[AhmatAhmatov1959]

I've had a go at making this, and had some success. But also made some mistakes. I ordered an L79L05 instead of L79L09. It still seemed to detect things, but not quite the way it should.

Sourcing a genuine BSP230 is somewhat expensive ($20 - 30), though cloned ones are availiable they most certainly would be a compromise. I've came across DMP45H150DHE-13, and may try it as a cheaper alternative. It's unknown what difference it'll make and if it needs different gate drive characteristics. I can get BSP225 from digikey but it's at risk of avalanching. I am probably going to stick with BSP230

I'm looking for ways to improve on the design. The gain of INA125 seems slightly out of spec, risking non linear gain setting and unstable operation. Though admittedly, i'm not an engineer. I just like to read datasheets, and work on car wiring. I'm going to either try a 6.04 ohm precision surface mount resistor (RN73C2A6R04BTDF) or reduce gain as low as 1,281 (47 ohms). Previously I used CPF15R0000BEE14 as a precision 5 ohm resistor.
This gain change is based on some questionable advice from AI, which says gains above 120 db may be too unstable. This hopefully would give similar response by changing the code
//PR4 = (unsigned int)(ADCTarget * (original gain / new gain)) + audioTone + 128;
PR4 = (unsigned int)(ADCTarget * (12004 / 1281)) + audioTone + 128;

This change in gain is in conjunction with changes to NE5534 and LM6171, but I think I may be almost trying to over engineer it, when it may be working at it's best the way it has been designed originally.

INA125 Rg	6Ω (Gain ≈10,000)	24–60Ω (Gain ≈2,500 to 1,000)	Lower noise/offset, higher bandwidth
NE5534 feedback R	100Ω	220–470Ω	Lower gain, better stability
LM6171 feedback C	10pF	22–33pF	Lower bandwidth, less high-freq noise

Hello. Please advise the sound amplifier circuit for an 8 ohm speaker with volume control. I made it on a 386 chip and didn't like it. Thank you.

[van0014]

I've had a go at making this, and had some success. But also made some mistakes. I ordered an L79L05 instead of L79L09. It still seemed to detect things, but not quite the way it should.

Sourcing a genuine BSP230 is somewhat expensive ($20 - 30), though cloned ones are availiable they most certainly would be a compromise. I've came across DMP45H150DHE-13, and may try it as a cheaper alternative. It's unknown what difference it'll make and if it needs different gate drive characteristics. I can get BSP225 from digikey but it's at risk of avalanching. I am probably going to stick with BSP230

I'm looking for ways to improve on the design. The gain of INA125 seems slightly out of spec, risking non linear gain setting and unstable operation. Though admittedly, i'm not an engineer. I just like to read datasheets, and work on car wiring. I'm going to either try a 6.04 ohm precision surface mount resistor (RN73C2A6R04BTDF) or reduce gain as low as 1,281 (47 ohms). Previously I used CPF15R0000BEE14 as a precision 5 ohm resistor.
This gain change is based on some questionable advice from AI, which says gains above 120 db may be too unstable. This hopefully would give similar response by changing the code
//PR4 = (unsigned int)(ADCTarget * (original gain / new gain)) + audioTone + 128;
PR4 = (unsigned int)(ADCTarget * (12004 / 1281)) + audioTone + 128;

This change in gain is in conjunction with changes to NE5534 and LM6171, but I think I may be almost trying to over engineer it, when it may be working at it's best the way it has been designed originally.

INA125 Rg	6Ω (Gain ≈10,000)	24–60Ω (Gain ≈2,500 to 1,000)	Lower noise/offset, higher bandwidth
NE5534 feedback R	100Ω	220–470Ω	Lower gain, better stability
LM6171 feedback C	10pF	22–33pF	Lower bandwidth, less high-freq noise

[Technologyh]

Did this project stop? Is it now ready to make it? Can you help us.

[Technologyh]

Go over the topics from the beginning and you understand.

[van0014]

After having the PCBs and parts for a few days, I couldn’t help but start putting it together. It took me a while to get the hang of soldering. Mostly I solder car wires of about 1.5mm squared. I won’t be getting high marks for soldering. Though the IC sockets were easiest, and some of those joints might even have the recommended amount of solder. Most other joints have a bit too much. I chose lead free HASL for the PCB tinning.

All that’s left is the 100uF charge pump capacitors (I ordered 6.3v and it might not be enough. More to be ordered), the BSP230 (will a BSP225 be ok here?) and the coil socket and screen parts.

some of my components look odd. Resistors are 1%, and 1/4W or higher, though they are small. In hindsight, I should have looked into the voltage rating of these. 200v is the limit, though they handle more intermittently. Clock capacitors are C0G / NP0, and I used ceramic caps for the 1uF parts, X8R. The hope is that parts with better tolerances or less temperature variations may be beneficial.

The downside is, the more I stray from Moodz’ component choices, the more risk there is that some components may need changing. Or worse, scope testing. I haven’t got the talent he has. I just like to read datasheets. I work on car wiring mostly.

Moodz, thankyou for posting your design and project. I really enjoy reading through all your posts, and there’s many talented people on these forums. I’ve been itching to put something together on a PCB for a long time