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

[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

[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]

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]

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]

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 have a toroidal ferrite with a diameter of 40mm and a thickness of 15mm. It’s barely detectable at 10cm. It gives a weak response, even at 0cm from the coil. I can detect some copper PCB, 100x150mm, at 45cm maximum. Very strong when closer. An aluminium empty panadol packet, 8x5cm, can be detected at 35-40cm. Very strong signal when closer. A silver coin of 40mm diameter can be noticed at 11cm. It doesn’t give much response, not like aluminium and copper

[AhmatAhmatov1959]

I have a toroidal ferrite with a diameter of 40mm and a thickness of 15mm. It’s barely detectable at 10cm. It gives a weak response, even at 0cm from the coil. I can detect some copper PCB, 100x150mm, at 45cm maximum. Very strong when closer. An aluminium empty panadol packet, 8x5cm, can be detected at 35-40cm. Very strong signal when closer. A silver coin of 40mm diameter can be noticed at 11cm. It doesn’t give much response, not like aluminium and copper

I installed 7806 at the input. The voltage on the coil was 320v. Sensitivity increased. I left the device on all night, nothing overheated, although all the parts are from Ali. The coil Ring was 220mm in diameter without a screen and inductance 270mcG. The other day I will go out into the field and if the influence of the soil will be, I will install 7806 and cover the coil with another layer of graphite.

[van0014]

You got better sensitivity with 7806? That's worth trying! I'll get one added to my next order.
I've tried a few different mosfets, convinced i'm unable to get a genuine BSP230. and so far, the genuine BSP225 performs the best. For a while I had the damping resistor R12 at 470, based on old advice for increasing sensitivity, but 330 works much better. Next I will try with a 180 - 200 ohm R12 to compensate for the "DMP45H150DHE-13" - Rds On resistance of 150 ohms. But this will require unsoldering the BSP225 and to risk destroying it and loosing some sensitivity. I have yet to test the coil voltage and to see if it is avalanching because of the bsp225
Another change could be a 47uH inductor inline with the charge pump output. But because it's running so smoothly, even without shielding the circuit board, I might not add it.

[AhmatAhmatov1959]

You got better sensitivity with 7806? That's worth trying! I'll get one added to my next order.
I've tried a few different mosfets, convinced i'm unable to get a genuine BSP230. and so far, the genuine BSP225 performs the best. For a while I had the damping resistor R12 at 470, based on old advice for increasing sensitivity, but 330 works much better. Next I will try with a 180 - 200 ohm R12 to compensate for the "DMP45H150DHE-13" - Rds On resistance of 150 ohms. But this will require unsoldering the BSP225 and to risk destroying it and loosing some sensitivity. I have yet to test the coil voltage and to see if it is avalanching because of the bsp225
Another change could be a 47uH inductor inline with the charge pump output. But because it's running so smoothly, even without shielding the circuit board, I might not add it.

Shielding of the printed circuit board is necessary. My printed circuit board without shielding felt a hand at a distance of 10-15 cm. I found old broken gold and silver earrings, I will test them today. I am from Russia, I would like to know where you are from.

[van0014]

Shielding of the printed circuit board is necessary. My printed circuit board without shielding felt a hand at a distance of 10-15 cm. I found old broken gold and silver earrings, I will test them today. I am from Russia, I would like to know where you are from.

If your printed circuit board detects a hand at 10-15cm, I think i've built mine wrong. I used higher precision parts with 25 or 50 parts per million / degree celcius (ppm/°c), and I thought that's why it didn't respond. It's when I touch the IRF9640 or other metal that the metal detector notices.
I am from Australia, specifically Victoria.
I am hoping to connect the oscilloscope again and to find out how to get mine detecting a hand. The coil finds large pieces of copper and aluminium from 30-45cm away but it can't find a hand near the printed circuit board.

[van0014]

I think my BSP225 is avalanching, or i’ve chosen a wrong component. It seems to be 1us or less that it’s quenched in, with both 330 ohm damping and 2x parallel 330 ohm resistors for 165 ohm damping

channel 1, blue, should actually be 1v/div, i’m using x10 probe switch for both channels but didn’t properly set the scope for it

[moodz]

I think my BSP225 is avalanching, or i’ve chosen a wrong component. It seems to be 1us or less that it’s quenched in, with both 330 ohm damping and 2x parallel 330 ohm resistors for 165 ohm damping

channel 1, blue, should actually be 1v/div, i’m using x10 probe switch for both channels but didn’t properly set the scope for it

yup ... that is definitely avalanching ..... the MAGPI uses a constant current damping principle ...which is non linear in respect of voltage and current. If you add a damping resistor ( linear in respect of voltage and current ) then the faster non-linear damping will be affected ( feedback loop is no longer sensing current properly ).

Make sure the TX time on is not too long and causes flybacks that will avalanche the damping mosfet.

if you are having trouble finding the BSP225 ... try this ..

[moodz]

Shielding of the printed circuit board is necessary. My printed circuit board without shielding felt a hand at a distance of 10-15 cm. I found old broken gold and silver earrings, I will test them today. I am from Russia, I would like to know where you are from.

If your hand is detected near the PCB then this is almost certainly due to high frequency oscillations of the 5 volt linear regulator ( 7805 ). Your hand capacitance is varying the oscillation ( like a Theramin ).
The high voltage flyback gets into the linear voltage control circuit of the regulator forming a feedback driven oscillator. This is usually fixed by directly grounding the tab of the 7805 to the coil ground at the coil connector by a non inductive connection ( ie dont use a long piece of wire ). In addition a shielded box is a good idea.

[van0014]

yup ... that is definitely avalanching ..... the MAGPI uses a constant current damping principle ...which is non linear in respect of voltage and current. If you add a damping resistor ( linear in respect of voltage and current ) then the faster non-linear damping will be affected ( feedback loop is no longer sensing current properly ).

Make sure the TX time on is not too long and causes flybacks that will avalanche the damping mosfet.

if you are having trouble finding the BSP225 ... try this ..

Aah, I thought there was something a bit off with my setup! I've ordered some BSP230 from Alibaba, hoping to get some genuine ones. BSP225 is currently easy to get from Digikey, but i suspect that the 50v less Vds is why it's avalanching. The part you've used originally is BSP230, which is a whopping 300Vds P-channel. The closest replacement I could find with the same or higher voltage was DMP45H150DHE-13, with 450Vds, and also a reasonable 60pf input capacitance. The biggest difference I found was Rds On, at 150Ohm. Which I ordered a few of, hoping the resistance wouldn't matter. Then I got some 180 Ohm resistors to use for R12, hoping that would give me an equivalent circuit function to your original design. I've been thinking of R12 as a damping resistor, though now I realize that a damping resistor would be fitted before the constant current damping, and I should've said R12 instead.

[moodz]

Aah, I thought there was something a bit off with my setup! I've ordered some BSP230 from Alibaba, hoping to get some genuine ones. BSP225 is currently easy to get from Digikey, but i suspect that the 50v less Vds is why it's avalanching. The part you've used originally is BSP230, which is a whopping 300Vds P-channel. The closest replacement I could find with the same or higher voltage was DMP45H150DHE-13, with 450Vds, and also a reasonable 60pf input capacitance. The biggest difference I found was Rds On, at 150Ohm. Which I ordered a few of, hoping the resistance wouldn't matter. Then I got some 180 Ohm resistors to use for R12, hoping that would give me an equivalent circuit function to your original design. I've been thinking of R12 as a damping resistor, though now I realize that a damping resistor would be fitted before the constant current damping, and I should've said R12 instead.

You are right about the low capacitance input and generally you dont want the TX or the damping mosfet to avalanche. So a 300 volt mosfet is better than a 250 volt ...however with constant current damping the Rds on wants to be in 10s of ohms not 100s as there will be an issue as the flyback voltage decays below the IR ( amps x resistance ) point where amps is the damping current and resistance is the Rds on.
The R12 ( I am not looking at the schem ) mops up the small residual leftover damping in a linear way after the diode to ground off the source of the damping mosfet stops conduction.
There is a way to reconfigure this arrangement very simply to create an "ideal" diode off the source of the damping mosfet .... can you see how to do it ?? This will give make the active damping even faster.