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

[van0014]

What is the reaction to ferrite and gold. On my homemade coil with a screen resistance of 150 ohms per 1 cm, gold weighing 0.3 grams, the distance was 5 cm. I applied 2 more layers of graffite to reduce the effect of ferrite. The screen resistance became 20 ohms per 1 cm. The effect of ferrite did not decrease, and gold is not seen closely. Red brick is not seen.Aluminum foil measuring 15*15 mm is seen behind a red brick at a distance of 15 cm. I went out into the field and there is a reaction to the earth's magnetic field. It is impossible to conduct a search. I started making a basket coil. As soon as I finish, I will report the result.

Ferrite torus is found at about 5 - 10cm. I had been disconnecting pin 4 of the INA125P. I think normally this detector tends to cancel out ferrite

The coil resistance should be low, about 0.5 ohms and 300uH. Also it is important to tune the X2S setting to match your coil. The setting should always be set once you find thd timing that gets the best depth. It doesn’t save, but is critical to match it, and preferably use an oscilloscope. Otherwise increase it (or maybe even decrease) until depth reaches maximum

[AhmatAhmatov1959]

What is the reaction to ferrite and gold. On my homemade coil with a screen resistance of 150 ohms per 1 cm, gold weighing 0.3 grams, the distance was 5 cm. I applied 2 more layers of graffite to reduce the effect of ferrite. The screen resistance became 20 ohms per 1 cm. The effect of ferrite did not decrease, and gold is not seen closely. Red brick is not seen.Aluminum foil measuring 15*15 mm is seen behind a red brick at a distance of 15 cm. I went out into the field and there is a reaction to the earth's magnetic field. It is impossible to conduct a search. I started making a basket coil. As soon as I finish, I will report the result.

I forgot to ask what chip you have, I have PIK32..150

[AhmatAhmatov1959]

This detector makes a nice sound, and I’d been spending an unusual amount of time just seeing how fast I could swing a (nearly 1 meter) screwdriver past the coil and still get a good signal from it. That’s how fast I should therefore be able to swing the coil, right!
I started swinging it as close as I could get without hitting it, and it makes a nice swishy sound in the air. And the speaker noise gives good feedback too. i’m having a bit of fun with this. And I know it’s not meant to be a toy and i’m in my 30s, but it really was captivating me


I’ve been getting much better results by adjusting the X sample point. Though i’m using the commander coil, setting it to 2.06 has given me really good sensitivity compared to before. I can now pick up a 5c piece at about10cm. Though the scope trace for the flyback (not shown) was still clipping or in avalanche, and I have no idea how this circuit can be operating so well and with such sensitivity if it really is still maxing out.
It’s really fun to use the scope, even if i’m not probing the right spots. Also this circuit is quite enjoyable to work with.

What is the reaction to ferrite and gold. On my homemade coil with a screen resistance of 150 ohms per 1 cm, gold weighing 0.3 grams, the distance was 5 cm. I applied 2 more layers of graffite to reduce the effect of ferrite. The screen resistance became 20 ohms per 1 cm. The effect of ferrite did not decrease, and gold is not seen closely. Red brick is not seen.Aluminum foil measuring 15*15 mm is seen behind a red brick at a distance of 15 cm. I went out into the field and there is a reaction to the earth's magnetic field. It is impossible to conduct a search. I started making a basket coil. As soon as I finish, I will report the result.

[van0014]

This detector makes a nice sound, and I’d been spending an unusual amount of time just seeing how fast I could swing a (nearly 1 meter) screwdriver past the coil and still get a good signal from it. That’s how fast I should therefore be able to swing the coil, right!
I started swinging it as close as I could get without hitting it, and it makes a nice swishy sound in the air. And the speaker noise gives good feedback too. i’m having a bit of fun with this. And I know it’s not meant to be a toy and i’m in my 30s, but it really was captivating me


I’ve been getting much better results by adjusting the X sample point. Though i’m using the commander coil, setting it to 2.06 has given me really good sensitivity compared to before. I can now pick up a 5c piece at about10cm. Though the scope trace for the flyback (not shown) was still clipping or in avalanche, and I have no idea how this circuit can be operating so well and with such sensitivity if it really is still maxing out.
It’s really fun to use the scope, even if i’m not probing the right spots. Also this circuit is quite enjoyable to work with.

[van0014]

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.

An Ideal diode, well I tried, but went for an AI search. I could put a MUR160 (so I don't have to order a more suitable diode) across the (leftover damping) R12 resistor, with the cathode facing the MOSFET. Though i'm also thinking that 'damping option 2' in your original schematic could be the ideal diode setup. Your circuit is making more sense with these descriptions. I tried to understand it in the same way a standard pi circuit works, and misunderstood how the diodes and R12 behave. This will give me a few options, and I may soon be able to show a mate how comparable your design is to his '6000, but due to my mismatched components he got a 5c piece at about 25cm and I got it only by touching it with the coil. And before I told him more about your design (i'm wanting to show him this forum), he left thinking it wasn't very sensitive. He says the 6000 outperforms the 7000. I want to lend him my copy of ITMD 3, because he currently cannot understand why a detector isn't built that can go an extra foot deeper than the current technology. Though I am convinced it is more of a limitation of physics than it is electronics. So I alluded to the main limitation being coil size, but reading that book will be the best way to form an independent and accurate understanding.

[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.

[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]

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.

[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 ..

[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

[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.

[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]

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]

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]

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