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

[David_1]

Not if you know it doesn't matter. I hook them up according to what makes the layout easiest.

from pdf

[Carl-NC]

Not if you know it doesn't matter. I hook them up according to what makes the layout easiest.

[Dean Sarelius]

The switches are bidirectional so it doesn't matter whether the input is on S or D.

Hi Carl
Yes I agree with you in principle but as I said the DG411 all the test circuits are applying the input to the source pins so best practice dictates that you should follow the test criteria.

[Carl-NC]

The switches are bidirectional so it doesn't matter whether the input is on S or D.

[IBGold]

Hi Paul,

Package arrived today with your permission I want to make a few changes and I have some questions the changes first,
.1. I want to remove the DC power socket and replace with a LTW that I use reason found on the other device the DC plugs were very noisy .
.2. Remove the 3.5 mono socket and replace with a 3.5 stereo one wired as a mono as that is how the Bluetooth TX that goes to my hearing aids is configured.
.3. After initial testing I want to remove the encoder and fit it into an enclosure which will also house the screen and fit on the handle I have the screen and the enclosure is almost complete.
Now for the questions .
.1.I intend running the Magpie V3 using my existing 2S Li-Ion 7200mAh is that OK?
.2. I notice that the encoder is wired differently to the pictures you posted earlier two wires on this encoder are transposed to the ones in the pictures the plugs on the boards are all the same as each other so which is correct.
.3. I intend to run the screen and encoder Via a shielded 9 core cable via an 8 pin plug and socket on your box and hard wired to the screen box does this sound feasible?
.4. I notice that their is no On/Off switch should I add one between power socket + positive (my LTWW socket) and the + wire to the board unless of course you have something already enabled to turn the power On/Off?
That should do for now.

Regards, Ian.

[Dean Sarelius]

Hi Moodz,
Just laying out the schematic and note that the datasheet for the DG411 all the test circuits are applying the input to the source pins.
This would mean that the source pins P3(S1), P14(S2),P11(S3) and P6(S4) should be tied to the output of the opamp.
I will be making this change to my schematic also.
Suggest if you think all these changes deserve a new thread let me know and I will kick it off as MAGPI V3.1.
Cheers,
Dean

[Dean Sarelius]

Hi Dean I have scoped out the actual signals at the input / output to the preamp on the V3 for a complete transmit cycle ( 30us on / 30us off ) and the X sample pulse from the PIC32.

The top Light Blu trace is the X sample pulse.
The Pink trace is the input to the preamp.
The Darker Blu trace is the preamp output.

You should be able to see that the input to the preamp never exceeds 4.5 volts positive and 1 volt negative. This is because there are two diodes ( one damping and one protective to +5 volts ) across the input to the preamp.
So the input to the preamp never exceeds the supply rails and cannot due the diodes.
Hope this clarifies.

I can see you have gone to a fair bit of trouble to simulate the circuit. The coil I use is 0.5 ohms possibly 0.6 ohms. but this should not affect the result.

Cant tell from your results but was the damping control loop settled when you measured ?

moodz.

Hi Moodz,
Succesfully simulated your circuit with and without the buffer, I must say this is a very interesting circuit I would really like to know where you got the ZPD concept from..?
When comparing the results there doesnt appear to be much of a difference in the performance both circuits perform exactly as expected providing the much needed negative bias voltage for Q2.
The bias voltage settles at around -4V and it takes approximatley 90ms to reach this value with and without the buffer.
Below are screen shots results with the addition of a buffer using the NE5532 A and B one for the buffer the other for the TX feedback replacing the NE5534.
Since the buffered circuit works I will make these changes to my design and start laying out with the new schematic.
Simulations were completed with Multisim.
Screenshot 1
Blue = Bias Voltage Q2
Purple = TARG

Screenshot 2
Green = Output from NE5532AIP
Red = Input to LM6171AIM

[Dean Sarelius]

I'm not sure if this will help but your simulation appears to be missing the isolation diode between the TX coil and the TX driver.

Yes I noticed that too and put the diode back in but without any change. The simulator prefers gear rather than trapazoidal so not sure if that could be causing some issues also..?
I have swapped out the DG411 with the ADG411 as well as with regular voltage controlled switches have tried long and short time intervals between interations always running extended siulations to capture the damping.
I think it could be an issue with Multisim so think I will try on another simulator maybe LTSpice, Proteous or Circuitmaker.
Will let you know if one of these are succesfull.

[Auto-Mation-Assist]

Hi Moodz,
I have been unseccessfull in simulating your circuit within Multisim , just wondering if you have any LTSpice file which you can share perhaps..?

I'm not sure if this will help but your simulation appears to be missing the isolation diode between the TX coil and the TX driver.

[Dean Sarelius]

Hi Moodz,
I have been unseccessfull in simulating your circuit within Multisim , just wondering if you have any LTSpice file which you can share perhaps..?

[Dean Sarelius]

Hi Dean I have scoped out the actual signals at the input / output to the preamp on the V3 for a complete transmit cycle ( 30us on / 30us off ) and the X sample pulse from the PIC32.

The top Light Blu trace is the X sample pulse.
The Pink trace is the input to the preamp.
The Darker Blu trace is the preamp output.

You should be able to see that the input to the preamp never exceeds 4.5 volts positive and 1 volt negative. This is because there are two diodes ( one damping and one protective to +5 volts ) across the input to the preamp.
So the input to the preamp never exceeds the supply rails and cannot due the diodes.
Hope this clarifies.

I can see you have gone to a fair bit of trouble to simulate the circuit. The coil I use is 0.5 ohms possibly 0.6 ohms. but this should not affect the result.

Cant tell from your results but was the damping control loop settled when you measured ?

moodz.

Hi Moodz,
I think I know where the issue is and it is with respect to charging the gate capacitor C1.
Without the bias there is no damping of the flyback hence the flyback is able to fall deeper than it should.
I can see on your scope the flyback is settling around zero volts where it should be however in my simulations it is passing the zero volt line and heading into the 6V region.
For some reason I am having issues to get the DG411 model to sample the pulse at 1.6us for the bias cap and am still working through it.
Hopefully will have it working soon.
Thanks again for your help..cheers

[moodz]

Hi Dean I have scoped out the actual signals at the input / output to the preamp on the V3 for a complete transmit cycle ( 30us on / 30us off ) and the X sample pulse from the PIC32.

The top Light Blu trace is the X sample pulse.
The Pink trace is the input to the preamp.
The Darker Blu trace is the preamp output.

You should be able to see that the input to the preamp never exceeds 4.5 volts positive and 1 volt negative. This is because there are two diodes ( one damping and one protective to +5 volts ) across the input to the preamp.
So the input to the preamp never exceeds the supply rails and cannot due the diodes.
Hope this clarifies.

I can see you have gone to a fair bit of trouble to simulate the circuit. The coil I use is 0.5 ohms possibly 0.6 ohms. but this should not affect the result.

Cant tell from your results but was the damping control loop settled when you measured ?

moodz.

[Dean Sarelius]

Hi Moodz,
After completing simulations with the original circuit there is only one major issue which has jumped out that needs to be considered.
Since this is a high side switch configuration the flyback has a tendency to reach 6 or 7 volts at the 1-2us region of the return pulse refer screen shot below of the pulse measured at the drain of BSP230 in my case this is the drain of the BSP304.
Referring to Channel A there are two markers Marker 1 (x1,y1) and Marker 2 (x2,y2).
Marker 1 (light blue) is the coil voltage just before switch off y1 = 4.7952V while Marker 2 (yellow) is the return voltage y2 = 6.4451V.
Just for reference the time difference between Marker 1 and Marker 2 is highlited with dx of 2.083us this was with a coil inductance 300uH, Rs 1.2ohm and Cp=100pf.
As you can see the return voltage at the 2us region is above the threshold of the supply rail to the op-amp which would necessitate increasing the the supply voltage to the LM6171, NE5534 and DG411 switches.
For reference have included screen shot pdf of the simulated circuit.
I am running simulations changing the supply voltage to 9V and will feedback my results shortly.



Moodz front end complete withou.pdf

[Dean Sarelius]

Hi Dean ... so all good ..if the buffer results in lower noise on the output then good. Most detector designs I have seen sample right off the output of the preamp with no buffering.
The X sample should occur as close as possible to the end of the flyback and for most coils the sweet spot is 1.1 to 1.8 microseconds.
With resistive sampling the width should be approx 0.1 microseconds but ppl can play with this to adjust for noise and sensitivity.

I found a lot of difficult targets with a GPZ7000 ... ( small nuggets, old buckshot, hotrocks ) ... The V3 is able to see them with about the same sensitivity.
The V3 is no better on hotrocks than the GPZ ... though the GPZ does not find alot of hotrocks.

moodz

Hi Moodz,
Thats awesome if your design is as good as the GPZ7000 then its happy days.
If you feel confident the V5 could be ready for release within the next few weeks then will prefer to hold off and lay out the board for a bi-polar design.
Have been running some simulations of the V3 and can see after approximatley 20-30ms the gate of the fet settles to around 0V so I gather this is the zero point you mention..?
cheers

[moodz]

Hi Dean ... so all good ..if the buffer results in lower noise on the output then good. Most detector designs I have seen sample right off the output of the preamp with no buffering.
The X sample should occur as close as possible to the end of the flyback and for most coils the sweet spot is 1.1 to 1.8 microseconds.
With resistive sampling the width should be approx 0.1 microseconds but ppl can play with this to adjust for noise and sensitivity.

I found a lot of difficult targets with a GPZ7000 ... ( small nuggets, old buckshot, hotrocks ) ... The V3 is able to see them with about the same sensitivity.
The V3 is no better on hotrocks than the GPZ ... though the GPZ does not find alot of hotrocks.

moodz