NEW !!! Full differential PI front end.

[Muntari]

Hi Aziz,

My design is undergoing some upgrades, new proccessor, new firmware.

Besides this, my time has been taken up with a sub-project related to the MPI and also I purchased a company late last year which has required most (read 99% !) of my time. So the MPI project has taken a back seat for a few months.

Will the MPI see light of day...yes it will...does it work....yes it does..when will it be ready.... when we have all the usual production issues ironed out and legal matters confirmed.

I will post on another thread when we are close.

In the meantime, Moodz is doing a great job with his beast...I like it.



Cheers

Brian K

[gadgetmaker]

Just a crazy idea

Moodz,

Why not try to drive both coils, one then the other by simply adding another fet and then use the two signals to cancel any dc offset during A to D conversion?

Karl

[gadgetmaker]

4066 just use a 74HCT4066

I have used 74HCT4066's for fast pixel overlays for video; they should work well.

[Aziz]

Hi Aziz,

Small point but .... credits to Moodz this is his design not mine....

cheers

Brian K

Oh , I am sorry for this. I ment moodz of course.

I also would like to see your design Brian. It's long time since you didn't publish details of it.

Aziz

[Muntari]

Hi Aziz,

Small point but .... credits to Moodz this is his design not mine....

cheers

Brian K

[Muntari]

Something like this perhaps...

Cheers

Brian K

[Carl-NC]

doh ... just realised that explanation is wrong sort of.. when the PIC port is high the 4066 is ON. When the PIC port is low the 4066 is OFF. The diodes prevent the PIC high level from driving the port ... this is done by the pull up resistor to get correct bias.

moodz (again )

I don't think this circuit will do what you want it to do. The pull-ups won't pull up to +15 when the PIC outputs are at +5. They will only go to 5.7V, which probably isn't enough to switch the 4066. You really need a bipolar (with base R) or a FET in place of the diodes.

- Carl

[Aziz]

Industry standard analog switches

Hi Brian,

the CD4066 has not a logic level shifter built in (*shame*). There are DGxxx devices that do it. But there are also improved versions available:
MAX313
MAX392
MAX333A

These analog switches makes the driving with MCU logic levels easy. Some of them are precision type and cost more.

You can also try the CD4053 (only 3 switches).

I like your new design.
Aziz

[WM6]

Excellent and very inventive moodz.
Someone will ask you for full schematic soon (and maybe for kit or preprogramed pic too).

[Muntari]

Hi Moodz,
Yep, gottcha, just looked at PWM port line source / sink specs, I was having a seniors moment...

I was originally concerned with damage to port pins but given your resistor values, should be ok.


Cheers

Brian K

[moodz]

doh ... just realised that explanation is wrong sort of.. when the PIC port is high the 4066 is ON. When the PIC port is low the 4066 is OFF. The diodes prevent the PIC high level from driving the port ... this is done by the pull up resistor to get correct bias.

moodz (again )

[moodz]

Hi Brian ..... D5 and D6 are correct ... the PIC port will try to source current when high and sink when low ( ie current reverses ) so the diodes allow the port to pull low but the pull up resistor to +15 volts pulls the control input of the 4066 up ( ie ON ) and the diode blocks the high bias from the PIC when the PIC output is high ( ie OFF ). I am not an expert at 4066 control but it definitely does not work without the diodes.

Version 2 will do away with the differential integrator and do it all in software ... time of course is one resource I dont have at the moment.

moodz

[Muntari]

Hi Modz,

Is the orientation of D5 and D6 correct?

Looks interesting though

Cheers

Brian K

[moodz]

zpi v1.0

.. been a bit busy lately but did get round to making up the diff coil demonstrator platform. Based on the good ol surfmaster design except with a diff coil front end and dspic back end ... note also the design is DC coupled all the way to the ADC.
I do have some fancy amps in the parts bin but have stuck with the good ol CA series as I have lots of em and like they say ... a good engineer dont buy what he wants he makes it out of what he can get ( or has in this case ) ... anyway the circuit works superbly with these antiques and demonstrates the benefit of the diff coil .. which is the purpose of this demonstrator circuit.
The diff coil I am using on this particular version is 22 cm in diameter, 3 ohms total resistance and has 60 turns. ( yes you read right ... six - oh ... turns ). The single control is an ALPS rotary encoder with push button switch into the dspic quadrature encoder. There is no display whatsoever. ( Oz is full of snakes and mineshafts ) Menu is accessed by pushing the controller knob and a PWM voice prompt is injected into the audio output eg 'VOL' 'DELAY' 'DISC' 'SENS' then twist knob to set level with beep rate indicating level etc thanks to stored samples in the generous ROM they give you in the dspic. Target signal is a rising click to tone with warble for discrim function.
The power supply and audio amp are on a separate board not shown below ... mainly because I have not drawn it up yet.
Moodz.

[simonbaker]

You are right Aziz ... however an oscillating system is one that does not have constraints ... the damping resistor is one kind of constraint however it is passive ... by applying an active forcing function of known limits the oscillation may be removed in the same manner ... this is done in amplifiers for example with compensation which is not a damping resistor. The feedback in an amplifier is a type of active forcing function that modifies the input condition.
I will need to investigate further ... however my aim with this circuit is to produce a very fast reversal magnetic field in the ground / target.
So far the results are good ... the down side is the extreme voltages produced at the MOSFET ... even 5 volts of drive produces over 700 volts ... this is probably due to the 'Q' of the 'filter' circuit I am using to produce the coil forcing function.
Regards,

moodz.

Very interesting stuff you are pursuing, keep it up

You and Aziz make a good team... we're going to see some great new PIs one day...

-SB