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

[moodz]

Thanks Moodz,
Regarding the clipping, have set the timing at 1.6us with 100ns sample.
To avoid the clipping in your experience should I set the timing to be closer to the return pulse ie shorter or further away say 1.8us...?

The best way to resolve clipping is to set the sample pulse to midway of the clipping "pulse". In the V3 the flyback is about 200 - 250 negative volts and will then swing positive if not damped ... the flyback damping error is therefore positive at the input of the preamp which amplifies and inverts this error voltage.
If the error sample is too early you will be sampling the actual flyback and if the sample is too late then in either case ( too early or too late ) the magnitude of the damping error voltage will cause clipping.
For a 30 microsecond TX time the sample pulse might be 80 to 85 counts ( corresponding to 1.6 microseconds ) however I have mentioned before that this timing depends on the SRF of the coil when it is attached to the detector ( so to take account of the capacitance that the front end as well ).
This 1.6 microseconds was determined for a REAL circuit .. not a simulation. The simulation timing might be different as its harder to account for all the stray capacitances in a simulation. ( could be more or less than a real circuit ).

Short answer is set it to the middle of the clipping.

In the pic below the error signal does not exceed -5 volts ( thus not clipping ).



moodz

[Emersonpaz]

what is the meaning of this resistor R21 and GND on both sides

[Rick S]

Moodz,
Building your MD I want to stay as close as possible the components used in the schematic. Build the MAGPI V3 first, then do mods, up grades etc... Where did you purchase the crystal for the PIC. Having
hard time finding a thru-hole 10 MHZ 10pf oscillator. SMD 10MHZ 10pf oscillators find them in most electronic warehouses. All the Geotech projects I have built, one of them for example TGSL, become
a headache with all the changes to the first build. For me I want to KISS. I enjoy your cool head approach to this project.

[Dean Sarelius]

The best way to resolve clipping is to set the sample pulse to midway of the clipping "pulse". In the V3 the flyback is about 200 - 250 negative volts and will then swing positive if not damped ... the flyback damping error is therefore positive at the input of the preamp which amplifies and inverts this error voltage.
If the error sample is too early you will be sampling the actual flyback and if the sample is too late then in either case ( too early or too late ) the magnitude of the damping error voltage will cause clipping.
For a 30 microsecond TX time the sample pulse might be 80 to 85 counts ( corresponding to 1.6 microseconds ) however I have mentioned before that this timing depends on the SRF of the coil when it is attached to the detector ( so to take account of the capacitance that the front end as well ).
This 1.6 microseconds was determined for a REAL circuit .. not a simulation. The simulation timing might be different as its harder to account for all the stray capacitances in a simulation. ( could be more or less than a real circuit ).

Short answer is set it to the middle of the clipping.

In the pic below the error signal does not exceed -5 volts ( thus not clipping ).



moodz

Hi Moodz,
Adjusting the timing to minimise the clipping the best I could get is pictured below green being the ouput from the buffer and red the input to the LM6171.
Timing is 1.3us and 100ns sample does this look ok to you or is it still too deep..?

[moodz]

Hi Moodz,
Adjusting the timing to minimise the clipping the best I could get is pictured below green being the ouput from the buffer and red the input to the LM6171.
Timing is 1.3us and 100ns sample does this look ok to you or is it still too deep..?

Hmmm ... the negative going error looks better but the waveform is now clipping at the 5 volts .... the only clipping during the RX cycle should be during the flyback .. which is the first thing that happens in the RX period.
Should look like the CRO shot posted earlier ...
A large target can cause clipping ?? Remove all targets from your sim if you have them.

moodz.

[moodz]

what is the meaning of this resistor R21 and GND on both sides

Sorry about that its a zero ohm ( 0R ) resistor .... wire link on board. near the DG411 chip ... see photo of complete board.

moodz

[moodz]

Moodz,
Building your MD I want to stay as close as possible the components used in the schematic. Build the MAGPI V3 first, then do mods, up grades etc... Where did you purchase the crystal for the PIC. Having
hard time finding a thru-hole 10 MHZ 10pf oscillator. SMD 10MHZ 10pf oscillators find them in most electronic warehouses. All the Geotech projects I have built, one of them for example TGSL, become
a headache with all the changes to the first build. For me I want to KISS. I enjoy your cool head approach to this project.

Hi Rick .. yeh it can be a problem ... but the crystal you can get from here ..

https://au.element14.com/multicomp/m...0mhz%20crystal

Plenty in stock. About 50 cents.

moodz

[Rick S]

Moodz,
Thanks for your help. Still collecting parts.

[darov922]

Thanks Dean .. dont get me wrong I am not trying to dismiss your ideas for improvement .. I just want to lock down the V3 hardware as there are some built up units already operating by various people and whereas we can change the software because that only involves re-programming those existing units ... if we change the hardware then those existing units and ones being built up might become obsolete and those people would not be happy.

For your info ... I have V4 in simulation already with NMOS and significantly higher power and V5 which is bipolar ... not sure if target sensistivity will increase that much though we hopefully will start to see a discrimination function.

moodz

I am assembling the components to make the V3.0 version...however I want to incorporate the future updates of the V4 and V5 version. I see that these improvements are only in the TX circuit, therefore the RX circuit would remain unchanged... am I correct? I would like to make a PCB with the unalterable part and another PCB with the current TX, if it's not too much to ask: could you indicate with a red line on the schematic diagram which things have already changed in V4 and V5? Thanks for your time and effort. Dario

[IBGold]

Hi Paul,

I can report the encoder was correct except works back to front and no smoke on switch on in your next 1.2 code version can you make the default volume at the bottom of the scale in lieu of the top as is now could cause harm and allow it to go lower in volume say to 1 in lieu of current 10 because with headphones it is still too loud can not go low enough to get a threshold other than that all seems working including screen but cannot access the other menu items probably because they are not enabled with this code version and I note the voltage reading reads 1 volt low battery reading actual 8.01 volts screen reading 7.01 volts other than that seems sensitive enough.

Regards, Ian.

[Dean Sarelius]

Sorry about that its a zero ohm ( 0R ) resistor .... wire link on board. near the DG411 chip ... see photo of complete board.

moodz

Hi Moodz,
About the battery level reading from the PIC, if you were to use say an 11.1V battery to power the unit what would be your recomendation for the resistor values R4 and R9..?

[moodz]

Hi Moodz,
About the battery level reading from the PIC, if you were to use say an 11.1V battery to power the unit what would be your recomendation for the resistor values R4 and R9..?

Hi Dean,
If you are using a 11.1V battery it would read within +/-1% of 11.1 volts typically.

I have several units and they are all OK.

R4 and R9 value text is vertical sorry about that.

Is you simulation having trouble at this voltage ?

moodz

[moodz]

Hi Paul,

I can report the encoder was correct except works back to front and no smoke on switch on in your next 1.2 code version can you make the default volume at the bottom of the scale in lieu of the top as is now could cause harm and allow it to go lower in volume say to 1 in lieu of current 10 because with headphones it is still too loud can not go low enough to get a threshold other than that all seems working including screen but cannot access the other menu items probably because they are not enabled with this code version and I note the voltage reading reads 1 volt low battery reading actual 8.01 volts screen reading 7.01 volts other than that seems sensitive enough.

Regards, Ian.

Hi Ian ... The encoder direction is easy enough to fix. I put a diode in series with the power in your box ... you can remove ( not required if you are wired right ). The diode will be dropping some voltage otherwise something is wrong.
The voltage should read within %1 or so. My units do :-)
The volume setting is easy fixed in code or insert a series resistor in your audio line.
Yeh the other menu items disabled in code as not sure you would get the screen going. Easy to fix.

moodz

[moodz]

I am assembling the components to make the V3.0 version...however I want to incorporate the future updates of the V4 and V5 version. I see that these improvements are only in the TX circuit, therefore the RX circuit would remain unchanged... am I correct? I would like to make a PCB with the unalterable part and another PCB with the current TX, if it's not too much to ask: could you indicate with a red line on the schematic diagram which things have already changed in V4 and V5? Thanks for your time and effort. Dario

Some of the diodes will have to be turned around and the surface mount mosfet changed. But yes it is certainly possible to re-use most of the board with a TX add on board.

moodz.

[serci78]

Hi Moodz,which mplab ide version are you using?