Voodoo Main Discussion

[godigit1]

Well I am surprised, but thinking about it ... the outer loop affects both of the inner two coils equally.
For this configuration to balance, the two inner coils must (I assume) be exactly the same inductance.

Hi Qiaozhi,

The outer two coils are 359 uh combined inner coil alone is 135 uh the RX coil is .993mH,
this coil was designed in thought only for the Voodoo.

I'm done experimenting at this point I have multiple coils styles to try on the Voodoo but im going to build one of these in Pi values to test performance on a working PI.

About both coils needing to be the same inductance, I think it depends on where the two coils will cross. Meaning the closer matched they will have a nicer overlap and bigger lap if rx is smaller . Smaller lap if inductance is higher as in the Test coil.
More about that in time if it does well on a PI.

Take Care

[MartyJ1963]

Nice work Lamoiz! Regards, Marty.

[MartyJ1963]

Great job on the Coil Godigit! Looking forward to seeing your results. When you have time, could you give us a rundown on the build process of your new coil please? I'd like to have a go at it too,,,Thanks, Regards, Marty.

[zakari]

hi
thanks george for your explanation. i cant make this circuit because ebay and amazon dont have service in my country.and i cant buy your book
this year the component is very expensive in my country. i am only checking this thread and enjoy from your knowledge and member's progress

best regard
zakari

[lamoiz]

PI mode is ok, with a coil of 0.4 mh, I move on .. after the aperitif ..

[lamoiz]

disc channel, ok .. but now we have to make a real coil, for the moment the tests were done with recuperated coils. where are you?

[surfdetector]

If you fit a damping resistor (without the coil) then you should see a set of TX pulses across the resistor. Without the coil there will be no feedback pulse to damage your scope probe if you forget to switch to the x10 setting.
I assume you've fitted the PIC and flashed it with the hex code? If so, then the +5V supply will be present, and there will also be a TX oscillator pulse at pin 29.

Hi George,
What size Damping Resistor did you use for the Fisher F75 coil? Thanks

[lamoiz]

I have adjustment problems, the PI coil used is made of silicone wire, and .430uh, r 2.2ohm, damp 650ohm; a test on the felezjoo measures a delay of 14us .. it is a rectangular coil, the tp3 signal on the oscilo is not good .. I will take pictures of all this ..

[Qiaozhi]

Hi George,
What size Damping Resistor did you use for the Fisher F75 coil? Thanks

Unfortunately I didn't record the damping resistor value for the various coils. I sort of expected everyone would use the damping resistor tool to determine the correct value for themselves. However, I did find that most of the coils were critically damped with either 470R or 680R. Since the Fisher coil has an inductance of 696uH, I suspect it was 470R. Since the TX circuit uses active switch-off for the mosfet, I found that damping resistor values tended to be higher than with passive switch-off circuits such as the Baracuda.

[lamoiz]

les photos

[Qiaozhi]

les photos
[ATTACH]53769[/ATTACH][ATTACH]53770[/ATTACH][ATTACH]53771[/ATTACH][ATTACH]53772[/ATTACH]

Try rotating the coil around, vertical as well as horizontal. Apart from the interference it looks OK to me.

[lamoiz]

good evening George,
Could you tell us more about the R30 and R22 trimmer, how to properly adjust R30 offset and how to properly adjust R22 ...? (with a screwdriver ... yes ...) where should we measure and how much?
thank you.

[Qiaozhi]

good evening George,
Could you tell us more about the R30 and R22 trimmer, how to properly adjust R30 offset and how to properly adjust R22 ...? (with a screwdriver ... yes ...) where should we measure and how much?
thank you.

Adjust R30 so that the signal at TP3 settles near 0V.
R22 is the gain adjustment for the DISC channel. Simply turn the preset to its lowest resistance setting for initial testing. The adjustment is provided in case you want to experiment with a higher gain setting. This preset is discussed on page 75.

[lamoiz]

Try rotating the coil around, vertical as well as horizontal. Apart from the interference it looks OK to me.

yes I do not know where the interference comes from, I am in the workshop, I do not know ..

[lamoiz]

Adjust R30 so that the signal at TP3 settles near 0V.
R22 is the gain adjustment for the DISC channel. Simply turn the preset to its lowest resistance setting for initial testing. The adjustment is provided in case you want to experiment with a higher gain setting. This preset is discussed on page 75.

thank you very much George.