Getting ready to build the MPP

[6666]

Thanks dan.

[Chet]

-------------

Just came across this thread and have enjoyed reading your progress in making your CHance PI basket coils. As you mention above I did run into slot depth issues and this is partly because I intentionally wound more turns on the oval coil in order to do close comparison tests against my 335uh round coil. Once the tests are completed I will reduce turns to have a 300uh coil and test results. Especially on the oval coil my inner slots will be .450 to .500" deep only on the rounded ends. These mono coils are the best I know of and are the only ones I now build after three years of optimizing them. The self resonant frequency of my 335uh coils with twisted pair feeds are in excess of 1 MHz and they are critically damped at 1000 to 1100 ohms.
Good luck with your builds!
Regards,

Dan

Hi Dan

I agree with you on the effectiveness of the CHance PI basket coil. Thank you for sharing your build procedures in that forum. It was valuable information and steps that made it easy for the rest of us to follow successfully.

Thank you,
Chet

[baum7154]

Hi Dan

I agree with you on the effectiveness of the CHance PI basket coil. Thank you for sharing your build procedures in that forum. It was valuable information and steps that made it easy for the rest of us to follow successfully.

Thank you,
Chet

_____________________

Thank you Chet for your endorsement of this unique coil geometry and the efforts I made to perpetuate it in the Chance PI Coil forum. While it is a bit more difficult to fabricate the coil form and to wind I wanted to make it easy for others to build it knowing that in most cases the difficulty of building an effective separate shield is eliminated. This design is fast, self shielding, and with feed line made of continuation of the coil wire eliminates solder joints in the coil. It also eliminates the signal attenuation and additional capacitance of a separate shield. It can also be lighter in weight if care is taken in construction and if it's ever necessary, a separate graphite shield can be added later.

On the topic of scalability of the elliptical coil form PDFs posted in this forum I found in my early efforts that enlargement/reduction of drawings on a copier enlarges/reduces everything, as should be expected. This means that the 1" width of the coil form and it's slots are also enlarged/reduced and these dimensions should be kept to original design dimensions no matter the coil size. As an example, doubling the size of a coil form on a copier will spread the windings out to 2"... too much. I have not built a 2" or 3" wide coil form to test but it seems that self shielding may be negatively affected by the additional width. I think the best practice is to modify the drawings for each coil size in order to keep form width at about 1".

I look forward to test results of this elliptical coil.

Merry Christmas to all!

Dan

[jladre]

Merry Christmas!.. can i ask if it is necessary to ground the aluminum box case of my MD? Because i think if i ground the box it will consume power.

[baum7154]

Yes you should ground it. Why do you think it will draw more power?

[jladre]

Thank you for the answer..will it just my opinion to draw more power because the aluminum box may consume a little power from the battery..im just a newbie in electronics and need much knowledge..

[Silver Dollar]

Well Santa brought me all the parts to build this MD so I'm ready to start building!

The aluminum box will not use any power. You need 2 contacts for power to run through.
There might be a little loss as it acts as a capacitor a little...

[Silver Dollar]

Darn I ordered parts mainly to get the LT1054 and I ordered the wrong one!
It has 16 SMT pins not 8 pin DIP. I geuss I'll have to fudge it in...

[baum7154]

Thank you for the answer..will it just my opinion to draw more power because the aluminum box may consume a little power from the battery..im just a newbie in electronics and need much knowledge..

-------------------------

The only effect you will see from grounding the metal box is better performance because of the RF/EMI shielding it will provide.

Dan

[jladre]

Thank you Silver Dollar and baum7154 for the explanation..now im gonna ground it)

[Achillion]

Established a working MPP

Since this is my first post I believe it is appropriate to introduce myself briefly. My name is Jacob, I’m Dutch but now living in North Queensland, Australia. I’m interested in the electronics side of metal detecting and that’s how I ended up at this site. I’m member of the local metal detecting club and my aim is to build my own PI gold detector with performance that can compete with commercial detectors.

I just completed the Mini Pulse Plus and will use this design as the base platform trying to further develop and improve, which was the intention of the MPP project (all credits to Qiaozhi and others who initiated this project).

My approach is to focus on each of the building blocks individually and see if there opportunities for improvement. I read post of the many bright people here on this forum which helped me a lot. I hope I'm able to contribute also.

As a first step I focused on the search coil design and build the Oval Basket Weave coil with some slight modifications. Still experimenting with various other designs also. Along the way I crafted vacuum mold table to make a suitable housing. I’m able to detect a square cm aluminum (coke can) at about 0.5 inch with the basic MPP.

I used a 4mm PE base with 0.12mm2 26AWG PTFE insulated silver plated stranded occ copper. Instead of slots I drilled holes to maintain separation at the crossings. I’m not sure though if this is the optimal design to lower parasitic capacitance. Will post some photo’s once I know how to.

Cheers,
Jacob

[Achillion]

Pictures of basket weave oval coil and housing.

[multieagle]

Great looking coil. Must have been murder drawing upwards of a 100' of wire through each hole! Will follow to see how it reacts in actual use.

[baum7154]

You are very patient and persistent to have drilled all those holes and then threaded all that length through them! If I counted right it looks like you did about 30 turns on the form. The holes indeed help separation of the wires and should help keep capacitance lower. What voltage rating is the PTFE insulation of the wire? It will be interesting to see what the Self Resonant Frequency of this coil measures. Goooooood job!

Regards,

Dan

[multieagle]

Hi KRinAZ, from post #75; “I measured a 4' length of twisted # 22 Teflon wires with thinner insulation than yours. It measured 39pf on the capacitance meter. Good to know - think there's any coax that would be lower in capacitance?”


I use Blue Jeans LC-1 Audio Cable at 12.2 pF/ft, it gets close to matching twisted pairs. It is very durable and handles better than twisted wires. And it looks better. If you plan on making a number of coils it is cheaper to buy one long cable and cut to length as you use it. Just toss the two connectors that come already attached.


http://www.bluejeanscable.com/store/audio/

In process of putting together the oval basket weave coil. I have some surplus wire rolls, 175/46 (0.04 mm) Litz Wire, single layer nylon insulation, 0.90 mm diameter and 24AWG enamal insulated single core magnetic wire. I'm leaning toward the Litz. For this 8x10" design, what would be the estimated turns for approx. 300-325uH result?