Replies to Minipulse Plus

[josewashere]

Have you tried your woven coil? Been thinking of making one here but they just seem too hard to shield

[CAS]

Just finished my MMP and found it a pretty straight forward build. Instructions are easy to follow and the quality of the board from Silverdog is good. Its only an experimental board so I am not going to put it all in a case but I think it would definitely benefit from sheilding. In my workshop there is lots of RF interference from fluros, lots of SMPS and various other instruments so there was quite a bit of noise on most of the test points. I am also using an unsheilded, 345uH relatively high capacitance coil and running the board from a 12v 10A power supply which doesnt help. Even so, I am pretty impressed with the air tests. With a small 3mm bolt I get about 10cm.

[Qiaozhi]

Just finished my MMP and found it a pretty straight forward build. Instructions are easy to follow and the quality of the board from Silverdog is good. Its only an experimental board so I am not going to put it all in a case but I think it would definitely benefit from sheilding. In my workshop there is lots of RF interference from fluros, lots of SMPS and various other instruments so there was quite a bit of noise on most of the test points. I am also using an unsheilded, 345uH relatively high capacitance coil and running the board from a 12v 10A power supply which doesnt help. Even so, I am pretty impressed with the air tests. With a small 3mm bolt I get about 10cm.

Even though you're using the MPP as an experimental board, and do not intend to put it in a case, please email me some photos of the completed PCB. It doesn't matter if it looks like a rat's nest. I will then add this info to the Completed Projects thread. I'm certain there are many other completed MPP boards out there, but either everyone is being shy at wanting to display their work, or they think the detector needs to be in a nice shiny box and mounted on a stem. What it looks like is not important.

[Davor]

Have you tried your woven coil? Been thinking of making one here but they just seem too hard to shield

Not yet. Most probably on Monday. I populated the most of the board, but something else came up.
The idea of a "spider basket" coil is to wind the hot end of a coil inside, and wind around and around towards the cold end and in effect the hot end becomes encapsulated in increasingly "colder" windings. That way the static-prone end becomes shielded in the very coil it is made of. Of course, I have no idea if it really works, and I made mine free-style, which means it is ugly-ish. It will serve its testing purpose.

[Silver Dollar]

I just ordered a PCB. Here's my BasketWeave Coil. It measures 320uh and 1.5 ohms.
I'm hopeing it shields itself via the outer windings. I just drilled alternating holes approx.
the size of 6 or 8 wires. If you look close I had to add an extra row as the wires take
more space when wound. I don't have a working PI to try it on yet but soon.

[Davor]

@Qiaozhi, I may suggest a small improvement for a future release of the board. I placed a MUR460 diode in series with R3 resistor (my choice, not a suggestion), but it turned a bit of a struggle, as the diode's pins are very thick. I had to grind one pin so that it may enter a hole. Having larger holes there could be beneficial, as R3 has thick-ish pins as well.

I also have a suggestion to clarify a small detail regarding a damping procedure. Resistor R12 (1k) is in parallel with the damping resistor R1 if monocoil is used, and it is a part of a negative feedback circuit of an op amp. Therefore, when adjusting a damping resistor, one must have U5 (NE5532) running, or otherwise R12 is not going to show its 1k resistance at small amplitudes. Perhaps it would be a good idea to split this resistor in two 510ohm in series to avoid arcing, or at least give it a bit more room, as most obviously many will go for higher voltages and faster coils, and this resistor will be forced to take the most damping load on itself.

[Davor]

Here's my BasketWeave Coil.

Yours is much better looking than mine

[Qiaozhi]

Resistor R12 (1k) is in parallel with the damping resistor R1 if monocoil is used, and it is a part of a negative feedback circuit of an op amp. Therefore, when adjusting a damping resistor, one must have U5 (NE5532) running, or otherwise R12 is not going to show its 1k resistance at small amplitudes.

That's correct. You should always make the damping resistor adjustment with the coil connected to the detector, and with the preamp running.

[josewashere]

That's a great looking coil and looks like it could be shielded if needed by wrapping some spacer material and applying a shield over that.
It could well be ok as it is given that even just twisting two wires together creates a shielding effect.

[CAS]

I just ordered a PCB. Here's my BasketWeave Coil. It measures 320uh and 1.5 ohms.
I'm hopeing it shields itself via the outer windings. I just drilled alternating holes approx.
the size of 6 or 8 wires. If you look close I had to add an extra row as the wires take
more space when wound. I don't have a working PI to try it on yet but soon.

[ATTACH]30887[/ATTACH]

What diameter did you make that coil and approx how many turns of wire? Any idea on what capacitance it turned out to be?

[Silver Dollar]

the diameter is 7.5" or 19cm. How do you measure the capacitance?

[Silver Dollar]

Ahh I see you need to find the resonant frequency and then
back calculate the capacitance. I don't have anything to do
that with at this time. Once I get a PI detector running I can
pulse the coil and see what frequency it rings at.

[Davor]

GB circuit works!

GB circuit works! I made it on a protoboard together with a 555 generator to mimic real world timing, and I only skipped trimmers to avoid clutter - fixed values are OK for the proof-of-concept. Anyway, the timing works as it should. The next step is to place the components onto a perfboard and hook it to its proper places.
The attached files are as follows:

1. the corrected schematic using simple NAND CD4011 instead of a slightly unpredictable CD4093, and taking control over Schmitt trigger by means of simple resistors
2. CRO photo of a same thing in jpg format - obviously working as advertised
3. same thing, only as a zipped LTspice folder

[Qiaozhi]

GB circuit works!

Do you have this connected to a Minipulse Plus, or is it just standalone at the moment?

[Davor]

It is completely disassembled at this moment. I'll put everything on a perfboard one of these days, but first I'll have to make a MPP work without it. It is populated (Ivconic style, but with IC sockets) and I have a coil, so it will be soon.