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Offline GoldDigger1950
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« Reply #170 on: January 30, 2011, 04:34:58 pm »
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Quote:Posted by ppodg
OK.
Let's start it all over again.
Our friend has found the photo with all necessary data, probably this one: coil_cpi2.jpg
and wants to know the wire length!!!
Diameter - no problem, but everyone ought to remember p=2*pi*r = 2*pi*d where pi=3,14...
This is a somehow unusual detector and some 'engineering' knowledge is usefull.

I don't agree with you about the coil parameters. For the detector itself both inductance and resistance are important, because of the coil time constant (TC=L/R). For the owner diameter is importan, because of the range (inversely proportional to small target sensitivity). However for this specific detector ALL THESE PARAMETES CAN BE VERY IMPORANT. Just learn how it works Smiley .

No, you are incorrect. The overall inductance is important but the single most important value in a coil design is the inductance. Without it, you do not have proper oscillation or even none at all. This is what he has. No oscillation. It doesn't work. The reason? He is focusing on the coil resistance. The COIL resistance has more to do with the amount of power needed to energize it to maximum field strength. The resistance of the circuit in terms of the snubber resistor on the FET (or other solid state switch) will determine the decay time. The COIL RESISTANCE has absolutely nothing to do with discharge timing.

On the one hand, you declare that you disagree about coil parameters and then go on to describe overall circuit parameters. Focus on the issue at hand please. The coil resistance remains irrelevant to the design for frequency and operating purposes. For field size and strength, it may require a circuit redesign in order to function in an existing detector.

I have been in the electronics engineering field for more than 40 years with lots and lots of experience in designing metal detectors. I have answered hundreds of these kinds of questions and taught some very keen people the realities of coil design. You do not have any obligation to become one of them.

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« Last Edit: January 30, 2011, 04:39:10 pm by GoldDigger1950 »
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« Reply #171 on: January 30, 2011, 07:23:57 pm »
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You are wrong again Smiley

1. PI detectors do not oscillate, almost all will generate all timings without a coil - the real system timer or 'oscillator' does not depend on the coil.
2. The Pi coil oscillates only if underdumped (too high dumper resistance), this is a faulty behavior.
3. Both inductance and resistance do have influence on the 'fet on' time in some detectors like sd series (and my own projects/prototypes), because in some models the moment of fet switching off depends on the coil current threshold. When the coil peak coil current in a ww2 deep relic seeker achieves 5..10A the resistance becomes really critical.
4. Try to use an sd-family member with a high-resistant (10ohm or more) coil and compare the result to other popular PIs - cs6, impulse, sandshark or even goldquest for example - witch the came coil, of course.  Grin
5. You are Right, "The COIL resistance has more to do with the amount of power needed to energize it to maximum field strength. The resistance of the circuit in terms of the snubber resistor on the FET (or other solid state switch) will determine the decay time. The COIL RESISTANCE has absolutely nothing to do with discharge timing."
- Of course if you mean flashback discharge. It can have a little to do with the slow dvt-like multi-step discharge...

6. What is the title of our thread? "Focus on the issue at hand please." Smiley We are talking about the particular coil for the particular PI! Just have a look at at the coil charging/discharging processes in this detector and read about them in Candy's 6653838 patent (in my private opinion both construction and timings of 'chance' are far from being optimal, though it successfully incorporates dvt-like technology - just like gpx does; btw, how about high-res coils in gpx? Devil).

7. I have been in the electronics engineering field for more than 30 years with lots and lots of experience in designing scientific instrumentation. I hardly ever discuss on md fora although I know some really smart pi designers. "You do not have any obligation to become one of them."  Devil

Regards,
ppodg

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« Last Edit: January 30, 2011, 08:08:36 pm by ppodg »
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Offline GoldDigger1950
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« Reply #172 on: January 30, 2011, 11:00:39 pm »
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Quote:Posted by ppodg
You are wrong again Smiley

You are still discussing oranges when the topic is apples.

But do press on. You have to work very hard to be right so I pronounce you right. Feel better now?

Now back to my original comment to you. I was asking you very politely to give more details regarding the coil question. Your reply was adequate but not at all complete nor correct. I was hoping you'd do the right thing and come back with a formula and a tiny bit of explanation about why you derived what you did. Instead, you don't try to shoe the horse, you bring a stampede of cows.

How about looking around here a bit before you leap on me with both boots and miss like you did. The people on this forum are a mix of skill levels and do not understand what we are discussing. There are people in this thread asking questions who have only built model cars as kits before taking on a metal detector. Then you have people who are technicians in other areas. Very few have the skills to design a working coil but the good guys here try their best to teach rather than simply give up an answer. Worse yet, one this dubious.

Posted on: January 31, 2011, 06:48:19 AM
Quote:Posted by ppodg
What is the title of our thread? "Focus on the issue at hand please." Smiley We are talking about the particular coil for the particular PI!

Oh, really? Which one? You're being silly now. Stop it. You're making me laugh.

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« Reply #173 on: January 31, 2011, 09:42:23 am »
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Quote:Posted by ppodg

 in Candy's 6653838 patent (in my private opinion both construction and timings of 'chance' are far from being optimal, though it successfully incorporates dvt-like technology - just like gpx does; btw, how about high-res coils in gpx? Devil).



Hi ppodg,

can you explain from where you got info that the author of "Chance" attempt to integrate  DVT technology in his PI detector?
I can only find forums claim that the author has built in "Chance" (software emulation of) MPS technology, which is something different from DVT and published in other patent: 5,537,041.

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« Last Edit: January 31, 2011, 09:53:58 am by WM6 »
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« Reply #174 on: January 31, 2011, 12:31:24 pm »
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To Mr GoldDigger1950:
In point 6. just change 'thread' to 'topic' and look out - this topic can be dangerous - Russian red bears, Bulgarian umbrellas, Greek crisis, English bowlers and some other European freaks - including me!  Cheesy

And seriously - in my opinion newbies should start with well known analog devices. To play with this very experimental project some basic knowledge (and some Russian language) seems necessary; this is not a kit; I'd call it an educational toy for desgners. Its usefullness is restricted and this is why I strongly discourage the beginners from building this detector. Perhaps it would be a funny toy for You becouse of Your experience and knowledge of electronics, coils and Oz ground. On the other hand - who knows, perhaps children would have a lot of fun with it - paricularly in legendary Australian ground?

To Mr WM6:
1. have a look at the schematic - the power part is exactly like 6653838. Btw, the coil seems horribly overdamped - with a low c coil 0k8..1kohm should be enough.
2. now have a look at the work cycle...
   a. q9 off, q3 on for ca 50us, then multiple (3x as I remember) a/d convertion - a normal pi sequence
   b. q9 on for ca 200us and simultaneously a train of short q3 on pulses with slow discharges but no flashbacks (q3&d4 short-circuit the coil)! The current slope looks like powered from a much smaller voltage (with some ripple)! To get a final flashback the q9 must go off before the q3 - and then a/ds like previously - all described in the 6653838 - see fig8.

Regards,
ppodg


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« Last Edit: February 01, 2011, 06:08:51 am by GoldDigger1950 »
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« Reply #175 on: January 31, 2011, 03:51:20 pm »
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your discussion is beyond my hands .......
anyone know the ideal thickness for the metra-carat coil (3mm, 4mm, 5mm?)

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« Reply #176 on: January 31, 2011, 06:23:53 pm »
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Quote:Posted by ppodg

And seriously - in my opinion newbies should start with well known analog devices. To play with this very experimental project some basic knowledge (and some Russian language) seems necessary; this is not a kit; I'd call it an educational toy for desgners. Its usefullness is restricted and this is why I strongly discourage the beginners from building this detector. Perhaps it would be a funny toy for You becouse of Your experience and knowledge of electronics, coils and Oz ground. On the other hand - who knows, perhaps children would have a lot of fun with it - paricularly in legendary Australian ground?

To Mr WM6:
1. have a look at the schematic - the power part is exactly like 6653838. Btw, the coil seems horribly overdamped - with a low c coil 0k8..1kohm should be enough.
2. now have a look at the work cycle...
   a. q9 off, q3 on for ca 50us, then multiple (3x as I remember) a/d convertion - a normal pi sequence
   b. q9 on for ca 200us and simultaneously a train of short q3 on pulses with slow discharges but no flashbacks (q3&d4 short-circuit the coil)! The current slope looks like powered from a much smaller voltage (with some ripple)! To get a final flashback the q9 must go off before the q3 - and then a/ds like previously - all described in the 6653838 - see fig8.



Very interesting and deep in matter opinion, thank you.

I do not understand this (probably of my limited English):

"The current slope looks like powered from a much smaller voltage (with some ripple)! "

Which current slope?

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« Reply #177 on: January 31, 2011, 06:32:08 pm »
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 the coil current slope  Smiley

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« Reply #178 on: January 31, 2011, 07:03:40 pm »
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Quote:Posted by PPODG
And seriously - in my opinion newbies should start with well known analog devices. To play with this very experimental project some basic knowledge (and some Russian language) seems necessary; this is not a kit; I'd call it an educational toy for desgners. Its usefullness is restricted and this is why I strongly discourage the beginners from building this detector.


Well.... I guess that one was also aimed at me as I was too lazy to do the wire length calcs. Embarrassed  Will never hear the end of this one.... As far as newbies building this detector, I agree it is not for the novice. Not an an engineer here but a good bit of experience. (44 years in electronics). I'll tackle any project DC to daylight. Haven't done much assembler since the 6502 but the Atmega8 looks fairly simple. Main issue I see on this one is I can't read Russian and the translation web pages leave a bit to be desired.   


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« Reply #179 on: January 31, 2011, 07:54:38 pm »
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 Wink

Several version of hex are obtainable, some fellow even sells PCBs, but my recommendation is:
1. get at least the newest hex
2. simulate it or just load to the mega8 and force to run
3. get all signals to a scope
4. try to write your own timing
6. well... try to write your own analysis... based on Candy's patent work...

and meanwhile go to a better uc Smiley ie simply create your own detector!  Great

I've never built this detector (nor going to build), but its general conception is very interesting - only few plain electronic parts and the advanced pulsing&analysis. What is more, the physical device can be even simplified.

Regards,
ppodg

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