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Offline GoldDigger1950Topic starter
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« on: October 15, 2010, 08:05:27 pm »
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Go to the top right corner of this page. See the search bar? Type in the word "schematics" without the quotation marks. Select "Entire Forum" from the pull down menu. Press search.

8 pages of 35 results per page are returned. Each of those results may have hundreds of replies to this question. Get busy helping yourself a little bit and reading.

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It's all about that moment when metal that hasn't seen the light of day for generations frees itself from the soil and presents itself to me.
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« Reply #1 on: February 02, 2011, 12:21:20 pm »
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Also google "metal detector schematics" , "metal detector design", or "metal detector build".
 Cool


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Offline DOOLEY1972
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« Reply #2 on: March 28, 2011, 05:53:39 am »
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hello, i'm a new member and came here looking for answers,don't know if anyone has all the answers,but was hoping collective minds would get pretty close.
my forte / hobby is electronics,and my aim has always been to take an idea, or start from scratch (harder) and try to perfect it as far as possible,dont like the job to be done "HALF ASSED" , my mind is now fixated on metal detectors and have been searching google for circuits of all types of detector, its a mine field out there, pardon the pun, going over the same old junk. when "reading" some schematics posted i think some could be posted for a laugh or to mislead,designs which make no sense,wrong values on components ,and some so obvious they will never work at all.
i have an old ?30 detector from radio shack, had it for years,good for finding pipes but thats it,went through a stage of being out every weekend with it,it was so poor i gave up,as i think most people do.
give em a decent detector,they will be hooked for life,like fishing as a kid,catch nothing,give up,catch fish,fish for life.
so i'm on the look out for as many circuits as possible.
at the moment i'm thinking PI  is the way i want to go,better depth / penitration, but lack of any real discrimination,of poss vlf, but using a higher power level.
oh well, thats my 2 peneth worth,ON WITH THE HUNT !

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« Reply #3 on: March 28, 2011, 09:03:38 am »
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Dooly, now that you have your five post, look in the down load Section.

We try to have enough info to do a build.  Start to finish.

Eugene has posted a number of complete ideas.

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Offline xavier
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« Reply #4 on: March 28, 2011, 10:46:58 am »
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Hi Dooly

I did the same thing as you looked on the net and found a lot of rubbish then there were some that looked like they could work but found out that they worked poorly from other members that had build them. One day the DBP2010 was posted on the forum I decided to go with it as there were members that had build it and that I would be able to get the assistance needed should things go wrong and boy did they ever go wrong any how to cut a long story short I have been busy with this detector for well over a year but now I have a machine that works and if I may say so myself I think that it works rather well. I take great pleasure in making commercial detectors look stupid with this PI and if there is someone too close by with a VLF well it goes nuts LOL ho I guess that I must tell you that I have made quite a few changes to it like a 280mm coil instead of a 1m x 1m coil change the frequency form 90hz to 400hz did some changes to the PCB too. 

All the best
Xavier


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So many questions so little time

Offline DOOLEY1972
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« Reply #5 on: March 29, 2011, 09:34:22 am »
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my old saying is that "everything can be,and should be modified" even manifacturers don't get everything spot on,quite often i rekon they get it "near enough to do the job".
Xavier, 400hz, sounds interesting , more samples per second , but higher power useage , thinking of a couple of lead gell's on waist band to last a day.
doesn't leave allot of time in between pulses to get a sample , everything will have to timed spot on , tempting thought,
bet that's about the limit of hz with a PI , good on ya' push things to the limit !



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Offline xavier
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« Reply #6 on: March 29, 2011, 09:45:14 am »
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Hi DOOLEY1972

I actually get three days out of it (I don't detect for more than three to four hours) consumption is around 200mA and the battery that I use is a 2.6Ah 12V I incorporated a pin pointer on it not much depth with it but a good 100mm on a small coin but better if the coin is in an upright position. Now I?m trying to find a way to get different audio signals for different metals (scratching my head) LOL

Regards Xavier


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So many questions so little time

Offline DOOLEY1972
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« Reply #7 on: March 29, 2011, 02:00:57 pm »
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iv'e just been doing some calculation on the micro second scale,
most of the pi circuits out there pulse the coil for 165 u/s
wait / delay for 30 to 50 u / s
then sample for 50 u / s
total 265 u / s
now even if we allow say an extra 200 u / s for the coil decay / settling down,
this means a theoretical maximum of 2200 hz possible,
when you said about 400 hz when most are 100 hz , i thought this fellow is pushing the limits, and thats a good thing,
so the question is, how long would a coil need to settle down ?? if 200 u / s is long enough then 2200 hz is possible,
100 hz allows 4400 u / s to settle down,
your 400 hz allows 1100 u / s to settle down,
so the thing is , would we need the coil to settle down , i mean , as soon as the sample has been taken , then it could be pulsed again , which would allow a freq of about 4000hz  would be possible,
coil capacitance would have to be as low as possible,
have attatched graph i found, looks a bit crude, but after some study and though , waiting seems pointless.
any thoughts ??

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Offline GoldDigger1950Topic starter
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« Reply #8 on: March 29, 2011, 02:23:53 pm »
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For PI, the pulse is transmitted followed by a delay. The internal resistance of the coil and the resistor on the control board determine the field collapse time. The transmitter required enough power be generated to overcome those resistances and give you a usable field. Then, to collapse the field, the resistance is paramount. Like any load, the lower the resistance, the faster the collapse. The receiver then detects the signal left behind by the metal in the target area. Your PI transmitter electromagnetic field energizes metal inside of the field which causes current flow inside of ferrite targets or on the surface of non ferrite targets.

In a ferrite target, the orientation of the field induced is linear, from north to south, and the receiver sees it as a polarized transmitter. Non ferrite targets build up a field on the surface of the object that generates eddy currents of magnetic fields in tiny circular patterns. This field is a bit weaker than in ferrite targets and is non polarized or multi-polarized. That last factor depends on the shape of the article and the size. In a PI machine, a chunky, bumpy silver ring can be missed because of this.

Doing calculations is fine but empirical measurements on actual equipment will tell you more. In your case, you didn't take the internal resistance into account and measurements with a scope would have had you scratching your head for a while until it occurred to you. Asking questions here is the best way to get an understanding of the inner workings.

Elsewhere on this forum, I have defined a small probe you can build for next to nothing. Used with a PC sound card and some free software, you can actually map a transmitters field, see the signals in real time on your PC and watch what happens when you put metal inside the field. It's a fascinating way to get an understanding of how a detector works.

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It's all about that moment when metal that hasn't seen the light of day for generations frees itself from the soil and presents itself to me.
Let's Talk Treasure!

Offline DOOLEY1972
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« Reply #9 on: March 31, 2011, 09:33:53 am »
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here is one of those genius / nutter idea's iv'e just had,
we take a sample on the field colapse downward slope , normal ,
wonder if it would be possible to take a sample on the power up slope ??
if a metal object in the field slows down the colapsing field , then it will also slow down the field when it is being
built up , which can be measured , would be looking for a "low" on the build up side and a "high" on the colapse side.
now at the moment we can not have real descrimination on a pi,
well we are only measuring one field , either north or south , depending which way coil was wound,
if we measure the up side , then we have both ,
now , ferrous and non ferrous metals behave diferantly in an oscillating field yes ?? hence discrimination being possible with vlf,
well if we have both up and down measurement in a pi then would it not be possible to compare and somehow get discrimination from this ??
hope this made sense, only a thought.

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