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http://www.thunting.com/smf/index.php/topic,18582.msg120908.html#msg120908

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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http://www.thunting.com/smf/index.php/topic,18582.msg157645.html#msg157645

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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http://www.thunting.com/smf/index.php/topic,18582.msg157725.html#msg157725

Xavier

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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http://www.thunting.com/smf/index.php/topic,18582.msg158093.html#msg158093

Xavier

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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http://www.thunting.com/smf/index.php/topic,18582.msg158202.html#msg158202