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Offline Cornelius
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« Reply #30 on: January 07, 2010, 05:56:19 pm »
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Al , it could be two wires which are shielded  . If you have two wires individually shielded  , that should work too . Don't worry about this  . Remember that there are two wires going to ( and from ) the coil  . These wires should be shielded  ( with the shield going to ground ) . Wether both wires are shielded  individually is of no importance  .  Cornelius

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Offline alimanTopic starter
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« Reply #31 on: January 07, 2010, 10:33:49 pm »
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Thanks again Cornelius !
Another question, how many ohms approx. should the completed 200mm x 20 turns of 26 gauge wire coil, read?

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« Reply #32 on: January 07, 2010, 11:01:06 pm »
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Quote:Posted by aliman
Thanks again Cornelius !
Another question, how many ohms approx. should the completed 200mm x 20 turns of 26 gauge wire coil, read?


Resistance makes no difference at all. Impedance is what counts. Wrap as per directions and don't fret over the resistance.

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« Reply #33 on: January 07, 2010, 11:40:35 pm »
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Hi Cornelius, I've a question to ask you...Would a basic tech/trade school course in electronics be enough schooling in electronics to enable a person to build metal detectors? Or would a person need to be an electronics engineering grad to know his/her stuff well enough to design and build VLF or other type units?  I'm interested in building a VLF or TR unit with good depth and a good discriminator...maybe an ID meter.

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Offline GoldDigger1950
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« Reply #34 on: January 07, 2010, 11:52:16 pm »
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Quote:Posted by treasuremomo
Hi Cornelius, I've a question to ask you...Would a basic tech/trade school course in electronics be enough schooling in electronics to enable a person to build metal detectors? Or would a person need to be an electronics engineering grad to know his/her stuff well enough to design and build VLF or other type units?  I'm interested in building a VLF or TR unit with good depth and a good discriminator...maybe an ID meter.


If you can solder, read and understand a schematic, you can build a metal detector.

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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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Offline alimanTopic starter
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« Reply #35 on: January 08, 2010, 07:52:10 am »
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Impedance!, that's right.
Thanks  again

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« Reply #36 on: January 08, 2010, 08:30:19 am »
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Here is some coil info to give you some Idea's!

Common pulse induction search coils with their physical properties Size Shape Turns Wire size Inductance Resistance

SIZE                     TURNS        WIRE SIZE                INDUCT    RESISTANCE

? 120 mm Round      36 ?     0.40 mm / 0.14 mm2     405 ?H     1.9 Ohm
? 150 mm Round      31 ?     0.40 mm / 0.14 mm2     394 ?H     2.0 Ohm
? 175 mm Round      28 ?     0.40 mm / 0.14 mm2     387 ?H     2.1 Ohm
? 200 mm Round      26 ?     0.40 mm / 0.14 mm2     406 ?H     2.2 Ohm
? 250 mm Round      22 ?     0.40 mm / 0.14 mm2     380 ?H     2.3 Ohm
? 300 mm Round      20 ?     0.50 mm / 0.20 mm2     390 ?H     1.6 Ohm
? 400 mm Round      17 ?     0.50 mm / 0.20 mm2     396 ?H     1.8 Ohm
? 500 mm Round      15 ?     0.50 mm / 0.20 mm2     400 ?H     2.0 Ohm
1.0 x 1.0 m Square    10 ?     0.66 mm / 0.34 mm2     406 ?H     2.0 Ohm
1.4 x 1.4 m Square      8 ?     0.66 mm / 0.34 mm2     387 ?H     2.2 Ohm
1.8 x 1.8 m Square      7 ?     0.80 mm / 0.50 mm2     398 ?H     1.7 Ohm


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Offline alimanTopic starter
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« Reply #37 on: January 11, 2010, 04:20:07 pm »
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YAHOO its here ! Thanks so much Cornelius, the Sandbanks metal detector arrived today. I can't wait to get it up and running. For the power supply could I use two 7.2 v NiCad battery packs instead of the two 9 v batteries ? I also have a small 12v lead acid battery of 9.5 A/h capacity, much heavier though. i've included pic of the batteies.

Aliman

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Offline Cornelius
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« Reply #38 on: January 11, 2010, 04:26:40 pm »
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Ali , that was fast .  Use the two 12V batteries for the besr result .Be careful with the polarities though !!!!!!!! . Have fun with the detector  . Do not consider this a toy , it is NOT .     Cornelius

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« Reply #39 on: January 11, 2010, 04:45:36 pm »
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So, should I use the 12v lead acid battery, not the two 7.2v in series ?

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