Another P.I. link

		Quote:			Posted by DOOLEY1972
	cheers GD , so , it's not overpowering / saturation of the ground i'm facing , it's flexing / movement of my bundle coil caused by heat , i'm using pvc insulated wire , which poss allows more movement than enameled copper wire as well , so , rewinding of coil required and then poss set in resin or something like is required , all makes sense now , as any coil to coil movement can give a false signal , decent coil required then , followed by turning the power back up , cheers GD ,  Smiley Smiley Smiley

You're limited by physics as to the depth of penetration, mate. Your signal is an audio frequency electromagnetic wave, not one of sound pressure like SONAR. Because it is electromagnetic, the minerals in the soil (ALL soil is mineralized to some degree), moisture or lack of moisture, granularity, size of the granules, composition of the soil granules and plant/animal presence all affect the range your signal can penetrate and subsequently be "seen" by the receiver. In fact, your penetration signal is normally twice what you would expect based on the depth of targets you see.

The reason for that is mostly the receiver sensitivity and not the transmitter power. Also, in order for your receiver to do its best work, the transmitter must have been silent for a short time so that the field from the transmit pulse doesn't overdrive or swamp the receiver. That waiting time is the pulse width that we discuss here when we talk about the PI detector. After the TX pulse goes out into the ground, a short period of waiting happens before the receiver is turned on and working. Your TX pulse induces eddy currents into metal objects. Ferrous objects have those currents internal to the item because they are magnetic and the fields enter the object. Non-ferrous items have those currents on the surface of the item because there are no internal lines of flux to set up.

In either case, those signals are very tiny and your receiver coil plays the biggest role in sensing the residual eddy currents. Those currents don't last very long at all so the timing of the receiver is also critical.

As you can see, physics is the limiting factor and not the transmitter power or the soil itself.

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Hi all
been distracted
good work on your MD Dooley
be back soon

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hello 6666,

was thinking this thread had died,

not allot to report since last post,

i'm now dual channel , dual tone with my red green led's also ,

results are ok ish , now back to having a stable machine by reducing gain by using a 47K pot again ,

she goes high note / green on gold , silver , nickle and unfortunatley ring pulls ,
she goes low note / red on steel , iron ,"normal alu"

unfortunate thing is copper coins , when flat = low note red led,
 but when on edge = high note green led,

and very corroded iron for some reason is also high,

so i sort of have discrim , but not how i intended it , i'm digging all high note green led's now and it is resulting in nickle coins , lead roof strips , ringpulls and degraded iron ,

but did find last week 3 pieces of what looks to be silver chunks about 1-2 grams each , and by weight / size not alu or lead , tested with soldering iron and didn't melt , does silver oucur naturaly in the ground ??

also , is there something special about ring pulls , they result in a high responce whereas my alu test piece is a low , but then there are many grades of alu arn't they.

have intended to do a full schematic with what i have ended up with , but think we were sort of there with your previous posts ,

is the modified one worth building , not sure , it is better than single channel , but , not sure if it's worth doing , i'm going to continue using though ,

don't think PI discrim will ever match an IB with notch on discrim , but then IB not as good at the depth ,
 so you takes your choice.  

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		Quote:			Posted by 6666
	Hi Xavier just wondering what you used to draw the pcb for this project ? thanks 6666

Hi there 6666

I use DesignSpark it's a free program that you can download fully functional and NO limitations what's so ever.

All the best
Xavier

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Xavier

Hi Robc
well thanks for the heads up that the cct works ok
what coil did you use ?

interesting about your new doggy friend
6666

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