build my own PI detector

		Quote:			Posted by Peti80
	Hi Guys, i've started to build my PI detector, but the problem is, that i have a ringing on the back EMF pulse, no matter how i damp the coil. It keeps sitting superponed on the decaying pulse. It's amplitude is about 10% of the pulse and about 10 times the frequency, and decaying as the pulse amplitude decays. Unfortunately i don't know how to post pics -i guess i'm not allowed yet-, so i cannot show it. It is a MOSFET driven coil, 11" diameter, 22turns, made of 26AWG regular wire, mined from an ethernet cable. Do you have any ideas how to get rid of it? Its getting smaller as the microseconds pass, but it's not doing good to the following amplifier stage..

Go out and get yourself some magnet wire. Wire inside an ethernet cable won't be insulated with varnish. Your problem is coming from incorrect impedance because your coil is essential one loop of 4 gauge wire. Each loop of the wire is shorting out against the adjacent loop. Varnished wire is needed for winding coils.

If you can't buy magnet wire where you live, find an old, broken down TV set and remove a transformer from the power supply section. De-wind that for your magnet wire. Also, look at the big copper coil around the throat of the picture tube or from the tube on a CRT monitor. They're often the right gauge or near enough to calculate a new coil winding scheme. Just avoid using bare wire as it simply will not work. Even if you left the insulation on, the windings are too far apart to give you the correct impedance.

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		Quote:			Posted by Peti80
	Thanks, it's a good idea! I have an old coil made of magnet wire, i'll try that. The coil is not shorted, it has the insulation on, so maybe that is too thick. I was hoping for a lower capacitance by having the turns more separated by the thick insu.

Actually, the increased distance will increase the capacitance up to a limit. Remember, your insulation is double thickness between the windings since each wire has insulation all around it. Find an old TV set and strip the wire you need from it.

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Both the Gary and the Hammer Head is a kick butt starter platform.

The Hammer Head has morphed into a PIC thing.  No Board available.

Gary offerse a Kit for some thing like $70. USD.

The Boards for the Hammer Head are no longer availible .

I don't do Comuter crap.

I just sent my money to SilverDog for the PI Board+ parts.

It works for sure and is the basic clone of the Surf PI detector.

Board,  Board Parts, for just $50.00 ..........

Can't go wrong on that one.





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Hi,

You might try the Hammerhead also.  Check it out at the Geotech forums.  Periodically, someone buys more pc boards and has them for sale for those who don't want to build their own board.

Reg

Posted on: January 08, 2011, 10:09:23 AM

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Hi,



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