Pinpointer with tone discrimination Metaldetector

		Quote:			Posted by cool2010
	nice idea yes yes Ufos and aliens.. i think nasa will invite you for drink tea or coffee..

One lump or two? 

Dusty Carl

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A bad day at gold prospecting or metal detecting is better than a good day at work.

  man in blacks 

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for wortex one...

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		Quote:			Posted by cool2010
	for wortex

That is a similar coil, but not a pi-wound.. Thanks for sharing.

Dusty Carl

Posted on: April 27, 2015, 12:15:31 pm

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Done bench testing. Frequency is relatively stable, but with extreme changes not good, but seldom does external temps change 20°F in a few minutes. Here are my thoughts so far:
This is a pinpointer, so metal type feature is superfluous. We are using an expensive metal detector with discrimination on it to find the target first, so it is not necessary. A pinpointer's purpose is to find in a hole that you have already dug and determined in advance what you feel is a valuable target. Only one case where it might be used that i know of. A bottle cap and a coin in the same hole. But then again,  you should  always check a dug hole again for other targets.
This project originally started out to be a pinpointer for kids on the Russian site. It looks like the'Tim Àllen' syndrome took over from there. If he had kept going, it might have had ground balance, auto GEB, threshold and volume. He has employed ADC algorithms, lookup tables, and all sorts of things to the software to do a simple job which is to determine a sudden frequency change. Overkill at the best. What happened to the addage "KISS" (keep it simple stupid)?

Dusty Carl

Another thing on the pinpointer. Seems to be more stable when the no target frequency is close to 20 Khz. Itrimmed mine with an appropriate capacitor.


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A bad day at gold prospecting or metal detecting is better than a good day at work.

Homie,
The two cross coupled PNP transistors plus the coil and the capacitor form an oscillator whose frequency is determined by the inductance and capacitance of the combination. The oscillator frequency gets pulled up or down depending on the type of metal brought close to the coil. Sorry about the long explanation, but I think I covered everything. The crystal is used to run the controller internally.

Dusty Carl

Posted on: April 27, 2015, 04:10:27 pm

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		Quote:			Posted by golddustcarl
	Ok, back to business. I have a question. Does anyone know how to wind a coil like the one in the attachment? They were used back in the old 'radio' days and sometimes used Litz wire for the windings, or some like the one in the pix. Ham operators might recognize them. Dusty Carl

More info: This is called a PI-wound coil. Some trucker hams called it a "PIE" coil because it had several sections stacked up which looked like a stack of pies in a case on the counter of their favorite truck stop.  It's features are low interwinding capacitance and medium inductance and was commonly used as an RF choke in the bias circuit of a transmitter's final. Lots of times it had it's own little shielded box in the transmitter. Had to be careful with resistance being to high and not being self-resonant at any frequencies being transmitted by the transmitter or else it would smoke. If there was a core, the DC current in the coil would magnetize the core and lower the inductance which might make it resonant in the transmit band and explode.
All in all I would like to know if someone knows how to wind it. I have searched the internet, found a few venders, some photos of them but no DIY info.
Dusty Carl[/size]

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A bad day at gold prospecting or metal detecting is better than a good day at work.