Discriminating BFO detector

Technos . You are wrong . There is a discriminating BFO detector . I sent the schematic to Darkkitten and Xavier  . They may give you the right schematics if they feel llike it .   Cornelius

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		Quote:			Posted by darkkitten2000
	Hi, this is a lovely circuit able to discriminate ferrous and diamagnetic materials - coins and nails or other small ferous particles (unless the ferrous forms a loop, obviously, but that is usually not problematic) fairly well, it will find small coins (i.e. 1 EUR cent) up to few cm (one or two), larger ones up to some 8 cm and very large targets down to some 20cm. Fairly good for such a simple circuit. The "ground effect" forces the user to hold the coil at same hight over ground, this takes some practice. For a simple circuit, it would hardly do it any better. I am building now an ETI 561 BFO, just to compare. regards, d.

I down loaded that schematic a while back.

Looking forward to your project.

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hi
can you give any information about its penetration depth

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Posted by GoldDigger1950 in March 30, 2010:

"Modern design uses de-tuned phase locked loops and comparators to accomplish the stability and keep the circuitry tuned properly while also allowing full tone discrimination."

GoldDigger, You're right. The author of this project, R. C. V. Macario, B. Sc., Ph. D., M.I.I.E., University College of Swansea has done this PLL before upgrading his article to be printed in the magazine WIRELESS WORLD, Yuly 1978.
The title of article is "Discriminative metal detector. A sensitive instrument which can differentiate between ferrous and non-ferrous metals by measuring a phase change". He uses for PLL an IC type CD4046.
Cornelius sent in this topic "Discriminating BFO detector",  two different  pcb designs. I give them below side by side for comparison. The left figure is sent by him on November 09, 2009, and the right one - on December 13, 2009. Note that they have the same number 909003-1-4.
As I stated in my previous posting, this project is improved by its author. The attached figure shows the improvement described in above mentioned article. With this improvement Macario creates the first "Motion BFO detector", in which the operator does not need to adjust frequently the reference oscillator; enough is just to press the S1 key for fast settling.

Cornelius, please dig your archives with information and found the circuit diagram and parts list valid for the left pcb. It uses PLL IC CD4046 in shown position instead conventional reference oscillator. Wait so eagerly that information from you!

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Hi Junote,
The reply # 76 relates to reference oscillator in this project, however this part is not important for sensitivity and discrimination. Search oscillator (SO) is the most important part of a discriminating regenerative (BFO type) detector. The SO used in this project is incompetent designed.
A competent designed SO should have two control knobs (amplitude and phase) and an induction balanced search head (separate TX and RX windings connected as oscillating circuit).  I posted a lot theory for BFO SO in geotech1 forum.
Mike

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