Building Non-motion detector with discrimination...Help

[ericEE]

I'm looking for a bit a help. I'm working on building a non-motion VLF detector that can detect and discriminate with audio. Everything I have found so far shows detectors working in pinpoint mode but also in all-metals. I'm also trying to understand what is changing in the circuitry with switching to pinpoint mode. I've been using a Garrett 250 for comparison. I can provide greater detail of what I'm trying to detect and why if you send me a PM. Any help or direction is appreciated.

[scs]

This detector works well...

[Skippy]

Yes, some C-Scope's will satisfy your needs.
"I'm also trying to understand what is changing in the circuitry with switching to pinpoint mode"
Motion-mode removes (using filters) the static signal from the coil (imperfect null) and most of the ground signal, leaving mainly the target signal, which is evaluated for tone-generation/not. Pinpoint-mode takes a reading of the total signal from the coil, 'remembers' it, and subsequently tells you if the signal gets stronger as you then move the search-coil.

[Funfinder]

The White's Beachcomber 60 has discrimination and is probably pretty simple to built
but I have no idea how good are the chances for you with some schematics ...

It needs just one speaker, two potentiometers, one trigger-button
and perhaps some analog voltmeter used as display and for battery-check.

user manual:
https://www.whiteselectronics.com/wp...16/07/bc60.pdf

25mm coin with ca. 15cm coil (6'') at ca. 20cm, max. depth ca. 80cm

Funny, someone who lives just 40min from the Whites factory in
Oregon away, found a Beachcomber for just 5$ at a garage sale:
http://www.americandetectorist.com/f...es-Beachcomber


disc. test:
https://www.youtube.com/watch?v=mb2_kNX53LM

pcb:
https://www.youtube.com/watch?v=7QZmD4LuV_o

[ericEE]

Thank you for the information so far. Currently I am attempting to use a Tesoro Golden Sabre Lite circuit as a base. I'm trying to understand what kind of output I will/should get from the demodulation circuit (DC or sinusoid). In the circuits current form it compares two DC signals and when they both go high I get the audio frequency out (as a beep I believe). What I am trying to do is produce a continuous audio signal that varies in beep frequency or amplitude in relation to distance from the target (similar to the functionality of the Garrett Pro-Pointer or "pinpoint mode" on a detector). However, the caveat is that I need to produce one type of tone for a ferrous metal and another for non-ferrous.

I know the search area (80 square feet), there will be no other metals in the search area except for an 1 aluminum and 1 steel plate (approx the size of a saucer plate), and the plate will be on the surface covered by a plastic tarp.

I feel like I should be able to "look" at the phase difference between the TX and RX signal, use that to choose which audio frequency I need to output to the speaker (my discrimination), and then vary the amplitude based on distance (I would prefer no audio until the beginning of detection and then increase volume of the respective tone as I get closer).

Any ideas?

[kt315]

Currently I am attempting to use a Tesoro Golden Sabre Lite circuit as a base.

ok. Lite is be cause lite, ie without all-metal mode while in your start point is 'Everything I have found so far shows detectors working in pinpoint mode but also in all-metals.'
you have to determine what you want. btw all-metal mode and pinpoint one are same and one part of circuit.

[ericEE]

I should rephrase. The TGSL circuit is being used as a base because it was the clearest to read and had a lot of documentation about what is happening in that circuit. It has the basics for discrimination and produces an audio tone, although not a continuous one. I own a Garrett Ace 250 and Pro-Pointer and when I refer to pinpoint mode I am using their continuous tone functionality corresponding to distance as a reference for the part of the desired functionality I'm looking for. I understand that pinpoint mode detects all metals. However, my desired circuit response would combine the continuous tone functionality of pinpoint mode with discrimination to produce and different continuous audio tone based on the phase shift produced by the detected metal. And I really only need two different tones for each type of metal (steel and aluminum). Hopefully this clears up any of my previous contradictory or confusing statements.

[Altra]

Are your targets in soil, wood or cardboard boxes? If you don't have to deal with ground minerals. You can use a single channel TR circuit with the phase adjusted to read negative on iron and positive on aluminum. You will still need to deal with circuit drift.

[ericEE]

The targets will be right on the surface, only covered by a plastic tarp. What do you mean by circuit drift?

[kt315]

my desired circuit response would combine the continuous tone functionality of pinpoint mode with discrimination to produce and different continuous audio tone based on the phase shift produced by the detected metal.

this does Nautilus VLF.