TGSL Tuning & troubleshooting

[Jerry]

Very Nice! I like that tone separation.

Jerry

[simonbaker]

I think phase is not important, if we accept this:
Instead some metals are discriminated at disc pot position e.g 4,
having different null phase shift, we achieve the same discrimination at disc pot position 3 or 5,
depending how bigger or lower null phase we’ll have. That’s not affect tgsl very much in this way.


Is it correct?

I didn't quite understand your wording, so this is what I think:

It depends on how you achieve the different null phase shift. If you simply change your coil overlap to make a different null phase, then no, it should not affect the DISC pot position for discriminating a certain metal -- that is the important point. In other words, if Nickel is rejected at DISC pot position 4, and then you shift your coil overlap slightly to change the null signal phase, Nickel will still be rejected at DISC pot position 4.

However, if you change the resonant frequency of the RX coil tank, or change the TX oscillator frequency, you may shift the DISC pot position somewhat.

-SB

[eduardo1979]

TGSL-EDU 2 Tones Schematic.

TGSL-EDU 2 Tones Schematic.

[johnsmith77]

But if our null signal is of a certain phase, the JFet will turn on when the output of the LF353 is at the negative half of the sinusoid. Depending on your null signal, it could be between -1 and -2 volts. This would cause the JFet to become forward biased, because when the Gate is at zero volts, the Drain/Source is between -1 and -2 volts -- the Gate is more positive than the Drain/Source.

-SB

I checked oscillograms posted in TGSL thread. GEB and DISC samplings are shifted about 90 degrees.
So if 1st JFet will turn on when the output of the LF353 is at the negative half of the sinusoid, then 2nd JFet will turn on when the output of the LF353 is at the positive half of the sinusoid. Should GEB and DISC samplings be at the zero crossings to prevent JFets from forward biasing ?

[johnsmith77]

TGSL-EDU 2 Tones Schematic.

Nice idea!
Does it works like this?:

Iron: low tone
Coin: low+high=middle
Iron+coin: low+high=middle

First channel: Ferrous discriminated
Second channel: all metalls accepted

[eduardo1979]

Iron=low tone
Coin=high tone
Iron+Coin=combined tone.(low+high) tones.

[johnsmith77]

Iron=low tone
Coin=high tone
Iron+Coin=combined tone.(low+high) tones.

I clearly understand output U106 (ferrous discriminated). Two channels: GEB and DISC are used.

Question is: Output U107 non ferrous discriminated? how? Can we discriminate using only GEB channel?

Thanks

[eduardo1979]

Yes.

[simonbaker]

I checked oscillograms posted in TGSL thread. GEB and DISC samplings are shifted about 90 degrees.
So if 1st JFet will turn on when the output of the LF353 is at the negative half of the sinusoid, then 2nd JFet will turn on when the output of the LF353 is at the positive half of the sinusoid. Should GEB and DISC samplings be at the zero crossings to prevent JFets from forward biasing ?

Not exactly. The GEB pot is set by using ferrite as target and setting so no beep is heard (I think using ALL METAL mode is recommended). This may be quite close to centering GEB sync pulse over zero crossing of null signal, but not necessarily.

The DISC pot is simply adjusted for whatever metals you want to discriminate. As mentioned before, it is not related to the null signal zero crossing.

However, if your null signal phase is "peculiar", you may experience forward biasing during some portion of the DISC pot range or the GEB pot range. In this case, you should try to adjust your coil overlap so to minimize the forward biasing situations while still having a null signal near the minimum.

You can probably tolerate -.7 volts at the JFet source (C12/C15), but if it goes much lower than that, you will likely have some forward biasing of the JFet.

-SB

[johnsmith77]

You can probably tolerate -.7 volts at the JFet source (C12/C15), but if it goes much lower than that, you will likely have some forward biasing of the JFet.

-SB

Hello.

So if i have null voltage 1.4ppV on pin 7, it consists of positive period +0.7V and negative period -0.7V. I will not be able reach less than -0.7. Should worry only they whose null voltage are higher?

Best Regards

[simonbaker]

Hello.

So if i have null voltage 1.4ppV on pin 7, it consists of positive period +0.7V and negative period -0.7V. I will not be able reach less than -0.7. Should worry only they whose null voltage are higher?

Best Regards

I think that is correct.

-SB

[simonbaker]

I got her all fixed up.. Sorry about such a stupid mistake !! I just hope that I didn't screw up someones project. I fixed some other minor errors that have been bugging me too. I'll keep it a living document. Additions and corrections welcome!!

Don

Thought of a small addition to these documents -- revision tracking. It would be useful to put a small section with revision descriptions and a revision number on each revision of this extremely useful (TGSL 101) document near the front of the document.

I realized this would be useful because I just spent a half hour trying to convince myself I had the latest version (and locating the latest -- the document releases seem to be divided between two threads, "Tesoro Golden Sabre" and "TGSL Tuning & Troubleshooting").

I had remembered a recent revision of the grounding diagram for the RX cable. If my documents had mentioned that revision, I would have been at peace that I had what I needed.

Cheers!

-SB

[satdaveuk]

TGSL pcb with circuit numbers

Something else which would be handy is a PCB layout with circuit ref numbers, and if it had the transistor connections as well what a time saver that would be.
Dont think there is one here, maybe when one of us have the time would be worth doing instead of forever having to resolder wires due to having to flip the board over all the time.
Just a thought

Regards

[satdaveuk]

Coil checker

By the way Simon, sure it was you posted circuit diagram of the coil checker.
Im building it almost finshed Done the PCB all holes drilled used ground plain as well, looks nice.
You said a 2n2907 will do for the occillator, am I correct?
Made the PCB with express pcb.
Soon as I got it up and running will post it all in tools if thats ok.

Regards

[simonbaker]

By the way Simon, sure it was you posted circuit diagram of the coil checker.
Im building it almost finshed Done the PCB all holes drilled used ground plain as well, looks nice.
You said a 2n2907 will do for the occillator, am I correct?
Made the PCB with express pcb.
Soon as I got it up and running will post it all in tools if thats ok.

Regards

I think maybe someone else's idea, doesn't sound familiar. I know I use 2n2907 for my TGSL oscillator.

Cheers,

-SB