TESORO GOLDEN SABRE

[ivconic]

OK. Problem is solved,TGSL is working just fine. But i experimented further.Some thing can not match here?
I cant achieve same oscilogramm at pin 1. of LF353 as ApBerg's posted here:

[ApBerg]

Disc pot

Hello Frends.

Porklvr:
Either change to a 10k Disc pot, or parallel a 10k fixed resistor across the 100k pot, and see what happens. It will very likely cause a different curve
to the Discrimination potentiometer effect (to be more like the original), but things should smooth out.

Your right ! , when placing a 10k resistor parallel across the 100k pot the erretic noise I had on high sens setting is gone !

Now I have replaced the 100k disc pot for a 50K pot. There is now and then some faint noise,... it lets you know it is still alive... I like that.

On a 20 cm opencenter coil a 1 euro is detect in air at 28cm, this is with the KT315 1M resistor

Best regards.

Ap

[ivconic]

Now, when problem solved...i have to apologise to KT315 again!
I deserved rotten tomato in face now! Why? Because that 1M resistor KT315 suggested, now is making a lot of sense! Geo do not make any mod with 555 until you try this one! Just put 1M across diode (parallel) as i posted on previous pages. It will improve audio very much, than you decide about modding it further or not.
Since TGSL is working in both modes very stabile i intend to retreive switch with 1M resitor...

Quiaozhi, that scope is approx. 450euros here in my country. To much for my budget. But also i am very tempted to buy it! I'll see i next week and decide...
Regards!

[Qiaozhi]

Now, this one is more like it !!! 'Beast" in small package! But with double price...
I have 10 days to rethink on this....

Looks good, and it has two channels. The previous one was also a Velleman kit, but Maplins don't sell this one. In the UK it costs £355.

[Geo]

Geo, welcome to the club! I knew you'll make it!

..

Hi Ivica.
Good news..... good detector with very good sensitivity.
Bad news............ very bad audio. When the signal is hight it sounds hard, bat when the signal is very low it sounds very low and not a real tone but a ks...ks....ks Agrrrr. I must try to put a audio with 555 so the tone to be the same ........ bip or not.
Who is your solution or your opinion????
Regards

[Geo]

Hi Geo,
fine. If you tune coil and it's 32cm diameter you'll get more depth I think.

As you can see the TGS circuit is good for depth with small things... much like some PI detectors with small coils!

My only thoughts are about sensitivity to very small objects like 1eur-cent sized things... maybe the 32cm coil would detect them at lower distance
cause of field shape/density.

Let me know.

Kind regards,
Max

Hi Max
Later i will try to detect the 1euro-cent......... "a little hard to find this coin". As i wrote before i detect the 2euro-cent at 28 cm. I believe that about the same for 1euro-cent. Offcource in "all metal" mode. At afternoon i will try at discrimination made and i hope to be about the same (2..3 cm is not problem). Also i nust to remember to connect a diode 1N4148 at one LM308 (it missing.... pcb error)
Regards

[ivconic]

Geo, welcome to the club! I knew you'll make it!

Max, see picture bellow; that was mother ....capacitor!!!

Nothing much to explain; i traced signal from oscillator and noticed nice shape before capacitor and quite deformed after it... When replaced signal had much better shape. When tested on coins and other items...great work!
Yes i am gonna add notch "substitution" today to see differences...
Until than...

Still slleping....uahhhh..

[Max]

Max:
Hi Ap,
thanks for the good qualiry pictures. Last 4 are like what I have... but I haven't a sinus at pin1 of LF353. Are you sure you are sampling at pin1 ? I'm referring to the original schematic... as in the picture under the red circle

Hello Max.

The signal is from 353-1 it is however not 2 v p/p, but 2 volts per division...
The signals are from the goldy, not from the GS with notch.

Ap

Hi Ap,
thanks for the info.

So I have a problem on disc ! Maybe is similar to Ivconic's problem ... the capacitor !

I have just graphite pots... not wire wound so think the problem could be at capacitor.

Thanks again,
Max

[ApBerg]

LF353-1

Max:
Hi Ap,
thanks for the good qualiry pictures. Last 4 are like what I have... but I haven't a sinus at pin1 of LF353. Are you sure you are sampling at pin1 ? I'm referring to the original schematic... as in the picture under the red circle

Hello Max.

The signal is from 353-1 it is however not 2 v p/p, but 2 volts per division...
The signals are from the goldy, not from the GS with notch.

Ap

[Max]

Hi,
about scope... here frequencies are so low that one could also look for products like:

http://www.virtins.com/

Kind of sound card scopes , func gen and spectrum analyzers...

or just use some homemade adapter for sound card directly....

Of course, there are cheap portable digital scopes for less than 100eur now... but they are really limited too (2MHz analog BW) and so I don't think that's a good choice preferring one instead of sound card for small BF frequency signals monitoring.

Anyway, if have to buy a cheap, portable one I'll choose one with at least 10-12MHz BW (or better 20MHz) not less cause otherwise is wasted money only...

I like very much portable 100MHz tektronics ... but they aren't cheap... so for that small things they aren't the right choice.

Kind regards,
Max

[Max]

Ok. I found the problem. It was inside the coil (wrong connection). My coil is from Cl3 32cm with 6.2mH for Tx and 5mH for Rx.Frequency is 14.1Mhz. I don't made fine tune the Rx.... i only connected a 5n6 parallel with 15n. So i took 40cm for a 30mm coin..... 36...37co for 2Euro .......... 34...35cm for 1 euro and 28cm for 2cents. All measurements are in all metal mode with sens at full. I connected a LM386 for better audio (but ir wants something yet). Today i will connect the 5mH to the Tx and i will put a capacitor to make oscillator to work at 14Khz and i will fine tune the Rx. Also i will try the Discrimination mode and the notch.
I want to take 5...6cm more so to be near the XLT or GTI2500. Maybe a better coil is the solution, but the free time is another problem.
Bye

Hi Geo,
fine. If you tune coil and it's 32cm diameter you'll get more depth I think.

As you can see the TGS circuit is good for depth with small things... much like some PI detectors with small coils!

My only thoughts are about sensitivity to very small objects like 1eur-cent sized things... maybe the 32cm coil would detect them at lower distance cause of field shape/density.

Let me know.

Kind regards,
Max

[Max]

Finally problem is SOLVED for real!!!!!!!
But i have to admit - without oscilloscope (even obsolete) i would never find out what was the real problem!!! Also i have to thank to all of you on great support and efforts involved here!

Problem WAS damn %&^%$#@%$^%$$@%$% 100pF capacitor C9 at LF353!!!
I bought 10 of those brand new from same supplier! Even checked each of those with capacitance meter!? Each showed 105-115pF on meter!!!
I would never have any doubts more on those.....but after all possible doubts i decided few hours ago to take oscilloscope probe and "trace" signal after each component....without much of a concept...And i founded it! Damn $%$% capacitor. Out of circuitry it is acting like good one. Included in circuitry it is not good at all. I simply replaced those with first came handy to me - ordinary ceramic capacitors....and it is working PERFECT!
Like Max stated; now i can adjust Sense at Maximum and Disc at minimum.......no chatters, no "beep's"....Calm and silent like stone!
Also in All Metal mode with Sense to Maximum....working PERFECT...no false signals at all!!!!
On coins depth remained same but on larger items...like Cola can depth (distance) raised for 30% more !!!! It can detect Cola can over 80cm in the air now, with 27cm coil. Havent checked yet distances with larger Eliptical coil 32cm...To tired...i'll continue tomorow with testing...
Now i can adjust everything by the book! GEB trimmer is now adjusted right in the middle...everything else same as Max described earlier...Huh!!!!

Damn local suppliers....thieves!


Again, people, thank you so very much for suggestions and efforts here!
Best regards!

Hi,
very good Ivconic... you solved the big problem! Congratulations!

I think you need also the 10K fixed resistor to have much safer operations like porkluvr showed by simulation.

When you rotate the GEB trimpot you could find positions where bleeping appears... look for that over the point you can null for ferrite. Seems this is the greater instability area ... and that's truly important know what's behaviour there cause you have to use detector in that zone on real soil.

What about wrong cap ? Isn't it ceramic (my capacitor there is ceramic)
What was the problem with it ?

Please explain better.

Kind regards,
Max

[Max]

Ivconic, the reason that the pin 1 waveform is so out of control, is because you have removed the original GS notch level 10k potentiometer
that was directly paralled with the 100k discriminate pot. By removing the notch circuit, you have increased the gain of the opamp - at
the same time as you also increase the likleyhood of oscillation because of the higher feedback resistance.

Either change to a 10k Disc pot, or parallel a 10k fixed resistor across the 100k pot, and see what happens. It will very likely cause a different curve
to the Discrimination potentiometer effect (to be more like the original), but things should smooth out.

The LF353 is not a rail-to rail opamp. By having raised the circuit's gain, you have run out of dynamic headroom!
It feel stupid for not realizing this sooner.

Hi porkluvr,
you are right on this, I've checked and results from simulations are the same as I can see on scope... with some minor difference.

It's better adding a fixed resistor to modified schematics... cause , also, not all LF353 are the same out there.

I was thinking few days ago at something related to that...cause when I turn the notch pot, even with notch disabled by switch, I can ear differences on the audio... and that's cause of current flowing in.
But then I forget to investigate more on circuit about that...

I have all graphite pots, not wire-wound ones on TGS... and that's true that a modification must be made according original gain of LF353 half... you showed why. It's really important for stability.

Kind regards,
Max

[Max]

Hello Frends.

Qiaozhi, in the past I had some problems with wire wound pots, when replaced by a 'normal' pot the problems were gone, can it be that there is an L function ?

Well made some screenshots, transmit sinus is 2 v p/p also the 353-1 is 2 v p/p for the r25 and r26 signals it is 0.2 v p/p ( I hope..... can be wrong )

First is LF353-1 then two from r25-q7 then two r26 q6

Ap

Hi Ap,
thanks for the good qualiry pictures. Last 4 are like what I have... but I haven't a sinus at pin1 of LF353. Are you sure you are sampling at pin1 ? I'm referring to the original schematic... as in the picture under the red circle.

It's strange if you have a perfect sinus there and I haven't it.

1st picture is maybe the signal at output of preamp (pin 7) ?

My signal is a parabolic like in the picture I've posted... and has a superimposed sinusoidal damped signal.

Let me know.

Kind regards,
Max

[Geo]

Good

Ok. I found the problem. It was inside the coil (wrong connection). My coil is from Cl3 32cm with 6.2mH for Tx and 5mH for Rx.Frequency is 14.1Mhz. I don't made fine tune the Rx.... i only connected a 5n6 parallel with 15n. So i took 40cm for a 30mm coin..... 36...37co for 2Euro .......... 34...35cm for 1 euro and 28cm for 2cents. All measurements are in all metal mode with sens at full. I connected a LM386 for better audio (but ir wants something yet). Today i will connect the 5mH to the Tx and i will put a capacitor to make oscillator to work at 14Khz and i will fine tune the Rx. Also i will try the Discrimination mode and the notch.
I want to take 5...6cm more so to be near the XLT or GTI2500. Maybe a better coil is the solution, but the free time is another problem.
Bye