TGSL Tuning & troubleshooting

[ashefr10]

Hi telome exact it is this stage that make this voltage condition that you will plug your coil or no tension.

slt telome exact c'est bien cet étage qui fabriquent cette tension à condition que tu y branches ta bobine sinon pas de tension .

[tellome]

Hello,

I have a doubt:
Where are create the -5V ?
I think it is where I draw a circle but I don't shure ?!

Scuse my so Frenchy English :-)

[sdesic]

dont get too hung up on the ferrite thing its a guide


If you dont have much mineralisation in your local soil it will still work

S

Moving on, thank you.
Must field test this detector so I will know.

[golfnut]

dont get too hung up on the ferrite thing its a guide


If you dont have much mineralisation in your local soil it will still work

S

[sdesic]

experimented with RX coil wire (upper one on PCB) connected with GND or SHIELD
and it works for silver and aluminium and clad US quarter
small silver is not lost

Bigger ferrite can be found still or if I get close to coil

[sdesic]

Found two of those trimmers for induction from radio equipment - taken out screw (ferrite). They are 5mm long 3mm thick. Tried to eliminate them with GB trimmer and did (one of them is taped on to wooden stick). But it is same thing with aluminium and silver
(on stick also so I don't touch them - only one tiny beep when I bring them on to coil)
It is better if I turn coin sideways to coil then goes beep but close to coils.

Tried one more ferrite ring broken in half it is about same ... it can be rejected 10 cm away but if I bring it closer to coil it beeps again
both rejection loose silver quarter and regular quarter 1970 and other silvers and other silver coins are recognised.

I have also found that if I use ferrite stick 3-4 cm long it can be found if I wave it facing coils strait sides,
and when I turn 90 degrees if vanishes or breaks (sound is broken)... same air depth

[Qiaozhi]

what size ?

As Davor said, the size is not critical. The one I often use is 10mm long with a 5mm diameter, although one half of a large pot core is OK. I've used both. As long as its not a ring, since it then tends to look like a lump of iron.

[Davor]

Just about any size will do. I have a little bag of various cores, rings included, and it is quite handy for waving. It is good not to get too close to coil though. TGSL and such tend to saturate.

[sdesic]

what size ?

[Qiaozhi]

I replaced original 15nF capacitor parallel to RX to 10nF polyester film
reversed wires on RX coil (I had double beeps)
GB trimmer is set to less value (40%) to reject ferrite ring 3 cm
I then loose silver US quarter and clad quarter and aluminium coin ...
can someone explain why?

it can detect small silver coin 1.7cm (92.5%) but can't detect bigger silver 30g about 3.5 cm
detects old silver coin (83.5%)2.5 cm
all this in all metal mode

can I ignore GB settings and move on ?

Try ground balancing with a ferrite slug instead of the ferrite ring. The shape of the ferrite ring allows it to sustain eddy currents for too long, with the result that your GB point is not in the correct position.



You can retrieve the ferrite slug from a tunable inductor, as shown above. Then glue it onto the end of a length of wooden doweling to make yourself a tuning wand.

[sdesic]

I replaced original 15nF capacitor parallel to RX to 10nF polyester film
reversed wires on RX coil (I had double beeps)
GB trimmer is set to less value (40%) to reject ferrite ring 3 cm
I then loose silver US quarter and clad quarter and aluminium coin ...
can someone explain why?

it can detect small silver coin 1.7cm (92.5%) but can't detect bigger silver 30g about 3.5 cm
detects old silver coin (83.5%)2.5 cm
all this in all metal mode

can I ignore GB settings and move on ?

[sdesic]

Simon,

I will do some testing and experimenting as I now have working TGSL EDU thanks to you and all others who helped.
I don't have coil placed in epoxy yet but I will try it in field and experiment with GB.
Lot's of variants to try.
It is far better than I had week ago with my Surf Pi Pro and digging every shrapnel and peace of metal that it found.

I must look for bulgarian coil "enclosure" thing. Epoxy. Stem. Battery holder, XLR 4 pin ...

1. I think I have two so I will reverse RX connections
2. will try 10nF again
3. mylar is my shielding - emergency blanket
4. allways can try other USB cable... better - thicker
5. ground on connector to box (now wires)

In all metal mode ...
Coin is hand
Silver US quarter 1964. and before 90% silver 10% copper

[golfnut]

Some coins are mild steel with a nickel coat.

So at the final op amp filter output the ..

Nickel is trying to push a positive signal - which if nickel alone would "ping"
Iron is trying to push a negative signal - which if Iron alone may give a "clip" sound - rejected"

In this special case the Plus from the Nickel and the minus from the Iron - - these sum to zero and the comparator does not get tripped and you dont hear anything. Ive had that with these designs.

S

[simonbaker]

Managed to null coils on 40mV pin 7 of LF353 U101a
managed to reject peace of ferrite (ring about 2.8cm in diameter or two of those together)
my GB trimmer is at 62.2k
but I reject US silver quarter but not smaller 1cm silver
it can detect quarter if I turn it 90 deg. if it is flat no detection
same with 30g silver round ... detects it if I "point it" to coil
I also lost aluminium coins 2,2 cm or it breaks sound - same rotation helps
smaller aluminium 1,7 cm it detects

same thing in all metal mode and in disc

when I turn GB pot to middle it comes back (big silver and aluminium)
I loose small silver 1 cm and small aluminium 1.7 cm

If I turn back GB trimmer to 40k it detects all and ferrite in all metal mode
ferrite and iron is not detected on disc

Final tuning can take many experiments -- especially since all of us make different coils. Most people make several coils for that reason, and Ivconic found many times one coil is a dud and another works great without any obvious reason. He also does fine tuning of GB control "by ear" to not lose depth of coins -- with some possible ground sensitivity.

Things to check:

1. Coil polarity -- are RX leads reversed or not. When RX leads reversed, usually get a double-beep for targets at about 12 to 15 cm depth.

2. RX capacitor -- I don't know if you replaced .015 uF C6 with something else -- but small variations of capacitor can make a difference.

3. Coil shielding -- some people have different ideas and materials, you will see on this website.

4. Cable to coil -- you should be OK with USB as others have succeeded there, but other types can be tried.

5. Grounding of coil -- some people ground RX inverting lead to coil shield, some don't. Worth experimenting with.

Surprising that you detect coin "edgewise" but not flat -- were you using discrimination? What do you hold the coin with?

I think real silver may not be possible to discriminate out completely with the TGSL design -- may be perfectly normal.

I'll be gone for week, have fun! Good work getting your kit running.

-SB

[sdesic]

Managed to null coils on 40mV pin 7 of LF353 U101a
managed to reject peace of ferrite (ring about 2.8cm in diameter or two of those together)
my GB trimmer is at 62.2k
but I reject US silver quarter but not smaller 1cm silver
it can detect quarter if I turn it 90 deg. if it is flat no detection
same with 30g silver round ... detects it if I "point it" to coil
I also lost aluminium coins 2,2 cm or it breaks sound - same rotation helps
smaller aluminium 1,7 cm it detects

same thing in all metal mode and in disc

when I turn GB pot to middle it comes back (big silver and aluminium)
I loose small silver 1 cm and small aluminium 1.7 cm

If I turn back GB trimmer to 40k it detects all and ferrite in all metal mode
ferrite and iron is not detected on disc