TGSL Tuning & troubleshooting

[seadoggy]

What is best replacement for LM 308???

[Sulfid76]

Hi! in tgsl I tried to put different chips. On 5534 the stable worked not was raised. I delivered to TL081 - works well!

[zoomix]

Hello,

Here is finally the TGSL functioning properly. Very diffcult to achieve a proper coil.

Dicrimination works fine
impeccable GB

Test in air:
https://www.youtube.com/watch?v=Zu7G7DSoCXE

I am testing in the earth:

50cent euro is taken by TGSL at 20 cm and I compared with the Goldmaxx power who also takes limit.

I noticed that the TGSL must be swept slowly to make the target.

I would now improved sensitivity because I noticed the potentiometer varies very little

have you some tips to make measurements of sensitivity and improved?

Thanks

[Finderskeepers]

Not work with original Tesoro concentric coil 5 pin, 7" , 3 cm for a coin, i try all possibilities with wires of tx and rx with different capacitors, I think a component is dead, how to find it.

I have the same problem with a original 8" coil, 5 pin and get the same detection depth. Will let you know of any improvements. On your -5 volt supply line, does it read -6.3 volts.

regards

Finderskeepers

[Hyena]

Hi,
I made TGSL by Qiaozhi's complete details.
Its really amazing machine. I use 12+4,7nF caps for C6. Then i tried replaced LM393 with TL082 and I was able to use 12+5,8nF (and still get ground ballance in GP pot range) and I finished with very nice depths.

1€ detection in 32cm, golden mens wedding ring in 37cm. Ferrite rejection worked, discrimination worked very well even with full hand of steel things it was quiet. Sensitivity to max and no chatters, absolutelly silent.

While I tried different things (gold, another coins...) it somehow started to chatter, it is like machine gun now. I did not change anything, coil was still balanced.
I did this in garage with TGSL powered by adapter, but there is not another electrical device execept osciloscope which can be "ocasional" noise source, I thing. I replaced TL082 back to LM393 but nothing changed. Even when i turned sens to min, this machine gun still chatters, only with slightly different frequency (somewhere about 3-5 chatters per second). I tried switch off osciloscope (which was all the time connected to Tx and pin 7 of LM393/TL082). But it chattered anyway.

Did anyone notice similar behavior? Should I check something? I can make video if it helps...

[Gwil]

"TGSL powered by adapter"

I wonder if this is your problem. Metal detectors can be very vulnerable to noise on their power supply. How is it on battery power?

[ripsdevala]

My problem with tet..tet...tet..... Is :
Change the 15nf Rx caps to 10nf, try different value to match your need from 10nf to 15nf, but my Tx caps is change from 22nf to 20nf to get 14.5khz

Rips

[Gwil]

If the detector used to work OK it is unlikely to need component values changed now.

[mikebg]

Hi,
I made TGSL by Qiaozhi's complete details.
Its really amazing machine. I use 12+4,7nF caps for C6. Then i tried replaced LM393 with TL082 and I was able to use 12+5,8nF (and still get ground ballance in GP pot range) and I finished with very nice depths.

1€ detection in 32cm, golden mens wedding ring in 37cm. Ferrite rejection worked, discrimination worked very well even with full hand of steel things it was quiet. Sensitivity to max and no chatters, absolutelly silent.

While I tried different things (gold, another coins...) it somehow started to chatter, it is like machine gun now. I did not change anything, coil was still balanced.
I did this in garage with TGSL powered by adapter, but there is not another electrical device execept osciloscope which can be "ocasional" noise source, I thing. I replaced TL082 back to LM393 but nothing changed. Even when i turned sens to min, this machine gun still chatters, only with slightly different frequency (somewhere about 3-5 chatters per second). I tried switch off osciloscope (which was all the time connected to Tx and pin 7 of LM393/TL082). But it chattered anyway.

Did anyone notice similar behavior? Should I check something? I can make video if it helps...

Disable TX to see how RX operates.

[Gwil]

Disabling the transmitter will also disable the -5V supply, so probably not a good idea.

[satdaveuk]

Hi Hyena
Dont touch it, You already proved you have a good build.
The chatting is typical to the design in built up locations.
More lightly than not your picking up EMF from the AC mains supply
They also don't like florescent lighting.
Both my builds are the same.
Just hope now you have not balls it up by fiddling with it .
All the best Dave

Just load battery's to it and take it into a field with no over head lines.
I will guarantee it will work like a dream

[Hyena]

"TGSL powered by adapter"
I wonder if this is your problem. Metal detectors can be very vulnerable to noise on their power supply. How is it on battery power?

I tried it with bateries, but it was the same.

My problem with tet..tet...tet..... Is :
Change the 15nf Rx caps to 10nf, try different value to match your need from 10nf to 15nf, but my Tx caps is change from 22nf to 20nf to get 14.5khz
Rips

When I have been searching for maximal depth, I tried different values for C6 from 12nF up to 19nF. It has an effect on Rx Vpp, bot not to this chattering. Yes, for values about 12nF it chatters less, but air depth was terribly small. Highest Vpp with GB pot able to reject ferrite was 18,1nF with GB pot in 1/4. Any higher cap shifts rejection out of this GB pots range. Its a pitty, because thiss Vpp (while coil is still nulled) seems to have impact to air depth. Best behavior was with 18,1nF - biggest depth and working discrimination. So I want to test little different inductance for Rx and play with this Rx Vpp - its a good job for long winter evenings

Hi Hyena
Dont touch it, You already proved you have a good build.
The chatting is typical to the design in built up locations.
More lightly than not your picking up EMF from the AC mains supply
They also don't like florescent lighting.
Both my builds are the same.
Just hope now you have not balls it up by fiddling with it .
All the best Dave
Just load battery's to it and take it into a field with no over head lines.
I will guarantee it will work like a dream

Hi Dave, its a great idea! I still have coils just laying on paper box. So I will make coil enclosure and other mechanical components at the weekend and I will try it on fields. I will report how it works.

Thank you all for ideas!!!

All the best,
Tomas

[Hyena]

machine gun chatters...

Hi all, unfortunatelly I am back again

I tried to close it in grounded alu case and walk in nearby forest (actually I live inside this forest), but results are the same.

I made 1st TGSL by Qiahozhis complete details with all parts the same like in schematics. Then I made DD coil. Inductances are practically exact 6 and 6,5mH (I used 0,3mm magnet wire so coils has lower resistence than those from manual). I shielded them (Thinnest aluminium I can find -> 15-20mm wide strip with 3-5mm overlap of turns and 5-10mm gap in shield). I measured resistence across shield and it was conductive (few ohms). Shields are connected together with Tx- and grounded in box. I tried to ground Rx- to shields as I saw in some schematics, but even this does not help.

Does it matter where I connect this? I mean Rx- with shields and Tx-? If join is in coil or in the box? until now I always connected this on coil end of cable.

So I thought Its a PCB mistake -> made new pcb -> this time TGSL EDU (only difference is J113 instead of BF245c, because I dont even have J107 and I am out of BF245c). But troubles remains... So now i suspect the coil/shields. I used thin alu sheet. Shield itself does not change inductance remarkably - only 0,03mH for each and the same direction - so this has no efect to inductance at all.

This alu shield is total mess. Lot of work against few minutes of spraying... I still have coils not diyed in enclosure so I still can take down this shield and make conductive enclosure with clear coils...

Do you have any susspects in this case? I do not have any original coil so I am not able to check this. I can make photos or video about this, but text is always faster.

Thanks for any information!

All the best, Tomas.

[CDI]

Hi Tomas, on my setup, RX- and TX- are both connected in coil housing with both alu shield's.
How much mv u have on pin 7 LF353?
Try to replace LF353 with LM833, has lower noise. Also, if u have TL081 on your pcb, try with 071.
Btw, in the past, i maked 3 TGSL's, 2 of them worked good, one of them (maybe my first) has the same problem like your, but i think that was bad shield.
No one of them was mounted in metal case, just ABS plastic enclosure.

[Hyena]

machine gun

I found out that in area where I tested detector are also cables to bloody purifier!!! When I took it out of this last 230V/50Hz range it was silent with sensitivity to max. Its really interesting project and I want thank to all, who shared all informations about this awesome detector!