TGSL troubleshooting questions

[Davor]

With extra care and some help with a chip of a milk carton (that contains extra thin aluminium foil) you can null your coil further. Also if you experience no chatters at all, you are most probably using LM358's in gain blocks, which means your Sens potentiometer can't reach that low, and that you are actually missing some serious dBs and potential inches of depth.

There are two potential solutions to this.

LM358 is a BJT input op amp and with resistor values as per the schematic you can expect about -15mV offset to compensate. Current setup goes down to 0V, so placing 1M5 resistor between pin 2 and -5V would get you there.

As LM358 is quite noisy in 1/f region (of interest) it would be better if it was replaced by a less noisy TL072 that also comes with ~0V offset. It would reduce noise (and chatters) while keeping all gain, and you don't have to add anything else to your board. Just plug these in and be amazed that you also have chatters and additional depth

.......................................

BTW, when observing videos on youtube pay attention to the choice of coins they use - those are all old coins made of real materials, and not nowadays junk coins made with lots of nickel and other rubbish.

[zoomtronic]

With extra care and some help with a chip of a milk carton (that contains extra thin aluminium foil) you can null your coil further. Also if you experience no chatters at all, you are most probably using LM358's in gain blocks, which means your Sens potentiometer can't reach that low, and that you are actually missing some serious dBs and potential inches of depth.

There are two potential solutions to this.

LM358 is a BJT input op amp and with resistor values as per the schematic you can expect about -15mV offset to compensate. Current setup goes down to 0V, so placing 1M5 resistor between pin 2 and -5V would get you there.

As LM358 is quite noisy in 1/f region (of interest) it would be better if it was replaced by a less noisy TL072 that also comes with ~0V offset. It would reduce noise (and chatters) while keeping all gain, and you don't have to add anything else to your board. Just plug these in and be amazed that you also have chatters and additional depth

.......................................

BTW, when observing videos on youtube pay attention to the choice of coins they use - those are all old coins made of real materials, and not nowadays junk coins made with lots of nickel and other rubbish.

I have following results:
on LM358 pins i have these voltages:
pin:
1 +0.640v
2 +0.643v
3 +0.631v 0% DISC and +1.063v on 100% DISC
4 -06.23v
5 -0.498v
6 -0.504v
7 -0.508v
8 +7.97v

where i should put resistor 1M5 between pin 2 of LM358 and pin 4 (-5v) ?

[Davor]

Gee, that was a bit too quick from my side. Pin 2 or pin 6 (same thing) were supposed to be pins of a LM393 comparator, while LM358 were supposed to be LM308s that precede it. Only now I looked at the schematic to realise my error. Sorry.

LM308 has half input bias current than LM358, so you can put 3M3 resistor between pin 2 of LM393 to -5V (pin 4 of LM393) It will slide the minimum Sens voltage so that you just about reach the chatters.

[zoomtronic]

TGSL PCB wiring

Gee, that was a bit too quick from my side. Pin 2 or pin 6 (same thing) were supposed to be pins of a LM393 comparator, while LM358 were supposed to be LM308s that precede it. Only now I looked at the schematic to realise my error. Sorry.

LM308 has half input bias current than LM358, so you can put 3M3 resistor between pin 2 of LM393 to -5V (pin 4 of LM393) It will slide the minimum Sens voltage so that you just about reach the chatters.

Here is the screenshot of TGSL PCB, first picture is how i wired up PCB, and second is i guess proper LM 358 to boost, am I correct?

[Davor]

Yes, that's the one. 3M3 is my estimate, and I expect you to reach chatters with Sens potentiometer this way. In case you find too much chatters, just increase this resistor.

[zoomtronic]

Yes, that's the one. 3M3 is my estimate, and I expect you to reach chatters with Sens potentiometer this way. In case you find too much chatters, just increase this resistor.

I did tried to place 3M3 between pins 2 and 4 and i didn't notice any change.
I did some research on previous posts on forum, and i get more cases like mine, all those were related to electrical noise
in environment where device is tested, or directly related to the coil balancing issue. Mine is balanced to the 120 mV on pin 7, as i understand from previous posts, that value is actually 120/47=2.55 mV on coil. So far with that i am done with coil nulling, in that point it detects way better than in higher value on pin 7 u101.
I also placed ferrite interference arrestor on speaker lead. Chatter i did not get with 3M3 resistor. Even on max sensitivity , what now?

[zoomtronic]

ok, I got chatters by nulling the coil deeper, now in max sensitivity i have chatters, but detection still stands 15-20 cm for coin 5 serbian dinars. I guess next ting to look will be pcb itself, an adjusting it to be more sensitive

[zoomix]

Original Tesoro coil for TGSL

Hello, I would like to know the original models coils that I can put on TGSL or IGSL.

I see that there are models 14/19khz and 10/12khz.the original detectors saber II and silver work 10 Khz.


What original Tesoro coil inductance has the 5.9 and 6.5 mh?

http://www.detecteursdemetaux.net/disques-tesoro, fr, 3.21. cfm

If you know, give me as much info on the model to avoid the error.

Thank you in advance for your answers.

[ashefr10]

Hello, you're it possible to increase by about 5 cm detection depth by changing some component values. thank you

[Finderskeepers]

Hello, I would like to know the original models coils that I can put on TGSL or IGSL.

I see that there are models 14/19khz and 10/12khz.the original detectors saber II and silver work 10 Khz.
O

What original Tesoro coil inductance has the 5.9 and 6.5 mh?

http://www.detecteursdemetaux.net/disques-tesoro, fr, 3.21. cfm

If you know, give me as much info on the model to avoid the error.

Thank you in advance for your answers.

Bought an original tesoro coil with 5 pin connector and will not work on tgsl. My homemade coil works well . Figure that one out?

[Qiaozhi]

Bought an original tesoro coil with 5 pin connector and will not work on tgsl. My homemade coil works well . Figure that one out?

What do you mean by "will not work"?
Please elucidate.

[Finderskeepers]

Left this project alone for a few weeks and got my tgsl working this weekend . Built the TGSL-V3 circuit and a bypass capacitor was causing it grief. Furthermore, I replaced capacitors C14,C17 with 10uf bipolar and R29,R31 with 1M (as per TGSL-EDU version) and got a big improvement in detection depth. One euro coin detects (air test) at 37 cm, an increase of 8cm.

[paku]

With extra care and some help with a chip of a milk carton (that contains extra thin aluminium foil) you can null your coil further. Also if you experience no chatters at all, you are most probably using LM358's in gain blocks, which means your Sens potentiometer can't reach that low, and that you are actually missing some serious dBs and potential inches of depth.

There are two potential solutions to this.

LM358 is a BJT input op amp and with resistor values as per the schematic you can expect about -15mV offset to compensate. Current setup goes down to 0V, so placing 1M5 resistor between pin 2 and -5V would get you there.

As LM358 is quite noisy in 1/f region (of interest) it would be better if it was replaced by a less noisy TL072 that also comes with ~0V offset. It would reduce noise (and chatters) while keeping all gain, and you don't have to add anything else to your board. Just plug these in and be amazed that you also have chatters and additional depth

.......................................

BTW, when observing videos on youtube pay attention to the choice of coins they use - those are all old coins made of real materials, and not nowadays junk coins made with lots of nickel and other rubbish.

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