IGSL

[giuhalftrack]

My Igsl tgsl behave in a strange manner...

cannot adjust trimmer TR3 (100k)

i get no sound at all or a continuous tone (mix of two tones) sometimes it works (with <10 cm
detection depth) but soon the long tone or silence return

First i try to adjust trimmer tr3 but i can't find rigth position, after i replace tr3 with multiturn
trimmer and again i can't find right position...

after i try to replace tuning capacitors (C4, C43) with 15nF (J tollerance) (like TGSL schematics) and then i return to
4n7F (K tollerance) and 10nF (K tollerance) (i try different ones).

I use the original 8" tesoro silver umax coil, (waithing to build my own coil)

anyone have similar problems ? thanks in advance !

[Davor]

Could you please post a part of schematic you are referring to? I have troubles finding that particular trimmer on my schemes.

[giuhalftrack]

Could you please post a part of schematic you are referring to? I have troubles finding that particular trimmer on my schemes.

schematics is the one, currently on silverdog.
stars marks the trimmer and the capacitors.

Thank you Davor

[Davor]

As for the trimmer, you are supposed to obtain oscillation of the Tx oscillator. Once you do, the amount of bias you are adjusting with this trimmer is supposed to be fine tuned so that the oscillation is as clean as possible, but for the time being just go with any kind of oscillation. You'll fine tune it later on.

I'm not familiar with your coil and to determine what capacitances are needed you'll need to know the coils' inductances. In case both inductances are as per the TGSL specification at 6 and 6.5mH just leave it be. In other instances you'll have to do some corrections. Can you determine the coils' inductances?

For the instability problem I'd be looking somewhere else. Most probably your lab has some noise source that your coil picks, say laptop PSU or something.

If you get tones out, you obviously have Tx oscillating. There are a few points where troubles may lurk.

First try to set R37 and R57 for less offending tone. Also when problems start try adjusting Disc sens P3 and P4 to just about stop instability. Next you'll have to adjust Ground Balance by waving some pieces of ferrite in front of your coil to find positions where waving ferrite is just cancelled. If you continue playing with Rx input capacitors you'll need to re-adjust ground balance.

Don't worry, it will work.

[giuhalftrack]

As for the trimmer, you are supposed to obtain oscillation of the Tx oscillator. Once you do, the amount of bias you are adjusting with this trimmer is supposed to be fine tuned so that the oscillation is as clean as possible, but for the time being just go with any kind of oscillation. You'll fine tune it later on.

unfortunately i'm not equipped with oscilloscope then i use a pc based software (visual analyzer) i can't see frequencies below 14 khz (due to pc sound card limitations), but i think the oscillation always take place.

I'm not familiar with your coil and to determine what capacitances are needed you'll need to know the coils' inductances. In case both inductances are as per the TGSL specification at 6 and 6.5mH just leave it be. In other instances you'll have to do some corrections. Can you determine the coils' inductances?

according to geotech1 database of coil my coil have this parameters:
Name Brown 8" ("donut" coil)
TX-L 5.59mH
TX-R (ohms) 21.2
RX-L 6.23mH
RX-R (ohms) 22.1

slightly different from igsl-tgsl coil parameter.

i can take a look inside a tesoro silver umax to read a value of tuning capacitor, (it make sense ?)

For the instability problem I'd be looking somewhere else. Most probably your lab has some noise source that your coil picks, say laptop PSU or something.
If you get tones out, you obviously have Tx oscillating. There are a few points where troubles may lurk.

First try to set R37 and R57 for less offending tone. Also when problems start try adjusting Disc sens P3 and P4 to just about stop instability. Next you'll have to adjust Ground Balance by waving some pieces of ferrite in front of your coil to find positions where waving ferrite is just cancelled. If you continue playing with Rx input capacitors you'll need to re-adjust ground balance.

Don't worry, it will work.

ok tonight i try again, now i'm going to search how to calculate capacitance needed for my coil specification (i'm out of electronics work from 20 years i don't remember much things)

thank you

[Davor]

No worries, inductances are close enough. Just stick with the original values.
Try finding some electrically quiet area with some half a meter distance from metals to do your initial adjustments. Make sure you tune GEB correctly, and from there you'll find the rest.

[axljackass]

hi guys a little bit confuse here...which one is the working schematic?
a lot of rev had been did lately

thanks

[Davor]

You'll find working schematics at the beginning of the thread and not over page #20. Main difference is in adaptations for different coils, so you have Musketeer and TGSL coils. Most of the insides are identical, differences being only at the very front end.

[giuhalftrack]

No worries, inductances are close enough. Just stick with the original values.
Try finding some electrically quiet area with some half a meter distance from metals to do your initial adjustments. Make sure you tune GEB correctly, and from there you'll find the rest.

ok Davor is working... but...

I have a very poor detectiond depth (10cm - 4") on a 1 euro coin, and again strange behave.

low tone for non-ferrous sound good.

hight tone for ferrous sound "dirty" to explain this, you need to remember early age hip hop sampled drums ok?
but it goes a clear higt tone only when object is at 2 cm - 1", i suppose is something
like my silver umax: a distant target gives a "broke - crispy" sound i don't know if this sound is normal in IGSL.

I had several errors in my setup (all fix now )... ground pot for ferrous channel reversed , low power supply.


so.. my questions:

1 - is the "dirty" sound normal for distan objects ?
2 - i need to mess with TR3 trimmer ? (adjusting the "nice sinus wave", oscillator trimmer) ?

please consider that:
wires from pcb to coil connector shielded (lenght 10 cm) and some components like TR3 trimmer and tuning capacitors are on
breadboard..

[Davor]

Make sure your GEB is set right. Most probably it is not adjusted properly. Once you do, you may try playing with TR3 to see if it affects detection distance. Disc Sens also affects distance. A choice of opamps in gain stages as well. In case you used LM324's there, you'd lose some significant distance.

A huge advantage of IGSL over other rigs is that you may overlap indication for ferric and non ferric objects so that nowadays coins that are full of nickel sound in double tone. To make it work right, use a piece of Al foil as a target and set the Disc pots to activate both Fe and non-Fe channels. Once you succeed, mark these positions of the pots and play with the nickels ... you'll soon get the idea.

There is a mistake in IGSL that affects the adjustability of Disc sens, and unfortunately it happens on the two comparators - the pins are swapped. Your rig will work, but Fe indication will act a bit funny. When you are up to it just see my mods and do something about it.

[der_fisherman]

To set this up with a clean sine wave (the reason Ivconic put the trimmer there in the first place), you do really need a scope, but as you are getting sounds (and the correct voltages) it must be working reasonably well, so leave it alone till you have a scope available.
I don't think that using a meter on AC will help much, but you might like to set the trimmer for the highest possible voltage output for example......but don't expect much change! I have never personally tried it myself....
regards
Andy

[Davor]

My musketeer IGSL oscillator is a bit different, but in a way does the same job, and I observed the FFT of these oscillations. Point is, as expected, that the purest oscillations are obtained near the border of spontaneous starting the oscillations. You actually do not need a scope to find this spot. First you establish oscillation, and then you lower the amplitude by TR3. When the oscillation stops just go back a little to the point it starts back again, and a little notch more - that's it.

I think for the next edition of IGSL some balanced oscillator will be a perfect choice. Beside the obvious advantages of suppressed 2nd harmonic (for which this tuning fuss is all about), and the lack of tuning, these can work in a very economic regime using very little current for they work.

[axljackass]

guys whats the difference between igsl musketeer abd igsl tgsl?curios only.thanks guys

[Davor]

A Tx oscillator and tank capacitors for the coils are the hardware differences.
TGSL coils are 6mH/6.5mH, while musketeer with working frequency about 14.6kHz.
Musketeer is 1mH/15mH with working frequency about 8.5kHz.

Mine is Musketeer version and I made my own coil. My Tx coil is slightly more than 1mH and resonant frequency with untouched capacitors is about 8kHz. My Rx coil is with a centre tap and both coils are unshielded.

IMHO the large difference in Musketeer coils addresses some interesting issues and that was my reason to go for it. Low inductance of Tx coil makes for stronger fields at the same applied voltage. High inductance of the Rx coil is beneficial for the larger received voltage for the same target response.

Both these effects would not make significant difference in real world, but makes a kind of guideline when you start a project, and it was all the same to me because I knew I'd be making my own coils. Someone with no notion of building a coil would chose cheaper coils.

[giuhalftrack]

My ......purest oscillations are obtained near the border of spontaneous starting the oscillations. You actually do not need a scope to find this spot. First you establish oscillation, and then you lower the amplitude by TR3. When the oscillation stops just go back a little to the point it starts back ....

ok I agree with this tecnique !!! this is the reason why i put a multiturn trimmer instead of classic tr3 trimmer.... cause the adjusting of tr3 with a screwdriver is so difficult !!!.

thanks to all for feedback and now i'm going to try.. try and try.. again until succes come