TESORO GOLDEN SABRE

[eduardo1979]

TGSL

[eduardo1979]

TGSL

[eduardo1979]

Hi I am posting my TGSL circuit is tested and works great no errors and maximum sensitivity to cop a gold wedding ring to 35 cm in the air the cancellation of the coil is 4 mV.

[dfbowers]

I built the TGS, and used Ivoniics DD coil design. I get pretty good depth, very good steel and iron discrimination, but it doesnt seem to reject aluminum pulltabs and other aluminum.I set the coil using a scope, but the receive signal seemed to shift after the epoxy hardened. If you have built the TGS or TGSL please comment on your metal detectors aluminum rejection capabilities, and if there is anything I can do to fix mine.
thanks

I can reject pull tabs at about the mid range setting of the disc pot.
I'm going to suggest that your phasing is a little off, maybe due to a difference in inductance. Do you have the ability to measure your coils?

Can you GB to a ferrite slug ok? (maybe another clue).

I have found that a difference of about 5 turns between the Tx and Rx coil is optimal for what I am building. Also, coil calculators suggest 5 turns difference as well. 101 turns for Tx and 106 turns for Rx. I could never reproduce Ivconics coils exactly but close!

Or.. Change C6 slightly.

Don

[ApBerg]

Hello Wiltran,

You can try to adjust the coil with some ferrite beats, look at the scope at the results when you move the beats over the coil surface. You will see that it affects your nulling.
I always used to set the coils at receive 3-5 mV and amplitude rise for gold ...
The ground pot setting is also affecting your disc , look how large silver is disappearing
if wrong adjusted !!

Regards.

Ap

[Wiltran]

TGS Aluminum pulltab Discrimination

I built the TGS, and used Ivoniics DD coil design. I get pretty good depth, very good steel and iron discrimination, but it doesnt seem to reject aluminum pulltabs and other aluminum.I set the coil using a scope, but the receive signal seemed to shift after the epoxy hardened. If you have built the TGS or TGSL please comment on your metal detectors aluminum rejection capabilities, and if there is anything I can do to fix mine.
thanks

[raff33]

Hi Dennis the Mennis,
many thanks for help

[Dennis the Mennis]

Hi Raff ,

I think the most important thing is that you don't get a double beep when a target is detected ( > 6-7cm ).
If so : flip / turn your coil ( tx or rx ) or switch the connections on your coil ( tx or rx )
Otherwise it should be ok and if in doubt : experiment for the best result

regards Dennis the Mennis

Hi,
cann anyone guide me please eatch directuos of winding is correct ?
many thanks

[raff33]

Hi,
cann anyone guide me please eatch directuos of winding is correct ?
many thanks

[akademiker]

Finally found the bad boy! The 15nF in the RX part wasnt really 15nF, but more like 18nF <.< now I replaced him (hammertime) with with the closest to 16nF I could find (16,17nF +/- 2,5%) and now the discrimination works kinda good, rejecting ferrit rod completely while accepting silver, and can even discriminate a bottlecap (made out of thin iron here in germany) while accepting a goldring (at less than 20cm). In this option it ignores 1e completly, even in all metal mode <.<

TX is now 14,285kHz
RX is now tuned to 15,596kHz, which is 109% of TX

RX is shifted exatcly 4µS, which is about 20° at 14,285kHz

The sinus output at Pin7 of U101a has an amplitude of 1,8V and my signals at the both gates of the mosfets look kinda upside down, exactly inverted version of these: http://www.geotech1.com/forums/showp...postcount=3896

[daviddwilson]

Few observations:

1.) This detector reject small iron objects when in disc. mode completly - in other words: minimum rejection level is well above nail rejection.

2.) But still objects like tin plated iron boxes are not possible to discriminate well agains other metals - so no mirracle here.

3) Notch feature is very interesting - kind of a analog accept-reject circuitry. For example I can filter (accept) ONLY my gold ring and no other metal make even a sound!!

4) Sound is really poor, it is about the same as CLIII. I belive this is the main difference between GoldenSabre and GoldenSabreII.

5) Coil. Thanks Max I also saw that KT315 post:
rx 1.35mH 12ohm
tx 10mH 55ohm
Hm - I actually made a good gimmick to reverse Tx/Rx of whites DD coil to test GoldenSabre. But still I wonder if those values are correct. Will try to hunt for best coils in OO configuration. First I need Tx for 12-15 kHz - then I'll experiment with different Rx inductances.. and post results here.
ANY IDEAS, HINTS ...

6) Ground adjust trimmer: It works perfect - I can adjust it to the worst ground ever (I have few bags of detectors-nightmare: these are from one layer of soil near iron smelting furnace we found at excavations last year).

7) About those 4.7uF caps: I use polyester (100V) but are way too big for this board - so I orderd few multilayered-ceramics probably well enough for the job.

porkluvr thanks for non-blury shematic and corrected values. These are also corrected on parts-placement (componentzijde) picture kurtie100 posted. No mistakes also on PCB - we could just wish for such complete projects like this one.

As winding strength or size errors make a differents, you must do some adjustment for the 165 turns.
If you have to lift up the 12 cm coil to get a nulling : then you have to reduce the number of 12 cm turns.
If you have to move the 12 cm coil out of the center towards the 22 cm coil: then you have to add some 12 cm coil turns
Look at pin 7 from LF 353 for nice sinus signal, if not adjust the 15 nF cap.


___________________
watch movies online

[akademiker]

I soldered a 10k resistor in parallel to the disc pot and now the problems in Img1,3,6 are gone, but still aweful depth >

When I look at pin 7 of 101a I always get a squarewave from -2V to 2V, nulling just changes the phase and somehow its 12kHz, but it should be 15,5kHz according to RX and C6(just measured).

Edit: I switched RX End and Start and now I could null till a sinus about 0,5V. But I nulled while analyzing the Gate of TR4, so it looks like in http://www.geotech1.com/forums/showp...postcount=3896 and now i get around 23cm for an euro, but disc is not working and in all metal mode its "motorboating"

At the Gate of TR5 I get a full sinus wave, but it should be just a half wave, right?

[Mullihaka]

I had the same problem with the waveform of the U102a pin 1. In the original design of the TGS (not the light version) there's a 10k pot in parallel with the R18. I soldered a 10k resistor in parallel with the disc pot. After that, the disc pulse was neat.

Andy

[porkluvr]

If you will put a 10pf capacitor across U101b between pins 1 and 2 that should take care of the amplifier instability. It will have some effect on the DISC pot phase response but that effect should be relatively insignificant.

By the way, it you compare the Bandito and the TGS DISC phase shifters, you'll see they have the same topology except that Bandito uses a capacitor like I suggest.

You can possibly get by with a smaller value cap but 10pf should squash yer U101b oscillations dead.

[akademiker]

ok, sensitivity has increased a little bit, but still only 20cm for a silver coin and about 12cm for 1e :/
TX is running at 14,49kHz, according to scope, RX is tuned to 15,5kHz
6,6mH for RX and TX 6,2mH (I swear they were 6,5 and 6,2 without shielding :/ )

I attached some scope pics, the input and output of U101b seems wrong to me.
Trigger reference for all pics is tx signal.