TESORO GOLDEN SABRE

[simonbaker]

This circuit uploaded in this thread at the past
And again .

Looking back again at this latest posted schematic on page http://thunting.com/geotech/forums/s...12692&page=117

Final LM358 has 12 volt supply instead of 8v -- is that intended?

Other new addition is R55 1M resistor and switch SW2 labeled "Audio" -- is that proven a good addition?

(BTW: Even though takes space, each time someone builds TGS, good to post schematic so we know which one and can discuss and compare.)

Cheers,

-SB

[simonbaker]

12 Volts is 4V less than normal, so you will surely loose some depth cos of that. Are you using zener diod 4v3 or lower than that?
Also what are the supply voltage? I get +8V and - 7V
12-13" is not bad result at all, some of us could not start that good with pcb#1 so ...

Yes, 12-13 with sens not at max is a good detector, find good stuff with it as is. If make better, icing on cake!

Oscillator voltage depends directly on zener voltage and Vgs-cutoff of JFet. (Right now I have 10v p-p.) More zener volts and/or more Vgs-cutoff = more oscillator voltage. You can get distortion though -- but does it matter? One way to increase voltage is put diodes such as LED in series with zener, make volt drop higher. Of course, proof is in field if makes deeper detection. Or substitute JFet with greater Vgs-cutoff.

Regards,

-SB

[simonbaker]

Good morning all,
I hope you all do not mind me jumping in, I have been following this project with great interest for a while now, and finally got the bug to build Ivconics TGSL version 2 weeks ago. I have been out of the electronics hobby for about 20 years, so I am quite a bit quite a bit rusty at it I see I have quite a bit to learn! I do have over 25 years experience detecting here in the States. So far, all of my problems have been centered around the coil. I wound a 11" DD, 100 turns TX, 103 turns RX. I am measuring 12V P-P and 14.7 Khz at TX with O-Scope. Aluminum tape used for shielding. My initial air-test depth results are below without the audio boost mod, with the detector at a slight chatter:

US Penny – 12”
US Nickel – 13”
US Dime – 11”
US Quarter – 13”


All of my interference is electrical in nature (my workshop is in the attic of my home) and due to the fact that the coil is not secure. Any little vibration at the coil makes the detector go nuts!!! Once I finish tuning and securing the coil, will test outside. I know the figures above will only improve. For those that have gotten the circuit to where it is now, my hat is off to you, great work

Mike

Would you kindly post that schematic as attachment or provide a link to the thread page where you got it? Always confusing what's what in such a long thread.

Cheers!

-SB

[pulltabmike]

Hi,
not bad for a start.

"...Any little vibration at the coil makes the detector go nuts!!!..."

This is usually happen when cable is not suitable or not wired up correctly in search head or at detector. Other case is when GEB trimmer is not adjusted properly. To check this you can use ferrite rod and see if detection on it occurs. If yes than adjust GEB trimm softly to stop detection on ferrite, just to hear some rare "cracks" when rod is 2-3" away from coil surface. Doesn't matter if this done in All Metal or Disc Mode, in both ways you can adjust it. In case of Disc mode, keep Disc pot at "1"...
OK, in case you can not "reject" ferrite rod by adjusting GEB trimmer, than coil is not nulled well.
But first recheck cable wirements. You have some draw on these pages how to wire up that correctly. I posted it some time ago...dont remember on which page.
Wish you success, regards!

Thanks Ivconic,

Ordered a length of Belden 8273 to use as coil cable. Should be here tomorrow. Since it has 2 drain leads, I was planning on hooking the TX shielding to one, and RX shielding to other and connect to ground in the box. Or do you think this is overkill? Original cable used was a scrap piece I had off of one of my Minelabs.

Mike

[pulltabmike]

hi pulltabmike....
I will make TGSL 1265 latest version.did you use 0.25mm wire?
Regards....

I used 30 AWG coated wire (0.28mm Wire) that I bought through Amazon.com.

Mike

[pulltabmike]

12 Volts is 4V less than normal, so you will surely loose some depth cos of that. Are you using zener diod 4v3 or lower than that?
Also what are the supply voltage? I get +8V and - 7V
12-13" is not bad result at all, some of us could not start that good with pcb#1 so ...

Hi Eclipse,

It could be my scope, will double check once I am finished the new board I am building. I used a 4v3 zener diode. I am reading app. +7.8V and -6.3V. Using power supply set at 12V to power board.

Thanks,

Mike

[pulltabmike]

Hi,
yes, you have to fix the coils cause vibrations will be detected easy.

In a part of my house I have used in past to test TGS/TGSL even my steps on the floor were detected... not to talk of heavy vehicles etc... any vibration detected like it was a seismic sensor!

Now I test in better conditions so I have not often that problems but sure it's always a good idea having good fixing at coils.

Anyway, I think your results are good enough to invest more time in critical tuning... on soil the tgs is amazing if not too minerals.

Kind regards,
Max

Hi Max,

I was pulling my hair out when nulling the coil, every footstep downstairs was knocking it out Plan on sending my wife shopping when I get around to fine-tuning it!

Mike

[pulltabmike]

Would you kindly post that schematic as attachment or provide a link to the thread page where you got it? Always confusing what's what in such a long thread.

Cheers!

-SB

Here you go SB Only mods I did to board was to add attachment points for the wiring to the pots.

Mike

[ivconic]

Thanks Ivconic,

Ordered a length of Belden 8273 to use as coil cable. Should be here tomorrow. Since it has 2 drain leads, I was planning on hooking the TX shielding to one, and RX shielding to other and connect to ground in the box. Or do you think this is overkill? Original cable used was a scrap piece I had off of one of my Minelabs.

Mike

Worth of trying. I used once 2 separate coaxials (simillar to Minelab's) and it worked. Had extra job to readjust GEB cose cable type and it wirements do affects phase in some cases strongly. I think Belden would do the job just fine. Please inform us when test it.

[ivconic]

Yes, 12-13 with sens not at max is a good detector, find good stuff with it as is. If make better, icing on cake!

Oscillator voltage depends directly on zener voltage and Vgs-cutoff of JFet. (Right now I have 10v p-p.) More zener volts and/or more Vgs-cutoff = more oscillator voltage. You can get distortion though -- but does it matter? One way to increase voltage is put diodes such as LED in series with zener, make volt drop higher. Of course, proof is in field if makes deeper detection. Or substitute JFet with greater Vgs-cutoff.

Regards,

-SB

Strange? I omitted whole fet part from my last few TGS's and it is working the same. Also get 16vpp the same as was in the past.
I think fet part with zener is just sort of "fuse" there and in normal conditions do not affect signal amplitude at all. It is inactive all the time. Fet is "opened" and actually 2N2907 base is connected via 47K to ground.

[ivconic]

Hi Max,

I was pulling my hair out when nulling the coil, every footstep downstairs was knocking it out Plan on sending my wife shopping when I get around to fine-tuning it!

Mike

Guess what? Today i got mad due impossibillity to null one coil!?
I spent all day trying to balance it without success. Finally i muss coil and stamped madly on it jumping and swearing. Than made another coil and again had a lot of problems to null that too?? Finally i recured the fact that i DO have scope now!! (poor me..... i totally forgot that recently got scope - used to work without it so long time).
So connected pin 7. of LF353 on scope and saw pretty ugly oscillogramm! Not a sinus, not a square...but something very strange!? After 15 minutes i discovered micro junction on brand new coil connector!?!?! Damn! Damn! Damn! I destroyed first coil and lost all day just for that! Damn local supplier!
So when junction removed, nulling was easilly performed just in 10 minutes....sheeeesh!!!
Today i learned another lesson! Huh...life is difficult from time to time!

[simonbaker]

Strange? I omitted whole fet part from my last few TGS's and it is working the same. Also get 16vpp the same as was in the past.
I think fet part with zener is just sort of "fuse" there and in normal conditions do not affect signal amplitude at all. It is inactive all the time. Fet is "opened" and actually 2N2907 base is connected via 47K to ground.

I always wondered if that JFet really helped performance. I feel purpose is to operate oscillator more in linear region of transistor for less distortion (with less voltage), but who cares about distortion? Your tests are the truth, must not matter much.

However, JFet definitely affects my oscillator voltage (makes it smaller compared to grounding 47k). Depends on JFet Vgss-cutoff though -- maybe yours is on all the time, so shorting not change anything! Might as well bypass it then!

Regards,

-SB

[simonbaker]

Here you go SB Only mods I did to board was to add attachment points for the wiring to the pots.

Mike

Thanks! Looks like you use infamous "Gift Pack" circuitry.

Note: schematic and PCB not match exactly -- schematic shows two 4.7k resistors on outputs of LM393 (U106). However, not on PCB. Just one of those mysteries...I am only one who cares though...it works fine apparently...

-SB

[simonbaker]

Sorry for the delay, im attaching now the eagle file. Its made with Eagle 5.
Don't remember free or professional version, if I did it with prof, there is a big chance that you won't be able to open it. Check for errors, use it as is
I found the problem causing that I was unable to null the coil properly.
And next thing in the menu: changing the phase shift between Rx and Tx signals seems almost impossible just using the method of moving the two coils. The thing is I am now able to adjust the amplitude having 5mV/Div on the scope and Its hard to see even the peaks in the voltage, less than 1mVpp for sure! How much exactly I don't know perhaps around 0.1-0.2Vpp.
BUT: I can't adjust phase in this case. I can do that measuring on the output of LF353, but this will automaticly disable the good ballance achieved!
So the dilemma now is ways to achive phase shifting, not using Rx and Tx:

1. Using metal pieces, What type: Al, Cu, Fe... Drawbacks of this method? I know it's used by DIY-ers not by famous manifacturers (mineleb, tesoro) this must have a reason.
2. Using different values of resistors in the Rx preamp part. I've seen circuits which you can change resistor's values in Rx part to achieve phase shift
3. Others??

Regards

Hi Eclipse -

My job is to go crazy over different versions of TGSL schematics...

I notice some differences in your schematic from others. You have R41, R42 4k7 resistors on outputs of T1018 comparators IC7. Ivconic PCB and many of his schematics don't have them. Are they on your PCB?

Also, your final op amp driving audio (IC8B) has different bias to inverting input, just a 30k resistor to ground. That is different from all schematics I've seen. Is that on your PCB also?

Otherwise, looks like Gift Pack schematic with 555 astable audio enhancement.

But if those differences on your PCB, maybe perform different from Ivconic's?

Regards,

-SB

[eclipse]

Hi SB,
I took ivconics board and redisigned it. RH audio for test, visual low batt,
monostable (all those blocks are manually connected but onboard).
Adding ground plane took out 1/2 of the jumpers, also some traces were optimized. Added 1K resistor and I made the 2x100K into one 220K.
All capacitors were replaced with other larger footprint (otherwise there is no space for them). Replaced for BF245.
Otherwise everything is the same as the schematic.

I think i have failure, maybe board mistake or pcb manifacturing deffect or both. I had problems with getting it work good, after all I trashed it for now, took all valued components out and these days I'll assemble new standard board. When I get it working good (with chatters'n stuff) I'll go back to see what's wrong with that design.
Regards