TESORO GOLDEN SABRE

[Qiaozhi]

I thought that too at first, but:

A) Why only hysteresis on one channel, not other?

B) Output impedance (low) of LM308 shunts the feedback, has virtually no effect.

I have another idea what it was originally for, but too far out to mention now.

Thanks, cheers!

-SB

It's only required on one channel, because the outputs are wire-ored, And it makes sense to place the hysteresis on the ground balance channel, because the disc channel only acts to disable the output when ferrous targets are present.

[simonbaker]

Hi,
Qiaozhi is right: when coil is made right and you are around right phase between TX/RX you'll not get iron detection in disc mode, just all metal you'll detect it.

The geb trimpot is not for nulling iron: you MUST get it nulled by discriminator circuit when coil is made right.

The trimpot serves for what indicated : ground balance tuning

If you use a small ferrite rod you'll see that, when coil is made right way, you can null its effects at about middle position.

Problem is that interfere also with e.g. silver detection... so I experienced detuning a bit the trimpot to gain good silver detection again...but still ignoring almost the ferrite.

Iron is always rejected by good coil+discriminator circuit.

ALSO, NOTICE: when I wrote "IRON" I mean soft, pure iron... like in iron nails and the like... not steel alloys.

Sometimes people confuse soft iron with steel stuff... steels kinds have sometimes very different magnetic behaviour than soft iron things.
That's why you'll detect that thing.

An easy try: find a real iron nail stuff...5-7cm long you'll be sure it's just iron. Then find a 5cent (eur cent) coin.

They try to detect them in disc mode: on soft iron , if you made detector/coil good you'll get no signal at all. But you'll still detect the 5cents.

Why ? People think that 5cents are made of copper alloy... it isn't. It's just covered by that stuff, inside they are made of steel alloy core really detectable by MDs...

You can find other countries coins made of that metal alloy and all are detected easy, made actually of steel.

Kind regards,
Max

I think you may have solved it! I'm using steel to test, steel washer, bottle caps. I think maybe we cannot discriminate it because it is even past silver. That would explain it, iron vs. steel. I'll test.

Thanks, regards,

-SB

[simonbaker]

It's only required on one channel, because the outputs are wire-ored, And it makes sense to place the hysteresis on the ground balance channel, because the disc channel only acts to disable the output when ferrous targets are present.

AND for postive output, OR for negative. Positive makes audio beep on TGSL in current circuit -- so noise on either channel could make chatter. Not clear to me but I see the idea.

Regards,

-SB

[eclipse]

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

[Max]

I think this is correct. Since all targets cause a phase-shift to the left, then moving the pulse to the right is causing it to sample slightly negative.
How much does the sample pulse move when you've made the adjustment? Is it about 1us?

Hi,
thanks, that's the answer and question I expected. As always you provide really informative posts.

Now it's about clear to me.

The delay when shifting to the right is about 1.2 us.

I've made some calculations and cause my frequency is around 14.7KHz at oscillator I get that 1.2us are about 6.3°, in that case -6.3°, cause shift is to the right, so a bit more than expected -5°.

But now, thanks to you, I'm sure of what I'm doing... so can check it very careful to get -5° (and lose a bit of depth on silver but gain more stability on various harder soils).

I've read again yesterday the G. Payne's article... found it interesting (as always... read maybe 10 times already!) and in it I see he talks about the motion/non-motion settings... talking of +0.5° fixed setting for the motion MDs (to overcome various soils... with much sacrifice of sensitivity when soil phase is far from zero).

The advantage of manual geb control is fairly evident stuff...but also the drawback of user experience required to tune it properly.

I still think is better having manual geb control on TGS too, even if I mantain geb trimpot in test boards I've made, what do you think about ?

The real puzzle, expecially for few experienced users, on motion MDs about geb tuning is that you have to make the ear to that variations... and move coil at right speed...I experienced that in bandidoII, where manual say one must tune for geb in motion mode... but I found it's much easier do that in non-motion mode... cause you don't need bobbing up and down the coil so fast as in motion mode.

Any good hint to do it better in motion mode using manual geb pot without losing an arm ?

Kind regards,
Max

[eclipse]

Max place 2 circuit 2 point switch for GEB. When the switch is UP position you get Fixed ballance which uses the trimpot preset.
In Down position - Manual ballance, which ommits the trimpot on the board and lets you tune it with POT on the front panel - the way Musket Advantage and RH are done!
You just need few more holes in the board around the GEB pot so you can switch on/off the the trimmer there.

[Max]

Max place 2 circuit 2 point switch for GEB. When the switch is UP position you get Fixed ballance which uses the trimpot preset.
In Down position - Manual ballance, which ommits the trimpot on the board and lets you tune it with POT on the front panel - the way Musket Advantage and RH are done!
You just need few more holes in the board around the GEB pot so you can switch on/off the the trimmer there.

Hi,
yes, that's the idea. I think all the potential could be explored just having manual ground balance on panel... cause not every soil is good for the preset value.

I think, I'll do that way in next thing I will assemble.

Kind regards,
Max

[Qiaozhi]

I still think is better having manual geb control on TGS too, even if I mantain geb trimpot in test boards I've made, what do you think about ?

Whether you need an external GEB control, or not, really depends on your soil conditions. If the conditions are fairly consistent, then an internal pot will be ok.
Have you thought about attaching a meter to the output of the GEB sample gate to enable easier ground balancing? I think that some C-Scope detectors have this facility.

[Max]

Whether you need an external GEB control, or not, really depends on your soil conditions. If the conditions are fairly consistent, then an internal pot will be ok.
Have you thought about attaching a meter to the output of the GEB sample gate to enable easier ground balancing? I think that some C-Scope detectors have this facility.

Hi,
thanks for that idea... I had no thoughts about before. I saw something similar in old MDs but really was thinking at Tesoro's way of just hear the threshold rise/fall and totally forgot about that old way that could be really interesting feature in that kind of MDs.

I could also put inside something more accurate than a simple meter... like e.g. some op amp comparators...stage that will give e.g. visual informations about voltage there... kind of 2 red leds and one green.

When too negative one red will light up others down... when in right interval of say 2mV the green led will light up and others down... and last when too positive the other red led will light up...

Like with e.g. exposure meters... just if right light you'll see the green there!

seems interesting project for some spare time...

Kind regards,
Max

[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

Thanks for posting Eagle file.

Glad your coil nulling now. Can you tell us how you fixed problem nulling? Would be helpful information.

I am trying to understand importance of this phase of nulling residue signal. I would like to see comparison of real TGSL with one coil with wrong phase and one with "correct" phase, both nulled to same voltage.

My thinking is it only should matter for non-motion pinpoint mode.

The reason is: for motion mode, the nulling residue should just make a constant voltage after the JFet detector (filtered by capacitor).

Each target has it's own signal which is added or subtracted. Motion detector responds to difference, ignores constant nulling residue.

Why should it matter whether nulling residue voltage is tiny negative or tiny positive because only target signal passes through bandpass filter?

But proof is in the pudding -- would like to see actual tests. So please save those bad coils!!!

Regards,
-SB

(just upgraded to Windows Vista -- smileys all dancing around now, whoa!)

[simonbaker]

I think you may have solved it! I'm using steel to test, steel washer, bottle caps. I think maybe we cannot discriminate it because it is even past silver. That would explain it, iron vs. steel. I'll test.

Thanks, regards,

-SB

I tried normal iron nail, and it discriminated correctly. (By the way, coil much more sensitive to nail when perpendicular to straight edge of D coil).

I also tried same steel washer, etc. with my Tesoro Compadre, and it also sounds like a target (not discriminated), so I think TGSL working same as Compadre.

Now I think maybe a notch filter would be really useful to have, even if just to get rid of the steel. My measurements show steel quite a bit past silver in phase.

Cheers,

-SB

[Max]

I tried normal iron nail, and it discriminated correctly. (By the way, coil much more sensitive to nail when perpendicular to straight edge of D coil).

I also tried same steel washer, etc. with my Tesoro Compadre, and it also sounds like a target (not discriminated), so I think TGSL working same as Compadre.

Now I think maybe a notch filter would be really useful to have, even if just to get rid of the steel. My measurements show steel quite a bit past silver in phase.

Cheers,

-SB

Hi,
indeed it is. If you look at Jack Gifford's patent about tesoro's discriminator circuit you'll see it actually treat steel bottle caps as regular target... that could be avoided using disc knob (understanding it's steel before digging) but actually really far in phase from pure, soft iron.

That's the truth about iron disc: soft iron is easy rejected by disc circuit... while steel isn't and is a task for the user do that or dig it anyway in case of dubts.

Today it's a problem... many steel washers and screws around... also steel nails are a big waste of time... not to talk of horseshoes etc etc steel is everywhere....today

Sure, in more advanced machines VID informations solve that issue. Problem is that many times, expecially at depth, VID stuff is unreliable... and you'll end up digging every target to be sure don't miss the good stuff.

Kind regards,
Max

[Qiaozhi]

(just upgraded to Windows Vista -- smileys all dancing around now, whoa!)

Are you sure that was an upgrade?

[simonbaker]

Hi,
indeed it is. If you look at Jack Gifford's patent about tesoro's discriminator circuit you'll see it actually treat steel bottle caps as regular target... that could be avoided using disc knob (understanding it's steel before digging) but actually really far in phase from pure, soft iron.

That's the truth about iron disc: soft iron is easy rejected by disc circuit... while steel isn't and is a task for the user do that or dig it anyway in case of dubts.

Today it's a problem... many steel washers and screws around... also steel nails are a big waste of time... not to talk of horseshoes etc etc steel is everywhere....today

Sure, in more advanced machines VID informations solve that issue. Problem is that many times, expecially at depth, VID stuff is unreliable... and you'll end up digging every target to be sure don't miss the good stuff.

Kind regards,
Max

I just did additional test with Compadre (5.75 inch coil). I'm reporting so I don't leave bad information.

If turn discrimination all way max on Compadre, silver clad quarter still beeps, but steel washer mostly disappears. Very old silver-half dollar (not clad, mostly silver) has very weak signal.

This is not quite in agreement with my tests I did with my TGSL circuit, because I measure steel washer phase as greater from TX signal than silver clad quarter.

(I measure phase to right of TX signal; not think of it as left shift from null signal).

But I measured these phases very close to coil.

This is very useful to know about steel and iron. Now with Compadre if I thumb the disc knob and if it shows quarter, I can go further and if it disappears, maybe not quarter, maybe steel.

I play today with TGSL circuit, and steel washer now act a little differently -- maybe depends on whether neighbors turn on vacuum cleaner -- anyway, better discriminated. Maybe I had GB at one end.

As usual, lot's of playing needed to get good understanding of TGSL pots and performance.

Cheers,

-SB

[Fred]

Are you sure that was an upgrade?

Yes, the machine is upgraded now: it has more power over the user