TESORO GOLDEN SABRE

[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

[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]

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

[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]

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]

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

[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

[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

[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]

I think this feedback resistor provides some hysteresis for the comparator. i.e. it stops any spurious oscillations.
The diode/resistor combination forms a precision clamp circuit, to keep the output at a fixed value.

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.

"Clamping" (clipping) -- yes, but important? Wouldn't V+ be good too, just driver for audio?

I have another idea what they were originally for, but too far out to say now (probably wrong too. ).

Thanks, cheers!

-SB

[Qiaozhi]

I hate those chinees too.But they are everywhere!People buy this crap for a lot of money.Strange?
And those seben are everywhere.

If you stop to think for a moment ... you are also copying other people's work.

[amtech2005]

TESORO GOLDEN SABRE

Oh never mind my pc - nothing really important in it. Only dozen of trojans and few of S.Layout files...
What i suspect is that there are some buggy cameras in my workshop, behind my back!?
Yes i agree, God only knows what is phase shift at your coil Simon...???!
Make another one.
When phase shifted much out of proper angle, everything is possiblle. I had not experimented that way; to see all the possible side effects...
Usually it goes this way: ferrite,iron,thin silver,thin al foil..etc..etc.


Amtech if you want file, here it is... but seems you missunderstood me? I never traced and made copy of this nonsenced 3009..i only used its pcb shape and dimensions to draw TGSL...so if you looking for original 3009 trace...ha, i dont have it. Who need that crap anyway?

Thank-You Ivconic for the sprint file. I always am very interested in what american model's the chinese copy. I wanted to know if the md3009 was the fisher 1265 or 1266 ??? If we find and identify , identical circuits or clones and the performance / depth is not good , then the chinese must be making very bad and cheap quality search-coils . I have not seen anything new or great from china . They are not going to make good money on garbage . A company called Famous Trails based in california sells 3 or 4 chinese detectors , but are way over-priced for the quality and performance . The pictures I posted below , they are made in china and sold by a big u.s. distributor , they work good , but have a very high breakdown rate . Is it the quality of parts , or the programmable chips do not hold the memory very long ??? ....Maybe someday soon we will see a real "super detector" from China and very inexpensive , but it has not happened .......... not yet anyway !!!!................Eugene

[Qiaozhi]

When I do the detune I have instead something maybe 56 or 57Kohm , the trimpot screw is rotated to the left... I get a right shift of sample gate signal and so (cause it samples on positive edge , at zero crossing, of the signal) I get a slightly positive voltage as mean value... the 25-30mV I told you above.

Now... do you think it's something -5° when I do so ?

Kind 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?

[Max]

For real soil conditions the ground balance needs to be set slightly negative, somewhere between 0 and -5 degrees, but nulling the coil using the output of the ground channel sample gate is a good starting point. Then (as Max says) slightly adjust the GEB pot away from the ideal position.
George Payne has explained it quite well in this article ->
http://www.jb-ms.com/Baron/gb.htm

Hi,
yes, I read the article a number of times... It's really illuminating stuff...

What is not clear to me till now is about the small detune at geb trimpot required to get more sens to silver items.

When at initial point, trimpot at middle as explained, and find phase looking at minimum amplitude at gate output, I get exactly 50 kohm there at trimpot.

When I do the detune I have instead something maybe 56 or 57Kohm , the trimpot screw is rotated to the left... I get a right shift of sample gate signal and so (cause it samples on positive edge , at zero crossing, of the signal) I get a slightly positive voltage as mean value... the 25-30mV I told you above.

Now... do you think it's something -5° when I do so ?

Kind regards,
Max

[Qiaozhi]

Hi,
You mean pin7 lf353?

And Ivica you are rare bird but we are same blud.Smash it with the hammer!
)))
I hate those chinees too.But they are everywhere!People buy this crap for a lot of money.Strange?
And those seben are everywhere.

No - I mean the connection between TR5 (source pin), C12 and R28.
This is the output of the ground channel sample gate.