TESORO GOLDEN SABRE

[ivconic]

A bit better sketch

This is my usuall setup. You may notice that i am using 4-lead cable. It is acting excellent. I made over 30 devices so far using this setup.
Actually...no need for 4-lead cable here. 3-lead cable will do the job just fine. I am using 4-lead cose it is easy to obtain it in local shops, here.

[Max]

Actually, i was thinking to experiment with more complex filtering;
super cap and small choke.
Now, job is to accuratelly calculate choke for this filter... we have 3.5-7kHz (approx) spikes there.. So choke must cover that bandpass.
Hmmm.... i would not be offended much if somebody help here with choke calculations..!

Hi,
so I think you mean we need an LC low-pass at 3.5Khz cut-off, right ?

Anything above in frequency will be attenuated by 20db/decade constant slope, ok ?

If so... suppose your big capacitor is 47000uF (47milliFarads) you'll get from forumla of simple LC low-pass that frequency of cut-off is by:

F=1/2*pi*sqrt(L*C)

... so the sqrt(L*C) = 1/2*pi*F

then L= 1/(4*pi^2*F^2*C)

now F = 3.5Khz = 3500Hz

Then L= 1/(4*3.1416*3.1416*3500*3500*0.047) = 4.39E-08

Then L = 43.9nH (about) to get required cutoff.

Kind regards,
Max

[ivconic]

Hi,
so I think you mean we need an LC low-pass at 3.5Khz cut-off, right ?

Anything above in frequency will be attenuated by 20db/decade constant slope, ok ?

If so... suppose your big capacitor is 47000uF (47milliFarads) you'll get from forumla of simple LC low-pass that frequency of cut-off is by:

F=1/2*pi*sqrt(L*C)

... so the sqrt(L*C) = 1/2*pi*F

then L= 1/(4*pi^2*F^2*C)

now F = 3.5Khz = 3500Hz

Then L= 1/(4*3.1416*3.1416*3500*3500*0.047) = 4.39E-08

Then L = 43.9nH (about) to get required cutoff.

Kind regards,
Max

43.9nH !!! Sheeeesh!!! Where to find such small choke!?!?!

[ivconic]

Or....let's "humanize" choke value and use some other capacitance in formula, ok?

[simonbaker]

43.9nH !!! Sheeeesh!!! Where to find such small choke!?!?!

It should be fine to use bigger choke as long as resistance is very low. You only want to pass DC (zero frequency), so why not use bigger choke and make cutoff even lower?

Regards,

-SB

[Max]

43.9nH !!! Sheeeesh!!! Where to find such small choke!?!?!

Hi,
you just asked for the value... not where you could buy one!

Anyway... I think nH level inductors can be made about easy at home!

Do you remember the induction heating topic...?

Kind regards,
Max

[metaldetector107]

nulling

Dear Sir
thanks for replying me
i have made a test of nulling coil as you described for me
but i couldnot get less than 4.7mv
i spent half a day before it was easy to null as Ivconic way only few seconds
but honsely i belive in your way in nulling but dont tell Ivconic he gets angry very soon
lets see what i done i put 100k GB resistor on mid position
and put a -lead on body and
+lead on pin7 of LF353 is it right??
please if you dont mind explain for me i know you reported many times
just this time again please by the way the result was around 10cm for silver coin 1.7cm ..
Dear Qia the 100k GB is around 96k i tried to get exact value but i could not cuz of resistor tolarance

thanks alot

[metaldetector107]

equivalent

Dear Ivconic
what are the best replacement for 2n2222 and 2n2907
thanks in advance

[ivconic]

Dear Ivconic
what are the best replacement for 2n2222 and 2n2907
thanks in advance

Depends where? At what place? I am sure you are asking about TGS so...;
At chopper stage BC557 and BC547 works just fine. Also 2N3904 and 2N3906. BC327 and BC337 also...
At TX, instead 2N2907 you may use BC327. Between TX and 4024, instead 2N2222 any other Uni NPN will do the job just fine. It is just simple buffer. You may use BC546, BC547, BC548, BC337, 2N2904, S9014......etc...etc..

[metaldetector107]

Replacement

Dear Ivco
i have nothing more than TGSL i am dreaming of it everyday
yes of course because i am run out of 2n2222 and 2n2907
thanks
by the way i made your last TGSL PCB only but some caps values
are deffrent from the schematic example
on .lay there are many 0.1uf but on schematic only one any help

[ivconic]

It is true. I added many decoupling caps there to improve more S/N ratio on that pcb. And yes..indeed; that pcb is really the best so far!
Dont worry - just put those caps there and enjoy!

[simonbaker]

Dear Sir
thanks for replying me
i have made a test of nulling coil as you described for me
but i couldnot get less than 4.7mv
i spent half a day before it was easy to null as Ivconic way only few seconds
but honsely i belive in your way in nulling but dont tell Ivconic he gets angry very soon
lets see what i done i put 100k GB resistor on mid position
and put a -lead on body and
+lead on pin7 of LF353 is it right??
please if you dont mind explain for me i know you reported many times
just this time again please by the way the result was around 10cm for silver coin 1.7cm ..
Dear Qia the 100k GB is around 96k i tried to get exact value but i could not cuz of resistor tolarance

thanks alot

It is not easy to understand exactly what you are doing. GB resistor is not part of nulling procedure (I think).

and put a -lead on body and

Do you mean ground?

but i couldnot get less than 4.7mv

That voltage may be OK.

But please do this experiment. Try changing coil positions until you get the maximum distance for detection of coin. Then tell us what the distance is and what the voltage at pin 7 is.

- Are you using oscilliscope or voltmeter?

- Do you have a digital camera? I would like to see pictures of your coils, cable, PCB, and oscilloscope images.

Don't give up. It takes patience and experiments. Just ask Ivconic.

Regards,

-SB

[Qiaozhi]

Dear Sir
thanks for replying me
i have made a test of nulling coil as you described for me
but i couldnot get less than 4.7mv
i spent half a day before it was easy to null as Ivconic way only few seconds
but honsely i belive in your way in nulling but dont tell Ivconic he gets angry very soon
lets see what i done i put 100k GB resistor on mid position
and put a -lead on body and
+lead on pin7 of LF353 is it right??
please if you dont mind explain for me i know you reported many times
just this time again please by the way the result was around 10cm for silver coin 1.7cm ..
Dear Qia the 100k GB is around 96k i tried to get exact value but i could not cuz of resistor tolarance

thanks alot

OK - I see you've posted the same message here that you sent in your PM.

Therefore I'll also post my reply here, so that others can see the answer:

----------------------------------------------------------------------

No - you are measuring the signal in the wrong place. There are 2 JFETs in the design, labeled J107. The lower one is located in the GEB channel, and you must measure at the source pin of this transistor. i.e. across C12 (0.22uF).
But ... first move the coils together until you get close to the null point, when measured at the output of the pre-amp U101a. Then continue increasing the overlap of the coils until the voltage at the source pin of TR5 reaches zero. You do not have to be really accurate with this, as you can adjust the GEB control to compensate.
Next, if you re-measure the voltage at the output of the pre-amp, it will not be zero. This is normal. Tesoro coils have a residual voltage of about 15mV, which results in around 600mV to 700mV at the pre-amp output.
If the discrimination rejects non-ferrous instead of ferrous, then flip over the RX coil connections and start again.

[metaldetector107]

SHIELD

hi all again
i asked Max about the shield inside TV coax cable to use instead of
kitchen alaminum foil becus it strong and easy to tighten it not like
alaminum foil which is so weak so u cant tighen it...
Max said TV cable shiel does effect on performance
IN % please caus i am tired with alaminum foil i dont like my coils cous of it?
any help
best regards

[metaldetector107]

TGSL

Dear Ivco Max Qiaozh

i asked Max about the shield inside TV coax cable to use instead of
kitchen alaminum foil becus it strong and easy to tighten it not like
alaminum foil which is so weak so u cant tighen it...
Max said TV cable shiel does effect on performance?
IN % please caus i am tired with alaminum foil i dont like my coils cous of it?
another thing capacitor and resistor tolarence i usually test for exact value before putting on PCB does tolarence is important?
does tolarence chamges when the circuit is closed i mean any different when the circuit is ON or OFF?
any help
best regards