Silver Sabre Plus & PCB

[Leto]

Hi to all.

As told Silver Sabre is quite good detector.
It somewhat simpler than Golden Sabre but also easyer to use.
I'm working on PCB.. so if anyone know/sees any mistake in below drawing
please let me know...

[Leto]

Checking everything

Last time it was very usefull to show here drafting model of PCB...
...Ivconic spoted few mistakes immediatly.

[Leto]

...PCB

Board should look something like this .. one sided.

Better resolution layout comes when device will be tested.
* I count here on Ivconic as this PCB is his idea (.. and also painfull small dimensions).

[exciter]

hope it will work
Good luck. Will build it also, when its running

[Leto]

update..

Few minor errors on board, discovered while building the thing..

attached is corrected version in .dxf format

Sensitivity pot is now equipped with two resistors slots to choose:
*to ground
*to negative (Sean Goddard's mod)

hopefully tomorow I'll get the missing parts and see if it works.

[Leto]

pushing on...

Hi to all..

Finaly I placed everything on the board..
BAD RESULTS
only anoying sound from speaker I almost destroyed treshold pot turning it all around...
definately mistakes in the circuit drawing and I spoted one in battery check part of the circuit:
510k resistor paralleled with diode should probably go to - (not +)??
Anyway I disconnected this part of the circuit (I also prefer true voltmeter as battery indicator) and speaker stoped screaming .
Also circuit now works OK but with strange side-effects.
Disc is not working perfectly also there is some chatter from the speaker.
I wonder if there are other mistakes on circuit drawing..
I'll make another - better PCB so please disregard previous posts..

[Max]

Hi to all..

Finaly I placed everything on the board..
BAD RESULTS
only anoying sound from speaker I almost destroyed treshold pot turning it all around...
definately mistakes in the circuit drawing and I spoted one in battery check part of the circuit:
510k resistor paralleled with diode should probably go to - (not +)??
Anyway I disconnected this part of the circuit (I also prefer true voltmeter as battery indicator) and speaker stoped screaming .
Also circuit now works OK but with strange side-effects.
Disc is not working perfectly also there is some chatter from the speaker.
I wonder if there are other mistakes on circuit drawing..
I'll make another - better PCB so please disregard previous posts..

Hi Leto,
are you using all same components as in schematic ??? I've just looked at schematic and seems resonable, also if there could be some errors.
Have you used tis75 or another type ? It's obsolete now and hard to find...

About the continuos screaming could be the fet in the battery checker...have you checked pinout ? fets could have different pinouts from one manifacturer to another, also same part number (amazing thing)! solution: just find the right datasheet by manifacturer before using them.
Usually, manifacturers prints a logo near the part number.

To find datasheets faster (and for free) of same part from various industries, try this: http://www.datasheetarchive.com/

If disc isn't working any good problem could be more serious e.g. bad capacitors values in schematic...
But, if your fets are all the same and wrong connected you can't keep disc working any good too. Solving the battery checker problem could solve disc too ?

Best regards,
Max

[Leto]

SS Stranges...

Hi Max,

Thanks for insights.
I tried with BF245c and BF245a.
I used BF245c also as substitution for tis75 in Golden Sabre so I expect no problems with FETs as GS works flawless.
Attached part of the circuit (battery checker?) is identical in many tesoro circuits but in one respect -> resistor (510k) paralleled with diode is allways connected to - (negative)
Does this part of the circuit do something else than battery check - I do not know.
Have to make also better coil for this project, I used only two scrap coils in OO configuration to do the testing.

Real problem is that I'm really short on time these days.

[Max]

Hi Max,

Thanks for insights.
I tried with BF245c and BF245a.
I used BF245c also as substitution for tis75 in Golden Sabre so I expect no problems with FETs as GS works flawless.
Attached part of the circuit (battery checker?) is identical in many tesoro circuits but in one respect -> resistor (510k) paralleled with diode is allways connected to - (negative)
Does this part of the circuit do something else than battery check - I do not know.
Have to make also better coil for this project, I used only two scrap coils in OO configuration to do the testing.

Real problem is that I'm really short on time these days.

Hi Leto,
ok fets are then ok. Well, about this part of schematic here yes I think it's just to check battery status. When you switch on capacitor (tantalium 10u) needs charging, positive +Vb is at drain lead, and a variable voltage is on gate of fet. Now when the +vrail voltage (+5 volts) is too near +Vb (due e.g. battery discharged or during charge) the Vgd is low in absolute value (Vgd near to zero) and then the fet conducts current, so emitter of transistor is about at +Vb by the 1k resistor and transistor is in saturation thus resulting in a pull-up action on 2n2222 audio stage transistor. So you have sound cause negative transients on audio control line gives you a low frequency tone to show up.

When battery is good you have that +vrail and +vb are separated by a gap of many volts (ideally 4) and then, after capacitor charge, Vgd is negative enough for fet to be off (after pinch-off region -> hi-impedence state). This way when 10u charges the gap makes fet switch-off and then no pull-up action is now on base of 2n2222 transistor, thus resulting in no sound.

As in other designs, where tesoro used op. amp. for battery checker, all is related to the gap amplitude between +5rail and +vb, cause a low gap means a discharged battery connected...and results in bleeping sound or continuos and without abrupt stop of it.
Duration is always related to cap charge rate.

I think that, if you want, you can disconnect those parts without compromising work of other parts of the circuit.

Best regards,
Max

[Leto]

finally..

Great news:
Silver Sabre works perfectly...

Reason for prevous disc. problems: bad coil
I had peak amplitudes separated by 5Khz (I removed tuning caps after experimenting with Golden S. and completely forgot about it.)
I would never thougt that untuned coils can completely reverse discrimination as effect (picking only iron).

Max!
thanks for dissecting battery check part of the circuit - I appreciate such posts very much. True It seems that this parts can be ommited with no problems at all.

In few days I'll prepare new PCB with gnd planes around Rx part, maybe also better sound and few other tweaks.

P.S. any known params. for Tesoro SS+ coils? Please post them here.

[Max]

Great news:
Silver Sabre works perfectly...

Reason for prevous disc. problems: bad coil
I had peak amplitudes separated by 5Khz (I removed tuning caps after experimenting with Golden S. and completely forgot about it.)
I would never thougt that untuned coils can completely reverse discrimination as effect (picking only iron).

Max!
thanks for dissecting battery check part of the circuit - I appreciate such posts very much. True It seems that this parts can be ommited with no problems at all.

In few days I'll prepare new PCB with gnd planes around Rx part, maybe also better sound and few other tweaks.

P.S. any known params. for Tesoro SS+ coils? Please post them here.

Hi Leto,
congratulations ! Nice work on silver sabre, I'm really happy you have success with this project.
Keep going this way !

I think you could use the values for bandidoII umax.

Tesoro concentric
Rx 3,4 6.2mH 22 ohms
Tx 1,5 5.7mH 22 ohms

you could made spider as well.

For DD you could try:
RX 130 turns suitable former to get a 22cm halve
TX 120 turns idem
wire 0.30 mm (free of varnish)

then keep rx flat on bottom and tx over.

Best regards,
Max

[Leto]

Last view ..

Thanks Max.

Posted picture shows my Silver Sabre Plus with battery check circuit removed.
Parts will be salvaged for the new board I'm making - so this it's last view..
Maybe you can spot some dandruff - thats only because I was searching so hard with my head over the PCB for nonexistent mistakes .
Anybody trying to make this - be warned - do not use previos PCB files as the better one is on the way.

P.S. I recieved another PCB layout for SS+ from a friend same day as my sabre proved to be working
- shame it would spare me hours of using my head - bad luck

[exciter]

Nice work.
Looking forward to you new PCB´s

[Leto]

oscillators

question for more educated..

Probably all of you noticed two basic Tx oscillators types used in tesoro metal detectors. One one the left is the most basic form of Colpitts oscillator and it is used in SilverSabre and Bandido circuitry. The one on the right side is bit more complex and can be found in Eldorado, Golden & Royal Sabre, Inca,...

My question would be: what this resistor, capacitator, 4.3V zenner, diode and FET are for??

[Max]

question for more educated..

Probably all of you noticed two basic Tx oscillators types used in tesoro metal detectors. One one the left is the most basic form of Colpitts oscillator and it is used in SilverSabre and Bandido circuitry. The one on the right side is bit more complex and can be found in Eldorado, Golden & Royal Sabre, Inca,...

My question would be: what this resistor, capacitator, 4.3V zenner, diode and FET are for??

Hi Leto,
my idea, explained in another post some time ago, is that the fet is a feedback component here. I think that sometimes e.g. when a big iron mass is near the coil the oscillator could stop running so you'll lost the f/2 signal used to feed the 4024, then lose the -V rail voltage.
Not only.

I think that fet here serves as autoporalization circuitry to give the 2N2907 always correct polarization in correlation with also e.g. soil conditions (presence of iron oxides, mineralization).
Think e.g. at small movements during sweeping that put the coil at various height over the soil: if there is much mineralization there could be problems due to false signals cause of static polarization and gnd signal strenght.

I think that they realized that a static polarization scheme is not good for every condition or model... and they found an easy solution that way.

Think that more "critical" detectors use the complex scheme and (marketing intended) "recreational" ones use the simple.

For "critical" I mean e.g. GoldenSabre... a detector with gold nugget hunting in mind or Eldorado... a truly all-in-one machine.

The truth is that with one or another osc, most of the times, are all the other parts and right use that make all them good MDs.

Kind regards,
Max