TESORO GOLDEN SABRE

[satdaveuk]

dont worry, I use C version too and it works great.
I also tried B version but didnt see any changes.

Cheers mate, nice to here good tideings from time to time

[simonbaker]

Here I am presenting the final version. I cleaned things up a bit and tried to clarify a few points that members had asked about. In particular, I added a few of Simon's plots that show the frequency response of some of the filter sections.

Don

It is a great overview. Maybe it should be added to Qiaozhi's sticky thread on the TGSL with Ivconic's info?

-SB

[dfbowers]

It is a great overview. Maybe it should be added to Qiaozhi's sticky thread on the TGSL with Ivconic's info?

-SB

Still need a part 3! Troubleshooting.

Then 200 level, with all the equations and circuit analysis..

[Dennis the Mennis]

Filter in practice : Spectrum Analyzer

I think I used to understand this stuff around 30 years ago - maybe not -- but this is my current "understanding":

U103 is basically just a slightly peculiar bandpass filter - peculiar because it has unity gain at zero and infinite frequencies (rather than zero gain) with a nice fat gain (36 db) at the center frequency of about 11 Hz. (Yes, capacitor C14 is a crucial player in the filter band -- it is not just a shock absorber -- the value is critical in shaping the filter.)

The unity gain means that the output exactly tracks (output equals non-inverting input) any DC bias voltage (by nature of the negative feedback loop). It also exactly tracks high frequencies. Frequencies around 11 Hz are amplified greatly and so become relatively more important, thus the low-bandpass nature.

So, whatever DC bias appears at the non-inverting input will also be present in the output. This is not a "feature" I think, just an artifact that is tolerated because the next filter stage (LM308 ) removes the DC bias and rolls off the high frequencies. The Synchronous Detector (SD) "summing" capacitors C12 and C15 also roll off the high frequencies.

I believe it is the "bandpass" nature of the overall filter (removal of DC bias) that makes the TGSL a "motion detector" (i.e. if you leave the coil over the target, the signal will die out).

Those DC biases that appear at the non-inverting inputs of U103 are due to our "null" signal passing through the SD and accumulating on capacitors C12 and C15. They will be different for the DISC and GB channels because of the different sync pulse phases. But ultimately those DC biases are simply ignored -- their main significance, I feel, is that it means we have to choose a "null" signal phase that does not forward bias the JFets in the SD and screw up the works.

So bottom line is I just see U103 as a bandpass filter stage with an unfortunate DC gain of 1 that is a tolerated tradeoff for the advantage of using the non-inverting input as a high impedance input (to be easy on the SD).

-SB

For anyone's interest :

Here some graphs of a spectrum analyzer in practice ( averages are shown )


U103 Vin vs Vout ( 190 Hz) :





U103 Vout vs U104 Vout ( 190 Hz ):





U103 Vout vs U104 Vout ( 6 kHz ):




kind regards ,

Dennis the Mennis

[dfbowers]

Now all the previous boards have gone, I have just taken delivery of some new ones, based on the TGSL-EDU design by Eduardo, and very sexy they are too, black with immersion gold (well it is Golden Sabre)

Hopefully these are 100% correct.
It would be nice to have a matching schematic and "idiots" guide, I will start a new thread TGSL-EDU, and post details of these boards, if anyone can help populate the thread with useful info , scope pics, coil help etc.. it would be a great help to members

regards

Silverdog

I finished TGSL#4 tonight.. This one with the complete kit from Silverdog. The parts selection is good! I was testing Euros in the 40cm range with excellent stability, so this one is a little hotter than my previous builds with Ivconics version.

One note.. The GB pot will tune opposite from Ivconics version. It drove me absolutely nuts until I figured it out!!! You must start in the fully clockwise position in the AM mode and tune counter clockwise until ferrite slugs are rejected. Otherwise, U.S. quarters and small silver will be rejected and you will be scratching your head.

Also, Silverdog.. double check your ICs that you are shipping as I was missing one of the LM393s and had an extra LM358. Don't send me a replacement though as I have extras.

Good job!
Don

[simonbaker]

For anyone's interest :

Here some graphs of a spectrum analyzer in practice ( averages are shown )


U103 Vin vs Vout ( 190 Hz) :


[ATTACH]15591[/ATTACH]


U103 Vout vs U104 Vout ( 190 Hz ):


[ATTACH]15593[/ATTACH]


U103 Vout vs U104 Vout ( 6 kHz ):

[ATTACH]15592[/ATTACH]


kind regards ,

Dennis the Mennis

Hi DtM!

Those are interesting graphs, but they don't make sense to me.

Can you describe exactly how you made the measurements, the equipment, any connections to your TGS?

Could you also make a similar spectral analysis of a simple resistor network (such as a voltage divider) for a reference?

Let's see if we can get better agreement with LTSpice.

-SB

[simonbaker]

I finished TGSL#4 tonight.. This one with the complete kit from Silverdog. The parts selection is good! I was testing Euros in the 40cm range with excellent stability, so this one is a little hotter than my previous builds with Ivconics version.

One note.. The GB pot will tune opposite from Ivconics version. It drove me absolutely nuts until I figured it out!!! You must start in the fully clockwise position in the AM mode and tune counter clockwise until ferrite slugs are rejected. Otherwise, U.S. quarters and small silver will be rejected and you will be scratching your head.

Also, Silverdog.. double check your ICs that you are shipping as I was missing one of the LM393s and had an extra LM358. Don't send me a replacement though as I have extras.

Good job!
Don

One note.. The GB pot will tune opposite from Ivconics version. It drove me absolutely nuts until I figured it out!!! You must start in the fully clockwise position in the AM mode and tune counter clockwise until ferrite slugs are rejected. Otherwise, U.S. quarters and small silver will be rejected and you will be scratching your head.

Is that an onboard pot, or can we just switch wires to make it familiar?

Sounds like a nice model. It will be interesting to see how it compares with previous versions in real ground.

Did you find the resistors lay flat, or must they be mounted vertical in come cases?

-SB

P.S. If anyone has a complete schematic for the Silverdog/eduardo, can they post it?

[simonbaker]

Still need a part 3! Troubleshooting.

Then 200 level, with all the equations and circuit analysis..

Sounds great! If I can help let me know. (Probably can't resist putting in 2 cents on occasion anyway...)

Cheers,

-SB

[dfbowers]

Is that an onboard pot, or can we just switch wires to make it familiar?

Sounds like a nice model. It will be interesting to see how it compares with previous versions in real ground.

Did you find the resistors lay flat, or must they be mounted vertical in come cases?

-SB

P.S. If anyone has a complete schematic for the Silverdog/eduardo, can they post it?

I used the onboard pot. The problem is that in the AM mode there is a "range" where ferrite is rejected. It will be accepted on either side of that, and it must be set up on the correct "edge" of the null range, so you have to know what side you are on. When switching to the disc mode, quarters will be rejected on one side (CCW) and accepted on the other (CW) of the GB pot. The only other clue is that you will get a double or single beep with ferrite depending.. in the AM mode. If you GB in the DISC mode you will not notice this "feature"

With Ivconics version, the surface mount pot that I used tunes opposite.

Resistors mount fine. You must make sharp bends to fit in the holes, but no problems at all. The lead spacing for the polarized caps is a little wide but I can still fit them ok. They COULD be about 1mm further apart or use caps with narrower lead spacing. I can measure them and post. Again, not a problem.

Some of the holes have been enlarged as well so all external wires of about 20 gauge fit great now as well as the holes for the 7808.

I will post a revised schematic in the next few days and send a copy to Andy as well.

BTW. do you have an original schematic that I can modify or is the PDF locked? I have been doing screen captures in the past but resolution suffers a little that way.

Don

[simonbaker]

I used the onboard pot. The problem is that in the AM mode there is a "range" where ferrite is rejected. It will be accepted on either side of that, and it must be set up on the correct "edge" of the null range, so you have to know what side you are on. When switching to the disc mode, quarters will be rejected on one side (CCW) and accepted on the other (CW) of the GB pot. The only other clue is that you will get a double or single beep with ferrite depending.. in the AM mode. If you GB in the DISC mode you will not notice this "feature"

With Ivconics version, the surface mount pot that I used tunes opposite.

Resistors mount fine. You must make sharp bends to fit in the holes, but no problems at all. The lead spacing for the polarized caps is a little wide but I can still fit them ok. They COULD be about 1mm further apart or use caps with narrower lead spacing. I can measure them and post. Again, not a problem.

Some of the holes have been enlarged as well so all external wires of about 20 gauge fit great now as well as the holes for the 7808.

I will post a revised schematic in the next few days and send a copy to Andy as well.

BTW. do you have an original schematic that I can modify or is the PDF locked? I have been doing screen captures in the past but resolution suffers a little that way.

Don

Hi Don:

Attached is an ExpressSCH schematic, the one I drew for Qiaozhi's sticky "TGSL Complete Details" thread (http://www.geotech1.com/forums/showthread.php?t=15710).

You can modify it with the free ExpressSCH program which you can get here:
http://www.expresspcb.com/ExpressPCBHtm/Download.htm .

It's a pretty easy program to learn, basically just drag and drop, connect lines.

I have modded this schematic many times to create other versions. The mods I have made in other versions include:

1. dfbowers mod on the sensitivity control.
2. voltage divider to reduce ringing in the LF353 DISC driver. (unconventional)
3. simpler way to "tie off" the unused LM358 without extra resistors.

I'm not sure which schematic is closest to the silverdog/eduardo, but the mods were not major. I can send others if needed.

-SB

[dfbowers]

Simon,

Here U go.. I changed what I could find. I will PM Eduardo to see if he can double check me before sending the final to Andy (Silverdog).

Most notable, the 100nF bypass caps have been deleted and replaced with a single 100uF cap. I don't really like that idea but does not seem to cause any problems. The 100nF caps don't show on the original schematic anyway. They only show on the parts placement.

C14 and C17 have been replaced with 22uF caps
R29 and R31 have been replaced with 1m resistors
TR9 deleted
R55 and R52 changed to 100 ohms
C27 changed to 220uF
Added 5k6 resistor between base and emitter of TR3
100 ohm resistor added between TR2 emitter and speaker

BTW.. How did you export to a .pdf?

Don

[dfbowers]

Here is the bitmap file as well.

[dfbowers]

I checked with Eduardo.. Deleted R37 and added one label on bypass cap.
Don

[simonbaker]

I checked with Eduardo.. Deleted R37 and added one label on bypass cap.
Don

This is great, thanks!

I added your change history to the schematic notes and renamed it as Rev E.4, put credit to you for changes.

I noticed some new parts do not have an "Id". An "Id" is placed by right-clicking on the component and typing in the name that Eduardo gave the part, such as "R27" or "C54", etc.

I don't know if all the other part Ids still correspond to the names eduardo used on his PCB.

It is really useful to get the Ids correct, because this ".sch" file can be linked to an ExpressPCB layout file for anyone who wants to make an eduardo style layout with that program (cheapo self-flagellators like myself).

I wish I had made a version with Ivconic's bypass caps too. Not too late I suppose.

Regards,

-SB

[simonbaker]

LM358 tie off

Side note:

I notice on eduardo's schematic the unused LM358 is "tied off" using several resistors.

I looked into this and became convinced that you can tie off the op amp without needing resistors. See photos below for comparison.

However, I'm interested if others have opinion on this. It seems useful to simplify our PCBs if we can get rid of any unnecessary parts.

-SB