TGSL Experiments

[Dennis the Mennis]

Yeah, sometimes a PCB gets touchy and they are the devil to know why. I keep trying though.

Not sure which PCB you are using. Some TGSL PCBs had a long, snaking ground trace between the speaker ground and the battery ground. I think the silverdog pcb has a better, more direct, arrangement... anyway, you could try a jumper wire from the speaker ground to the battery ground (yes it is a ground loop, but worth a try) to see if you get less motorboating.

Also, of course the sensitivity pot can affect motorboating, especially if you have the "dfbowers mod" that gives more range to the sensitivity pot.

But sometimes it is something else and can be a mystery.

As for the "cannon ball" -- I was thinking maybe rig up a simple LM358 wideband amp, simple 2 resistors, etc. to amplify the signal on a little breadboard, maybe 100x gain, with big cap to take out DC bias from input. Fun stuff.

Keep up the good work, we'll see...

Cheers,

-SB

Hi Simon ,

I have the 'old' TGS pcb from Kurtie without any mods ( yet )
Whenver I'm around a ElectronicShop I'll buy the components needed for the test

See the next picture : this is the signal of both FET's with a 1 euro passing at about 3 cm ( Uc12 & Uc15 )

Couldn't hook the cannonball at the lightswitch

.










You also asked for a more detailed graph of a target signal at the LM308 output :








Hope this one will do ?

This a 1 Euro passing at about 10 cm .

kind regards ,

Danny

[simonbaker]

Hi Simon ,

I have the 'old' TGS pcb from Kurtie without any mods ( yet )
Whenver I'm around a ElectronicShop I'll buy the components needed for the test

See the next picture : this is the signal of both FET's with a 1 euro passing at about 3 cm ( Uc12 & Uc15 )

Couldn't hook the cannonball at the lightswitch


You also asked for a more detailed graph of a target signal at the LM308 output :

Hope this one will do ?

This a 1 Euro passing at about 10 cm .

kind regards ,

Danny

That is great, thanks!

Very interesting to see how far negative the signals at the JFets go -- I wonder if it would be the same at greater depths. I guess it might.

But it seems we will have a hard time knowing without some special filtering -- even with amplification, there will be too much noise to see unless we use your "cannon ball" approach.

Is there a smoothing filter that would not introduce significant dynamics into the signal but would bring out weak signals from the noise? Maybe...

-SB

[Jerry]

Threshold Control

I like having a background tone or noise of some kind when metal detecting. It lets me know that everything is working and it is possible to hear the tiniest of changes for potential targets. Ivconic touched on this several years ago when he added a threshold control to the TGSL but it never made it through to the final design. It appears again in the IGSL.

A couple years ago, I did the dfbowers mod for sensitivity. (see below) This worked but I was only able to advance the Sens control to about 6 or 7 before the detector became unstable.

The addition of the Threshold control in addition to dfbowers mod makes it possible to run the gain much high yet have a fairly stable detector.

The addition of the 100K pot and 200K resistor are from the Tesoro Lobo schematic
W.L. 6/90. Nothing really new here on my part, just copying ideas from others and seeing how they work.

You can work the Sens and Thres controls in tandom advance one reduce the other, etc.
I find that I gain several more inches of depth.

Jerry

[simonbaker]

I like having a background tone or noise of some kind when metal detecting. It lets me know that everything is working and it is possible to hear the tiniest of changes for potential targets. Ivconic touched on this several years ago when he added a threshold control to the TGSL but it never made it through to the final design. It appears again in the IGSL.

A couple years ago, I did the dfbowers mod for sensitivity. (see below) This worked but I was only able to advance the Sens control to about 6 or 7 before the detector became unstable.

The addition of the Threshold control in addition to dfbowers mod makes it possible to run the gain much high yet have a fairly stable detector.

The addition of the 100K pot and 200K resistor are from the Tesoro Lobo schematic
W.L. 6/90. Nothing really new here on my part, just copying ideas from others and seeing how they work.

You can work the Sens and Thres controls in tandom advance one reduce the other, etc.
I find that I gain several more inches of depth.

Jerry

Glad you got a chance to try it and report -- thanks! Something to put on my list of tinkering subjects...

Cheers,

-SB

[satdaveuk]

Thanks for that Jerry did that on my first build think it was ivonics that did it in the early days.
What id really like if you or someone here could work out a simple way of introducing non motion for pinpoint mode, it has its advantage in certain situations like the otherday i was finding the rest of 1940s MK1 Milliner granade which most was within a crater in sandunes, I ended up clearing up with the Whites DFX to find the very small peaces.

[der_fisherman]

Thanks for that Jerry did that on my first build think it was ivonics that did it in the early days.
What id really like if you or someone here could work out a simple way of introducing non motion for pinpoint mode, it has its advantage in certain situations like the otherday i was finding the rest of 1940s MK1 Milliner granade which most was within a crater in sandunes, I ended up clearing up with the Whites DFX to find the very small peaces.

Theoretically, you could add a small extra pcb with say the circuit of a VLF non movement MD and simply switch between them. The extra electronics will not weigh or cost much, adjusted to use the same battery and coil, a few extra pots, slightly out of the way (other side) on the box......
I hasten to add that I have never actually done this, but I do think that your idea is better than carrying a separate pin-pointer! I have enough with a spade, trowel and my bag of valuable finds!!!
Say the old EPE 549 for example. I made one years ago and it worked well....small PCB and only two controls, volume & sensitivity, it reacts to all metals as built.....though I made a slight adjustment to the coil so that I knew if it was iron/steel or non ferrous......
Regards
Andy

[simonbaker]

Thanks for that Jerry did that on my first build think it was ivonics that did it in the early days.
What id really like if you or someone here could work out a simple way of introducing non motion for pinpoint mode, it has its advantage in certain situations like the otherday i was finding the rest of 1940s MK1 Milliner granade which most was within a crater in sandunes, I ended up clearing up with the Whites DFX to find the very small peaces.

I think if you don't mind giving up a lot of depth, a pinpoint mode might be feasible. Good project anyway.

-SB

[satdaveuk]

Theoretically, you could add a small extra pcb with say the circuit of a VLF non movement MD and simply switch between them. The extra electronics will not weigh or cost much, adjusted to use the same battery and coil, a few extra pots, slightly out of the way (other side) on the box......
I hasten to add that I have never actually done this, but I do think that your idea is better than carrying a separate pin-pointer! I have enough with a spade, trowel and my bag of valuable finds!!!
Say the old EPE 549 for example. I made one years ago and it worked well....small PCB and only two controls, volume & sensitivity, it reacts to all metals as built.....though I made a slight adjustment to the coil so that I knew if it was iron/steel or non ferrous......
Regards
Andy

Hi andy and Simon
Certainly another avenue to look into but i was thinking more on the lines of introducing extra circuitry to what is already there and by doing that there should be know reason to loose depth, The dfx when triggered into pinpoint mode is one very powerful all metal none motion detector.
We need to look further into Tesro models or similar of that era that had pinpoint modes, there must be someone on here that can come up with a solution, if not ill try and do my homework on the subject.

Also matter of interest do you know if anyone actually fitted a working VDI to this model, I know ivonics did try with the IGSL but dont know how sucessful it was or wether he tryed on the TGSL.

Warm regards

[porkluvr]

I think if you don't mind giving up a lot of depth, a pinpoint mode might be feasible. Good project anyway.

-SB

Why should you be worried about giving up depth? I dunno, you might be right...

Anyway, Tesoro added a no-motion pinpoint/all-metal mode to the Royal Sabre whose similarity to the Golden is remarkable. It looks like it would be a simple matter to implement pinpoint for the TGSL using Royal Sabre as a template.

[Jerry]

Took me a while to find it but I remember pinpoint feature being discussed a few times in the past. http://www.geotech1.com/forums/showt...=12692&page=62
Start with post #1545 and read back and forth from there.

Jerry

[simonbaker]

Hi andy and Simon
Certainly another avenue to look into but i was thinking more on the lines of introducing extra circuitry to what is already there and by doing that there should be know reason to loose depth, The dfx when triggered into pinpoint mode is one very powerful all metal none motion detector.
We need to look further into Tesro models or similar of that era that had pinpoint modes, there must be someone on here that can come up with a solution, if not ill try and do my homework on the subject.

Also matter of interest do you know if anyone actually fitted a working VDI to this model, I know ivonics did try with the IGSL but dont know how sucessful it was or wether he tryed on the TGSL.

Warm regards

True pinpoint mode is tricky because I think you slowly drift out of calibration -- otherwise, we wouldn't need motion mode.

For the TGSL, the first thing I'd try would be a pseudo-pinpoint, where we extend the lower end of our bandpass filters almost to zero Hz -- by switching in really big capacitors at a couple of points. We'd pick up some low frequency noise, but maybe it would work as a reasonable pinpointer.

For true pinpoint, I would think you would need to cut some sensitivity to handle the inevitable drift of our null signal, etc.

But maybe there are some really clever ways to do it. I've seen circuits with what look like "bias reducer" feedback loops through op amps to the non-inverting inputs of the main filter op amps -- however, I think these still are not 100% true pinpoint modes, they still slowly adjust to changes.

I would think it would be hard to beat those pocket pinpointer devices, since their tiny search coils should really pinpoint the target.

-SB

[Davor]

There is a nice little pinpointer that Silverdog is toying with, Minimax-PP II and a video that is linked on a topic shows a motion detection properties.
I guess it is not the motion detection per se to be worrying about, but the time constant of it.

[ashefr10]

CHANGE C7 modified phasing 4 uS

hello , I changed the capacitor C7 10 pF to 5 pF on my to change my TGSL phase shift and so I went from 16 µSto 6.5 µS are what this is correct?

[porkluvr]

hello , I changed the capacitor C7 10 pF to 5 pF on my to change my TGSL phase shift and so I went from 16 µS to 6.5 µS are what this is correct?

That should be close enough.

If your rx signal advanced by 9.5us the best way to explain that is, because you had the wrong value of capacitor to start with. Instead of 10pF that was more like 100pF!

So, try it as is... or if you install a 10pF capacitor your signal delay should change by only about 1.4uS.

[ashefr10]

That should be close enough.

If your rx signal advanced by 9.5us the best way to explain that is, because you had the wrong value of capacitor to start with. Instead of 10pF that was more like 100pF!

So, try it as is... or if you install a 10pF capacitor your signal delay should change by only about 1.4uS.

NO, I did not get me wrong, I took the values in the nomenclature of the scheme and the value of 10 pF is present.