igsl tgsl potentiometers wiring

[turbo1600]

hi, any body got a schematic on how to wire up the potentiometers used in the igsl tgsl. ?

thanks, mark k

[FatBob]

I have this but it's for the modified version;

[turbo1600]

I have this but it's for the modified version;

[ATTACH]35997[/ATTACH]

thanks !!!!! any idea on what the differances are ?
mk

[FatBob]

Well here's a schematic. He tied the two GEB's together and the 2 Volumes. And tweaked the
channels for less phase shift. I just got a board in the mail today so am looking at the docs on
this project;



I never saw a wiring diagram for the pots except the one I posted. I'll make one one of these days.

[Davor]

I'm dealing with other things now, but in some undefined future I'll unbundle the GEB channels and use one as an All metal discrimination reference, and the other as a GEB. With some further tweaking I expect IGSL to become a proper beach machine as well.

But so far this is it. Note that there is a pin swap necessary for the Fe channel to work properly. So far I did not work out a decent way to go about it. My device has pins in the air, and wires doing the swapping job. Not nice, but works properly.

[FatBob]

I found another thread with a pot wiring diagram;
http://www.geotech1.com/forums/showt...highlight=igsl

It's in Message #748

I'd be interested in a beach mod as most of my detecting is on the sunny Florida beaches!

[Davor]

Oh I remember. It was a spring break '93 in Miami. Almost toxic concentrations of pheromones.

You are lucky in a sense that there is not much iron there, if any at all. Easy workaround approach to GB at beaches would be to swap signal for audio processing (100k from GB channels) to go from Disc channels instead. If you do it with a DPDT switch, you may have a machine that works well on both dry land and a beach.
There is a small caveat though. When you use Disc as GB and GB as all metal reference, you need to have Disc phase adjusted to exactly salt water response, and not some arbitrary phase that helps you identify foil or pulltabs. Maybe the best way to go about it would be to use another switch that provides comparators with fixed phase that is tuned to salt in beach mode, and a freedom of choice in dry land mode.

[FatBob]

So something like this for the Poor Man's Beach mod?

[Davor]

No, you need to pick signal from Disc channels instead of GB channels. Look at R39 and R58 - they go from GB channels to become audio after being gated at discrimination comparators. You need to pick signal from Disc channels instead, and with the same set of 100k resistors. You may also put the same resistor in parallel with diodes in Disc channel so that tone is smoother.

[FatBob]

So something like this?



Then we can slide the Disc down away from salt?

I never really quite understood where salt was located as apposed to Ferrite
and why we are not concerned with the width of the samples so much.

We should be able to narrow the disc pulse to avoid salt right? (Or maybe we
need a notch to see good stuff on both sides of it)...

Oh here's a pic I found recently;

Salt is above iron. So somehow we need to use both disc's and set one below and one above salt....

[Davor]

Precisely, and that's exactly what you have when you apply a pin swap mode. It means the input pins at U4c and U7d must be swapped against the original IGSL.
The way you connected the Disc channels would work exclusively for beach conditions. So a proper mod would be a DPDT switch to chose between the two. Also the discrimination phase setup should be swapable, and fixed for beach. OK, you may keep them fixed, but in that case you lose the benefits of overlapped sound.
And it would still be a workaround.
Proper way to do it is to make a single GB channel with phase span ~90° to cover both dry land ferrites, and wet beach salts. And it must be supplied to an absolute value circuit to give meaningful response at any given phase. It would render mode switching unnecessary.

[Qiaozhi]

We should be able to narrow the disc pulse to avoid salt right?

Even if you set the DISC so that it rejects the signal from salt, you will still have a reaction from the GB channel. If the salt signal was consistent from one place to another, you could get rid of it by ground balancing. But the problem is that it's not. Effectively you have a ground signal that keeps changing.

[Davor]

I wanted to keep it simple, but I think the whole concept may need a little explanation.

With VLF IB detectors you have generally 2 phases of interest. IGSL is an amalgamation of two detectors so it has total 4 phases, but the concept is the same.
These phases control the switches that demodulate signal from Rx coil. When a signal is in phase with the switching phase, the demodulated value is positive. When in opposite phase it is negative, and a special case is when they are at precisely 90° where output is zero, regardless of signal strength.

GB is a channel that is aligned at precisely 90° against the offending ground response. In case of dry land with ferrite particles, the ground response is very close to the Tx phase, but at wet beaches it is 90° away, in between ferrous and non-ferrous targets.

For discrimination we use those 2 phases that are ~90° apart, in order to pass only the signals that are positive for all metals, and those that are positive for non-ferrous metals (in case of non-ferrous discrimination). Classic detectors use All metal reference also as a GB, which does not work on beaches. Problem is that in order to have correct discrimination, all metal reference must remain at ~90° against Tx.

Hence, we must have either a separate GB, or a swapable GB that alternatively uses one or the other discrimination phases for dry land or beach searching.