Super TGSL With H Bridge TX Diff RX Quad Sampling

[Silver Dollar]

No that's a built in decoupling cap the sockets came like that. Good to know not to worry about the noise.

I did remove a couple of germanium transistors from an old shortwave radio the other day. I wonder if their
worth anything on Ebay. A lot of the older chips aren't available anymore so are bringing big prices there.
I found some old A/D's and DAC's and checked the prices and I could get $100 for 4 of them!

[Silver Dollar]

Hmm, if we're not using that 3rd 4053 switch for salt maybe I can make a pinpoint mode with it.

Only one more opamp and voila! I'll have to draw something up...

[golfnut]

Hi Davor / SD I was looking at the schematic earlier and I see C23 on preamp - it looks a little odd there is that a typo? S

[Silver Dollar]

I found out what you were talking about. There was a change from the original preamp with the
quad addon to a new slightly different one see the images below;

I also included the most up to date schematic...

[Silver Dollar]

I decided to add pinpointer mode and tweaked the audio a little. Here's the schematic;

[Davor]

I'm afraid your tweak will make audio very binary, and IMHO that's not a very good idea.
Since you've put the slow channel, it would be very opportune to enable it's full potential, leave it connected to the GEB phase, but the discrimination "ferrite chanel" put to a separate fixed ferrite channel. It would make it a whole class better than the rest of the crowd. I can tweak the phase shifter to provide a ferrite channel, and also pre-shift the other two channels so that a whole contraption happily accepts different coils.

[Davor]

Can you put the .sch file so that I can add the changes to it?

[Silver Dollar]

Here you go...

[paku]

Nice project
this schematic hasbeen release or still under lab discussion

[Davor]

This is still in development.

[paku]

this is nice project bro keep it up

[Silver Dollar]

Unfortunately we are stopped for now as I am on a 5 week sabbatical with no access to my lab!

I am investigating some possible audio mods but cannot try them in hardware for a bit. Stay tuned!

[Davor]

No worries, I'm also kinda busy but I'll make my input soon.

At this moment I have something funny building up mentally, a kind of sniffing device with wide and narrow searching sides, all metal and ~30kHz operation. Cheap as chips and with almost no tuning at all. It is so very different than anything else ever built for metal detecting, and I have no idea will it sink or float. At this moment I'm pitching it for a pinpointer, but we'll see what happens next. Exclusively garden variety parts, and a very few of them.

[Silver Dollar]

Sounds interesting. I'm thinking higher frequencies are better.
Not sure why the big guys went down to 6.5 Khz? Maybe to avoid radiation laws?

All metal seems to be better as inadequate discrimination means you dig everything anyways.
Though I as at a beach with the wife and after 20 minutes of digging junk she was looking
for a way to discriminate!

I have a kids detector that works somewhat but I've been looking for something easy to replace
the circuitry with that will perform a bit better. This might just fit the bill!

[Davor]

Higher frequencies are better for poor conducting materials. Pont is that each material has a certain octave within which it gives the most displacement against the Tx, so such range is the best for such material. The exception are the thin foils of any metal, as they act as very poor conductors. Natural gold often comes in thin flakes, so naturally all gold seeking machines are operating at high frequencies or short delays in PI.
BFO-s also work better with high frequencies, but that's another story.

If you are after large ... ish chunks of metal, lower frequencies are beneficial. Coins and artefacts. Usually the best return and fun.