Delta Pulse - Take 2

[sunita.pradhan]

OR is it better to connect a DC to DC buck converter ?

[sunita.pradhan]

Can we use voltage dividers (using resistors) across 12v power supplies +ve &-ve to supply power (6 v) to an additional LM386 amplifier circuit on delta pulse.
If yes where should we place these resistors ?
Sorry !! i have a very little knowledge on electronics..

[kt315]

Hello Anatoly,

both boards works fine and I experimenting with coils. * But I have one question,
I search a box for the pcb, which have you taken ?

----
i suggest this one 200*175*70mm

https://www.aliexpress.com/item/4000...archweb201603_

[Vadim18]

Oh, now i understand.
Thanks for explanation.

[kt315]

you show my o-scope pic... yes, that is mine... but one men in Greece ASKED ME to RETUNE DP board on lowest FIRST SAMPLE DELAY
and 300 Hz frequency. while i was categorically against any retuning. then he had turned up south cunning...
he paid for board... and told again about the retuning -! i warned him that then i do not bring any burden for future unstability -!
so you just took the pic from a context that you do not mention.
BTW he got this unstability and asked me "to solve the trouble".

[Vadim18]

Hi Anatoliy!
Maybe you mentioned some other DP circuit with modifications? Yes DP will be more usable with first sample greater than 40uS.
In my circuit i have 22-100 uS range.

[kt315]

and work with Delay in the middle (>=45uS)
---
minimal FIRST SAMPLE DELAY in DP is 40us. it is not middle.
pleasure

[Vadim18]

Hi to all.
From my experience.
If anybody want to use DP for big targets, say twice more big than rusty nails, and work with Delay in the middle (>=45uS) of position - no LF357 are needed, just use jellybean lf356, tl071, or even lf355.
Such broadband amplifier like lf357 is retribution for power simlicity, not for sensitivity and will add only unusable noise and treshold instability.
But, if main target for DP - coins, small targets, than you must hunt for lf357 treashure first.
Otherwise, just leave LF357 for Elon, if you don't need them. let them fly to space...
Good luck.

[sunita.pradhan]

Thanks Qiaozhi & KT315 for your inputs !!

[kt315]

DP is a deeper and works with long FIRST SAMPLE DELAY 40us minimum value.
in reality i set 110-120, that is clipping small ferrous targets out, just as a garbage.
if you re-tune the sch on short FIRST SAMPLE DELAY you have to remember (REMEMBER)
that you must retune the damping resistor more preciasely - just go in hammerhead, bara, surfmaster etc topics
where this matter is crushingteeth chewed everyday time.

[Qiaozhi]

Question !!! Why a higher value damping resistor has good response to small objects initially... but performance degrades after sometimes. In my case of spiral COIL(335uH), 4 OHMs has very good response to small gold with quiet a distance for sometime but gradually performance reduces with time..and need to retune it again.

As I've said before concerning correct damping resistor values, slight underdamping can (in some cases) provide some extra sensitivity compared to critical damping, but the result is an increase in instability. In your case, the instability probably occurs because of component tolerance changes due to temperature.

[sunita.pradhan]

Question !!! Why a higher value damping resistor has good response to small objects initially... but performance degrades after sometimes. In my case of spiral COIL(335uH), 4 OHMs has very good response to small gold with quiet a distance for sometime but gradually performance reduces with time..and need to retune it again.

[kt315]

not so actuel for Delta Pulse. why? looking the pic.

[surfdetector]

Thanks for the tip buddy. actually the damping resistor must not be correct as there is no adjustment for this coil.

I did a video on making the damping resistor jig here:

https://youtu.be/CrJ5tFFmWyo

[ivconic]

No sweat. Glad to contribute when see enthusiasm and good work.
...
As for so many "knobs" on front panel... well...
It is nice to have them all on front panel when testing and on workbench, in educational purposes.
But on real site in real searching you'll see how distracting those can be.
Itching you all the time to try slightly different setup on each of those.