TD3X ( pi )

[DOOLEY]

thank you Thomas,

I had never seen that before.

audio websites have any previously discussed adding lots of capacitance
to whichever side is your output side,

not sure how to implement the solution you have shown in a dc coupled stage,
but worthy of consideration.

[Thomas]

Here is something I came across that might be workable?

[DOOLEY]

hello all,

its just a "standard" Pi,
doesn't discriminate,
doesn't eliminate red brick or mineralization any more than any other Pi.
as far as im aware.

just built something slightly different and thought I would share.

2 stage pre-amp instead of single.

dual op-amp arrangement to minus off the earth field.

and,
rather the "normal" capacitor and resistor for motion operation I
used sample and hold for the reference voltage,

the idea was for the final stage to disconnect the sample and hold from updating
during target response so that the voltage in the hold capacitors remained the same ready
for the next detection,
therefore allowing for non motion operation.

wasn't 100% successful as I replied to 6666 earlier,
unfortunately,
4066's tend to have a little voltage surge when they open,
this sometimes alters the voltage on the sample and hold capacitors so unfortunately
the final detection stage remains "on" after the target has passed.

however,
lowering sensitivity doesn't solve that problem,
but,
the threshold remains above the extra voltage added to the sample and hold
capacitors by the 4066.

would be nice if there was a drop in replacement for a 4066 that didn't have a "click".
wondering if the old 4016's would have been a better choice,
they may do the same,
not sure.

[daverave]

very interesting detector and much food for thought.

[Finderskeepers]

Great work!

[Orbit]

I do not understand whose detector do you Dooleys or Ivconic ? Is this detector eliminates...stronger mineralization red brick I do not believe ?!

[DOOLEY]

hello 6666.

ah yes,
the 4093 chip is powered from the +8v rail and the earth rail.
this doesn't show on the schematic due to the program I used to draw it,
(circuit wizard)

some of the chips have "hidden power"
usually +5v.
can be changed on the program to any voltage,
but still doesn't show on the schematic.

yes,
VR5 on the lower earth field cancel TL062 ( IC3B)
is a 1k multi turn preset .
the upper TL062 ( IC3A )
has a 470 ohm added to its 47k ,
so that VR5 can go " above and below " to zero out earth field balance.

since making this project I have had chance to fully evaluate its operation
on beaches whilst away on holls.

when in the "non motion" mode every now and then it "latches" on to a full bleep ,
and zero has to be pressed.
since found out this is a problem with the 4066 chip.........

when they open a tiny "surge" or "click" is passed on to the storage capacitors,
this is documented on many audio websites about the problem.

poss a different method should have been used there,
not sure what though.

motion mode is very reliable ,
fast or slow,
non motion I now only use for pinpointing.

[6666]

earth field cancelling is something I saw on a post way back from sacho ( Bulgaria )

Found some time to check out your creation, would you mind expanding the description of this method a little bit, thanks.
How did you power the 4093's ?
Is VR5 1K ?

[DOOLEY]

ok,
below is the corrected schematic of the timing,

all sheets have been checked and re-checked for errors,
and all are fine,
what you see is what's in my final built 100% working unit.



the difference between the 2 schematics was an overlooked missing link
between pins 4 and 8 on the first 555.

if anyone has any questions about what does what,
or any particular part of the schematics please feel free to ask.

[6666]

Hello 6666,

Yes,
I thought of having a go at putting it all on
One sheet for everyone to follow,
Just not got one done.


Luckily professional diagram and pcb on it's
Way courtesy of of that kind fellow ivconic.

Single sheets would be fine with updates.

[DOOLEY]

hello WM6,

sorry about that,
I just wrote and didn't think about clarity that way.

no,
no discrimination,
same as any other "standard" Pi detector.

when I said about the "double wobble" I was talking about
the partial double bleep that Pi's do (and some IB COILS) when they pass
over either nails or screws,
and rings,
depending on orientation.

and I think the variable pitch makes that effect easier to hear.

so no,
no ferrous / non-ferrous discrimination ( I wish ) lol.

just the ability to hear nails and rings more clearly.....

[WM6]

Yes, nothing without great PCB-maestro designer ivconic.

Dooley, you wrote pretty slangish to me - non native and weak English speaker.
Can you explain this your statement:

"did this so the "double wobble" of rings,
yeah,
and nails can be much more easily heard."

Does this mean that we have here PI capable to some sort of audio-distinguish between Ferro and Non-Ferrous targets?

[DOOLEY]

Hello 6666,

Yes,
I thought of having a go at putting it all on
One sheet for everyone to follow,
Just not got one done.


Luckily professional diagram and pcb on it's
Way courtesy of of that kind fellow ivconic.

[6666]

Dooley it would be good practice to publish a corrected schematic with a date on it, that way everybody has the up to date info, and they may not understand english, just a suggestion.

[DOOLEY]

just a quick update,

can't believe I overlooked this,

only when ivconic pointed it out to me I realized !!!

on the 1st 555, pin 8 is not connected to +8v like pin 4 is,
error happened when I moved over the 555 to the right to gain some space,
and "the program" deleted the link between pins 4 and 8,
sorry about that.

have checked and re checked the diagrams and all else appears fine.

silly mistakes eh, and I missed it.