IDX-PRO+VDI

[jlsilicon]

Anybody have thoughts on using the Lt1115 for U1 in place of the Op177 ?
It has very low noise like 1nV ...

Or the Lm4562 - 3nV with Slew = 20V/usec

[jlsilicon]

Also, ... thoughts on using the Lt1115 for U1 in place of the Op177 ( ne5534 ) ?
It has very low noise like 1nV with slew=10V/usec ...

Or the Lm4562 - Noise = 3nV with Slew = 20V/usec

( While the Op177 - Noise=120nV , Slew = 0.3V/usec )

[jlsilicon]

More into understanding the possibilities:

Can I modify C37 from 100nF , to maybe 200nF or 300nF (maybe with a Switch) to change the TX Frequency ?

Or maybe add a Fine-tune Potentiometer there (maybe the R10 - 2.7K to a 2.2K res + 4.7K Pot) ... ?

- for adjustable Frequencies ...
Maybe a Dual Frequency Coin and Gold Metal Detector.

[jlsilicon]

http://www.geotech1.com/forums/showt...752#post218752

Is this (the previous nexus article) to suggest that a particularly wound Coil can only support 1 (and only 1) Best central resonant Frequency ?
- no matter the Voltage supplied or Parallel Capacitor or series Resistor ?

... How about a Coil with multiple Winding-# Connection Leads - for Multiple (Switchable) Frequencies ?
- Obviously it would need switchable matching Capacitors ... (just a little improvisation needed) ...

Such as 2 addtional Taps for each Coil:

TX: 35turn 0.587uH 1uF 6.5KHz
0> @ 0t = + 0t
+> @ 5t = + 5t
+> @ 15t = + 10t
35> @ 35t = + 20t
=> 5t (17KHz) , 10t (12KHz) , 15t (9.9KHz) , 20t (8.6KHz) , 30t (7KHz) , 35t (6.5KHz)

RX: 270turn 35.6mH 33nF 6.5KHz
0> @ 0t = + 0t
+> @ 38.5t = + 38.5t
+> @ 116t = + 77t
35> @ 270t = + 154t
=> 38.5t , 77t , 116t , 154t , 231t , 270t

- And, calculated Switchable Caps for each Coil.

[CDI]

About frequency, i tried Eduardo's combination of caps for 12 Khz:
330n for TX
From 7 to 10n for RX stage
Has much better response and higher depth for smaller coins, and discrimination is quite better.

[jlsilicon]

Great !
- Can you give me a Link or # to Eduardo's suggestion ?
- Thanks.

[jlsilicon]

Okay,

Reading back around: #826,#842,#846, #1355, #1656, #2039,#2041, ...

I found suggestions for TX/RX of:
* 8KHz/11.5KHz
* 11.6KHz/8.5KHz
* 7.5KHz/15.5KHz
* 13KHz/10KHz
* 18K/..

Is this saying that all that I need to adjust is the Coil Caps ?
- none of the TX/RX pcb circuitry needs to be changed also ?

-

02-28-2014, 08:09 PM #2216
golfnut

Hi Barry, for tweaking the freq - I first simulated how the phase shifters work at 6.5kHz is spice.

Then put my 12kHz freq in the model and it wasnt that much different so I had confidence to ham up a test.

I made a smaller L Tx coil with 0.3mm and tuned it with the appropraiate cap to give a clean looking sinus,
and it was about 12.5k this is a useful all round number
- it will see this small silver and small gold but still get some depth on bronze and artifacts, all in most soils...

Low freq machines up to 6k see chunky items well.

Freqs over 15k tend to see small stuff well.

When you get to about 18k up, they see larger coins etc not quite so well. Rules of thumb from my limited experience.

If you want a bit of both go for something in middle 12.5k was just what I had
and it sees small aincient silver hammereds at 0.6gram or a lead gun powder measure or brass fitting from a black bess!.

For all boxes ticked we could try a dual freq machine!

-

... Golfnut - do you have any other instructions for this ?

[jlsilicon]

ok - found your earlier suggestions ...
- thanks golfnut !

[basellafe]

Can i use tl074 eqeivalent of lf347 or there is a problem with use

[CDI]

Can i use tl074 eqeivalent of lf347 or there is a problem with use

Yes, u can without problem. Maybe u will get a little bit less sensitivity and chater using TL074, but it will work. LM324 work also.

[Koala]

I guess you pumped 12 volt's directly. I tried this method once, but everything what i reached with this is maybe 2 - 3 against 8 volt's.

Upping the Tx voltage has only a marginal increase in depth but has a marginal adverse affect in amongst the trash. The current Tx power is a good compromise for depth, trash and battery life.


I can see the benefits for air testing or very quite fields

[CDI]

Upping the Tx voltage has only a marginal increase in depth but has a marginal adverse affect in amongst the trash. The current Tx power is a good compromise for depth, trash and battery life.


I can see the benefits for air testing or very quite fields

How much voltage did u drived to TX stage?

[Koala]

How much voltage did u drived to TX stage?

I tried the golfnut mod of supple the Tx supply via 12 volts


Peak to peak goes from 16V to 20V.

No noticeable depth increase. No easy to test as you don't get exactly the same each time you test. Slightly different threshold, ground balance, discrimination or ground conditions all affect the result. I would say within testing errors

I have a penny buried in my lawn. With enough discrimination to exclude small iron its an iffy signal with my IDX running both TX's

However its an easy target with my Bandido with 12 volts peak to peak and a smaller coil.

[CDI]

I tried the golfnut mod of supple the Tx supply via 12 volts


Peak to peak goes from 16V to 20V.

No noticeable depth increase. No easy to test as you don't get exactly the same each time you test. Slightly different threshold, ground balance, discrimination or ground conditions all affect the result. I would say within testing errors

I have a penny buried in my lawn. With enough discrimination to exclude small iron its an iffy signal with my IDX running both TX's

However its an easy target with my Bandido with 12 volts peak to peak and a smaller coil.

Thank's Koala for answer. U didn't tell how much inches is buried penny...
Can u please post lay file for Bandido that u maked?
Ofcourse in tgsl/bandido thread.

[Koala]

Thank's Koala for answer. U didn't tell how much inches is buried penny...
Can u please post lay file for Bandido that u maked?
Ofcourse in tgsl/bandido thread.

Its a pre decimal penny that's badly corroded 10" down with a bit of grass on top of that. (about half its original thickness) a bit of iron about 12" away

Both the Bandido with 5.75" coil and IDX with "10 will pick it up quite easy. However with the IDX set with the same discrimination as the Bandido it only gives a slight crack that would not be a dig signal.


http://www.geotech1.com/forums/showt...ito-Info-Build

If I was to start again I might chose to build the Eldorado. Just been asked to find a horseshoe. The bandido does not go to 0 discrimination. Not a big problem as the all metal mode is great especially the no motion