IDX-PRO+VDI

[jlsilicon]

Quick Notes on things that could be improved in design:

1) The Transmitter Oscillator is just a couple of Transistors with an Inductor. This means that Oscillation could be influenced by the Coil and so the Target. Even a little deviation reduces accuracy considering the Receiver is so sensitive. So, a crystal would be better to use. Or, the micro (if used) could supply the Osc.

2) We should use the Receiver Amplified Input (instead of reading both R and X (resistance and Reactance) after OpAmp filters) , and the Transmitter Osc input - directly to the Micro (Arduino, PIC, etc). So, remove the use of OpAmps to isolate the R and X signals. Because, the Osc Freq is only about 6.5KHz , while the Micros can read the Inputs in the 100KHz-1MHz ranges. Then, the R and X Values can be calculated by the Micro at its convenience. This would result in less circuitry and better accuracy.

[golfnut]

1) The Transmitter Oscillator is just a couple of Transistors with an Inductor. This means that Oscillation could be influenced by the Coil and so the Target. Even a little deviation reduces accuracy considering the Receiver is so sensitive. So, a crystal would be better to use. Or, the micro (if used) could supply the Osc.


The resonant aspect of the tx cct is just so efficient, as u get relatively large Tx currents, and field from top up current frowm tanl losses.

Yes the Tx phase gets kicked about and wont be the same amount oin the Rx tank, so I agree with you there



2) We should use the Receiver Amplified Input (instead of reading both R and X (resistance and Reactance) after OpAmp filters) , and the Transmitter Osc input - directly to the Micro (Arduino, PIC, etc). So, remove the use of OpAmps to isolate the R and X signals. Because, the Osc Freq is only about 6.5KHz , while the Micros can read the Inputs in the 100KHz-1MHz ranges. Then, the R and X Values can be calculated by the Micro at its convenience. This would result in less circuitry and better accuracy

If your saying dont mix down to an I.F. just grab the preamp out and process for phase info. I think some machines do this , mat be wrong tho

[ampirate]

I still can not understnd this Coil building and Inductance.
Shown here in the Blog:

  DD COIL 27cm=11in (yielding 9.25in dia each with 28in circ)
    TX=35 TURNS , 0.25in thick 
      0.70 Wire
      1uF PARALLEL CAPACITOR 
      Ind=0,587mH
    RX=270 TURNS , 0.1in thick 
      0,18 Wire
      33nF PARALLEL CAPACITOR
      Ind=36,5mH

Which seems to match the Coil Calculators on line
- that specify RX would be (as 9in diam coil, and 270 windings) as about 36mH.

I wound a new coil with awg35 (0.15mm) Wire, as a 9in diameter single coil
- which should bend into half of an 11in DD Coil.

But when I measured Inductance with my Meter (many times), it read as 47mH.
I then tested the Meter on a manufactured smd coil labeled as 471k = 470uH - which the meter read as 473uH
- quite close - so the meter seems accurate.

So, whats the problem ??

[Silver Dollar]

Well the inductance will change when you bend the circle into a "D" also
.15mm is not .18mm so your inductance will be off for that too...

[Koala]

Are you sure it's 9" pretty sure it's closer to 8"

Seem to remember using an old winding for a PI and from memory was 8.25"

you could draw the TGSL form on a piece of card and measure the edge with a piece of string

[ampirate]

Well the inductance will change when you bend the circle into a "D" also
.15mm is not .18mm so your inductance will be off for that too...

Well, bending it into a D - only resulted in minus of abour 3mH,
- so I needed to remove about 25 winds down to 245 winds - to give me down to 36.5mH
.. still don't understand why ...

[ampirate]

Are you sure it's 9" pretty sure it's closer to 8"
Seem to remember using an old winding for a PI and from memory was 8.25"
you could draw the TGSL form on a piece of card and measure the edge with a piece of string

I see ..

The Coil Calculator shows:
> 270T, 9.25in => Ind=35.3mH
> 270T, 8in => Ind=30.3mH

Well, that would explain it !
- Thanks.

[golfnut]

Also thinner wire will give more L

[Davor]

... only because it is packed more tightly.

[jlsilicon]

thanks guys

[seadoggy]

My new IDX pro board with pot in board.

[Koala]

My new IDX pro board with pot in board.

Nice, well done, lots of hard work.

Does it work well.

Not strictly necessary but I do like a multi turn for the ground balance.

Should be nice and easy to package

[seadoggy]

Nice, well done, lots of hard work.

Does it work well.

Not strictly necessary but I do like a multi turn for the ground balance.

Should be nice and easy to package

Thx alot Koala!,Work very very well,its is very stable.my old board is not stable like this with pot in board.This is my best IDX ever.

[ampirate]

If I am building this board from scratch,
- is there any specific type(s) needed for the Caps ?

[Koala]

If I am building this board from scratch,
- is there any specific type(s) needed for the Caps ?

Yes.

The more stable the capacitors the more stable and less drifting your detector will be

I used polyester for mine except for the polarized ones around the PSU and is fine

Two of the caps on the original Whites board were 1% can't remember which two they were see if I can look it up for you.