IDX-PRO+VDI

[eduardo1979]

The key to this project is our partner forum "elbombaci". I have the hex code, which is the "demo" version. I'm sorry, but is not in my power to give details on this project. "Elbombaci" has it all. Greetings.

[6666]

Thats a very interesting video thanks,
What happens when you place the coil on the ground and then wave the objects over the coil ?

[dfbowers]

Nice! Can you give us some details on your project? That certainly blows my Arduino project away!

[golfnut]

https://www.youtube.com/watch?v=m4JxYgdNRz0

Nice with clock guage..

s

[eduardo1979]

https://www.youtube.com/watch?v=m4JxYgdNRz0

[der_fisherman]

You are F*****G brilliant!!!!
Thanks for the excellent work and for sharing with us all.
Andy

[6666]

Amazingly enough, rubber contact cement can become conductive if enough graphite is mixed with it. (maybe someone can comment on the effectiveness of this practice, but I can demonstrate that it does work).

Great work Don
interesting about just rubbing the paper with graphite.
No need to doubt your results with the rubber glue.

I used to make rocket motor igniters useing a pair of wires
with the ends stripped and dunked in conductive glue, and allowed to dry.

That glue was made from ping pong balls (nitrocellulose ) dissolved in acetone
and then mixed with graphite, the dry resistance was only a couple of ohms,
you had to be quick with dunking the wires in the main pile of glue,
when the glue was fresh the end dry resistance of the igniter was only a couple of ohms.

BUT as the main pile of glue started to set and you continued to dunk the wires , then the "dry" resistance increased,
so you had to stop dunking when you could see the main pile of glue starting to set,
it made great igniters, been meaning to apply this home made conductive glue to some shielding
for a test one day, IE Mylar.

The ping pong balls have to be the right ones, (nitrocellulose ) not the plastic ones.

[eduardo1979]

Very good job Don. I have a stock coil (concentric) of 9.5 "and it works great. Here in Spain there are areas with highly mineralized land, land of red clay, and concentric coils barely detect a coin. Coils DD, compared to concentric defend themselves a little better in these conditions. Congratulations on your good work.

[dfbowers]

My project of the week..

http://www.youtube.com/watch?v=buU4h2QpgOw

I wanted to see how cheap I could build an 8" coplaner coil for IDX. Turns out, under $20.00! I did have to break out the vacuum forming machine. This was not an easy project compared to a DD coil as tuning was a little tricky between the Tx coil and the bucking coil.

Start with a sheet of 1/2 inch foam board from a craft store - It's "large cell" foam, that is somewhat brittle but also stiff.
It is cut into a donut shape to accept a spool for the Rx coil.
The Rx coil is wound on a homemade spool of cardboard with a foam center.
The foam "donut" is then glued to a sheet of stiff cardboard and the Rx spool is glued into the center.

The Tx coil is made on a separate former and held together with Cyan glue. Then this coil is simply glued into a channel cut into the foam. The bucking coil is wound opposite the direction of the Tx coil - directly on top of the Rx coil.
After tuning and nulling, the inner ring is filled with slow cure epoxy.

Rx coil - 3.25" - "about" 425t for 34 AWG wire (35 mH) wound counter clockwise + 33nF cap
Tx coil - 7.5" - 34t for 22 AWG wire (583uH) wound counter clockwise + 1 uF cap
Bucking coil - about 11 turns wound on top of Rx coil wound clockwise

For the best null, the hot end of the Tx coil must be connected to "Tx start" (P8 pin 1)
The grounded end of the Rx coil must be the wire closest to the bucking coil - " Rx end" (P8 pins 3 & 4).

For the tricky part - When the bucking coil is wound around the Rx coil opposite direction from the Tx coil, the frequency goes up by about 60Hz, so a turn or 2 will have to be added to the Tx coil to bring the frequency back down to 6.59kHz.After tuning and nulling, the inner ring is filled with slow cure epoxy.

For shielding, I used heavy gauge paper, covered with graphite powder from the hardware store. I just dumped some on the paper and rubbed it in until I got a conductive sheet of paper. The paper ended up with about 35k Ohms of resistance across the entire sheet yet is not detectable by the coil. A drain wire is then attached with masking tape and a bit of conductive glue made from a slurry of rubber contact cement and epoxy. Amazingly enough, rubber contact cement can become conductive if enough graphite is mixed with it. (maybe someone can comment on the effectiveness of this practice, but I can demonstrate that it does work).

For a cable, I just used Belden 8723.
Enjoy!
Don

[maxfly]

Hi all,
more simple questions. In the VDI schematic what is the purpose of pin 2 on PIC and what should the voltage be after r2? Would this affect readings?

Max

[maxfly]

I need Help with VDI adjustment!!!!


I have finally found an original Whites Blue Max 800 for IDX Pro with VDI. Everything is working fine with large coin detected at around 30cm, plroblem is that as a target gets closer to coil the VDI number creeps either up for low numbers or down for high signal with +45 being the most stable area. An AU 50c will start out at +26 and end up +45 when very close to coil. The Disc pot suffers a bit of creep but not like that! I though these problems would go away with original coil. VDI numbers start to show on screen at about half the distance that audio detection is made, is that normal?? I have scope ect for testing. nobody seems to have had this issue yet,

Thanks
Max

From what I have read the "Blue Max 800 Precision Scan" should work on the IDX Pro with VDI, Can anyone confirm this?
This coil came on a perfect condition Classic SL ID with LCD readout. Are there any alarm bells ringing to say this coil won't work correctly?

Max

[maxfly]

Ok, so I have checked all resistors values between U1 opamp to end of disc circuit and found some values I'm not sure of. Maybe someone could clarify. R57 seems abit low at 4.6k, would that matter? I have a 180k placed at R2, is that correct? Peak to peak voltage at U1 pin 6 is 17mv with no target and rises to 50mv with large nikel coin put right on coil, is that normal? Next I guess is to pull the caps in this circuit and test,

Any comments would be great,

Max

[Davor]

TGSL and IDX share the same illness: poor compressor. They both can become much better rigs with only a slight modification. I'll explain it in detail when I'm up to it. At the moment I'm in re-decoration business. My apartment needs it.

[golfnut]

I experienced it unfortunately.

I noticed the gain endstopping when scoping in XY one time - Rx chain compresses like mad with a tractor wheelnut and goes non linear - the phase dexterity is lost and signals beat their way to the comparator and sound off as would non ferrous.



I was toying with the idea of a gain control (AGC) to slash the gain of the front end with large iron signals.


The Preamp could have n gain taps with cmos switches to select R's for gain -controlled from an A/D post demod.

Similar to ..



S

[szucs_g]

i have the problem with large iron objects. The Disc cracks or give some plops, but my original Mi´nelab Musketeer have this problem too. So i belive this is ok ..

I experienced it unfortunately.