IDX-PRO+VDI

[dfbowers]

I received an Email from Mr SLopov containing the following text:
" ....Have received finished pcb for IDX (I dont have enough time right now to prepare my ow .n pcb) from a close friend.
And prepared 2 coils. One DD19cm and one DD27cm.
For DD19 I read with multimeter:
TX 0.568mH 5,7 Ohms and RX 25.8mH 70 Ohms (will tell you caps that I used and freq. in my next email).
And DD27: TX 0.973mH 7,1 Ohms and RX 8,4mH 22,2 Ohms
with this one I try to replicate quicksilver coil for CZ series.
So briefly. The smaller coil is with good depth and not good SENS and GB.
The DD27 is compensated with 470n+220n+15n+15n =720n? With those caps I read 6.5kHz from TX. Havent used oscilloscope so far. Only multimeter.
For RX I soldered 22n +10n+4n7=36,7n. With this setup I can get 1€ coin for app. 30cm in house. But if I mouve coin slow then sound is none or barely noticed. Also this is with sens at 90% and treshold at 90%. And device is getting random beeps .Maybe noise interfaces.
How to tune those coils right way?
I read your posts.You are the only person who try to explain those details to public. Thanks
http://www.geotech1.com/forums/showthread.php?t=17949
So please explain this:
What is coupling coefficient and how can I manipulate it in reality?Also where to connect this 6M8 resistor? between hot leads for TX and RX?"
Here is the first of my answers relating to design and adjustment of IDX:

INDUCTION BALANCE
Induction balance is the most important thing when we try to increase sensitivity of a metal detector.
Coupling coefficient k shows what part of magnetic field generated by TX coil L1 is coupled with RX coil L2 and induces AIR signal. It is calculated by formula k=M/sqrt(L1*L2) where M is mutual inductance, L1 and L2 are self-inductances of TX and RX coil. Note that always k<1 when we have separate TX and RX coils. Only at monoicoil (the worst principle for search head) we have k=1 because M=L, L1=L and L2=L where L is self-inductance.
M and k are proportional to AIR signal existing in input of RX. The sensitivity of a metal detector depends on gain of RX preamp. To increase the gain, we need minimal AIR&GND signal because it will saturate the preamp.
Induction balance means that k or M are minimal. That makes the AIR signal minimal.
We can adjust induction balance by:
1. Loop deformation. Attached image shows a piece of wood or plastic (pos. 1) which makes deformation of both coils.
2. Aditional turn or bucking winding. Attached image shows the wire lead (pos. 2) of coil which is shifted for fine adjustment of induction balance.
3. Small shifted cores shown as pos. 3 in the image. They are placed near to sensitive area of search head and can be made of ferrite, iron and aluminium.
4. Mutual resistance pos. 4. It is formed for example ly a 4M7 potentiometer and a 4M7 resistor.
5. Mutual capacitance 5 (shown as a trim capacitor).
To adjust induction balance, we should connect an oscope 9 to output of preamp 6. An 1kOhm resistor 8 is used to avoid capacitance load of preamp. A potentiometer 7 is connected in feedback path to adjust gain of preamp near to saturation.
I will describe the procedure for induction balancing after explanation of design and and adjustment of TX and RX tanks to resonance frequencies.
Will be continued.

Perfect! I always enjoy your enlightenment. Same concept that is used on Nautilus, except all adjustment are in the control box. Also, a little easier to accomplish correct phase feedback with a center-tapped TX coil since you can reference the ground better.

Question: For a small bucking winding, #2, it will be diffucult to shield this with a DD coil. Do you suppose this would be of concern? With CC coils, all is enclosed in a graphite shielded shell.
Don

[szucs_g]

Would be super nice if someone would check the connections vdi ....

Many greetings marc

Connecting the speakers good? Not the original points soldered?

[Schatztaucher]

I can not say ..... my circuit board is not yet ... am still in the coils .... but if you don's idx in the video to see and hear, everything seems to be ok .... the circuit board has its of silverdog ..... where the connectors for the speakers are the same

[szucs_g]

I can not say ..... my circuit board is not yet ... am still in the coils .... but if you don's idx in the video to see and hear, everything seems to be ok .... the circuit board has its of silverdog ..... where the connectors for the speakers are the same

De ez a kép nem a silverdog féle. Ez a módosított idx. OK. Látom, hogyan gondoltad.

[dekoratör]

http://www.deephaven.co.uk/lc.html

here is a nice simple little calculator for playing with coil values for this project

Capacitance:1000 nf

Inductance: 0.570 mh

Resonant Frequency:6.666 khz ()

[dfbowers]

Connecting the speakers good? Not the original points soldered?

Sorry, There is a mistake on the diagram. The speaker connection is obvious though, right behind P1.

Don

[szucs_g]

The SMD resistor R27, I changed. This makes it easier to position. I've seen here on the board that there is a version of IDX, where you have left it (R27).

Already completed the PCB, soldered everything. Comes the test. All have taken the IC. :-)

[szucs_g]

Sorry, There is a mistake on the diagram. The speaker connection is obvious though, right behind P1.

Don

The original circuit of the loudspeaker and ended in the headphone jack.

[mikebg]

Perfect! I always enjoy your enlightenment. Same concept that is used on Nautilus, except all adjustment are in the control box. Also, a little easier to accomplish correct phase feedback with a center-tapped TX coil since you can reference the ground better.

Question: For a small bucking winding, #2, it will be diffucult to shield this with a DD coil. Do you suppose this would be of concern? With CC coils, all is enclosed in a graphite shielded shell.
Don

Don, #2 is not a winding and even it is not a whole turn. It is the "cold" lead of a coil. I think you wont use for fine adjustment the "hot" leads of the TX and RX coil.

[Schatztaucher]

yes, now I get the error with the speaker and found ... I had not seen noticed

[Schatztaucher]

hi,
my tx coil is finished and looks great ...... unfortunately I had to have two coils rx throw in the garbage. Wire 0.15 is really not easy to wrap. I will dilute the third time the epoxy and install floating in my wrapping machine, in order to make a thin layer of glue ....

regards

[Schatztaucher]

what happens at the first switch on?

have my coils ready. have now all assembled to see what happens. First, nothing happens. Then I pushed the pin point, and a tone is heard. with the treshhold I can influence him. Perhaps I have soldered the pin point the wrong way on. I see in the next days. vdi display indicates correct. can detect my idx not yet .... I zeroed the coil still not right. But I think I'm on the right way.

question: what happens when you switch on when everything is wired correctly and the coils are set to zero? I can measure any voltages, eg connections to the coils or at other points, to see that everything is working properly?

king regards

[dekoratör]

Hi, I've finished pcb idx. but there are some problems. There are always a good depth and bring u5. When I wear very little depth. Threshold pot and does not work.
When inserting u 4, and no changes have drawn any time does not change a thing. pot and the sens does not work. I checked all solders. and parts are also okay. u4 and u5 lm393 LM358. helping
Thank you for
best regards ...

[detecto]

IDX-SMD PCB???

Does someone have SMD pcb in sprint layot?

[juice2839]

Question on the VDI

Hi all. I just started reading this Forum a couple days ago and now have read through it several times. Big thanks to you guys that have posted schematics and info. I ordered a pcb kit from Silverdog. I was planning to make the VDI pcb myself. I was looking at the schematic and it is using no Crystal? is the code setup to use the internal clock? Also has anyone made a nice clean guide to making search coils? Both types would be neat. I gleened enough info from the thread to built a coil I think. Thanks again for all the info. Also how does this detector compare with say a classic I,II or three? I was thinking about building one of the classic III's, but the schematic looks very close to this. Thanks