Chance Pi problem....¿¿¿????

[baum7154]

Winding Spider coil

The winding of this coil is accomplished by starting in one of the slots and then placing the wire in the third slot clockwise on the opposite side of the ring. Continue clockwise with the third opposite slot until you make five complete turns around the ring and you will see that you are going to lay your wire in the next slot parallel with the prior winding in that slot. You do not want any parallel windings in the slots. To avoid this go back to your last slot where the wires crossed pependicular to each other and jog forward from there just one more slot. Then continue winding into the third slot on the opposite side for five more turns around the ring. Once again you will notice that you must jog one slot to avoid laying wires parallel to each other in the slot. They must always cross each other in the slots. Continue this until you have the requisite number of turns.

I used 26AWG enameled wire in the coil I wound. With the thin enamel insulation I'm sure the capacitance is significantly greater than it would be with teflon insulated wire. My next coil will be wound with 23AWG solid copper wire insulated with teflon. It is larger wire than I'd like but I have lots of it that I got for free by stripping out some CAT6 cable.

It took me a little while to understand what the Russian winding drawings were telling me but the pictures were truly worth a thousand words. I must be pretty close to a thousand words here already! Sorry for the long explanation.

Happy winding!

Dan

[satdaveuk]

Hi Dan
Dont say sorry because you been a great help, putting your instructions together with the files gives me a compleat picture of how to do it.
I got some cat6 although down to the last 15 meters, how long lenth do you need to make the coil to your spec? because its worth trying on my project.
Many thanks to your indepth experiments and results.

Regards
Dave

[6666]

Thanks for the extra info dan

[baum7154]

Winding spider coil

You are welcome!

If you are going to use the wire scavenged from CAT5 or 6 cable please make sure it is 'Plenum' rated cable. Plenum rated cable requires the use of Teflon insulation on the wires so that toxic gases are not produced in the building ventilation system. That is what I stripped out after researching the manufacturer specs. I can't guarantee that all other types of CAT 5 or 6 cable use Teflon insulation. I recently wrote about this in the Forums thread titled 'Teflon Wire' and described the process of stripping the wires from the cable.

Smaller gauge wire results in less capacitance too so it might be interesting to try using some of the 30AWG teflon insulated solid wire I see advertised on EBAY. It is a trade off of higher resistance using 30AWG for lower capacitance when compared to the 23AWG wire that I have. Since I already have the 23 AWG wire I'm going to wind a new coil with it. Will probably have to add a 2ohm series resistor due to the low resistance of the larger wire. I'm also going to widen out the coil form to about 1.25" to 1.50" because deeper slots are required to hold the larger wire gauge and the thicker Teflon insulation. I'm leaning toward the 1.50" width as it will allow the coil to be spread a bit further apart and reduce capacitance. Greater spread will also require a few more turns for a given inductance and more turns are good for sensitivity.

Regards,

Dan

[baum7154]

How much wire length?

Dave,

For an 8" spider coil of approximately 400uh I used about 85' of wire and trimmed it to spec. Your 15 meter length of CAT 5 will yield 49' lengths of wire. You could splice it in a convenient spot as you wind the wire on the form. I think 75' of wire on the form would get you in the range of 350uh. I don't think one splice would cause a problem do you?

Dan

[baum7154]

Teflon insulated wire

The following is my post from the COILS part of the Technology forum:

Cheap Teflon solid copper wire source
I have not seen this source for untinned solid copper Teflon wire listed anywhere on this forum. After seeing all kinds of silver plated stranded teflon wire on EBAY I recently stumbled upon CAT5 and CAT6 PLENUM RATED cable. This cable is typically composed of several twisted pairs of 23 or 24 awg plain copper wire and is usually Teflon insulated. The Superior Essex brand of 77-240-2B cable lists it's wire insulation as FEP, a Dupont designator for one of it's teflon products.

The downside of using this wire is that you have to strip the outer sheath and untwist the inner pairs from each other. The the cable does come with a nylon sheath stripper thread with the wires so stripping the sheath is not difficult. The inner core can be unwound with a cordless drill by clamping one end of the wire bundle to a table or vise and the other end pinched in the drill chuck. Gently pull the bundle taut and set the chuck to unwind the bundle and you will eventually have 4 sets of twisted pairs colored Blue, Orange, Green, and Brown.

Once again you can unwind each of these twisted pairs using the cordless drill. In the end you will have 8 each 23awg teflon insulated solid copper wires. If you want to straighten the slight twisting ripple from the wires you can weave and pull them through a set of 4 to 6 nails clamped in a vise jaw and set about a 1/2 inch apart. They are woven through the nails much the same as a skier goes through slalom gates.

A 75' piece of this cable will yield about 600' of this wire.

Have fun!

Dan

[satdaveuk]

Dave,

For an 8" spider coil of approximately 400uh I used about 85' of wire and trimmed it to spec. Your 15 meter length of CAT 5 will yield 49' lengths of wire. You could splice it in a convenient spot as you wind the wire on the form. I think 75' of wire on the form would get you in the range of 350uh. I don't think one splice would cause a problem do you?

Dan

When im in the workshop tomorow will check if its teflon and to the spec as you stated, if it is then as you say will do the one join, after all it is in experimental stages.
You know Dan i know coaxal cables inside out due to my trade, but never realized theres different branded grades of cat 6, the only thing i got to be careful about when using for internal networking installations is that its LSF like coaxal distribution which means low smoke and fumes, which is incase of fire giveing off toxic fumes, but never progressed to find out what material difference actually was, just know its more exspensive.
With coax runs im always using 75ohm and work out the db losses per 100 meters and add or devide from that gives me the spec of cable im going to install.
When im feeding say 2-3 blocks of apartments at long distances from one source these days its easer and cheaper to use fiber optic then end user distribution with coax.
Maybe in the fucture there will be a place for fiber optic within metal detectors from coil to control assembly because things like capacitance, and EMI do not exsist, its brilliant stuff I can run thousands of meters without any loss at all unlike the traditional coaxal cable where you need launch amps, through amps to keep the signals going and of course every time you introduce another ampilfier into the system your increasing noise figures so then filters etc come into play.

All the best
Dave

[bernte_one]

hello

can anybody post a chance shematic here
especially the pin connection from chance to lcd
i have 1602A lcd it shown only blue light but no characters

i think connection ist wrong

many thanks

[joop]

Do you have chance.pdf, the schematic is on the first page. Top image: PIC connections, BOTTOM LCD connections.

[bernte_one]

ah ok many thanks

i take a clother look on the pcb (was not build from me)

there was a missing wire link under 1000uF cap und the contrast pot has a broken wire

unit works now (lcd and option menue) but has constant tone with two tested coils

seems that chance only works with the basket type coil (but this is curious)

all other pi units i have work also with other coils

i have to test other coils and will check the rigt specs for damping resistor

regards and thanks for quick answer

[joop]

Hi Bernt,

play around with the guard interval in the menu. It will need a different setting if you don't use the basket coil.

[silverdog]

Hi Bernt,

play around with the guard interval in the menu. It will need a different setting if you don't use the basket coil.

This is very true, my chance with a mono coil needed the guard interval upped to around 35 before the beeping settled

[Firebox]

My chance PI

Hi,

here are some pictures from my Chance PI from silverdog. He is not ready yet, but i am working
I put the chance in a "russian case" for test

Regards

[baum7154]

Nice job on the Chance! What is the diameter of the coil you have? What distance are you able to detect various metals? Can you detect a 1cm X 1cm piece of aluminum foil?

The Guard Interval is an indirect indication of the speed of your coil, the lower the number the faster the coil. I have an 8" spider coil that operates at 19 on the Guard Interval and will continue to experiment with getting lower numbers on future builds. However this is generally only important for detecting small gold so if that is not your target it doesn't matter too much.

Regards

Dan

[georgi.g.zhelev]

http://www.youtube.com/watch?v=EUPfrlB5gZ8

CHANCE , VIDEO TEST.