chance pi build

[woodbob123]

started my new kit from silverdog today Chance PI hit my first problem have a copy of board layout and bill of materials that come from a previous version. Can anyone show me the correct up to date layout and parts list please, Also is there a simple line drawing of the connections between board and display that i can follow. Thanks

[silverdog]

You can find the amendments on the authors website http://fandy.hut2.ru/Chance.htm

unfortunately he never updated the original schematic

[satdaveuk]

You can find the amendments on the authors website http://fandy.hut2.ru/Chance.htm

unfortunately he never updated the original schematic

I may be wrong here but thinking maybe Silverdogs home page has a circuit on it, i know he has some on there for sure but wether hes the chance on there remains to be seen, worth checking Bob.
By the way best of luck on that one
I myself is taking a long break from making anything till at least next year now, due to work and family commitments unless something really really good gets posted, because these detectors we are building are ok but nothing compared to some of the manufactured detectors i own so im building them, then they go in the spare bedroom and collect dust.
Thinking of selling the lot apart from a couple of Whites machines if you know anyone who would like to make me a sensable offer, got Minlab, Fisher, C-scope, Crapy china one, two TGSLs with manufacturesTesoro coils, Minipulse 3 working up to spec, and proberly other stuff like spare shafts, coils, if I look in theres proberly more, everythings working.
All the best
Dave

[satdaveuk]

Sorry silverdog lol just realized it was your last posting, god you can tell im tired, just muddle on Bob cant be worse than what i went through with the Minipulse 3, them who dares and all that

[woodbob123]

Thanks guys had looked at a previous link but it kept coming up with an error read through all the post's i could before my brain hurt lol, can see the changes now. Satdave quite a lot of bids and watchers on a old detector i put on e-bay could be a good time for a clear out, following the recent treasure programme on TV.

[satdaveuk]

Thanks guys had looked at a previous link but it kept coming up with an error read through all the post's i could before my brain hurt lol, can see the changes now. Satdave quite a lot of bids and watchers on a old detector i put on e-bay could be a good time for a clear out, following the recent treasure programme on TV.

Trouble with ebay is they take to much commision, great for buying but crap for selling, how much did you get for your old detector and what % did fleebay charge plus there listing charges?

[woodbob123]

what I sold was a cheap detector started at 99p for repair spares missing batt box and i had removed the stem for a barracuda build. It did beep but thats about all!! got over 20 for that. If you e-mail or pm a list happy to post it on 3 club sites for you with your details you can sort out prices direct then.

[baum7154]

L1 choke And Chance build

I have been building/optimizing the Chance for about two years. Started with software version 0.8.4 and currently running 1.2.1. The software much improved the performance.

Recommend the axial lead 220uh choke be avoided and replaced with one capable of greater current handling capacity. I wound my chokes on toroids using 26 awg enameled copper wire.

Also the author's original basket weave coil is OK for coins and jewelry but not for fine/small gold flakes. I am using a 'spider wound' 8" coil for small gold detection shielded with graphite al la Satdaveuk process outlined in the COILS forum with a heading of Graphite Shielding.

All schematics of the Chance detector are in detached form but the website is pretty clear. If you have Silverdog's recent boards you can ignore the Mods required for the older production boards. I have done one of each.

I use the OP37 opamp as it has superior parameters to the NE5534.

Regards,

Dan

[6666]

Hi Dan
did you take any pictures of your 'spider wound' 8" coil when you made it ?

6666

[baum7154]

Spider Coil & choke

I did not take a picture of my spider coil but it is built on a 4.5 mm Lexan form that I machined with 37 slots on the outer rim and 37 on the inner rim staggered to the midpoint between the outer slots. This is quite similar to the form pictured back in the Chance Problem thread. I wound this coil with 26 awg enameled wire and I believe it was 37 turns of wire. The form is 2.5cm in width and the slots are cut 6mm deep. I used an LCR meter to get the coil to a value of 412uh including the shield and coax.

The Choke is 280UH measured with my LCR meter. Gold placer always registers on the left of the scale and Iron always on the right. Gold alloys like 10K register mid scale.

Regards,
Dan

[baum7154]

I'm reposting this from the Chance PI Problem thread because I think it is more appropriate here. This isn't so much about a Chance problem as it is about optimization and improvement of the Chance PI detector and the associated coil.

I've been away from the forum for a while but have been doing more optimization on my Chance PI. The current coil I am using is 8" dia wound in the previously discussed 'spider' configuration on a .091" thick 1.050" wide polycarbonate form machined with 37 slots .400" deep on the inside and outside rims. The wire I am using is Teflon insulated stranded, silver plated, #26 AWG, .040" O.D. and after extensive testing the optimum inductance for small gold detection with my electronics is 330 to 340uh and about 2.0 ohms resistance. On this coil form this is achieved with 32 turns wound in spider coil fashion.

I have also eliminated the coax feed to the coil as it contributes too much capacitance thus slowing the coil down. Instead I use a continuation of the coil wires twisted at a rate of 3 twists per inch. This I will sheath with heat shrink. The low capacitance coil created in this way will run at a Guard Interval setting of 17 on my Chance PI. My previous best was a setting of 19. This 8" configuration will detect a 1cm square of .001" thick aluminum foil at 4" in air. It will also detect a 10.5 grain piece of dental gold at 4" and an 8.4 grain piece at 2". This will also detect my 10K gold ring at 12" in air.

I am running this coil without shielding at this point until I can determine if it is truly necessary. In thinking about this specific coil winding configuration I wonder if it somewhat self shields when the outermost winding end is connected to system ground. This is because the successive windings are wound over and around all previous windings. I am also looking at the possible increase in sensitivity if the outermost winding end is connected instead to the high side of the system in/out. In that case graphite shielding in the range of 2000 ohms per inch may be required.

[baum7154]

One more thing about Guard Interval. I was able to get down to a 16 setting of the Guard Interval by reducing the turns of the aforementioned coil to 28 turns but the sensitivity to small gold suffered. The coil was at an inductance of about 280 uh at that point.

Also on my next coil I will try to find some 28 AWG Teflon insulated wire and the smaller wire size should help to further reduce capacitance.

In my previous post on Cheap Teflon Wire above, that wire was used to wind a spider coil on the very same form described above. Because the wire was 23AWG and had thinner Teflon insulation thickness, it would not operate below a Guard Interval setting of 19. This was due to greater capacitance from both the thicker wire and the thinner insulation. Still it would be very good wire to use for a coil not intended to search for small gold.

[baum7154]

As I recall from testing, any selection of Iron Mask does somewhat degrade small gold detection. However the tests I have done are air tests on top of my pool table in the basement of my house, being careful not to have metal within 3 feet of the coil top and bottom and more than 2 feet from the coil edges. All flourescent lights turned off and all TVs and radios off. In fact having my old CRT TV in the basement turned on prevents the detector from operating properly. That said, the performance outside and away from civilization and it's electromagnetic signature may very well improve.

The settings of the Chance parameters for my tests are: Barrier - 1, Volume - 3, Guard interval - 17, Iron Mask - NO. I try to keep my supply voltage at 12 volts nominal from Nimh rechargeable cells. Max current draw with display lit is about 115 ma and about 90 ma without display lit.

A friend of mine has an 18 grain gold nugget he will lend me for further tests and I'll post the results here as soon as possible. I'm hopeful to detect this natural nugget at > 4 inches using the 8" coil...we'll see.

I'll also test the effects of Iron Mask 1 on detection distance this next week and let you know. Since the Iron Mask function is driven by time I believe any large piece of metal has the potential to present as Iron or be screened out by the masking. Wouldn't it be a shame to miss a golf ball size nugget because the Iron Mask screened it out? The discrimination does an OK job on targets of similar small sizes with gold consistently showing up on the left of the scale. Silver consistently shows up near the right end of the scale and Iron always at the right end. Bigger slower targets go towards the right end.

[6666]

Baum7154
interesting work you are doing
is this the coil you are using ?
cheers

[satdaveuk]

As I recall from testing, any selection of Iron Mask does somewhat degrade small gold detection. However the tests I have done are air tests on top of my pool table in the basement of my house, being careful not to have metal within 3 feet of the coil top and bottom and more than 2 feet from the coil edges. All flourescent lights turned off and all TVs and radios off. In fact having my old CRT TV in the basement turned on prevents the detector from operating properly. That said, the performance outside and away from civilization and it's electromagnetic signature may very well improve.

The settings of the Chance parameters for my tests are: Barrier - 1, Volume - 3, Guard interval - 17, Iron Mask - NO. I try to keep my supply voltage at 12 volts nominal from Nimh rechargeable cells. Max current draw with display lit is about 115 ma and about 90 ma without display lit.

A friend of mine has an 18 grain gold nugget he will lend me for further tests and I'll post the results here as soon as possible. I'm hopeful to detect this natural nugget at > 4 inches using the 8" coil...we'll see.

I'll also test the effects of Iron Mask 1 on detection distance this next week and let you know. Since the Iron Mask function is driven by time I believe any large piece of metal has the potential to present as Iron or be screened out by the masking. Wouldn't it be a shame to miss a golf ball size nugget because the Iron Mask screened it out? The discrimination does an OK job on targets of similar small sizes with gold consistently showing up on the left of the scale. Silver consistently shows up near the right end of the scale and Iron always at the right end. Bigger slower targets go towards the right end.

Hi Dan
First of all well done on your perseverance and drive to reach your goal by making a coil that works to the specification that you were wanting.
Although not contributing to the Chance thread because I have not built one have been following your experiments with interest.
Can I ask you a couple of questions Dan.... In your opinion is the Chance worth the build?, secondly how accurate in your opinion is the display readout?
The reason why I ask is because in general although building projects on here are great fun and a learning curve they don't perform to the standards of almost all manufactured detectors I have here.
The only one Ive built that is different and feel it was all worth due to its simplesty and component count is the Barracuda, the Minipulse 3 has its advantages far as depth with large objects and sure it will have its uses one day if I visit the desert lol.
The tgsl was a good build in fact I built two of them but the Whites prism which is now produced with a different label for £199 beats it hands down far as depth and accuracy so it puts the TGSLs in the corner getting cobwebs .
Anyway keep up the good work
Regards