Chance Pi problem....¿¿¿????

[sido]

Thanks Hannu, i thought maybe i was the only one with that problem.

Will try with recommended coil.

Regards Sido

[WM6]

For me it's working much better with recommended coil.
I just don't know how to make shielding for this basket coil.

You do not need to shield this coil.

But if you insist then use conductive graphite spray on coil housing.

You can connect wire to graphite painting this way: glue bare copper wire to coil housing with epoxy resin. After hardened, follow with sanding epoxy resin to bare copper wire. So you can get fixed free surface contact and you can spray with graphite all over inner side of coil housing. Wire contact from graphite shielding will be usually soldered to coil cable shielding. That is all.

[baum7154]

Any new coil info

I'm looking for info on the best 8" to 12" fast coil design to use with version 1.2.1. to be used in gold prospecting. My detector currently adjusts through all possible settings but is unresponsive to any targets. After making all the mods for version 1.2.1 the unit constantly buzzed and after troubleshooting I found that I had placed the bipolar transistor in circuit backwards by following the original component outline for the FET it replaced on the circuit board. The transistor was replaced and correctly placed in circuit and the buzzing stopped. It should be noted that I have a circuit board from Silverdog that was originally designed for the 0.8.4 version of firmware. Now I am reading that the coil is critical to the operation of this detector but mine is not detecting a 6"X4" piece of aluminum but does sporadically get 'musical' when set to zero mask, 7 barrier, and 20 to 35 on the balance. I have a pretty close copy of the author's original coil that is made on 1/8" lexan instead of 1/4" dielectric. It is wound with teflon insulated stranded 24 ga silver plated wire but it doesn't really work. It did work pretty well with the version 0.8.4 firmware but was unstable. Current draw is about 90 to 100 ma with a 12 vdc supply. Any ideas would be appreciated.

[baum7154]

Best coil design for gold searching

My unit does respond very sporadically and with repeated ZEROing. The Receive signal level as indicated on the display bar never goes above 2 increments. I am using a vial of gold flakes equivalent to about a match head in volume, but have also used a US nickle, and a long nose pliers as targets in air tests.

What are the possible reasons for the lack of signal strength?

What is the best fast coil design for gold ?

I have wound three coils and they seem to function best in the Guard Interval range of 20 to 28 but this is sporadic and I think my lack of signal strength is a big part of the problem.

Thanks for the help!

[joop]

debugging this PI-design is almost impossible without an oscilloscope. Can you measure the output if U5 with a scope and show us the result?

[baum7154]

U5 output on scope

I can give it a try, my scope is an old Tektronix 7603 without storage

[joop]

No problem, just make pics of the screen. We can then compare it with a working Chance detector.

[Finderskeepers]

d.i.y. programmer for chance pi

Hello all,
I have built this detector and I'm quite happy with its performance. This d.i.y. pulse induction machine with tone identification takes some practice in knowing whats a good target and whats bad, but dont rely too much on the marker on the lcd screen - i dont find it accurate. I too had problems from the beginning with my circuit. The 200uh inductor was getting very hot and it did not respond to any targets. I had decided to build my own programmer and reloaded the firmware with ponyprog2000 onto the atmega8 chip that I pruchase from silverdog and now it works great. Thanks mickstv for posting the schematic (post #29). I have attached photos of my detector and programmer. As for depth (firmware version 1.2.0), with a minelab 11" monocoil it detects a mans wedding ring at about 30cm and that is with the guard interval set at 22 and barrier at 1. When iron mask is set at 3 or/and the guard interval/barrier set to a higher value you will lose depth.

[Mudflap]

Nice job on the build! Looks terrific. I've been for the design to stabilize a bit before I start. Since I bought the original pc the design has changed several times!! Looks like your Atmel programmer worked out well.

[smity]

You need to have an eye on his elbow.

[baum7154]

Update on Chance troubleshooting /fix

I finally got some time to continue troubleshooting my Chance. After rechecking the xmtr I found that it was not transmitting because Q2 was not installed in the proper way. Transmitter immediately started working as seen on my scope using a second coil to pick up the Chance output through the air. However the Chance receiver constantly buzzed and troubleshooting the Damper stage showed good signal traces all the way to the gate of Q9. It turned out that Q9 (IRF9640)was open and it was replaced. The Chance immediately started working again. Sweet relief!

I earlier wound an 8" fast basketweave spider coil of 400mh, 1.2 ohms and it works pretty well with it even though I used too large of solid copper enameled wire (20 ga). With the Guard Interval set at 21 to 23 and the Barrier set at 4 or lower I get some intermittent audio chatter and the detector will solidly detect a glass vial of gold flakes totaling about a match head in volume at about 3.5". 1/4 of a crown from a tooth is detected at about 6" in air.

I need to spend some time with this detector learning what it is trying to tell me. The unit is highly responsive to US coins at about 8-10" and popcans are seen at 20" with this coil. Gold is best detected at the lowest possible Guard Interval setting in a range from 21 to 25 and the Barrier set as low as possible below 4, Iron Mask was set at 1. I should mention that this unit is not integrated into a completed detector yet, just a bare circuit board not yet in a shielded metal housing, no boom or coil housing

I bought a Chinese L/C meter on Ebay for $36 to help in my coil winding and it works very well. I think it is a model LS-200. It saves so much doubt and time in trying to get a working coil and, in future experimentation on other coil designs.

I'm thinking of winding an elliptical 6"X8" spider coil to get a 'Blade' like search pattern and I think 24ga solid copper wire or Litz wire will be the best choice. First I need to integrate the detector into a complete unit. More later as progress is made. Summer is here and the dredge piles are calling me!

Dan

[baum7154]

Chance fix

I forgot to mention that I replaced the 220uh axial lead rf choke (L1)with one I hand wound on a toroid core. I used the L/C meter to get it to 220 uh. The difference is that I used 26 ga solid copper wireto wind the toroid giving it much greater current delivery capability.

Does any one know if the LCD display uses 8 bit parallel data or is it 4 bit?

[joop]

Only 4 datalines are connected to the display, so it is 4-bit.

[baum7154]

Chance update

Just finished rewinding the fast basketweave spider coil with #24 awg wire. With 34 turns the 8" coil measures 388 uh & 1.7 ohms. This coil is apparently faster as it now allows the Chance Guard Interval to run at 19 but the old coil would only start working at 20 to 21. A 14.6 grain piece of dental gold is now solidly detected at 4".

Thanks for the info on the display bits!

[baum7154]

Chance update

Current consumption on the Chance with the rewound coil is now 87ma. Took it out in the yard and tried it out and it seems to detect targets better in the earth than in the air. Ran out of time but will try to document detection depths in the ground.

Also thinking of vacuum forming a housing for the coil and filling it with urethane foam. Anyone have any input/advice on this process?