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hi baum7154 do these mods apply with the latest boards off silverdog, also is there an amended parts list other than the one on silverdogs site.
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-------------Originally posted by angleiron View Post
Hi Angleiron,
The mods necessary to run the latest Version 1.2.1 firmware are already incorporated in the current boards sold by Silverdollar. All other mod enhancements (post 297 summary) I have posted in this thread are applicable to the standard boards now offered. The parts list on Silverdogs site has been amended for the current circuit boards.
Happy New Year,
DanComment
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hi dan thanks for the quick answer and info, had the board a bit only just got around to build it, i cant get my head around the piggy back board for the dual amp suppose you havent a pcb overlay for it i could copy thanks for your help
happy new year
daveComment
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---------------Originally posted by angleiron View Post
Angleiron I recommend that you install a gold plated IC socket for the OP37 amp and build the original Chance as designed. That gold IC socket will allow you to plug in the 2 stage amp later. I can post a PC board layout for the 2 stage amp. Another tip is to install a couple of gold plated socket pins for the clock crystal. I'm now in the process of another mod to allow the Chance PI to sample at under 7us to improve small gold detection. More on this later!
i look forward to hearing about your build.
DanComment
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Its just a daughter pcb that plugs into the original IC socket on main PCBi cant get my head around the piggy back board for the dual amp
this is not a picture of it, but only to give you the idea.
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Quite awhile ago I posted pictures of the daughter board in post #161 of this thread. There are several pix in various stages of completion. The first pic shows six holes larger than the others and these accommodate the socket pins that plug into the original single stage IC socket to achieve the interface from the motherboard. It should be noted that the second offset pot has been eliminated and this will simplify this board a bit.
DanComment
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OVERCLOCKING CHANCE PI DETECTOR FOR SHORTER SAMPLE DELAYS
---------------------------------------------------------------------------Originally posted by Tepco View Post
For some time I have wanted to get faster sampling on my Chance PI detector in order to improve small gold detection. I remembered the above suggestion from my friend TEPCO in his post here of 4-28-14 and finally got around to making modifications to my Chance PI. I installed two socket pins where the clock crystal is located on the mother board. This allowed me to quickly change clock crystals and observe the results.
As the ATMEGA Micro Controller can be clocked up to 16mHz I went through several crystals of increasing frequency and settled on a 14.31818mHz crystal. This frequency allows the detector to sample at 6.984us (7us) using a CHANCE PI 'Guard Interval' minimum setting of '10'. Each Guard Interval incremental increase adds .6984us to the Sample Delay. My newly constructed 3:1 328uh 3DSS Racetrack coil is installed and critically damped to operate at this 7us sample delay. Unfortunately my 335uh 8" round 3DSS coil will not operate at full supply voltage at less than about 7.7us.
RESULTS
1. All of the multipulse transmit parameters are now about 23% shorter i.e. the 120us long burst pulse before flyback is now 93us.
2. All of the audio detection tones are now higher frequency but are unchanged in their format and are fully useful.
3. VDI discrimination was initially affected and a reduction from 11 to 9 signal strength units for saturation occurred but this was corrected by adjusting the 2 stage amp offset for proper A/D input.
4. The ability to detect a gold flake of .95 grain was improved.
5. Detection of a .25" X .25" aluminum can target was improved.
6. Detection of a 4.5 grain piece of jewelry 14kt gold was improved.
7. Stability of the detector at the shortest sampling delay is improved.
NOTE: The detector always takes about 5-7 minutes to 'warm up and stabilize'.
I'll get some hard numbers on the detection distance improvement posted here soon. It appears that overclocking is a viable way to get down to 7us or even 6.5us sample delay on this detector with a very fast coil.
Regards
DanComment
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OVERCLOCKING CHANCE PI DETECTOR FOR SHORTER SAMPLE DELAYS
Some additional info on the changes to the Multipulse transmit parameters with overclocking:
1. The multipulse burst rate has risen from 227 bursts per second to 279 bursts per second.
2. As each burst is made up of 16 pulses the pulse rate is now about 4464 per second while flybacks still occur at 279 per second.
DanComment
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thanks baum7154 and 6666 for info on the amp board got a better idea now, i take my hat off to your dedication to this project i shall be following your postings closely, sadly my build is not progressing as quickly as yours ,thank you for your input .
daveComment
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You are most welcome Dave. I have always found knowledgeable members willing to help on this forum for any question asked. As your build progresses don't hesitate if you have any questions.
I'll be posting that 2 stage PC layout this weekend minus the second stage amp offset adjust pot that has been eliminated. The first stage pot alone does all the adjustment needed to make the Analog to Digital chip happy. This adjustment significantly affects sensitivity and discrimination.
I'm looking forward to the completion of your CHANCE PI. A good fast coil either round or 'Racetrack' in 3DSS winding pattern as detailed in the CHANCE PI Coil thread of the COILS forum is the best match I have found for the CHANCE PI detector.
Good luck on your build.
DanComment
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CHANCE PI device based patentUS5506506Comment
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The answer to that is in the designers head, if he is even aware of US5506506. What I do know is that this detector and the original coil were not initially designed to detect small gold but rather coins, artifacts, jewelry, and generally larger targets. That said, the platform offers great potential as a small gold detector. It needed a fast coil, a 2 stage amp that would not saturate, and shorter sample delay in order to perform well on small gold. These hardware changes I have addressed, implemented, and documented for others to try.
If I could make a request of FAndy for a software improvement it would be to allow the Guard Interval to go as low as a setting of '4' which would equate to about 3.5us. The ability to adjust the sample window duration. Also I would like to lower the frequency of the audio detection tones for copper, silver, and iron at the right end of the VDI scale. These changes would be enough to test the limits of the design. The mods that exist now are intended to give this detector the ability to find small gold nuggets in the range of 5 grains and up.
Regards,
DanComment
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One more request I'd make of FAndy on Chance PI software improvement would be selection of transmit pulse duration. This would open up the device to optimization for any target material of most reasonable sizes.
DanComment
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Drawing of the original 2 Stage Amp board
Attached below are two pictures of the 2 Stage Amp PC board layout. The first pic is of the component side of the board with the reverse side traces shown in bold. The second is of the reverse trace side of the board.
I should note that the tab above the cutaway section of the board at the upper right on the component side picture is no longer needed as it was where the second stage offset pot was located. This pot has been eliminated. The board should measure 0.8" wide by 1.025" long with this part removed.
DanComment
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thanks dan for the traces for the amp board, i am looking at getting a scope, funds are limited, would a pc scope ie(hantek 6022be priced @ 41 pounds on ebay) be goood enough for these projects and able to handle the coil voltages and timings.
daveComment
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