chance pi build

[baum7154]

According to the published specs it should do the job. Unfortunately I don't have any first hand knowledge of this scope but perhaps a forum member with hands on can comment.

Dan

[6666]

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.
dave

Looking at some of the customer comments the hardware is good but the software is not to good, get their latest download off their site.

[angleiron]

well i have bitten the bullet and ordered the scope so we will see when it arrives, and thanks again for your inputs much appreciated.
dave

[baum7154]

MODIFIED CHANCE PI TESTS WITH 3DSS COIL

After overclocking my Chance PI to operate at a sample delay of 6.98us and damping the 4" X 12.5" 3DSS Racetrack coil I also decided to change the interstage coupling resistor in the 2 stage amp from 1K to 166 ohms. This also necessitated changing the filter cap to a value of 1410pf.

I decided to run some target sample tests as a comparison point to previous tests for First Detection & Detector Tone Lockup with the standard being three consecutive passes to validate the distance. The problem is air tests are inaccurate for determining true depth in soil. The second problem is that everything here is covered in a foot of snow. Forum member ANDY (6666) suggested another test method a while ago placing the coil on the ground and passing the standard targets over the coil. This has the effect of reducing the detection distances of air tests and is more realistic in its results I believe. Since doing the tests outdoors in this season is not possible I found a quiet spot in the concrete floor of my basement where fortunately no steel re-bar has been placed and set up the detector with the 3DSS coil resting flat on the carpet and began passing the targets over the coil with a plastic ruler vertical in the coil, for distance measurement. I took the extra step of placing two packets of black sand 2" over the search coil, equivalent to about 2 teaspoons spread over 5 square inches. The following are the test results:

TARGET-----------------------1st DETECTION-------------------------------TONE LOCKUP

ALUMINUM SODA CAN---------20"--------------------------------------------15"

STEEL BOTTLE CAP-------------14"--------------------------------------------9"

US NICKLE----------------------10"--------------------------------------------8"

US SOLID COPPER PENNY------7"---------------------------------------------5.5"

US SILVER DIME----------------7.75"------------------------------------------5"

8.5 grain DENTAL GOLD--------3.75"------------------------------------------3"

4.5 grain 14kt GOLD HEAD-----3.0"-------------------------------------------2"

1/4" X 1/4" SODA CAN WALL---2.75"-----------------------------------------2.25" ------Note: Solid detection distance of this target has improved 1.5" from similar over soil test last summer.


I believe these modifications have improved the performance of the CHANCE PI and enable the 8" 'blade' search field of the 3DSS Racetrack coil to better detect small gold even though it is only 4" wide.

Regards,
Dan

[daverave]

looks like not good on low conductive items like gold

[baum7154]

Well that depends on what you consider good on small i.e. 4.5 grain or <1/3gram gold, actually .29 gram gold. Do you have a datapoint on such a target or the 1/4" X 1/4" soda can with a 4" coil over soil? A larger coil limited to possibly 7 or 8" diameter might do better at its tiny focus point of greatest sensitivity, but this coil is intended for an 8" long search field of consistent sensitivity to quickly cover an area.

regards,

Dan

[homefire]

Is there a any other Alignments needed on the Chance other then the Damping Resistor ? Things like Zero Volts ? Delay Timing ? Do we have a Link ?

[baum7154]

Is there a any other Alignments needed on the Chance other then the Damping Resistor ? Things like Zero Volts ? Delay Timing ? Do we have a Link ?

------------------------------------------------------------------------

If you have the version 1.2.1 software and the current version of that board there are no other alignments to be made as designed other than performing critical damping on the coil. Sample Delay is selectable by the menu selection called GUARD INTERVAL. Sample window width is fixed at 12.5us.

That said if you build and install the 2 stage amp modification for this detector you will have an amp offset pot that must be adjusted for best sensitivity/discrimination. I recommend, if you have not already done so, to read this thread from the beginning. I am happy to answer what ever questions I can though.

Regards,

Dan

[homefire]

I read all and seen no mention . Thank You.

[baum7154]

Chance Link

I read all and seen no mention . Thank You.

-----------------------------------------------
Take a look here at the original Russian link: http://fandy.hut2.ru/Chance.htm

Please ignore all the original coil build instructions as it is not good for small gold and is not shielded so it is not suitable for shorter sample delays.

[baum7154]

LIMITED-2 STAGE AMP for CHANCE PI - Design Update

The attached diagram is the latest revision for the 2 stage Chance PI preamp. It incorporates a lower 166 ohm interstage coupling resistor and the capacitance change to keep the 677 kHz filter value. It is necessary to readjust the 1st stage offset pot for optimum A/D sensitivity and discrimination. For a description of this amp operation see my post #125 in this thread.

Dan

[baum7154]

CHANCE PI-2 Stage Amp-Direct Toner Heat Transfer to PCB Mask

Attached is my direct heat transfer to PCB mask for the 2 Stage Amp modification. These masks are for the ground plane/component side of the board and for the Trace side of the board. I will be posting complete fabrication of this direct plug in mod/upgrade of the front end amp.



Regards,

Dant

[baum7154]

CHANCE PI-2 Stage Amp-Direct Toner Heat Transfer to PCB Mask

Attached is my direct heat transfer to PCB mask for the 2 Stage Amp modification. These masks are for the ground plane/component side of the board and for the Trace side of the board. I will be posting complete fabrication of this direct plug in mod/upgrade of the front end amp.



Regards,

Dan

[bernte_one]

Thx, but bad Quality.

if you send me better files i can redraw them with layout Software and from there to pdf or bmp with high res

[baum7154]

Thanks Bernt1. What kind of files do you need to do the pdf or the bmp? Post 329 has the traces and post 341 has the latest circuit revisions. Additionally I have the original drilling coordinates I used on the milling machine all in inches.

Dan