chance pi build

[baum7154]

I look forward to hearing the progress on your Chance PI builds. Keep us posted!

Dan

[vbeeeks]

ok, the Pcb's are in - Atmegas arrive tomorrow so allow a couple of days for those to be ready
Both options can be found in the PCB section of my shop http://www.silverdog.co.uk/shop/inde...tegory&path=35
good luck

Silverdog (Andy) request you to kindly pm me the latest gerber for v1.2.1 PCB so I'll get it fabricated in my geography, it's pretty impossible to order the same from my place - I am in for Chance-2015 experimentation. Thanks in advance. I know time is not on my side vis a vis those getting ready kits from you.

[kellogs]

Hi baum 7154 wondering how you are going i have been plodding along i was wondering if you could help i have been looking for the stickers that go on the front control panel thought you might know where i could purchase them from thanks for your help Kindest Regards kellogs

[baum7154]

Hi baum 7154 wondering how you are going i have been plodding along i was wondering if you could help i have been looking for the stickers that go on the front control panel thought you might know where i could purchase them from thanks for your help Kindest Regards kellogs

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

Hi Kellogs good to hear you are on your way with the Chance PI project.

The labels on my detector are ones I printed with a BROTHER 'P-Touch' labeler using 1/4" CLEAR self adhesive tape with Black text. They are pretty durable and have held up well for several seasons. Eventually they will need to be replaced but so far, so good.

Any maker of label printers probably has similar 1/4' CLEAR tape with black type options so it would not need to be a Brother product.

Also there have been several discussions on the forums here about printing complete front panel layouts with your computer and self adhesive material.

Check it out, if I find the thread I will repost it here.

Regards,

Dan

[kellogs]

Hi Dan thanks for getting back to yes it seems to be the way to go i have two projects on the go just before the chance pi was mad available i investigated the mirage pi kit and the have a up to date kit called primo 2 for me and new metal detector hobbyist it is value for money as the kit comes in different builds i have purchased the one with search 5in and 10in made up so have been concentrating on that i will keep you posted on how i go thanks once again Kindest Regards kellogs

[Sacchetti]

As promised here is the latest version of the 2 Stage Amp schematic. It is much simplified from the prototype posted earlier. There are 3 each 1st order 530 kHz filters in play but I am still unsure that this will be the final optimum cutoff frequency. Will post any more changes.

Hi!
The connection relative to the offset trimmer can be is not correct.
This is the correct schematic taken from the datasheet.

It is better to bypass the positive and negative power supply adding two caps (100nF) near the IC to improve the stability.

[baum7154]

Hi Dan

Thank you for running the test and the good explanation. 128 grains at 9" is really good. It will be interesting to hear more results from your friends nuggets. Especially if he has any really large ones.

Thank you,
Chet

[ATTACH]33148[/ATTACH]

Hi!
The connection relative to the offset trimmer can be is not correct.
This is the correct schematic taken from the datasheet.

It is better to bypass the positive and negative power supply adding two caps (100nF) near the IC to improve the stability.

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

Thank you Sachetti for pointing out the error on my drawing from Post #243. You are correct that the wiper of the offset pot should go to pin 7 or V+. I rechecked my postings of the schematics and in the original post of the prototype the schematic is correct showing the connection to pin 7. Somehow I screwed up that connection on the latest drawing. I will repost a corrected drawing also showing the capacitance values for the 677 kHz filters now in use on my Chance PI. I tried other lower frequency values over the past year and they were not better than the 677 kHz filters.

Regarding the the power bypass caps there are 2 each .1uf caps on the amp board at the OP37. This is not shown on the second stage OP37 but the .1uf caps serve it too as they are only about 10mm lead length apart.

Thanks again,

Dan

[baum7154]

Attached is a picture of a corrected and updated schematic of the Chance PI amp using 677khz filters.

[Sacchetti]

Attached is a picture of a corrected and updated schematic of the Chance PI amp using 677khz filters.

[ATTACH]33150[/ATTACH]

Hi!

The cap in the second stage of 42pf do not exist as commercial value.
I think is possible to use a standard 39pf with long wires.
Long and near wires add some extra pf!

About offset I think it is not mandatory to add this regulation because this IC has the offset internal trimmed with laser at factory.
And to measure with precision under 1mV it is necessary to use a very good and expensive instrument (not chinese but some HP or Fluke for example has this capability).

Therefore if you add this regulation on the first amp because you have this instrument, then it is better also to add the same regulation also to the second amp.
Can be you have used only one on first stage to produce a perfect zero after the second stage but it is a little different from have a perfect zero on both amp.

Have a good day!

[baum7154]

[QUOTE=Sacchetti;205746]Hi!

The cap in the second stage of 42pf do not exist as commercial value.
I think is possible to use a standard 39pf with long wires.
Long and near wires add some extra pf!

About offset I think it is not mandatory to add this regulation because this IC has the offset internal trimmed with laser at factory.
And to measure with precision under 1mV it is necessary to use a very good and expensive instrument (not chinese but some HP or Fluke for example has this capability).

Therefore if you add this regulation on the first amp because you have this instrument, then it is better also to add the same regulation also to the second amp.
Can be you have used only one on first stage to produce a perfect zero after the second stage but it is a little different from have a perfect zero on both amp.

Have a good day

-------___

Hi Sachetti ,

Your comments have been addressed I think in my postings 201, 243, & 255 of this thread but in response, in the latest design of my 2 stage amp I eliminated the offset pot on the second stage because it was not necessary as the first stage offset does a fine job of adjusting the level to the A/D and this is an important setting for the Chance PI performance. Yes I am aware that the OP 37 is nicely trimmed at the factory and I took the additional step of using the high performance trimmed amps as well. As it turns out the offset pot allows the use of the standard OP37 amps because you must set the A/D input no matter which amp is used. However the first stage offset pot is mandatory to set that level against the A/D voltage reference.

Regarding the filter cap values I simply have an assortment of ceramic caps from 2pf through 56pf that I paralleled to get the values shown in the schematic.

If you have not already done so I encourage you to read this thread from the beginning to end as there is a great deal of information on Chance PI optimization in it. I also recommend that you get the Chance PI board from Silverdog and build it. I can use some more collaboration on this very sophisticated detector. As mine is modified right now I am pleased with its performance and capabilities.


Regards,

Dan

[Sacchetti]

[QUOTE=baum7154;205748]

Hi!

The cap in the second stage of 42pf do not exist as commercial value.
I think is possible to use a standard 39pf with long wires.
Long and near wires add some extra pf!

About offset I think it is not mandatory to add this regulation because this IC has the offset internal trimmed with laser at factory.
And to measure with precision under 1mV it is necessary to use a very good and expensive instrument (not chinese but some HP or Fluke for example has this capability).

Therefore if you add this regulation on the first amp because you have this instrument, then it is better also to add the same regulation also to the second amp.
Can be you have used only one on first stage to produce a perfect zero after the second stage but it is a little different from have a perfect zero on both amp.

Have a good day

-------___

Hi Sachetti ,

Your comments have been addressed I think in my postings 201, 243, & 255 of this thread but in response, in the latest design of my 2 stage amp I eliminated the offset pot on the second stage because it was not necessary as the first stage offset does a fine job of adjusting the level to the A/D and this is an important setting for the Chance PI performance. Yes I am aware that the OP 37 is nicely trimmed at the factory and I took the additional step of using the high performance trimmed amps as well. As it turns out the offset pot allows the use of the standard OP37 amps because you must set the A/D input no matter which amp is used. However the first stage offset pot is mandatory to set that level against the A/D voltage reference.

Regarding the filter cap values I simply have an assortment of ceramic caps from 2pf through 56pf that I paralleled to get the values shown in the schematic.

If you have not already done so I encourage you to read this thread from the beginning to end as there is a great deal of information on Chance PI optimization in it. I also recommend that you get the Chance PI board from Silverdog and build it. I can use some more collaboration on this very sophisticated detector. As mine is modified right now I am pleased with its performance and capabilities.


Regards,

Dan

OK

[Sacchetti]

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

Hi Dan,
which LCR meter do you have?

[baum7154]

It is a Chinese made LC200A meter sold on EBay and it works well.

Here is a picture:

[baum7154]

New 3DSS (3D wound, self shielding) Coil on my Chance PI

Attached are two photos of my new coil installed on the Chance PI. Still need to set critical damping on the coil before field tests.





Full details of this coil build are posted on the Chance PI Coil thread of the COILS forum.

Dan

[baum7154]

Chance PI with a Whites Space Saver rod and 3:1 3DSS Coil

Happy New Year!

Just finished a boom/rod upgrade to replace my original PVC boom with a Whites 3 piece Space Saver rod purchased on EBay. This upgrade reduced the Chance PI detector weight to 3lb 14oz including battery and a 4X12.5" 3DSS oval coil. When broken down it easily fits into a small backpack for trips into the back country. Pictures are attached below.





Regards,

Dan