Beginners PI metal detector plans

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	Re: Beginners PI metal detector plans « Reply #20 on: April 30, 2011, 03:57:56 pm »

	Quote:	Posted by GoldDigger1950
Thanks, Xavier. One other thing I forgot to mention and I'm sure you'll agree is that any mods should wait until after the project is working. You and I both had a few issues to deal with before it was working correctly and adding a mod only increases the likelyhood of inducting a problem.

I'll bear that in mind, thanks Great

... i'll build the circuit and coil first ... test to see if works ok before adding the Mod, test once more, and finally look at mounting it in its watertight casing.

1st thing 1st need to get them parts ordered

Thanks again for all the info ... i cannot wait until i get it all built!!! Rider

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	Re: Beginners PI metal detector plans « Reply #21 on: April 30, 2011, 04:05:49 pm »

	Quote:	Posted by Lord Dracon
1st thing 1st need to get them parts ordered Smiley

I use Futurlec for most parts I need. They even have a UK order desk.

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Just about the best prices on the web. When you order, get a few spares and socket your ICs for convenience in replacing if you need to. Be mindful of every component going in the right place and look carefully at the board for jumpers that have to be added. As I recall, there are three of them. Use a discarded resistor leg for jumpers.

Have great fun. This is a super project and Silverdog's boards make it a dream to build.

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	Re: Beginners PI metal detector plans « Reply #22 on: May 01, 2011, 05:38:33 am »

	Quote:	Posted by GoldDigger1950
Thanks, Xavier. One other thing I forgot to mention and I'm sure you'll agree is that any mods should wait until after the project is working. You and I both had a few issues to deal with before it was working correctly and adding a mod only increases the likelyhood of inducting a problem.

I couldn't agree with you more unfortunately the way the board is silk screened makes it easy to make a mistake in the placement of the components and it's always better to get it working first the way that it is. As for the coil I will measure it then post the data on this thread it will make things so much easier for Lord Dracon

All the best
Xavier

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	Re: Beginners PI metal detector plans « Reply #23 on: May 01, 2011, 02:33:26 pm »

Thanks, Homefire. Appreciate the schematic.
/r
jiminy

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	Re: Beginners PI metal detector plans « Reply #24 on: May 02, 2011, 12:20:05 am »

Thanks for mod homefire and dont forget the cap from pin 5 on the 555

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	Re: Beginners PI metal detector plans « Reply #25 on: May 10, 2011, 09:06:25 am »

Still at it

Just wondering .... what should the coil be on this PI Undecided

... seen some notes but am unsure about
the search coil, is it 20 turns of #24 SWG or AWG (coated) @ 9" Dia ? would a larger coil be better?

I have a load of 24swg (.56mm) coated copper wire. -- will this do?

Also would a round coil or oval coil be better? i was thinking of using an oval coil but what would the specs be on this? Undecided

was thinking of a search head of 12" x 7" .... approx

also do the cables to the coil need to be shielded?

now here's one for you all ... integrating a second coil into the equation a second 6" round coil in parallel with the main coil (located inside the main coil area)? would this work or cause too much interference? poss better detection of non-ferrous materials??/. more accurate pinpointer? possibly switched so can use one, other or both at same time? any ideas?

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	Re: Beginners PI metal detector plans « Reply #26 on: May 10, 2011, 09:42:30 am »

A oval coil just would shape your foot print of the feild longer one way and not as deep as the feild of a round coil I would think.

24 swg wire should work but is a wee bit small from the norm. I'm thinking 22 is the norm.

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	Re: Beginners PI metal detector plans « Reply #27 on: July 23, 2011, 01:34:37 pm »

Hello,
I completed a Silver Dog kit and built several coils. Currently I have a 22awg 7.5" ID 24 turn @ 240uH flat mono coil hooked up. I have set the damping resistor to eliminate ringing which was pretty straight forward. I used a wirewound power pot and resistor to set this.
I now am playing with the offset and delay. I tried to adjust the pots to empirically get the best detect distance, but by looking at the various TP's and inputs and output to the opamp and integration stages, I cannot make heads or tails of where the best theoretical signal should adjusted to.

Can anyone comment on what signals to be looking and what the optimal adjustment would look like. OR point me to a write up where this was discussed? I have searched extensively and read everything going back 5 years on Surf PI.

I can detect a ring at ~10cm and a small can at 20cm in air which is not great based on comments around the board. The coil is well made (neat, flat and epoxied) and so there is something not quite right.

Other questions,
1. Is the offset adjusted with or without a coil?
2. can the tuning be optimized with a scope as well.

Any help would be appreciated.

Tommyb

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	Re: Beginners PI metal detector plans « Reply #28 on: July 24, 2011, 03:38:39 am »

Hi Tommyb

I have been playing around with flat coils and they have proven to be a pain in the butt. My suggestion to you is make a normal jumble wound coil you,ll have less capacitance. I have build this detector too and a small coin can be detected in air at about 200mm also remember that this detector requires you to have motion I have found that the faster motion gives a better detection depth. The coil that I use is 280mm inductance 250uH wire gauge awg 23 (22 to 24 will do)

All the best
Xavier

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	Re: Beginners PI metal detector plans « Reply #29 on: July 24, 2011, 11:06:02 am »

Hi Xavier,
Thank you for taking the time to post back. Ill try a jumbled coil as you suggest. It is funny how the coil science has so many opinions.
My first coil was a two layer flat wound....hoping to get a greater field concentration in a smaller coil. I will go back to it when I figure the basics out. The real questions are help on setting up theoretical values with a scope. Here the basic questions:
1. Is offset adjusted without a coil (or pulse set to 0)? Are we adjusting the offset so that the V at the output Pin 6 of the opamp is 0V? I know this is simple in theory but I am coming the learning curve. Help?
2. Is Delay set using TP1 and TP2. Where is the delay start point measured from? I assume it is the when the preamp signal starts to decay from saturation? The end point is the rising slope of the sampling pulse?

Future thoughts:
Can the MOSFET and tank cap be placed down at the coil and the signal be feed back to the preamp? This may eliminate the impedance challenge of the coax cable?

Any help would be appreciated.

tommyb

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