Strange damping on Surf PI 1.2 please help

[antalaz]

Hi everyone !

I've managed to build a Surf Pi from Silverdog' kits.
It's working quite good (it can detect metal, so the main function is ok I think )

I would like to setup my damping resistor and my delay,so i made some research on the forum and i've found a post from Tepco where he is explaining how to figure it out with a scope.

I'm trying to execute his instructions but when I try to visualize the signal from the coil, It does not looks like a "normal" signal.
You'll see more details in pics attached to this post.

I'm using an homemade spiral coil.

I'm sure that i'm not the one who encountered this problem.

Thank in advance for your help !

[chemelec]

Pictures are TINY, hard to determine if correct or not.
Might also help if you post a link to those instructions from TEPCO.

[mickstv]

It looks under damped, it should look more like the yellow curve shown below. So you need a lower value resistor.

Also your pictures don't look right, check to make sure the ground connection of the oscilloscope is connected to battery -

[Ferric Toes]

With a decent size picture it appears that the scope has the AC input selected. Switch to DC to get a correct picture.

Eric.

[reptooyep]

I would like to setup my damping resistor and my delay,so i made some research on the forum and i've found a post from Tepco where he is explaining how to figure it out with a scope.

Hi,
It would be a VERY good idea if you share the link to this procedure cause i hasked the question few days ago in another thread without getting any clear answer ..
Thanks

[hecbom]

Is this what you are looking for?

http://www.geotech1.com/forums/showt...uda-and-SurfPI

[antalaz]

I finally made it, i'll post some pictures soon

Btw hebcom posted the right link

[antalaz]

Here is the curve of my coil.

I haven't shielded it yet, do you think it worth it ? is it a good coil in your opinion?

I've tested it on the beach and i've detected very small pieces of metal (almost as big as rice grain) but there is false signals due to the lack of shield.

[Sean_Goddard]

10" 22 Turns of 16AWG magnet wire, tune the 1st sample delay and threshold. With an added snubber, my Silverdog SM PI picks up a .22 sized nuggest at 11" in airwith a good clear signal. If you push the audio then you can still hear a change at 14". Shield is sprayed nickel with a 2mm gap.

[antalaz]

What do you mean by snubber? Where do you add it?

[macross]

What do you mean by snubber? Where do you add it?

I think he was talking about a snubber circuit https://en.wikipedia.org/wiki/Snubber

[antalaz]

I think you're right, but what would be the purpose in our circuit ? Just trying to understand, i'm not a native english and i try to understand pi technology, so i guess i have two difficulties to deal with

[davy74]

This is good stuff, Good luck with getting your coil damping setup, I'll be following your progress.
I just finished my Surf PI build today & am now just reaching this stage, I have an LCR meter & oscilloscope on order
My build is detailed in two posts at the end of this thread; [http://www.geotech1.com/forums/showt...4-Surf-PI-1-2]
Any feedback is welcome regarding my question on expected depth.
I deliberatly added more turns of wire to allow me the option of removing a few if need be? - once I get the LCR meter -
I used the braided wire taken from a computer monitor tube coil - looks like this is litz wire? very dense but fine braid?
I might have just landed lucky though because as can be seen in my air test video, the machine is out perfoming my GTAX550 on every sample item.
Definately a rewarding new facet of the hobby for me
Sorry to jump in on existing thread, I'm a noob on the forum & need to learn how to post a new thread.

[davy74]

Looking at the snubber - a discrete component with resistor & capacitor? was something like this once used in old style car ignition distributors opposite the points??

[davy74]

10" 22 Turns of 16AWG magnet wire, tune the 1st sample delay and threshold. With an added snubber, my Silverdog SM PI picks up a .22 sized nuggest at 11" in airwith a good clear signal. If you push the audio then you can still hear a change at 14". Shield is sprayed nickel with a 2mm gap.

Where do you add the snubber?