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Offline Lord Dracon
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« Reply #30 on: August 14, 2015, 04:41:08 pm »
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I was thinking 2 in 1 ... if does not work mebe pin pointer will have t be in the arm rest.


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« Reply #31 on: August 17, 2015, 01:32:46 am »
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  Rider   Mad  Rider oohh my SurfPI kits should be arriving today/tomorrow... I sure hope its today....!soo excited!  Rider  Mad  Rider
 
  Pray  Detecting      Laola         Laola    Pray  Detecting

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« Reply #32 on: July 09, 2022, 03:45:14 pm »
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Sorry for digging up an old thread, but i've just started getting back to where i left off in 2015, it been a mad few years... I hope you are all keeping well.

Well, I eventually built the coils I had invisioned in my head and they worked surprisingly well (2 concentric coils.) 1x 9.5" Dia and 1x 4" dia connected in series.. I literally just read Homefires link to the patent .. whaa .. someone beat me to it.  Violent .. wish i had read and understood this in 2015 Angry . The only diffrence between my design and the patent is the Damping resistors, which i did not insert .. that might explain the ringing when passing over an object .. there was me thinking it was just a threshold issue i was experiencing and was having trouble trying to correct/get rid of...

Well I now know to insert a couple of damping resistors, this should clear up the noise. (the issue of not having an oscilloscope.. yes i've still not bought one  Grin - someone i know had one connected via bluetooth to his mobile .. a tiny kit .. but works great .. anyone else have experience of these? ). Anyhow i'm still wondering whether the damping resistors will affect detection depth (something i need to test as currently getting great detection on a small gold earring at 11" in air and a gold ring at 15")

What is the formula for calculating the 2 damping resistors (one before each coil going to ground). I'm thinking that the resistors are calculated using the ratio of the impedance of the two coils, a bit like a voltage divider. But then I suppose capacitance also comes into the equation. However, to hazard a guess i would say the total resistance of the coil circuit needs to be equilavent to that set out in the plans for the coil of approx 1.3 ohms .. therefore resistors in parallel should also all add upto this including the resistance of the wire. hopefully i'm going along the right track. (thinking aloud), any advice would be appreciated.





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Offline nickel_n
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« Reply #33 on: July 10, 2022, 04:44:40 pm »
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good read for PI coil and how to work out damping resistor

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Making aFastPulse Induction Mono CoilAPractical How.pdf


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Offline Lord Dracon
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« Reply #34 on: July 11, 2022, 10:55:02 am »
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Great document.. what a read!..  looking at the project, I really need to invest in a cheap and reliable oscilloscope.. going to be stuck until then.. my coil design/parameters cannot be that far off if it is able to detect smallish gold without damping resistors... just a bit noisy that's all.. hard to adjust threshold to keep noise down. (That might be the ringing on the coil I'm getting outputted to audio)
Anyone have any advice for a cheap oscilloscope (self build kit is an option if it makes it cheaper). I have heard of Bluetooth ones that connect via android are they any good or better to get standalone?
All advice is appreciated.

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« Reply #35 on: July 11, 2022, 01:35:54 pm »
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I was thinking of getting an oscilloscope that my budget allows, something like this...

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Comments welcome.. (mods please delete post, if this type of post is not allowed.. no misuse intended.just advice required.. thanks)

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Offline nickel_n
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« Reply #36 on: July 11, 2022, 02:37:09 pm »
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its all good with the post  Smiley
but looks like that for the same price or there about you can get an older analog scope from eBay.
i think will save you a lot of trouble
look also here:

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« Last Edit: July 11, 2022, 02:46:27 pm by nickel_n »
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