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Offline Mike In2mudTopic starter
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« on: November 04, 2015, 01:50:02 pm »
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Hi Golddust Carl,
I liked your ideas you had using a different approach to PI detectors in your first posts on this site.

I've been trying to follow the progress of your PI  you posted under PI Designs & Deepseekers >New Idea and Please, more clear schematic!
I have built the circuit shown in your schematic and have used 22 SWG (0.711mm), which is equivalent to your  21-22 AWG (0.643-0.724mm) to wire the coils, they are tightly bound with Spiral-Wrap. The 8" coil is 407uH  and the 6" coil is 430uH.
My problem is firstly that I can only get a maximum of 5-6us pulse at the resistor divider, the secondary point (no target), whereas you get a 10us pulse.
Secondly I cannot even vary the pulse enough to set-up the Ferrous, Non Ferrous levels unless I heavily dampen the primary coil using an 82R resistor across it, which gets very hot. The circuit is drawing 400mA.
I cannot get any sensitivity from the coil even using a large piece of copper and separately a large piece of iron. If I use a higher value resistor to damp the coil then the width of the pulse is reduced significantly below the 12us. threshold.
If I carefully look at the pulse at the resistor divider, I can see no change in the shape of the pulse, when metal is brought near the coils.
I must confess I am stumped at the moment, all the problems appear to centre around the coil area, but I think I have constructed them both correctly.

Best regards Mike


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Offline geoscash1
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« Reply #1 on: December 12, 2015, 08:44:00 pm »
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Hi Mike,

Saw your post and then reread the old thread, were you ever able to get this working or are you still having problems with it?

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Offline Mike In2mudTopic starter
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« Reply #2 on: December 13, 2015, 05:47:30 am »
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Hi Geoscash1,

The first circuit I built (the one mentioned above), I tried to cut down on the IC count to fit my Control Box, I succeeded in getting it working, BUT I couldn't get the exact 250uS pulse width at the MOSFET, which is important.

After PM e-mails with Golddust Carl I completely rebuilt the circuit as per his drawing. The circuit now works fine.

I wound both the coils near to 400uH and set up the damping, but as yet I can only detect large chunks of metal. I cannot detect coins at all.

Large Iron is now detected at 3 and Large Copper at 2 with the sound just starting in the background. If I set it to be just silent first, then nothing is detected.

That is the stage I am at now, still trying but haven't got there yet.

Best regards Mike.


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