PI Detector New Idea re-visited.

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


Linkback:

You are not allowed to view links.
Please Register or Login

http://www.thunting.com/smf/index.php/topic,61089.msg303228.html#msg303228

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.


Linkback:

You are not allowed to view links.
Please Register or Login

http://www.thunting.com/smf/index.php/topic,61089.msg305282.html#msg305282