PICKINI V4 - an easy to build, self adjusting PI detector

[Qiaozhi]

Yep, something weird going on with the forum me thinks .. maybe an administrator should chime in?

There's no problem with the forum. You must have attached it incorrectly.
Sometimes people add a link to a file that's on their personal computer, rather than uploading it in the correct manner. Then, of course, no-one else can see it except themselves. Another reason for attachments going AWOL, is when the link points to a file elsewhere on the internet, and that file has been deleted.

[SaltyDog]

Yep, something weird going on with the forum me thinks .. maybe an administrator should chime in?

[6666]

Strange if you click the attachment in post #16 it says invalid , but if you click the quoted text in Ibgold's post it shows the graphic

[IBGold]

Oh, I don't see why it is invalid .. it worked when I clicked it when 1st posted, don't know why it is invalid now .. it's just a .png file

Mind you, I have cliked on a number of attachements from other users and I get that message too .. is the forum having issues?

I will try again ...

[ATTACH]49655[/ATTACH]

That works now.

Regards, Ian.

[SaltyDog]

Oh, I don't see why it is invalid .. it worked when I clicked it when 1st posted, don't know why it is invalid now .. it's just a .png file

Mind you, I have cliked on a number of attachements from other users and I get that message too .. is the forum having issues?

I will try again ...

[6666]

I don't see any text, what are you saying? I only see "Invalid Attachment specified"

click your attachment

[SaltyDog]

Invalid Attachment specified.

I don't see any text, what are you saying? I only see "Invalid Attachment specified"

[6666]

Hi Bernard,

I am thinking, without too many modifications, it is possible to do simple two tone discrimination, by just some simple code changes (as per the White's PI)

If you have a look at the attached image, it shows the pulse decay for different metals (ferrous, non-ferrous). If you judiciously choose the slice level (i.e maybe some manual control), then you would get the pulse width "decreasing" for non-ferrous.
(i.e if you put a line at 0.3v on the graph, then non-ferrous would give you 5us, no target 7us, and ferrous 12us .. as an example)

If you map that to a different tone (and/or light) we could get some form of discrimination ..

Let me know what your thoughts are ... I could have a go at the code changes to try it out ...

You would of course need a fast coil ..

[ATTACH]49654[/ATTACH]

Invalid Attachment specified.

[SaltyDog]

Thanks for the replies.

It seems from the graph I posted, that to reliably detect non-ferrous, you need the pre-amp to come out of saturation within 4us, that means a fast op-amp, which the LM318 is, and also a fast coil. I think with a basket weave coil or a spider weave coil with Litz wire (or equivalent) is the only option to get discrimination ..

If you don't have all those ducks in a row, it won't be reliable ..

My 2c.

[waltr]

I have two tone working on my HammerHead 2. To do this I use the Three Sample GEB method with the first two samples going in the differential integrator. Low conductors swing the integrator output low and high conductors swing the integrator output high. This then goes to a VCO circuit (actually a small pic that does a Voltage in to tone out function).

Works great to determine a high verse a low conductor but Iron can go either way depending on its size, shape and exact composition (alloy). So never worked to disc out iron.

[BC547]

I tried it once with 2 comparators at different slicing levels: one low and another one closer to steady state.
You will notice with a scope that the decay curve angle is different for ferrous and other metals.
Taking into account these 2 pulse widths, you can derive the decay angle.

Tried this and eventually gave up on it. I had a max of 500 Hz for ferrous and 1kHz for other materials.
But I abandoned it after some field tests. Don't remember what was wrong exactly, but it was never a guarantee not to dig any iron...
Feel free to adapt the code any way you like.
You could also consider adding 2 ADC samples on the flyback and combine differential voltage samping with pulse width measurement...

[SaltyDog]

Hi Bernard,

I am thinking, without too many modifications, it is possible to do simple two tone discrimination, by just some simple code changes (as per the White's PI)

If you have a look at the attached image, it shows the pulse decay for different metals (ferrous, non-ferrous). If you judiciously choose the slice level (i.e maybe some manual control), then you would get the pulse width "decreasing" for non-ferrous.
(i.e if you put a line at 0.3v on the graph, then non-ferrous would give you 5us, no target 7us, and ferrous 12us .. as an example)

If you map that to a different tone (and/or light) we could get some form of discrimination ..

Let me know what your thoughts are ... I could have a go at the code changes to try it out ...

You would of course need a fast coil ..

[SaltyDog]

A MOSFET IS a Transistor!!!!

True, but as Bernard picked up, I was referring to the symbol .. seems I was not making myself clear enough for you ...

[waltr]

I am an electronics engineer of some 50 years, I do know what the difference is between a transistor and a mosfet is.

A MOSFET IS a Transistor!!!!

[SaltyDog]

That explains it all many thanks..