Surf PI 1.2 discrimination mod

[nathmurr]

Hi I have built a PI 1.2 detector with spiral coil and pinpointer, took it out yesterday, worked great and picked up lots of objects including one which was a foot deep, however I would kind of like to discriminate between different metals with the PI 1.2 as the place I went was full of junk, does anyone know how this might be achieved or whether this has been done before. I am thinking the only way to do this is to analyse the pulse received for pulse length with a DSP or microcontroller to filter out the longer pulse lengths and feed a signal back to the op amp. There is around 1.6ms of time to do so which I think is easily achievable however before I go down this route I was wondering if anyone has done this before as it is going to take me a little while to do this. I can't think of any easy way to do this with analogue electronics. Thanks

[FatBob]

Well discrimination is not generally associated with PI type MD's.

Though Tinker found some method to extract that info from the signal.

Here's a reply from him from a while back"

Breakthrough!!!!! Full discrimination with PI


Experimenting with the TEM pulse method, I tried something different.
PI in differential mode.
The coil arrangement used is a TX coil of 450mm diameter and 300uH inductance, 0.8 Ohm resistance coil and cable.
The RX coil is 225mm diameter, 300uH inductance, center tapped.


The Flyback is captured with a 200nF capacitor and re conducted to the battery to save power, limiting the Flyback peak to 200V.


The PI runs at 4300 pulses per second, TX of 150uS. about 6.2A coil current at switch off.


Differential mode:


Attenuate the 200V TX Flyback to the same 30V level of the RX Flyback and then subtract the TX Flyback from the RX.
The resulting signal wave shape is shown in the picture annexed.


The target signal has a very good S/N and the sensitivity is high. To my great surprise, the FE discrimination is very good too.


Testing different metal targets, I found that the response is very different for different metals.


How does that work?????????????


Looking at the Lissajous curves, I found that the target response is in fact a phase shift as well as a amplitude change.


So this method does make it possible to discriminate targets by the phase shift, just like a VHF does.


The big difference is the amount of power in the coil.


By recycling most of the power of the TX, a very strong magnetic field with high di/dt can be built, that gives very deep ground penetration.


Tinkerer"

[godigit1]

Has or is Tinkerer's design being manufactured or developed or just go by the way side due to patents?
I have some of his old drawings but he would have to give the o.k if they could be put here. Or to anyone for that matter.
No code with them though!
{O.k I was able to relocate the plans I have they are open and out there already.
I copied them in 2010 so I was not sure! }

[Tinkerer]

Has or is Tinkerer's design being manufactured or developed or just go by the way side due to patents?
I have some of his old drawings but he would have to give the o.k if they could be put here. Or to anyone for that matter.
No code with them though!
{O.k I was able to relocate the plans I have they are open and out there already.
I copied them in 2010 so I was not sure! }

Tinkerer's designs are not commercially orientated, so patents have no importance. However, some of the stuff is quite complex and my ability to explain is minimal.
If you are inclined to experiment and tinker, I can help with a hint from time to time, not more than that, as I am a bit busy on different projects at present.

[godigit1]

Hi Tinkerer
From all of us thanks for that, .
Your clean energy sines through your posts.
Be Well