Surf Pi 1.2 almost completed...

[ice413]

Recived my Surf Pi kit last week, and assembled it yesterday. Started with huge error !! I accidently missplaced two of the IC, and nothing happens when i switch it on.
Well, put the IC where they should be and put the power on. Beeeeeeeeeeep from the piezo for a few sec, then silence. Nothing happens.
Found a new piezo and now its work as it should. Adjust the offset and start test.
It's behavior was strange, and of course i wonder why. I know i've read somewhere that PI should NOT have shileded coils, and i have.
Remove the shield and voilá !
In air it's detect a regular weddingring ( 18k gold ) at 15 - 20 cm, the same with a 4mm screw.
I'm happy with that, and now i start with the shaft.
My plan is to use an old crutch, any comments on that ?
Could the alu-crutch interfere with the coil ?

[homefire]

Just use pvc from the Aluminum to the coil. What's wrong with Shielding Coil on a PI? It works for me.

[Qiaozhi]

Just use pvc from the Aluminum to the coil. What's wrong with Shielding Coil on a PI? It works for me.

I suspect he had the shield as a complete loop. In this case it would act as a shorted turn and prevent the unit from working correctly.

PI detectors with large coils, and a long sample delay, do not need to be shielded. However, a shield is recommended for the Surf-PI.

[ice413]

Hi again.

Ok, I will try add a new shield next week. The shield i have from beginning was alu-foil wrapped around the coil, then grounded on PCB.
I dont remember where i read that PI dont need shields, but i will do as you said, try again.
My coil i relative small, ~15cm in dia, 0.5mm 17 turns. It gives me almost exactly 200 uH and 1 Ohm.

[ice413]

Hmm, i'm now tried 3 different coils, with and without shield, and i cant get the one with shield to work OK.
So, the last coil is:
20meter of cat5(one pair, orange & orange/white), 20 rounds, dia=20cm, and it seems to work fine.
My problem now is the groundbalance, it's beep every time i move it over the ground.
If i hold the coil ~4-5 cm over the ground it works OK.
So, wnet out for the first fieldtest, and after 3 minutes i found this, around 3cm deep:


a worthless swedish 50-öring, but what the heck, it's my first find !!

I will continuing try with other coils and shield, i'm clearly make something wrong.

[golfnut]

small coils worked well for me on surf, e..g. 7"

10" seemed a a bit weak on mine

[ice413]

I will try some different coils over time.
What i need to fix soon is to replace the piezo with a headphone.
Here i will need som help. What i know about eletronic, it's not so smart to connect the 3.5mm jack direct to +12v.
So, what do i need between piezo and headphonejack ? Someone maybe already did this and have a solution.