Help to solve my baracuda's problem

[skylly]

I have made a baracuda metal detector yet.
Every thing is ok. It can detector a small coin at about 22cm with a 20cm coil (220uh). I use mofset as 9530.
But it's very sensitive to coil movement, maybe there circuit problem?

[Silver Dollar]

That's a nice small board. It would be even better in SMT.

Sensitive to coil movement is your coil shielded?

[skylly]

not shielded yet.
I think shielded is not necessary for a PI coil.

[kt315]

a history was I got PCB pics from Alexismex with huge difficulties. but got. what I see there. Alex did not upsolder the components
and did not measure them. that is the problem the information is not so full as we all waiting in it. its real problem.
as I many times wrote SAT part was deleted too from new release of the board. you have to measure 1000 times and only 1 time to cut the cloth.
but nobody does such way - taken crude schematic and fully confident all are OK, as the result is bad unstability abnormal function.

[skylly]

a history was I got PCB pics from Alexismex with huge difficulties. but got. what I see there. Alex did not upsolder the components
and did not measure them. that is the problem the information is not so full as we all waiting in it. its real problem.
as I many times wrote SAT part was deleted too from new release of the board. you have to measure 1000 times and only 1 time to cut the cloth.
but nobody does such way - taken crude schematic and fully confident all are OK, as the result is bad unstability abnormal function.

maybe I need to learn some basic knowlege sometime....
as u said，it is really a difficult thing， anyway, thank for your long reply, and wish you share your experiences more.

[Silver Dollar]

not shielded yet.

Well I can tell you this, any capacitance in the coil will react to your body's capacitance as
a voltage divider. So if you are picking up 5V of AC (measured on my own hand) then the circuit
will see some of that voltage. So either don't touch the coil and test it outside or shield it.

I have read that Eric Foster uses a shield even on balanced coils and was even playing with
double shielding. So you might get away with out a shield but using one will result in a more
stable coil...

[kt315]

coil shielded itself because one ("cold") its end setting on the ground of the schematic. skylly may be does not notice electromagnetic influence
inside the room inside the house. it is big. the human body accumulaites as EMF so ESF and it is some kinda the retranslator of both.

[skylly]

Thank for all your advice。I don't have enough time for a while now.
I 'll try shield coil and test my detector outside sometimes in the future.

[skylly]

I have free time now. and want to test my detector outside.
At first, need a shell for circuit board.
I would like to order a headphone amplifier shell,
like this

but the shell is made of aluminum alloy, I don't know whether it make interference?

[Koala]

I have free time now. and want to test my detector outside.
At first, need a shell for circuit board.
I would like to order a headphone amplifier shell,
like this [ATTACH=CONFIG]31910[/ATTACH]

but the shell is made of aluminum alloy, I don't know whether it make interference?

The shield of a metal box is better than a plastic box. Just make sure there enough room for the big capacitor and clearance underneath to avoid a short.

[Silver Dollar]

Also make sure anything tied to the case is really ground as many PI circuits are "upside Down".

[skylly]

After waiting for a few days, Finally got my box,

[skylly]

more picture here:

power suply: a moveable power with 12v output.


appearance:


the front panel.


together:


the coil with audio line(audio line has Shield), but coil haven't shield yet, I'm finding aluminum foil now...

[skylly]

some more question.
I have done surf pi and barracuda pi and blind squirrel pi.
surf and barracuda both are motion detector, but blind is no motion.
I don't like motion, is there other detector is no motion like blind squirrel?
I want to make new detector with no motion.

[kt315]

use fat coaxial multistrand cable.