Noise,
Just wondered if anybody know if shielding something in a metal box 0.8 mm will illuminate any noise going inside it im building a 328 inside a metal box to shield it from external rf / emi
Thank you
Well, the box will eliminate radiated noise going in that way, but unless you have taken steps to protect any wires going in and out, they will carry all sorts of garbage into the box. This is especially true if you are in an environment like automotive or where there is a bunch of rf energy around.
And you need proper sealing of the lid for the box to be properly RF-tight, a narrow slot is as good
as a window to RF interference in the UHF/microwave range. The thickness of the box walls is more
or less immaterial, RF current only flows on the surface of conductors.
But as has been pointed out any cables entering the box can carry interference if not carefully addressed,
using only shielded cables is a good way to go (its always done for RF circuitry). But without knowing
the nature of the EMI its hard to know what the best precautions are.
MarkT:
a narrow slot is as good as a window to RF interference in the UHF/microwave range.
That's why I've always said tinfoil hats will never protect you. You need a tinfoil suit.
Even if you could eliminate all external EMI through shielding, you could lose it all by poor circuit design, creating your own EMI from within.
The noise source is a frequency inverter i do plan on using screened cables.
I plan to earth the metal box to chassis earth, as well
Screens cable will not help keep the interference in the box. It is very simplistic to think a box will keep in all radiation. What happens in practice is the RF bounces about inside and resonates the cavity generating more noise than you would have without a box. I have often worked in circuits where removing any box actually reduced the RF radiation.
What can be a help is feed through capacitors on the power rails.
I was going to make small smaill sections within the box to see if that helped as well
I was planning to add c's as well
Would a couple of high value resistors help maby like a 100k on the positive to gnd?
Would a couple of high value resistors help maby like a 100k on the positive to gnd?
No.
I was planning to add c's as well
Feed through capacitors are the only way to get the RF to follow the path to ground when going through the box side.
Thanks mike