Hello
I plan to build a 328 that will be in a noisy inviormet i was reading up on ferite beads and saw ferite beads surface mount ones
Wonder if somebody can tell me how to use them to suppress noise are they used on supply voltage to the processor and gnd,s?
or on the signel lines, like inputs and outputs and analog inputs
Im guessing they are used on inputs if they are how does one select the correct value?
Thank you
The answer is: it depends.
What is the source of the noise? How fast do your signals need to be? Can you draw the spectrum of the noise? Conducted? Radiated? What power supply? Signal inputs? Signal outputs?
Ferrite beads are often used on power supply lines. It is much like putting an inductor there.
Ferrite beads may be used on signal lines, but only if you can stand the higher impedance at higher frequencies.
They are not usually used on ground lines because you usually want a low impedance to ground at all frequencies.
Ferrite beads are not magic. You need to know a thing or two about the expected environment.
Read this ferrites and see some pro's and con's with ferrites and how to apply them
The sorce of the noise is frequency inverter sopposd to be 0 to 50 hz, but im sure they make many different frequencies
Beads are heavily used in RF circuitry to suppress parasitic oscillations because they can be very lossy
inductors (low Q), if the right ferrite is used for the frequencies of interest. Resistors can serve the
same purpose less efficiently.
For noise suppression I'd work on reducing the impedance to ground via capacitors first, decoupling
the supply and suppressing interfence on low bandwidth signals with RC filtering and so forth.
Ground plane and metal enclosure are important too.
The sorce of the noise is frequency inverter sopposd to be 0 to 50 hz, but im sure they make many different frequencies
You'd need a LOT more inductance for those low frequencies (or any "reasonable" harmonics of those frequencies).
If you are switching the AC power (such as a switching regulator or a dimmer) you can get radio frequencies and a bead might help.
Thank you
My noise will be going into a power supply one of those shielded switch mode supply which will supply my processor
It will be comming from the cabling i have 4 wires which carry a noisy inverter 240v ac and the noise will transfer onto the 3 wires of the supply to the power supply
I hope a lot of the noise will go to gnd of the case of the supply but i, sure a lot will be trasfered onto the 0 and the 12v output of the supply so i will experiemet with shielding inductors and c,s and ferite beads
vaj4088:
They are not usually used on ground lines because you usually want a low impedance to ground at all frequencies.
Except in the ground lead of the USB on the Arduino Mega, check out the schematic. 
But these sorts of things are normally used to suppress high frequency currents that cause equipment to fail EM emissions tests for FCC and other regulatory bodies.