> how should I select the proper caps for filtering? not the voltage, I had
my
> lesson :-)
> I mean what the proper value, I don't want to put overkill caps cause I
have
> a small room problem.
> are they any exact calculation for it or it try & error case?

You are rectifying an AC voltage.  The caps are charged at the peaks of the
waveform, and must provide the power to the circuit in between.  If I
remember right, you are using a full wave rectifier with 50Hz power.  That
means the caps will be recharged every 10mS.  Pretend that the caps get
charged instantaneously every 10mS.  The choice of cap then depends on how
much current the circuit will draw and how much voltage droop it can
tolerate.

For example, lets say the caps must be able to support 100mA continuous
current draw with a maximum of 5V droop.

  100mA * 10mS = 1mCoulomb

  1mCoulomb / 5V = 200uF


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