Confused dude, and by orders of magnitude, dude

[terry michaels]

Message text written by INTERNET:WeAreAs1 at aol.com
>A quick 'n' dumb question:

When entering capacitor values into formulas which call for values of R and
C,
are basic "C" units expressed as microfarads or farads?  For example, when
solving for cutoff frequency in a classic 3-opamp state-variable filter,
the
formula is given as:

                  1
Fc = _____________
          2 * pi * R * C   

Obviously, R is expressed in Ohms, but is C expressed as Farads or
Microfarads?  That is to say, if my chosen cap value is 0.1uf, should I
enter
C as 0.1, or should I enter it as 0.00000000000001 ?

Also, it is assumed that all formulas requiring a C value will adhere to
this
definition of C?

Anxiously awaiting in breathless ignorance,

Michael Bacich
<

Hi Michael:

R is in Ohms, C is in Farads.  If those values are inconvenient, you can
scale values together: C in microfarads, R in megohms, or C in microfarads,
Fc in megahertz, or C in microfarads, R in kilo ohms, Fc in kilohertz, etc.
As a mental reminder, the time constant for a one meg resistor connected to
a one uF capacitor is one second, frequency is 1/6 Hz.

All formulas should use C in Farads.

Terry Michaels