Frequency and Capacitance meter

n [...] idea is to use the 555 as a monostable, and trigger it with a fixed frequency clock. Duty cycle will be proportional to capacitance.

Circuit will look something like:

+5 ---+---------------+---+
     |               |   |
     R            +----------+
     |(see below) |  8   4   |
 +---+------+-----|7        3|------/\/\/\---+------- Vout
 :          |     |  LMC555  |               |
 C to test  +-----|6         |             -----
 :                |          |             -----
ground       +-----|2        5|----+          |
            |     |    1     |    |        ground
            |     +----------+  0.1 uF
            |          |          |
  Clock ----+        ground     ground
    ^
(see | next section - CMOS Oscillator)

The ON time for the monostable is about 1.1RC, so component values that should work would be a 50 Hz clock, say a 1 Hz low-pass filter on the output, and R = 9.09K, 1%. That combination will give an output of one volt per microfarad. Switch R in decades for smaller capacitors. Trim R for calibration.