>
>Why do it the hard way (diodes)?
>You just need ONE 74HC14, and your unknown
>R is the feedback resistor and the C hangs off the input pin.
>You get an oscillator period which is proportional
>to R if the thresholds don't move with temperature.


Because the diodes are necessary to factor out the C.
The period of the "simple" version is proportional to the resistor
allright, and the capacitor, and the temperature...

The diode version measures a known R and unknown C against Unknown R and
Unknown C, all at the same temperature.

C/C =1 so the ratio is simply Rknown/Runknown.

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