# Need help with Relaxation Oscillator with Parasitic Capacitance

I am trying to build a capacitance meter using a simple relaxation oscillator with a fixed resistor R in series with a capacitor to be measured C. I am applying the formula where Freq=frequency and K is a constant.:

                             C = K / ( R * Freq )


I have however noticed parasitic capacitance in the circuit that affects the measured capacitance and frequency. I am therefore looking for a correct formula that takes into consideration of 2 extra parasitic phantom capacitors, C1 which is in parallel with R and C2 which is in parallel with C. The resulting formula should be in the form of:

                             C = f( R, C1, C2, K, Freq)


Looking forward to any assistance with this problem.

• And what about parasitic resistive effects of the capacitor to be measured? I am afraid, it is not possible to eliminate all parasitic effects. – LvW Jun 30 '15 at 18:34