Measuring Capacitor Value

[craigfoo]

I'm trying to figure out the best way to measure the value of a capacitor in a circuit and if the value is out of spec, give feedback. The circuit would have some way of knowing what it's supposed to read and what the tolerance of the cap is. Would a microcontroller be best suited for this or is there a way I can do it in the analog domain?

[alanb]

I don't think that you will have much success trying to measure the capacity of a capacitor when in circuit due to the effect of other circuit elements. If you just want to find the ESR there are several meters available for this that in most circumstances will give an acceptably accurate indication of the ESR. I have a small microcontroller based meter from Peak electronics and am happy with the results.   

[tszaboo]

Do you want to do this on a live circuit (eg. Power supply) or is it for a test system, periodically checking if the stuff still works?